Loading...
HomeMy WebLinkAboutVirginia Creek TMDL_finalTotal Maximum Daily Load Fecal Coliform Virginia Creek, North Carolina [Waterbody IDs: 18-87-9-1; 18-87-9a; 18-87-9b] Final Report March 2022 Prepared by: NC Department of Environmental Quality Division of Water Resources 1617 Mail Service Center Raleigh, NC 27699-1617 White Oak River Basin Approved by EPA June 14, 2022 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ i Table of Contents List of Abbreviations ..................................................................................................................................... ii SUMMARY SHEET ......................................................................................................................................... iii 1 INTRODUCTION .................................................................................................................................... 1 1.1 TMDL Components ...................................................................................................................... 2 1.2 Documentation of Impairment .................................................................................................... 4 1.3 Watershed Description ................................................................................................................ 5 1.4 Water Quality Characterization ................................................................................................... 6 2 SOURCE ASSESSMENT .......................................................................................................................... 7 2.1 Nonpoint Source Assessment ...................................................................................................... 7 2.2 Point Source Assessment............................................................................................................. 8 3 TOTAL MAXIMUM DAILY LOADS AND LOAD ALLOCATION .................................................................. 8 3.1 TMDL Objective ........................................................................................................................... 8 3.2 Modeling ...................................................................................................................................... 9 3.2.1 Approach ................................................................................................................................. 9 3.2.2 Existing Load Calculation ....................................................................................................... 10 3.2.3 TMDL Calculation .................................................................................................................. 11 3.3 TMDL Allocation ........................................................................................................................ 12 3.3.1 Margin of Safety .................................................................................................................... 13 3.3.2 Waste Load Allocation (WLA) ................................................................................................ 13 3.3.3 Load Allocation (LA) .............................................................................................................. 14 3.3.4 Critical Condition and Seasonal Variation ............................................................................. 14 3.3.5 TMDL Summary ..................................................................................................................... 16 4 TMDL IMPLEMENTATION PLAN ......................................................................................................... 16 5 PUBLIC PARTICIPATION ...................................................................................................................... 17 6 FURTHER INFORMATION .................................................................................................................... 17 7 REFERENCES ....................................................................................................................................... 18 Appendix A: NCDMF Monitoring Data Summary ....................................................................................... 19 Appendix B: Virginia Creek Steady-State Tidal Prism Model Inputs and Parameters ................................ 22 Appendix C: NCDMF Mapping of Potential Pollution Sources in B-8 Growing Area .................................. 23 Appendix D: Public Notification of TMDL for Fecal Coliform for Virginia Creek ......................................... 24 Appendix E: Public Comments Responsiveness Summary ......................................................................... 25 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ ii List of Abbreviations AU Assessment Unit BMP Best Management Practice CFR Code of Federal Regulations cfu Colony forming unit CWA Clean Water Act EPA Environmental Protection Agency FC Fecal Coliform Bacteria HQW High Quality Waters supplemental classification HUC Hydrologic Unit Code LA Load Allocation MF MF is an abbreviation for the membrane filter procedure for bacteriological analysis ml Milliliter(s) MOS Margin of Safety MPN Most Probable Number NCAC NC Administration Code NCDMF North Carolina Division of Marine Fisheries NCDOT North Carolina Department of Transportation NCDWR North Carolina Division of Water Resources NLCD National Land Cover Database NOAA National Oceanic and Atmospheric Administration NPDES National Pollutant Discharge Elimination System NSSP National Shellfish Sanitation Program ROW NCDOT road right of way SA Class SA water body: suitable for commercial shellfishing and all other tidal saltwater use TMDL Total Maximum Daily Load USGS United States Geological Survey WLA Waste Load Allocation WRRI Water Resources Research Institute of UNC Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ iii SUMMARY SHEET Total Maximum Daily Load (TMDL) 1. 