Bacteria Monitoring Program

• From April 2017 to April 2018, Stormwater Utility staff used the Level II Coliscan Easy-Gel method to measure the bacteria levels in streams across the City.
• As of April 2018, staff transitioned to using the IDEXX^® Colilert method. The Virginia Department of Environmental Quality (DEQ) recognizes the Colilert method as a Level III method.  Level III methods and associated data can be used by DEQ as if the DEQ collected and processed the samples.  
• Staff collects samples at 41 sites on the Roanoke River and its tributaries once per month, resulting in at least 492 samples collected annually.  
• As the program continues to evolve, sampling sites are added or adjusted based on new data in order to locate bacteria sources.

Preliminary Results:

Since there are many variables that affect the bacteria levels of the Roanoke River and its tributaries including: temperature, wildlife, sunlight, nutrients, turbidity, as well as nearby septic systems, potential sanitary sewer overflows, or illicit connections, it is premature to provide in-depth analysis of the data collected to date.  There are, however, observable seasonal variances, with higher bacteria in summer and fall and lower bacteria in winter, as well as higher bacteria after rainfall events.  Over time the program will establish a baseline of data to help prioritize source tracking and other remediation efforts.  

The Recreational Water Quality Standard set by the Virginia Department of Environmental Quality (DEQ) is in freshwater, E. coli bacteria shall not exceed a geometric mean of 126 counts/100ml and shall not have greater than a 10% excursion frequency of a statistical threshold value (STV) of 410 counts/100 ml, both in an assessment period of up to 90 days..

The bar graph below shows the median indicator bacteria levels for streams from the bacteria monitoring program.  The x-axis includes the sampled streams with the total number of samples taken in brackets after the stream name.  The number of sampling sites varies per watershed based on percentage of the watershed within the City’s jurisdictional boundaries, access, and other risk factors.  The y-axis represents the average fecal indicator bacteria (E. coli) levels and includes the red dashed-line depicting the DEQ/VDH threshold of a healthy stream at 235 CFUs/100ml.  While the bar graph illustrates the median or average bacteria levels, the vertical black dimension lines represent the percentage of bacteria levels above and below the 25% (bottom) and 75% (top) quartile. See a map of the different streams and watersheds in the City here. Since current sampling practices do not fit the new standard of a 90 day sampling window, the below map simply shows the range of sample scores, over the course of the calendar year, in relation to the statistical threshold value, one part of the updated DEQ Recreational Water Quality Standard.

Next Steps:

1. In 2019, Stormwater staff began a source tracking program to determine sources of bacteria, in addition to the baseline monitoring. Staff coordinates with the Hampton Roads Sanitation District to use their technology which utilizes microbial source tracking to identify if the E.coli source is human or another source. This new technology allows for more advanced tracking and elimination of bacteria sources. Using this method, there have been multiple successful repairs made to remove human sourced bacteria sources from the City MS4 system. Staff continues to track sources of bacteria with this method in City watersheds.
2. Stormwater will continue to work with our colleagues at the Western Virginia Water Authority (WVWA) to track down and remove potential sewer related bacteria sources. This partnership has already resulted in successful improvements or repairs including: Franklin Rd. and Wonju St. repair (Ore Branch), Grandin Rd. and Sherwood Ave. repair (Roanoke River), West Fork Carvin Creek repair (Carvin Creek), Roanoke River crossing at Piedmont Park repair (Roanoke River), Melrose Ave two repairs (Horton's Branch), Hamilton Ave and Howbert Ave. repair (Roanoke River), Campbell Ave pipe lining (Trout Run), Salem Ave & 3rd St. repair (Trout Run), Brambleton & Rosewood Ave. repair (Murray Run),  upstream of Laurel Ridge Rd Nw repair (Lick Run), and Andrews Rd NW repair (Lick Run).