Fecal Coliform Total Maximum Daily Load Development for Holdens Creek, Sandy Bottom Branch, and Unnamed Tributary to Sandy Bottom Branch, Accomack County, Virginia
Virginia Department of Environmental Quality
629 East Main Street
Richmond, VA 23218
Draft
Prepared by
Virginia Institute of Marine Science
Gloucester Point, VA
March, 2008
Table of Contents
List of Tables iv
List of Figures v
List of Abbreviations vi
EXECUTIVE SUMMARY vii
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Impairment Listing 1
1.3 Watershed Location and Description 1
2.0 WATERSHED CHARACTERIZATION 6
2.1 Topology, Soil, and Climate 6
2.2 Land Use 6
2.3 Water Quality Data 9
3.1 General 14
3.2 Point Source 14
3.3 Nonpoint Source 14
3.4 Bacterial Source Tracking 16
4.0 TMDL DEVELOPMENT 18
4.1 Modeling Approach 18
4.2 Non-Tidal Region TMDL Development 18
4.3 The TMDL Calculation for Shellfish Growing Area 21
4.4 Waste Load Allocation 24
4.5 Load Allocation 24
4.6 Margin of Safety 25
4.7 Consideration of Critical Conditions and Seasonal Variation 25
4.8 TMDL Summary 26
5.0 IMPLEMENTATION AND PUBLIC PARTICIPATION 27
5.1 General 27
5.2 Staged Implementation 27
5.3 Stage 1 Scenarios 28
5.4 Reasonable Assurance for Implementation 28
5.5 Public Participation 32
REFERENCES 33
Appendix A: Summary of Deficiencies in the Holdens Creek Watershed A1
Appendix B: Calculation of Population Numbers B1
Appendix C: TMDL Development C1
C.1 General C1
C.2 Flow Simulation C1
C.3 Non-Tidal TMDL Calculation C3
C.4 TMDL Calculation for Shellfish Growing Area C8
List of Tables
Table 1.1: The Water Type, Designated Uses, Impairments, List Years and Water Quality Criteria for the Five River Segments 4
Table 2.1: Land Use of the Holdens Creek Watershed 7
Table 2.2: The Bacteria Observations in VA-DEQ and VDH-DSS Stations 9
Table 2.3: Geometric Means and 90th Percentiles of the Fecal Coliform Observations for the Most Recent Three Years 10
Table 3.1: Human, Dog, Livestock, and Wildlife Populations of Holdens Creek Watershed 15
Table 3.2: Non-point Source Load Distribution using BST 17
Table 4.1: Summary of E. Coli TMDLs under Different Flow Regimes 21
Table 4.2: Existing Load, Allowable Load, and Required Reduction Based on the Geometric Mean for Fecal Coliform 23
Table 4.3: Existing Load, Allowable Load, and Required Reduction Based on the 90th Percentile for Fecal Coliform 23
Table 4.4: Load Allocation and Required Reduction for E. Coli for SBB and UTSBB 24
Table 4.5: Holdens Creek Fecal Coliform Load Allocation and Required Reduction Based on the 90th Percentile 25
Table 4.6: E. Coli TMDL Summary for SBB and UTSBB 26
Table 4.7: Fecal Coliform TMDL Summary for Holdens Creek 26
Table A-1: Summary of Deficiencies in the Holdens Creek Watershed according to the VDH-DSS Shoreline Survey from March 2007 to September 2007 A1
Table C-1: Summary of Model Calibration Errors C2
Table C-2: Summary Statistics for the Posterior Distributions of the Estimated Loads (Log Transferred) C6
Table C-3: Current Load, Allowable Load, and Required Reduction Based on the Geometric Mean for Fecal Coliform C10
Table C-4: Current Load, Allowable Load, and Required Reduction Based on the 90th percentile for Fecal Coliform C11
Table C-5: Summary Statistics for the Posterior Distributions of the Estimated Loads (Geometric Mean) C11
Table C-6: Summary Statistics for the Posterior Distributions of the Estimated Loads (90th Percentile) C12
List of Figures
Figure 1.1: Location Map of the Holdens Creek Watershed, Holdens Creek, SBB, and UTSBB 2
Figure 1.2: Delineation of the Impaired Waterbodies of the Holdens Creek Watershed 3
Figure 2.1: Land Use of the Holdens Creek Watershed 7
Figure 2.2: Percentage Land Use of the Holdens Creek Watershed 9
Figure 2.3: Fecal Coliform Observations from 1998 to 2007 at Station 7-HLD002.67 and the Water Quality Criteria for Shellfish Growing Waters 11
Figure 2.4: Entercococci Observations from 2002 to 2007 at Station 7-HLD002.67; the Red Line Indicates the 104 Counts/100 ml Criterion 11
Figure 2.5: E. Coli Observations from 2002 to 2007 at Station 7-SBB000.17 12
Figure 2.6: Fecal Coliform Observations from 1998 to 2007 at Station 7-SBB000.17 12
Figure 2.7: E. Coli Observations from 2002 to 2007 at Station 7-XAZ000.30; the Pink Line Indicates the Instantaneous Criterion of 235 counts/100 ml 12
Figure 2.8: Fecal Coliform Observations from 1999 to 2007 at Station 7-XAZ000.30 13
Figure 2.9: Fecal Coliform Observations from 2001 to 2008 at Station 75-S7 and the Water Quality Criteria for Shellfish Growing Waters 13
