Total Maximum Daily Load of Bacteria for Pettit Branch in 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 Figures iv
List of Tables 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
1.4 Pollutant of Concern 2
1.5 Designated Uses and Applicable Water Quality Standard 2
2.0 WATERSHED CHARACTERIZATION 4
2.1 Topology, Soil, and Climate 4
2.2 Landuse 4
2.3 Water Quality Data 6
3.0 SOURCE ASSESSMENT 9
3.1 General 9
3.2 Population Number Summaries 9
3.3 Septic System Inputs 9
3.4 Bacterial Source Tracking 10
4.0 TMDL DEVELOPMENT 12
4.1 Modeling Approach 12
4.2 The TMDL Calculation 13
4.3 Load Allocation 16
4.4 Margin of Safety 17
4.5 Consideration of Critical Conditions and Seasonal Variation 18
5.0 IMPLEMENTATION AND PUBLIC PARTICIPATION 19
5.1 General 19
5.2 Staged Implementation 19
5.3 Stage 1 Scenarios 20
5.4 Reasonable Assurance for Implementation 20
5.5 Public Participation 24
REFERENCES 25
Appendix A: Calculation of Population Numbers A1
Appendix B: TMDL Development B1
List of Figures
Figure 1.1: Location Map of the Pettit Branch, the Impacted Segment, and the VA-DEQ Water Quality Station 2
Figure 2.1: Landuse of the Pettit Branch 5
Figure 2.2: Percentage Landuse of the Pettit Branch 6
Figure 2.3: Fecal Coliform Observations from 1993 to 2007 at Station 7-PET000.80 7
Figure 2.4: E. Coli Observations from 1993 to 2007 at Station 7-PET000.80. The Red Line Indicates the 235 counts/100 ml Criterion 8
Figure 3.1: Septic System Locations in the Pettit Branch Watershed 10
Figure 4.1: Flow Duration Curve from LSPC Model Simulation (2000-2007) 13
Figure 4.2: TMDLs as a Function of Temperature under Low, Median, and High Flow Conditions 14
Figure 4.3: Estimated Existing Daily Loads and the TMDLs under Different Flow Conditions (Error Bars Designate Standard Deviations) 15
Figure 4.4: Existing Loads of Three Flow Regimes and the TMDLs 15
Figure 4.5: Illustration of Load Reduction for Each Flow Regime 16
Figure B-1: Distribution of E. Coli with Flow B2
Figure B-2: Distribution of E. Coli vs. Temperature B2
Figure B-3: Time Series Comparison of Daily Stream Flow between Model Simulation and Observed Data from USGS Gage 01484800 B3
Figure B-4: Segmentation of the Pettit Branch Watershed into 4 Sub-watersheds B4
Figure B-5: Comparison of Modeled Concentration Results with the Observations B7
List of Tables
Table 2.1: Landuse within the Pettit Branch Watershed 5
Table 3.1: Human, Dog, Livestock, and Wildlife Populations in Pettit Branch 9
Table 4.1: Summary of TMDLs under Different Regimes 16
Table B-1: Summary of Model Calibration Errors B3
Table B-2: Summary Statistics for the Posterior Distributions of the Estimated Loads (Log Transferred) B6
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
LSPC / Loading Simulation Program C++
MOS / Margin of Safety
NPDES / National Pollutant Discharge Elimination System
SWCB / State Water Control Board
TMDL / Total Maximum Daily Load
UAA / Use Attainability Analysis
USGS / United States Geological Survey
VA-DEQ / Virginia Department of Environmental Quality
VA-DCR / Virginia Department of Conservation and Recreation
VPDES / Virginia Pollutant Discharge Elimination System
WLA / Wasteload Allocation
WQMIRA / Water Quality Monitoring, Information, and Restoration Act
WQMP / Water Quality Management Plans
EXECUTIVE SUMMARY
Background
The Pettit Branch (VAT-D02R) is located in Accomack County, Virginia. It is a tributary of the Assawoman Creek (United States Geological Survey (USGS) Hydrologic Unit Code 02080110), which discharges directly to the Atlantic Ocean. The Pettit Branch was listed as impaired on Virginia’s 2006 303(d) Total Maximum Daily Load (TMDL) Priority List and Report due to violation of the State’s water quality standard for Escherichia coli (E. Coli). The Virginia Department of Environmental Quality (VA-DEQ) assessed the water quality of the Pettit Branch from 2002 through the present time. During this period, 62% of water quality samples collected exceeded the water quality standard of single sample maximum of 235 counts/100 ml. The impaired segment of the stream is approximately 2,710 meters (1.7 miles) long and extends from the headwaters downstream to the start of tidal limit.