303(d) Listed Waterbody Information State: North Carolina County: Pender Major River Basin: White Oak River Basin Watershed: USGS HUC 03030001040010 Impaired Waterbody (2020 303(d) List): Waterbody Name – [AU] Description Water Quality Classification1 Acres Mullett Run - [18-87-9-1] From source to Virginia Creek SA;HQW 7.5 Virginia Creek - [18-87-9a] From source to 0.75 miles inland of Intercoastal Waterway SA;HQW 23.5 Virginia Creek - [18-87-9b] From 0.75 miles inland of ICWW to Intercoastal Waterway SA;HQW 73.6 1. See List of Abbreviations on page ii Constituent(s) of Concern: Fecal Coliform Bacteria Designated Uses: Shellfish harvesting, biological integrity, propagation of aquatic life, and recreation. Applicable Tidal Salt Water Quality Standards for Class SA Waters: “Organisms of coliform group: fecal coliform group not to exceed a median MF of 14/100 ml and not more than 10 percent of the samples shall exceed an MF count of 43/100 ml in those areas most probably exposed to fecal contamination during the most unfavorable hydrographic and pollution conditions.” For the approval of shellfish growing areas “the median fecal coliform Most Probable Number (MPN) or the geometric mean MPN of water shall not exceed 14 per 100 milliliters, and not more than 10 percent of the samples shall exceed a fecal coliform MPN of 43 per 100 milliliters (per five tube decimal dilution) in those portions of areas most probably exposed to fecal contamination during most unfavorable hydrographic conditions”(15A NCAC 18A .0431 Standards for an Approved Shellfish Growing Area). In addition, “a minimum of the 30 most recent randomly collected samples from each sample station shall be used to calculate the median or geometric mean and 90th percentile to determine compliance with this standard” (NSSP, 2017). Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ iv TMDL Target: The TMDL is calculated in this analysis as the fecal coliform loads that will result in median fecal coliform MPN at 14 per 100 milliliters, and the 90th percentile of fecal coliform MPN at 43 per 100 milliliters, using data from May 2011 to July 2016. 2.TMDL Development Development Tools (Analysis/Modeling): Spreadsheet-based steady-state tidal prism model Critical Conditions: The 90th percentile concentration is the concentration exceeded only 10% of the time. Since the data used for model simulation spans 5 years, the critical condition is implicitly included in the value of the 90th percentile of model results. Seasonal Variation: Given the long-term flow and water quality data record used to estimate the fecal coliform load, the seasonal variability is implicitly included in the analysis. 3.TMDL Allocation Summary Waterbody( Model Segment) AUs Fecal Coliform Load (MPN/day) % Reduction Existing Load WLA2 LA MOS TMDL Lower Virginia Creek (m1) 18-87-9a; 18-87-9b < TMDL1 0.2E+9 3.60E+11 4.0E+10 4.0E+11 0 Upper Virginia Creek (m2) 18-87-9a 2.5E+11 3.0E+9 1.59E+11 1.8E+10 1.8E+11 28% Mullett Run (b1) 18-87-9-1; 18-87-9a 8.2E+10 1.6E+9 5.15E+10 5.9E+9 5.9E+10 28% 1.For Lower Virginia Creek, the calculated existing load is less than the estimated TMDL, and hence no reduction is needed. The FC water quality standard will be met in model segment m1 once the TMDL is implemented and loading is reduced from the watershed of segments m2 and b1. 2.WLA applies to NCDOT. 4.Public Notice Date: January 31, 2022 - March 4, 2022 5.Submittal Date: May 19, 2022 6.Establishment Date: June 14, 2022 7.EPA Lead on TMDL (EPA or blank): 8.Endangered Species (yes or blank): Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ v 9. MS4s Contributions to Impairment (Yes or Blank): 10. TMDL Considers Point Source, Nonpoint Source, or both: Both Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 1 1 INTRODUCTION Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental Protection Agency’s (EPA) implementing regulations direct each State to develop a Total Maximum Daily Load (TMDL) for each impaired segment on the North Carolina (NC) 303(d) list, taking into account seasonal variations and a protective margin of safety (MOS) to account for uncertainty. A TMDL reflects the total pollutant loading that a waterbody can receive and still meet water quality standards. TMDLs are established to achieve and maintain water quality standards. A water quality standard is the combination of a designated use for a particular body of water and the water quality criteria designed to protect that use. Designated uses include activities such as swimming, drinking water supply, and shellfish propagation and harvest. Water quality criteria consist of narrative statements and numeric values designed to protect the designated uses. Criteria may differ among waters with different designated uses. The Virginia Creek watershed is located in the White Oak River Basin (HUC 03030001040010) along the North Carolina coast in Pender County. The river is located within the shellfish area designated B-8 by the North Carolina Division of Marine Fisheries (NCDMF). Most of the shellfish growing area is conditionally approved -closed (Figure 1.1) (NCDMF, 2016). The area is being updated to prohibited (https://www.arcgis.com/apps/webappviewer/index.html?id=5759aa19d7484a3b82a8e 440fba643aa). When shellfish harvesting is the designated use, the primary parameter of concern is fecal coliform bacteria. Fecal coliform bacteria are found in the intestinal tract of humans and other warm-blooded animals. Few fecal coliform bacteria are pathogenic; however, the presence of elevated levels of fecal coliform in shellfish waters indicates recent sources of pollution. Some common waterborne diseases associated with the consumption of raw clams and oysters harvested from polluted water include viral and bacterial gastroenteritis and hepatitis A. Fecal coliform in surface waters may come from point sources (e.g., NPDES stormwater conveyances) and nonpoint sources. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 2 Figure 1.1 – Virginia Creek Shellfish Growing Area (B-8) Classifications (NCDMF, 2016) 1.1 TMDL Components The 303(d) process requires that a TMDL be developed for each of the waters appearing in Category 5 of a state’s Integrated Report. The objective of a TMDL is to estimate allowable pollutant loads and allocate to known sources so that actions may be taken to restore the water to its intended uses (USEPA, 1991). This TMDL is the total amount of a pollutant that can be assimilated by the receiving water while still achieving North Carolina’s water quality criteria for shellfish waters. Currently, TMDLs are expressed as a “mass per unit time, toxicity, or other appropriate measure” (40 CFR 130.2(i)). It is also important to note that the TMDLs presented herein are not literal daily limits. These loads are based on an averaging period that is defined by the water quality criteria. Generally, the primary components of a TMDL, as identified by EPA (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 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 3 water quality standards. North Carolina indicates known pollutants on the 303(d) list. • Source Assessment. All sources that contribute to the impairment should be identified and loads quantified, where sufficient data exist. • Reduction Target. Estimation or level of pollutant reduction needed to achieve water quality goal. The level of pollution should be characterized for the waterbody, 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 wasteload allocation portion of the TMDL accounts for the loads associated with existing and future point sources. Similarly, the load allocation portion of the TMDL accounts for the loads associated with existing and future non-point sources, stormwater, and natural background. • Margin of Safety. The margin of safety addresses uncertainties associated with pollutant loads, modeling techniques, and data collection. Per EPA (USEPA, 2000), 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 or disapproval. Once EPA approves a TMDL, then the waterbody may be moved to Category 4t of the North Carolina Integrated Report (corresponds to EPA Category 4a). Waterbodies remain in Category 4t until shellfish growing is approved for harvesting by NCDMF. Where conditions are not appropriate for the development of a TMDL, management strategies may still result in the restoration of water quality. TMDLs are comprised of the sum of individual wasteload allocations (WLAs) for point sources, load allocations (LAs) for nonpoint sources, and natural background levels. The TMDL must include a margin of safety (MOS), either implicitly or explicitly, that accounts for the uncertainty in the relationship between pollutant loads and the quality of the receiving waterbody, and in the scientific and technical understanding of water quality in natural systems. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 4 1.2 Documentation of Impairment The North Carolina Division of Water Resources (NCDWR) Surface Water and Wetlands classification for these impaired waters is Class SA, HQW Waters – Shellfish Harvesting Waters (15A NCAC 02B.0221 Tidal Salt Water Quality Standards for Class SA Waters). Class SA waters are waterbodies suitable for commercial shellfishing and all other tidal saltwater use (NCAD, 2003). Three segments, or assessment units, of Virginia Creek and its tributaries have been included in Category 5 of the 2020 North Carolina Integrated Report, as shown below in Table 1.1. Table 1.1 – Virginia Creek Impaired Assessment Units Waterbody Name – [AU] Description Water Quality Classification Acres Mullett Run - [18-87-9-1] From source to Virginia Creek SA;HQW 7.5 Virginia Creek - [18-87-9a] From source to 0.75 miles inland of Intercoastal Waterway SA;HQW 23.5 Virginia Creek - [18-87-9b] From 0.75 miles inland of ICWW to Intercoastal Waterway SA;HQW 73.6 These restricted shellfish harvesting areas are identified as areas that do not meet their designated uses. Waters within this classification, according to 15A NCAC 02B.0221 (Tidal Salt Water Quality Standards for Class SA Waters), must meet the following water quality standard in order to meet their designated use: Organisms of coliform group: fecal coliform group not to exceed a median MF of 14/100 ml and not more than 10 percent of the samples shall exceed an MF count of 43/100 ml in those areas most probably exposed to fecal contamination during the most unfavorable hydrographic and pollution conditions. In addition, for approval of shellfish growing areas “the median fecal coliform Most Probable Number (MPN) or the geometric mean MPN of water shall not exceed 14 per 100 milliliters, and not more than 10 percent of the samples shall exceed a fecal coliform MPN of 43 per 100 milliliters (per five tube decimal dilution) in those portions of areas most probably exposed to fecal contamination during most unfavorable hydrographic conditions” (15A NCAC 18A .0431 Standards for an Approved Shellfish Growing Area). In addition, “a minimum of the 30 most recent randomly collected samples from each sample station shall be used to calculate the median or geometric mean and 90th percentile to determine compliance with this standard” (NSSP, 2017). For this report, the monitoring data averaging period was based on the systematic random sampling strategy outlined in the National Shellfish Sanitation Program’s Model Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 5 Ordinance and guidance document. The most recent five-year period of data that was available was used, May 2011 to July 2016. Data summary can be found in Appendix A. 1.3 Watershed Description Virginia Creek and its tributaries fall within the NCDMF B-8 Growing Area in Pender County. The watershed covers about 10.4 square miles. Oyster and clam production are good throughout the area, however most of the shellfish beds areas are closed, due to high fecal coliform pollution. The 2011 National Land Cover Database (NLCD) was used to obtain land cover characteristics of the watershed. Land cover distribution is shown in Figure 1.2 and land cover statistics are shown in Table 1.2. Around 32% of the watershed is different types of wetlands and 24% is developed lands. The dominant tide in this region is the lunar semi-diurnal (M2) tide. The mean tidal range at NOAA station Wrightsville Beach (Station ID: 8658163) to the south is 3.98 ft and 3.11 ft at Beaufort, Duke Marine Lab (Station ID: 8656483) to the north. Virginia Creek opens to the shallow Intracoastal Waterway, instead of open ocean, the mean tidal range at Virginia Creek is expected to be slightly lower, around 3 feet. Table 1.2 – 2011 Land Cover Distribution of the Virginia Creek Watershed