Nancy T. Norton, P.E.
Virginia Department of Environmental Quality
The 1972 Clean Water Act, introduced the term Total Maximum Daily Loads to describe the amount of pollutant that a stream can accept without becoming impaired for uses that were defined by Congress. In Middle Creek, Aquatic Life Use was impaired. This use addresses the ability for aquatic organisms to thrive in the stream. The benthic organisms were impaired in 1996. In 2003, during TMDL study, surveys indicate the stream now fully supports this use. v
TMDL Allocation Study
What is it and how does it affect me?
Once a stream is identified as not meeting water quality standards, Virginia must determine the source of the pollutant. There are four basic steps in a TMDL study.
First, information is gathered that describes the stream characteristics. This information includes pollutant concentrations in the stream, stream flow and all of the possible sources of the pollutant. Public participation is important in this step because landowners know much of the information needed to help clean up the stream. For example, landowners know whether there are public sewers or septic systems and the condition of the septic systems. They can confirm livestock and wildlife numbers and locations in the area as well. During this stage, Middle Creek was sampled twice and found to fully support the aquatic life use.
After data and information has been analyzed, a mathematical model is developed that helps predict the amount of pollutant that the stream can handle without violating the water quality standard. Then, the model is run several times under different scenarios. Using high rainfall event flows and using drought conditions or low flows in the model allow us to determine the most critical times that the stream may be impaired. Since this stream appears to no longer violate water quality standards, the model scenarios will not be completed.
Instead of a draft report outlining the amount of pollutant that must be reduced from each source, we are proposing to draft a memo to EPA justifying our reasons for removing the stream from the impaired list.
Absence of Aquatic Life
Why is it a concern?
Small aquatic creatures naturally occur in streams. They live in and under the rocks during part or all of their lives. These creatures provide an important link in the food chain.
Water with a rich and varied range of aquatic creatures is usually a healthy environment. In essence, they are an early warning system for stream health. If they are not present this tells us that something has occurred to either reduce the places where they live or to poison or kill them.
Since aquatic creatures are part of the food chain, their absence can effect the numbers and variety of fish living in the stream. During their life cycle, they may emerge from the water and provide food for birds or other animals. Certain of these aquatic creatures can be viewed as the janitors of the streams by shredding leaves and other plant materials, changing them to energy sources that are available for other species to use. It is because of their many functions, that streams are impaired without their presence. Department of Environmental Quality biologists rate stream health based on the occurrence and number of sensitive bugs.
