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FINAL TURBIDITY TOTAL MAXIMUM DAILY LOAD FOR BLACK BEAR CREEK, OKLAHOMA (621200030010_00) Prepared for: OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY Prepared by: AUGUST 2010 FIANL TURBIDITY TOTAL MAXIMUM DAILY LOAD FOR BLACK BEAR CREEK, OKLAHOMA (621200030010_00) OKWBID 621200030010_00 Prepared for: OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY Prepared by: 8000 Centre Park Drive, Suite 200 Austin, TX 78754 AUGUST 2010 Oklahoma Department of Environmental Quality: FY07/08 106 Carryover Grant (I-006400-08) Funding for the development of this TMDL Report was provided through a federal Clean Water Act grant to the Oklahoma Department of Environmental Quality from the U.S. Environmental Protection Agency. Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx i FINAL August 2010 TABLE OF CONTENTS EXECUTIVE SUMMARY ................................................................................................. ES-1 SECTION 1 INTRODUCTION ............................................................................................. 1-1 1.1 TMDL Program Background ..................................................................................... 1-1 1.2 Watershed Description ............................................................................................... 1-4 1.3 Stream Flow Data ....................................................................................................... 1-7 SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET ...... 2-1 2.1 Oklahoma Water Quality Standards ........................................................................... 2-1 2.2 Problem Identification ................................................................................................ 2-3 2.3 Water Quality Target .................................................................................................. 2-4 SECTION 3 POLLUTANT SOURCE ASSESSMENT ....................................................... 3-1 3.1 NPDES-Permitted Facilities ....................................................................................... 3-1 3.1.1 Continuous Point Source Discharges ............................................................. 3-2 3.1.2 Concentrated Animal Feeding Operations ..................................................... 3-5 3.1.3 Rock, Sand and Gravel Quarries .................................................................... 3-5 3.1.4 Stormwater Permits for MS4 and Construction Activities ............................. 3-5 3.1.5 Section 404 permits ........................................................................................ 3-5 3.2 Nonpoint Sources ....................................................................................................... 3-6 SECTION 4 TECHNICAL APPROACH AND METHODS .............................................. 4-1 4.1 Determining a Surrogate Target ................................................................................. 4-1 4.2 Using Load Duration Curves to Develop TMDLs ..................................................... 4-4 4.3 Development of Flow Duration Curves ..................................................................... 4-4 4.4 Development of TMDLs Using Load Duration Curves ............................................. 4-6 SECTION 5 TMDL CALCULATIONS ................................................................................ 5-1 5.1 Estimated Loading and Critical Conditions ............................................................... 5-1 5.2 Wasteload Allocation ................................................................................................. 5-2 5.2.1 Section 404 permits ........................................................................................ 5-3 5.3 Load Allocation .......................................................................................................... 5-3 5.4 Seasonal Variability .................................................................................................... 5-3 5.5 Margin of Safety ......................................................................................................... 5-3 5.6 TMDL Calculations .................................................................................................... 5-4 5.7 Reasonable Assurances .............................................................................................. 5-5 SECTION 6 PUBLIC PARTICIPATION ............................................................................ 6-1 SECTION 7 REFERENCES .................................................................................................. 7-1 Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx ii FINAL August 2010 APPENDICES Appendix A Ambient Water Quality Data 1998 - 2007 Appendix B Projected Flow exceedance frequencies for Black Bear Creek Flow Duration Curve Appendix C State of Oklahoma Antidegradation Policy LIST OF FIGURES Figure 1-1 Watersheds Not Supporting Fish and Wildlife Propagation Use within the Study Area ...................................................................................................... 1-3 Figure 1-2 Land Use Map by Watershed ............................................................................... 1-6 Figure 3-1 Locations of NPDES-Permitted Facilities in the Study Area ............................... 3-4 Figure 4-1 Linear Regression for TSS-Turbidity under Base-flow Conditions for Black Bear Creek (OK 62100030010_00) ........................................................... 4-3 Figure 4-2 Flow Duration Curve for Black Bear Creek (OK621200030010_00) ................. 4-6 Figure 5-1 Load Duration Curve for Total Suspended Solids in Black Bear Creek (OK621200030010_00) ........................................................................................ 5-2 Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx iii FINAL August 2010 LIST OF TABLES Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List ................................................................................. ES-2 Table ES-2 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 ................................................................................................................... ES-3 Table ES-3 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 ................................................................................................................... ES-3 Table ES-4 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) .......................................................................... ES-6 Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision ........ 1-2 Table 1-2 County Population and Density ............................................................................ 1-4 Table 1-3 Average Annual Precipitation by Watershed ....................................................... 1-4 Table 1-4 Land Use Summaries by Watershed ..................................................................... 1-5 Table 2-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List .................................................................................... 2-2 Table 2-2 Summary of All Turbidity Samples 1998 - 2007 ................................................. 2-3 Table 2-3 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 ...................................................................................................................... 2-3 Table 2-4 Summary of All TSS Samples 1998 - 2007 ......................................................... 2-4 Table 2-5 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 ...................................................................................................................... 2-4 Table 3-1 Point Source Discharges in the Study Area .......................................................... 3-2 Table 3-2 Discharge Monitoring Data for NPDES Facilities in the Study Area .................. 3-3 Table 3-3 Rock, Sand and Gravel Quarries .......................................................................... 3-5 Table 3-4 Stormwater Permits for Construction Activities .................................................. 3-6 Table 5-1 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) ............................................................................. 5-4 Table 5-2 Partial List of Oklahoma Water Quality Management Agencies ......................... 5-6 Black Bear Creek TMDL Acronyms and Abbreviations FINAL Turbidity TMDL_Black_Bear_Creek.docx iv FINAL August 2010 ACRONYMS AND ABBREVIATIONS BMP best management practice CAFO Concentrated Animal Feeding Operation CFR Code of Federal Regulations cfs Cubic feet per second CPP Continuing planning process CWA Clean Water Act DMR Discharge monitoring report IQR interquartile range LA Load allocation LDC Load duration curve LOC line of organic correlation mg Million gallons mgd Million gallons per day mg/L milligram per liter MOS Margin of safety MS4 Municipal separate storm sewer system NPDES National Pollutant Discharge Elimination System NRCS National Resources Conservation Service NTU nephelometric turbidity unit OLS ordinary least square regression O.S. Oklahoma statutes ODAFF Oklahoma Department of Agriculture, Food and Forestry ODEQ Oklahoma Department of Environmental Quality OPDES Oklahoma Pollutant Discharge Elimination System OWRB Oklahoma Water Resources Board PRG Percent reduction goal TMDL Total maximum daily load TSS Total suspended solids USDA U.S. Department of Agriculture USEPA U.S. Environmental Protection Agency USGS U.S. Geological Survey WLA Wasteload allocation WQM Water quality monitoring WQS Water quality standard WWTP Wastewater treatment plant Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-1 FINAL August 2010 EXECUTIVE SUMMARY This report documents the data and assessment used to establish a TMDL for Black Bear Creek, a tributary of the Arkansas River. The 2008 Integrated Water Quality Assessment Report (Oklahoma Department of Environmental Quality [ODEQ] 2008) identified Black Bear Creek as impaired for turbidity. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the CWA, Water Quality Planning and Management Regulations (40 CFR Part 130), USEPA guidance, and ODEQ guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003). The purpose of this TMDL report is to establish pollutant load allocations for turbidity in impaired waterbodies, which is the first step toward restoring water quality. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. TMDLs also establish the pollutant load allocation necessary to meet the WQS established for a waterbody based on the relationship between pollutant sources and in-stream water quality conditions. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural process in aquatic systems, model assumptions, and data limitations. This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce turbidity loadings within each watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process involving stakeholders who live and work in the watershed; tribes; and local, state, and federal government agencies. E.1 Problem Identification and Water Quality Target The TMDL in this report address fish and wildlife propagation for the subcategory warm water aquatic community. Table ES-1, an excerpt from Appendix B of the 2008 Integrated Report (ODEQ 2008), summarizes the warm water aquatic community use attainment status and the scheduled date for TMDL development established by ODEQ for the impaired waterbody of the Study Area. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-2 FINAL August 2010 Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category TMDL Date Priority Warm Water Aquatic Community OK621200030010_00 Black Bear Creek 68.0 5a 2013 2 N N = Not Supporting; 5a = TMDL is underway or will be scheduled Source: 2008 Integrated Report, ODEQ 2008 The data in Table ES-2 were used to support the decision to place Black Bear Creek on the ODEQ 2008 303(d) list (ODEQ 2008 for nonsupport of the Fish and Wildlife Propagation use based on turbidity levels observed in the waterbody. Turbidity is a measure of water clarity and is caused by suspended particles in the water column. Because turbidity cannot be expressed as a mass load, total suspended solids (TSS) are used as a surrogate in this TMDL. Therefore, both turbidity and TSS data are presented to support TMDL development. The numeric criteria for turbidity to maintain and protect the use of “Fish and Wildlife Propagation” from Title 785:45-5-12 (f) (7) is as follows: (A) Turbidity from other than natural sources shall be restricted to not exceed the following numerical limits: 1. Cool Water Aquatic Community/Trout Fisheries: 10 NTUs; 2. Lakes: 25 NTU; and 3. Other surface waters: 50 NTUs. (B) In waters where background turbidity exceeds these values, turbidity from point sources will be restricted to not exceed ambient levels. (C) Numerical criteria listed in (A) of this paragraph apply only to seasonal base flow conditions. (D) Elevated turbidity levels may be expected during, and for several days after, a runoff event. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-3 FINAL August 2010 Table ES-2 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of Turbidity Samples Collected During Base Flow Conditions Number of Samples Exceeding 50 NTU during Base Flow Conditions Percentage of Samples Exceeding Criterion during Base Flow Conditions Average Turbidity (NTU) Per WQM Station during Base Flow Conditions 621200030010-001AT 51 18 35% 60 OK621200030010D 18 10 56% 111 OK621200030010G 23 6 26% 54 OK621200030010M 22 16 73% 99 OK621200030010W 24 5 21% 42 Table ES-3 presents a subset of total suspended solids data for samples collected during base flow conditions. Water quality data for turbidity and TSS are provided in Appendix A. Table ES-3 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of TSS Samples Collected During Base Flow Conditions Average TSS (mg/L) Per WQM Station during Base Flow Conditions OK621200030010-001AT 18 46 OK621200030010D 18 50 OK621200030010G 7 53 OK621200030010M 18 54 OK621200030010W 19 44 The Code of Federal Regulations (40 CFR §130.7(c)(1)) states that, “TMDLs shall be established at levels necessary to attain and maintain the applicable narrative and numerical water quality standards.” An individual water quality target established for turbidity must demonstrate compliance with the numeric criteria prescribed in the Oklahoma WQS (OWRB 2008). According to the Oklahoma WQS [785:45-5-12(f)(7)], the turbidity criterion for streams with warm water aquatic community (WWAC) beneficial use is 50 NTUs (OWRB 2008). The turbidity of 50 NTUs applies only to seasonal base flow conditions. Turbidity levels are expected to be elevated during, and for several days after, a storm event. TMDLs for turbidity in streams designated as warm water aquatic community must take into account that no more than 10 percent of the samples may exceed the numeric criterion of 50 NTU. However, as described above, because turbidity cannot be expressed as a mass load, TSS is used as a surrogate in this TMDL. Since there is no numeric criterion in the Oklahoma WQS for TSS, a specific method must be developed to convert the turbidity criterion to TSS based on a relationship between turbidity and TSS. The method for deriving the relationship between turbidity and TSS, and for calculating a water body specific water quality target using TSS, is summarized in Section 4 of this report. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-4 FINAL August 2010 E.2 Pollutant Source Assessment A pollutant source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Turbidity may originate from NPDES-permitted facilities, fields, construction sites, quarries, stormwater runoff and eroding stream banks. The 2008 Integrated Water Quality Assessment Report (ODEQ 2008) listed potential sources of turbidity in Black Bear Creek (OK621200030010_00) as clean sediments, grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, petroleum/natural gas activities, rangeland grazing, and other unknown sources. There are four NPDES-permitted facilities and no municipal separate storm sewer systems or CAFOs in the Study Area. There are approximately 2,400 permitted mining acres operated by four different quarries located within the Study Area. There are general stormwater permits for two facilities located within the Study Area. The relative homogeneous land use/land cover categories within the Study Area are associated with agricultural and range management activities. This suggests that various nonpoint sources of TSS include sediments originating from grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, rangeland grazing and other sources of sediment loading (ODEQ 2008). Elevated turbidity measurements can be caused by stream bank erosion processes, stormwater runoff events and other channel disturbances. However, there is insufficient data available to quantify contributions of TSS from these processes. TSS or sediment loading can also occur under non-runoff conditions as a result of anthropogenic activities in riparian corridors which cause erosive conditions. Sediment loading of streams can also originate from natural erosion processes, including the weathering of soil, rocks, and uncultivated land; geological abrasion; and other natural phenomena. Given the lack of data to establish the background conditions for TSS/turbidity, separating background loading from nonpoint sources is not feasible in this TMDL development. E.3 Using Load Duration Curves to Develop TMDLs Turbidity is a commonly measured indicator of the suspended solids load in streams. However, turbidity is an optical property of water, and measures scattering of light by suspended solids and colloidal matter. To develop TMDLs, a gravimetric (mass-based) measure of solids loading is required to express loads. There is often a strong relationship between the total suspended solids concentration and turbidity. Therefore, the TSS load, which is expressed as mass per time, is used as a surrogate for turbidity and represents the maximum one-day load the stream can assimilate while still attaining the WQS. To determine the relationship between turbidity and TSS, a linear regression between TSS and turbidity was developed using data collected from 1998 to 2007 at four stations within the Study Area. Prior to developing the regression the following steps were taken to refine the dataset: Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-5 FINAL August 2010 Assign values to censored data (i.e., measured concentrations lower than the analytical quantitation limit and, thus, reported as less than the quantitation limit). For example, using 9.99 to replace samples reported as “<10”; Remove data collected under high flow conditions exceeding the base-flow criterion. This means that measurements corresponding to flow exceedance frequencies lower than 25% were not used in the regression; Check rainfall data on the day when samples were collected and on the previous two days. If there was a significant rainfall event (>= 1.0 inch) in any of these days, the sample will be excluded from regression analysis with one exception. If the significant rainfall happened on the sampling day and the turbidity reading was less than 25 NTUs (half of turbidity standard for streams), the sample will not be excluded from analysis because most likely the rainfall occurred after the sample was taken; andLog-transform both turbidity and TSS data to minimize effects of their non-linear data distributions. The TMDL calculations presented in this report are derived from load duration curves (LDC). LDCs facilitate rapid development of TMDLs, and as a TMDL development tool, are effective at identifying whether impairments are associated with point or nonpoint sources. The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the USGS (or project flow using Oklahoma TMDL Toolbox if station is ungaged); sorting the flow data and calculating flow exceedance frequencies for the time period and season of interest; obtaining available turbidity and TSS water quality data; matching the water quality observations with the flow data from the same date; displaying a curve on a plot that represents the allowable load multiplying the actual or estimated flow by the WQtarget for TSS; multiplying the flow by the water quality parameter concentration to calculate daily loads (for sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2); then plotting the flow exceedance frequencies and daily load observations in a load duration plot. The culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve: TMDL (lb/day) = WQtarget * flow (cfs) * unit conversion factor where: WQtarget = 40.6 mg/L (TSS) unit conversion factor = 5.39377 L*s*lb /(ft3*day*mg) The flow exceedance frequency (x-value of each point) is obtained by looking up the historical exceedance frequency of the measured or estimated flow; in other words, the percent of historical observations that equal or exceed the measured or estimated flow. Historical observations of TSS and/or turbidity concentrations are paired with flow data and are plotted on the LDC. The TSS load (or the y-value of each point) is calculated by multiplying the TSS Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-6 FINAL August 2010 concentration (measured or converted from turbidity) (mg/L) by the instantaneous flow (cfs) at the same site and time, with appropriate volumetric and time unit conversions. TSS loads representing exceedance of water quality criteria fall above the water quality criterion line. E.4 TMDL Calculations The objective of a TMDL is to estimate allowable pollutant loads and to allocate these loads to the known pollutant sources in the watershed so appropriate control measures can be implemented and the WQS achieved. A TMDL is expressed as the sum of three elements as described in the following mathematical equation: TMDL = Σ WLA + Σ LA + MOS The WLA is the portion of the TMDL allocated to existing and future point sources. The LA is the portion of the TMDL allocated to nonpoint sources, including natural background sources. The MOS is intended to ensure that WQS will be met. Thus, the allowable pollutant load that can be allocated to point and nonpoint sources can then be defined as the TMDL minus the MOS. The overall Percent Reduction Goal (PRG) is calculated as the reduction in load required so no more than 10 percent of the samples collected under base-flow conditions would exceed TMDL targets for TSS. The PRG for Black Bear Creek is calculated to be 60.3 percent. The maximum assimilative capacity of a stream depends on the flow conditions of the stream. The higher the flow is, the more wasteload the stream can handle without violating water quality standards. Thus, the TMDL, WLA, LA, and MOS will vary with flow condition, and are calculated at every 5th flow interval percentile (Table ES-4). Table ES-4 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) Percentile Flow (cfs) TMDL (lb/day) WLA (lb/day) LA (lb/day) MOS WWTP MS4 (lb/day) Future Growth 0 18260 NA 0 0 NA NA NA 5 1616 NA 0 0 NA NA NA 10 695 NA 0 0 NA NA NA 15 386 NA 0 0 NA NA NA 20 245 NA 0 0 NA NA NA 25 166 34,024 153 0 340 30,128 3,402 30 113 23,140 153 0 231 20,441 2,314 35 82 16,787 153 0 168 14,787 1,679 40 61 12,482 153 0 125 10,956 1,248 45 48 9,756 153 0 98 8,530 976 50 37 7,481 153 0 75 6,505 748 55 30 6,128 153 0 61 5,301 613 60 24 4,981 153 0 50 4,279 498 65 20 4,079 153 0 41 3,477 408 70 18 3,628 153 0 36 3,075 363 75 14 2,951 153 0 30 2,473 295 Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-7 FINAL August 2010 80 11 2,214 153 0 22 1,817 221 85 8 1,640 153 0 16 1,306 164 90 5 1,066 153 0 11 795 107 95 2 451 153 0 5 248 45 100 0 0 0 0 0 0 0 E.5 Reasonable Assurance ODEQ will collaborate with a host of other state agencies and local governments working within the boundaries of state and local regulations to target available funding and technical assistance to support implementation of pollution controls and management measures. Various water quality management programs and funding sources provide a reasonable assurance that the pollutant reductions as required by this TMDL can be achieved and water quality can be restored to maintain designated uses. ODEQ’s Continuing Planning Process (CPP), required by the CWA §303(e)(3) and 40 CFR 130.5, summarizes Oklahoma’s commitments and programs aimed at restoring and protecting water quality throughout the state (ODEQ 2006). The CPP can be viewed from ODEQ’s website. Table 5-2 provides a partial list of the state partner agencies ODEQ will collaborate with to address point and nonpoint source reduction goals established by TMDLs. Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-1 FINAL August 2010 SECTION 1 INTRODUCTION 1.1 TMDL Program Background Section 303(d) of the Clean Water Act (CWA) and U.S. Environmental Protection Agency (USEPA) Water Quality Planning and Management Regulations (40 Code of Federal Regulations [CFR] Part 130) require states to develop total maximum daily loads (TMDL) for waterbodies not meeting designated uses where technology-based controls are in place. TMDLs establish the allowable loadings of pollutants or other quantifiable parameters for a waterbody based on the relationship between pollution sources and in-stream water quality conditions, so states can implement water quality-based controls to reduce pollution from point and nonpoint sources and restore and maintain water quality (USEPA 1991). This report documents the data and assessment used to establish a turbidity TMDL for Black Bear Creek, a tributary of the Arkansas River. The 2008 Integrated Water Quality Assessment Report (Oklahoma Department of Environmental Quality [ODEQ] 2008) identified Black Bear Creek as impaired for turbidity. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the CWA, Water Quality Planning and Management Regulations (40 CFR Part 130), USEPA guidance, and ODEQ guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003). The purpose of this TMDL report is to establish pollutant load allocations for turbidity in impaired waterbodies, which is the first step toward restoring water quality. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. TMDLs also establish the pollutant load allocation necessary to meet the WQS established for a waterbody based on the relationship between pollutant sources and in-stream water quality conditions. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural process in aquatic systems, model assumptions, and data limitations. This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce turbidity loadings within each watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process involving stakeholders who live and work in the watershed; tribes; and local, state, and federal government agencies. This TMDL report focuses on waterbodies that ODEQ placed in Category 5 [303(d) list] of the Water Quality in Oklahoma, 2008 Integrated Report (2008 Integrated Report) for the beneficial use category Fish and Wildlife Propagation for Black Bear Creek OK621200030010_00. Figure 1-1 is a location map showing the impaired segment of this Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-2 FINAL August 2010 Oklahoma waterbody and its contributing watershed. This map also displays the locations of the water quality monitoring (WQM) stations used as the basis for placement of this waterbody on the Oklahoma 303(d) list. The waterbody and its surrounding watershed are hereinafter referred to as the Study Area. The TMDL established in this report is a necessary step in the process to develop the turbidity controls needed to restore the fish and wildlife propagation designated for the waterbody. Table 1-1 provides a description of the locations of the WQM stations on the 303(d)-listed waterbody. Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision WQM Station WQM Station Location Description WQM Station Location Legal Descriptions Latitude Longitude OK621200030010W Black Bear Creek: Upper NE¼ NE¼ NE¼ Section 32-22N-1E 36.346222 -97.210833 OK621200030010M Black Bear Creek: Upper W.B. Section 9-21N- 3E 36.306778 -96.9960278 621200030010-001AT Black Bear Creek:, SH 18, Pawnee NA 36.3434116 -96.79985 OK621200030010D Black Bear Creek: Lower Sections 31/32 22N- 6E 36.339861 -96.69211 OK621200030010G Black Bear Creek: Lower SE¼ NW¼ NE¼ Section 1-21N-4E 36.33986 -96.69211 Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-3 FINAL August 2010 Figure 1-1 Watersheds Not Supporting Fish and Wildlife Propagation Use within the Study Area Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-4 FINAL August 2010 1.2 Watershed Description General. The Arkansas River Basin is located in the northern portion of Oklahoma. The waterbody addressed in this report is located in Noble, Pawnee, and Payne Counties. The Study Area is located in the Central Great Plains ecoregion of Oklahoma. Table 1-2, derived from the 2000 U.S. Census, shows that the counties where these watersheds are located are sparsely populated (U.S. Census Bureau 2000). Table 1-2 County Population and Density County Name Population (2000 Census) Population Density (per square mile) Noble 11,411 15.6 Pawnee 16,612 29.2 Payne 68,190 99.4 Climate. Table 1-3 summarizes the average annual precipitation for the waterbody. Average annual precipitation for the waterbody is 38.4 inches (Oklahoma Climate Survey 2007). Table 1-3 Average Annual Precipitation by Watershed Black Bear Creek Precipitation Summary Waterbody Name Waterbody ID Average Annual (inches) Black Bear Creek OK621200030010_00 38.4 Land Use. Table 1-4 summarizes the acreages and the corresponding percentages of the land use categories for the contributing watershed associated with the Oklahoma waterbody. The land use/land cover data were derived from the U.S. Geological Survey (USGS) 2001 National Land Cover Dataset (USGS 2007). The land use categories are displayed in Figure 1-2. The primary land use category in the Study Area is Grassland, which makes up 63 percent of the watershed. The second most common land use within the Study Area is cultivated land and deciduous forest at 14 and 13.2 percent, respectively. Pawnee, the largest city within the Black Bear Creek watershed, has an estimated population of 2,230 (U.S. Census Bureau 2000). Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-5 FINAL August 2010 Table 1-4 Land Use Summaries by Watershed Landuse Category Black Bear Creek Waterbody ID OK621200030010_00 Percent Herbaceous Wetlands 0% Percent Woody Wetlands 0% Percent Cultivated 14.0% Percent Pasture/Hay 3.6% Percent Grassland 62.9% Percent Shrubland 0% Percent Mixed Forest 0% Percent Evergreen Forest 0% Percent Deciduous Forest 13.2% Percent Barren 0% Percent Developed - High Intensity 0% Percent Developed - Medium Intensity 0% Percent Developed - Low Intensity 0.7% Percent Developed - Open 4.4% Percent Water 0.8% Acres Herbaceous Wetlands 9 Acres Woody Wetlands 0 Acres Cultivated 33,924 Acres Pasture/Hay 8,630 Acres Grassland 152,130 Acres Shrubland 0 Acres Mixed Forest 0 Acres Evergreen Forest 760 Acres Deciduous Forest 31,878 Acres Barren 5 Acres Developed - High Intensity 39 Acres Developed - Medium Intensity 199 Acres Developed - Low Intensity 1,712 Acres Developed - Open 10,668 Acres Water 2,056 Total (Acres) 242,011 Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-6 FINAL August 2010 Figure 1-2 Land Use Map by Watershed Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-7 FINAL August 2010 1.3 Stream Flow Data Stream flow characteristics and data are key information when conducting water quality assessments such as TMDLs. The USGS operates flow gages throughout Oklahoma. There is one gage station in the Black Bear Creek watershed with historical flow data: USGS gage 07153000, Black Bear Creek at SH 18 at Pawnee. The location of this USGS gage station is displayed in Figure 1-1. This gage has operated continuously since 1944 and the median flow is 35 cubic feet per second (cfs). In addition, some flow measurements were collected at the same time TSS and turbidity water quality samples were collected at various WQM stations. These data are included in Appendix A along with turbidity and TSS data. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-1 FINAL August 2010 SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET 2.1 Oklahoma Water Quality Standards Title 785 of the Oklahoma Administrative Code authorizes the Oklahoma Water Resources Board (OWRB) to promulgate Oklahoma’s water quality standards and implementation procedures (OWRB 2008). The OWRB has statutory authority and responsibility concerning establishment of state water quality standards, as provided under 82 Oklahoma Statute [O.S.], §1085.30. This statute authorizes the OWRB to promulgate rules …which establish classifications of uses of waters of the state, criteria to maintain and protect such classifications, and other standards or policies pertaining to the quality of such waters. [O.S. 82:1085:30(A)]. Beneficial uses are designated for all waters of the state. Such uses are protected through restrictions imposed by the antidegradation policy statement (See Appendix C), narrative water quality criteria, and numerical criteria (OWRB 2008). The beneficial uses designated for Black Bear Creek (OK621200030010) include primary body contact recreation, warm water aquatic community, public/private water supply, fish consumption, agriculture and aesthetics. The TMDL in this report addresses the fish and wildlife propagation beneficial use for the subcategory warm water aquatic community. Table 2-1, an excerpt from Appendix B of the 2008 Integrated Report (ODEQ 2008), summarizes the warm water aquatic community use attainment status and the scheduled date for TMDL development established by ODEQ for the impaired waterbody of the Study Area. The 2008 Integrated Report (ODEQ 2008) identifies the Black Bear Creek as Priority 2 for TMDL development. Priority 2 waterbodies are targeted for TMDL development by 2013. The TMDL established in this report is a necessary step in the process to restore the fish and wildlife propagation designation for this waterbody. The numeric criteria for turbidity to maintain and protect the use of “Fish and Wildlife Propagation” from Title 785:45-5-12 (f) (7) is as follows: (A) Turbidity from other than natural sources shall be restricted to not exceed the following numerical limits: 4. Cool Water Aquatic Community/Trout Fisheries: 10 NTUs; 5. Lakes: 25 NTU; and 6. Other surface waters: 50 NTUs. (B) In waters where background turbidity exceeds these values, turbidity from point sources will be restricted to not exceed ambient levels. (C) Numerical criteria listed in (A) of this paragraph apply only to seasonal base flow conditions. (D) Elevated turbidity levels may be expected during, and for several days after, a runoff event. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-2 FINAL August 2010 Table 2-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category TMDL Date Priority Warm Water Aquatic Community OK621200030010_00 Black Bear Creek 68.0 5a 2013 2 N N = Not Supporting; 5a = TMDL is underway or will be scheduled Source: 2008 Integrated Report, ODEQ 2008 To implement Oklahoma’s WQS for Fish and Wildlife Propagation, OWRB promulgated Chapter 46, Implementation of Oklahoma’s Water Quality Standards (OWRB 2008). The excerpt below from Chapter 46: 785:46-15-5, stipulates how water quality data will be assessed to determine support of fish and wildlife propagation as well as how the water quality target for TMDLs will be defined for turbidity. Assessment of Fish and Wildlife Propagation support (a) Scope. The provisions of this Section shall be used to determine whether the beneficial use of Fish and Wildlife Propagation or any subcategory thereof designated in OAC 785:45 for a waterbody is supported. (e) Turbidity. The criteria for turbidity stated in 785:45-5-12(f)(7) shall constitute the screening levels for turbidity. The tests for use support shall follow the default protocol in 785:46-15-4(b). 785:46-15-4. Default protocols (b) Short term average numerical parameters. (1) Short term average numerical parameters are based upon exposure periods of less than seven days. Short term average parameters to which this Section applies include, but are not limited to, sample standards and turbidity. (2) A beneficial use shall be deemed to be fully supported for a given parameter whose criterion is based upon a short term average if 10% or less of the samples for that parameter exceed the applicable screening level prescribed in this Subchapter. (3) A beneficial use shall be deemed to be fully supported but threatened if the use is supported currently but the appropriate state environmental agency determines that available data indicate that during the next five years the use may become not supported due to anticipated sources or adverse trends of pollution not prevented or controlled. If data from the preceding two year period indicate a trend away from impairment, the appropriate agency shall remove the threatened status. (4) A beneficial use shall be deemed to be not supported for a given parameter whose criterion is based upon a short term average if at least 10% of the samples for that parameter exceed the applicable screening level prescribed in this Subchapter. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-3 FINAL August 2010 2.2 Problem Identification Turbidity is a measure of water clarity and is caused by suspended particles in the water column. Because turbidity cannot be expressed as a mass load, total suspended solids (TSS) are used as a surrogate in this TMDL. Therefore, both turbidity and TSS data are presented in this section. Table 2-2 summarizes water quality data collected from the WQM stations between 1998 and 2007 for turbidity. However, as stipulated in Title 785:45-5-12 (f) (7) (C), numeric criteria for turbidity only apply under base flow conditions. While the base flow condition is not specifically defined in the Oklahoma Water Quality Standards, DEQ considers base flow conditions to be all flows less than the 25% flow exceedance frequency (i.e., the lower 75 percent of flows) which is consistent with the USGS Streamflow Conditions Index (USGS 2009). Therefore, Table 2-3 was prepared to represent the subset of data for samples collected during base flow conditions. Water quality samples collected under flow conditions greater than the 25% flow exceedance frequency were therefore excluded from the data set used for TMDL analysis. The data in Table 2-3 were used to support the decision to place Black Bear Creek on the ODEQ 2008 303(d) list (ODEQ 2008 for nonsupport of the Fish and Wildlife Propagation use based on turbidity levels observed in the waterbody. Table 2-2 Summary of All Turbidity Samples 1998 - 2007 WQM Station Number of Turbidity Samples Number of Samples Exceed 50 Nephelometric Turbidity Units (NTU) Percentage of Samples Exceeding Criterion Average Turbidity (NTU) Per WQM Station 621200030010-001AT 70 36 51% 132 OK621200030010D 21 13 59% 126 OK621200030010G 28 11 39% 195 OK621200030010M 27 21 78% 126 OK621200030010W 28 9 32% 61 Table 2-3 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of Turbidity Samples Collected During Base Flow Conditions Number of Samples Exceeding 50 NTU during Base Flow Conditions Percentage of Samples Exceeding Criterion during Base Flow Conditions Average Turbidity (NTU) Per WQM Station during Base Flow Conditions 621200030010-001AT 51 18 35% 60 OK621200030010D 18 10 56% 111 OK621200030010G 23 6 26% 54 OK621200030010M 22 16 73% 99 OK621200030010W 24 5 21% 42 Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-4 FINAL August 2010 Table 2-4 summarizes water quality data collected from the WQM stations between 1998 and 2007 for TSS. Table 2-5 presents a subset of these data for samples collected during base flow conditions. Water quality data for turbidity and TSS are provided in Appendix A. Table 2-4 Summary of All TSS Samples 1998 - 2007 WQM Station Number of TSS Samples Average TSS (mg/L) Per WQM Station OK621200030010-001AT 30 110 OK621200030010D 24 238 OK621200030010G 10 421 OK621200030010M 24 239 OK621200030010W 24 420 Table 2-5 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of TSS Samples Collected During Base Flow Conditions Average TSS (mg/L) Per WQM Station during Base Flow Conditions OK621200030010-001AT 18 46 OK621200030010D 18 50 OK621200030010G 7 53 OK621200030010M 18 54 OK621200030010W 19 44 2.3 Water Quality Target The Code of Federal Regulations (40 CFR §130.7(c)(1)) states that, “TMDLs shall be established at levels necessary to attain and maintain the applicable narrative and numerical water quality standards.” An individual water quality target established for turbidity must demonstrate compliance with the numeric criteria prescribed in the Oklahoma WQS (OWRB 2008). According to the Oklahoma WQS [785:45-5-12(f)(7)], the turbidity criterion for streams with warm water aquatic community (WWAC) beneficial use is 50 NTUs (OWRB 2008). The turbidity of 50 NTUs applies only to seasonal base flow conditions. Turbidity levels are expected to be elevated during, and for several days after, a storm event. TMDLs for turbidity in streams designated as warm water aquatic community must take into account that no more than 10 percent of the samples may exceed the numeric criterion of 50 NTU. However, as described above, because turbidity cannot be expressed as a mass load, TSS is used as a surrogate in this TMDL. Since there is no numeric criterion in the Oklahoma WQS for TSS, a specific method must be developed to convert the turbidity criterion to TSS based on a relationship between turbidity and TSS. The method for deriving the relationship between turbidity and TSS, and for calculating a water body specific water quality target using TSS, is summarized in Section 4 of this report. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-1 FINAL August 2010 SECTION 3 POLLUTANT SOURCE ASSESSMENT A pollutant source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Turbidity may originate from NPDES-permitted facilities, fields, construction sites, quarries, stormwater runoff and eroding stream banks. Point sources are permitted through the NPDES program. NPDES-permitted facilities that discharge treated wastewater are required to monitor for TSS in accordance with their permit. Nonpoint sources are diffuse sources that typically cannot be identified as entering a waterbody through a discrete conveyance at a single location. These sources may involve land activities that contribute TSS to surface water as a result of rainfall runoff. For the TMDL in this report, all sources of pollutant loading not regulated by NPDES permits are considered nonpoint sources. The 2008 Integrated Water Quality Assessment Report (ODEQ 2008) listed potential sources of turbidity in Black Bear Creek (OK621200030010_00) as clean sediments, grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, petroleum/natural gas activities, rangeland grazing, and other unknown sources. 3.1 NPDES-Permitted Facilities Under 40CFR, §122.2, a point source is described as a discernable, confined, and discrete conveyance from which pollutants are or may be discharged to surface waters. . NPDES-permitted facilities can be characterized as continuous or stormwater related discharges. NPDES-permitted facilities classified as point sources include: NPDES municipal wastewater treatment plant (WWTP); NPDES Industrial WWTP Discharges; NPDES municipal separate storm sewer discharge (MS4); NPDES Concentrated Animal Feeding Operation (CAFO); NPDES multi-sector general permits; and NPDES construction stormwater discharges. Continuous point source discharges from municipal and industrial WWTPs, could result in discharge of elevated concentrations of TSS if a facility is not properly maintained, is of poor design, or flow rates exceed capacity. However, in most cases suspended solids discharged by WWTPs consist primarily of organic solids rather than inorganic suspended solids (i.e., soil and sediment particles from erosion or sediment resuspension). Discharges of organic suspended solids from WWTPs are addressed by ODEQ through its permitting of point sources to maintain WQS for dissolved oxygen and are not considered a potential source of turbidity in this TMDL report. Discharges of TSS will be considered to be organic suspended solid if the discharge permit includes a limit for BOD or CBOD. Only WWTP discharges of inorganic suspended solids will be considered and will receive wasteload allocations. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-2 FINAL August 2010 Stormwater runoff from MS4 areas, facilities under multi-sector general permits, and NPDES construction stormwater discharges, which are regulated under the USEPA NPDES Program, can contain TSS concentrations. 40 C.F.R. § 130.2(h) requires that NPDES-regulated storm water discharges must be addressed by the wasteload allocation component of a TMDL. However, any stormwater discharge by definition occurs during or immediately following periods of rainfall and elevated flow conditions when where Oklahoma Water Quality Standard for turbidity does not apply. Oklahoma Water Quality Standards specify that the criteria for turbidity “apply only to seasonal base flow conditions” and go on to say “Elevated turbidity levels may be expected during, and for several days after, a runoff event” [OAC 785:45-5- 12(f)(7)]. In other words, the turbidity impairment status is limited to base flow conditions and stormwater discharges from MS4 areas or construction sites do not contribute to the violation of Oklahoma’s turbidity standard. Therefore, WLA for NPDES-regulated storm water discharges is essentially considered unnecessary in this TMDL report and will not be included in the TMDL calculations. 3.1.1 Continuous Point Source Discharges There are four NPDES-permitted facilities in the Black Bear Creek (OK621200030010_00) watershed. A list of these facilities is included in Table 3-1 and facility locations are displayed in Figure 3-1. Table 3-1 Point Source Discharges in the Study Area NPDES Permit No. Facility Name County Name SIC Code Facility Type TSS Permit Limit (mg/L) BOD5 Permit Limit (mg/L) OK0002534 City of Pawnee Pawnee 4941 Water Supply 30 - OK0026654 City of Pawnee Pawnee 4952 Sewerage Systems 45 25 OK0028517 Town of Glencoe Payne 4952 Sewerage Systems 22.5 37.5 OKG950016 The Quapaw Company Pawnee 1422 Crushed and Broken Limestone 45* - *Permit limit for outfalls 001 and 002 Discharge Monitoring Reports (DMR) for 2007 and 2008 were available for the facilities listed in Table 3-1. Table 3-2 lists the DMR data available for the NPDES facilities. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-3 FINAL August 2010 Table 3-2 Discharge Monitoring Data for NPDES Facilities in the Study Area NPDES Monitoring End Date Outfall Maximum Flow (mgd) Average Flow (mgd) Maximum TSS (mg/L) Average TSS (mg/L) OK0002534 06/30/08 001 0.211 5 5 05/31/08 001 0.075 5 5 04/30/08 001 0.046 5.5 5.5 03/31/08 001 0.173 50 50 02/29/08 001 0.00029 50 50 01/31/08 001 0.2 4 4 12/31/07 001 0.000101 12 12 11/30/07 001 0.000082 3.5 3.5 10/31/07 001 0.000235 17 17 08/31/07 001 no discharge 07/31/07 001 0.244 8.5 8.5 06/30/07 001 0.178 8.5 8.5 OK0026654 06/30/08 001 0.3107 0.2771 8 7 05/31/08 001 0.3119 0.2457 10 8 04/30/08 001 0.2883 0.2274 5 10.77 03/31/08 001 0.3018 0.207 7.5 6.5 02/29/08 001 0.3147 0.1798 13 10.25 01/31/08 001 0.2475 0.2054 12 11.5 12/31/07 001 0.36 0.2426 6 4.5 11/30/07 001 0.2655 0.1551 4 3 10/31/07 001 0.2993 0.1932 22 15.75 09/30/07 001 0.3085 0.18923 5 4.5 08/31/07 001 0.2856 0.1205 3 2.75 07/31/07 001 0.316 0.264 5.5 5 06/30/07 001 0.334 0.257 8.5 7.25 OK0028517 10/31/07 001 0.064 0.064 85 85 09/30/07 001 0.064 0.064 35 35 08/31/07 001 0.064 0.064 66 66 07/31/07 001 0.064 0.064 48 48 06/30/07 001 0.064 0.064 84 84 05/31/08 001 0.064 0.064 55.5 55.5 04/30/08 001 0.064 0.064 77.5 77.5 03/31/08 001 0.064 0.064 96 96 02/29/08 001 0.064 0.064 78 78 01/31/08 001 0.064 0.064 45 45 12/31/07 001 0.064 0.064 65 65 11/30/07 001 0.064 0.064 88 88 OKG950016 05/31/08 - 6/30/2008 001 No discharge 04/30/08 001 0.12 0.12 34.5 34.5 12/31/04 to 03/31/08 001 No discharge 06/30/08 002 0.012 0.012 181 181 05/31/08 002 0.2 0.2 30 30 04/30/08 002 0.24 0.24 90 90 12/31/04 to 03/31/08 002 No discharge Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-4 FINAL August 2010 Figure 3-1 Locations of NPDES-Permitted Facilities in the Study Area Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-5 FINAL August 2010 3.1.2 Concentrated Animal Feeding Operations There are no CAFOs in the Study Area. 3.1.3 Rock, Sand and Gravel Quarries Operators of Rock, Sand and Gravel Quarries in Oklahoma are regulated with a general permit (OKG950000). The general permit does not allow discharge of wastewater to waterbodies included in Oklahoma’s 303(d) List of impaired water bodies listed for turbidity for which a TMDL has not been performed or the result of the TMDL indicates that discharge limits more stringent than 45 mg/l for TSS are required (ODEQ 2009). Table 3-3 summarizes data from the Oklahoma Department of Mines and provides the permitted mining acres for each of the four quarries located within the Study Area. The locations of these quarries are shown in Figure 3-1. Table 3-3 Rock, Sand and Gravel Quarries Company Name County Permit ID Product Permitted Acres Permit Issue Date Permit Renewal Date Mining Expiration Date* Stewart Stone (Pawnee Quarry Pit 3) Pawnee L.E.-1760-D Limestone 906.50 12/1/1999 11/30/2008 11/30/2029 Stewart Stone (Privett) Pawnee L.E.-1270 Limestone 333.00 12/1/2000 11/30/2008 11/30/2008 Stewart Stone (Pawnee) Pawnee L.E.-1734 Limestone 655.00 10/1/1999 9/30/2008 9/30/2029 Quapaw Co. (Brensing) Pawnee L.E.-1598-A Limestone 500.00 3/1/1998 2/28/2009 2/28/2022 3.1.4 Stormwater Permits for MS4 and Construction Activities There are no urbanized areas designated as MS4s within this Study Area. A general stormwater permit is required for construction activities. Permittees are authorized to discharge pollutants in stormwater runoff associated with construction activities for construction sites. Stormwater discharges occur only during or immediately following periods of rainfall and elevated flow conditions when the turbidity criteria do not apply and are not considered potential contributors to turbidity impairment. 3.1.5 Section 404 permits Section 404 of the Clean Water Act (CWA) establishes a program to regulate the discharge of dredged or fill material into waters of the United States, including wetlands. Activities in waters of the United States regulated under this program include fill for development, water resource projects (such as dams and levees), infrastructure development (such as highways and airports) and mining projects. Section 404 requires a permit before dredged or fill material may be discharged into waters of the United States, unless the activity is exempt from Section 404 regulation (e.g. certain farming and forestry activities). Section 404 permits are administrated by the U.S. Army Corps of Engineers. EPA reviews and provides comments on each permit application to make sure it adequately protects water Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-6 FINAL August 2010 quality and complies with applicable guidelines. Both USACE and EPA can take enforcement actions for violations of Section 404. Discharge of dredged or fill material in waters can be a significant source of turbidity/TSS. The federal Clean Water Act requires that a permit be issued for activities which discharge dredged or fill materials into the waters of the United States, including wetlands. The state of Oklahoma will use its Section 401 certification authority to ensure Section 404 permits protect Oklahoma water quality standards. 3.2 Nonpoint Sources Nonpoint sources include those sources that cannot be identified as entering the waterbody at a specific location. The relatively homogeneous land use/land cover categories within the Study Area are associated with agricultural and range management activities. This suggests that potential nonpoint sources of TSS include sediments originating from grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, rangeland grazing and other sources of sediment loading (ODEQ 2008). Elevated turbidity measurements can be caused by stream bank erosion processes, stormwater runoff events, and channel disturbances. However, there is insufficient data available to quantify contributions of TSS from these processes. TSS or sediment loading can also occur under non-runoff conditions as a result of anthropogenic activities in riparian corridors which cause erosive conditions. Sediment loading of streams can also originate from natural erosion processes, including the weathering of soil, rocks, and uncultivated land; geological abrasion; and other natural phenomena. Given the lack of data to establish the background conditions for TSS/turbidity, separating background loading from nonpoint sources is not feasible in this TMDL development. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-1 FINAL August 2010 SECTION 4 TECHNICAL APPROACH AND METHODS The objective of a TMDL is to estimate allowable pollutant loads and to allocate these loads to the known pollutant sources in the watershed so appropriate control measures can be implemented and the WQS achieved. A TMDL is expressed as the sum of three elements as described in the following mathematical equation: TMDL = Σ WLA + Σ LA + MOS The WLA is the portion of the TMDL allocated to existing and future point sources. The LA is the portion of the TMDL allocated to nonpoint sources, including natural background sources. The MOS is intended to ensure that WQS will be met. Thus, the allowable pollutant load that can be allocated to point and nonpoint sources can then be defined as the TMDL minus the MOS. 4.1 Determining a Surrogate Target 40 CFR, §130.2(1), states that TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures. Turbidity is a commonly measured indicator of the suspended solids load in streams. However, turbidity is an optical property of water, and measures scattering of light by suspended solids and colloidal matter. To develop TMDLs, a gravimetric (mass-based) measure of solids loading is required to express loads. There is often a strong relationship between the total suspended solids concentration and turbidity. Therefore, the TSS load, which is expressed as mass per time, is used as a surrogate for turbidity and represents the maximum one-day load the stream can assimilate while still attaining the WQS. To determine the relationship between turbidity and TSS, a linear regression between TSS and turbidity was developed using data collected from 1998 to 2007 at four stations within the Study Area. Prior to developing the regression the following steps were taken to refine the dataset: Assign values to censored data (i.e., measured concentrations lower than the analytical quantitation limit and, thus, reported as less than the quantitation limit). For example, using 9.99 to replace samples reported as “<10”; Remove data collected under high flow conditions exceeding the base-flow criterion. This means that measurements corresponding to flow exceedance frequencies lower than 25% were not used in the regression; Check rainfall data on the day when samples were collected and on the previous two days. If there was a significant rainfall event (>= 1.0 inch) in any of these days, the sample will be excluded from regression analysis with one exception. If the significant rainfall happened on the sampling day and the turbidity reading was less than 25 NTUs (half of turbidity standard for streams), the sample will not be excluded from analysis because most likely the rainfall occurred after the sample was taken; andLog-transform both turbidity and TSS data to minimize effects of their non-linear data distributions. When ordinary least squares regression (OLS) is applied to ascertain the best relationship between two variables (i.e., X and Y), one variable (Y) is considered “dependent” on the other Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-2 FINAL August 2010 variable (X), but X must be considered “independent” of the other, and known without measurement error. OLS minimizes the differences, or residuals, between measured Y values and Y values predicted based on the X variable. For current purposes, a relationship is necessary to predict TSS concentrations from measured turbidity values, but also to translate the TSS-based TMDL back to in-stream turbidity values. For this purpose, an alternate regression fitting procedure known as the line of organic correlation (LOC) was applied. The LOC has three advantages over OLS (Helsel and Hirsch 2002): LOC minimizes fitted residuals in both the X and Y directions; It provides a unique best-fit line regardless of which parameter is used as the independent variable; and Regression-fitted values have the same variance as the original data. The LOC minimizes the areas of the right triangles formed by horizontal and vertical lines drawn from observations to the fitted line. The slope of the LOC line equals the geometric mean of the Y on X (TSS on turbidity) and X on Y (turbidity on TSS) OLS slopes, and is calculated as: x y s s m1 m m' sign[r] where m1 is the slope of the LOC line, m is the TSS on turbidity OLS slope, m’ is the turbidity on TSS OLS slope, r is the TSS-turbidity correlation coefficient, sy is the standard deviation of the TSS measurements, and sx is the standard deviation of the turbidity measurements. The intercept of the LOC (b1) is subsequently found by fitting the line with the LOC slope through the point (mean turbidity, mean TSS). The correlation between TSS and turbidity, along with the LOC and the OLS lines are shown in Figure 4-1. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-3 FINAL August 2010 Figure 4-1 Linear Regression for TSS-Turbidity under Base-flow Conditions for Black Bear Creek (OK 62100030010_00) The normalized root mean square error (NRMSE) and R-square (R2) were used as the primary measures of goodness-of-fit. As shown in Figure 4-1, the LOC yields a NRMSE value of 11.7% which means the root mean square error (RMSE) is 11.7% of the average of the measured TSS values. The R-square (R2) value indicates the fraction of the total variance in TSS or turbidity observations that is explained by the LOC. It was noted that there were a few outliers that exerted undue influence on the regression relationship. These outliers were identified by applying the Tukey’s Boxplot method (Tukey 1977) to the dataset of the distances from observed points to the regression line. The Tukey Method is based on the interquartile range (IQR), the difference between the 75th percentile (Q3) and 25th percentile (Q1) of distances between observed points and the LOC. Using the Tukey method, any point with an error greater than Q3 + 1.5* IQR or less than Q1 – 1.5*IQR was identified as an outlier and removed from the regression dataset. The above regressions were calculated using the dataset with outliers removed. The Tukey Method is equivalent to using three times the standard deviation to identify outliers if the residuals (observed - predicted) follow a normal distribution. The probability of sampling results being within three standard deviations of the mean is 99.73% while the probability for the Tukey Method is 99.65%. If three times the standard deviation is used to identify outliers, it is necessary to first confirm that the residuals are indeed normally distributed. This is difficult to do because of the size limitations of the existing turbidity & TSS dataset. Tukey’s method does not rely on any assumption about the distribution of the residuals. It can be used regardless of the shape of distribution. 