3.0 SOURCE ASSESSMENT 14
Figure 3.1: Septic System Locations in the Holdens Creek Watershed 16
Figure 3.2: Locations of the BST Monitoring Stations 17
Figure 3.3: Mean Fecal Coliform Contributions by BST 17
Figure 4.1: Flow Duration Curve of the SBB and UTSBB 19
Figure 4.2: TMDLs as a Function of Temperature under Low, Median, and High Flow Conditions 20
Figure 4.3: Illustration of Loading Distribution and Load Reduction for Each Flow Regime 21
Figure A-1: The Location of the Deficiencies in the Holdens Creek Watershed A2
Figure C-1: Time Series Comparison of Daily Stream Flow between Model Simulation and Observed Data from USGS Gage 01484800 C2
Figure C-2: Watershed Segmentation of Holdens Creek C3
Figure C-3: Flow Duration Curve from LSPC Model Simulation (2000-2007) C3
Figure C-4: Comparison of Modeled Concentration Results with the Observations C7
Figure C-5: Estimated Existing Daily Loads and the TMDLs under Different Flow Conditions (Error Bars Designate Loading Standard Deviations) C8
Figure C-6: Model Simulation of Salinity along Holdens Creek. The Error Bars Are Standard Deviations of the Observations C9
List of Abbreviations
BST / Bacterial Source TrackingCFR / Code of Federal Regulations
CI / Confidence Interval
CWA / Clean Water Act
EPA / Environmental Protection Agency
GIS / Geographic Information System
LA / Load Allocation
LDC / Load Duration Curve
LSPC / Loading Simulation Program C++
MOS / Margin of Safety
MOU / Memorandum of Understanding
MS4 / Municipal separate storm sewer system
NOAA / National Oceanic and Atmospheric Administration
NPDES / National Pollutant Discharge Elimination System
SBB / Sandy Bottom Branch
UTSBB / Unnamed Tributary to Sandy Bottom Branch
SWCB / State Water Control Board
TMDL / Total Maximum Daily Load
UAA / Use Attainability Analysis
USFWS / United States Fish and Wildlife Service
USGS / United States Geological Survey
VA-DEQ / Virginia Department of Environmental Quality
VA-DCR / Virginia Department of Conservation and Recreation
VADGIF / Virginia Department of Game and Inland Fisheries
VPDES / Virginia Pollutant Discharge Elimination System
WLA / Wasteload Allocation
WQMIRA / Water Quality Monitoring, Information, and Restoration Act
WQMP / Water Quality Management Plans
WQS / Water Quality Standard
EXECUTIVE SUMMARY
Background
The Holdens Creek (VAT-C10E), Sandy Bottom Branch (SBB, VAT-C10R_SBB01A00), and Unnamed Tributary to Sandy Bottom Branch (UTSBB, VAT-C10R_XAZ01A00) are located in Accomack County, Virginia. The UTSBB discharges to the SBB, and the latter discharges to Holdens Creek, which eventually discharges to the Pocomoke Sound of the Chesapeake Bay. These streams were listed as impaired on Virginia’s 2006 303(d) Total Maximum Daily Load Priority List and Report (VA-DEQ, 2006) due to violations of the State’s water quality standards (WQSs) for various fecal bacteria. The Virginia Department of Environmental Quality (VA-DEQ) assessed the water quality of these streams from 1973 through the present time. Based on the water quality observations of the most recent 10 years, Holdens Creek does not support its shellfish growing water use, and the SBB, UTSBB, and upper Holdens Creek do not support their recreational uses. Therefore, the Total Maximum Daily Loads (TMDLs) have been developed to meet these WQSs.
Sources of Bacteria
There is one fecal bacteria point source, Tyson Farms Inc., that discharges wastewaters into the UTSBB. The potential bacteria nonpoint sources in the watershed include livestock, wildlife, land application of biosolids, pets, and failing septic systems. Bacterial source tracking (BST) samples collected in the watershed during the fall of 2007 verified that livestock, wildlife and humans are sources contributing to fecal coliform WQS violations.
Modeling Approach
For the recreational designated use of SBB and UTSBB, a distributed-source model was applied to calculate the existing loads and TMDLs under different flow regimes. For the shellfish growing designated use of the upper and lower portions of Holdens Creek, a tidally-averaged transport model was used to calculate the existing loads and TMDLs. To better handle the uncertainties associated with the observed data and estimated loads, the Bayesian parameter estimation approach was used to compute the loadings and bacteria decay constant k0. For the recreational designated use of the upper Holdens Creek, the WQS will be met simultaneously as the shellfish growing use is attained.
