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Home My WebLink AboutApprovedMuddyCreekandYadkinTurbidity11.18.11Total Maximum Daily Load for Turbidity for Muddy Creek and the Yadkin River in North Carolina [Assessment Units 12-94-(0.5)c, 12-(80.7), 12-(86.7)] Final Report November 2011 Prepared by: NC Department of Environment and Natural Resources Division of Water Quality Planning Section 1617 Mail Service Center Raleigh, NC 27699-1617 (919) 807-6300 Yadkin-Pee Dee River Basin i TMDL Summary Sheet 303(d) List Information State: North Carolina Counties: Davidson, Davie, Forsyth, Yadkin Basin: Yadkin-Pee Dee River Basin Waterbody Name Assessment Unit (AU): Class 10 digit HU Impairment Miles Muddy Creek 12-94-(0.5)c C 0304010113 Turbidity 4.8 Yadkin River 12-(80.7) WS-IV 0304010110 Turbidity 9.4 Yadkin River 12-(86.7) WS-IV 0304010115 Turbidity 10 Constituent of Concern: Turbidity Reason for Listing: Standard Violations Applicable Water Quality Standard: The turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units (NTU) in streams not designated as trout waters and 10 NTU in stream, lakes or reservoirs designated as trout water; for lakes and reservoirs not designated as trout waters, the turbidity shall not exceed 25 NTU; if turbidity exceeds these levels due to natural background conditions, the existing turbidity level cannot be increased. Compliance with this turbidity standard can be met when land management activities employ Best Management Practices (BMPs) recommended by the Designated Nonpoint Source Agency. BMPs must be in full compliance with all specifications governing the proper design, installation, operation and maintenance of such BMPs. ii TMDL Development Analysis/Modeling: Load duration curves are based on cumulative frequency distribution of flow conditions in the watershed. Allowable loads are average loads over the recurrence interval between the 90th and 10th percent flow exceeded (excludes extreme drought (>90th percentile) and floods (<10th percentile). Percent reductions are expressed as the average value between existing loads (typically calculated using an equation to fit a curve through actual water quality violations) and the allowable load at each percent flow exceeded. Turbidity is a measure of cloudiness and is reported in Nephelometric Turbidity Units (NTU). Therefore, turbidity is not measured in terms of concentrations and cannot be directly converted into loadings required for developing a load duration curve. For this reason, total suspended solid (TSS) was selected as the measure for this study. Critical Conditions: Critical conditions are accounted in the load duration curve analysis by using an extended period of stream flow and water quality data, and by examining at what flow (percent flow exceeded) the existing load violations occur. Seasonal Variation: Seasonal variation in hydrology, climatic conditions, and watershed activities are represented through the use of a continuous flow gage and the use of all readily available water quality data collected in the watershed. TMDL Allocation Summary Pollutants/Watershed Existing Load WLA LA MOS TMDL Total Suspended Sediment (tons/day) Muddy Creek 44.3 5.462 16.14 10% 21.6 Yadkin River 361.50 4.014 146.986 10% 151.00 Notes: WLA = Wasteload Allocation, LA = Load Allocation, MOS = Margin of Safety. 1. LA = TMDL – WLA – MOS. 2. TMDL represents the average allowable load between the 90th and 10th percent recurrence interval. 3. Explicit (10%) margin of safety is considered. Public Notice Date: July 26, 2011 Submittal Date: 10/19/2011 EPA Approval Date: 11/17/2011 iii Table of Contents 1.0 Introduction ............................................................................................................................ 1 1.1 TMDL Definition .............................................................................................................. 1 1.2 Water Quality Target: North Carolina Standards and Classifications ............................. 2 1.3 Watershed Description ................................................................................................... 3 1.4 Water Quality Monitoring............................................................................................... 9 2.0 General Source Assessment .................................................................................................. 10 2.1 Nonpoint Sources of Turbidity ...................................................................................... 10 2.2 Point Sources of Turbidity ............................................................................................. 11 3.0 Muddy Creek ......................................................................................................................... 12 3.1 Source Assessment ....................................................................................................... 12 3.2 Technical Approach ....................................................................................................... 12 3.3 Flow Duration Curve ..................................................................................................... 13 3.4 Load Duration Curve ..................................................................................................... 14 3.5 TMDL ............................................................................................................................. 15 3.5.1 Margin of Safety (MOS) ............................................................................................ 16 3.6 Target Reduction ........................................................................................................... 16 3.7 TMDL Allocation ............................................................................................................ 17 3.7.1 Waste Load Allocation (WLA) ................................................................................... 17 3.7.2 Load Allocation (LA) .................................................................................................. 18 3.7.3 Critical Condition and Seasonal Variation ................................................................ 19 4.0 Yadkin River........................................................................................................................... 19 4.1 Source Assessment ....................................................................................................... 19 4.2 Technical Approach ....................................................................................................... 20 4.3 Flow Duration Curve ..................................................................................................... 21 4.4 Load Duration Curve ..................................................................................................... 22 4.5 TMDL ............................................................................................................................. 23 4.5.1 Margin of Safety (MOS) ............................................................................................ 24 4.6 Target Reduction ........................................................................................................... 24 4.7 TMDL Allocation ............................................................................................................ 25 4.7.1 Waste Load Allocation (WLA) ................................................................................... 25 4.7.2 Load Allocation (LA) .................................................................................................. 27 4.7.3 Critical Condition and Seasonal Variation ................................................................ 27 5.0 Summary and Future Implementation ................................................................................. 28 5.1 TMDL Implementation .................................................................................................. 28 iv 6.0 Public Participation ............................................................................................................... 29 7.0 References ............................................................................................................................ 30 Appendix A: Land Cover Data in Square Miles and Percent Area for the Impaired Watersheds 31 Appendix B. Water Quality Data Used for TMDL Development ................................................... 32 Appendix C. Load Reduction Estimations .................................................................................... 35 Appendix D: Public Notification of TMDL for Yadkin River Basin Turbidity TMDLS ..................... 37 Appendix E: Public Comments ...................................................................................................... 38 1 1.0 Introduction 1.1 TMDL Definition This report presents the development of turbidity TMDLs for two waterbodies (three assessment units) in the Yadkin-Pee Dee River Basin (Figure 1.1) in North Carolina. As identified by the North Carolina Division of Water Quality (DWQ), the impaired segments of each waterbody are described in Table 1.1. Figure 1.1 Location of the Yadkin River Basin within North Carolina Table 1.1 Description of turbidity impaired assessment units Waterbody Name Description Assessment Unit (AU): Class Miles Muddy Creek From SR 2995 to a point 0.8 mile upstream of mouth 12-94-(0.5)c C 4.8 Yadkin River From a point 0.3 mile upstream of Bashavia Creek to mouth of Hauser Cr. 12-(80.7) WS-IV 9.4 Yadkin River From Davie County water supply intake to a point 0.5 mile upstream of Carters Creek 12-(86.7) WS-IV 10 Section 303(d) of the Clean Water Act (CWA) requires States to develop a list of waterbodies that do not meet water quality standards. The list, referred to as the 303(d) list, is submitted biennially to the U.S. Environment Protection Agency (USEPA) for review and approval. The 303(d) process requires that a Total Maximum Daily Load (TMDL) be developed for each of the waters appearing on the 303(d) list. The objective of a TMDL is to allocate allowable pollutant loads to known sources so that actions may be taken to restore the water to its intended uses (USEPA, 1991). Generally, the primary components of a TMDL, as identified by USEPA (1991, 2000) and the Federal Advisory Committee (USEPA, 1998) are as follows: Target identification or selection of pollutant(s) and end-point(s) for consideration. The pollutant and end-point are generally associated with measurable water quality related characteristics that indicate compliance with water quality standards. 