Snowmelt and runoff debris continue to complicate efforts by the District of Columbia Water and Sewer Authority to make progress on repairing the 72-inch break. The Potomac Interceptor sanitary sewer line, which on Jan. 19 released what observers say could be as much as 300 million gallons of raw sewage into the Potomac River outside Washington, DC.
Experts consider the event to be the largest sewage spill in US history.
The agency, known as DC Water, has largely managed to avoid additional emissions through a temporary pumping system that uses a dry section of the adjacent C&O Canal as a temporary bypass around the damaged section while a repair plan is formulated.
The agency has not responded to ENR’s requests to identify the contractors involved in the cleanup and containment effort, or to elaborate on information in public statements.
In a Feb. 11 “open letter” posted on its website, DC Water Director General and CEO David L. Gadis said the agency’s “immediate priorities have been environmental containment, monitoring and stabilization, working closely with federal, state and local partners to assess water quality, ecological impacts and necessary remediation.”
New complications
Complicating the effort is the unexpected discovery of a large rock dam blockage within the damaged sewer line that has been difficult to remove with existing DC water machinery and pumping capacity.
Work was accelerated by the Feb. 13 arrival at the site from out of state of five 13-million-gallon-per-day pumps, which will provide capacity to more fully isolate the damaged section of pipeline and allow workers to remove the large rock dam about 30 feet from the break and formulate and implement a repair strategy. At least two are expected to be operational by February 15 as rain and snowmelt will lead to higher flows.
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DC Water crews are also digging two new access wells to support the full installation of the improved bypass pumping system. “These additional pumps will increase the redundancy and capacity of the system as work progresses,” he said. “It is expected to take an additional 4-6 weeks to put in place a system that will add larger bypass pumps at a new location and stabilize the site so that heavy machinery can begin to safely remove large rocks and blocks from the sewer network.”
The agency says keeping up with higher flows from melting snow has added other hurdles, as pumps must be taken offline periodically to clear wipes and other debris that isn’t being removed. This has led to several small overflows, including a Feb. 8 incident totaling less than 5,000 gallons. The agency says an earth dam and ditch system captured and redirected the wastewater into the sewer system, preventing discharge into the river.
“Until full functionality of the Potomac Interceptor is restored, there is a residual risk of additional limited overflows,” DC Water said in a statement.
said Dean Naujoks, who holds the title of Potomac Riverkeeper The Baltimore Sun Feb. 10 that the spill is likely larger than the 2017 US-Mexico border spill that leaked 230 million gallons.
Looking ahead to future issues
While some reports estimate that the extended diversion and repair effort will cost at least $10 million, its ultimate effect on DC Water’s infrastructure upgrade initiatives has not been disclosed. The agency has touted a ten-year, $625 million program to rehabilitate sections of the Potomac Interceptor, with the area where the break occurred among the targeted locations. A quarter-mile away, D.C.-based Fort Meyer Construction Corp. has been working since last fall on a $9.6 million project to upgrade an 800-foot segment of the 16-foot-deep interceptor using slip methods.
It remains unclear whether or how the breakup will alter the scope and cost of the long-term upgrade program.
Gadis’ letter said the incident points to the risks America’s utilities face in relying on decades-old infrastructure to serve communities and protect waterways. The failure of the more than 60-year-old Potomac Interceptor, he said, “reinforces why sustained investment and vigilance are essential.”
That sentiment was echoed by Hedrick Belin, president of the Potomac Conservancy. While he credits DC Water for its ongoing program to prevent combined sewage overflows in several area waterways, the failure of the Potomac Interceptor “makes it clear that outdated and weak infrastructure remains one of the biggest threats to the health of the Potomac River, and that accountability, transparency and monitoring are essential.”
Belin called on DC Water to release the most recent assessment of the pipe’s structural integrity and order an open investigation into the failure, “including whether warning signs were missed and whether preventative maintenance or upgrades could have prevented the disaster.” The agency should also identify and publicly share other known or potential weaknesses in the system by the end of March, with a clear timeline and action plan to address them.
“This incident must not further undermine public confidence in our water safety and infrastructure,” Belin added.
The effects of the spill on the water quality of the Potomac River also remain to be determined. DC Water says its own test results show mostly decreasing trends, although levels of E. coli continue to fluctuate over time “due to the residual impacts of the incident and the ongoing influences of weather conditions such as precipitation, snowmelt, temperature variability,” as well as other natural sources of E. coli bacteria such as wildlife.
According to a local report, DC Water says it is working with an outside company to develop a plan to repair the area after the pipe is repaired, but without further details about the company or the cleanup strategy.
The Potomac Riverkeepers Network cited preliminary modeling data from the Maryland Department of the Environment indicating that sewage pollution is likely to affect water quality more than 30 miles downstream. Bacteria linked to staph infections have also been found at one-third of state-run sampling sites. However, aside from the ban on shellfish harvesting near the Chesapeake Bay, Naujoks said officials in Maryland, D.C. or Virginia have not issued any public health warnings.
“They need to inform residents about the serious public health risks of this sewage spill,” he said.