1 10 100 1000 1 10 100 1000 TSS (mg/L) Turbidity (NTU) Data LOC OLS - TSS on Turbidity OLS - Turbidity on TSS log(TSS) = 0.8561*log(Turb) + 0.1544 R2 = 0.747 Normalized RMSE = 11.7% Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-4 FINAL August 2010 Using the regression equation shown in Figure 4-1, a turbidity value of 50 NTU (standard applicable to Black Bear Creek) corresponds to a TSS concentration of 40.6 mg/L. 4.2 Using Load Duration Curves to Develop TMDLs The TMDL calculations presented in this report are derived from load duration curves (LDC). LDCs facilitate rapid development of TMDLs, and as a TMDL development tool, indicate whether impairments are associated with point or nonpoint sources. The technical approach for using LDCs for TMDL development includes the four following steps described in Subsections 4.3 through 4.5 below: Preparing flow duration curves for gaged and ungaged WQM stations; Estimating loading in the receiving water using measured TSS water quality data and turbidity-converted data; Determining the overall percent reduction goal (PRG) necessary to attain WQS; and Historically, in developing WLAs for pollutants from point sources, it was customary to designate a critical low flow condition (e.g., 7Q2) at which the maximum permissible loading was calculated. As water quality management efforts expanded in scope to quantitatively address nonpoint sources of pollution and various types of pollutants, it became clear that this single critical low flow condition was inadequate to ensure adequate water quality across a range of flow conditions. Use of the LDC obviates the need to determine a design storm or selected flow recurrence interval with which to characterize the appropriate flow level for the assessment of critical conditions. For waterbodies impacted by both point and nonpoint sources, the “nonpoint source critical condition” would typically occur during high flows, when rainfall runoff would contribute the bulk of the pollutant load, while the “point source critical condition” would typically occur during low flows, when point source discharges would dominate the base flow of the impaired water. However, flow range is only a general indicator of the relative proportion of point/nonpoint contributions. It is not used in this report to quantify point source or nonpoint source contributions. Violations that occur during low flows may not be caused exclusively by point sources. Violations have been noted in some watersheds that contain no point sources. LDCs display the maximum allowable load over the complete range of flow conditions by a line using the calculation of flow multiplied by the water quality criterion. The TMDL can be expressed as a continuous function of flow, equal to the line, or as a discrete value derived from a specific flow condition. 4.3 Development of Flow Duration Curves Flow duration curves serve as the foundation of LDCs and are graphical representations of the flow characteristics of a stream at a given site. Flow duration curves utilize the historical hydrologic record from stream gages to forecast future recurrence frequencies. Many WQM stations throughout Oklahoma do not have long-term flow data; therefore, flow frequencies must be estimated. The most basic method to estimate flows at an ungaged site involves 1) identifying a downstream flow gage; 2) calculating the contributing drainage areas of the ungaged sites and the flow gage; and 3) calculating daily flows at the ungaged site by using the flow at the gaged site multiplied by the drainage area ratio. A more complex approach used to support this analysis also considers watershed differences in rainfall, land use, and the Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-5 FINAL August 2010 hydrologic properties of soil that govern runoff and retention. For the Black Bear Creek watershed, flows were projected using data from USGS 07153000, Black Bear Creek at SH 18 at Pawnee. A more detailed explanation of the methods for estimating flow at ungaged WQM stations is provided in Appendix B. Flow duration curves are a type of cumulative distribution function. The flow duration curve represents the fraction of flow observations that equal or exceed a given flow at the site of interest. The observed flow values are first ranked from highest to lowest then, for each observation, the percentage of observations equal to or exceeding that flow is calculated. The flow value is read from the ordinate (y-axis), which is typically on a logarithmic scale since the high flows would otherwise overwhelm the low flows. The flow exceedance frequency is read from the abscissa (x-axis), which is numbered from 0 to 100 percent, and may or may not be logarithmic. The flow exceedance frequency is defined as percent of time a given flow was equaled or exceeded based on daily flow values. Therefore, the lowest measured flow occurs at an exceedance frequency of 100 percent indicating that flow has equaled or exceeded this value 100 percent of the time, while the highest measured flow is found at an exceedance frequency of 0 percent. The median flow occurs at a flow exceedance frequency of 50 percent. The flow exceedance frequencies of the USGS gage used to project flows for this report are provided in Appendix B. While the number of observations required to develop a flow duration curve is not rigorously specified, a flow duration curve is usually based on more than 1 year of observations, and encompasses inter-annual and seasonal variation. Ideally, the drought of record and flood of record are included in the observations. For this purpose, the long-term flow gaging stations operated by the USGS are utilized (USGS 2007a). A typical semi-log flow duration curve exhibits a sigmoidal shape, bending upward near a flow exceedance frequency value of 0 percent and downward at a frequency near 100 percent, often with a relatively constant slope in between. For sites that on occasion exhibit no flow, the curve will intersect the abscissa at a frequency less than 100 percent. As the number of observations at a site increases, the line of the LDC tends to appear smoother. However, at extreme low and high flow values, flow duration curves may exhibit a “stair step” effect due to the USGS flow data rounding conventions near the limits of quantitation. Flow duration curves are generated using a DEQ automated application referred to as the Oklahoma TMDL toolbox. Figure 4-2 shows the flow duration curve generated from the Oklahoma TMDL toolbox for Black Bear Creek using flow data from 1984 to 2006. The USGS National Water Information System serves as the primary source of flow measurements for the application. All available daily average flow values for all gages in Oklahoma, as well as the nearest upstream and downstream gages in adjacent states, were retrieved for use in the application. The application includes a data update module that automatically downloads the most recent USGS data and appends it to the existing flow database. Some instantaneous flow measurements were available from various agencies. These were not combined with the daily average flows or used in calculating flow percentiles, but were matched to TSS and/or turbidity grab measurements collected at the same site and time. When available, these instantaneous flow measurements were used in lieu of the daily average flow to calculate instantaneous TSS loads. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-6 FINAL August 2010 Figure 4-2 Flow Duration Curve for Black Bear Creek (OK621200030010_00) 4.4 Development of TMDLs Using Load Duration Curves The final step in the TMDL calculation process involves a group of additional computations derived from the preparation of LDCs. These computations are necessary to derive a PRG (which is one method of presenting how much TSS loading must be reduced to meet turbidity WQS in the impaired watershed). Step 1: Generate LDCs. LDCs are similar in appearance to flow duration curves; however, the ordinate is expressed in terms of a load typically in lbs/day. The curve represents the water quality target for TSS (40.6 mg/L) expressed in terms of a load through multiplication by the continuum of flows historically observed at this site. The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the USGS (or project flow using Oklahoma TMDL Toolbox if station is ungaged); sorting the flow data and calculating flow exceedance frequency for the time period and season of interest; obtaining available turbidity and TSS water quality data; matching the water quality observations with the flow data from the same date; displaying a curve on a plot that represents the allowable load multiplying the actual or estimated flow by the WQtarget for TSS; multiplying the flow by the water quality parameter concentration to calculate daily loads (for sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2); then 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 0 10 20 30 40 50 60 70 80 90 100 Flow (cfs) Flow Exceedence Frequency (%) Flow Duration Curver (OK410600010030_00) High flow conditions Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-7 FINAL August 2010 plotting the flow exceedance frequencies and daily load observations in a load duration plot. The culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve: TMDL (lb/day) = WQtarget * flow (cfs) * unit conversion factor where: WQtarget = 40.6 mg/L (TSS) unit conversion factor = 5.39377 L*s*lb /(ft3*day*mg) The flow exceedance frequency (x-value of each point) is obtained by looking up the historical exceedance frequency of the measured or estimated flow; in other words, the percent of historical observations that equal or exceed the measured or estimated flow. Historical observations of TSS and/or turbidity concentrations are paired with flow data and are plotted on the LDC. The TSS load (or the y-value of each point) is calculated by multiplying the TSS concentration (measured or converted from turbidity) (mg/L) by the instantaneous flow (cfs) at the same site and time, with appropriate volumetric and time unit conversions. TSS loads representing exceedance of water quality criteria fall above the TMDL line. As noted earlier, runoff has a strong influence on loading of nonpoint source pollution yet flows do not always correspond directly to local runoff. High flows may occur in dry weather due to upstream precipitation events or releases form upstream dams. Runoff influence may be observed with low or moderate flows depending on antecedent conditions. Step 2: Define MOS. The MOS may be defined explicitly or implicitly. A typical explicit approach would reserve some specific fraction of the TMDL as the MOS. In an implicit approach, conservative assumptions used in developing the TMDL are relied upon to provide an MOS to assure that WQSs are attained. For turbidity (TSS) TMDLs an explicit MOS is derived from the NRMSE established by the turbidity/TSS regression analysis conducted for each waterbody. This approach for setting an explicit MOS has been used in other approved turbidity TMDLs. For the TMDLs in this report, an explicit MOS of 10 percent was selected. Step 3: Calculate WLA. As previously stated, the pollutant load allocation for point sources is defined by the WLA. For TMDL development purposes when addressing turbidity or TSS, a WLA will be established for wastewater (continuous) discharges in impaired watersheds that do not have a BOD or CBOD permit limit but do have a TSS limit. These point source discharges of inorganic suspended solids will be assigned a TSS WLA as part of turbidity TMDLs to ensure WQS can be maintained. The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading will vary with flow condition. TMDLs can be expressed in terms of maximum allowable concentrations, or as different maximum loads allowable under different flow conditions, rather than single maximum load values. A load-based approach meets the requirements of 40 CFR, 130.2(i) for expressing TMDLs “in terms of mass per time, toxicity, or other appropriate measures.” WLA for WWTP. WLAs may be set to zero for watersheds with no existing or planned continuous permitted point sources. For watersheds with permitted point sources discharging inorganic suspended solids, WLAs may be derived. A WLA may be calculated for each active Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-8 FINAL August 2010 NPDES wastewater discharger using a mass balance approach as shown in the equation below. The permitted flow rate used for each point source discharge and the water quality criterion concentration are used to estimate the WLA for each wastewater facility. In cases where a permitted flow rate is not available for a WWTP, then the maximum monthly average flow rate derived from DMRs can be used. All WLA values for each NPDES wastewater discharger are then summed to represent the total WLA for the watershed. WLA = WQtarget * flow * unit conversion factor (lb/day) where: WQtarget = 40.6 mg/L (TSS); flow (106 gal/day) = permitted flow unit conversion factor = 8.3445 L*lb/(gal*mg) WLA for Permitted Stormwater. For turbidity TMDLs, WLAs for permitted stormwater such as MS4s, construction, and multi-sector general permits are not calculated since these discharges occur under high flow conditions when the turbidity criteria do not apply. Step 4: Calculate LA. Given the lack of data and the variability of storm events, it is difficult to quantify discharges that accurately represent projected loadings from nonpoint sources. LAs can be calculated under different flow conditions as the water quality target load minus the WLA. The LA is represented by the area under the LDC but above the WLA. The LA at any particular flow exceedance is calculated as shown in the equation below. LA = TMDL - WLA - MOS Step 5: Estimate LA Load Reduction. After existing loading estimates are computed, nonpoint load reduction estimates are calculated by using the difference between estimated existing loading and the allowable load expressed by the LDC (TMDL-MOS). This difference is expressed as the overall PRG for the impaired waterbody. For turbidity, the PRG is the load reduction that ensures that no more than 10 percent of the samples under flow-base conditions exceed the TMDL. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-1 FINAL August 2010 SECTION 5 TMDL CALCULATIONS 5.1 Estimated Loading and Critical Conditions USEPA regulations at 40 CFR 130.7(c) (1) require TMDLs to take into account critical conditions for stream flow, loading, and all applicable water quality standards. To accomplish this, available instream WQM data were evaluated with respect to flows and magnitude of water quality criteria exceedance using LDCs. To calculate the TSS load at the WQtarget, the flow rate at each flow exceedance frequency is multiplied by a unit conversion factor (5.39377 L*s*lb /ft3/day/mg) and the TSS target (40.6 mg/L). This calculation produces the maximum TSS load in the stream that will result in attainment of the 50 NTU standard for turbidity. The allowable TSS loads at the WQS establish the TMDL and are plotted versus flow exceedance frequency as a LDC. The x-axis indicates the flow exceedance frequency, while the y-axis is expressed in terms of a TSS load in pounds per day. To estimate existing loading, TSS and turbidity observations from 1998 to 2007 are paired with the flows measured or estimated in that segment on the same date. For sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2. Pollutant loads are then calculated by multiplying the TSS concentration by the flow rate and the unit conversion factor. The associated flow exceedance frequency is then matched with the measured flow from the tables provided in Appendix B. The observed TSS or converted turbidity loads are then added to the LDC plot as points. These points represent individual ambient water quality samples of TSS. Points above the LDC indicate the TSS target was exceeded at the time of sampling. Conversely, points under the LDC indicate the sample did not exceed the WQtarget. Figure 5-1 shows the LDC developed for this Black Bear Creek. It is noted that the LDC plot includes data under all flow conditions to show the overall condition of the stream. However, it is noted that the turbidity standard only applies for base-flow conditions. Thus, when assessing beneficial use support, only the portion of the graph corresponding to flows from the 25% to the 100% flow exceedance frequencies should be used. The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading varies with flow condition. Existing loading, and load reductions required to meet the TMDL water quality target can also be calculated under different flow conditions. The difference between existing loading and the water quality target is used to calculate the loading reductions required. The overall PRG is calculated for Black Bear Creek as the reduction in load required so no more than 10 percent of the samples collected under base-flow conditions would exceed 36.5 mg/L (90 percent of the TSS WQtarget to account for the explicit MOS). This is done through an iterative process of taking a series of percent reduction values applying each value uniformly between the concentrations of samples and verifying that no more than 10 percent of the samples exceed the water quality target concentration. The concentrations are derived from only those samples collected after high flow samples are excluded. The PRG for Black Bear Creek is calculated to be 60.3 percent. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-2 FINAL August 2010 Figure 5-1 Load Duration Curve for Total Suspended Solids in Black Bear Creek (OK621200030010_00) As shown in Figure 5-1, TSS levels exceed the water quality target during all flow conditions, possibly indicating water quality impairments due to nonpoint sources or a combination of point and nonpoint sources. 5.2 Wasteload Allocation NPDES-permitted facilities discharging inorganic TSS are allocated a daily wasteload calculated as their permitted flow rate multiplied by the water quality target. In other words, the facilities are required to meet instream criteria in their discharge. If the current monthly TSS limits of a facility are greater than instream TSS criteria, the new limits equal to instream criteria will be applied to the facility as their permit is renewed. There are only two NPDES-permitted facilities discharging inorganic TSS to Black Bear Creek (OK0002534 and OKG950016). The WLA for these facilities is derived as follows: WLA_WWTP = WQtarget * flow * unit conversion factor (lb/day) WLA= 40.6 mg/L *0.484 MGD* 8.3445 L*lb/gal/mg = 153.4 lb/day flow = 0.244+0.24 MGD = maximum monthly average self-reported flows for OK0002534 and OKG950016 No wasteload allocations are needed for stormwater dischargers. By definition, any stormwater discharge occurs during periods of rainfall and elevated flow conditions. Oklahoma’s Water Quality Standards specify that the criteria for turbidity “apply only to seasonal base flow conditions” and go on to say “Elevated turbidity levels may be expected during, and for several days after, a runoff event” [OAC 785:45-5-12(f)(7)]. Therefore, WLA 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0 10 20 30 40 50 60 70 80 90 100 TSS Load (lbs/day) Flow Exceedence Frequency (%) Load Duration Curver (OK410600010030_00) TSS data Turb data ->TSS LDC High flow conditions Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-3 FINAL August 2010 for NPDES-regulated storm water discharges is essentially considered unnecessary in this TMDL report and will not be included in the TMDL calculations. Conditions in existing stormwater permits are sufficient to protect receiving waters. To accommodate the potential for future growth in the watershed, 1% of TSS loading is reserved as part of the WLA. 5.2.1 Section 404 permits No TSS wasteload allocations were set aside for Section 404 permits. The state will use its Section 401 certification authority to ensure Section 404 permits protect Oklahoma water quality standards and comply with TSS TMDLs in this report. Section 404 permits will be conditioned to meet one of the following two conditions to be certified by the state: Include TSS limits in the permit and establish a monitoring requirement to ensure compliance with turbidity standard and TSS TMDLs. Submit to the ODEQ a BMP turbidity reduction plan which should include all practicable turbidity control techniques. The turbidity reduction plan must be approved first before a Section 404 permit can be issued. 5.3 Load Allocation As discussed in Section 3.2, pollutant loading to the receiving streams of each waterbody emanate from a number of different nonpoint sources. The data analysis and the LDCs demonstrate that exceedances of the turbidity WQS at the WQM stations are the result of a variety of nonpoint sources. The LA is calculated as the difference between the TMDL, MOS, and WLA as follows: LA = TMDL – WLA_WWTP –WLA_growth - MOS 5.4 Seasonal Variability Federal regulations (40 CFR §130.7(c)(1)) require that TMDLs account for seasonal variation in watershed conditions and pollutant loading. The TMDL established in this report adhere to the seasonal application of the Oklahoma WQS for turbidity, which applies to seasonal base flow conditions only. Seasonal variation was also accounted for in this TMDL by using more than 5 years of water quality data and by using the longest period of USGS flow records possible when estimating flows to develop flow exceedance frequencies. 5.5 Margin of Safety Federal regulations (40 CFR §130.7(c)(1)) require that TMDLs include an MOS. The MOS is a conservative measure incorporated into the TMDL equation that accounts for the lack of knowledge associated with calculating the allowable pollutant loading to ensure WQSs are attained. USEPA guidance allows for use of implicit or explicit expressions of the MOS, or both. When conservative assumptions are used in development of the TMDL, or conservative factors are used in the calculations, the MOS is implicit. When a specific percentage of the TMDL is set aside to account for lack of knowledge, then the MOS is considered explicit. An explicit Margin of Safety of 10% was selected in this TMDL report. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-4 FINAL August 2010 5.6 TMDL Calculations This TMDL was derived using the LDC method. A TMDL is expressed as the sum of all WLAs (point source loads), LAs (nonpoint source loads), and an appropriate MOS, which attempts to account for lack of knowledge concerning the relationship between effluent limitations and water quality. This definition can be expressed by the following equation: TMDL = Σ WLA + Σ LA + MOS The TMDL represents a continuum of desired load over all flow conditions, rather than fixed at a single value, because loading capacity varies as a function of the flow present in the stream. The higher the flow is, the more wasteload the stream can handle without violating water quality standards. Regardless of the magnitude of the WLA calculated in these TMDLs, future new discharges or increased load from existing discharges will be considered consistent with the TMDL provided the NPDES permit requires instream criteria to be met. The TMDL, WLA, LA, and MOS are calculated at every 5th flow interval percentile (Table 5-1). Table 5-1 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) Percentile Flow (cfs) TMDL (lb/day) WLA (lb/day) LA (lb/day) MOS WWTP MS4 (lb/day) Future Growth 0 18260 NA 0 0 NA NA NA 5 1616 NA 0 0 NA NA NA 10 695 NA 0 0 NA NA NA 15 386 NA 0 0 NA NA NA 20 245 NA 0 0 NA NA NA 25 166 34,024 153 0 340 30,128 3,402 30 113 23,140 153 0 231 20,441 2,314 35 82 16,787 153 0 168 14,787 1,679 40 61 12,482 153 0 125 10,956 1,248 45 48 9,756 153 0 98 8,530 976 50 37 7,481 153 0 75 6,505 748 55 30 6,128 153 0 61 5,301 613 60 24 4,981 153 0 50 4,279 498 65 20 4,079 153 0 41 3,477 408 70 18 3,628 153 0 36 3,075 363 75 14 2,951 153 0 30 2,473 295 80 11 2,214 153 0 22 1,817 221 85 8 1,640 153 0 16 1,306 164 90 5 1,066 153 0 11 795 107 95 2 451 153 0 5 248 45 100 0 0 0 0 0 0 0 Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-5 FINAL August 2010 5.7 Reasonable Assurances ODEQ will collaborate with a host of other state agencies and local governments working within the boundaries of state and local regulations to target available funding and technical assistance to support implementation of pollution controls and management measures. Various water quality management programs and funding sources provide a reasonable assurance that the pollutant reductions as required by this TMDL can be achieved and water quality can be restored to maintain designated uses. ODEQ’s Continuing Planning Process (CPP), required by the CWA §303(e)(3) and 40 CFR 130.5, summarizes Oklahoma’s commitments and programs aimed at restoring and protecting water quality throughout the state (ODEQ 2006). The CPP can be viewed from ODEQ’s website at 2006 Continuing Planning Process. Table 5-2 provides a partial list of the state partner agencies ODEQ will collaborate with to address point and nonpoint source reduction goals established by TMDLs. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-6 FINAL August 2010 Table 5-2 Partial List of Oklahoma Water Quality Management Agencies Agency Web Link Oklahoma Conservation Commission http://www.conservation.ok.gov Oklahoma Department of Wildlife Conservation http://www.wildlifedepartment.com/ Oklahoma Department of Agriculture, Food, and Forestry http://www.oda.state.ok.us/aems.htm Oklahoma Water Resources Board http://www.owrb.ok.gov Nonpoint source pollution in Oklahoma is managed by the Oklahoma Conservation Commission (OCC). The OCC works with state partners such as Oklahoma Department of Agriculture, Food, and Forestry (ODAFF) and federal partners such as USEPA and the National Resources Conservation Service (NRCS), to address water quality problems similar to those seen in the Study Area. The primary mechanisms used for management of nonpoint source pollution are incentive-based programs that support the installation of BMPs and public education and outreach. Other programs include regulations and permits for CAFOs. The CAFO Act, as administered by the ODAFF, provides CAFO operators the necessary tools and information to deal with the manure and wastewater animals produce so streams, lakes, ponds, and groundwater sources are not polluted. As authorized by Section 402 of the CWA, the ODEQ has delegation of the NPDES Program in Oklahoma, except for certain jurisdictional areas related to agriculture and the oil and gas industry retained by State Department of Agriculture and Oklahoma Corporation Commission, for which the USEPA has retained permitting authority. The NPDES Program in Oklahoma is implemented via Title 252, Chapter 606 of the Oklahoma Pollution Discharge Elimination System (OPDES) Act and in accordance with the agreement between ODEQ and USEPA relating to administration and enforcement of the delegated NPDES Program. Implementation of point source WLAs is done through permits issued under the OPDES program. The reduction rate called for in this TMDL report is 60.3 percent. The ODEQ recognizes that achieving such high reduction maybe difficult, especially since unregulated nonpoint sources are a major cause of the impairment. Black Bear Creek TMDL Public Participation FINAL Turbidity TMDL_Black_Bear_Creek.docx 6-1 FINAL August 2010 SECTION 6 PUBLIC PARTICIPATION This report was submitted to EPA for technical review and was technically accepted on July 01, 2010. A public notice was circulated on July 15, 2010 to local newspapers and/or other publications in the area affected by this TMDL and persons on the DEQ contact list. The public comment period ended on August 30, 2010. No requests for a public meeting were received. No comments were received. Black Bear Creek TMDL References FINAL Turbidity TMDL_Black_Bear_Creek.docx 7-1 FINAL August 2010 SECTION 7 REFERENCES Helsel, D.R. and R.M. Hirsch 2002. Statistical Methods in Water Resources. U.S. Department of the Interior, U.S. Geological Survey, September 2002. ODEQ 2006. Continuing Planning Process. 2006 Edition. ODEQ 2008. Water Quality in Oklahoma, 2008 Integrated Report. 2008 ODEQ 2009. Fact Sheet: General Wastewater Permit For Rock, Sand, And Gravel Quarries; To Construct Or Operate Industrial Wastewater Surface Impoundments; And/Or To Land Apply Industrial Wastewater For Dust Suppression, Or To Recycle Wastewater As Wash Water, General Permit No. OKG950000. Oklahoma Climate Survey. 2007. Viewed August 29, 2005 in http://climate.ocs.ou.edu/county_climate/Products/County_Climatologies/ OWRB. 2008. Oklahoma Water Resources Board. 