Northwest Branch Sewer Inspection and Repair, Washington Suburban Sanitary Commission, Montgomery County, MD

WSSC Emergency Repair

BH provided engineering and construction management assistance for the inspection and repair of a failed 66-inch PCCP. This low-pressure interceptor is one of several major conveyance sewers for the Northwest Branch Sewer Basin.

BH provided an initial engineering assessment of the broken pipe. The contractor’s plan to contain the site was reviewed and modified to ensure high flows were contained within the low-pressure interceptor. The emergency containment design used equipment and materials readily available to the contractor and WSSC sewer maintenance facility.

BH helped WSSC develop contract documents for the $1.5 million line stop, bypass, and line tap/entry port installation project. Both the inspection and the repair work required bypass pumping around the broken section of pipe. The bypass pumping was setup by installing two 66-inch diameter line stops, one at either end of the stretch of pipe to be repaired and inspected. The bypass pumping design called for eight 12-inch pumps to be used to bypass up to a peak flow of 47 MGD. Seven line taps (entry ports) were also installed along the 1,800-foot stretch.

BH provided direct pipe cleaning and inspection services for the 66-inch PCCP through a subconsultant cleaning and televising contractor with large diameter pipe capabilities. The inspection used Redzone technology, which combines CCTV inspection, a laser survey device to map the inside of the pipe, and sonar evaluation of submerged sections that could not be dewatered.

The inspection allowed BH and WSSC to identify the types of materials to be used to repair the pipe and prevent its future decay by hydrogen sulfide. WSSC decided to replace 155 feet of 66-inch PCCP with new PCCP pipe, and to line 700 feet of pipe to repair the line and prevent future deterioration.

The pipe lining used a state-of-the-art PVC liner provided by SekiSui, a Japanese company specializing in spiral-wound pipeline rehabilitation (SPR) liners and with a proven record of successful installations of the product.

This task order also included the inspection of a 48-inch PCCP part of the Northwest Branch conveyance system and a 36-inch PCCP part of the Broad Creek conveyance system directly upstream of the Piscataway Wastewater Treatment Facility, and is located in part under the heavily traveled four-lane Indian Head Highway. BH also provided on-site full time construction inspection for the installation of the line stops, manways, and installation of the SPR PVC liner pipe.