Based on the assessment of Pettit Branch’s water quality impairment, it does not support its designated use of primary contact recreation (e.g., swimming and fishing). In order to meet its designated use, a TMDL has been developed to meet the E. Coli standard.
Sources of E. Coli
As there is no point source such as a waste water treatment plant (WWTP) in the Pettit Branch watershed, the potential E. Coli sources in the watershed are nonpoint, including livestock, wildlife, land application of biosolids, pets, failing septic systems, and uncontrolled discharges (straight pipes conveying gray water from kitchen and laundry areas of private homes, etc.). Bacterial source tracking (BST) samples collected in the watershed during the fall of 2007 verified that livestock, wildlife and humans are the major sources contributing to fecal coliform water quality standards violations.
Modeling Approach
A watershed model, Loading Simulation Program C++ (LSPC), was applied to estimate flow and velocity in the stream. The model parameters were calibrated against USGS Gage 01484800 in Guy Creek near Nassawadox and applied to the Pettit Branch watershed. The model outputs from year 2002-2007 are used to estimate the flow in the Pettit Branch.
A steady state distributed-source water quality model was used. The inverse Bayesian parameter estimation approach, together with the simulated flows, observed or water quality standard E. Coli concentrations, and temperatures were used to calculate the allocable and existinloadings from the watershed based on the methodology of using duration curves under different flow and temperature conditions.
Determination of Sources of Existing Loadings
To assist in partitioning the loads from the diverse sources within the watershed, water quality samples of E. Coli were collected for one year and evaluated using an antibiotic resistance analysis in a process called 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 E. Coli 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 Scenarios
For the recreation use impairment, the appropriate water quality standard was determined to be a single value of 235 counts/100 ml for E. Coli. Calculated results of the model were used to establish the existing loads in the system. The loads necessary to meet water quality standards (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 value. The difference between the TMDL and the highest existing loading within each flow regime represents the necessary level of reduction. The maximum reduction required to meet water quality standard is approximately 88.2%. Finally the results of the BST were used to partition the load allocation (LA) that would meet water quality standards according to source, as summarized below for different flow intervals.
Reduction Summary for Flow Interval of <0.5 cfs
Source / BST Allocation% of Total Load / Current Load
(Counts/Day) / LA
(Counts/Day) / Reduction
Needed (%)
Livestock
Wildlife
Human
Pets
Total / 100 / 1.73E+10 / 3.19E+09 / 83.4
Reduction Summary for Flow Interval of 1-2 cfs
Source / BST Allocation% / Current Load
(Counts/Day) / LA
(Counts/Day) / Reduction
Needed (%)
Livestock
Wildlife
Human
Pets
Total / 100 / 4.00E+10 / 7.31E+9 / 82.9
Reduction Summary for Flow Interval of > 2 cfs
Source / BST Allocation% / Current Load
(Counts/Day) / LA
(Counts/Day) / Reduction
Needed (%)
Livestock
Wildlife
Human
Pets
Total / 100 / 9.55E+10 / 1.18E+10 / 88.2
Margin of Safety
In order to account for uncertainty in modeled output, a margin of safety (MOS) was incorporated into the TMDL development process. A MOS 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 the Pettit Branch, the temperature is an important factor affecting bacteria decay rate and consequently allowable loading. A low decay rate corresponding to temperature at 1 ℃ is used as a conservative estimate. Therefore, MOS is treated implicitly.