2008 Water Quality Standards. Tukey, J.W. 1977. Exploratory Data Analysis. Addison-Wesely. U.S. Census Bureau 2000. http://www.census.gov/main/www/cen2000.html USEPA 1991. Guidance for Water Quality-Based Decisions: The TMDL Process. Office of Water, USEPA 440/4-91-001. USEPA 2003. Guidance for 2004 Assessment, Listing and Reporting Requirements Pursuant to Sections 303(d) and 305(b) of the Clean Water Act, TMDL -01-03 - Diane Regas-- July 21, 2003. USGS 2007. Multi-Resolution Land Characteristics Consortium. http://www.mrlc.gov/index.asp USGS 2007a. USGS Daily Streamflow Data. http://waterdata.usgs.gov/nwis/sw USGS 2009. USGS National Water Information System Website. http://waterdata.usgs.gov/nwis/?percentile_help Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-1 FINAL August 2010 APPENDIX A AMBIENT WATER QUALITY DATA 1998 - 2007 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-2 FINAL August 2010 Appendix A Ambient Water Quality Data 1998 - 2007 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200030010-001AT 12/01/1998 603 240 high flow 621200030010-001AT 01/20/1999 12 22 621200030010-001AT 02/09/1999 388 204 high flow 621200030010-001AT 03/07/1999 70 64 621200030010-001AT 04/06/1999 89 62 high flow 621200030010-001AT 04/06/1999 84 62 high flow 621200030010-001AT 05/17/1999 400 264 high flow 621200030010-001AT 06/08/1999 135 62 621200030010-001AT 06/08/1999 135 61 621200030010-001AT 07/07/1999 225 206 high flow 621200030010-001AT 07/07/1999 225 196 high flow 621200030010-001AT 08/03/1999 20 17 621200030010-001AT 08/03/1999 20 24 621200030010-001AT 09/08/1999 43 48 Rainfall 621200030010-001AT 09/08/1999 43 54 Rainfall 621200030010-001AT 10/19/1999 16 16 621200030010-001AT 10/19/1999 16 18 621200030010-001AT 11/16/1999 20 10 621200030010-001AT 11/16/1999 20 14 621200030010-001AT 12/14/1999 441 312 high flow 621200030010-001AT 12/14/1999 441 320 high flow 621200030010-001AT 02/01/2000 30 621200030010-001AT 02/23/2000 80 high flow 621200030010-001AT 05/16/2000 145 200 621200030010-001AT 06/21/2000 394 320 high flow 621200030010-001AT 08/02/2000 289 164 high flow 621200030010-001AT 08/22/2000 17 22 621200030010-001AT 09/20/2000 23 < 1 621200030010-001AT 10/17/2000 50 34 Rainfall 621200030010-001AT 11/14/2000 155 92 621200030010-001AT 2/7/2001 85 621200030010-001AT 3/7/2001 460 high flow 621200030010-001AT 4/4/2001 40 621200030010-001AT 5/9/2001 25 621200030010-001AT 6/6/2001 213 high flow 621200030010-001AT 7/11/2001 12 621200030010-001AT 8/8/2001 15 621200030010-001AT 10/3/2001 14 621200030010-001AT 2/6/2002 59 621200030010-001AT 3/13/2002 30 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-3 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200030010-001AT 4/10/2002 99 621200030010-001AT 5/8/2002 72 621200030010-001AT 6/4/2002 137 621200030010-001AT 7/9/2002 18 621200030010-001AT 8/26/2002 348 high flow 621200030010-001AT 9/23/2002 495 high flow 621200030010-001AT 10/28/2002 588 high flow 621200030010-001AT 12/2/2002 21 621200030010-001AT 1/21/2003 17 621200030010-001AT 3/5/2003 119 high flow 621200030010-001AT 4/2/2003 40 621200030010-001AT 5/5/2003 49 621200030010-001AT 6/10/2003 122 621200030010-001AT 7/8/2003 46 621200030010-001AT 8/13/2003 23 621200030010-001AT 9/17/2003 448 621200030010-001AT 10/13/2003 59 621200030010-001AT 11/19/2003 372 high flow 621200030010-001AT 12/17/2003 47 621200030010-001AT 1/13/2004 17 621200030010-001AT 5/3/2004 34 621200030010-001AT 6/15/2004 78 621200030010-001AT 7/19/2004 17 621200030010-001AT 8/23/2004 90 621200030010-001AT 9/28/2004 26 621200030010-001AT 10/26/2004 76 621200030010-001AT 11/29/2004 163 621200030010-001AT 1/31/2005 54 621200030010-001AT 2/23/2005 45 high flow 621200030010-001AT 4/19/2005 13 621200030010-001AT 6/6/2005 27 621200030010-001AT 7/18/2005 31 621200-03-0010D 07/23/2002 30.1 18 10.368 621200-03-0010D 08/27/2002 529 <10 68.463 621200-03-0010D 10/01/2002 154 32 24.206 621200-03-0010D 11/05/2002 206 112 79.02 621200-03-0010D 12/03/2002 22.2 14 18.876 621200-03-0010D 01/14/2003 41.1 <10 33.586 621200-03-0010D 02/19/2003 2.09 17 28.936 621200-03-0010D 03/25/2003 141 103 372.5 high flow 621200-03-0010D 04/29/2003 100 66 89.875 621200-03-0010D 06/03/2003 89.7 71 26.374 621200-03-0010D 07/08/2003 104 70 11.195 621200-03-0010D 08/06/2003 40.6 2.044 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-4 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010D 08/12/2003 40.5 30 1.962 621200-03-0010D 09/16/2003 329 172 48.996 621200-03-0010D 10/21/2003 127 36 19.438 621200-03-0010D 12/02/2003 74.1 16 9.051 621200-03-0010D 01/06/2004 35.7 21 7.5 621200-03-0010D 02/10/2004 221 162 588.151 high flow 621200-03-0010D 03/16/2004 281 231 496 high flow 621200-03-0010D 04/20/2004 17.6 <10 79.166 621200-03-0010D 06/08/2004 56.4 53 76.518 621200-03-0010D 05/30/2007 >1000 618 high flow 621200-03-0010D 06/26/2007 93 high flow 621200-03-0010D 08/06/2007 19 621200-03-0010D 09/11/2007 3040 2000 high flow 621200-03-0010G 03/17/1998 918 1360 high flow 621200-03-0010G 04/13/1998 45.4 44.5 84.955 621200-03-0010G 05/20/1998 96.8 82 116.065 621200-03-0010G 05/26/1998 589 536 storm water 621200-03-0010G 06/17/1998 105 76 22.631 621200-03-0010G 07/23/1998 32.8 35 6.354 621200-03-0010G 07/26/1998 17.8 621200-03-0010G 08/10/1998 26.9 621200-03-0010G 08/17/1998 26.8 31.5 4.638 621200-03-0010G 08/23/1998 23.2 621200-03-0010G 09/17/1998 24.5 2.261 621200-03-0010G 09/21/1998 16.9 17 2.001 621200-03-0010G 10/05/1998 1608 1950 high flow 621200-03-0010G 10/27/1998 157 82.7 33.309 621200-03-0010G 06/17/2002 980 high flow 621200-03-0010G 06/24/2002 112 621200-03-0010G 07/01/2002 32.8 621200-03-0010G 07/15/2002 41 621200-03-0010G 08/12/2002 47.9 621200-03-0010G 10/21/2002 9.21 621200-03-0010G 12/02/2002 10.2 621200-03-0010G 05/27/2003 105 high flow 621200-03-0010G 06/23/2003 36.1 621200-03-0010G 07/17/2003 36.1 2.679 621200-03-0010G 07/28/2003 22.1 621200-03-0010G 08/25/2003 20.5 621200-03-0010G 09/29/2003 193 621200-03-0010G 10/20/2003 116 621200-03-0010M 07/23/2002 61.7 18 4.061 621200-03-0010M 08/27/2002 489 11 27.849 621200-03-0010M 10/01/2002 64.9 80 12.924 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-5 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010M 11/05/2002 178 111 66.193 621200-03-0010M 12/03/2002 9.74 <10 9.702 621200-03-0010M 01/14/2003 21.6 <10 26.029 621200-03-0010M 02/19/2003 18 13 18.463 621200-03-0010M 03/25/2003 147 127 195.191 high flow 621200-03-0010M 04/29/2003 143 116 69.07 621200-03-0010M 05/27/2003 125 high flow 621200-03-0010M 06/03/2003 80.7 76 15.155 621200-03-0010M 06/24/2003 135 16.958 621200-03-0010M 07/08/2003 78.7 75 3.946 621200-03-0010M 07/28/2003 78.5 621200-03-0010M 08/12/2003 58.4 40 1.013 621200-03-0010M 08/25/2003 36.1 621200-03-0010M 09/16/2003 143 64 14.422 621200-03-0010M 09/29/2003 137 621200-03-0010M 10/20/2003 120 621200-03-0010M 10/21/2003 103 52 5.226 621200-03-0010M 12/02/2003 58.6 19 5.511 621200-03-0010M 01/06/2004 10.3 10 6.409 621200-03-0010M 02/10/2004 314 167 209.74 high flow 621200-03-0010M 03/16/2004 272 232 high flow 621200-03-0010M 04/20/2004 15.9 23 30.749 621200-03-0010M 06/08/2004 141 110 15.57 621200-03-0010M 05/29/2007 358 290 high flow 621200-03-0010M 06/26/2007 1182 high flow 621200-03-0010M 07/30/2007 44 621200-03-0010M 09/10/2007 2404 high flow 621200-03-0010W 08/05/2002 57.4 <10 1.48 621200-03-0010W 09/03/2002 18.2 19 3.55 621200-03-0010W 09/30/2002 39.2 23 14.63 621200-03-0010W 11/04/2002 167 61 54.956 621200-03-0010W 12/02/2002 6.29 17 10.661 621200-03-0010W 01/14/2003 14.8 35 18.97 621200-03-0010W 02/18/2003 8.36 <10 15.985 621200-03-0010W 03/24/2003 116 92 195.265 high flow 621200-03-0010W 04/28/2003 79.4 59 45.412 621200-03-0010W 05/27/2003 93.6 high flow 621200-03-0010W 06/03/2003 41.4 46 17.639 621200-03-0010W 06/05/2003 36 13.622 621200-03-0010W 06/23/2003 36 621200-03-0010W 07/07/2003 30.6 36 4.082 621200-03-0010W 07/28/2003 43.3 621200-03-0010W 08/11/2003 29.2 29 0.671 621200-03-0010W 08/25/2003 25.1 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-6 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010W 09/15/2003 98.2 125 8.606 Rainfall 621200-03-0010W 09/29/2003 23.5 621200-03-0010W 10/20/2003 34.3 22 3.113 621200-03-0010W 10/20/2003 37.7 621200-03-0010W 12/01/2003 20.6 <10 3.198 621200-03-0010W 01/05/2004 12.5 18 4.471 621200-03-0010W 02/09/2004 122 147 150.954 621200-03-0010W 03/15/2004 249 143 401.482 high flow 621200-03-0010W 04/19/2004 10.6 20 31.852 621200-03-0010W 06/01/2004 16.1 18 3.385 621200-03-0010W 05/29/2007 246 578 high flow 621200-03-0010W 06/26/2007 383 high flow 621200-03-0010W 07/30/2007 21 621200-03-0010W 09/10/2007 6932 high flow 1 High flow = Sample was not collected under base flow conditions (sample collected at flows greater that 25% flow exceedance frequency. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx FINAL August 2010 APPENDIX B PROJECTED FLOW EXCEEDANCE FREQUENCIES Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-1 FINAL August 2010 Appendix B Projected Flow exceedance frequencies for Black Bear Creek Flow Duration Curve WBID Segment OK62120030010_00 USGS Gage Reference 07153000 Flow Exceedance Frequency (%) Flow (cfs) Flow Exceedance Frequency (%) Flow (cfs) Flow Exceedance Frequency (%) Flow (cfs) 0 18260.1 34 88.5 68 18.8 1 4869.4 35 81.9 69 17.7 2 3386.4 36 77.5 70 17.7 3 2523.2 37 71.9 71 16.6 4 1980.9 38 68.6 72 15.5 5 1615.7 39 64.2 73 15.5 6 1350.1 40 60.9 74 14.4 7 1128.8 41 57.5 75 14.4 8 958.4 42 54.2 76 13.3 9 821.2 43 52.0 77 13.3 10 695.0 44 49.8 78 12.2 11 618.6 45 47.6 79 11.1 12 541.2 46 45.4 80 10.8 13 485.8 47 43.2 81 10.3 14 434.9 48 39.8 82 9.7 15 386.2 49 38.7 83 9.1 16 349.7 50 36.5 84 8.5 17 320.9 51 35.4 85 8.0 18 292.2 52 33.2 86 7.4 19 263.4 53 32.1 87 6.9 20 244.6 54 31.0 88 6.3 21 224.7 55 29.9 89 5.9 22 205.8 56 27.7 90 5.2 23 190.3 57 26.6 91 4.6 24 177.1 58 25.5 92 4.1 25 166.0 59 25.5 93 3.5 26 152.7 60 24.3 94 3.0 27 141.7 61 23.2 95 2.2 28 131.7 62 22.1 96 1.4 29 121.7 63 22.1 97 0.8 30 112.9 64 21.0 98 0.3 31 106.2 65 19.9 99 0.02 32 100.7 66 19.9 100 0 33 94.1 67 18.8 Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-2 FINAL August 2010 Appendix B General Method for Estimating Flow at WQM Stations Flows duration curve will be developed using existing USGS measured flow where the data exist from a gage on the stream segment of interest, or by estimating flow for stream segments with no corresponding flow record. Flow data to support flow duration curves and load duration curves will be derived for each Oklahoma stream segment in the following priority: i) In cases where a USGS flow gage occurs on, or within one-half mile upstream or downstream of the Oklahoma stream segment. a. If simultaneously collected flow data matching the water quality sample collection date are available, these flow measurements will be used. b. If flow measurements at the coincident gage are missing for some dates on which water quality samples were collected, the gaps in the flow record will be filled, or the record will be extended, by estimating flow based on measured streamflows at a nearby gage. First, the most appropriate nearby stream gage is identified. All flow data are first log-transformed to linearize the data because flow data are highly skewed. Linear regressions are then developed between 1) daily streamflow at the gage to be filled/extended, and 2) streamflow at all gages within 95 miles that have at least 300 daily flow measurements on matching dates. The station with the best flow relationship, as indicated by the highest r-squared value, is selected as the index gage. R-squared indicates the fraction of the variance in flow explained by the regression. The regression is then used to estimate flow at the gage to be filled/extended from flow at the index station. Flows will not be estimated based on regressions with r-squared values less than 0.25, even if that is the best regression. In some cases, it will be necessary to fill/extend flow records from two or more index gages. The flow record will be filled/extended to the extent possible based on the best index gage (highest r-squared value), and remaining gaps will be filled from the next best index gage (second highest r-squared value), and so forth. c. Flow duration curves will be based on both measured flows only and on the filled or extended flow time series calculated from other gages using regression. d. On a stream impounded by dams to form reservoirs of sufficient size to impact stream flow, only flows measured after the date of the most recent impoundment will be used to develop the flow duration curve. This also applies to reservoirs on major tributaries to the stream. ii) In the case no coincident flow data are available for a stream segment, but flow gage(s) are present upstream and/or downstream without a major reservoir between, flows will be estimated for the stream segment from an upstream or downstream gage using a watershed area ratio method derived by delineating subwatersheds, and relying on the NRCS runoff curve numbers and antecedent rainfall condition. Drainage subbasins will first be delineated for all impaired 303(d)-listed WQM stations, along with all USGS flow stations located in the 8-digit HUCs with Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-3 FINAL August 2010 impaired streams. Parsons will then identify all the USGS gage stations upstream and downstream of the subwatersheds with 303(d) listed WQM stations. a. Watershed delineations are performed using ESRI Arc Hydro with a 30 m resolution National Elevation Dataset (NED) digital elevation model, and National Hydrography Dataset (NHD) streams. The area of each watershed will be calculated following watershed delineation. b. The watershed average curve number is calculated from soil properties and land cover as described in the U.S. Department of Agriculture (USDA) Publication TR-55: Urban Hydrology for Small Watersheds. The soil hydrologic group is extracted from NRCS STATSGO soil data, and land use category from the 2001 National Land Cover Dataset (NLCD). Based on land use and the hydrologic soil group, SCS curve numbers are estimated at the 30-meter resolution of the NLCD grid as shown in Table 7. The average curve number is then calculated from all the grid cells within the delineated watershed. c. The average rainfall is calculated for each watershed from gridded average annual precipitation datasets for the period 1971-2000 (Spatial Climate Analysis Service, Oregon State University, http://www.ocs.oregonstate.edu/prism/, created 20 Feb 2004). Table B-1 Runoff Curve Numbers for Various Land Use Categories and Hydrologic Soil Groups NLCD Land Use Category Curve number for hydrologic soil group A B C D 0 in case of zero 100 100 100 100 11 Open Water 100 100 100 100 12 Perennial Ice/Snow 100 100 100 100 21 Developed, Open Space 39 61 74 80 22 Developed, Low Intensity 57 72 81 86 23 Developed, Medium Intensity 77 85 90 92 24 Developed, High Intensity 89 92 94 95 31 Barren Land (Rock/Sand/Clay) 77 86 91 94 32 Unconsolidated Shore 77 86 91 94 41 Deciduous Forest 37 48 57 63 42 Evergreen Forest 45 58 73 80 43 Mixed Forest 43 65 76 82 51 Dwarf Scrub 40 51 63 70 52 Shrub/Scrub 40 51 63 70 71 Grasslands/Herbaceous 40 51 63 70 72 Sedge/Herbaceous 40 51 63 70 73 Lichens 40 51 63 70 74 Moss 40 51 63 70 81 Pasture/Hay 35 56 70 77 82 Cultivated Crops 64 75 82 85 90-99 Wetlands 100 100 100 100 Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-4 FINAL August 2010 d. The method used to project flow from a gaged location to an ungaged location was adapted by combining aspects of two other flow projection methodologies developed by Furness (Furness, 1959) and Wurbs (Wurbs, 2000). Furness Method The Furness method has been employed in Kansas by both the USGS and Kansas Department of Health and Environment to estimate flow-duration curves. The method typically uses maps, graphs, and computations to identify six unique factors of flow duration for ungaged sites. These factors include: the mean streamflow and percentage duration of mean streamflow; the ratio of 1-percent-duration streamflow to mean streamflow ; the ratio of 0.1-percent-duration streamflow to 1-percent-duration streamflow; the ratio of 50-percentduration streamflow to mean streamflow; the percentage duration of appreciable (0.10 ft /s) streamflow; and average slope of the flow-duration curve. Furness defined appreciable flow as 0.10 ft/s. This value of streamflow was important because, for many years, this was the smallest non-zero streamflow value reported in most Kansas streamflow records. The average slope of the duration curve is a graphical approximation of the variability index, which is the standard deviation of the logarithms of the streamflows (Furness, 1959, p. 202-204, figs. 147 and 148). On a duration curve that fits the log-normal distribution exactly, the variability index is equal to the ratio of the streamflow at the 15.87-percent-duration point to the streamflow at the 50-percent-duration point. Because duration curves usually do not exactly fit the log-normal distribution, the average-slope line is drawn through an arbitrary point, and the slope is transferred to a position approximately defined by the previously estimated points. The method provides a means of both describing shape of the flow duration curve and scaling the magnitude of the curve to another location, basically generating a new flow duration curve with a very similar shape but different magnitude at the ungaged location. Wurbs Modified NRCS Method As a part of the Texas water availability modeling (WAM) system developed by Texas Natural Resources Conservation Commission (TNRCC), now known as the Texas Commission on Environmental Quality (TCEQ), and partner agencies, various contractors developed models of all Texas rivers. As a part of developing the model code to be used, Dr. Ralph Wurbs of Texas A&M University researched methods to distribute flows from gaged locations to ungaged locations. (Wurbs, 2006) His results included the development of a modified Natural Resource Conservation Service (NRCS) curve-number (CN) method for distributing flows from gaged locations to ungaged locations. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-5 FINAL August 2010 This modified NRCS method is based on the following relationship between rainfall depth, P in inches, and runoff depth, Q in inches (NRCS, 1985; McCuen, 2005): (P I ) S (P I ) Q a 2 a (1) where: Q = runoff depth (inches) P = rainfall (inches) S = potential maximum retention after runoff begins (inches) Ia = initial abstraction (inches) If P < 0.2, Q = 0. Initial abstraction has been found to be empirically related to S by the equation Ia = 0.2*S (2) Thus, the runoff curve number equation can be rewritten: P 0.8S (P 0.2S) Q 2 (3) S is related to the curve number (CN) by: 10 CN 1000 S (4) P and Q in inches must be multiplied by the watershed area to obtain volumes. The potential maximum retention, S in inches, represents an upper limit on the amount of water that can be abstracted by the watershed through surface storage, infiltration, and other hydrologic abstractions. For convenience, S is expressed in terms of a curve number CN, which is a dimensionless watershed parameter ranging from 0 to 100. A CN of 100 represents a limiting condition of a perfectly impervious watershed with zero retention and thus all the rainfall becoming runoff. A CN of zero conceptually represents the other extreme with the watershed abstracting all rainfall with no runoff regardless of the rainfall amount. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-6 FINAL August 2010 First, S is calculated from the average curve number for the gaged watershed. Next, the daily historic flows at the gage are converted to depth basis (as used in equations 1 and 3) by dividing by its drainage area, then converted to inches. Equation 3 is then solved for daily precipitation depth of the gaged site, Pgaged. The daily precipitation depth for the ungaged site is then calculated as the precipitation depth of the gaged site multiplied by the ratio of the long-term average precipitation in the watersheds of the ungaged and gaged sites: gaged ungaged ungaged gaged M M P P (5) where M is the mean annual precipitation of the watershed in inches. The daily precipitation depth for the ungaged watershed, along with the average curve number of the ungaged watershed, are then used to calculate the depth equivalent daily flow Q of the ungaged site. Finally, the volumetric flow rate at the ungaged site is calculated by multiplying by the area of the watershed of the ungaged site and converted to cubic feet. In a subsequent study (Wurbs, 2006), Wurbs evaluated the predictive ability of various flow distribution methods including: Distribution of flows in proportion to drainage area; Flow distribution equation with ratios for various watershed parameters; Modified NRCS curve-number method; Regression equations relating flows to watershed characteristics; Use of recorded data at gaging stations to develop precipitation-runoff relationships; and Use of watershed (precipitation-runoff) computer models such as SWAT. As a part of the analysis, the methods were used to predict flows at one gaged station to another gage station so that fit statistics could be calculated to evaluate the efficacy of each of the methods. Based upon similar analyses performed for many gaged sites which reinforced the tests performed as part of the study, Wurbs observed that temporal variations in flows are dramatic, ranging from zero flows to major floods. Mean flows are reproduced reasonably well with the all flow distribution methods and the NRCS CN method reproduces the mean closest. Accuracy in predicting mean flows is much better than the accuracy of predicting the flow-frequency relationship. Performance in reproducing flow-frequency relationships is better than for reproducing flows for individual flows. Wurbs concluded that the NRCS CN method, the drainage area ratio method, and drainage area – CN – mean annual precipitation depth (MP) ratio methods all yield similar levels of accuracy. If the CN and MP are the same for the gaged and ungaged watersheds, the three alternative methods yield identical results. Drainage area is the most important watershed parameter. However, the NRCS method adaptation is preferable in those situations in which differences in CN (land use and soil type) and Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-7 FINAL August 2010 long-term MP are significantly different between the gaged and ungaged watersheds. The CN and MP are usually similar but not identical. Generalized Flow Projection Methodology In the first several versions of the TMDL toolbox, all flows at ungaged sites that required projection from a gaged site were performed with the Modified NRCS CN method. This led a number of problems with flow projections in the early versions. As described previously, the NRCS method, in common with all others, reproduces the mean or central tendency best but the accuracy of the fit degrades towards the extremes of the frequency spectrum. Part of the degradation in accuracy is due to the quite non-linear nature of the NRCS equations. On the low flow end of the frequency spectrum, Equation 2 above constitutes a low flow limit below which the NRCS equations are not applicable at all. Given the flashy nature of most streams in locations for which the toolbox was developed, high and low flows are relatively more common and spurious results from the limits of the equations abounded. In an effort to increase the flow prediction efficacy and remedy the failure of the NRCS CN method at the extremes of the flow spectrum, we developed what is effectively a hybrid of the NRCS CN method and the Furness method. Noting the facts that all tested projection methods, and particularly the NRCS CN method, perform best near the central tendency or mean and that none of the methods predict the entire flow frequency spectrum well, we decided to adopt an assumption that is implicit in the Furness method. The Furness method implicitly assumes that the shape of the flow frequency curve at an upstream site is related to and similar to the shape of the flow frequency curve at site downstream. As described previously, the Furness method employs several relationships derived between the mean flows and flows at differing frequencies to replicate the shape of the flow frequency curve at the projected site, while utilizing other regressed relationships to scale the magnitude of the curve. Since, as part of the toolbox calculations, the entire flow frequency curve at a 1% interval is calculated for every USGS gage utilizing very long periods of record, we decided to use this vector in association with the mean flow to project the flow frequency curve. In the ideal situation flows are projected from an ungaged location from a downstream gaged location. The toolbox also has the capability to project flows from and upstream gaged location if there is no useable downstream gage. iii) In the rare case where no coincident flow data are available for a WQM station and no gages are present upstream or downstream, flows will be estimated for the WQM station from a gage on an adjacent watershed of similar size and properties, via the same procedure described above for upstream or downstream gages. Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx FINAL August 2010 APPENDIX C STATE OF OKLAHOMA ANTIDEGRADATION POLICY Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx C-1 FINAL August 2010 Appendix C State of Oklahoma Antidegradation Policy 785:45-3-1. Purpose; Antidegradation policy statement (a) Waters of the state constitute a valuable resource and shall be protected, maintained and improved for the benefit of all the citizens. (b) It is the policy of the State of Oklahoma to protect all waters of the state from degradation of water quality, as provided in OAC 785:45-3-2 and Subchapter 13 of OAC 785:46. 785:45-3-2. Applications of antidegradation policy (a) Application to outstanding resource waters (ORW). Certain waters of the state constitute an outstanding resource or have exceptional recreational and/or ecological significance. These waters include streams designated "Scenic River" or "ORW" in Appendix A of this Chapter, and waters of the State located within watersheds of Scenic Rivers. Additionally, these may include waters located within National and State parks, forests, wilderness areas, wildlife management areas, and wildlife refuges, and waters which contain species listed pursuant to the federal Endangered Species Act as described in 785:45-5-25(c)(2)(A) and 785:46-13-6(c). No degradation of water quality shall be allowed in these waters. (b) Application to high quality waters (HQW). It is recognized that certain waters of the state possess existing water quality which exceeds those levels necessary to support propagation of fishes, shellfishes, wildlife, and recreation in and on the water. These high quality waters shall be maintained and protected. (c) Application to beneficial uses. No water quality degradation which will interfere with the attainment or maintenance of an existing or designated beneficial use shall be allowed. (d) Application to improved waters. As the quality of any waters of the state improve, no degradation of such improved waters shall be allowed. 785:46-13-1. Applicability and scope (a) The rules in this Subchapter provide a framework for implementing the antidegradation policy stated in OAC 785:45-3-2 for all waters of the state. This policy and framework includes three tiers, or levels, of protection. (b) The three tiers of protection are as follows: (1) Tier 1. Attainment or maintenance of an existing or designated beneficial use. (2) Tier 2. Maintenance or protection of High Quality Waters and Sensitive Public and Private Water Supply waters. (3) Tier 3. No degradation of water quality allowed in Outstanding Resource Waters. Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx C-2 FINAL August 2010 (c) In addition to the three tiers of protection, this Subchapter provides rules to implement the protection of waters in areas listed in Appendix B of OAC 785:45. Although Appendix B areas are not mentioned in OAC 785:45-3-2, the framework for protection of Appendix B areas is similar to the implementation framework for the antidegradation policy. (d) In circumstances where more than one beneficial use limitation exists for a waterbody, the most protective limitation shall apply. For example, all antidegradation policy implementation rules applicable to Tier 1 waterbodies shall be applicable also to Tier 2 and Tier 3 waterbodies or areas, and implementation rules applicable to Tier 2 waterbodies shall be applicable also to Tier 3 waterbodies. (e) Publicly owned treatment works may use design flow, mass loadings or concentration, as appropriate, to calculate compliance with the increased loading requirements of this section if those flows, loadings or concentrations were approved by the Oklahoma Department of Environmental Quality as a portion of Oklahoma's Water Quality Management Plan prior to the application of the ORW, HQW or SWS limitation. 785:46-13-2. Definitions The following words and terms, when used in this Subchapter, shall have the following meaning, unless the context clearly indicates otherwise: "Specified pollutants" means (A) Oxygen demanding substances, measured as Carbonaceous Biochemical Oxygen Demand (CBOD) and/or Biochemical Oxygen Demand (BOD); (B) Ammonia Nitrogen and/or Total Organic Nitrogen; (C) Phosphorus; (D) Total Suspended Solids (TSS); and (E) Such other substances as may be determined by the Oklahoma Water Resources Board or the permitting authority. 785:46-13-3. Tier 1 protection; attainment or maintenance of an existing or designated beneficial use (a) General. (1) Beneficial uses which are existing or designated
Object Description
Description
Title | Turbidity Black Bear |
OkDocs Class# | E4850.3 T131b 2010 |
Digital Format | PDF, Adobe Reader required |
ODL electronic copy | Downloaded from agency website: http://www.deq.state.ok.us/wqdnew/tmdl/BlackBearCreekFinalTurbidityTMDL_083110.pdf |