2 Source assessment. All sources that contribute to the impairment should be identified and loads quantified, where sufficient data exist. Assimilative Capacity. Estimation of level of pollutant reduction needed to achieve water quality goal. The level of pollution should be characterized for the water body, highlighting how current conditions deviate from the target end-point. Generally, this component is identified through water quality modeling. Allocation of Pollutant Loads. Allocating pollutant control responsibility to the sources of impairment. The waste load allocation portion of the TMDL accounts for the loads associated with point sources, including NPDES stormwater. Similarly, the load allocation portion of the TMDL accounts for the loads associated with nonpoint sources. Margin of Safety. The margin of safety addresses uncertainties associated with pollutant loads, modeling techniques, and data collection. Per EPA (2000a), the margin of safety may be expressed explicitly as unallocated assimilative capacity or implicitly due to conservative assumptions. Seasonal Variation. The TMDL should consider seasonal variation in the pollutant loads and end-point. Variability can arise due to stream flows, temperatures, and exceptional events (e.g., droughts, hurricanes). Critical Conditions. Critical conditions indicate the combination of environmental factors that result in just meeting the water quality criterion and have an acceptably low frequency of occurrence. Section 303(d) of the CWA requires EPA to review all TMDLs for approval. Once EPA approves a TMDL, the water body is moved off the 303(d) list. Waterbodies remain impaired until compliance with water quality standards is achieved. 1.2 Water Quality Target: North Carolina Standards and Classifications The North Carolina fresh water quality standard for turbidity (15A NCAC 02B. 0211) states: The turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units (NTU) in streams not designated as trout waters and 10 NTU in stream, lakes or reservoirs designated as trout water; for lakes and reservoirs not designated as trout waters, the turbidity shall not exceed 25 NTU; if turbidity exceeds these levels due to natural background conditions, the existing turbidity level cannot be increased. Compliance with this turbidity standard can be met when land management activities employ Best Management Practices (BMPs) recommended by the Designated Nonpoint 3 Source Agency. BMPs must be in full compliance with all specifications governing the proper design, installation, operation and maintenance of such BMPs. 1.3 Watershed Description The impaired waterbodies are located in the Yadkin-Pee Dee River Basin. Watersheds of the impaired waterbodies were delineated using USGS -12 digit HUCs. Location maps for the impaired waterbodies are shown in the following Figures. Land Cover The land cover dataset used for this project was created by the NC Center for Geographic Information and Analysis (CGIA) for the upper portion of the Yadkin River Basin, including the entire High Rock Lake watershed. Data are derived from Landsat 5 imagery from 2006 and 2007. The methodology used to create this dataset was based on that used to create the 2001 National Land Cover Database (NLCD). Land cover distribution maps of the watersheds are shown in the following figures, and a comparison is shown in Figure 1.20. A detailed land cover distribution by square miles and percent area are shown for each impaired watershed in Appendix A. Figure 1.21 shows the land cover distribution adjacent to streams. These data were derived by using GIS to select only land cover grid cells that were intersected by a 1:24000 stream segment. 4 Figure 1.2 Muddy Creek watershed 5 Figure 1.3 Land cover distribution in the Muddy Creek watershed 6 Figure 1.4 Impaired section of the Yadkin River watershed 7 Figure 1.5 Land cover distribution of the Yadkin River Watershed 8 Figure 1.6 Land cover distribution in the impaired watersheds 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Muddy Creek Yadkin River Developed, High Intensity Developed, Medium Intensity Developed, Low Intensity Developed, Open Space Barren Land Cultivated Crops Pasture/Hay Grassland/Herbaceous Scrub/Shrub Deciduous Forest Mixed Forest Evergreen Forest Emergent Herbaceous Wetland Woody Wetlands Open Water 9 Figure 1.7 Land cover adjacent to streams in the impaired watersheds 1.4 Water Quality Monitoring Turbidity and total suspended solids (TSS) data collected monthly at DWQ Ambient Monitoring Stations and one Yadkin Pee Dee River Basin Association were used for the TMDLs. The data period used for the TMDLs was from 2000 through 2009. The data used for the 2010 303(d) list assessment are summarized in Table 1.2. Detailed data used in this study is included in Appendix B. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Muddy Creek Yadkin River Developed, High Intensity Developed, Medium Intensity Developed, Low Intensity Developed, Open Space Barren Land Cultivated Crops Pasture/Hay Grassland/Herbaceous Shrub/Scrub Deciduous Forest Mixed Forest Evergreen Forest Herbaceous Wetlands Woody Wetlands Open Water 10 Table 1.2 Summary of 2010 turbidity assessment (data from 2004-2008) Waterbody Assessment Unit Station Number of Samples Number Exceeding Standard Exceeding Percentage Muddy Creek 12-94-(0.5)c Q2710000 17 3 17.6 Yadkin River 12-(80.7) Q2040000 75 10 13.3 Yadkin River 12-(86.7) Q2180000 60 7 11. 7 2.0 General Source Assessment Turbidity is a measure of the cloudiness of water. In a waterbody, the cloudiness can be increased due to silt and clay from watershed and stream erosion, organic detritus from streams and wastewater, and phytoplankton growth. In this study, turbidity is measured in Nephelometric Turbidity Units (NTU), which is significantly correlated with total suspended solid (TSS) in this watershed. The relationship between turbidity and TSS is discussed below. 2.1 Nonpoint Sources of Turbidity Potential sources of turbidity from nonpoint sources are forests, agricultural lands, land disturbance, urban runoff, and stream channel erosion. Surface runoff is the main carrier of sediments from forests and agricultural land. Normally, runoff flowing through undisturbed forest carries insignificant amounts of sediments. Runoff flowing through agricultural land can carry a substantial amount of sediments, depending on erodibility of soils, types of agricultural practices, crop type and density, rainfall intensity, and existence and type of agricultural BMPs. Urbanization also increases the amount of sediment transported to receiving waters. Impervious urban landscapes like roads, bridges, parking lots, and buildings prevent rainwater from percolating into the ground. In impervious areas, rainwater remains above the land surface, gathers sediments and solid materials, and runs off in large amounts. 11 2.2 Point Sources of Turbidity Point sources are distinguished from nonpoint sources in that they discharge directly into streams at discrete points. Point sources of turbidity consist primarily of industries, wastewater treatment plants, and Municipal Separate Storm Sewer Systems (MS4). Municipal storm sewer systems can quickly channel urban runoff from roads and other impervious surfaces. When it leaves the system and empties into a stream, large volumes of quickly flowing runoff erode stream banks, damage streamside vegetation, and widen stream channels. The amount of sediment depends on erodibility of soils, types of surfaces, vegetation, rainfall intensity, and existence and type of BMPs. DWQ implements the Clean Water Act National Pollutant Discharge Elimination System (NPDES) permit program to control water pollution due to point sources. Individual homes that are connected to a municipal system, use a septic system, or do not have a surface discharge do not need an NPDES permit; however, industrial, municipal, and other facilities must obtain permits if their discharges go directly to surface waters. NPDES-Regulated Municipal and Industrial Wastewater Treatment Facilities Discharges from wastewater treatment facilities may contribute sediment to receiving waters as total suspended solids (TSS) and/or turbidity. Municipal and industrial treatment plants are assigned enforceable TSS limits to protect water quality. Notices of violation and civil penalties are examples of enforcement tools DWQ uses in order to bring non-compliant facilities into compliance. NPDES Stormwater Permits Most stormwater permittees are subject to TSS benchmarks. Relatively few permittees are required by the stormwater permits to monitor or address turbidity per se. Generally, permitted facilities are required to develop a stormwater pollution prevention plan, and conduct qualitative and/or quantative monitoring at stormwater outfalls. Monitoring parameters and monitoring frequency are selected for each site, or each industry group, based on DWQ’s assessment of the stormwater runoff pollution risks posed by the particular industrial activities under consideration. Municipal Separate Storm Sewer System (MS4) EPA requires NPDES permitted stormwater to be placed in the waste load allocation (WLA) of a TMDL (Wayland, 2002). In 1990, EPA promulgated rules establishing Phase I of the NPDES stormwater program. The Phase I program for Municipal Separate Storm Sewer System (MS4) requires operators of medium and large MS4s, which generally serve populations of 100,000 or greater, to implement a stormwater management program as a means to control polluted discharges from these MS4s. Phase II of the program expanded permit requirements to construction disturbing an acre or more and smaller communities (< 100,000 population) and public entities that own or operate an MS4. 12 3.0 Muddy Creek 3.1 Source Assessment Nonpoint Sources Potential sources of turbidity from nonpoint sources are described in section 2.1 Point Sources NPDES wastewater and stormwater permittees upstream of an Ambient Monitoring Site that is not impaired (not intersected by the impaired waterbody) are not subject to the TMDL. Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an unimpaired ambient monitoring site are subject to the TMDL and are discussed below. NPDES Wastewater Permits There are three facilities that discharge wastewater continuously to Muddy Creek and tributaries under the NPDES program (Table 3.1). In general, facilities are permitted to discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are shown in Figure 1.2. Table 3.1 NPDES Wastewater Dischargers in the Muddy Creek Watershed Permit Number Facility Name Permit Flow (gpd) Total Suspended Solids Monthly Average Limit NC0070033 Quail Run Mobile Home Park 17,000 30 mg/L NC0083941 Spring Creek WWTP 80,000 30 mg/L NC0086011 Neilson WTP 48,000,000 30 mg/L MS4 and Individual Stormwater Permits The Village of Clemmons (NCS000247), Winston Salem (NCS000410) and the NCDOT (NCS000250) are all MS4 stormwater permittees in the Muddy Creek Watershed. 3.2 Technical Approach Endpoint for Turbidity Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not measured in terms of concentrations and cannot be directly converted into loadings required for developing a load duration curve. For this reason, TSS was selected as the measure for this study. 