E. coli is a type of bacteria that’s found in the digestive tract of warm-blooded animals — including people. If high levels of E. coli are found in a stream or river, there’s the potential for disease-causing pathogens to also be present. In 1996, Four Mile Run was listed as an “impaired water” for E. coli and a Total Maximum Daily Load (TMDL) was established for the nontidal portions of the stream. More information about the Four Mile Run TMDL can be found on the Northern Virginia Regional Commission website.
We use the Virginia Department of Environmental Quality (DEQ)-recommended Coliscan Easygel kit with our volunteer program. While not laboratory quality, the Coliscan Easygel test results are a reliable, low-cost indicator to determine if further testing or investigation is warranted.
Where Is the Bacteria Coming From?
- Concentrated wildlife. In an urban area, wildlife often concentrates near streams.
- Storm sewer systems. The pipes can provide a habitat for bacteria to reproduce underground. Ultraviolet light (sunlight) kills bacteria.
- Sanitary sewer pipe breaks or leaks.
- Pet waste. Picking up after your pet is not just a courtesy, but a public health issue.
What Do High Bacteria Levels in the Water Mean to Me?
It means there’s a greater possibility that illness-causing pathogens could be in the water. While there’s no guarantee the water will make you ill, it’s a sign that additional care should be taken. Always wash your hands after working or playing in our streams.
Should I Be Worried?
No. Activities that involve touching the water are safe. But always thoroughly wash your hands after coming into contact with stream water and never drink it. We don’t recommend submerging your body into stream waters (swimming) where water can enter your body. Learn more about enjoying streams safely.
Below are links to volunteer-collected E. coli data from Four Mile Run and a few of its tributaries since 2010. Those data aren’t considered laboratory-quality and are used to identify potential areas of concern that may require additional investigation or monitoring. Recent rainfall amounts and human error can influence the data. If the County suspects that human error may have impacted the data, staff will work with the volunteers to clarify and correct their monitoring methods.
Bacteria Monitoring Data
- Doctor’s Branch
- Donaldson Run
- Four Mile Run
- Gulf Branch
- Little Pimmit Run
- Lower Long Branch
- Lubber Run
- Upper Long Branch
- Windy Run
In each graph, the blue line indicates the measured bacteria levels.
The red line represents the primary contact recreation water quality standard, 235 E. coli CFU/100 mL; this standard, set by the state, represents the highest measure of E. coli allowable in freshwater to safely participate in primary contact recreation. Primary contact recreation activities have a high probability for total body immersion or ingestion of water, like swimming, canoeing and kayaking. More information is available in the Virginia Administrative Code for this standard.
The green line represents the secondary contact recreation water quality standard, 1,173 E. coli CFU/100 mL. DEQ has not applied this standard to any of Virginia’s waterways to date, but it’s still valuable information. This standard allows us to evaluate the suitability of our waters for secondary contact recreation activities that don’t have a high probability of total body immersion or water ingestion, like skipping rocks or fishing. The County’s guidance for safe stream usage follows the state’s allowable secondary contact activities.