Land Cover Area (square mile) Area (%) Open Water 0.30 2.9 Developed, Open Space 1.53 14.7 Developed, Low Intensity 0.87 8.4 Developed, Medium Intensity 0.11 1.0 Developed, High Intensity 0.02 0.2 Barren Land 0.07 0.6 Deciduous Forest 0.02 0.2 Evergreen Forest 1.01 9.6 Mixed Forest 0.35 3.4 Shrub/Scrub 0.80 7.6 Herbaceous 0.75 7.2 Cultivated Crops 1.26 12.1 Woody Wetlands 2.58 24.7 Emergent Herbaceous Wetlands 0.78 7.4 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 6 Figure 1.2 – 2011 NLCD Land Cover of the Virginia Creek Watershed 1.4 Water Quality Characterization The Shellfish Sanitation and Recreational Water Quality Section of the NCDMF is responsible for classifying shellfish harvesting waters to ensure oysters and clams are safe for human consumption. NCDMF adheres to the requirements of the National Shellfish Sanitation Program, with oversight by the U.S. Food and Drug Administration. NCDMF conducts shoreline surveys and collects routine bacteria water quality samples in the shellfish-growing areas of North Carolina. The data are used to determine if the water quality criteria are being met. If the water quality criteria are exceeded, the shellfish areas are closed to harvest, at least temporarily, and consequently the designated use is not being achieved. NCDMF is monitoring shellfish growing regions throughout North Carolina. Virginia Creek is sampled using the systematic random sampling strategy as outlined in the National Shellfish Sanitation Program’s Model Ordinance and guidance document. There are four fecal coliform monitoring stations sampled by the NCDMF within Virginia Creek, as shown in Figure 1.1. NCDMF data from May 2011 to July 2016 are summarized in Table 13 for all the stations within B-8 area, including the 4 stations in Virginia Creek. Sources: Esri, GEBCO, NOAA, National Geographic, DeLorme, HERE, Geonames.org, and other contributors NLCD_2011 Woody Wetlands Shrub/Scrub Open Water Mixed Forest Herbaceuous Evergreen Forest Emergent Herbaceuous Wetlands Developed, Open Space Developed, Medium Intensity Developed, Low Intensity Developed, High Intensity Deciduous Forest Cultivated Crops Barren Land Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 7 The 2016 NCDMF Sanitary Survey Report notes one station (Station 18) had estimated 90th percentile at 53 MPN for that period, which exceeded the criteria. The three other stations (i.e. Stations 17, 46 and 46A) in Virginia Creek met the standard for Approved status. However, the Report also notes that a rainfall impacts analysis suggested the area was susceptible to bacteriological contamination at a lower threshold than what is defined within the management plan of NCDMF (2016). Reclassification for the affected sub-region (covering station 17, 46 and 46A) in Virginia Creek were not made but close monitoring for further improvement was recommended. 2 SOURCE ASSESSMENT 2.1 Nonpoint Source Assessment Non-point sources are diffuse sources that typically cannot be identified as entering a water body at a single location. Nonpoint source loading typically occurs during rain events when surface runoff transports water carrying fecal coliform over the land surface and discharges it into the stream network. The transport of fecal coliform from the land to the restricted shellfish harvesting area is dictated by the hydrology, soil type, land use, and topography of the watershed. There are many types of nonpoint sources in watersheds that contribute to the restricted shellfish harvesting areas. The most recent NCDMF Sanitary Survey (NCDMF, 2016) documented potential sources of fecal coliform in Virginia Creek. The survey suggested that runoff from impervious surfaces, subdivisions, and other cleared land remains the primary contributor to fecal coliform levels throughout B-8. Subdivisions are noted in the survey as an indicator of population growth, as well as for their tendency to concentrate potential sources of pollution such as septic systems, pet wastes, and stormwater. In general, there has been relatively little development within this growing area during the last several years. Overall, 96 subdivisions were noted in the B-8 growing area during the shoreline survey in 2014. Six of these subdivisions are new, and several of the pre-existing subdivisions surveyed are expanded since the last survey was conducted in 2011. The majority of homes and businesses within the B-8 growing area are served by individual septic systems. Wildlife in the watershed are considered to make up background concentrations of fecal coliform. Wildlife, including raccoon, deer, opossum, and waterfowl, are present throughout the B-8 area. Waste from these animals can be transported through stormwater ditches into shellfishing waters, and have some impact on the growing area during rainfall events. Grazing animals contribute fecal coliform through either direct access to streams or runoff from deposition or manure spreading. According to the shoreline survey, there are several horse stables within the watershed. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 8 Agricultural fields of soybeans, corn, tobacco, and winter wheat, as well as a few large forested areas are also likely to contribute contaminants to the creeks and waterways following rain events. The cultivated crops land cover is concentrated near the river and runoff could be a contributing factor if manure is improperly applied, particularly if just before a storm event. Nonpoint source contributions to the bacterial levels from human activities generally arise from malfunctioning or improperly-sited septic systems and their associated drain fields, or illicit connections of sanitary sewage to the stormwater conveyance system. The majority of onsite systems in the growing area were visited and inspected during the shoreline survey (NCDMF, 2016) and no ongoing failures or illicit discharges were located. 