13 In order to determine the relationship between TSS and turbidity in Muddy Creek, a regression equation between the two parameters was developed using the observed data collected from January 2000 through December 2009 at ambient station, Q2600000, on Muddy Creek. The relationship is shown in Equation 3.1. The coefficient of determination (R-Square) between the two parameters was 0.92, showing a strong relationship between the two parameters. The R2 value is the percentage of the total variation in turbidity that is explained or accounted for by the fitted regression (TSS). y = 1.2741x - 3.7835 R² = 0.8947 (3.1) Where Y = TSS in mg/l and X = turbidity in NTU. The corresponding TSS value at the turbidity standard of 50 NTU is 60 mg/L. Methodology The load duration curve method is intended to be a simple method to calculate pollutant reductions. This method was chosen for Muddy Creek because of the availability of long- term data. It is also an efficient method to calculate a percent load reduction from nonpoint sources. The methodology used to develop the load duration curve was based on Cleland (2002). The required load reduction was determined based on water quality monitoring and stream flow data from January 2000 through December 2009. 3.3 Flow Duration Curve Development of a flow duration curve is the first step of the load duration approach. A flow duration curve employs a cumulative frequency distribution of measured daily stream flow over the period of record. The curve relates flow values measured at the monitoring station for the percent of time the flow values were equaled or exceeded. Flows are ranked from lowest, which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1 percent of the time. Reliability of the flow duration curve depends on the period of record available at monitoring stations. Accuracy of the curve increases when longer periods of record are used. The flow duration curve, shown in Figure 3.1, was used to determine the seasonality and flow regimes during which the exceedances of the pollutants occurred. Figure 3.1 Flow Duration Curve for the Daily flow data were used from USGS the DWQ water quality monitoring 3.4 Load Duration Curve A load duration curve is developed by multi by the pollutant concentrations and the appropriate conversion factors. allowable and existing loads are plotted against the flow recurrence interval. The allowable load is based on the water quality numerical curve. The target line is represented by the line drawn through the allowable load data points and hence, it determines the assimilative capacity of a stream or river under dif conditions. Any values above the line are exceeded loads and the values below the line are acceptable loads. Therefore, a load duration curve can help define the flow regime during which exceedances occur. Exceedances that occur during low continuous or point source discharges, which are generally diluted during storm events. Exceedances that occur during high mixture of point and non-point sources may Existing TSS loads to Muddy Creek were determined by multiplying the observed TSS concentration by the flow observed on the date of observation and converting the result to daily loading values. The assimilative multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full range of measured flow values. ation Curve for the Muddy Creek at DWQ Station Q2600000 Daily flow data were used from USGS Muddy Creek gauging station 02115860, co water quality monitoring station. A load duration curve is developed by multiplying the flow values along the flow duration curve by the pollutant concentrations and the appropriate conversion factors. As shown allowable and existing loads are plotted against the flow recurrence interval. The allowable d on the water quality numerical standard, margin of safety, and flow duration curve. The target line is represented by the line drawn through the allowable load data points and hence, it determines the assimilative capacity of a stream or river under dif conditions. Any values above the line are exceeded loads and the values below the line are acceptable loads. Therefore, a load duration curve can help define the flow regime during which exceedances occur. Exceedances that occur during low-flow events are likely caused by continuous or point source discharges, which are generally diluted during storm events. Exceedances that occur during high-flow events are generally driven by storm-event runoff. A point sources may cause exceedances during normal flows. Existing TSS loads to Muddy Creek were determined by multiplying the observed TSS concentration by the flow observed on the date of observation and converting the result to daily loading values. The assimilative capacities of the waterbodies were determined by multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full 14 at DWQ Station Q2600000 gauging station 02115860, co-located with plying the flow values along the flow duration curve As shown in Figure 3.2, allowable and existing loads are plotted against the flow recurrence interval. The allowable , margin of safety, and flow duration curve. The target line is represented by the line drawn through the allowable load data points and hence, it determines the assimilative capacity of a stream or river under different flow conditions. Any values above the line are exceeded loads and the values below the line are acceptable loads. Therefore, a load duration curve can help define the flow regime during ow events are likely caused by continuous or point source discharges, which are generally diluted during storm events. event runoff. A cause exceedances during normal flows. Existing TSS loads to Muddy Creek were determined by multiplying the observed TSS concentration by the flow observed on the date of observation and converting the result to were determined by multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full Figure 3.2 Load Duration Curve for Muddy Creek at DWQ station Q2600000 For Muddy Creek, the standard violations occurred during typical to high flow conditions. exceedances during low-flow conditions suggest that point sources in the watershed may not be a significant source of TSS in this watershed. flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In addition most of the exceedances occurred during summer when increase runoff. Stormwater runoff would carry a substantial amount of sediments and solid materials from impermeable as we result of high and transitional flows. exceeds the resistance of the lateral (side) soil material. considered unmanageable and hence are 3.5 TMDL Total Maximum Daily Load (TMDL) can be defined as the t assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality. This definition can be expressed by equation 3 ve for Muddy Creek at DWQ station Q2600000 violations occurred during typical to high flow conditions. conditions suggest that point sources in the watershed may not SS in this watershed. The higher loads during high and transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In addition most of the exceedances occurred during summer when thunderstorms noff. Stormwater runoff would carry a substantial amount of sediments and solid materials from impermeable as well as permeable land surfaces. Bank erosion may be another result of high and transitional flows. Bank erosion occurs when high volume and velo exceeds the resistance of the lateral (side) soil material. The loads during high flow period are idered unmanageable and hence are excluded in the TMDL estimation in this study. Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load priate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality. This can be expressed by equation 3.2. 15 violations occurred during typical to high flow conditions. No conditions suggest that point sources in the watershed may not The higher loads during high and transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In thunderstorms would noff. Stormwater runoff would carry a substantial amount of sediments and solid . Bank erosion may be another Bank erosion occurs when high volume and velocity runoff The loads during high flow period are excluded in the TMDL estimation in this study. otal amount of pollutant that can be assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load priate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality. This 16 ∑∑++=MOSLAsWLAsTMDL (3.2) The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in order to implement control measures and to achieve water quality standards. The Code of Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are expressed as tons per day. TMDLs represent the maximum one-day load the river can assimilate and maintain the water quality criterion. Load duration curve approach was utilized to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are described below. 3.5.1 Margin of Safety (MOS) Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the simulated relationship between the pollutants and the water quality standard. In this study, the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent lower than the water quality target for turbidity. 3.6 Target Reduction To determine the amount of turbidity reduction necessary to comply with the water quality standard, exceedances of the estimated standard (estimated as 60 mg TSS/L) were identified within the 10th to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is not included in the TMDL calculation to allow cases of extreme drought or flood to be excluded. An exponential curve equation for the data points violating the water quality criterion was estimated. The equation is presented in Equation 3.3. y = 63.197e-0.745x R² = 0.2299 (3.3) Where, Y = TSS (tons/day) and X = Percent Flow Exceeded. To present the TMDLs as a single value, the existing load was calculated from the exponential curve equation as the average of the load violations occurring between 10% and 90% flow exceedances. The average load was calculated by using percent flow exceedances in multiples of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL target value, which includes the 10 percent MOS. The target curve based on the allowable load and the exponential curve based on the exceedances are shown in Figure 3.3. The necessary percent reduction was calculated by taking the difference between the average of the exponential curve load estimates and the average of the allowable load estimates. For example, at each recurrence interval between 10 and 90 (again using recurrence intervals in multiples of 5), the equation of the exponential curve was used to estimate the existing load. 17 The allowable load was then calculated in a similar fashion by substituting the allowable load curve. The estimated values are given in Appendix C. Figure 3.3 Load duration curve allowable TSS load and existing total TSS load violation in Muddy Creek The exponential line representing the exceeding TSS loads in Figure 3.3 has a lower R-Square value due to presence of an observation that is numerically distant from the rest of the loads. 