Download “Cheaper, Better, Faster” Bacteria TMDLs

Virginia's Use of Bacteria Source Tracking to Develop
“Cheaper, Better, Faster” Bacteria TMDLs
1. What is Bacteria Source Tracking (BST)?
The term “Bacteria Source Tracking” (BST) in connection with water quality
management describes the use of various technologies to determine the source of
bacteria in a given body of water. Nationally, several procedures for BST in two major
categories (biochemical methods, molecular or DNA fingerprinting methods) are
currently in use or under development. In Virginia, the methods used most frequently
are antibiotic resistance analysis (biochemical) as well as ribotyping and pulse field gel
electrophoresis (molecular). The underlying assumption in these methods is that
bacteria carried by different hosts will exhibit distinctive patterns either in their response
to antibiotics or in their genetic code.
DNA - based methods offer very precise source identification (i.e. identification of
individual animal types), but their utility is limited due to the expense and the timeconsuming nature of the procedures. Biochemical methods are simpler, faster, and less
costly, but they have typically been used for less precise analyses (i.e. identification of
major source group such as human, livestock, wildlife).
2. How has BST been used in Virginia’s bacteria TMDLs?
BST has been used in several watershed studies to determine the dominant sources of
fecal contamination in Virginia’s streams and estuarine waters. The most assertive use
of BST occurred in three bacteria TMDLs, where loading inputs to the watershed model
were adjusted until the average annual loading by source as represented by the model
was equal to the average annual percentage of the source in the water samples as
determined by BST. In other TMDLs, BST helped to support model output showing that
wildlife was a significant contributor to the fecal coliform contamination in the waterbody.
BST has also been very helpful in stakeholder meetings by demonstrating the sources
that were contributing bacteria to the stream through data. Due to the BST analysis, the
stakeholders were much more receptive of the load allocations developed during the
TMDL process.
3. What are the potential future applications of BST in bacteria TMDLs?
Virginia is currently pursuing the use of BST as the primary tool for source identification
and allocation development, striving for “cheaper, better, and faster” bacteria TMDLs.
BST will allow us to use measured data rather than relying on assumptions of source
distributions within the watershed and on highly complex, data – intensive watershed
models such as HSPF, which give the illusion of detail and accuracy that may be
inappropriate for bacteria TMDLs.
1) Application in Shellfish Waters
Together with the EPA Region III, Virginia is developing a BST – based approach for
TMDLs in fecal coliform impaired shellfish waters. The shellfish method involves
calculating an “allowable loading” for the TMDL study area using the volume of water
and the numeric value of the applicable bacteria standard. The actual fecal coliform
bacteria loading of the TMDL study area will be determined by using the volume of water
in the TMDL study area and the fecal coliform bacteria data collected by the Division of
Shellfish Sanitation. Sources of the bacteria will be determined from the BST analysis.
Using the loading and BST source information, the TMDL allocation or reductions
needed to attain water quality will be calculated by comparison of the “allowable loading”
with the actual loading.
2) Virginia’s Proposed “Cheaper Better Faster” Application in Freshwater
Streams
In addition to the shellfish TMDLs, Virginia is investigating the potential use of a
cheaper, better, faster method to develop TMDLs for fecal coliform bacteria impaired
freshwater streams. This method is similar to the flow duration method recently
developed by Kansas, but the pollutant source identification is made through a BST
analysis. Using the flow duration data from the stream flow frequency analysis and the
applicable value of the bacteria water quality standard, the “allowable loading” of the
TMDL watershed is developed. The actual bacteria loads for the stream are calculated
using daily stream flow values and the ambient bacteria data. The TMDL allocation or
bacteria reductions needed for the attainment of the water quality is calculated by
comparison of the “allowable loading” with the "actual stream loading". Source
reductions (human, cattle, canine, poultry, wildlife, etc,) are determined by using the
BST analysis.