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Full text | FINAL TURBIDITY TOTAL MAXIMUM DAILY LOAD FOR BLACK BEAR CREEK, OKLAHOMA (621200030010_00) Prepared for: OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY Prepared by: AUGUST 2010 FIANL TURBIDITY TOTAL MAXIMUM DAILY LOAD FOR BLACK BEAR CREEK, OKLAHOMA (621200030010_00) OKWBID 621200030010_00 Prepared for: OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY Prepared by: 8000 Centre Park Drive, Suite 200 Austin, TX 78754 AUGUST 2010 Oklahoma Department of Environmental Quality: FY07/08 106 Carryover Grant (I-006400-08) Funding for the development of this TMDL Report was provided through a federal Clean Water Act grant to the Oklahoma Department of Environmental Quality from the U.S. Environmental Protection Agency. Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx i FINAL August 2010 TABLE OF CONTENTS EXECUTIVE SUMMARY ................................................................................................. ES-1 SECTION 1 INTRODUCTION ............................................................................................. 1-1 1.1 TMDL Program Background ..................................................................................... 1-1 1.2 Watershed Description ............................................................................................... 1-4 1.3 Stream Flow Data ....................................................................................................... 1-7 SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET ...... 2-1 2.1 Oklahoma Water Quality Standards ........................................................................... 2-1 2.2 Problem Identification ................................................................................................ 2-3 2.3 Water Quality Target .................................................................................................. 2-4 SECTION 3 POLLUTANT SOURCE ASSESSMENT ....................................................... 3-1 3.1 NPDES-Permitted Facilities ....................................................................................... 3-1 3.1.1 Continuous Point Source Discharges ............................................................. 3-2 3.1.2 Concentrated Animal Feeding Operations ..................................................... 3-5 3.1.3 Rock, Sand and Gravel Quarries .................................................................... 3-5 3.1.4 Stormwater Permits for MS4 and Construction Activities ............................. 3-5 3.1.5 Section 404 permits ........................................................................................ 3-5 3.2 Nonpoint Sources ....................................................................................................... 3-6 SECTION 4 TECHNICAL APPROACH AND METHODS .............................................. 4-1 4.1 Determining a Surrogate Target ................................................................................. 4-1 4.2 Using Load Duration Curves to Develop TMDLs ..................................................... 4-4 4.3 Development of Flow Duration Curves ..................................................................... 4-4 4.4 Development of TMDLs Using Load Duration Curves ............................................. 4-6 SECTION 5 TMDL CALCULATIONS ................................................................................ 5-1 5.1 Estimated Loading and Critical Conditions ............................................................... 5-1 5.2 Wasteload Allocation ................................................................................................. 5-2 5.2.1 Section 404 permits ........................................................................................ 5-3 5.3 Load Allocation .......................................................................................................... 5-3 5.4 Seasonal Variability .................................................................................................... 5-3 5.5 Margin of Safety ......................................................................................................... 5-3 5.6 TMDL Calculations .................................................................................................... 5-4 5.7 Reasonable Assurances .............................................................................................. 5-5 SECTION 6 PUBLIC PARTICIPATION ............................................................................ 6-1 SECTION 7 REFERENCES .................................................................................................. 7-1 Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx ii FINAL August 2010 APPENDICES Appendix A Ambient Water Quality Data 1998 - 2007 Appendix B Projected Flow exceedance frequencies for Black Bear Creek Flow Duration Curve Appendix C State of Oklahoma Antidegradation Policy LIST OF FIGURES Figure 1-1 Watersheds Not Supporting Fish and Wildlife Propagation Use within the Study Area ...................................................................................................... 1-3 Figure 1-2 Land Use Map by Watershed ............................................................................... 1-6 Figure 3-1 Locations of NPDES-Permitted Facilities in the Study Area ............................... 3-4 Figure 4-1 Linear Regression for TSS-Turbidity under Base-flow Conditions for Black Bear Creek (OK 62100030010_00) ........................................................... 4-3 Figure 4-2 Flow Duration Curve for Black Bear Creek (OK621200030010_00) ................. 4-6 Figure 5-1 Load Duration Curve for Total Suspended Solids in Black Bear Creek (OK621200030010_00) ........................................................................................ 5-2 Black Bear Creek TMDL Table of Contents FINAL Turbidity TMDL_Black_Bear_Creek.docx iii FINAL August 2010 LIST OF TABLES Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List ................................................................................. ES-2 Table ES-2 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 ................................................................................................................... ES-3 Table ES-3 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 ................................................................................................................... ES-3 Table ES-4 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) .......................................................................... ES-6 Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision ........ 1-2 Table 1-2 County Population and Density ............................................................................ 1-4 Table 1-3 Average Annual Precipitation by Watershed ....................................................... 1-4 Table 1-4 Land Use Summaries by Watershed ..................................................................... 1-5 Table 2-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List .................................................................................... 2-2 Table 2-2 Summary of All Turbidity Samples 1998 - 2007 ................................................. 2-3 Table 2-3 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 ...................................................................................................................... 2-3 Table 2-4 Summary of All TSS Samples 1998 - 2007 ......................................................... 2-4 Table 2-5 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 ...................................................................................................................... 2-4 Table 3-1 Point Source Discharges in the Study Area .......................................................... 3-2 Table 3-2 Discharge Monitoring Data for NPDES Facilities in the Study Area .................. 3-3 Table 3-3 Rock, Sand and Gravel Quarries .......................................................................... 3-5 Table 3-4 Stormwater Permits for Construction Activities .................................................. 3-6 Table 5-1 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) ............................................................................. 5-4 Table 5-2 Partial List of Oklahoma Water Quality Management Agencies ......................... 5-6 Black Bear Creek TMDL Acronyms and Abbreviations FINAL Turbidity TMDL_Black_Bear_Creek.docx iv FINAL August 2010 ACRONYMS AND ABBREVIATIONS BMP best management practice CAFO Concentrated Animal Feeding Operation CFR Code of Federal Regulations cfs Cubic feet per second CPP Continuing planning process CWA Clean Water Act DMR Discharge monitoring report IQR interquartile range LA Load allocation LDC Load duration curve LOC line of organic correlation mg Million gallons mgd Million gallons per day mg/L milligram per liter MOS Margin of safety MS4 Municipal separate storm sewer system NPDES National Pollutant Discharge Elimination System NRCS National Resources Conservation Service NTU nephelometric turbidity unit OLS ordinary least square regression O.S. Oklahoma statutes ODAFF Oklahoma Department of Agriculture, Food and Forestry ODEQ Oklahoma Department of Environmental Quality OPDES Oklahoma Pollutant Discharge Elimination System OWRB Oklahoma Water Resources Board PRG Percent reduction goal TMDL Total maximum daily load TSS Total suspended solids USDA U.S. Department of Agriculture USEPA U.S. Environmental Protection Agency USGS U.S. Geological Survey WLA Wasteload allocation WQM Water quality monitoring WQS Water quality standard WWTP Wastewater treatment plant Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-1 FINAL August 2010 EXECUTIVE SUMMARY This report documents the data and assessment used to establish a TMDL for Black Bear Creek, a tributary of the Arkansas River. The 2008 Integrated Water Quality Assessment Report (Oklahoma Department of Environmental Quality [ODEQ] 2008) identified Black Bear Creek as impaired for turbidity. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the CWA, Water Quality Planning and Management Regulations (40 CFR Part 130), USEPA guidance, and ODEQ guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003). The purpose of this TMDL report is to establish pollutant load allocations for turbidity in impaired waterbodies, which is the first step toward restoring water quality. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. TMDLs also establish the pollutant load allocation necessary to meet the WQS established for a waterbody based on the relationship between pollutant sources and in-stream water quality conditions. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural process in aquatic systems, model assumptions, and data limitations. This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce turbidity loadings within each watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process involving stakeholders who live and work in the watershed; tribes; and local, state, and federal government agencies. E.1 Problem Identification and Water Quality Target The TMDL in this report address fish and wildlife propagation for the subcategory warm water aquatic community. Table ES-1, an excerpt from Appendix B of the 2008 Integrated Report (ODEQ 2008), summarizes the warm water aquatic community use attainment status and the scheduled date for TMDL development established by ODEQ for the impaired waterbody of the Study Area. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-2 FINAL August 2010 Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category TMDL Date Priority Warm Water Aquatic Community OK621200030010_00 Black Bear Creek 68.0 5a 2013 2 N N = Not Supporting; 5a = TMDL is underway or will be scheduled Source: 2008 Integrated Report, ODEQ 2008 The data in Table ES-2 were used to support the decision to place Black Bear Creek on the ODEQ 2008 303(d) list (ODEQ 2008 for nonsupport of the Fish and Wildlife Propagation use based on turbidity levels observed in the waterbody. Turbidity is a measure of water clarity and is caused by suspended particles in the water column. Because turbidity cannot be expressed as a mass load, total suspended solids (TSS) are used as a surrogate in this TMDL. Therefore, both turbidity and TSS data are presented to support TMDL development. The numeric criteria for turbidity to maintain and protect the use of “Fish and Wildlife Propagation” from Title 785:45-5-12 (f) (7) is as follows: (A) Turbidity from other than natural sources shall be restricted to not exceed the following numerical limits: 1. Cool Water Aquatic Community/Trout Fisheries: 10 NTUs; 2. Lakes: 25 NTU; and 3. Other surface waters: 50 NTUs. (B) In waters where background turbidity exceeds these values, turbidity from point sources will be restricted to not exceed ambient levels. (C) Numerical criteria listed in (A) of this paragraph apply only to seasonal base flow conditions. (D) Elevated turbidity levels may be expected during, and for several days after, a runoff event. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-3 FINAL August 2010 Table ES-2 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of Turbidity Samples Collected During Base Flow Conditions Number of Samples Exceeding 50 NTU during Base Flow Conditions Percentage of Samples Exceeding Criterion during Base Flow Conditions Average Turbidity (NTU) Per WQM Station during Base Flow Conditions 621200030010-001AT 51 18 35% 60 OK621200030010D 18 10 56% 111 OK621200030010G 23 6 26% 54 OK621200030010M 22 16 73% 99 OK621200030010W 24 5 21% 42 Table ES-3 presents a subset of total suspended solids data for samples collected during base flow conditions. Water quality data for turbidity and TSS are provided in Appendix A. Table ES-3 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of TSS Samples Collected During Base Flow Conditions Average TSS (mg/L) Per WQM Station during Base Flow Conditions OK621200030010-001AT 18 46 OK621200030010D 18 50 OK621200030010G 7 53 OK621200030010M 18 54 OK621200030010W 19 44 The Code of Federal Regulations (40 CFR §130.7(c)(1)) states that, “TMDLs shall be established at levels necessary to attain and maintain the applicable narrative and numerical water quality standards.” An individual water quality target established for turbidity must demonstrate compliance with the numeric criteria prescribed in the Oklahoma WQS (OWRB 2008). According to the Oklahoma WQS [785:45-5-12(f)(7)], the turbidity criterion for streams with warm water aquatic community (WWAC) beneficial use is 50 NTUs (OWRB 2008). The turbidity of 50 NTUs applies only to seasonal base flow conditions. Turbidity levels are expected to be elevated during, and for several days after, a storm event. TMDLs for turbidity in streams designated as warm water aquatic community must take into account that no more than 10 percent of the samples may exceed the numeric criterion of 50 NTU. However, as described above, because turbidity cannot be expressed as a mass load, TSS is used as a surrogate in this TMDL. Since there is no numeric criterion in the Oklahoma WQS for TSS, a specific method must be developed to convert the turbidity criterion to TSS based on a relationship between turbidity and TSS. The method for deriving the relationship between turbidity and TSS, and for calculating a water body specific water quality target using TSS, is summarized in Section 4 of this report. Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-4 FINAL August 2010 E.2 Pollutant Source Assessment A pollutant source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Turbidity may originate from NPDES-permitted facilities, fields, construction sites, quarries, stormwater runoff and eroding stream banks. The 2008 Integrated Water Quality Assessment Report (ODEQ 2008) listed potential sources of turbidity in Black Bear Creek (OK621200030010_00) as clean sediments, grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, petroleum/natural gas activities, rangeland grazing, and other unknown sources. There are four NPDES-permitted facilities and no municipal separate storm sewer systems or CAFOs in the Study Area. There are approximately 2,400 permitted mining acres operated by four different quarries located within the Study Area. There are general stormwater permits for two facilities located within the Study Area. The relative homogeneous land use/land cover categories within the Study Area are associated with agricultural and range management activities. This suggests that various nonpoint sources of TSS include sediments originating from grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, rangeland grazing and other sources of sediment loading (ODEQ 2008). Elevated turbidity measurements can be caused by stream bank erosion processes, stormwater runoff events and other channel disturbances. However, there is insufficient data available to quantify contributions of TSS from these processes. TSS or sediment loading can also occur under non-runoff conditions as a result of anthropogenic activities in riparian corridors which cause erosive conditions. Sediment loading of streams can also originate from natural erosion processes, including the weathering of soil, rocks, and uncultivated land; geological abrasion; and other natural phenomena. Given the lack of data to establish the background conditions for TSS/turbidity, separating background loading from nonpoint sources is not feasible in this TMDL development. E.3 Using Load Duration Curves to Develop TMDLs Turbidity is a commonly measured indicator of the suspended solids load in streams. However, turbidity is an optical property of water, and measures scattering of light by suspended solids and colloidal matter. To develop TMDLs, a gravimetric (mass-based) measure of solids loading is required to express loads. There is often a strong relationship between the total suspended solids concentration and turbidity. Therefore, the TSS load, which is expressed as mass per time, is used as a surrogate for turbidity and represents the maximum one-day load the stream can assimilate while still attaining the WQS. To determine the relationship between turbidity and TSS, a linear regression between TSS and turbidity was developed using data collected from 1998 to 2007 at four stations within the Study Area. Prior to developing the regression the following steps were taken to refine the dataset: Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-5 FINAL August 2010 Assign values to censored data (i.e., measured concentrations lower than the analytical quantitation limit and, thus, reported as less than the quantitation limit). For example, using 9.99 to replace samples reported as “<10”; Remove data collected under high flow conditions exceeding the base-flow criterion. This means that measurements corresponding to flow exceedance frequencies lower than 25% were not used in the regression; Check rainfall data on the day when samples were collected and on the previous two days. If there was a significant rainfall event (>= 1.0 inch) in any of these days, the sample will be excluded from regression analysis with one exception. If the significant rainfall happened on the sampling day and the turbidity reading was less than 25 NTUs (half of turbidity standard for streams), the sample will not be excluded from analysis because most likely the rainfall occurred after the sample was taken; andLog-transform both turbidity and TSS data to minimize effects of their non-linear data distributions. The TMDL calculations presented in this report are derived from load duration curves (LDC). LDCs facilitate rapid development of TMDLs, and as a TMDL development tool, are effective at identifying whether impairments are associated with point or nonpoint sources. The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the USGS (or project flow using Oklahoma TMDL Toolbox if station is ungaged); sorting the flow data and calculating flow exceedance frequencies for the time period and season of interest; obtaining available turbidity and TSS water quality data; matching the water quality observations with the flow data from the same date; displaying a curve on a plot that represents the allowable load multiplying the actual or estimated flow by the WQtarget for TSS; multiplying the flow by the water quality parameter concentration to calculate daily loads (for sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2); then plotting the flow exceedance frequencies and daily load observations in a load duration plot. The culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve: TMDL (lb/day) = WQtarget * flow (cfs) * unit conversion factor where: WQtarget = 40.6 mg/L (TSS) unit conversion factor = 5.39377 L*s*lb /(ft3*day*mg) The flow exceedance frequency (x-value of each point) is obtained by looking up the historical exceedance frequency of the measured or estimated flow; in other words, the percent of historical observations that equal or exceed the measured or estimated flow. Historical observations of TSS and/or turbidity concentrations are paired with flow data and are plotted on the LDC. The TSS load (or the y-value of each point) is calculated by multiplying the TSS Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-6 FINAL August 2010 concentration (measured or converted from turbidity) (mg/L) by the instantaneous flow (cfs) at the same site and time, with appropriate volumetric and time unit conversions. TSS loads representing exceedance of water quality criteria fall above the water quality criterion line. E.4 TMDL Calculations The objective of a TMDL is to estimate allowable pollutant loads and to allocate these loads to the known pollutant sources in the watershed so appropriate control measures can be implemented and the WQS achieved. A TMDL is expressed as the sum of three elements as described in the following mathematical equation: TMDL = Σ WLA + Σ LA + MOS The WLA is the portion of the TMDL allocated to existing and future point sources. The LA is the portion of the TMDL allocated to nonpoint sources, including natural background sources. The MOS is intended to ensure that WQS will be met. Thus, the allowable pollutant load that can be allocated to point and nonpoint sources can then be defined as the TMDL minus the MOS. The overall Percent Reduction Goal (PRG) is calculated as the reduction in load required so no more than 10 percent of the samples collected under base-flow conditions would exceed TMDL targets for TSS. The PRG for Black Bear Creek is calculated to be 60.3 percent. The maximum assimilative capacity of a stream depends on the flow conditions of the stream. The higher the flow is, the more wasteload the stream can handle without violating water quality standards. Thus, the TMDL, WLA, LA, and MOS will vary with flow condition, and are calculated at every 5th flow interval percentile (Table ES-4). Table ES-4 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) Percentile Flow (cfs) TMDL (lb/day) WLA (lb/day) LA (lb/day) MOS WWTP MS4 (lb/day) Future Growth 0 18260 NA 0 0 NA NA NA 5 1616 NA 0 0 NA NA NA 10 695 NA 0 0 NA NA NA 15 386 NA 0 0 NA NA NA 20 245 NA 0 0 NA NA NA 25 166 34,024 153 0 340 30,128 3,402 30 113 23,140 153 0 231 20,441 2,314 35 82 16,787 153 0 168 14,787 1,679 40 61 12,482 153 0 125 10,956 1,248 45 48 9,756 153 0 98 8,530 976 50 37 7,481 153 0 75 6,505 748 55 30 6,128 153 0 61 5,301 613 60 24 4,981 153 0 50 4,279 498 65 20 4,079 153 0 41 3,477 408 70 18 3,628 153 0 36 3,075 363 75 14 2,951 153 0 30 2,473 295 Black Bear Creek TMDL Executive Summary FINAL Turbidity TMDL_Black_Bear_Creek.docx ES-7 FINAL August 2010 80 11 2,214 153 0 22 1,817 221 85 8 1,640 153 0 16 1,306 164 90 5 1,066 153 0 11 795 107 95 2 451 153 0 5 248 45 100 0 0 0 0 0 0 0 E.5 Reasonable Assurance ODEQ will collaborate with a host of other state agencies and local governments working within the boundaries of state and local regulations to target available funding and technical assistance to support implementation of pollution controls and management measures. Various water quality management programs and funding sources provide a reasonable assurance that the pollutant reductions as required by this TMDL can be achieved and water quality can be restored to maintain designated uses. ODEQ’s Continuing Planning Process (CPP), required by the CWA §303(e)(3) and 40 CFR 130.5, summarizes Oklahoma’s commitments and programs aimed at restoring and protecting water quality throughout the state (ODEQ 2006). The CPP can be viewed from ODEQ’s website. Table 5-2 provides a partial list of the state partner agencies ODEQ will collaborate with to address point and nonpoint source reduction goals established by TMDLs. Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-1 FINAL August 2010 SECTION 1 INTRODUCTION 1.1 TMDL Program Background Section 303(d) of the Clean Water Act (CWA) and U.S. Environmental Protection Agency (USEPA) Water Quality Planning and Management Regulations (40 Code of Federal Regulations [CFR] Part 130) require states to develop total maximum daily loads (TMDL) for waterbodies not meeting designated uses where technology-based controls are in place. TMDLs establish the allowable loadings of pollutants or other quantifiable parameters for a waterbody based on the relationship between pollution sources and in-stream water quality conditions, so states can implement water quality-based controls to reduce pollution from point and nonpoint sources and restore and maintain water quality (USEPA 1991). This report documents the data and assessment used to establish a turbidity TMDL for Black Bear Creek, a tributary of the Arkansas River. The 2008 Integrated Water Quality Assessment Report (Oklahoma Department of Environmental Quality [ODEQ] 2008) identified Black Bear Creek as impaired for turbidity. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the CWA, Water Quality Planning and Management Regulations (40 CFR Part 130), USEPA guidance, and ODEQ guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003). The purpose of this TMDL report is to establish pollutant load allocations for turbidity in impaired waterbodies, which is the first step toward restoring water quality. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. TMDLs also establish the pollutant load allocation necessary to meet the WQS established for a waterbody based on the relationship between pollutant sources and in-stream water quality conditions. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural process in aquatic systems, model assumptions, and data limitations. This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce turbidity loadings within each watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process involving stakeholders who live and work in the watershed; tribes; and local, state, and federal government agencies. This TMDL report focuses on waterbodies that ODEQ placed in Category 5 [303(d) list] of the Water Quality in Oklahoma, 2008 Integrated Report (2008 Integrated Report) for the beneficial use category Fish and Wildlife Propagation for Black Bear Creek OK621200030010_00. Figure 1-1 is a location map showing the impaired segment of this Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-2 FINAL August 2010 Oklahoma waterbody and its contributing watershed. This map also displays the locations of the water quality monitoring (WQM) stations used as the basis for placement of this waterbody on the Oklahoma 303(d) list. The waterbody and its surrounding watershed are hereinafter referred to as the Study Area. The TMDL established in this report is a necessary step in the process to develop the turbidity controls needed to restore the fish and wildlife propagation designated for the waterbody. Table 1-1 provides a description of the locations of the WQM stations on the 303(d)-listed waterbody. Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision WQM Station WQM Station Location Description WQM Station Location Legal Descriptions Latitude Longitude OK621200030010W Black Bear Creek: Upper NE¼ NE¼ NE¼ Section 32-22N-1E 36.346222 -97.210833 OK621200030010M Black Bear Creek: Upper W.B. Section 9-21N- 3E 36.306778 -96.9960278 621200030010-001AT Black Bear Creek:, SH 18, Pawnee NA 36.3434116 -96.79985 OK621200030010D Black Bear Creek: Lower Sections 31/32 22N- 6E 36.339861 -96.69211 OK621200030010G Black Bear Creek: Lower SE¼ NW¼ NE¼ Section 1-21N-4E 36.33986 -96.69211 Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-3 FINAL August 2010 Figure 1-1 Watersheds Not Supporting Fish and Wildlife Propagation Use within the Study Area Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-4 FINAL August 2010 1.2 Watershed Description General. The Arkansas River Basin is located in the northern portion of Oklahoma. The waterbody addressed in this report is located in Noble, Pawnee, and Payne Counties. The Study Area is located in the Central Great Plains ecoregion of Oklahoma. Table 1-2, derived from the 2000 U.S. Census, shows that the counties where these watersheds are located are sparsely populated (U.S. Census Bureau 2000). Table 1-2 County Population and Density County Name Population (2000 Census) Population Density (per square mile) Noble 11,411 15.6 Pawnee 16,612 29.2 Payne 68,190 99.4 Climate. Table 1-3 summarizes the average annual precipitation for the waterbody. Average annual precipitation for the waterbody is 38.4 inches (Oklahoma Climate Survey 2007). Table 1-3 Average Annual Precipitation by Watershed Black Bear Creek Precipitation Summary Waterbody Name Waterbody ID Average Annual (inches) Black Bear Creek OK621200030010_00 38.4 Land Use. Table 1-4 summarizes the acreages and the corresponding percentages of the land use categories for the contributing watershed associated with the Oklahoma waterbody. The land use/land cover data were derived from the U.S. Geological Survey (USGS) 2001 National Land Cover Dataset (USGS 2007). The land use categories are displayed in Figure 1-2. The primary land use category in the Study Area is Grassland, which makes up 63 percent of the watershed. The second most common land use within the Study Area is cultivated land and deciduous forest at 14 and 13.2 percent, respectively. Pawnee, the largest city within the Black Bear Creek watershed, has an estimated population of 2,230 (U.S. Census Bureau 2000). Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-5 FINAL August 2010 Table 1-4 Land Use Summaries by Watershed Landuse Category Black Bear Creek Waterbody ID OK621200030010_00 Percent Herbaceous Wetlands 0% Percent Woody Wetlands 0% Percent Cultivated 14.0% Percent Pasture/Hay 3.6% Percent Grassland 62.9% Percent Shrubland 0% Percent Mixed Forest 0% Percent Evergreen Forest 0% Percent Deciduous Forest 13.2% Percent Barren 0% Percent Developed - High Intensity 0% Percent Developed - Medium Intensity 0% Percent Developed - Low Intensity 0.7% Percent Developed - Open 4.4% Percent Water 0.8% Acres Herbaceous Wetlands 9 Acres Woody Wetlands 0 Acres Cultivated 33,924 Acres Pasture/Hay 8,630 Acres Grassland 152,130 Acres Shrubland 0 Acres Mixed Forest 0 Acres Evergreen Forest 760 Acres Deciduous Forest 31,878 Acres Barren 5 Acres Developed - High Intensity 39 Acres Developed - Medium Intensity 199 Acres Developed - Low Intensity 1,712 Acres Developed - Open 10,668 Acres Water 2,056 Total (Acres) 242,011 Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-6 FINAL August 2010 Figure 1-2 Land Use Map by Watershed Black Bear Creek TMDL Introduction FINAL Turbidity TMDL_Black_Bear_Creek.docx 1-7 FINAL August 2010 1.3 Stream Flow Data Stream flow characteristics and data are key information when conducting water quality assessments such as TMDLs. The USGS operates flow gages throughout Oklahoma. There is one gage station in the Black Bear Creek watershed with historical flow data: USGS gage 07153000, Black Bear Creek at SH 18 at Pawnee. The location of this USGS gage station is displayed in Figure 1-1. This gage has operated continuously since 1944 and the median flow is 35 cubic feet per second (cfs). In addition, some flow measurements were collected at the same time TSS and turbidity water quality samples were collected at various WQM stations. These data are included in Appendix A along with turbidity and TSS data. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-1 FINAL August 2010 SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET 2.1 Oklahoma Water Quality Standards Title 785 of the Oklahoma Administrative Code authorizes the Oklahoma Water Resources Board (OWRB) to promulgate Oklahoma’s water quality standards and implementation procedures (OWRB 2008). The OWRB has statutory authority and responsibility concerning establishment of state water quality standards, as provided under 82 Oklahoma Statute [O.S.], §1085.30. This statute authorizes the OWRB to promulgate rules …which establish classifications of uses of waters of the state, criteria to maintain and protect such classifications, and other standards or policies pertaining to the quality of such waters. [O.S. 82:1085:30(A)]. Beneficial uses are designated for all waters of the state. Such uses are protected through restrictions imposed by the antidegradation policy statement (See Appendix C), narrative water quality criteria, and numerical criteria (OWRB 2008). The beneficial uses designated for Black Bear Creek (OK621200030010) include primary body contact recreation, warm water aquatic community, public/private water supply, fish consumption, agriculture and aesthetics. The TMDL in this report addresses the fish and wildlife propagation beneficial use for the subcategory warm water aquatic community. Table 2-1, an excerpt from Appendix B of the 2008 Integrated Report (ODEQ 2008), summarizes the warm water aquatic community use attainment status and the scheduled date for TMDL development established by ODEQ for the impaired waterbody of the Study Area. The 2008 Integrated Report (ODEQ 2008) identifies the Black Bear Creek as Priority 2 for TMDL development. Priority 2 waterbodies are targeted for TMDL development by 2013. The TMDL established in this report is a necessary step in the process to restore the fish and wildlife propagation designation for this waterbody. The numeric criteria for turbidity to maintain and protect the use of “Fish and Wildlife Propagation” from Title 785:45-5-12 (f) (7) is as follows: (A) Turbidity from other than natural sources shall be restricted to not exceed the following numerical limits: 4. Cool Water Aquatic Community/Trout Fisheries: 10 NTUs; 5. Lakes: 25 NTU; and 6. Other surface waters: 50 NTUs. (B) In waters where background turbidity exceeds these values, turbidity from point sources will be restricted to not exceed ambient levels. (C) Numerical criteria listed in (A) of this paragraph apply only to seasonal base flow conditions. (D) Elevated turbidity levels may be expected during, and for several days after, a runoff event. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-2 FINAL August 2010 Table 2-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category TMDL Date Priority Warm Water Aquatic Community OK621200030010_00 Black Bear Creek 68.0 5a 2013 2 N N = Not Supporting; 5a = TMDL is underway or will be scheduled Source: 2008 Integrated Report, ODEQ 2008 To implement Oklahoma’s WQS for Fish and Wildlife Propagation, OWRB promulgated Chapter 46, Implementation of Oklahoma’s Water Quality Standards (OWRB 2008). The excerpt below from Chapter 46: 785:46-15-5, stipulates how water quality data will be assessed to determine support of fish and wildlife propagation as well as how the water quality target for TMDLs will be defined for turbidity. Assessment of Fish and Wildlife Propagation support (a) Scope. The provisions of this Section shall be used to determine whether the beneficial use of Fish and Wildlife Propagation or any subcategory thereof designated in OAC 785:45 for a waterbody is supported. (e) Turbidity. The criteria for turbidity stated in 785:45-5-12(f)(7) shall constitute the screening levels for turbidity. The tests for use support shall follow the default protocol in 785:46-15-4(b). 785:46-15-4. Default protocols (b) Short term average numerical parameters. (1) Short term average numerical parameters are based upon exposure periods of less than seven days. Short term average parameters to which this Section applies include, but are not limited to, sample standards and turbidity. (2) A beneficial use shall be deemed to be fully supported for a given parameter whose criterion is based upon a short term average if 10% or less of the samples for that parameter exceed the applicable screening level prescribed in this Subchapter. (3) A beneficial use shall be deemed to be fully supported but threatened if the use is supported currently but the appropriate state environmental agency determines that available data indicate that during the next five years the use may become not supported due to anticipated sources or adverse trends of pollution not prevented or controlled. If data from the preceding two year period indicate a trend away from impairment, the appropriate agency shall remove the threatened status. (4) A beneficial use shall be deemed to be not supported for a given parameter whose criterion is based upon a short term average if at least 10% of the samples for that parameter exceed the applicable screening level prescribed in this Subchapter. Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-3 FINAL August 2010 2.2 Problem Identification Turbidity is a measure of water clarity and is caused by suspended particles in the water column. Because turbidity cannot be expressed as a mass load, total suspended solids (TSS) are used as a surrogate in this TMDL. Therefore, both turbidity and TSS data are presented in this section. Table 2-2 summarizes water quality data collected from the WQM stations between 1998 and 2007 for turbidity. However, as stipulated in Title 785:45-5-12 (f) (7) (C), numeric criteria for turbidity only apply under base flow conditions. While the base flow condition is not specifically defined in the Oklahoma Water Quality Standards, DEQ considers base flow conditions to be all flows less than the 25% flow exceedance frequency (i.e., the lower 75 percent of flows) which is consistent with the USGS Streamflow Conditions Index (USGS 2009). Therefore, Table 2-3 was prepared to represent the subset of data for samples collected during base flow conditions. Water quality samples collected under flow conditions greater than the 25% flow exceedance frequency were therefore excluded from the data set used for TMDL analysis. The data in Table 2-3 were used to support the decision to place Black Bear Creek on the ODEQ 2008 303(d) list (ODEQ 2008 for nonsupport of the Fish and Wildlife Propagation use based on turbidity levels observed in the waterbody. Table 2-2 Summary of All Turbidity Samples 1998 - 2007 WQM Station Number of Turbidity Samples Number of Samples Exceed 50 Nephelometric Turbidity Units (NTU) Percentage of Samples Exceeding Criterion Average Turbidity (NTU) Per WQM Station 621200030010-001AT 70 36 51% 132 OK621200030010D 21 13 59% 126 OK621200030010G 28 11 39% 195 OK621200030010M 27 21 78% 126 OK621200030010W 28 9 32% 61 Table 2-3 Summary of Turbidity Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of Turbidity Samples Collected During Base Flow Conditions Number of Samples Exceeding 50 NTU during Base Flow Conditions Percentage of Samples Exceeding Criterion during Base Flow Conditions Average Turbidity (NTU) Per WQM Station during Base Flow Conditions 621200030010-001AT 51 18 35% 60 OK621200030010D 18 10 56% 111 OK621200030010G 23 6 26% 54 OK621200030010M 22 16 73% 99 OK621200030010W 24 5 21% 42 Black Bear Creek TMDL Problem Identification and Water Quality Target FINAL Turbidity TMDL_Black_Bear_Creek.docx 2-4 FINAL August 2010 Table 2-4 summarizes water quality data collected from the WQM stations between 1998 and 2007 for TSS. Table 2-5 presents a subset of these data for samples collected during base flow conditions. Water quality data for turbidity and TSS are provided in Appendix A. Table 2-4 Summary of All TSS Samples 1998 - 2007 WQM Station Number of TSS Samples Average TSS (mg/L) Per WQM Station OK621200030010-001AT 30 110 OK621200030010D 24 238 OK621200030010G 10 421 OK621200030010M 24 239 OK621200030010W 24 420 Table 2-5 Summary of TSS Samples Collected During Base Flow Conditions 1998 - 2007 WQM Station Number of TSS Samples Collected During Base Flow Conditions Average TSS (mg/L) Per WQM Station during Base Flow Conditions OK621200030010-001AT 18 46 OK621200030010D 18 50 OK621200030010G 7 53 OK621200030010M 18 54 OK621200030010W 19 44 2.3 Water Quality Target The Code of Federal Regulations (40 CFR §130.7(c)(1)) states that, “TMDLs shall be established at levels necessary to attain and maintain the applicable narrative and numerical water quality standards.” An individual water quality target established for turbidity must demonstrate compliance with the numeric criteria prescribed in the Oklahoma WQS (OWRB 2008). According to the Oklahoma WQS [785:45-5-12(f)(7)], the turbidity criterion for streams with warm water aquatic community (WWAC) beneficial use is 50 NTUs (OWRB 2008). The turbidity of 50 NTUs applies only to seasonal base flow conditions. Turbidity levels are expected to be elevated during, and for several days after, a storm event. TMDLs for turbidity in streams designated as warm water aquatic community must take into account that no more than 10 percent of the samples may exceed the numeric criterion of 50 NTU. However, as described above, because turbidity cannot be expressed as a mass load, TSS is used as a surrogate in this TMDL. Since there is no numeric criterion in the Oklahoma WQS for TSS, a specific method must be developed to convert the turbidity criterion to TSS based on a relationship between turbidity and TSS. The method for deriving the relationship between turbidity and TSS, and for calculating a water body specific water quality target using TSS, is summarized in Section 4 of this report. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-1 FINAL August 2010 SECTION 3 POLLUTANT SOURCE ASSESSMENT A pollutant source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Turbidity may originate from NPDES-permitted facilities, fields, construction sites, quarries, stormwater runoff and eroding stream banks. Point sources are permitted through the NPDES program. NPDES-permitted facilities that discharge treated wastewater are required to monitor for TSS in accordance with their permit. Nonpoint sources are diffuse sources that typically cannot be identified as entering a waterbody through a discrete conveyance at a single location. These sources may involve land activities that contribute TSS to surface water as a result of rainfall runoff. For the TMDL in this report, all sources of pollutant loading not regulated by NPDES permits are considered nonpoint sources. The 2008 Integrated Water Quality Assessment Report (ODEQ 2008) listed potential sources of turbidity in Black Bear Creek (OK621200030010_00) as clean sediments, grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, petroleum/natural gas activities, rangeland grazing, and other unknown sources. 3.1 NPDES-Permitted Facilities Under 40CFR, §122.2, a point source is described as a discernable, confined, and discrete conveyance from which pollutants are or may be discharged to surface waters. . NPDES-permitted facilities can be characterized as continuous or stormwater related discharges. NPDES-permitted facilities classified as point sources include: NPDES municipal wastewater treatment plant (WWTP); NPDES Industrial WWTP Discharges; NPDES municipal separate storm sewer discharge (MS4); NPDES Concentrated Animal Feeding Operation (CAFO); NPDES multi-sector general permits; and NPDES construction stormwater discharges. Continuous point source discharges from municipal and industrial WWTPs, could result in discharge of elevated concentrations of TSS if a facility is not properly maintained, is of poor design, or flow rates exceed capacity. However, in most cases suspended solids discharged by WWTPs consist primarily of organic solids rather than inorganic suspended solids (i.e., soil and sediment particles from erosion or sediment resuspension). Discharges of organic suspended solids from WWTPs are addressed by ODEQ through its permitting of point sources to maintain WQS for dissolved oxygen and are not considered a potential source of turbidity in this TMDL report. Discharges of TSS will be considered to be organic suspended solid if the discharge permit includes a limit for BOD or CBOD. Only WWTP discharges of inorganic suspended solids will be considered and will receive wasteload allocations. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-2 FINAL August 2010 Stormwater runoff from MS4 areas, facilities under multi-sector general permits, and NPDES construction stormwater discharges, which are regulated under the USEPA NPDES Program, can contain TSS concentrations. 40 C.F.R. § 130.2(h) requires that NPDES-regulated storm water discharges must be addressed by the wasteload allocation component of a TMDL. However, any stormwater discharge by definition occurs during or immediately following periods of rainfall and elevated flow conditions when where Oklahoma Water Quality Standard for turbidity does not apply. Oklahoma Water Quality Standards specify that the criteria for turbidity “apply only to seasonal base flow conditions” and go on to say “Elevated turbidity levels may be expected during, and for several days after, a runoff event” [OAC 785:45-5- 12(f)(7)]. In other words, the turbidity impairment status is limited to base flow conditions and stormwater discharges from MS4 areas or construction sites do not contribute to the violation of Oklahoma’s turbidity standard. Therefore, WLA for NPDES-regulated storm water discharges is essentially considered unnecessary in this TMDL report and will not be included in the TMDL calculations. 3.1.1 Continuous Point Source Discharges There are four NPDES-permitted facilities in the Black Bear Creek (OK621200030010_00) watershed. A list of these facilities is included in Table 3-1 and facility locations are displayed in Figure 3-1. Table 3-1 Point Source Discharges in the Study Area NPDES Permit No. Facility Name County Name SIC Code Facility Type TSS Permit Limit (mg/L) BOD5 Permit Limit (mg/L) OK0002534 City of Pawnee Pawnee 4941 Water Supply 30 - OK0026654 City of Pawnee Pawnee 4952 Sewerage Systems 45 25 OK0028517 Town of Glencoe Payne 4952 Sewerage Systems 22.5 37.5 OKG950016 The Quapaw Company Pawnee 1422 Crushed and Broken Limestone 45* - *Permit limit for outfalls 001 and 002 Discharge Monitoring Reports (DMR) for 2007 and 2008 were available for the facilities listed in Table 3-1. Table 3-2 lists the DMR data available for the NPDES facilities. Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-3 FINAL August 2010 Table 3-2 Discharge Monitoring Data for NPDES Facilities in the Study Area NPDES Monitoring End Date Outfall Maximum Flow (mgd) Average Flow (mgd) Maximum TSS (mg/L) Average TSS (mg/L) OK0002534 06/30/08 001 0.211 5 5 05/31/08 001 0.075 5 5 04/30/08 001 0.046 5.5 5.5 03/31/08 001 0.173 50 50 02/29/08 001 0.00029 50 50 01/31/08 001 0.2 4 4 12/31/07 001 0.000101 12 12 11/30/07 001 0.000082 3.5 3.5 10/31/07 001 0.000235 17 17 08/31/07 001 no discharge 07/31/07 001 0.244 8.5 8.5 06/30/07 001 0.178 8.5 8.5 OK0026654 06/30/08 001 0.3107 0.2771 8 7 05/31/08 001 0.3119 0.2457 10 8 04/30/08 001 0.2883 0.2274 5 10.77 03/31/08 001 0.3018 0.207 7.5 6.5 02/29/08 001 0.3147 0.1798 13 10.25 01/31/08 001 0.2475 0.2054 12 11.5 12/31/07 001 0.36 0.2426 6 4.5 11/30/07 001 0.2655 0.1551 4 3 10/31/07 001 0.2993 0.1932 22 15.75 09/30/07 001 0.3085 0.18923 5 4.5 08/31/07 001 0.2856 0.1205 3 2.75 07/31/07 001 0.316 0.264 5.5 5 06/30/07 001 0.334 0.257 8.5 7.25 OK0028517 10/31/07 001 0.064 0.064 85 85 09/30/07 001 0.064 0.064 35 35 08/31/07 001 0.064 0.064 66 66 07/31/07 001 0.064 0.064 48 48 06/30/07 001 0.064 0.064 84 84 05/31/08 001 0.064 0.064 55.5 55.5 04/30/08 001 0.064 0.064 77.5 77.5 03/31/08 001 0.064 0.064 96 96 02/29/08 001 0.064 0.064 78 78 01/31/08 001 0.064 0.064 45 45 12/31/07 001 0.064 0.064 65 65 11/30/07 001 0.064 0.064 88 88 OKG950016 05/31/08 - 6/30/2008 001 No discharge 04/30/08 001 0.12 0.12 34.5 34.5 12/31/04 to 03/31/08 001 No discharge 06/30/08 002 0.012 0.012 181 181 05/31/08 002 0.2 0.2 30 30 04/30/08 002 0.24 0.24 90 90 12/31/04 to 03/31/08 002 No discharge Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-4 FINAL August 2010 Figure 3-1 Locations of NPDES-Permitted Facilities in the Study Area Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-5 FINAL August 2010 3.1.2 Concentrated Animal Feeding Operations There are no CAFOs in the Study Area. 3.1.3 Rock, Sand and Gravel Quarries Operators of Rock, Sand and Gravel Quarries in Oklahoma are regulated with a general permit (OKG950000). The general permit does not allow discharge of wastewater to waterbodies included in Oklahoma’s 303(d) List of impaired water bodies listed for turbidity for which a TMDL has not been performed or the result of the TMDL indicates that discharge limits more stringent than 45 mg/l for TSS are required (ODEQ 2009). Table 3-3 summarizes data from the Oklahoma Department of Mines and provides the permitted mining acres for each of the four quarries located within the Study Area. The locations of these quarries are shown in Figure 3-1. Table 3-3 Rock, Sand and Gravel Quarries Company Name County Permit ID Product Permitted Acres Permit Issue Date Permit Renewal Date Mining Expiration Date* Stewart Stone (Pawnee Quarry Pit 3) Pawnee L.E.-1760-D Limestone 906.50 12/1/1999 11/30/2008 11/30/2029 Stewart Stone (Privett) Pawnee L.E.-1270 Limestone 333.00 12/1/2000 11/30/2008 11/30/2008 Stewart Stone (Pawnee) Pawnee L.E.-1734 Limestone 655.00 10/1/1999 9/30/2008 9/30/2029 Quapaw Co. (Brensing) Pawnee L.E.-1598-A Limestone 500.00 3/1/1998 2/28/2009 2/28/2022 3.1.4 Stormwater Permits for MS4 and Construction Activities There are no urbanized areas designated as MS4s within this Study Area. A general stormwater permit is required for construction activities. Permittees are authorized to discharge pollutants in stormwater runoff associated with construction activities for construction sites. Stormwater discharges occur only during or immediately following periods of rainfall and elevated flow conditions when the turbidity criteria do not apply and are not considered potential contributors to turbidity impairment. 3.1.5 Section 404 permits Section 404 of the Clean Water Act (CWA) establishes a program to regulate the discharge of dredged or fill material into waters of the United States, including wetlands. Activities in waters of the United States regulated under this program include fill for development, water resource projects (such as dams and levees), infrastructure development (such as highways and airports) and mining projects. Section 404 requires a permit before dredged or fill material may be discharged into waters of the United States, unless the activity is exempt from Section 404 regulation (e.g. certain farming and forestry activities). Section 404 permits are administrated by the U.S. Army Corps of Engineers. EPA reviews and provides comments on each permit application to make sure it adequately protects water Black Bear Creek TMDL Pollutant Source Assessment FINAL Turbidity TMDL_Black_Bear_Creek.docx 3-6 FINAL August 2010 quality and complies with applicable guidelines. Both USACE and EPA can take enforcement actions for violations of Section 404. Discharge of dredged or fill material in waters can be a significant source of turbidity/TSS. The federal Clean Water Act requires that a permit be issued for activities which discharge dredged or fill materials into the waters of the United States, including wetlands. The state of Oklahoma will use its Section 401 certification authority to ensure Section 404 permits protect Oklahoma water quality standards. 3.2 Nonpoint Sources Nonpoint sources include those sources that cannot be identified as entering the waterbody at a specific location. The relatively homogeneous land use/land cover categories within the Study Area are associated with agricultural and range management activities. This suggests that potential nonpoint sources of TSS include sediments originating from grazing in riparian corridors of streams and creeks, highway/road/bridge runoff (non-construction related), non-irrigated crop production, rangeland grazing and other sources of sediment loading (ODEQ 2008). Elevated turbidity measurements can be caused by stream bank erosion processes, stormwater runoff events, and channel disturbances. However, there is insufficient data available to quantify contributions of TSS from these processes. TSS or sediment loading can also occur under non-runoff conditions as a result of anthropogenic activities in riparian corridors which cause erosive conditions. Sediment loading of streams can also originate from natural erosion processes, including the weathering of soil, rocks, and uncultivated land; geological abrasion; and other natural phenomena. Given the lack of data to establish the background conditions for TSS/turbidity, separating background loading from nonpoint sources is not feasible in this TMDL development. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-1 FINAL August 2010 SECTION 4 TECHNICAL APPROACH AND METHODS The objective of a TMDL is to estimate allowable pollutant loads and to allocate these loads to the known pollutant sources in the watershed so appropriate control measures can be implemented and the WQS achieved. A TMDL is expressed as the sum of three elements as described in the following mathematical equation: TMDL = Σ WLA + Σ LA + MOS The WLA is the portion of the TMDL allocated to existing and future point sources. The LA is the portion of the TMDL allocated to nonpoint sources, including natural background sources. The MOS is intended to ensure that WQS will be met. Thus, the allowable pollutant load that can be allocated to point and nonpoint sources can then be defined as the TMDL minus the MOS. 4.1 Determining a Surrogate Target 40 CFR, §130.2(1), states that TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures. Turbidity is a commonly measured indicator of the suspended solids load in streams. However, turbidity is an optical property of water, and measures scattering of light by suspended solids and colloidal matter. To develop TMDLs, a gravimetric (mass-based) measure of solids loading is required to express loads. There is often a strong relationship between the total suspended solids concentration and turbidity. Therefore, the TSS load, which is expressed as mass per time, is used as a surrogate for turbidity and represents the maximum one-day load the stream can assimilate while still attaining the WQS. To determine the relationship between turbidity and TSS, a linear regression between TSS and turbidity was developed using data collected from 1998 to 2007 at four stations within the Study Area. Prior to developing the regression the following steps were taken to refine the dataset: Assign values to censored data (i.e., measured concentrations lower than the analytical quantitation limit and, thus, reported as less than the quantitation limit). For example, using 9.99 to replace samples reported as “<10”; Remove data collected under high flow conditions exceeding the base-flow criterion. This means that measurements corresponding to flow exceedance frequencies lower than 25% were not used in the regression; Check rainfall data on the day when samples were collected and on the previous two days. If there was a significant rainfall event (>= 1.0 inch) in any of these days, the sample will be excluded from regression analysis with one exception. If the significant rainfall happened on the sampling day and the turbidity reading was less than 25 NTUs (half of turbidity standard for streams), the sample will not be excluded from analysis because most likely the rainfall occurred after the sample was taken; andLog-transform both turbidity and TSS data to minimize effects of their non-linear data distributions. When ordinary least squares regression (OLS) is applied to ascertain the best relationship between two variables (i.e., X and Y), one variable (Y) is considered “dependent” on the other Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-2 FINAL August 2010 variable (X), but X must be considered “independent” of the other, and known without measurement error. OLS minimizes the differences, or residuals, between measured Y values and Y values predicted based on the X variable. For current purposes, a relationship is necessary to predict TSS concentrations from measured turbidity values, but also to translate the TSS-based TMDL back to in-stream turbidity values. For this purpose, an alternate regression fitting procedure known as the line of organic correlation (LOC) was applied. The LOC has three advantages over OLS (Helsel and Hirsch 2002): LOC minimizes fitted residuals in both the X and Y directions; It provides a unique best-fit line regardless of which parameter is used as the independent variable; and Regression-fitted values have the same variance as the original data. The LOC minimizes the areas of the right triangles formed by horizontal and vertical lines drawn from observations to the fitted line. The slope of the LOC line equals the geometric mean of the Y on X (TSS on turbidity) and X on Y (turbidity on TSS) OLS slopes, and is calculated as: x y s s m1 m m' sign[r] where m1 is the slope of the LOC line, m is the TSS on turbidity OLS slope, m’ is the turbidity on TSS OLS slope, r is the TSS-turbidity correlation coefficient, sy is the standard deviation of the TSS measurements, and sx is the standard deviation of the turbidity measurements. The intercept of the LOC (b1) is subsequently found by fitting the line with the LOC slope through the point (mean turbidity, mean TSS). The correlation between TSS and turbidity, along with the LOC and the OLS lines are shown in Figure 4-1. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-3 FINAL August 2010 Figure 4-1 Linear Regression for TSS-Turbidity under Base-flow Conditions for Black Bear Creek (OK 62100030010_00) The normalized root mean square error (NRMSE) and R-square (R2) were used as the primary measures of goodness-of-fit. As shown in Figure 4-1, the LOC yields a NRMSE value of 11.7% which means the root mean square error (RMSE) is 11.7% of the average of the measured TSS values. The R-square (R2) value indicates the fraction of the total variance in TSS or turbidity observations that is explained by the LOC. It was noted that there were a few outliers that exerted undue influence on the regression relationship. These outliers were identified by applying the Tukey’s Boxplot method (Tukey 1977) to the dataset of the distances from observed points to the regression line. The Tukey Method is based on the interquartile range (IQR), the difference between the 75th percentile (Q3) and 25th percentile (Q1) of distances between observed points and the LOC. Using the Tukey method, any point with an error greater than Q3 + 1.5* IQR or less than Q1 – 1.5*IQR was identified as an outlier and removed from the regression dataset. The above regressions were calculated using the dataset with outliers removed. The Tukey Method is equivalent to using three times the standard deviation to identify outliers if the residuals (observed - predicted) follow a normal distribution. The probability of sampling results being within three standard deviations of the mean is 99.73% while the probability for the Tukey Method is 99.65%. If three times the standard deviation is used to identify outliers, it is necessary to first confirm that the residuals are indeed normally distributed. This is difficult to do because of the size limitations of the existing turbidity & TSS dataset. Tukey’s method does not rely on any assumption about the distribution of the residuals. It can be used regardless of the shape of distribution. 