Recommendations for TMDL Implementation
The goal of this TMDL is to develop an allocation plan that achieves water quality standards 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 TMDL developed for the Pettit Branch watershed impairments provides 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 calibration and fecal production estimates are to be discussed in the second public meeting scheduled for March 26, 2008.
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1.0 INTRODUCTION
1.1 Background
Section 303(d) of the Clean Water Act (CWA) 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 water quality standards. TMDLs represent the total pollutant loading that a waterbody can receive without violating water quality standards. 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 water quality based controls to reduce pollution from both point and nonpoint sources to restore and maintain the quality of their water resources.
1.2 Impairment Listing
Pettit Branch was listed as impaired on Virginia’s 2006 305(b)/303(d) Water Quality Assessment Integrated Report due to violations of the State’s water quality standard for E. Coli bacteria. From 2002 to the present time, 62% of water quality samples collected by VA-DEQ exceeded the water quality standard. The 1.7-mile segment from its headwaters to the start of tidal water is impaired for recreational uses. It is targeted for TMDL development and completion by year 2010.
1.3 Watershed Location and Description
As the south shore tributary of the Assawoman Creek, the Pettit Branch is located in Accomack County, along the Eastern Shore of Virginia (Figure 1.1). The watershed is about 2,721,600 m2 (672.5 acres) in size. It is mainly an agricultural watershed (approximately 31% pasture and 28% row crops). Pettit Branch merges with Assawomen Creek and eventually discharges into the Atlantic Ocean.
Figure 1.1: Location Map of the Pettit Branch, the Impacted Segment, and the VA-DEQ Water Quality Station
1.4 Pollutant of Concern
Pollution from both point and nonpoint sources can lead to fecal coliform bacteria contamination of water bodies. Fecal coliform bacteria are found in the intestinal tract of warm-blooded animals and, consequently, fecal waste of warm-blooded animals contains fecal coliform. Even though most fecal coliform are not pathogenic, water bodies with fecal coliform bacteria are potential sources of pathogenic organisms. For contact recreational activities such as boating and swimming, health risks increase with increasing fecal coliform counts. If the fecal coliform concentration in a water body exceeds state water quality standards, the water body is listed for violation of the state bacteria standard for contact recreational uses. Virginia has adopted a water quality standard using E. Coli (a subset of the fecal coliform group).
1.5 Designated Uses and Applicable Water Quality Standard
1.5.1 Designation of Uses
According to Virginia Water Quality Standards (9 VAC 25-260-10), “All State waters, including wetlands, are designated for the following uses: recreational uses, e.g., swimming and boating; the propagation and growth of a balanced, indigenous population of aquatic life, including game fish, which might reasonably be expected to inhabit them; wildlife; and the production of edible and marketable natural resources, e.g., fish and shellfish.” Pettit Branch does not support the recreational (swimming) designated use due to violations of the bacteria criteria.
1.5.2 Bacteria Standard
The U.S EPA has recommended that all states adopt an E. Coli standard for freshwater and enterococci criteria for saltwaters and transition zones, as there is a stronger correlation between the concentration of these organisms and the incidence of gastrointestinal illness than there is with fecal coliform. E. Coli and enterococci are both bacteriological organisms that can be found in the intestinal tract of warm-blooded animals and are subsets of the fecal coliform and fecal streptococcus groups, respectively. In line with this recommendation, Virginia adopted and published revised bacteria criteria on June 17, 2002, which became effective on January 15, 2003. As of that date, the E. Coli standard described below applies to all freshwater streams in Virginia. Additionally, prior to June 30, 2008, the interim fecal coliform standard must be applied at any sampling station that has fewer than 12 samples of E. Coli.