Determination of Existing Loadings
To assist in partitioning the loads from the diverse sources within the watershed, water quality samples of fecal coliform bacteria were collected for one year and evaluated using an antibiotic resistance analysis in a process called bacterial source tracking (BST). These samples were compared to a reference library of fecal samples from known sources. The resulting data were used to assign portions of the load within the watershed to wildlife, humans, pets or livestock. The results of this analysis indicated that the primary source of fecal coliforms is wildlife with livestock as secondary contributors. The presence of a large signature attributable to one component is sufficient to establish potential directions for remediation under a future implementation plan.
Load Allocation
For the recreation use impairments of SBB and UTSBB, the appropriate WQS was determined to be a single value of 235 counts/100 ml for E. Coli. Calculated loading results from ambient water quality data were used to establish the existing loads in the system. The loads necessary to meet WQSs (TMDLs), grouped to low, medium, and high flow regimes, were calculated in a similar fashion using the water quality criterion in place of the ambient water quality data. The difference between the TMDL and the highest existing loading within each flow regime represents the necessary level of reduction. Finally the results of the BST were used to partition the load allocation that would meet WQSs according to source, as summarized below for different flow intervals.
Flow Interval / BSTAllocation / Current
Load
(Count/Day) / Load
Allocation
(Counts/Day) / Required
Reduction
I
flow >70% (0.46 cfs) / Livestock
Wildlife
Human
Pets
Total / 100% / 2.99E+10 / 1.81E+09
II
70% <flow <5%
(1.77 cfs) / Livestock
Wildlife
Human
Pets
Total / 100% / 1.69E+11 / 1.01E+10
III
>30%
(5.62 cfs) / Livestock
Wildlife
Human
Pets
Total / 100% / 4.01E+11 / 3.67E+10
For Holdens Creek shellfish waters, the appropriate WQSs were determined to be a geometric mean of 14 MPN/100 ml and a 90th percentile of 49 MPN/100 ml. Because the 90th criterion was more frequently exceeded and requires the largest reduction, the 90th percentile loading was used to allocate the source contributions, as summarized below:
Category / BSTAllocation / Current Load
(Counts/Day) / Load Allocation
(Counts/Day) / Required
Reduction
Livestock
Wildlife
Human
Pets
Total / 100% / 7.59E+13 / 7.09E+12 / 90.66%
Margin of Safety
In order to account for uncertainty in the modeled output, a margin of safety (MOS) was incorporated into the TMDL development process by making very conservative choices. A margin of safety can be incorporated implicitly in the models through the use of conservative estimates of model parameters, or explicitly as an additional load reduction requirement. As for Holdens Creek, SBB, and UTSBB, the temperature is an important factor affecting bacteria decay rate and consequently allowable loading, a low decay rate corresponding to temperature at 1 ℃ was used as a conservative estimate. As geometric mean and 90th percentile loads are required to be met at all times for the shellfish growing area, MOS is treated implicitly.
Recommendations for TMDL Implementation
The goal of this TMDL is to develop an allocation plan that achieves WQSs during the implementation phase. Virginia's 1997 Water Quality Monitoring, Information and Restoration Act states, in Section 62.1-44.19.7, that the "Board shall develop and implement a plan to achieve fully supporting status for impaired waters".
The TMDLs developed for Holdens Creek watershed impairments provide allocation scenarios that will be a starting point for developing implementation strategies. Additional monitoring aimed at targeting the necessary reductions is critical to implementation development. Once established, continued monitoring will aid in tracking success toward meeting water quality milestones.
Public participation is critical to the implementation process. Reductions in non-point source loading are the crucial factor in addressing the problem. These sources cannot be addressed without public understanding of, and support for, the implementation process. Stakeholder input will be critical from the onset of the implementation process in order to develop an implementation plan that will be truly effective.
Public Participation
Public participation was elicited at every stage of the TMDL development in order to receive inputs from stakeholders and to apprise the stakeholders of the progress made. Two public meetings were organized for this purpose. The first public meeting was held on February 13, 2008, to inform the stakeholders of TMDL development process and to obtain feedback. Results of the hydrologic model calibration, TMDL development, and fecal production estimates were discussed in the second public meeting on March 26, 2008.
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1.0 INTRODUCTION
1.1 Background
Section 303(d) of the Clean Water Act and the United States Environmental Protection Agency’s (USEPA’s) Water Quality Planning and Management Regulations (40 CFR Part 130) require states to develop TMDLs for waterbodies which are exceeding WQSs. TMDLs represent the total pollutant loading that a waterbody can receive without violating WQSs. The TMDL process establishes the allowable loadings of pollutants for a waterbody based on the relationship between pollution sources and in-stream water quality conditions. By following the TMDL process, states can establish controls based on water quality conditions to reduce pollution from both point and nonpoint sources to restore and maintain the quality of their water resources.
1.2 Impairment Listing
Holdens Creek, SBB, and UTSBB were listed as impaired on Virginia’s 2006 305(b)/303(d) Water Quality Assessment Integrated Report (VA-DEQ, 2006) due to violations of the State’s WQSs for fecal bacteria (See Sections 1.4.2 and 2.3 for detailed explanations).