1 10 100 1000 1 10 100 1000 TSS (mg/L) Turbidity (NTU) Data LOC OLS - TSS on Turbidity OLS - Turbidity on TSS log(TSS) = 0.8561*log(Turb) + 0.1544 R2 = 0.747 Normalized RMSE = 11.7% Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-4 FINAL August 2010 Using the regression equation shown in Figure 4-1, a turbidity value of 50 NTU (standard applicable to Black Bear Creek) corresponds to a TSS concentration of 40.6 mg/L. 4.2 Using Load Duration Curves to Develop TMDLs The TMDL calculations presented in this report are derived from load duration curves (LDC). LDCs facilitate rapid development of TMDLs, and as a TMDL development tool, indicate whether impairments are associated with point or nonpoint sources. The technical approach for using LDCs for TMDL development includes the four following steps described in Subsections 4.3 through 4.5 below: Preparing flow duration curves for gaged and ungaged WQM stations; Estimating loading in the receiving water using measured TSS water quality data and turbidity-converted data; Determining the overall percent reduction goal (PRG) necessary to attain WQS; and Historically, in developing WLAs for pollutants from point sources, it was customary to designate a critical low flow condition (e.g., 7Q2) at which the maximum permissible loading was calculated. As water quality management efforts expanded in scope to quantitatively address nonpoint sources of pollution and various types of pollutants, it became clear that this single critical low flow condition was inadequate to ensure adequate water quality across a range of flow conditions. Use of the LDC obviates the need to determine a design storm or selected flow recurrence interval with which to characterize the appropriate flow level for the assessment of critical conditions. For waterbodies impacted by both point and nonpoint sources, the “nonpoint source critical condition” would typically occur during high flows, when rainfall runoff would contribute the bulk of the pollutant load, while the “point source critical condition” would typically occur during low flows, when point source discharges would dominate the base flow of the impaired water. However, flow range is only a general indicator of the relative proportion of point/nonpoint contributions. It is not used in this report to quantify point source or nonpoint source contributions. Violations that occur during low flows may not be caused exclusively by point sources. Violations have been noted in some watersheds that contain no point sources. LDCs display the maximum allowable load over the complete range of flow conditions by a line using the calculation of flow multiplied by the water quality criterion. The TMDL can be expressed as a continuous function of flow, equal to the line, or as a discrete value derived from a specific flow condition. 4.3 Development of Flow Duration Curves Flow duration curves serve as the foundation of LDCs and are graphical representations of the flow characteristics of a stream at a given site. Flow duration curves utilize the historical hydrologic record from stream gages to forecast future recurrence frequencies. Many WQM stations throughout Oklahoma do not have long-term flow data; therefore, flow frequencies must be estimated. The most basic method to estimate flows at an ungaged site involves 1) identifying a downstream flow gage; 2) calculating the contributing drainage areas of the ungaged sites and the flow gage; and 3) calculating daily flows at the ungaged site by using the flow at the gaged site multiplied by the drainage area ratio. A more complex approach used to support this analysis also considers watershed differences in rainfall, land use, and the Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-5 FINAL August 2010 hydrologic properties of soil that govern runoff and retention. For the Black Bear Creek watershed, flows were projected using data from USGS 07153000, Black Bear Creek at SH 18 at Pawnee. A more detailed explanation of the methods for estimating flow at ungaged WQM stations is provided in Appendix B. Flow duration curves are a type of cumulative distribution function. The flow duration curve represents the fraction of flow observations that equal or exceed a given flow at the site of interest. The observed flow values are first ranked from highest to lowest then, for each observation, the percentage of observations equal to or exceeding that flow is calculated. The flow value is read from the ordinate (y-axis), which is typically on a logarithmic scale since the high flows would otherwise overwhelm the low flows. The flow exceedance frequency is read from the abscissa (x-axis), which is numbered from 0 to 100 percent, and may or may not be logarithmic. The flow exceedance frequency is defined as percent of time a given flow was equaled or exceeded based on daily flow values. Therefore, the lowest measured flow occurs at an exceedance frequency of 100 percent indicating that flow has equaled or exceeded this value 100 percent of the time, while the highest measured flow is found at an exceedance frequency of 0 percent. The median flow occurs at a flow exceedance frequency of 50 percent. The flow exceedance frequencies of the USGS gage used to project flows for this report are provided in Appendix B. While the number of observations required to develop a flow duration curve is not rigorously specified, a flow duration curve is usually based on more than 1 year of observations, and encompasses inter-annual and seasonal variation. Ideally, the drought of record and flood of record are included in the observations. For this purpose, the long-term flow gaging stations operated by the USGS are utilized (USGS 2007a). A typical semi-log flow duration curve exhibits a sigmoidal shape, bending upward near a flow exceedance frequency value of 0 percent and downward at a frequency near 100 percent, often with a relatively constant slope in between. For sites that on occasion exhibit no flow, the curve will intersect the abscissa at a frequency less than 100 percent. As the number of observations at a site increases, the line of the LDC tends to appear smoother. However, at extreme low and high flow values, flow duration curves may exhibit a “stair step” effect due to the USGS flow data rounding conventions near the limits of quantitation. Flow duration curves are generated using a DEQ automated application referred to as the Oklahoma TMDL toolbox. Figure 4-2 shows the flow duration curve generated from the Oklahoma TMDL toolbox for Black Bear Creek using flow data from 1984 to 2006. The USGS National Water Information System serves as the primary source of flow measurements for the application. All available daily average flow values for all gages in Oklahoma, as well as the nearest upstream and downstream gages in adjacent states, were retrieved for use in the application. The application includes a data update module that automatically downloads the most recent USGS data and appends it to the existing flow database. Some instantaneous flow measurements were available from various agencies. These were not combined with the daily average flows or used in calculating flow percentiles, but were matched to TSS and/or turbidity grab measurements collected at the same site and time. When available, these instantaneous flow measurements were used in lieu of the daily average flow to calculate instantaneous TSS loads. Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-6 FINAL August 2010 Figure 4-2 Flow Duration Curve for Black Bear Creek (OK621200030010_00) 4.4 Development of TMDLs Using Load Duration Curves The final step in the TMDL calculation process involves a group of additional computations derived from the preparation of LDCs. These computations are necessary to derive a PRG (which is one method of presenting how much TSS loading must be reduced to meet turbidity WQS in the impaired watershed). Step 1: Generate LDCs. LDCs are similar in appearance to flow duration curves; however, the ordinate is expressed in terms of a load typically in lbs/day. The curve represents the water quality target for TSS (40.6 mg/L) expressed in terms of a load through multiplication by the continuum of flows historically observed at this site. The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the USGS (or project flow using Oklahoma TMDL Toolbox if station is ungaged); sorting the flow data and calculating flow exceedance frequency for the time period and season of interest; obtaining available turbidity and TSS water quality data; matching the water quality observations with the flow data from the same date; displaying a curve on a plot that represents the allowable load multiplying the actual or estimated flow by the WQtarget for TSS; multiplying the flow by the water quality parameter concentration to calculate daily loads (for sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2); then 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 0 10 20 30 40 50 60 70 80 90 100 Flow (cfs) Flow Exceedence Frequency (%) Flow Duration Curver (OK410600010030_00) High flow conditions Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-7 FINAL August 2010 plotting the flow exceedance frequencies and daily load observations in a load duration plot. The culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve: TMDL (lb/day) = WQtarget * flow (cfs) * unit conversion factor where: WQtarget = 40.6 mg/L (TSS) unit conversion factor = 5.39377 L*s*lb /(ft3*day*mg) The flow exceedance frequency (x-value of each point) is obtained by looking up the historical exceedance frequency of the measured or estimated flow; in other words, the percent of historical observations that equal or exceed the measured or estimated flow. Historical observations of TSS and/or turbidity concentrations are paired with flow data and are plotted on the LDC. The TSS load (or the y-value of each point) is calculated by multiplying the TSS concentration (measured or converted from turbidity) (mg/L) by the instantaneous flow (cfs) at the same site and time, with appropriate volumetric and time unit conversions. TSS loads representing exceedance of water quality criteria fall above the TMDL line. As noted earlier, runoff has a strong influence on loading of nonpoint source pollution yet flows do not always correspond directly to local runoff. High flows may occur in dry weather due to upstream precipitation events or releases form upstream dams. Runoff influence may be observed with low or moderate flows depending on antecedent conditions. Step 2: Define MOS. The MOS may be defined explicitly or implicitly. A typical explicit approach would reserve some specific fraction of the TMDL as the MOS. In an implicit approach, conservative assumptions used in developing the TMDL are relied upon to provide an MOS to assure that WQSs are attained. For turbidity (TSS) TMDLs an explicit MOS is derived from the NRMSE established by the turbidity/TSS regression analysis conducted for each waterbody. This approach for setting an explicit MOS has been used in other approved turbidity TMDLs. For the TMDLs in this report, an explicit MOS of 10 percent was selected. Step 3: Calculate WLA. As previously stated, the pollutant load allocation for point sources is defined by the WLA. For TMDL development purposes when addressing turbidity or TSS, a WLA will be established for wastewater (continuous) discharges in impaired watersheds that do not have a BOD or CBOD permit limit but do have a TSS limit. These point source discharges of inorganic suspended solids will be assigned a TSS WLA as part of turbidity TMDLs to ensure WQS can be maintained. The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading will vary with flow condition. TMDLs can be expressed in terms of maximum allowable concentrations, or as different maximum loads allowable under different flow conditions, rather than single maximum load values. A load-based approach meets the requirements of 40 CFR, 130.2(i) for expressing TMDLs “in terms of mass per time, toxicity, or other appropriate measures.” WLA for WWTP. WLAs may be set to zero for watersheds with no existing or planned continuous permitted point sources. For watersheds with permitted point sources discharging inorganic suspended solids, WLAs may be derived. A WLA may be calculated for each active Black Bear Creek TMDL Technical Approach and Methods FINAL Turbidity TMDL_Black_Bear_Creek.docx 4-8 FINAL August 2010 NPDES wastewater discharger using a mass balance approach as shown in the equation below. The permitted flow rate used for each point source discharge and the water quality criterion concentration are used to estimate the WLA for each wastewater facility. In cases where a permitted flow rate is not available for a WWTP, then the maximum monthly average flow rate derived from DMRs can be used. All WLA values for each NPDES wastewater discharger are then summed to represent the total WLA for the watershed. WLA = WQtarget * flow * unit conversion factor (lb/day) where: WQtarget = 40.6 mg/L (TSS); flow (106 gal/day) = permitted flow unit conversion factor = 8.3445 L*lb/(gal*mg) WLA for Permitted Stormwater. For turbidity TMDLs, WLAs for permitted stormwater such as MS4s, construction, and multi-sector general permits are not calculated since these discharges occur under high flow conditions when the turbidity criteria do not apply. Step 4: Calculate LA. Given the lack of data and the variability of storm events, it is difficult to quantify discharges that accurately represent projected loadings from nonpoint sources. LAs can be calculated under different flow conditions as the water quality target load minus the WLA. The LA is represented by the area under the LDC but above the WLA. The LA at any particular flow exceedance is calculated as shown in the equation below. LA = TMDL - WLA - MOS Step 5: Estimate LA Load Reduction. After existing loading estimates are computed, nonpoint load reduction estimates are calculated by using the difference between estimated existing loading and the allowable load expressed by the LDC (TMDL-MOS). This difference is expressed as the overall PRG for the impaired waterbody. For turbidity, the PRG is the load reduction that ensures that no more than 10 percent of the samples under flow-base conditions exceed the TMDL. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-1 FINAL August 2010 SECTION 5 TMDL CALCULATIONS 5.1 Estimated Loading and Critical Conditions USEPA regulations at 40 CFR 130.7(c) (1) require TMDLs to take into account critical conditions for stream flow, loading, and all applicable water quality standards. To accomplish this, available instream WQM data were evaluated with respect to flows and magnitude of water quality criteria exceedance using LDCs. To calculate the TSS load at the WQtarget, the flow rate at each flow exceedance frequency is multiplied by a unit conversion factor (5.39377 L*s*lb /ft3/day/mg) and the TSS target (40.6 mg/L). This calculation produces the maximum TSS load in the stream that will result in attainment of the 50 NTU standard for turbidity. The allowable TSS loads at the WQS establish the TMDL and are plotted versus flow exceedance frequency as a LDC. The x-axis indicates the flow exceedance frequency, while the y-axis is expressed in terms of a TSS load in pounds per day. To estimate existing loading, TSS and turbidity observations from 1998 to 2007 are paired with the flows measured or estimated in that segment on the same date. For sampling events with both TSS and turbidity data, the measured TSS value is used; if only turbidity was measured, the value was converted to TSS using the regression equation in Figure 4-2. Pollutant loads are then calculated by multiplying the TSS concentration by the flow rate and the unit conversion factor. The associated flow exceedance frequency is then matched with the measured flow from the tables provided in Appendix B. The observed TSS or converted turbidity loads are then added to the LDC plot as points. These points represent individual ambient water quality samples of TSS. Points above the LDC indicate the TSS target was exceeded at the time of sampling. Conversely, points under the LDC indicate the sample did not exceed the WQtarget. Figure 5-1 shows the LDC developed for this Black Bear Creek. It is noted that the LDC plot includes data under all flow conditions to show the overall condition of the stream. However, it is noted that the turbidity standard only applies for base-flow conditions. Thus, when assessing beneficial use support, only the portion of the graph corresponding to flows from the 25% to the 100% flow exceedance frequencies should be used. The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading varies with flow condition. Existing loading, and load reductions required to meet the TMDL water quality target can also be calculated under different flow conditions. The difference between existing loading and the water quality target is used to calculate the loading reductions required. The overall PRG is calculated for Black Bear Creek as the reduction in load required so no more than 10 percent of the samples collected under base-flow conditions would exceed 36.5 mg/L (90 percent of the TSS WQtarget to account for the explicit MOS). This is done through an iterative process of taking a series of percent reduction values applying each value uniformly between the concentrations of samples and verifying that no more than 10 percent of the samples exceed the water quality target concentration. The concentrations are derived from only those samples collected after high flow samples are excluded. The PRG for Black Bear Creek is calculated to be 60.3 percent. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-2 FINAL August 2010 Figure 5-1 Load Duration Curve for Total Suspended Solids in Black Bear Creek (OK621200030010_00) As shown in Figure 5-1, TSS levels exceed the water quality target during all flow conditions, possibly indicating water quality impairments due to nonpoint sources or a combination of point and nonpoint sources. 5.2 Wasteload Allocation NPDES-permitted facilities discharging inorganic TSS are allocated a daily wasteload calculated as their permitted flow rate multiplied by the water quality target. In other words, the facilities are required to meet instream criteria in their discharge. If the current monthly TSS limits of a facility are greater than instream TSS criteria, the new limits equal to instream criteria will be applied to the facility as their permit is renewed. There are only two NPDES-permitted facilities discharging inorganic TSS to Black Bear Creek (OK0002534 and OKG950016). The WLA for these facilities is derived as follows: WLA_WWTP = WQtarget * flow * unit conversion factor (lb/day) WLA= 40.6 mg/L *0.484 MGD* 8.3445 L*lb/gal/mg = 153.4 lb/day flow = 0.244+0.24 MGD = maximum monthly average self-reported flows for OK0002534 and OKG950016 No wasteload allocations are needed for stormwater dischargers. By definition, any stormwater discharge occurs during periods of rainfall and elevated flow conditions. Oklahoma’s Water Quality Standards specify that the criteria for turbidity “apply only to seasonal base flow conditions” and go on to say “Elevated turbidity levels may be expected during, and for several days after, a runoff event” [OAC 785:45-5-12(f)(7)]. Therefore, WLA 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0 10 20 30 40 50 60 70 80 90 100 TSS Load (lbs/day) Flow Exceedence Frequency (%) Load Duration Curver (OK410600010030_00) TSS data Turb data ->TSS LDC High flow conditions Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-3 FINAL August 2010 for NPDES-regulated storm water discharges is essentially considered unnecessary in this TMDL report and will not be included in the TMDL calculations. Conditions in existing stormwater permits are sufficient to protect receiving waters. To accommodate the potential for future growth in the watershed, 1% of TSS loading is reserved as part of the WLA. 5.2.1 Section 404 permits No TSS wasteload allocations were set aside for Section 404 permits. The state will use its Section 401 certification authority to ensure Section 404 permits protect Oklahoma water quality standards and comply with TSS TMDLs in this report. Section 404 permits will be conditioned to meet one of the following two conditions to be certified by the state: Include TSS limits in the permit and establish a monitoring requirement to ensure compliance with turbidity standard and TSS TMDLs. Submit to the ODEQ a BMP turbidity reduction plan which should include all practicable turbidity control techniques. The turbidity reduction plan must be approved first before a Section 404 permit can be issued. 5.3 Load Allocation As discussed in Section 3.2, pollutant loading to the receiving streams of each waterbody emanate from a number of different nonpoint sources. The data analysis and the LDCs demonstrate that exceedances of the turbidity WQS at the WQM stations are the result of a variety of nonpoint sources. The LA is calculated as the difference between the TMDL, MOS, and WLA as follows: LA = TMDL – WLA_WWTP –WLA_growth - MOS 5.4 Seasonal Variability Federal regulations (40 CFR §130.7(c)(1)) require that TMDLs account for seasonal variation in watershed conditions and pollutant loading. The TMDL established in this report adhere to the seasonal application of the Oklahoma WQS for turbidity, which applies to seasonal base flow conditions only. Seasonal variation was also accounted for in this TMDL by using more than 5 years of water quality data and by using the longest period of USGS flow records possible when estimating flows to develop flow exceedance frequencies. 5.5 Margin of Safety Federal regulations (40 CFR §130.7(c)(1)) require that TMDLs include an MOS. The MOS is a conservative measure incorporated into the TMDL equation that accounts for the lack of knowledge associated with calculating the allowable pollutant loading to ensure WQSs are attained. USEPA guidance allows for use of implicit or explicit expressions of the MOS, or both. When conservative assumptions are used in development of the TMDL, or conservative factors are used in the calculations, the MOS is implicit. When a specific percentage of the TMDL is set aside to account for lack of knowledge, then the MOS is considered explicit. An explicit Margin of Safety of 10% was selected in this TMDL report. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-4 FINAL August 2010 5.6 TMDL Calculations This TMDL was derived using the LDC method. A TMDL is expressed as the sum of all WLAs (point source loads), LAs (nonpoint source loads), and an appropriate MOS, which attempts to account for lack of knowledge concerning the relationship between effluent limitations and water quality. This definition can be expressed by the following equation: TMDL = Σ WLA + Σ LA + MOS The TMDL represents a continuum of desired load over all flow conditions, rather than fixed at a single value, because loading capacity varies as a function of the flow present in the stream. The higher the flow is, the more wasteload the stream can handle without violating water quality standards. Regardless of the magnitude of the WLA calculated in these TMDLs, future new discharges or increased load from existing discharges will be considered consistent with the TMDL provided the NPDES permit requires instream criteria to be met. The TMDL, WLA, LA, and MOS are calculated at every 5th flow interval percentile (Table 5-1). Table 5-1 Turbidity TMDLs based on Total Suspended Solids Calculations for Black Bear Creek (OK621200030010_00) Percentile Flow (cfs) TMDL (lb/day) WLA (lb/day) LA (lb/day) MOS WWTP MS4 (lb/day) Future Growth 0 18260 NA 0 0 NA NA NA 5 1616 NA 0 0 NA NA NA 10 695 NA 0 0 NA NA NA 15 386 NA 0 0 NA NA NA 20 245 NA 0 0 NA NA NA 25 166 34,024 153 0 340 30,128 3,402 30 113 23,140 153 0 231 20,441 2,314 35 82 16,787 153 0 168 14,787 1,679 40 61 12,482 153 0 125 10,956 1,248 45 48 9,756 153 0 98 8,530 976 50 37 7,481 153 0 75 6,505 748 55 30 6,128 153 0 61 5,301 613 60 24 4,981 153 0 50 4,279 498 65 20 4,079 153 0 41 3,477 408 70 18 3,628 153 0 36 3,075 363 75 14 2,951 153 0 30 2,473 295 80 11 2,214 153 0 22 1,817 221 85 8 1,640 153 0 16 1,306 164 90 5 1,066 153 0 11 795 107 95 2 451 153 0 5 248 45 100 0 0 0 0 0 0 0 Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-5 FINAL August 2010 5.7 Reasonable Assurances ODEQ will collaborate with a host of other state agencies and local governments working within the boundaries of state and local regulations to target available funding and technical assistance to support implementation of pollution controls and management measures. Various water quality management programs and funding sources provide a reasonable assurance that the pollutant reductions as required by this TMDL can be achieved and water quality can be restored to maintain designated uses. ODEQ’s Continuing Planning Process (CPP), required by the CWA §303(e)(3) and 40 CFR 130.5, summarizes Oklahoma’s commitments and programs aimed at restoring and protecting water quality throughout the state (ODEQ 2006). The CPP can be viewed from ODEQ’s website at 2006 Continuing Planning Process. Table 5-2 provides a partial list of the state partner agencies ODEQ will collaborate with to address point and nonpoint source reduction goals established by TMDLs. Black Bear Creek TMDL TMDL Calculations FINAL Turbidity TMDL_Black_Bear_Creek.docx 5-6 FINAL August 2010 Table 5-2 Partial List of Oklahoma Water Quality Management Agencies Agency Web Link Oklahoma Conservation Commission http://www.conservation.ok.gov Oklahoma Department of Wildlife Conservation http://www.wildlifedepartment.com/ Oklahoma Department of Agriculture, Food, and Forestry http://www.oda.state.ok.us/aems.htm Oklahoma Water Resources Board http://www.owrb.ok.gov Nonpoint source pollution in Oklahoma is managed by the Oklahoma Conservation Commission (OCC). The OCC works with state partners such as Oklahoma Department of Agriculture, Food, and Forestry (ODAFF) and federal partners such as USEPA and the National Resources Conservation Service (NRCS), to address water quality problems similar to those seen in the Study Area. The primary mechanisms used for management of nonpoint source pollution are incentive-based programs that support the installation of BMPs and public education and outreach. Other programs include regulations and permits for CAFOs. The CAFO Act, as administered by the ODAFF, provides CAFO operators the necessary tools and information to deal with the manure and wastewater animals produce so streams, lakes, ponds, and groundwater sources are not polluted. As authorized by Section 402 of the CWA, the ODEQ has delegation of the NPDES Program in Oklahoma, except for certain jurisdictional areas related to agriculture and the oil and gas industry retained by State Department of Agriculture and Oklahoma Corporation Commission, for which the USEPA has retained permitting authority. The NPDES Program in Oklahoma is implemented via Title 252, Chapter 606 of the Oklahoma Pollution Discharge Elimination System (OPDES) Act and in accordance with the agreement between ODEQ and USEPA relating to administration and enforcement of the delegated NPDES Program. Implementation of point source WLAs is done through permits issued under the OPDES program. The reduction rate called for in this TMDL report is 60.3 percent. The ODEQ recognizes that achieving such high reduction maybe difficult, especially since unregulated nonpoint sources are a major cause of the impairment. Black Bear Creek TMDL Public Participation FINAL Turbidity TMDL_Black_Bear_Creek.docx 6-1 FINAL August 2010 SECTION 6 PUBLIC PARTICIPATION This report was submitted to EPA for technical review and was technically accepted on July 01, 2010. A public notice was circulated on July 15, 2010 to local newspapers and/or other publications in the area affected by this TMDL and persons on the DEQ contact list. The public comment period ended on August 30, 2010. No requests for a public meeting were received. No comments were received. Black Bear Creek TMDL References FINAL Turbidity TMDL_Black_Bear_Creek.docx 7-1 FINAL August 2010 SECTION 7 REFERENCES Helsel, D.R. and R.M. Hirsch 2002. Statistical Methods in Water Resources. U.S. Department of the Interior, U.S. Geological Survey, September 2002. ODEQ 2006. Continuing Planning Process. 2006 Edition. ODEQ 2008. Water Quality in Oklahoma, 2008 Integrated Report. 2008 ODEQ 2009. Fact Sheet: General Wastewater Permit For Rock, Sand, And Gravel Quarries; To Construct Or Operate Industrial Wastewater Surface Impoundments; And/Or To Land Apply Industrial Wastewater For Dust Suppression, Or To Recycle Wastewater As Wash Water, General Permit No. OKG950000. Oklahoma Climate Survey. 2007. Viewed August 29, 2005 in http://climate.ocs.ou.edu/county_climate/Products/County_Climatologies/ OWRB. 2008. Oklahoma Water Resources Board. 