2026 - Repair critical section of Potomac Interceptor near Pennyfield

The Potomac Interceptor (PI) sanitary sewer system includes a significant portion of its length within the Chesapeake and Ohio Canal National Historical Park in Maryland and Washington, D.C. The system, managed and operated by DC Water, was constructed in the 1960s from reinforced concrete pipe. This system, including the municipal sewer systems that feed it, transports sewage from a significant portion of Maryland, northern Virginia, and Washington, D.C. to the Blue Plains wastewater treatment facility. A portion of the PI system lies further upstream in Montgomery County, where it feeds into the main line of the PI after it crosses the Potomac River into Virginia, before crossing back into Maryland.

After recent inspections, DC Water proposes to complete immediate repairs of a short section of this upper system near Pennyfield Lock (Lock 22) in Potomac, MD. DC Water has identified that this area, falling between the parking lot at Pennyfield Lock and upstream County property, requires immediate repair. This pipe will be slip-lined with a smaller pipe comprised of fiberglass-reinforced pipe (FRP) or centrifugally cast fiberglass reinforced polymer mortar (CCFRPM).

On County property administered by Blockhouse Point Conservation Park, DC Water will install suction piping, powered by a number of pumps, to establish a sewage bypass around the area. One 24-inch diameter HDPE pipe will convey sewage along an existing, informal pedestrian trail, then turn east to parallel the PI until it reaches Manhole 410. Sewage will re-enter the PI through an approximately 8x10' discharge pit immediately above MH 410. Through wooded areas, the bypass pipe will require an approximate 10' wide corridor, which will be covered with geotextile separation fabric and mulch to facilitate site restoration.

DC Water will then apply a geopolymer coating to the inside of the pipe at and below Manhole 411. DC Water will then utilize excavated areas adjacent to the gravel access lane to complete slip-lining of the PI system between the two manholes.

Trees, shrubs, and understory plants will be removed where necessary to complete repairs, including for bypass piping and excavation areas. Vegetation material will be cut and removed from the park. The NPS coordinated with US Fish and Wildlife Service on potential impacts to listed species. Because of the urgent nature of needed repairs, the agencies will complete emergency Endangered Species Act consultation and will work with DC Water to incorporate conservation measures during their construction activities. Upon project completion, the NPS will work with DC Water to regrade, restore, and revegetate the site.

All excavation will be completed within the footprint of the existing pipeline so no new ground disturbance will occur. The project will avoid impacting known archeological sites as well as the historic culvert 30 in Muddy Branch. Construction and pipe delivery may temporarily affect visitor use and access, but these impacts will be short in duration during specific work activities. Parking and visitor access will remain open for Pennyfield Lock and Lockhouse 22. DC Water will coordinate with the County on potential closures of the County-owned boat ramp.

All work will be performed by DC Water and/or its designee/contractor within the existing DC Water right-of-way. This work will be permitted under NPS Special Use Permit. Questions about the Potomac Interceptor system and planned repair work can be addressed by DC Water: https://www.dcwater.com/potomacinterceptor.

Work is expected to begin with equipment staging during the week of June 1, 2026.