3.7 TMDL Allocation 3.7.1 Waste Load Allocation (WLA) Two wastewater treatment plants (WWTP), a water treatment plant, plus the Village of Clemmons, Winston Salem and the NC Department of Transportation hold NPDES permits in the Muddy Creek Watershed. The wastewater load contributions are shown in Table 3.2 Table 3.2 Existing NPDES WW Load Contributions Facility Name Permit Number Flow (gpd) Permit Limit (monthly max in mg/L) Load (tons/day) % of Average Ambient Station Load Quail Run Mobile Home Park NC0070033 17,000 30 0.0019 0.004 Spring Creek WWTP NC0083941 80,000 30 0.0091 0.02 Neilson WTP NC0086011 48,000,000 30 5.4510 10.92 y = 63.197e-0.745x R² = 0.2299 1.0 10.0 100.0 10% 20% 30% 40% 50% 60% 70% 80% 90% TS S ( t o n e s / d a y ) Percent Flow Exceeded Allowable load with MOS Existing load violation Expon. (Existing load violation) 18 In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged reaches the ambient station with no settling. Based on facility permit limits of flow and the monthly average permit limits for TSS, the combined WWTP load contributes approximately 11 percent of the average load at DWQ station Q2600000 based on data from years 2000 through 2009. It was concluded that the WWTPs are adequately regulated under existing permits and the waste load allocations in this TMDL were calculated at the existing permit limits. The NCDOT, Village of Clemmons, and Winston-Salem MS4 permittees were considered significant contributors, and were assigned a percent reduction identical to the nonpoint source reduction. The NCDOT, Village of Clemmons, and Winston-Salem are currently in compliance with their NPDES stormwater permits, and will continue to implement measures required by their permits. Because of the nature of drainage from roads and other impervious areas, data are not available (n/a) to calculate a WLA for the stormwater permittees as a load. The waste load allocation and required reductions for NPDES permittees in the Muddy Creek watershed are shown in Table 3.3. Table 3.3 NPDES waste load allocations and required reductions NPDES Permittee Permitted Load (tons/day) WLA (tons/day) Percent Reduction Required Quail Run Mobile Home Park 0.0019 0.0019 0% Spring Creek WWTP 0.0091 0.0091 0% Neilson WTP 5.4510 5.4510 0% Village of Clemmons – MS4 Stormwater N/A N/A 58% Winston Salem – MS4 Stormwater N/A N/A 58% NCDOT – MS4 Stormwater N/A N/A 58% 3.7.2 Load Allocation (LA) All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and forestlands are reported as the LA. The estimated TMDL and allocation of TSS to point and nonpoint sources are presented in Table 3.4. The estimated percent reduction needed from NPDES stormwater and nonpoint sources is 58%, as shown in Table 3.5. Table 3.4 Estimated TMDL and load allocation for TSS (tons/day) for Muddy Creek Pollutant Water Body Existing Load (tons/day) WLA LA MOS TMDL TSS Muddy Creek 44.3 5.462 16.14 Explicit 10% 21.6 Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10% 19 Table 3.5 Estimated reduction by source for TSS (tons/day) for Muddy Creek NPDES Wastewater WLA NPDES Stormwater WLA LA Existing Load (tons/day) 5.462 N/A 38.8 Allocation (tons/day) 5.462 N/A 16.14 Percent Reduction 0% 58% 58% 3.7.3 Critical Condition and Seasonal Variation Critical conditions are considered in the load duration curve analysis by using an extended period of stream flow and water quality data, and by examining the flows (percent flow exceeded) where the existing loads exceed the target. Seasonal variation is considered in the development of the TMDLs, because allocation applies to all seasons. In the load duration curves, the mark inside a square box indicates pollutant load during the summer period. The exceedances of turbidity occurred during normal to high flow periods. The result shows that wet weather under high-flow period is the critical period for turbidity in Muddy Creek. 4.0 Yadkin River 4.1 Source Assessment Nonpoint Sources Potential sources of turbidity from nonpoint sources are described in section 2.1 Point Sources NPDES wastewater and stormwater permittees upstream of an Ambient Monitoring Site that is not impaired (not intersected by the impaired waterbody) are not subject to the TMDL. Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an unimpaired ambient monitoring site are subject to the TMDL and are discussed below. NPDES Wastewater Permits There are 12 facilities that discharge wastewater continuously to the Yadkin River and tributaries under the NPDES program (Table 4.1). In general, facilities are permitted to discharge a monthly average TSS concentration up to 30 mg/L. Locations of dischargers are shown in Figure 1.4. 20 Table 4.1 NPDES Wastewater Dischargers in the Yadkin River Watershed Permit Number Facility Name Permit Flow (gpd) Total Suspended Solids Monthly Average Limit NC0029599 Courtney Elementary School WWTP 5,000 30 mg/L NC0029602 Forbush Elementary School WWTP 6,000 30 mg/L NC0029611 East Bend Elementary School WWTP 7,000 30 mg/L NC0031160 Pilot Mountain State Park WWTP 10,000 30 mg/L NC0034827 Old Richmond Elementary School 6,400 30 mg/L NC0055158 Bermuda Run WWTP 193,000 30 mg/L NC0061204 Scarlett Acres MHP WWTP 20,000 30 mg/L NC0063720 Forest Ridge WWTP 33,000 30 mg/L NC0064726 East Bend Industrial Park WWTP 10,000 30 mg/L NC0084212 Sparks Road WTP No Permit Limit 30 mg/L NC0084409 Wellesley Place WWTP 60,000 30 mg/L NC0086762 Northwest WTP 35,000,000 30 mg/L MS4 and Individual Stormwater Permits Lewisville (NCS000494) and the NCDOT (NCS000250) are MS4 stormwater permittees in the TMDL portion of the Yadkin River Watershed. 4.2 Technical Approach Endpoint for Turbidity Turbidity is a measure of cloudiness and is reported in NTU. Therefore, turbidity is not measured in terms of concentrations and cannot be directly converted into loadings required for developing a load duration curve. For this reason, TSS was selected as the measure for this study. In order to determine the relationship between TSS and turbidity in the Yadkin River, a regression equation between the two parameters was developed using the observed data collected from January 2000 through December 2009 at ambient station, Q2040000, on the Yadkin River. The relationship is shown in Equation 4.1. The coefficient of determination (R- Square) between the two parameters was 0.88, showing a strong relationship between the two parameters. The R2 value is the percentage of the total variation in turbidity that is explained or accounted for by the fitted regression (TSS). y = 0.0019x2 + 0.3773x + 12.931 R² = 0.8842 (4.1) Where Y = TSS in mg/l and X = turbidity in NTU. 21 The corresponding TSS value at the turbidity standard of 50 NTU is 37 mg/L. Methodology The load duration curve method is intended to be a simple method to calculate pollutant reductions. This method was chosen for the Yadkin River because of the availability of long- term data. It is also an efficient method to calculate a percent load reduction from nonpoint sources. The methodology used to develop the load duration curve was based on Cleland (2002).The required load reduction was determined based on water quality monitoring and stream flow data from February 2000 through December 2009. 4.3 Flow Duration Curve Development of a flow duration curve is the first step of the load duration approach. A flow duration curve employs a cumulative frequency distribution of measured daily stream flow over the period of record. The curve relates flow values measured at the monitoring station for the percent of time the flow values were equaled or exceeded. Flows are ranked from lowest, which are exceeded nearly 100 percent of the time, to highest, which are exceeded less than 1 percent of the time. Reliability of the flow duration curve depends on the period of record available at monitoring stations. Accuracy of the curve increases when longer periods of record are used. The flow duration curve, shown in Figure 4.1, was used to determine the seasonality and flow regimes during which the exceedances of the pollutants occurred. Figure 4.1 Flow Duration Curve for the Yadkin River at DWQ Station Q2040000 1 10 100 1000 10000 100000 0. 0 0 5 % 0. 0 1 0 % 0. 1 0 0 % 1. 0 0 0 % 5. 0 0 0 % 10 . 0 0 0 % 15 . 0 0 0 % 20 . 0 0 0 % 25 . 0 0 0 % 30 . 0 0 0 % 35 . 0 0 0 % 40 . 0 0 0 % 45 . 0 0 0 % 50 . 0 0 0 % 55 . 0 0 0 % 60 . 0 0 0 % 65 . 0 0 0 % 70 . 0 0 0 % 75 . 0 0 0 % 80 . 0 0 0 % 85 . 0 0 0 % 90 . 0 0 0 % 95 . 0 0 0 % 99 . 0 0 0 % 10 0 . 0 0 0 % Fl o w ( c f s ) Percent Flow Exceeded 22 Daily flow data were used from USGS Yadkin River gauging station 02115360, co-located with the DWQ water quality monitoring station. 4.4 Load Duration Curve A load duration curve is developed by multiplying the flow values along the flow duration curve by the pollutant concentrations and the appropriate conversion factors. As shown in Figure 4.2, allowable and existing loads are plotted against the flow recurrence interval. The allowable load is based on the water quality numerical standard, margin of safety, and flow duration curve. The target line is represented by the line drawn through the allowable load data points and hence, it determines the assimilative capacity of a stream or river under different flow conditions. Any values above the line are exceeded loads and the values below the line are acceptable loads. Therefore, a load duration curve can help define the flow regime during which exceedances occur. Exceedances that occur during low-flow events are likely caused by continuous or point source discharges, which are generally diluted during storm events. Exceedances that occur during high-flow events are generally driven by storm-event runoff. A mixture of point and non-point sources may cause exceedances during normal flows. Existing TSS loads to the Yadkin River were determined by multiplying the observed TSS concentration by the flow observed on the date of observation and converting the result to daily loading values. The assimilative capacities of the waterbodies were determined by multiplying the TSS concentration that is equivalent to a turbidity value of 50 NTU by the full range of measured flow values. Figure 4.2 Load Duration Curve for the Yadkin River at DWQ station Q2040000 For the Yadkin River, the standard conditions. Few exceedances during watershed may not be a significant source of TSS in this watershed. high and transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In addition most of the exceedances occurred during summer when thunderstorms would increase runoff. Stormwater runoff would sediments and solid materials from impermeable as we erosion may be another result of high and transitional flows. volume and velocity runoff exceeds the resist during high flow period are cons estimation in this study. 4.5 TMDL Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load allocations (LAs), and an appropriate margin of safety (MOS), uncertainty concerning the relationship between effluent limitations and water quality. This definition can be expressed by equation 4 Load Duration Curve for the Yadkin River at DWQ station Q2040000 standard violations occurred mostly during typical to high flow conditions. Few exceedances during low-flow conditions suggest that point sources in the watershed may not be a significant source of TSS in this watershed. The higher loads during high and transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In addition most of the exceedances occurred during summer when would increase runoff. Stormwater runoff would carry a substantial amount of sediments and solid materials from impermeable as well as permeable land surfaces. erosion may be another result of high and transitional flows. Bank erosion occurs when high volume and velocity runoff exceeds the resistance of the lateral (side) soil material. during high flow period are considered unmanageable and hence are excluded in the TMDL Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load allocations (LAs), and an appropriate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality. This can be expressed by equation 4.2. 