Friday, July 1, 2022

Fish Kill Mystery Solved

After multiple inquiries and ongoing investigation of the fish kill incident on Four Mile Run in mid-May, at last there is an explanation. In an email to the Four Mile Run Joint Task Force, Arlington County's deputy director of operations at the Department of Environmental Services provided the following information this afternoon:

Yesterday, June 30, after extensive testing of several systems at Arlington’s Water Pollution Control plant, we determined that there is an apparent leak or rupture in a segment of infrequently used piping at the plant. We believe that this is the likely culprit for the fish kill in Four Mile Run that was observed May 12.

On May 11, the piping had been circulating 7,000 gallons of a 5% sodium hypochlorite mixture. Some amount of this mixture appears to have leaked into the storm drain and then into Four Mile Run. The faulty piping has not been used since the May 11 process, and was fully taken out of service yesterday.

We have reported our findings to DEQ this morning.

The faulty piping is 2-inch plastic and handles discharge from a sump pump in our hypochlorite facility, routing the discharge back to the headworks of the plant. The sump pump is infrequently used, but was put in service May 11 due to an accidental spill of hypochlorite solution. The spill was contained within the containment chamber, which functioned as designed, and then pumped out to be treated through our typical process. We have not determined what or where the fault in the pipeline is, but a dye test of this piping yesterday showed color emerging in a storm sewer outfall into Four Mile Run.

To repeat, this pump and piping is rarely used, and we have disconnected and isolated them as we look for the failure point. Temporary pumps and piping are now in place.

A number of tests are scheduled for next week to identify where the discharge piping failed. We are confident no additional discharges have occurred since the May 11-12 incident. The piping will not be used unless and until it has been repaired.

We deeply regret this accident occurred and will work with DEQ, our regulatory agency, to ensure that we remain in full compliance with our permits and commitments to preserve the environment.

We are relieved to know that the equipment at fault has been identified and is being repaired, and are thankful to the Arlington County staff who kept working to track down the source, and to the many Four Mile Run volunteers and friends who kept pushing for answers. We are also pleased to have had a role in driving the decision to dye-test the containment system piping -- see the Virginia DEQ incident report for more details.