2008 Water Quality Standards. Tukey, J.W. 1977. Exploratory Data Analysis. Addison-Wesely. U.S. Census Bureau 2000. http://www.census.gov/main/www/cen2000.html USEPA 1991. Guidance for Water Quality-Based Decisions: The TMDL Process. Office of Water, USEPA 440/4-91-001. USEPA 2003. Guidance for 2004 Assessment, Listing and Reporting Requirements Pursuant to Sections 303(d) and 305(b) of the Clean Water Act, TMDL -01-03 - Diane Regas-- July 21, 2003. USGS 2007. Multi-Resolution Land Characteristics Consortium. http://www.mrlc.gov/index.asp USGS 2007a. USGS Daily Streamflow Data. http://waterdata.usgs.gov/nwis/sw USGS 2009. USGS National Water Information System Website. http://waterdata.usgs.gov/nwis/?percentile_help Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-1 FINAL August 2010 APPENDIX A AMBIENT WATER QUALITY DATA 1998 - 2007 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-2 FINAL August 2010 Appendix A Ambient Water Quality Data 1998 - 2007 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200030010-001AT 12/01/1998 603 240 high flow 621200030010-001AT 01/20/1999 12 22 621200030010-001AT 02/09/1999 388 204 high flow 621200030010-001AT 03/07/1999 70 64 621200030010-001AT 04/06/1999 89 62 high flow 621200030010-001AT 04/06/1999 84 62 high flow 621200030010-001AT 05/17/1999 400 264 high flow 621200030010-001AT 06/08/1999 135 62 621200030010-001AT 06/08/1999 135 61 621200030010-001AT 07/07/1999 225 206 high flow 621200030010-001AT 07/07/1999 225 196 high flow 621200030010-001AT 08/03/1999 20 17 621200030010-001AT 08/03/1999 20 24 621200030010-001AT 09/08/1999 43 48 Rainfall 621200030010-001AT 09/08/1999 43 54 Rainfall 621200030010-001AT 10/19/1999 16 16 621200030010-001AT 10/19/1999 16 18 621200030010-001AT 11/16/1999 20 10 621200030010-001AT 11/16/1999 20 14 621200030010-001AT 12/14/1999 441 312 high flow 621200030010-001AT 12/14/1999 441 320 high flow 621200030010-001AT 02/01/2000 30 621200030010-001AT 02/23/2000 80 high flow 621200030010-001AT 05/16/2000 145 200 621200030010-001AT 06/21/2000 394 320 high flow 621200030010-001AT 08/02/2000 289 164 high flow 621200030010-001AT 08/22/2000 17 22 621200030010-001AT 09/20/2000 23 < 1 621200030010-001AT 10/17/2000 50 34 Rainfall 621200030010-001AT 11/14/2000 155 92 621200030010-001AT 2/7/2001 85 621200030010-001AT 3/7/2001 460 high flow 621200030010-001AT 4/4/2001 40 621200030010-001AT 5/9/2001 25 621200030010-001AT 6/6/2001 213 high flow 621200030010-001AT 7/11/2001 12 621200030010-001AT 8/8/2001 15 621200030010-001AT 10/3/2001 14 621200030010-001AT 2/6/2002 59 621200030010-001AT 3/13/2002 30 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-3 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200030010-001AT 4/10/2002 99 621200030010-001AT 5/8/2002 72 621200030010-001AT 6/4/2002 137 621200030010-001AT 7/9/2002 18 621200030010-001AT 8/26/2002 348 high flow 621200030010-001AT 9/23/2002 495 high flow 621200030010-001AT 10/28/2002 588 high flow 621200030010-001AT 12/2/2002 21 621200030010-001AT 1/21/2003 17 621200030010-001AT 3/5/2003 119 high flow 621200030010-001AT 4/2/2003 40 621200030010-001AT 5/5/2003 49 621200030010-001AT 6/10/2003 122 621200030010-001AT 7/8/2003 46 621200030010-001AT 8/13/2003 23 621200030010-001AT 9/17/2003 448 621200030010-001AT 10/13/2003 59 621200030010-001AT 11/19/2003 372 high flow 621200030010-001AT 12/17/2003 47 621200030010-001AT 1/13/2004 17 621200030010-001AT 5/3/2004 34 621200030010-001AT 6/15/2004 78 621200030010-001AT 7/19/2004 17 621200030010-001AT 8/23/2004 90 621200030010-001AT 9/28/2004 26 621200030010-001AT 10/26/2004 76 621200030010-001AT 11/29/2004 163 621200030010-001AT 1/31/2005 54 621200030010-001AT 2/23/2005 45 high flow 621200030010-001AT 4/19/2005 13 621200030010-001AT 6/6/2005 27 621200030010-001AT 7/18/2005 31 621200-03-0010D 07/23/2002 30.1 18 10.368 621200-03-0010D 08/27/2002 529 <10 68.463 621200-03-0010D 10/01/2002 154 32 24.206 621200-03-0010D 11/05/2002 206 112 79.02 621200-03-0010D 12/03/2002 22.2 14 18.876 621200-03-0010D 01/14/2003 41.1 <10 33.586 621200-03-0010D 02/19/2003 2.09 17 28.936 621200-03-0010D 03/25/2003 141 103 372.5 high flow 621200-03-0010D 04/29/2003 100 66 89.875 621200-03-0010D 06/03/2003 89.7 71 26.374 621200-03-0010D 07/08/2003 104 70 11.195 621200-03-0010D 08/06/2003 40.6 2.044 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-4 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010D 08/12/2003 40.5 30 1.962 621200-03-0010D 09/16/2003 329 172 48.996 621200-03-0010D 10/21/2003 127 36 19.438 621200-03-0010D 12/02/2003 74.1 16 9.051 621200-03-0010D 01/06/2004 35.7 21 7.5 621200-03-0010D 02/10/2004 221 162 588.151 high flow 621200-03-0010D 03/16/2004 281 231 496 high flow 621200-03-0010D 04/20/2004 17.6 <10 79.166 621200-03-0010D 06/08/2004 56.4 53 76.518 621200-03-0010D 05/30/2007 >1000 618 high flow 621200-03-0010D 06/26/2007 93 high flow 621200-03-0010D 08/06/2007 19 621200-03-0010D 09/11/2007 3040 2000 high flow 621200-03-0010G 03/17/1998 918 1360 high flow 621200-03-0010G 04/13/1998 45.4 44.5 84.955 621200-03-0010G 05/20/1998 96.8 82 116.065 621200-03-0010G 05/26/1998 589 536 storm water 621200-03-0010G 06/17/1998 105 76 22.631 621200-03-0010G 07/23/1998 32.8 35 6.354 621200-03-0010G 07/26/1998 17.8 621200-03-0010G 08/10/1998 26.9 621200-03-0010G 08/17/1998 26.8 31.5 4.638 621200-03-0010G 08/23/1998 23.2 621200-03-0010G 09/17/1998 24.5 2.261 621200-03-0010G 09/21/1998 16.9 17 2.001 621200-03-0010G 10/05/1998 1608 1950 high flow 621200-03-0010G 10/27/1998 157 82.7 33.309 621200-03-0010G 06/17/2002 980 high flow 621200-03-0010G 06/24/2002 112 621200-03-0010G 07/01/2002 32.8 621200-03-0010G 07/15/2002 41 621200-03-0010G 08/12/2002 47.9 621200-03-0010G 10/21/2002 9.21 621200-03-0010G 12/02/2002 10.2 621200-03-0010G 05/27/2003 105 high flow 621200-03-0010G 06/23/2003 36.1 621200-03-0010G 07/17/2003 36.1 2.679 621200-03-0010G 07/28/2003 22.1 621200-03-0010G 08/25/2003 20.5 621200-03-0010G 09/29/2003 193 621200-03-0010G 10/20/2003 116 621200-03-0010M 07/23/2002 61.7 18 4.061 621200-03-0010M 08/27/2002 489 11 27.849 621200-03-0010M 10/01/2002 64.9 80 12.924 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-5 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010M 11/05/2002 178 111 66.193 621200-03-0010M 12/03/2002 9.74 <10 9.702 621200-03-0010M 01/14/2003 21.6 <10 26.029 621200-03-0010M 02/19/2003 18 13 18.463 621200-03-0010M 03/25/2003 147 127 195.191 high flow 621200-03-0010M 04/29/2003 143 116 69.07 621200-03-0010M 05/27/2003 125 high flow 621200-03-0010M 06/03/2003 80.7 76 15.155 621200-03-0010M 06/24/2003 135 16.958 621200-03-0010M 07/08/2003 78.7 75 3.946 621200-03-0010M 07/28/2003 78.5 621200-03-0010M 08/12/2003 58.4 40 1.013 621200-03-0010M 08/25/2003 36.1 621200-03-0010M 09/16/2003 143 64 14.422 621200-03-0010M 09/29/2003 137 621200-03-0010M 10/20/2003 120 621200-03-0010M 10/21/2003 103 52 5.226 621200-03-0010M 12/02/2003 58.6 19 5.511 621200-03-0010M 01/06/2004 10.3 10 6.409 621200-03-0010M 02/10/2004 314 167 209.74 high flow 621200-03-0010M 03/16/2004 272 232 high flow 621200-03-0010M 04/20/2004 15.9 23 30.749 621200-03-0010M 06/08/2004 141 110 15.57 621200-03-0010M 05/29/2007 358 290 high flow 621200-03-0010M 06/26/2007 1182 high flow 621200-03-0010M 07/30/2007 44 621200-03-0010M 09/10/2007 2404 high flow 621200-03-0010W 08/05/2002 57.4 <10 1.48 621200-03-0010W 09/03/2002 18.2 19 3.55 621200-03-0010W 09/30/2002 39.2 23 14.63 621200-03-0010W 11/04/2002 167 61 54.956 621200-03-0010W 12/02/2002 6.29 17 10.661 621200-03-0010W 01/14/2003 14.8 35 18.97 621200-03-0010W 02/18/2003 8.36 <10 15.985 621200-03-0010W 03/24/2003 116 92 195.265 high flow 621200-03-0010W 04/28/2003 79.4 59 45.412 621200-03-0010W 05/27/2003 93.6 high flow 621200-03-0010W 06/03/2003 41.4 46 17.639 621200-03-0010W 06/05/2003 36 13.622 621200-03-0010W 06/23/2003 36 621200-03-0010W 07/07/2003 30.6 36 4.082 621200-03-0010W 07/28/2003 43.3 621200-03-0010W 08/11/2003 29.2 29 0.671 621200-03-0010W 08/25/2003 25.1 Black Bear Creek TMDL Appendix A FINAL Turbidity TMDL_Black_Bear_Creek.docx A-6 FINAL August 2010 WQM Station Date Turbidity (NTU) Total Suspended Solids (mg/L) Flow (cfs) Flow condition1 621200-03-0010W 09/15/2003 98.2 125 8.606 Rainfall 621200-03-0010W 09/29/2003 23.5 621200-03-0010W 10/20/2003 34.3 22 3.113 621200-03-0010W 10/20/2003 37.7 621200-03-0010W 12/01/2003 20.6 <10 3.198 621200-03-0010W 01/05/2004 12.5 18 4.471 621200-03-0010W 02/09/2004 122 147 150.954 621200-03-0010W 03/15/2004 249 143 401.482 high flow 621200-03-0010W 04/19/2004 10.6 20 31.852 621200-03-0010W 06/01/2004 16.1 18 3.385 621200-03-0010W 05/29/2007 246 578 high flow 621200-03-0010W 06/26/2007 383 high flow 621200-03-0010W 07/30/2007 21 621200-03-0010W 09/10/2007 6932 high flow 1 High flow = Sample was not collected under base flow conditions (sample collected at flows greater that 25% flow exceedance frequency. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx FINAL August 2010 APPENDIX B PROJECTED FLOW EXCEEDANCE FREQUENCIES Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-1 FINAL August 2010 Appendix B Projected Flow exceedance frequencies for Black Bear Creek Flow Duration Curve WBID Segment OK62120030010_00 USGS Gage Reference 07153000 Flow Exceedance Frequency (%) Flow (cfs) Flow Exceedance Frequency (%) Flow (cfs) Flow Exceedance Frequency (%) Flow (cfs) 0 18260.1 34 88.5 68 18.8 1 4869.4 35 81.9 69 17.7 2 3386.4 36 77.5 70 17.7 3 2523.2 37 71.9 71 16.6 4 1980.9 38 68.6 72 15.5 5 1615.7 39 64.2 73 15.5 6 1350.1 40 60.9 74 14.4 7 1128.8 41 57.5 75 14.4 8 958.4 42 54.2 76 13.3 9 821.2 43 52.0 77 13.3 10 695.0 44 49.8 78 12.2 11 618.6 45 47.6 79 11.1 12 541.2 46 45.4 80 10.8 13 485.8 47 43.2 81 10.3 14 434.9 48 39.8 82 9.7 15 386.2 49 38.7 83 9.1 16 349.7 50 36.5 84 8.5 17 320.9 51 35.4 85 8.0 18 292.2 52 33.2 86 7.4 19 263.4 53 32.1 87 6.9 20 244.6 54 31.0 88 6.3 21 224.7 55 29.9 89 5.9 22 205.8 56 27.7 90 5.2 23 190.3 57 26.6 91 4.6 24 177.1 58 25.5 92 4.1 25 166.0 59 25.5 93 3.5 26 152.7 60 24.3 94 3.0 27 141.7 61 23.2 95 2.2 28 131.7 62 22.1 96 1.4 29 121.7 63 22.1 97 0.8 30 112.9 64 21.0 98 0.3 31 106.2 65 19.9 99 0.02 32 100.7 66 19.9 100 0 33 94.1 67 18.8 Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-2 FINAL August 2010 Appendix B General Method for Estimating Flow at WQM Stations Flows duration curve will be developed using existing USGS measured flow where the data exist from a gage on the stream segment of interest, or by estimating flow for stream segments with no corresponding flow record. Flow data to support flow duration curves and load duration curves will be derived for each Oklahoma stream segment in the following priority: i) In cases where a USGS flow gage occurs on, or within one-half mile upstream or downstream of the Oklahoma stream segment. a. If simultaneously collected flow data matching the water quality sample collection date are available, these flow measurements will be used. b. If flow measurements at the coincident gage are missing for some dates on which water quality samples were collected, the gaps in the flow record will be filled, or the record will be extended, by estimating flow based on measured streamflows at a nearby gage. First, the most appropriate nearby stream gage is identified. All flow data are first log-transformed to linearize the data because flow data are highly skewed. Linear regressions are then developed between 1) daily streamflow at the gage to be filled/extended, and 2) streamflow at all gages within 95 miles that have at least 300 daily flow measurements on matching dates. The station with the best flow relationship, as indicated by the highest r-squared value, is selected as the index gage. R-squared indicates the fraction of the variance in flow explained by the regression. The regression is then used to estimate flow at the gage to be filled/extended from flow at the index station. Flows will not be estimated based on regressions with r-squared values less than 0.25, even if that is the best regression. In some cases, it will be necessary to fill/extend flow records from two or more index gages. The flow record will be filled/extended to the extent possible based on the best index gage (highest r-squared value), and remaining gaps will be filled from the next best index gage (second highest r-squared value), and so forth. c. Flow duration curves will be based on both measured flows only and on the filled or extended flow time series calculated from other gages using regression. d. On a stream impounded by dams to form reservoirs of sufficient size to impact stream flow, only flows measured after the date of the most recent impoundment will be used to develop the flow duration curve. This also applies to reservoirs on major tributaries to the stream. ii) In the case no coincident flow data are available for a stream segment, but flow gage(s) are present upstream and/or downstream without a major reservoir between, flows will be estimated for the stream segment from an upstream or downstream gage using a watershed area ratio method derived by delineating subwatersheds, and relying on the NRCS runoff curve numbers and antecedent rainfall condition. Drainage subbasins will first be delineated for all impaired 303(d)-listed WQM stations, along with all USGS flow stations located in the 8-digit HUCs with Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-3 FINAL August 2010 impaired streams. Parsons will then identify all the USGS gage stations upstream and downstream of the subwatersheds with 303(d) listed WQM stations. a. Watershed delineations are performed using ESRI Arc Hydro with a 30 m resolution National Elevation Dataset (NED) digital elevation model, and National Hydrography Dataset (NHD) streams. The area of each watershed will be calculated following watershed delineation. b. The watershed average curve number is calculated from soil properties and land cover as described in the U.S. Department of Agriculture (USDA) Publication TR-55: Urban Hydrology for Small Watersheds. The soil hydrologic group is extracted from NRCS STATSGO soil data, and land use category from the 2001 National Land Cover Dataset (NLCD). Based on land use and the hydrologic soil group, SCS curve numbers are estimated at the 30-meter resolution of the NLCD grid as shown in Table 7. The average curve number is then calculated from all the grid cells within the delineated watershed. c. The average rainfall is calculated for each watershed from gridded average annual precipitation datasets for the period 1971-2000 (Spatial Climate Analysis Service, Oregon State University, http://www.ocs.oregonstate.edu/prism/, created 20 Feb 2004). Table B-1 Runoff Curve Numbers for Various Land Use Categories and Hydrologic Soil Groups NLCD Land Use Category Curve number for hydrologic soil group A B C D 0 in case of zero 100 100 100 100 11 Open Water 100 100 100 100 12 Perennial Ice/Snow 100 100 100 100 21 Developed, Open Space 39 61 74 80 22 Developed, Low Intensity 57 72 81 86 23 Developed, Medium Intensity 77 85 90 92 24 Developed, High Intensity 89 92 94 95 31 Barren Land (Rock/Sand/Clay) 77 86 91 94 32 Unconsolidated Shore 77 86 91 94 41 Deciduous Forest 37 48 57 63 42 Evergreen Forest 45 58 73 80 43 Mixed Forest 43 65 76 82 51 Dwarf Scrub 40 51 63 70 52 Shrub/Scrub 40 51 63 70 71 Grasslands/Herbaceous 40 51 63 70 72 Sedge/Herbaceous 40 51 63 70 73 Lichens 40 51 63 70 74 Moss 40 51 63 70 81 Pasture/Hay 35 56 70 77 82 Cultivated Crops 64 75 82 85 90-99 Wetlands 100 100 100 100 Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-4 FINAL August 2010 d. The method used to project flow from a gaged location to an ungaged location was adapted by combining aspects of two other flow projection methodologies developed by Furness (Furness, 1959) and Wurbs (Wurbs, 2000). Furness Method The Furness method has been employed in Kansas by both the USGS and Kansas Department of Health and Environment to estimate flow-duration curves. The method typically uses maps, graphs, and computations to identify six unique factors of flow duration for ungaged sites. These factors include: the mean streamflow and percentage duration of mean streamflow; the ratio of 1-percent-duration streamflow to mean streamflow ; the ratio of 0.1-percent-duration streamflow to 1-percent-duration streamflow; the ratio of 50-percentduration streamflow to mean streamflow; the percentage duration of appreciable (0.10 ft /s) streamflow; and average slope of the flow-duration curve. Furness defined appreciable flow as 0.10 ft/s. This value of streamflow was important because, for many years, this was the smallest non-zero streamflow value reported in most Kansas streamflow records. The average slope of the duration curve is a graphical approximation of the variability index, which is the standard deviation of the logarithms of the streamflows (Furness, 1959, p. 202-204, figs. 147 and 148). On a duration curve that fits the log-normal distribution exactly, the variability index is equal to the ratio of the streamflow at the 15.87-percent-duration point to the streamflow at the 50-percent-duration point. Because duration curves usually do not exactly fit the log-normal distribution, the average-slope line is drawn through an arbitrary point, and the slope is transferred to a position approximately defined by the previously estimated points. The method provides a means of both describing shape of the flow duration curve and scaling the magnitude of the curve to another location, basically generating a new flow duration curve with a very similar shape but different magnitude at the ungaged location. Wurbs Modified NRCS Method As a part of the Texas water availability modeling (WAM) system developed by Texas Natural Resources Conservation Commission (TNRCC), now known as the Texas Commission on Environmental Quality (TCEQ), and partner agencies, various contractors developed models of all Texas rivers. As a part of developing the model code to be used, Dr. Ralph Wurbs of Texas A&M University researched methods to distribute flows from gaged locations to ungaged locations. (Wurbs, 2006) His results included the development of a modified Natural Resource Conservation Service (NRCS) curve-number (CN) method for distributing flows from gaged locations to ungaged locations. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-5 FINAL August 2010 This modified NRCS method is based on the following relationship between rainfall depth, P in inches, and runoff depth, Q in inches (NRCS, 1985; McCuen, 2005): (P I ) S (P I ) Q a 2 a (1) where: Q = runoff depth (inches) P = rainfall (inches) S = potential maximum retention after runoff begins (inches) Ia = initial abstraction (inches) If P < 0.2, Q = 0. Initial abstraction has been found to be empirically related to S by the equation Ia = 0.2*S (2) Thus, the runoff curve number equation can be rewritten: P 0.8S (P 0.2S) Q 2 (3) S is related to the curve number (CN) by: 10 CN 1000 S (4) P and Q in inches must be multiplied by the watershed area to obtain volumes. The potential maximum retention, S in inches, represents an upper limit on the amount of water that can be abstracted by the watershed through surface storage, infiltration, and other hydrologic abstractions. For convenience, S is expressed in terms of a curve number CN, which is a dimensionless watershed parameter ranging from 0 to 100. A CN of 100 represents a limiting condition of a perfectly impervious watershed with zero retention and thus all the rainfall becoming runoff. A CN of zero conceptually represents the other extreme with the watershed abstracting all rainfall with no runoff regardless of the rainfall amount. Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-6 FINAL August 2010 First, S is calculated from the average curve number for the gaged watershed. Next, the daily historic flows at the gage are converted to depth basis (as used in equations 1 and 3) by dividing by its drainage area, then converted to inches. Equation 3 is then solved for daily precipitation depth of the gaged site, Pgaged. The daily precipitation depth for the ungaged site is then calculated as the precipitation depth of the gaged site multiplied by the ratio of the long-term average precipitation in the watersheds of the ungaged and gaged sites: gaged ungaged ungaged gaged M M P P (5) where M is the mean annual precipitation of the watershed in inches. The daily precipitation depth for the ungaged watershed, along with the average curve number of the ungaged watershed, are then used to calculate the depth equivalent daily flow Q of the ungaged site. Finally, the volumetric flow rate at the ungaged site is calculated by multiplying by the area of the watershed of the ungaged site and converted to cubic feet. In a subsequent study (Wurbs, 2006), Wurbs evaluated the predictive ability of various flow distribution methods including: Distribution of flows in proportion to drainage area; Flow distribution equation with ratios for various watershed parameters; Modified NRCS curve-number method; Regression equations relating flows to watershed characteristics; Use of recorded data at gaging stations to develop precipitation-runoff relationships; and Use of watershed (precipitation-runoff) computer models such as SWAT. As a part of the analysis, the methods were used to predict flows at one gaged station to another gage station so that fit statistics could be calculated to evaluate the efficacy of each of the methods. Based upon similar analyses performed for many gaged sites which reinforced the tests performed as part of the study, Wurbs observed that temporal variations in flows are dramatic, ranging from zero flows to major floods. Mean flows are reproduced reasonably well with the all flow distribution methods and the NRCS CN method reproduces the mean closest. Accuracy in predicting mean flows is much better than the accuracy of predicting the flow-frequency relationship. Performance in reproducing flow-frequency relationships is better than for reproducing flows for individual flows. Wurbs concluded that the NRCS CN method, the drainage area ratio method, and drainage area – CN – mean annual precipitation depth (MP) ratio methods all yield similar levels of accuracy. If the CN and MP are the same for the gaged and ungaged watersheds, the three alternative methods yield identical results. Drainage area is the most important watershed parameter. However, the NRCS method adaptation is preferable in those situations in which differences in CN (land use and soil type) and Black Bear Creek TMDLs Appendix B FINAL Turbidity TMDL_Black_Bear_Creek.docx B-7 FINAL August 2010 long-term MP are significantly different between the gaged and ungaged watersheds. The CN and MP are usually similar but not identical. Generalized Flow Projection Methodology In the first several versions of the TMDL toolbox, all flows at ungaged sites that required projection from a gaged site were performed with the Modified NRCS CN method. This led a number of problems with flow projections in the early versions. As described previously, the NRCS method, in common with all others, reproduces the mean or central tendency best but the accuracy of the fit degrades towards the extremes of the frequency spectrum. Part of the degradation in accuracy is due to the quite non-linear nature of the NRCS equations. On the low flow end of the frequency spectrum, Equation 2 above constitutes a low flow limit below which the NRCS equations are not applicable at all. Given the flashy nature of most streams in locations for which the toolbox was developed, high and low flows are relatively more common and spurious results from the limits of the equations abounded. In an effort to increase the flow prediction efficacy and remedy the failure of the NRCS CN method at the extremes of the flow spectrum, we developed what is effectively a hybrid of the NRCS CN method and the Furness method. Noting the facts that all tested projection methods, and particularly the NRCS CN method, perform best near the central tendency or mean and that none of the methods predict the entire flow frequency spectrum well, we decided to adopt an assumption that is implicit in the Furness method. The Furness method implicitly assumes that the shape of the flow frequency curve at an upstream site is related to and similar to the shape of the flow frequency curve at site downstream. As described previously, the Furness method employs several relationships derived between the mean flows and flows at differing frequencies to replicate the shape of the flow frequency curve at the projected site, while utilizing other regressed relationships to scale the magnitude of the curve. Since, as part of the toolbox calculations, the entire flow frequency curve at a 1% interval is calculated for every USGS gage utilizing very long periods of record, we decided to use this vector in association with the mean flow to project the flow frequency curve. In the ideal situation flows are projected from an ungaged location from a downstream gaged location. The toolbox also has the capability to project flows from and upstream gaged location if there is no useable downstream gage. iii) In the rare case where no coincident flow data are available for a WQM station and no gages are present upstream or downstream, flows will be estimated for the WQM station from a gage on an adjacent watershed of similar size and properties, via the same procedure described above for upstream or downstream gages. Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx FINAL August 2010 APPENDIX C STATE OF OKLAHOMA ANTIDEGRADATION POLICY Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx C-1 FINAL August 2010 Appendix C State of Oklahoma Antidegradation Policy 785:45-3-1. Purpose; Antidegradation policy statement (a) Waters of the state constitute a valuable resource and shall be protected, maintained and improved for the benefit of all the citizens. (b) It is the policy of the State of Oklahoma to protect all waters of the state from degradation of water quality, as provided in OAC 785:45-3-2 and Subchapter 13 of OAC 785:46. 785:45-3-2. Applications of antidegradation policy (a) Application to outstanding resource waters (ORW). Certain waters of the state constitute an outstanding resource or have exceptional recreational and/or ecological significance. These waters include streams designated "Scenic River" or "ORW" in Appendix A of this Chapter, and waters of the State located within watersheds of Scenic Rivers. Additionally, these may include waters located within National and State parks, forests, wilderness areas, wildlife management areas, and wildlife refuges, and waters which contain species listed pursuant to the federal Endangered Species Act as described in 785:45-5-25(c)(2)(A) and 785:46-13-6(c). No degradation of water quality shall be allowed in these waters. (b) Application to high quality waters (HQW). It is recognized that certain waters of the state possess existing water quality which exceeds those levels necessary to support propagation of fishes, shellfishes, wildlife, and recreation in and on the water. These high quality waters shall be maintained and protected. (c) Application to beneficial uses. No water quality degradation which will interfere with the attainment or maintenance of an existing or designated beneficial use shall be allowed. (d) Application to improved waters. As the quality of any waters of the state improve, no degradation of such improved waters shall be allowed. 785:46-13-1. Applicability and scope (a) The rules in this Subchapter provide a framework for implementing the antidegradation policy stated in OAC 785:45-3-2 for all waters of the state. This policy and framework includes three tiers, or levels, of protection. (b) The three tiers of protection are as follows: (1) Tier 1. Attainment or maintenance of an existing or designated beneficial use. (2) Tier 2. Maintenance or protection of High Quality Waters and Sensitive Public and Private Water Supply waters. (3) Tier 3. No degradation of water quality allowed in Outstanding Resource Waters. Black Bear Creek TMDL Appendix D FINAL Turbidity TMDL_Black_Bear_Creek.docx C-2 FINAL August 2010 (c) In addition to the three tiers of protection, this Subchapter provides rules to implement the protection of waters in areas listed in Appendix B of OAC 785:45. Although Appendix B areas are not mentioned in OAC 785:45-3-2, the framework for protection of Appendix B areas is similar to the implementation framework for the antidegradation policy. (d) In circumstances where more than one beneficial use limitation exists for a waterbody, the most protective limitation shall apply. For example, all antidegradation policy implementation rules applicable to Tier 1 waterbodies shall be applicable also to Tier 2 and Tier 3 waterbodies or areas, and implementation rules applicable to Tier 2 waterbodies shall be applicable also to Tier 3 waterbodies. (e) Publicly owned treatment works may use design flow, mass loadings or concentration, as appropriate, to calculate compliance with the increased loading requirements of this section if those flows, loadings or concentrations were approved by the Oklahoma Department of Environmental Quality as a portion of Oklahoma's Water Quality Management Plan prior to the application of the ORW, HQW or SWS limitation. 785:46-13-2. Definitions The following words and terms, when used in this Subchapter, shall have the following meaning, unless the context clearly indicates otherwise: "Specified pollutants" means (A) Oxygen demanding substances, measured as Carbonaceous Biochemical Oxygen Demand (CBOD) and/or Biochemical Oxygen Demand (BOD); (B) Ammonia Nitrogen and/or Total Organic Nitrogen; (C) Phosphorus; (D) Total Suspended Solids (TSS); and (E) Such other substances as may be determined by the Oklahoma Water Resources Board or the permitting authority. 785:46-13-3. Tier 1 protection; attainment or maintenance of an existing or designated beneficial use (a) General. (1) Beneficial uses which are existing or designated |
Date created | 2011-06-09 |
Date modified | 2011-06-09 |