23 to high flow conditions suggest that point sources in the er loads during high and transitional flows suggest that the sources of turbidity could be from storm runoff and/or bank erosion. In addition most of the exceedances occurred during summer when carry a substantial amount of ll as permeable land surfaces. Bank Bank erosion occurs when high ance of the lateral (side) soil material. The loads excluded in the TMDL Total Maximum Daily Load (TMDL) can be defined as the total amount of pollutant that can be assimilated by the receiving water body while achieving water quality standards. A TMDL can be expressed as the sum of all point source wasteload allocations (WLAs), nonpoint source load which takes into account any uncertainty concerning the relationship between effluent limitations and water quality. This 24 ∑∑++=MOSLAsWLAsTMDL (4.2) The purpose of the TMDL is to estimate allowable pollutant loads and to allocate those loads in order to implement control measures and to achieve water quality standards. The Code of Federal Regulations (40 CFR § 130.2 (1)) states that TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures. For TSS (measure for turbidity), TMDLs are expressed as tons per day. TMDLs represent the maximum one-day load the river can assimilate and maintain the water quality criterion. Load duration curve approach was utilized to estimate the TMDL for TSS. The systematic procedures adopted to estimate TMDLs are described below. 4.5.1 Margin of Safety (MOS) Conceptually, the MOS is included in the TMDL estimation to account for the uncertainty in the simulated relationship between the pollutants and the water quality standard. In this study, the MOS was explicitly included in the TMDL analysis by setting the TMDL target at 10 percent lower than the water quality target for turbidity. 4.6 Target Reduction To determine the amount of turbidity reduction necessary to comply with the water quality standard, exceedances of the standard (estimated as 37 mg TSS/L) were identified within the 10th to 90th percentile flow recurrence range. Typically the remaining flow recurrence range is not included in the TMDL calculation to allow cases of extreme drought or flood to be excluded. An power curve equation for the data points violating the water quality criterion was estimated. The equation is presented in Equation 4.3. y = 125.94x-0.983 R² = 0.606 (4.3) Where, Y = TSS (tons/day) and X = Percent Flow Exceeded. To present the TMDLs as a single value, the existing load was calculated from the power curve equation as the average of the load violations occurring between 10% and 90% flow exceedances. The average load was calculated by using percent flow exceedances in multiples of 5 percent. The allowable loadings for each exceedance were calculated from the TMDL target value, which includes the 10 percent MOS. The target curve based on the allowable load and the exponential curve based on the exceedances are shown in Figure 4.3. The necessary percent reduction was calculated by taking the difference between the average of the power curve load estimates and the average of the allowable load estimates. For example, at each recurrence interval between 10 and 90 (again using recurrence intervals in multiples of 5), the equation of the power curve was used to estimate the existing load. The 25 allowable load was then calculated in a similar fashion by substituting the allowable load curve. The estimated values are given in Appendix C. Figure 4.3 Load duration curve allowable TSS load and existing total TSS load violation in the Yadkin River 4.7 TMDL Allocation 4.7.1 Waste Load Allocation (WLA) Twelve wastewater treatment plants (WWTP) plus the Town of Lewisville, and the NC Department of Transportation hold NPDES permits in the TMDL portion of the Yadkin River Watershed. The wastewater load contributions are shown in Table 4.2. Table 4.2 Existing NPDES WW Load Contributions Facility Name Permit Number Flow (gpd) Permit Limit (monthly max in mg/L) Load (tons/day) % of Average Ambient Station Load Courtney Elementary School WWTP NC0029599 5,000 30 0.0006 0.0002 Forbush Elementary School WWTP NC0029602 6,000 30 0.0007 0.0002 East Bend Elementary School WWTP NC0029611 7,000 30 0.0008 0.0002 y = 125.94x-0.983 R² = 0.606 1.0 10.0 100.0 1000.0 10000.0 10% 20% 30% 40% 50% 60% 70% 80% 90% TS S ( t o n e s / d a y ) Percent Flow Exceeded Allowable load with MOS Existing Load Violation Power (Existing Load Violation) 26 Facility Name Permit Number Flow (gpd) Permit Limit (monthly max in mg/L) Load (tons/day) % of Average Ambient Station Load Pilot Mountain State Park WWTP NC0031160 10,000 30 0.0011 0.0003 Old Richmond Elementary School NC0034827 6,400 30 0.0007 0.0002 Bermuda Run WWTP NC0055158 193,000 30 0.0219 0.0061 Scarlett Acres MHP WWTP NC0061204 20,000 30 0.0023 0.0006 Forest Ridge WWTP NC0063720 33,000 30 0.0037 0.0010 East Bend Industrial Park WWTP NC0064726 10,000 30 0.0011 0.0003 Sparks Road WTP NC0084212 No Permit Limit 30 N/A N/A Wellesley Place WWTP NC0084409 60,000 30 0.0068 0.0019 Northwest WTP NC0086762 35,000,000 30 3.9747 1.0995 The Sparks Road WTP does not have a flow limit, therefore a load will not be calculated for this facility. In order to estimate contributions from the WWTPs, it was assumed that all TSS discharged reaches the ambient station with no settling. Based on facility permit limits of flow and the monthly average permit limits for TSS, the combined WWTP load contributes approximate 1% of the average load at DWQ station Q2040000 based on data from years 2000 through 2009. It appears that these WWTPs do not present a significant load to the Yadkin River. Therefore it was concluded that the WWTPs are adequately regulated under existing permits and the waste load allocations in this TMDL were calculated at the existing permit limits. The NCDOT and Lewisville MS4 permittees were considered significant contributors, and were assigned a percent reduction identical to the nonpoint source reduction. The NCDOT and Lewisville are currently in compliance with their NPDES stormwater permits, and will continue to implement measures required by their permits. Because of the nature of drainage from roads and other impervious areas, data are not available (n/a) to calculate a WLA for the stormwater permittees as a load. The waste load allocation and required reductions for NPDES permittees in the Yadkin River watershed are shown in Table 4.3. Table 4.3 NPDES waste load allocations and required reductions NPDES Permittee Permitted Load (tons/day) WLA (tons/day) Percent Reduction Required Courtney Elementary School WWTP 0.0006 0.0006 0% Forbush Elementary School WWTP 0.0007 0.0007 0% 27 NPDES Permittee Permitted Load (tons/day) WLA (tons/day) Percent Reduction Required East Bend Elementary School WWTP 0.0008 0.0008 0% Pilot Mountain State Park WWTP 0.0011 0.0011 0% Old Richmond Elementary School 0.0007 0.0007 0% Bermuda Run WWTP 0.0219 0.0219 0% Scarlett Acres MHP WWTP 0.0023 0.0023 0% Forest Ridge WWTP 0.0037 0.0037 0% East Bend Industrial Park WWTP 0.0011 0.0011 0% Sparks Road WTP N/A N/A N/A Wellesley Place WWTP 0.0068 0.0068 0% Northwest WTP 3.9747 3.9747 0% Lewisville - MS4 Stormwater N/A N/A 59% NCDOT – MS4 Stormwater N/A N/A 59% 4.7.2 Load Allocation (LA) All TSS loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and forestlands are reported as the LA. The estimated contributions of TSS from the nonpoint sources are presented in Table 4.4. The estimated percent reduction needed from nonpoint sources is 59%, as shown in Table 4.5. Table 4.4 Estimated TMDL and load allocation for TSS (tons/day) for the Yadkin River Pollutant Water Body Existing Load (tons/day) WLA LA MOS TMDL TSS Yadkin River 361.50 4.014 146.986 Explicit 10% 151.00 Note: The Margin of safety is included in the TMDL by lowering TSS value calculated at the 50 NTU standard by 10% Table 4.5 Estimated reduction by source for TSS (tons/day) for the Yadkin River NPDES Wastewater WLA NPDES Stormwater WLA LA Existing Load (tons/day) 4.014 N/A 357.489 Allocation (tons/day) 4.014 N/A 146.986 Percent Reduction 0% 59% 59% 4.7.3 Critical Condition and Seasonal Variation 28 Critical conditions are considered in the load duration curve analysis by using an extended period of stream flow and water quality data, and by examining the flows (percent flow exceeded) where the existing loads exceed the target. Seasonal variation is considered in the development of the TMDLs, because allocation applies to all seasons. In the load duration curves, the mark inside a square box indicates pollutant load during the summer period. The exceedances of turbidity occurred during normal to high flow periods. The result shows that wet weather under high-flow period is the critical period for turbidity in the Yadkin River. 5.0 Summary and Future Implementation This report presents the development of the Total Maximum Daily Loads (TMDL) for two waterbodies in the Yadkin Pee-Dee River Basin. Available water quality data were reviewed to determine the critical periods and the sources that lead to exceedances of the standard. The necessary percent reduction to meet the TMDL requirement was then calculated by taking a difference between the average of the curve load estimates and the average of the allowable load estimates. The summary of the results is as follows: • Muddy Creek: A 52% reduction in nonpoint source and NPDES stormwater contributions of TSS is required in order to meet the water quality standard. • Yadkin River: A 59% reduction in nonpoint source and NPDES stormwater contributions of TSS is required in order to meet the water quality standard. This reduction may be achieved in part through the reductions required for South Deep Creek. 5.1 TMDL Implementation This section is intended to provide some initial guidance for implementing this TMDL. In order for these waterbodies to meet water quality standards, reductions from both point and nonpoint sources are needed. Under the jurisdiction of the Clean Water Act, as it relates to the development and executions of Total Maximum Daily Loads, reductions in turbidity needed from non-regulated nonpoint sources such as agriculture and silviculture can only be expected to be implemented on a voluntary basis. Reductions in turbidity from permitted MS4 entities will be achieved through incremental measures required through their permitting, with strategies adapted to best reduce pollutant loads to the receiving watershed to the maximum extent practicable. The efficacy of all measures will be determined at the ambient monitoring stations relied upon by the NC DWQ to determine use support status of the waters of the state, which may include more data in the future. 