Snowmelt and flow debris continue to complicate the District of Columbia Water and Sewer Authority’s efforts to advance repair of the ruptured 72-in. Potomac Interceptor sanitary sewer line, which on Jan. 19 released what observers say could be up to 300 million gallons of raw sewage into the Potomac River just outside Washington, D.C.
Experts now consider the event the largest wastewater spill in U.S. history.
The agency, known as DC Water, has largely managed to prevent additional releases through a temporary pumping system that uses a dry section of the adjacent C&O Canal as a temporary bypass channel around the damaged section while a repair plan is formulated.
The agency has not responded to requests by ENR to identify the contractors involved in the cleanup and containment effort or elaborate on information in public statements.
In a Feb. 11 «open letter» published on its website, DC Water CEO and General Manager David L. Gadis said the agency’s “immediate priorities have been containment, environmental 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 disovery of a large rock dam blockage inside the damaged sewer line that has been difficult to remove with existing DC Water pumping and machinery capacity.
Work was set to expedite with the Feb. 13 site arrival from out of state, of five 13-million-gallon-per-day pumps, which will provide capacity to more fully isolate the damaged section of pipe and allow workers to remove the large rock dam about 30 ft away from the break and formulate and implement a repair strategy. At least two are expected to operate by Feb. 15, as rain and snowmelt will cause higher flows.
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DC Water crews also are excavating two new access pits to support full installation of the enhanced bypass pumping system. «These additional pumps will increase system redundancy and capacity as work progresses,» it said. «It’s expected to take an estimated 4-6 weeks of additional time to get a system in place that will add more, larger bypass pumps in a new location and stabilize the site for heavy machinery to safely begin removing the large rocks and boulders inside the sewer line.»
According to DC Water’s Feb. 15 update, crews are finishing fabrication of the steel bulkhead that will be installed late next week to block flow ahead of the damaged section of pipe. «This will allow crews to safely begin stabilizing the ground around the collapse, remove the rock dam obstructing the interceptor, and initiate permanent repairs to restore normal flow conditions,» it said.
Keeping up with higher flows resulting from snowmelt has added other hurdles, the agency saids, as pumps must be taken offline periodically to clear non-disposal wipes and other debris. That has resulted in several small overflows, including a Feb. 8 incident totaling less than 5,000 gallons. The agency says an earthen dam and a trench system captured and redirected the wastewater back into the sewer system, preventing discharge into the river.
“Until full functionality is restored to the Potomac Interceptor, there remains a residual risk of additional limited overflows,” DC Water said in a statement.
Dean Naujoks, who holds the title of Potomac Riverkeeper, told The Baltimore Sun Feb. 10 that the spill likely exceeds one that had occurred in 2017 on the U.S.-Mexico border, leaking 230 million gallons.
Looking at Future Issues
While some reports estimate the protracted bypass and repair effort will cost at least $10 million, its ultimate effect on DC Water’s infrastructure upgrade initiatives has not been communicated. The agency has touted a ten-year, $625-million program to rehabilitate sections of the Potomac Interceptor, with the area where the rupture occurred among the targeted locations. A quarter-mile away, D.C-based Fort Meyer Construction Corp. has worked since last fall on a $9.6-million project to upgrade an 800-ft segment of the 16-ft-deep interceptor using sliplining methods.
Not yet clear is whether or how the rupture will alter the scope and cost of the long-term upgrade program.
Gadis’s letter said the incident points to risks that U.S. utilities face in reliance on decades-old infrastructure to serve communities and protect waterways. The failure of the 60-plus-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 crediting 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 most significant threats to the Potomac River’s health, and that accountability, transparency and follow-through are essential.”
Belin called on DC Water to release the most recent assessment of pipeline structural integrity, and commission an open investigation into the failure, “including whether warning signs were missed and whether preventative maintenance or upgrades could have averted the disaster.” The agency should also identify and publicly share other known or potential weak points within 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.
Also yet to be determined are the spill’s effects on Potomac River water quality. DC Water says its own testing results show mostly decreasing trends, although E. coli levels are expected to continue fluctuating over time “due to residual impacts from the incident and ongoing influences from weather conditions such as precipitation, snowmelt, temperature variability,» as well as other natural sources of E. coli bacteria such as wildlife.
According to one local report, DC Water says it is working with an outside firm to develop a plan to remediate the area after the pipeline is repaired, but without further detail on the company or cleanup strategy..
The Potomac Riverkeepers Network cited preliminary modelling data from the Maryland Dept. of the Environment indicating that sewage contamination is likely affecting water quality more than 30 miles downriver. Bacteria connected with Staph infections has also been found at one-third of state-run sampling sites. Aside from a ban on shellfish harvesting closer to the Chesapeake Bay, however, Naujoks said no public health advisories have been issued by Maryland, D.C. or Virginia officials.
“They must inform the residents about the grave risks to public health from this sewage spill,” he said.
