In late January, I reported that a major rupture of the Potomac Interceptor sewer line in Maryland had been releasing an estimated tens of millions of gallons per day of untreated sewage into the Potomac River just upstream of Washington, D.C., following severe winter weather and an infrastructure failure in a 1960s-era pipeline.
The spill has raised serious public health concerns due to elevated E. coli and other pathogen levels. The event highlights broader national issues with aging water and wastewater infrastructure, with an EPA estimate that D.C. alone needs about $1.33 billion over 20 years to repair deteriorating sewers and that hundreds of billions are needed nationwide.
There is a troubling update to this story. Washington, D.C.‘s Water and Sewer Authority appears to have significantly miscalculated the level of E. coli emanating from this incident. Note that MPN in this context means “Most Probable Number” (a value calculated by recording the tested concentration of bacteria at various stages of dilution, then using standard MPN tables and the dilution factor to convert that pattern into an estimated number of organisms per unit volume of the original sample).
The agency just announced a correction to the initial E. coli levels reported, indicating they are actually 9,900% higher.
On Friday, Feb. 6, DC Water initially reported levels of E. coli at 2,420 MPN/100mL, then changed it to the actual level of E. coli present, 242,000 MPN/100mL, which is 9,900% higher than the initial report. The numbers came from a drainage channel at Swainson Island, adjacent to Cabin John, Maryland, in the Potomac River...
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