29 Nonpoint sources: Agricultural land comprises of 16 and 27 percent of the Muddy Creek and Yadkin River watersheds, respectively, based on 2007 land cover data. “Developed, Open Space” properties occupy 26 and 6 percent of the Muddy Creek and Yadkin River watersheds, respectively, based on 2007 land cover data. Reductions in turbidity from these and other rural nonpoint sources are needed to attain water quality standards in Muddy Creek and the Yadkin River. Reduction of turbidity will result from reduced overland flow and stormwater runoff, and improved land management. Landowners, stakeholder groups, local governments, and agencies are encouraged to utilize all available funding sources for water quality improvement projects within the watershed. The following programs provide technical and financial resources for reducing nonpoint source pollution: • North Carolina Soil and Water Conservation Division • The Natural Resources Conservation Service • Clean Water Act Section 319 Nonpoint Source Pollution Control Grant (not available to NC MS4 communities to address turbidity or total suspended solids reductions following the initiation of this TMDL) • North Carolina Clean Water Management Trust Fund • 205(j) Water Quality Management Planning Grant Point Sources: MS4 stormwater permittees identified in this TMDL and entities in the TMDL areas designated as MS4s in the future will be required to establish water quality recovery programs (WQRP), as described in their permits. The WQRP is a requirement under the stormwater permit when the entity is subject to an approved TMDL. The WQRP is designed by the entity and submitted to DWQ for approval. The program will outline ways to incrementally reduce turbidity. Example activities include ordinance enhancements, installing rain barrels, redevelopment with green infrastructure, or stormwater retrofits. MS4 stormwater permittees are considered in compliance with this TMDL if they meet the conditions of their MS4 stormwater permit, which includes complying with their WQRP.MS4s alone are not responsible for attaining water quality standards at the ambient monitoring stations; we expect this attainment to be achieved through reduction from MS4s along with agriculture operations and other nonpoint source contributors to the high turbidity levels in these waters. 6.0 Public Participation This TMDL was public noticed through the DWQ Modeling and TMDL unit website, through the Modeling and TMDL unit listserv, through the DWQ events calendar, and through the Water Resources Research Institute (WRRI) listserv of North Carolina State University. The announcement is provided in Appendix D. The TMDL was also available from DWQ’s website at http://portal.ncdenr.org/web/wq/ps/mtu/tmdl/tmdls during the comment period. The public comment period lasted from July 26 – August 25, 2011. NCDWQ received comments from seven entities. A summary of their comments and DWQ’s response is provided in Appendix E. 30 7.0 References Cleland, B.R. 2002. TMDL Development from the “Bottom Up” – Part II: Using load duration curves to connect the pieces. Proceedings from the WEF National TMDL Science and Policy 2002 Conference. U.S. Environmental Protection Agency (USEPA). 1991. Guidance for Water Quality-Based Decisions: The TMDL Process. Assessment and Watershed Protection Division, Washington, DC. U.S. Environmental Protection Agency (USEPA) 1998. Draft Final TMDL Federal Advisory Committee Report. U.S. Environmental Protection Agency, Federal Advisory Committee (FACA). Draft final TMDL Federal Advisory Committee Report. 4/28/98. U.S. Environmental Protection Agency (USEPA) 2000. Revisions to the Water Quality Planning and Management Regulation and Revisions to the National Pollutant Discharge Elimination System Program in Support of Revisions to the Water Quality Planning and management Regulation; Final Rule. Fed. Reg. 65:43586-43670 (July 13, 2000). Wayland, R. November 22, 2002. Memorandum from Rober Wayland of the U. S. Environmental Protection Agency to Water Division Directors. Subject: Establishing TMDL Waste Load Allocation for stormwater sources and NPDES permit requirements based on those allocations. 31 Appendix A: Land Cover Data in Square Miles and Percent Area for the Impaired Watersheds Description Muddy Creek Yadkin River Barren Land 0.3 0% 1.6 0% Cultivated Crops 2.3 1% 37.8 2% Deciduous Forest 28.2 11% 798.2 41% Developed, High Intensity 6.7 3% 7.7 0% Developed, Low Intensity 53.5 21% 116.3 6% Developed, Medium Intensity 14.2 6% 14.2 1% Developed, Open Space 65.2 26% 112.5 6% Emergent Herbaceous Wetland 0.0 0% 0.0 0% Evergreen Forest 26.8 10% 255.1 13% Grassland/Herbaceous 1.2 0% 7.6 0% Mixed Forest 13.8 5% 81.5 4% Open Water 1.4 1% 11.1 1% Pasture/Hay 37.3 15% 501.7 25% Scrub/Shrub 2.7 1% 21.1 1% Woody Wetlands 1.7 1% 2.3 0% Total SQMI 256 1969 32 Appendix B. Water Quality Data Used for TMDL Development 33 Muddy Creek DWQ Station Q2600000 and USGS station 02115860 Sample Date Flow (cfs) TSS (mg/L) Turbidity (NTU) TSS Load (tons/day) Sample Date Flow (cfs) TSS (mg/L) Turbidity (NTU) TSS Load (tons/day) 01/03/2000 115 3.00 4.30 0.93 11/28/2005 136 108.00 45.00 39.51 02/01/2000 151 12.00 15.00 4.87 12/19/2005 213 47.18 40.00 27.03 03/01/2000 132 2.00 4.60 0.71 01/18/2006 248 40.81 35.00 27.23 04/06/2000 223 24.00 19.00 14.40 02/23/2006 159 14.00 15.00 5.99 05/01/2000 177 8.00 9.00 3.81 04/25/2006 159 7.17 8.60 3.07 06/13/2000 93 18.00 12.00 4.50 05/11/2006 131 12.00 8.50 4.23 07/05/2000 92 20.42 19.00 5.05 06/28/2006 892 26.79 24.00 64.29 08/09/2000 88 17.88 17.00 4.23 08/03/2006 96 1.44 4.10 0.37 09/06/2000 181 11.51 12.00 5.60 08/23/2006 102 12.00 12.00 3.29 10/12/2000 78 1.57 4.20 0.33 09/28/2006 106 4.63 6.60 1.32 11/14/2000 92 2.84 5.20 0.70 10/26/2006 113 0.00 2.80 0.00 12/20/2000 117 4.12 6.20 1.30 11/20/2006 266 10.23 11.00 7.32 01/24/2001 126 6.28 7.90 2.13 12/19/2006 131 11.00 8.30 3.88 02/20/2001 117 9.00 11.00 2.83 01/25/2007 185 11.51 12.00 5.73 04/30/2001 102 1.31 4.00 0.36 02/26/2007 207 22.00 27.00 12.25 05/30/2001 102 18.00 15.00 4.94 03/28/2007 175 6.15 7.80 2.90 06/27/2001 110 7.94 9.20 2.35 04/30/2007 154 6.28 7.90 2.60 07/25/2001 59 6.28 7.90 1.00 05/22/2007 121 11.00 7.30 3.58 08/27/2001 76 4.00 4.60 0.82 06/26/2007 280 72.66 60.00 54.73 09/25/2001 162 91.77 75.00 39.99 07/11/2007 151 8.96 10.00 3.64 10/11/2001 63 -0.22 2.80 -0.04 08/07/2007 65 1.19 3.90 0.21 11/15/2001 71 3.00 16.00 0.57 09/24/2007 55 2.33 4.80 0.35 12/10/2001 78 16.60 16.00 3.48 10/23/2007 54 2.08 4.60 0.30 01/07/2002 111 36.99 32.00 11.04 11/05/2007 79 5.39 7.20 1.15 02/26/2002 101 5.00 3.90 1.36 12/10/2007 76 0.00 2.20 0.00 03/27/2002 147 44.63 38.00 17.65 01/30/2008 113 6.28 7.90 1.91 04/22/2002 112 12.78 13.00 3.85 02/27/2008 146 7.80 9.50 3.06 05/23/2002 80 10.00 8.90 2.15 03/25/2008 115 3.73 5.90 1.16 06/17/2002 57 7.68 9.00 1.18 04/16/2008 136 5.01 6.90 1.83 07/10/2002 45 5.01 6.90 0.61 05/29/2008 116 8.00 7.20 2.50 08/19/2002 54 6.00 7.70 0.87 06/23/2008 245 79.03 65.00 52.09 09/10/2002 42 0.17 3.10 0.02 07/28/2008 77 8.07 9.30 1.67 10/02/2002 87 0.55 3.40 0.13 08/27/2008 2580 546.00 310.00 3789.35 11/25/2002 140 4.12 6.20 1.55 09/25/2008 69 2.97 5.30 0.55 12/16/2002 255 17.88 17.00 12.26 10/23/2008 71 0.80 3.60 0.15 01/28/2003 120 0.68 3.50 0.22 12/01/2008 281 47.18 40.00 35.66 02/11/2003 143 6.00 6.40 2.31 12/18/2008 183 25.52 23.00 12.56 03/03/2003 270 30.62 27.00 22.24 01/20/2009 136 7.43 8.80 2.72 04/15/2003 459 24.25 22.00 29.94 02/19/2009 195 16.00 20.00 8.39 06/11/2003 366 28.07 25.00 27.64 03/26/2009 178 6.92 8.40 3.31 07/01/2003 243 8.45 9.60 5.52 05/05/2009 323 47.18 40.00 40.99 08/04/2003 528 230.00 180.00 326.67 06/04/2009 254 29.00 25.00 19.81 09/03/2003 235 8.19 9.40 5.18 06/29/2009 93 5.01 6.90 1.25 10/01/2003 184 7.05 8.50 3.49 07/22/2009 91 21.70 20.00 5.31 11/25/2003 207 9.00 9.10 5.01 08/25/2009 66 8.80 6.40 1.56 12/29/2003 188 2.46 4.90 1.24 09/21/2009 71 3.10 5.40 0.59 01/27/2004 172 2.33 4.80 1.08 10/21/2009 69 1.19 3.90 0.22 02/11/2004 245 18.00 22.00 11.86 11/30/2009 144 3.10 5.40 1.20 03/10/2004 176 3.61 5.80 1.71 12/10/2009 566 45.91 39.00 69.89 04/22/2004 176 12.78 13.00 6.05 05/10/2004 175 160.00 100.00 75.32 06/30/2004 165 10.23 11.00 4.54 07/20/2004 168 10.23 11.00 4.62 08/30/2004 121 7.00 5.10 2.28 09/14/2004 326 6.03 7.70 5.29 10/06/2004 178 16.60 16.00 7.95 11/23/2004 165 26.79 24.00 11.89 12/01/2004 194 6.15 7.80 3.21 01/04/2005 182 3.61 5.80 1.77 02/14/2005 182 16.00 8.60 7.83 03/09/2005 207 4.88 6.80 2.72 04/19/2005 217 7.81 9.10 4.56 05/05/2005 178 11.00 6.20 5.27 06/23/2005 154 11.51 12.00 4.77 07/21/2005 223 17.88 17.00 10.72 08/09/2005 338 728.00 500.00 661.91 10/18/2005 134 11.51 12.00 4.15 34 Yadkin River DWQ Station Q2040000 and USGS station 02115360 Sample Date Flow (cfs) TSS (mg/L) Turbidity (NTU) TSS Load (tons/day) Sample Date Flow (cfs) TSS (mg/L) Turbidity (NTU) TSS Load (tons/day) 01/06/2000 1180 15.75 7.2 49.98 07/13/2005 3880 58.00 60 605.36 02/09/2000 1350 3.00 5.5 10.89 07/27/2005 1820 23.00 24 112.60 03/08/2000 1110 5.00 6.5 14.93 08/09/2005 2870 282.14 290 2178.19 04/05/2000 3170 70.00 50 596.91 08/25/2005 1630 22.00 19 96.46 05/04/2000 1610 10.00 11 43.31 09/22/2005 1050 10.00 7.1 28.25 06/05/2000 1250 26.00 21 87.43 10/17/2005 1460 14.00 14 54.98 07/11/2000 806 8.00 15 17.35 10/25/2005 1240 6.80 3 22.68 08/14/2000 794 26.00 37 55.53 11/21/2005 1250 13.81 2.3 46.43 09/07/2000 1140 77.00 75 236.13 11/28/2005 1380 4.20 2.7 15.59 10/02/2000 838 19.45 16 43.85 01/05/2006 2560 4.00 25 27.55 11/01/2000 645 14.39 3.8 24.97 01/17/2006 3290 24.00 23 212.40 12/04/2000 689 4.00 14 7.41 02/01/2006 2160 8.20 6.5 47.65 01/02/2001 784 14.12 3.1 29.78 02/16/2006 1910 6.20 3.8 31.85 02/05/2001 948 14.51 4.1 37.00 03/02/2006 1680 4.80 3.6 21.69 04/30/2001 1040 18.00 9 50.36 03/15/2006 1540 12.00 5.9 49.71 05/23/2001 1970 102.99 140 545.79 03/30/2006 1200 4.80 4.7 15.49 06/07/2001 1350 60.00 36 217.89 04/06/2006 1140 14.00 6.3 42.93 07/10/2001 1100 131.98 170 390.53 04/27/2006 2060 33.00 21 182.87 08/27/2001 785 20.34 18 42.95 05/18/2006 1300 23.00 19 80.43 09/05/2001 984 22.00 12 58.23 06/01/2006 1050 9.80 8.3 27.68 10/02/2001 615 17.73 12 29.34 06/15/2006 1010 26.00 32 70.64 11/01/2001 606 16.89 10 27.54 06/26/2006 2510 32.00 8.2 216.06 12/11/2001 1890 110.00 100 559.25 07/17/2006 1300 40.00 95 139.88 01/28/2002 1840 26.45 31 130.93 07/27/2006 1440 48.00 31 185.93 02/26/2002 1020 15.54 6.7 42.65 08/07/2006 891 12.00 13 28.76 03/27/2002 2100 48.00 55 271.15 08/22/2006 1040 16.00 16 44.76 04/22/2002 1230 22.61 23 74.82 10/03/2006 1090 8.50 10 24.92 05/23/2002 801 19.45 16 41.92 10/26/2006 1170 14.75 4.7 46.41 06/17/2002 481 22.00 16 28.47 11/20/2006 3550 22.15 22 211.53 07/10/2002 396 18.59 14 19.80 12/20/2006 1440 13.92 2.6 53.94 08/19/2002 453 16.40 8.8 19.98 01/16/2007 2270 18.16 13 110.87 09/10/2002 324 34.00 2.5 29.63 03/21/2007 3260 19.89 17 174.46 10/02/2002 829 17.73 12 39.54 05/03/2007 1600 16.89 