2.2 Point Source Assessment All wastewater discharges to surface water in the State of North Carolina must receive a permit to control water pollution. The CWA initiated strict control of wastewater discharges with responsibility of enforcement given to the Environmental Protection Agency (EPA). The EPA then created the National Pollutant Discharge Elimination System (NPDES) to track and control point sources of pollution. The primary method of control is by issuing permits to discharge with limitations on wastewater flow and constituents. The EPA delegated permitting authority to the State of North Carolina in 1975. There are no operating wastewater treatment plants within the Virginia Creek Watershed. The NC Department of Transportation (NCDOT) has a number of roads in the project area, including Highway 17, and has a statewide Phase I NPDES stormwater permit (NCS000250). Stormwater has previously been considered a nonpoint source; however, NPDES-permitted sources are to be included in the wasteload allocation (WLA) per EPA guidance (USEPA, 2002). 3 TOTAL MAXIMUM DAILY LOADS AND LOAD ALLOCATION 3.1 TMDL Objective The TMDL objective is to meet North Carolina water quality fecal coliform standards of a median MF of 14 per 100 ml and not more than 10 percent of the samples shall exceed an MF count of 43 per 100 ml. In addition, the National Shellfish Sanitation Program (NSSP) standard for the approved classification of growing areas requires that fecal coliform concentrations not exceed a median or geometric mean of a MPN of 14 per 100 ml and the 90th percentile of a MPN of 43 per 100 ml, with a minimum of the 30 most recent samples used to calculate compliance. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 9 Both standards have the same numeric targets but the NSSP standard uses a minimum 30- sample averaging period. Data collected from May 2011 through July 2016 were used for the purpose of this TMDL. 3.2 Modeling 3.2.1 Approach Bay and coastal waters such as Virginia Creek and its tributaries are subject to the action of the tides. The ebb and flood of the tide serves to move water between locations exchanging and mixing with other water. The tide and amount of freshwater discharge into the embayment are the dominant influences on the transport of fecal coliform. Therefore, the TMDL was calculated using the steady-state tidal prism model. Compared to the volumetric method (EPA Shellfish Workshop, 2002), the steady-state tidal prism model incorporates the influences of tidally induced transport, freshwater input, and removal of fecal coliform via decay. Multiple segments may exist within the model domain. The model assumes that the embayment is well mixed within a single segment, and freshwater input, tidal range, and the first-order decay of fecal coliform are all constant. A brief description of the model is presented below. The steady-state tidal prism model calculates fecal coliform load using equation 3.1: 𝐿=[𝐶(𝑄𝑏+𝑘𝑉)−𝑄0𝐶0]× 𝐶𝑓 (3.1) where: L = fecal coliform load (counts per day) C = mean fecal coliform concentration (MPN /100ml) of the segment k = the fecal coliform removal/decay rate (per day) C0 = the fecal coliform concentration (MPN/100ml) entering the segment on the flood tide Q0 = the quantity of water entering the segment on the flood tide (m3 per tidal cycle) Qb = the quantity of mixed water that leaves the segment on the ebb tide (m3 per tidal cycle) V = the mean volume of the segment (m3) Cf = the unit conversion factor The fecal coliform decay rate, k, was set at 0.36 per tidal cycle, which is considered a conservative estimate. The value of the decay rate varies from between 0.3 and 3.0 in salt water (Thomann and Mueller, 1987). Qb and Q0 are estimated based on the steady state condition as follows: Qb = Q0 +Qf Q0 = βQT Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 10 where: Qf = mean freshwater input during one tidal cycle (m3 per tidal cycle) β = exchange ratio QT = the total ocean water entering the bay on the flood tide (m3 per tidal cycle) QT is calculated based on the tidal range. The dominant tide in this region is the lunar semi-diurnal (M2) tide with a tidal period of 12.42 hours. Therefore, the M2 tide is used for the representative tidal cycle. The mean tidal range is assumed to be 3 feet, slightly lower than the tidal range (3.11 feet) monitored at a nearby NOAA station at Beaufort, NC (Station ID: 8656483). In general, the exchange ratio varies from 0.3 to 0.7, based on the previous model tests in coastal embayments (Kuo et al., 1998; Shen et al., 2002). A mean value of 0.5 was used for the exchange ratio. The stream flow (Qf) used to represent the fresh water inflow was based on a ratio of the drainage area of the Virginia Creek watershed as compared to the drainage area and the stream flows measured by the U.S. Geological Survey at the New River gaging station (USGS 02093000) near Gum Branch, NC. The selection of the gaging station for use in the model is determined by its similarity in watershed characteristics to Virginia Creek watershed and the proximity of the station to the TMDL study area. Appendix B provides model inputs and parameters used for the 90th percentile calculations. 3.2.2 Existing Load Calculation The existing load was calculated by using Equation 3.1 and the existing median and 90th percentile concentrations for each model segment. Model segmentation is provided below in Figure 3.1. Existing median and 90th percentile concentrations are required for each segment as model inputs. For segment m1, these were calculated by combining monitoring data from all monitoring stations within the segment and calculating the overall median and the estimated 90th percentile fecal coliform concentrations. For segments m2 and b1, since no monitoring station existed within the segments, data from the most upstream station (Station 18) were used. Table 3.1 provides the monitoring stations used in each model segment and the overall median and 90th percentile concentrations. NCDMF conditional monitoring data were not used to calculate existing concentrations. Conditional monitoring only takes place in a few stations in the conditionally-approved open growing area in lower Virginia Creek (segment m0 and m1) after rainfall events to see if waters can be reopened to shellfishing. These concentrations tend to be inconsistently higher compared to stations where conditional monitoring data were not collected. Therefore, to avoid creating bias in the model, conditional data were not used to calculate existing loads. