Potomac Riverkeeper Network Summer 2019 Water Quality Monitoring Results

We had a highly successful summer protecting and defending the Potomac River through our citizen science water quality monitoring program. It’s a key feature of our Make the Potomac Swimmable Again Campaign. 

Over the summer, dozens of volunteers collected and analyzed water samples from the Potomac River from Fletcher’s Cove to National Harbor. Monitoring is a great way to track the health and viability of the river and learn how to improve water quality.

Teams obtained 200 water monitoring samples from 10 sites from early May through early October 2019. The samples that they collected met public health standards for E. coli bacteria 55.8% of the time.

The Tidal Basin collection site (PR 6) was the cleanest location, passing the E. coli bacteria test 90% of the time. This location appears to be shielded from regional runoff effects of the greater Potomac River. The National Harbor collection site was a close second with an 85% passing rate. At the other end of the scale, Battery Kemble Creek was the most frequently E. coli contaminated site regardless of rain effects as the location passed testing only 5% of the time. Foundry Branch performed only slightly better with a 10% pass rate.

Of the lower three Potomac sites (PR 8, 9 and 10), Oronoco Bay failed the most, likely due to its location near both a Combined Sewage Overflow site to the south and the mouth of Four Mile Run to the north.

The results demonstrate a measurable degree of correlation across locations and dates, providing substantial confidence in our testing results. 

Not surprisingly, measurable rainfall in three days prior to testing significantly increased the probability of E. coli test failure. Rainfall triggers both combined sewer overflows and stormwater pollution.

Beyond tracking rainfall at Reagan National Airport as a runoff indicator, our analysis used US Geologic Service streamflow gauges to correlate flow levels to downstream test results. We learned that the river appeared to recover from even the heaviest rain events in less than a week. 

We plan to launch our second summer of water quality monitoring in May to continue the Swimmable Potomac campaign. If resources permit, we hope to expand our sampling sites to include Four Mile Run, Little Hunting Creek, Dogue Creek, Pohick Bay Regional Park, and Occoquan Harbor Marina. If you are interested in supporting water quality monitoring at these sites, please contact Emily Franc at emily@prknetwork.org or would like to volunteer to collect and analyze samples next summer, please email us at volunteer@prknetwork.org.

We enjoyed a fantastic start and we are so eager to expand next year!