10 72.71 11/25/2002 1590 16.23 8.4 69.44 05/29/2007 1170 16.52 9.1 52.00 12/16/2002 3140 26.00 26 219.61 07/05/2007 1120 16.00 20 48.20 01/28/2003 1280 14.31 3.6 49.29 07/19/2007 1050 36.55 50 103.22 02/11/2003 1550 14.47 4 60.34 08/28/2007 636 16.15 8.2 27.63 03/03/2003 3110 27.00 25 225.88 09/13/2007 380 6.80 8.1 6.95 04/15/2003 6130 24.99 28 412.00 10/31/2007 1090 17.31 11 50.76 06/11/2003 4570 59.00 38 725.30 11/26/2007 659 13.77 2.2 24.41 07/01/2003 3300 20.79 19 184.51 01/02/2008 1790 15.00 19 72.23 08/04/2003 7300 567.47 450 11143.33 01/15/2008 1040 14.04 2.9 39.28 09/04/2003 10900 600.00 450 17592.60 02/27/2008 1340 15.14 5.7 54.59 10/13/2003 2160 14.63 4.4 84.99 03/25/2008 1660 10.00 8.6 44.65 11/18/2003 1950 15.54 6.7 81.54 04/14/2008 1580 19.00 16 80.75 12/02/2003 2490 10.00 8.1 66.98 05/12/2008 1490 37.00 55 148.30 01/28/2004 2110 13.81 2.3 78.38 06/09/2008 604 16.23 8.4 26.38 02/18/2004 2640 15.62 6.9 110.96 07/08/2008 823 58.00 130 128.40 03/22/2004 2050 6.00 10 33.09 08/06/2008 352 15.00 26 14.20 04/20/2004 2340 17.73 12 111.62 09/25/2008 446 17.31 11 20.77 06/01/2004 1770 24.03 26 114.39 10/08/2008 579 15.9895 7.8 24.90 06/22/2004 2310 79.00 75 490.90 11/20/2008 1010 14.4314 3.9 39.21 07/29/2004 1890 121.94 160 619.95 12/03/2008 973 15.1433 5.7 39.64 08/25/2004 1630 17.73 12 77.75 01/12/2009 3230 26 32 225.91 09/30/2004 6350 170.00 100 2903.86 02/05/2009 1070 15.4235 6.4 44.39 10/28/2004 2080 17.73 12 99.22 03/10/2009 1500 24 24 96.84 11/30/2004 2550 19.02 15 130.45 04/21/2009 2470 29 14 192.68 12/14/2004 2880 9.00 11 69.72 05/13/2009 2010 54 45 291.97 02/02/2005 2530 16.36 8.7 111.32 06/10/2009 3180 56 38 479.04 02/23/2005 2030 15.58 6.8 85.10 07/28/2009 1220 25 22 82.05 03/10/2005 2470 7.00 3.1 46.51 08/05/2009 1540 46 45 190.56 03/29/2005 10100 160.00 240 4347.04 10/01/2009 2190 49 35 288.66 04/25/2005 2600 15.00 14 104.91 10/26/2009 1230 6.8 7.2 22.50 05/05/2005 2170 9.00 5.3 52.54 11/04/2009 2100 17 19 96.03 05/10/2005 1970 8.00 4.6 42.39 06/02/2005 2010 26.00 16 140.58 06/16/2005 3080 31.00 45 256.84 07/06/2005 2930 123.00 250 969.45 35 Appendix C. Load Reduction Estimations Estimation of Load Reduction Required for TSS for Muddy Creek at Station Q4120000. % Flow Exceedance Allowable Load (tons/day Estimated Exceeding Load (tons/day) 10.00% 41.86 58.66 15.00% 34.58 56.52 20.00% 29.97 54.45 25.00% 27.50 52.46 30.00% 25.85 50.54 35.00% 24.40 48.69 40.00% 23.11 46.91 45.00% 21.61 45.20 50.00% 20.15 43.54 55.00% 19.01 41.95 60.00% 17.74 40.42 65.00% 16.71 38.94 70.00% 15.51 37.52 75.00% 14.25 36.14 80.00% 12.93 34.82 85.00% 11.64 33.55 90.00% 10.62 32.32 Average 21.61 44.27 Load Reduction Needed = 51% 36 Estimation of Load Reduction Required for TSS for the Yadkin River at DWQ Station Q2040000 % Flow Exceedance Allowable Load (tons/day Estimated Exceeding Load (tons/day) 10.00% 308.92 1211.05 15.00% 261.87 812.95 20.00% 229.91 612.70 25.00% 206.83 492.03 30.00% 191.74 411.30 35.00% 179.32 353.46 40.00% 164.22 309.98 45.00% 149.13 276.09 50.00% 134.93 248.93 55.00% 124.28 226.67 60.00% 113.63 208.09 65.00% 105.64 192.34 70.00% 97.65 178.83 75.00% 89.66 167.10 80.00% 80.28 156.83 85.00% 69.52 147.76 90.00% 59.36 139.68 Average 150.99 361.52 Load Reduction Needed = 58% Appendix D: Public Notification of TMDL for 37 Appendix D: Public Notification of TMDL for Yadkin River Basin Turbidity TMDLSYadkin River Basin Turbidity TMDLS 38 Appendix E: Public Comments 2011 Yadkin River Basin Turbidity TMDLs Public Comment Response Summary The comments received for this TMDL were based on the public comment version which included assessment units for Muddy Creek and the Yadkin River. These two waterbodies were not included in the final TMDL presented here in order to allow time to meet with and explain the TMDL process to the MS4 permittees that would be impacted by these TMDLs. However, the comments received regarding Muddy Creek and the Yadkin River were left in the response summary and are addressed below. Comments were received from: • Piedmont Triad Regional Council (PTRC) • Town of Lewisville • Salisbury-Rowan Utilities • Winston-Salem • Village of Clemmons • North Carolina Department of Transportation (NCDOT) • North Carolina Conservation Network 1) PTRC: Response: Each TMDL has a Load Allocation, Wasteload Allocation and Margin of Safety. The TMDL Load Allocations show the reductions needed from nonpoint sources. The TMDL does not suggest that the wasteload allocations alone will achieve water quality standard attainment. Reductions for the identified jurisdictions are identical to the reductions for nonpoint sources. 2) PTRC , Town of Lewisville, Winston-Salem, Village of Clemmons: The commenters mentioned that the Village of Clemmons and the Town of Lewisville have only been NPDES Phase II communities since 2005, and Winston-Salem since 2001. The commenters suggested that the DWQ acknowledge new stormwater ordinances and development regulations in this time period and the impacts of these requirements on the receiving streams have not had time to be assessed. Further, the need for additional expenses to mitigate stormwater sources of water quality pollutants is not readily apparent. Response: The data used in the TMDL was from years 2000-2009. Implementation of the TMDL will not necessarily incur additional significant costs to the affected NPDES permit holders. The DWQ Stormwater Permitting Unit will consider recent improvements and determine further permit requirements in the next permit renewal. 3) PTRC , Town of Lewisville, Village of Clemmons: Response: The implementation timeline will depend on your water quality recovery plan that you will submit as required under your stormwater permit. We expect the fulfillment of your water quality recovery plan to take several permit cycles. Because this TMDL can be implemented along with various existing permit requirements, and it only requires reductions in the named TMDL subwatersheds, it is not expected to trigger sprawl outside of MS4 jurisdictions. 4) PTRC, Town of Lewisville, Winston-Salem: The commenters acknowledged that a TMDL Load Allocation has no regulatory authority to require a reduction from nonpoint sources. However, the commenters requested a clearer representation of the presence of animal and forestry operations and communities enrolled in cost-share programs to manage runoff. The commenters also requested greater acknowledgement that rural land uses are contributing to the impairment. Response: General sources of nonpoint source pollution are described in section 2.1. The TMDL shows land cover for each watershed as well as land cover adjacent to streams for each watershed, including the distribution of agricultural lands (pasture/hay and crop). Further source assessment, including how land is managed, will be useful for TMDL implementation. Reductions in both point and nonpoint sources of turbidity are needed to meet water quality standards as stated in section 12. Reductions for the identified jurisdictions are identical to the reductions for nonpoint sources. 5) PTRC, Town of Lewisville: Response: The jurisdictions are encouraged to conduct additional monitoring to gain further knowledge of the watersheds’ pollution sources. In addition, DWQ indeed uses data from various outside sources; municipalities interested in collecting data to be used for use support assessment should contact DWQ. Please review this website on data sources and how to submit data http://portal.ncdenr.org/web/wq/ps/mtu/assessment#4. 6) PTRC, Town of Lewisville, Winston-Salem: Response: This is not a correlation between wet weather and TSS. The equation of this line was used to determine the target reduction as describe in section 6.6. Figure 6.2 shows that no exceedances occurred during low flow events. The R2 of 0.23 for Muddy Creek refers to strength of the linear relationship between the calculated existing load exceedances in Figure 6.3. This response also addresses similar comments for the Yadkin River. 7) PTRC and Winston-Salem: Response: The Salem Creek TMDL targeted Fecal Coliform. If the retrofits to reduce fecal coliform were targeted at stormwater, and also achieved a reduction in turbidity, this can be reflected in your water quality recovery program for your stormwater permit and count towards compliance with this TMDL. 8) PTRC: Response: Ambient station Q2040000 was used to develop the TMDL for both impaired segments of the Yadkin River for several reasons. One reason is that it is co-located with a USGS gage, which is ideal to develop the load duration curve. Second, the correlation of Turbidity vs. TSS for the lower ambient monitoring site, Q2180000, has an R2 of 0.579, which is less than the TSS vs turbidity R2 value of 0.88 for the ambient station (Q2040000) used in the TMDL. Finally, the turbidity data comparison between the two stations show that the data is comparable with median NTU values for Q2040000 and Q2180000 at 16 and 18 respectively for years 2000-2009. The change in reductions between the two stations would likely be insignificant, and uncertainty would be higher due to estimating flow and using the lower TSS vs NTU correlation from site Q2180000. 9) PTRC, Town of Lewisville: Response: Perhaps the commenters are referring to South Deep Creek. Reductions in South Deep Creek alone are not expected to attain the turbidity standard in the Yadkin River. Your water quality recovery program can reflect your implementation and monitoring timeline. 10) Town of Lewisville: Response: Reductions required in the TMDL for NPDES stormwater permittees will be implemented through the stormwater permit, in the form of a water quality recovery program submitted to DWQ by each permittee. This plan will outline how each permittee will improve water quality. Implementation of the TMDL will not necessarily incur additional significant costs to the affected NPDES permit holders. An implementation section has been added to the TMDL to clarify responsibilities of MS4 permittees. 11) Town of Lewisville: Response: Your water quality recovery program will describe how the Town will implement the TMDL. The monitoring you propose (see Comment 5) can assist with source identification and tracking of reductions. 12) Salisbury-Rowan Utilities: Response: Thank you. We have made these corrections in the text. 13) Winston-Salem: Response: These TMDLs were developed to address localized turbidity impairments in the High Rock Lake watershed. A separate analysis will be conducted to determine how to address the turbidity impairment in High Rock Lake. Winston-Salem is represented on the High Rock Lake nutrient TAC. 14) Winston-Salem: Response: This TMDL approach estimates TSS reduction for any flow exceeded between 10% and 90%. Therefore, we developed Figure 6.3 to show the relationship between percent flow exceeded and daily TSS load to estimate an averaged TSS reduction for the flow exceedance between 10% to 90%. Any method used would require some percent reduction in turbidity. Implementation of this TMDL will involve adaptive management, with the ultimate measure of success attainment of the standard instream. 