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 11 Figure 3.1. Model segments and the sub-watersheds of Virginia Creek. Table 3.1 – Monitoring stations and assessment units associated with each model segment Model Segment Waterbodies AU# Monitoring Stations Median FC (MPN/100ml) Estimated* 90th Percentile FC (MPN/100ml) m0 Ocean Boundary 17 2 9 m1 Lower Virginia Creek 18-87-9a; 18-87-9b 18, 46, 46A 4.5 32 m2 Upper Virginia Creek 18-87-9a 18 6.45 53 b1 Mullett Run 18-87-9-1; 18-87-9a 18 6.45 53 *method adopted by NCDMF (2016) and described in NSSP (2017) 3.2.3 TMDL Calculation The TMDL was calculated by using Equation 3.1 and the North Carolina water quality fecal coliform standards of a median of 14 counts per 100 ml and a 90th percentile of 43 counts per 100 ml. Table 3.2 presents the estimated TMDL for each segment. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 12 The percent load reduction needed to meet the fecal coliform standards was estimated using equation 3.2: Reduction = (Existing Load – TMDL)/Existing Load (3.2) Table 3.2 – Load Reduction Requirements under variations of standard criteria Standard Category Segment Standard (MPN/100ml) Existing Load (MPN/day) TMDL (MPN/day) Average Reduction Required Median m1 14 < TMDL 2.23E+11 0 m2 14 < TMDL 4.46E+10 0 b1 14 < TMDL 1.48E+10 0 90th Percentile m1 43 < TMDL 3.99E+11 0 m2 43 2.50E+11 1.80E+11 28% b1 43 8.20E+10 5.91E+10 28% Using median concentration and the corresponding median standard, the calculated existing loads are less than the TMDL in all segments. This is also reflected in the low median concentrations calculated from the monitoring data. In contrast, when 90th percentile concentrations and the corresponding 90th percentile water quality standard are used, a 28% load reduction is needed in the watersheds of segments m2 and b1. No reduction in loading is needed from the watershed of segment m1 due to its lower existing load than the TMDL. The FC water quality standard will be met in segments m1 once the TMDL is implemented and loading is reduced from the watersheds of segments m2 and b1. Required reductions in loading are higher for the 90th percentile model results (highlighted in orange in Table 3.2) and allow for both standards to be met. Therefore, the TMDL was calculated using the 90th percentile criterion. 3.3 TMDL Allocation 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 allocations (WLAs), nonpoint source 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 3.3. ++=MOSLAsWLAsTMDL (3.3) Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 13 The objective 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 fecal coliform contamination, TMDLs are expressed as counts, or colony forming units (cfu), per 100 milliliters. TMDLs represent the maximum one-day load the river can assimilate and maintain the water quality criterion. The systematic procedures adopted to estimate TMDLs are described below. 3.3.1 Margin of Safety A Margin of Safety (MOS) is required as part of a TMDL in recognition of many uncertainties in the understanding and simulation of water quality in natural systems. For example, knowledge is incomplete regarding the exact nature and magnitude of pollutant loads from various sources and the specific impacts of those pollutants on the chemical and biological quality of complex, natural water bodies. The MOS is intended to account for such uncertainties in a manner that is conservative from the standpoint of environmental protection. As a conservative estimate in the TMDL calculation, an explicit MOS of 10% is included. The explicit MOS was achieved by multiplying the TMDL by 10%. These loads are shown in Table 3.3. Table 3.3 – Margin of Safety Allocation Fecal Coliform Load (MPN/day) Standard Category Segment # TMDL MOS Allowable Load (TMDL-MOS) 90th Percentile m1 3.99E+11 3.99E+10 3.59E+11 m2 1.80E+11 1.80E+10 1.62E+11 b1 5.91E+10 5.91E+09 5.32E+10 3.3.2 Waste Load Allocation (WLA) As described in Section 2.2, NCDOT is the only NPDES-permitted discharge in the watershed included in the WLA as a contributing source. Data is not available to calculate the existing load for the NCDOT. The WLA for NCDOT land was isolated from other sources by multiplying the total load and the ratio of NCDOT road right of way (ROW) area to total subwatershed area. The NCDOT ROW area was calculated by multiplying the road length and width of US highways, NC roads, and state route roads within the watershed (AECOM, 2021). The NCDOT ROW is 2.3% of the total watershed area, as shown below in Table 3.4. The resulting WLA for NCDOT is provided below in Table 3.5. NCDOT should continue to implement measures required by the permit, including illicit discharge detection and elimination, post-construction controls, management of Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 14 hydraulic encroachments, sediment and erosion control, BMP retrofits, stormwater pollution prevention for industrial facilities, research, and education programs. Table 3.4 – Virginia Creek Watershed NCDOT Contributing Area by Subwatershed Segment # Total Sub-watershed Area (acres) NCDOT ROW Area (acres) NCDOT Land Area (% of total) m1 510.3 0.24 0.05% m2 3,444.3 69.9 2.0% b1 2,703.5 81.4 3.0% Total 6658.1 151.5 2.3% Table 3.5 – NPDES Wasteload Allocations NPDES Permittee Segment # NCDOT Existing Load (MPN/day) WLA (MPN/day) Percent Reduction NCDOT m1 N/A 0.2E+9 0% m2 N/A 3.0E+9 0% b1 N/A 1.6E+9 0% 3.3.3 Load Allocation (LA) All fecal coliform loadings from nonpoint sources such as non-MS4 urban land, agriculture land, and forestlands are reported as LAs. The LA allocations were estimated by subtracting the MOS and WLA allocations from the TMDL. The estimated allocations of fecal coliform loading for nonpoint sources are presented in Table 3.6. Table 3.6 – Nonpoint Source Allocation Segment # Existing Load (MPN/day) LA (MPN/day) Percent Reduction m1 N/A 3.60E+11 0% m2 N/A 1.59E+11 28% b1 N/A 5.15E+10 28% 3.3.4 Critical Condition and Seasonal Variation The EPA Code of Federal Regulations (40 CFR 130.7 (c) (1)) requires TMDLs to take into account critical conditions for stream flow, loading, and water quality parameters. The intent of this requirement is to ensure