Principio Interceptor 1000pxMRA developed the Technical Memorandum for replacement of the Charlestown Main Pump Station to serve the newly delineated Principio Sanitary Sewer Subdistrict. Based on the recommendations of the Memorandum, MRA designed the sewage pumping station with an initial capacity of 2,280 gpm (3.28 MGD) to serve the 0- to 15-year projected growth, capable of a capacity upgrade to 3,228 gpm (4.65 MGD) to serve growth beyond 15 years. The project is comprised of a three-pump station, 4,500 LF of 16-inch force main, and 2,118 LF of 10- to 21-inch gravity sewer. The existing station, built in the mid 1960s, with a capacity of 575 gpm, will be decommissioned and dismantled. A portion of the project was within the Chesapeake Bay Critical Area and the 100-year floodplain and required wetland mitigation. Installation included a crossing of Amtrak Railroad and MD Route 267 by bore and jack method.

Some unique challenges encountered by this project include developing a sequence of construction and testing to facilitate the transition from the existing to new sewage pumping station with consideration of three influent collector sewers without interruption of service, as well as developing the system curve, and pump and control selection to be hydraulically compatible with common use of an existing 24-­inch force main from the County’s main pump station to the wastewater treatment plant.