15) Village of Clemmons: Response: The Load Allocation reported in the TMDL sets a limit, or “allowance,” for turbidity originating from nonpoint sources. An implementation plan is not included in this TMDL. Local governments and other stakeholders are encouraged to design and carry out implementation plans. The monitoring proposed in Comment 5 could assist with source identification and tracking of reductions. Your water quality recovery program can describe how you will differentiate contributions from the Village of Clemmons from other sources. 16) Village of Clemmons: Response: Sand dredging operations are not permitted to exceed the turbidity standard of 50 NTU in Muddy Creek. Sand dredging operations are permitted under general permit NCG520000. Please call the DWQ Winston-Salem Regional Office at 336-771-5000 if you observe a sand dredging operation causing excess turbidity in Muddy Creek. 17) Village of Clemmons: Response: DWQ acknowledges that some soil types can make it more difficult to control erosion and turbidity. However Muddy Creek has met the turbidity standard in previous years. Muddy Creek was just added to the 303d list in 2010. 18) Village of Clemmons - Response: It is currently difficult to quantify a justifiable load from stormwater outfalls within each municipality without monitoring those outfalls. However, MS4 permittees cannot be ignored when addressing a turbidity impairment, especially during wet weather events. The Village has not been “singled out.” Nonpoint sources outside your jurisdiction have been assigned a load allocation. The monitoring proposed in Comment 5 could assist with source identification and tracking of reductions. Your water quality recovery program can describe how you will differentiate contributions from the Village of Clemmons from other sources. 19) Part 1 – NCDOT: Response: NPDES discharges not subject to the TMDLs are identified in the report by the description in the text (as repeated above). Water quality stations refer to Ambient Monitoring Sites as shown in the watershed maps in section 1.3 of the report. We have changed the term “water quality station” to “ambient monitoring site” in the text. Therefore an ambient monitoring site that is not impaired is shown on the watershed maps not falling within the 12 assessment units described in table 1.1 (also shown in red on the watershed maps in section 1.3). We would be happy to assist you with identifying areas of interest to you that are subject to the TMDL. Part 2 - Comment Continued from 19 – Part 1 Response: The paragraph above has been revised for clarification in the text as follows: “NPDES wastewater and stormwater permittees upstream of an Ambient Monitoring Site that is not impaired (not intersected by the impaired waterbody) are not subject to the TMDL. Permittees that discharge directly to, or upstream of the impairment, yet still downstream of an unimpaired ambient monitoring site are subject to the TMDL and are discussed below.” 20) NCDOT: Response: DWQ is open to new ideas or methods to calculate wasteload allocations for DOT stormwater in TMDLs. It is possible for a permittee to be in compliance with its current permit, yet need to make further reductions to achieve water quality standards instream. 21) Part 1 – NCDOT: Response: The dashed line in the load duration curve figures represents the best fit for the entire data set. As shown in Table 1.2 in the text, 11 to 14 percent of the data has exceeded the turbidity standard. This is why the majority of the dashed lines in the load duration curve figures are below the allowable load line. The load duration curve methodology uses only the points exceeding the allowable load to provide a formula to estimate the exceeding load at a variety of flow ranges. This also enables data points that fall in ranges of extreme flow or drought conditions to be excluded from the TMDL calculation. Part 2 – Continued from above Response: Seasonality is included in the TMDL by using a long term 10 years of data for the TMDLs. This allows for a variety of flow conditions and seasonal variation to be captured in the data. Part-3 Continued from above Response: The equation from the best-fit line from the exceeding loads is used to calculated load exceedances across multiple flow ranges that are not represented by actual data points. This is a good method to estimate or model reductions needed across multiple flow ranges. An alternative method would be to take the TSS value from the highest exceeding point between the 90th and 10th percentile flow exceedance range and reduce it to the TSS standard. Any method used would require some percent reduction in turbidity. Implementation of this TMDL will involve adaptive management, with the ultimate measure of success attainment of the standard instream. Part 4 – Continued from above Response: The load duration curve methodology uses only the points exceeding the allowable load to provide a formula, in this case 20th to 50th percentile, to estimate the exceeding load at a flow ranges from 10th to the 90th percentile. 22) NCDOT: Response: The 51% reduction shown in Appendix C is the overall reduction needed based on the TMDL of 21.6 tons/day TSS. However, because NPDES WW discharges are not required to make a reduction, the reductions shown in the TMDL text are based on that of the load allocation only which does not include the wasteload allocation of 5.462 tons/day TSS. 23) NCDOT: Response: The turbidity and TSS data used in the TMDL can be found in Appendix B. 24) Part 1 NCDOT: Response: The South Yadkin River watershed is a large drainage area (906 sqmi) and contains other impaired streams included in this TMDL. Each stream received a unique TMDL. Reductions achieved from the impaired streams upstream of the South Yadkin River impairment will also count as reductions for the South Yadkin River TMDL. There is a 3.25 mile stretch of the South Yadkin River that is currently not impaired located between Aus 12-108-(14.5) and 12-108-(19.5)b. Two small unnamed tributaries flow in from the northeast to the South Yadkin River in this stretch; this approximately 7.75 square mile area is not a large intervening drainage area. This 3.5 mile stretch is within the watershed draining to the impaired waters, and not above an unimpaired Ambient Monitoring Site, thus is subject to the TMDL. Part 2 – Continued from above Response: The South Yadkin River watershed is a large drainage area (906 sqmi) and contains other impaired streams included in this TMDL. Each stream received a unique TMDL. Reductions achieved from the impaired streams upstream of the South Yadkin River impairment will also count as reductions for the South Yadkin River TMDL. Ambient monitoring station Q3970000 was not used to calculate the TMDL for the lower impaired section (12-108-(19.5)b because there is no flow gage located with that station. Second, the correlation of Turbidity vs. TSS has an R2 of 0.552, which is less than the TSS vs NTU R2 value of 0.88 for the upstream ambient station (Q3460000) used in the TMDL. Finally, the turbidity data comparison between the two stations shows that the data is comparable with median NTU values for Q3460000 and Q3970000 both at 22 for years 2000-2009. The change in reductions between the two stations would likely be insignificant, and uncertainty would be high due to estimating flow and using the lower TSS vs NTU correlation from site Q3970000. 25) NCDOT : Response: Ambient station Q2040000 was used to develop the TMDL for both impaired segments of the Yadkin River for several reasons. One reason is that it is co-located with a USGS gage used to develop the load duration curve. Second, the correlation of Turbidity vs. TSS for the lower ambient monitoring site, Q2180000, has an R2 of 0.579, which is less than the TSS vs NTU R2 value of 0.88 for the ambient station (Q2040000) used in the TMDL. Finally, the turbidity data comparison between the two stations show that the data is comparable with median NTU values for Q2040000 and Q2180000 at 16 and 18 respectively for years 2000-2009. The change in reductions between the two stations would likely be insignificant, and uncertainty would be high due to estimating flow and using the lower TSS vs NTU correlation from site Q2180000. Reductions achieved through the South Deep Creek TMDL will count towards reductions in both assessment units of the Yadkin River TMDL. 26) NCDOT : Response: DWQ did not use data from ambient station Q1950000 because data collection at this station was discontinued in 2006. 27) North Carolina Conservation Network: Response: The highest 10% flows were excluded from the TMDL calculation to address extreme flows and this has been the general practice for most TMDLS developed using the LDC method so far. As the commenter suggested, if high flows are commonly occurring in an area a different implementation strategy can be employed to address these high flows. It should be noted that the load duration flow interval serves as an indicator of the hydrologic condition. Even though implementation is not a required element of the TMDL, the use of duration curve zones (e.g., high flow, moist, mid-range, dry, and low flow) presented in the TMDL provide useful information to direct potential implementation actions that most effectively address water quality concerns for various flow conditions. 28) North Carolina Conservation Network: Response: An implementation section has been added to the TMDL explaining how the TMDL will be implemented through NPDES stormwater permits. Addressing nonpoint sources of turbidity beyond regulatory authority requires the will and cooperation among the community to voluntarily adjust land management practices and to use incentive programs listed in Section 12.1 of the report. An implementation plan, although very useful, is not required in a TMDL. 29) North Carolina Conservation Network: Response: DWQ agrees high volume and resulting stream bank erosion is likely to contribute a significant portion of turbidity and that using volume as a surrogate parameter would be useful for turbidity TMDLs. DWQ is open to discussing the use of flow, or other innovative approaches for future TMDLs. 30) North Carolina Conservation Network: Response: DWQ agrees that volume from upstream locations will contribute to stream bank erosion in the impaired sections. However this TMDL is not intended to address flow. The paragraph mentioned above has been changed in the text in response to comment 19-Part 2. DWQ is open to discussing the use of flow, or other innovative approaches for future TMDLs. 31) North Carolina Conservation Network: Response: DWQ believes that a TMDL is not the best tool to address stormwater from construction sites due to the relative short time period in which sites are actually under construction and vulnerable to erosion. DWQ does not require on-site monitoring of stormwater runoff for construction sites and the uncertainty would be very high to estimate a load from construction sites with varying BMPs if DWQ were to base loading on construction stormwater runoff studies alone.