that the water quality of the waterbody is protected during times when it is most vulnerable. The critical condition accounts for the hydrologic variation in the watershed over many sampling years whereas the critical period is the condition under which a waterbody is the most likely to violate the water quality standard(s). The 90th percentile concentration is the concentration exceeded only 10% of the time. Since the data used for model simulation spans 5 years, the critical condition is implicitly Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 15 included in the value of the 90th percentile of model results. Given the length of the monitoring record and the standard’s recognition of unusual and infrequent events, the 90th percentile is used to cover critical conditions. The EPA also requires that these TMDL studies take into account seasonal variations. The consideration of critical condition and seasonal variation is to account for the hydrologic and source variations. Seasonal variations involve changes in surface runoff, stream flow, and water quality as a result of hydrologic and climatologic patterns. For the Virginia Creek TMDL study, variations due to changes in the hydrologic cycle as well as temporal variability in fecal coliform sources are accounted for by the use of the longterm data record to estimate the current load. The seasonal fecal coliform distribution for station 18 (located inside Segment m1 of Virginia Creek) is presented in Figure 3.2. Data are available in each season. High fecal coliform levels (> 14MPN) occur throughout the year in the estuary. These high concentrations result in a high 90th percentile concentration. Given the multiple year flow and water quality data record used to estimate the fecal coliform load, the seasonal variability is implicitly included in the analysis. Figure 3.2. Seasonal distribution of fecal coliform concentrations at Station 18 (log scale). Data used are from May 2011 to July 2016. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 16 3.3.5 TMDL Summary A summary of the TMDL is provided below in Table 3.7. Reductions in fecal coliform loading are required for Upper Virginia Creek and Mullett Run. Reductions in loading from these sub-watersheds allow for standards to be met throughout Virginia Creek. A 28% reduction is needed from both the upper Virginia Creek and its tributary Mullet Run. The combined drainage area from these two sub-watersheds is around 92% of the total drainage area of the entire watershed of Virginia Creek. The potential sources map produced by NCDMF (Appendix C) shows a concentrated amount of stormwater outfalls in this watershed. Table 3.7 – Estimated TMDL and Load Allocation for Fecal Coliform for Virginia Creek Waterbody( Model Segment) AUs Fecal Coliform Load (MPN/day) % Reduction Existing Load WLA2 LA MOS TMDL Lower Virginia Creek (m1) 18-87-9a; 18-87-9b < TMDL1 0.2E+9 3.60E+11 4.0E+10 4.0E+11 0 Upper Virginia Creek (m2) 18-87-9a 2.5E+11 3.0E+9 1.59E+11 1.8E+10 1.8E+11 28% Mullett Run (b1) 18-87-9-1; 18-87-9a 8.2E+10 1.6E+9 5.15E+10 5.9E+9 5.9E+10 28% 1. For Lower Virginia Creek, the calculated existing load is less than the estimated TMDL, and hence no reduction is needed. The FC water quality standard will be met in model segment m1 once the TMDL is implemented and loading is reduced from the watershed of segments m2 and b1. 2. WLA applies to NCDOT. 4 TMDL IMPLEMENTATION PLAN Comprehensive sanitary surveys were conducted by NC Shellfish Sanitation Section of DMF. Evaluations of properties in the area were conducted to determine potential sources of pollution entering shellfish growing waters (Appendix C). Point sources and nonpoint sources of fecal coliform of the Virginia Creek watershed is discussed in Section 2 of this document. Based on information provided in the most recent survey (NCDMF, 2016), implementation measures should include continued maintenance and repair of septic systems, stormwater controls, pet waste management, and proper manure application to crops. Local stakeholder groups, governments, and agencies are encouraged to develop an implementation plan and utilize funding sources for water quality improvement projects targeted at BMP construction and public outreach. Some potential funding sources Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 17 include the North Carolina Clean Water Management Trust Fund, and Section 319 and 205j funds. Individual land owners may apply for the Community Conservation Assistance Program and Agriculture Cost Share Program to improve the condition of their property. The next NCDMF Sanitary Survey for the B-8 shellfish growing area will help further identify current sources of bacteria and drainage pathways that allow bacteria to enter Virginia Creek and its tributaries and provide a mechanism to evaluate progress in attaining TMDL targets. NCDMF will continue to monitor water quality in Virginia Creek using the systematic random sampling strategy as outlined in the National Shellfish Sanitation Program’s Model Ordinance and guidance document. This data will be used to evaluate progress towards the goal of reaching water quality standards. 5 PUBLIC PARTICIPATION A draft of the TMDL was publicly noticed from January 31, 2022 through March 4, 2022 through various means including North Carolina’s TMDL listserv, the Water Resources Research Institute of UNC (WRRI) listserv, and DWR’s public notice calendar. The draft TMDL was available on DWR’s website throughout the public comment period. Appendix D contains the public notice. Appendix E summarizes public comments and responses, however, no public comments were submitted. 6 FURTHER INFORMATION Further information concerning North Carolina’s TMDL program can be found on the Internet at the Division of Water Resources website: https://deq.nc.gov/about/divisions/water-resources/planning/modeling- assessment/tmdls Technical questions regarding this TMDL should be directed to the following members of the DWR Modeling & Assessment Branch: Jing Lin e-mail: jing.lin@ncdenr.gov Pam Behm e-mail: pamela.behm@ncdenr.gov Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 18 7 REFERENCES AECOM. 