Canada Geese
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Total
Maximum Daily Load (TMDL)
Cattle in stream
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Problem
In Virginia, 464 stream segments with a total stream length of 2,166 miles are listed as impaired waters on the Commonwealth's
303(d) list due to violations of water-quality standards. Of these, 152 stream segments with a total length
of 1,165 miles are listed as a result of violations of Virginia's standard for fecal coliform bacteria - 1,000 fecal coliform bacteria per 100 ml. There are many potential
sources of fecal coliform bacteria within each impaired watershed, such as people, pets, livestock, and wildlife. As a result,
determining the source(s) of fecal coliform bacteria causing
these water-quality violations is highly uncertain. This uncertainty makes it difficult to define accurate waste-load allocations, develop supportable total
maximum daily loads (TMDLs), and direct source-control measures that are accepted by the public.
Objective
The primary objective of this study is to develop watershed models that can be used to assign
TMDLs for three stream segments listed on the Commonwealth's 303 (d) list for fecal coliform bacteria
violations. Specific objectives of this project are to: 1) produce a calibrated and verified model of watershed
hydrology and fecal coliform transport for each of the three selected stream segments, 2) develop a technical
approach for linking bacteria source tracking information into the watershed model, and 3) develop waste-load
allocations.
Relevance and Benefits
This study will provide a practical demonstration of incorporating bacteria
source tracking information into the TMDL development process. This study also will develop and demonstrate
improved modeling techniques that can be applied to the numerous stream segments in Virginia that are
impaired by fecal coliform bacteria. This information and these techniques can be transferred by the USGS and
the USEPA for application in neighboring states in the Middle-Atlantic region.
Approach
Three fecal coliform impaired streams were chosen (Accotink Creek, Christians Creek, and
Blacks Run) which represent the dominant land-uses within the state of Virginia - urban, agricultural, and
combined urban and agricultural. Within each watershed, streamflow and fecal coliform bacterial transport will
be simulated using the Hydrological Simulation Program - Fortran (HSPF) watershed model. Simulated
streamflow will be calibrated to match historical USGS streamflow data. Simulated instream fecal coliform
concentrations will be calibrated to observed fecal coliform concentrations and bacteria source tracking
data. Additional fecal coliform bacteria samples will be collected during elevated streamflow events. Data from
these high flow samples will be used to verify the model's ability to account for the variability found in fecal
coliform bacteria concentration as a result of increased streamflow. The calibrated and verified models of
hydrology and fecal coliform bacteria transport will be used to assign waste-load allocations and generate
TMDLs for Accotink Creek, Christians Creek, and Blacks Run.
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