2021. Memorandum, NCDOT Right-of-Way and Impervious Cover Area Land Use Analysis in Virginia Creek and Turkey Creek Watersheds. Kuo, A., Butt, A., Kim, S. and J. Lin. 1998. Application of a tidal prism water quality model to Virginia Small Coastal Basins. SRAMSOE No. 348. NCAD. 2003. NC Administration Code. NCDMF. 2016. Report of Sanitary Survey, Area B-8, Topsail Sound Area, May 2011 through July 2016. NC Division of Marine Fisheries, Shellfish Sanitation and Recreational Water Quality. NOAA. 2010. Tides Online. National Oceanic and Atmospheric Administration/National Ocean Service. Website: http://co-ops.nos.noaa.gov/ NSSP. 2017. National Shellfish Sanitation Program Guide for the control of Molluscan Shellfish 2007, US Food and Drug Administration, 2017. Website: https://www.fda.gov/Food/GuidanceRegulation/FederalStateFoodPrograms/ucm20067 54.htm Shen, J., H. Wang, and M. Sisson. 2002. Application of an Integrated Watershed and Tidal prism Model to the Poquoson Coastal Embayment (submitted to Department of Environmental Quality, Commonwealth of Virginia). Virginia Institute of Marine Science Special Report 380, Gloucester Point, VA. USEPA. 1991. Guidance for Water Quality-Based Decisions: The TMDL Process. Assessment and Watershed Protection Division, Washington, DC. USEPA. 1998. Draft Final TMDL Federal Advisory Committee Report. U.S. Environmental Protection Agency, Federal Advisory Committee. Draft final TMDL Federal Advisory Committee Report. 4/28/98. 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). USEPA. 2002. Wayland, Robert, H. and James A. Hanlon. "Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on Those WLAs". Memo to Water Division Directors Regions 1-10. United States Environmental Protection Agency, Washington, D.C. 22 November 2002. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 19 Appendix A: NCDMF Monitoring Data Summary Table A.1 Fecal coliform (MPN/100ml) random sampling data in Virginia Creek Date Stations 17 18 46 46A 5/31/2011 2 1.7 1.7 2 10/25/2011 2 6.8 6.8 13 12/14/2011 4.5 4.5 2 4.5 2/28/2012 1.7 33 7.8 4.5 5/22/2012 1.7 14 2 11 9/12/2012 4.5 13 11 6.8 10/17/2012 1.7 2 2 6.8 11/27/2012 6.1 4.5 4.5 2 12/18/2012 49 140 240 130 3/18/2013 2 4.5 4.5 13 4/25/2013 2 6.8 4.5 4.5 8/7/2013 1.7 1.7 2 7.8 10/15/2013 4.5 17 23 17 12/4/2013 2 1.7 4.5 1.7 12/18/2013 2 2 1.7 1.7 2/18/2014 1.7 4.5 1.7 2 5/28/2014 2 6.1 1.7 1.7 7/31/2014 2 27 4.5 2 10/28/2014 4.5 1.8 4.5 9.3 12/2/2014 1.7 9.3 4 17 12/11/2014 7.8 11 2 4 3/12/2015 2 2 4.5 11 4/13/2015 2 1.7 6.8 1.7 7/8/2015 1.7 1.7 2 7.8 11/5/2015 13 540 79 49 11/17/2015 13 79 23 17 12/2/2015 17 79 33 27 3/23/2016 1.7 1.7 1.8 1.7 4/26/2016 2 11 7.8 6.8 7/20/2016 2 13 1.7 2 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 20 Table A.2 Fecal coliform (MPN/100 ml) conditional sampling data in Virginia Creek. Conditional sampling data are not used in the TMDL analysis, included here for reference. Date Stations 17 46A 9/6/2011 4.5 6/4/2012 2 8/23/2012 7.8 9/4/2012 1.7 10/30/2012 49 11/1/2012 7.8 11/20/2012 130 11/23/2012 1.7 2/12/2013 4.5 4/23/2014 4.5 7/8/2014 1.7 8/13/2014 6.8 8/26/2014 1.7 9/16/2014 6.8 12/29/2014 11 1/28/2015 17 2/3/2015 2 6/8/2015 1.7 7/27/2015 1.7 8/17/2015 4.5 9/3/2015 11 9/30/2015 7.8 10/12/2015 110 10/15/2015 7.8 11/23/2015 70 11/27/2015 6.8 12/1/2015 22 12/2/2015 17 27 12/4/2015 4.5 2/18/2016 6.8 5/9/2016 1.7 6/10/2016 4.5 7/7/2016 7.8 9/15/2016 17 9/28/2016 49 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 21 Table A.3 Fecal coliform data summary statistics in Virginia Creek. Fecal Coliform Bacteria Concentration (MPN/100ml) Station # Samples Type of Sampling Median Geometric Mean Estimated 90th Percentile 17 30 Random 2 3.1368 9 35 Conditional 6.8 7.3996 37 18 30 Random 6.45 7.8727 53 46 30 Random 4.5 5.1676 25 46A 30 Random 6.8 6.1692 25 1 Conditional 27 27 27 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 22 Appendix B: Virginia Creek Steady-State Tidal Prism Model Inputs and Parameters Table B-1. Model Parameters Parameter TR β k Cf Description Mean tidal range Exchange ratio Decay rate Conversion factor Unit m N/A Per tidal cycle (1/T) T/day *100ml/m3 Value 0.9 0.5 0.36 19323.67 Table B-2. Model Inputs for 90th percentile Existing Loads Calculation Parameter VT VL Qf C Brief Description Local Tidal Prism Volume Low Tide Volume Fresh water input Mean FC Conc. of the segment unit m3 m3 m3/T MPN/100ml Open Boundary 9 M1 668525 527738 1240 32 M2 400637 234243 8373 53 B1 127102 70612 6571 53 Table B-3. Model Inputs for 90th percentile TMDL Loads Calculation Parameter VT VL Qf C Brief Description Local Tidal Prism Volume Low Tide Volume Fresh water input Mean FC Conc. of the segment unit m3 m3 m3/T MPN/100ml Open Boundary 9 M1 668525 527738 1240 32 M2 400637 234243 8373 43 B1 127102 70612 6571 43 Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 23 Appendix C: NCDMF Mapping of Potential Pollution Sources in B-8 Growing Area Figure C.1. NCDMF Mapping of Potential Pollution Sources in B-8 Growing area (NCDMF, 2016) Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 24 Appendix D: Public Notification of TMDL for Fecal Coliform for Virginia Creek From: dwr.TMDL303d@lists.deq.nc.gov on behalf of Painter, Andy To: dwr.TMDL303d@lists.deq.nc.gov Subject: [External] Draft Virginia Creek TMDL Available for Public Review Date: Monday, January 31, 2022 9:50:05 AM January 31, 2022 North Carolina Department of Environmental Quality Division of Water Resources Draft Total Maximum Daily Load (TMDL) for Fecal Coliform for Virginia Creek (White Oak River Basin), North Carolina Now Available for Public Comment The draft TMDL was developed to meet requirements of Section 303(d) of the Federal Water Pollution Control Act to address fecal coliform impairments. It is subject to approval by EPA. The Draft TMDL document can be found at: https://edocs.deq.nc.gov/WaterResources/DocView.aspx?dbid=0&id=2182079 Interested parties are invited to comment on the draft TMDL by March 4, 2022. Comments should be directed to TMDL303dComments@ncdenr.gov and must be received no later than 5 pm on March 4, 2022. Virginia Creek Fecal Coliform TMDL ________________________________________________________________________ 25 Appendix E: Public Comments Responsiveness Summary No comments were received.