RAS Pump Station No. 2 Rehabilitation and Coatings

Project Description

As part of the Phase II Wet Weather Improvements Project at the P Street Wastewater Treatment Plant, the existing influent pumping station for the P Street Plant was to be recommissioned as a second Return Activated Sludge (RAS) Pump Station, RAS Pump Station No. 2, for three converted secondary clarifiers. Once the influent pump station was taken out of service, an inspection of the structure was conducted by Hawkins-Weir prior to completing the conversion to a RAS Pump Station. The inspection revealed significant sulfide corrosion on the concrete and steel members located in the pump station’s wet well. The original pump station was constructed in 1965, and did not include any protective coatings or surface treatments.

During this same time period, an inspection was performed on the Sludge Storage Tank that is used to temporarily hold sludge before the dewatering process. This inspection was prompted due to failures of process piping located inside the tank. Unlike the RAS Pump Station No. 2, the Sludge Storage Tank included a 100% solids epoxy coating with its original construction in the early 1990’s. However, the tank inspection revealed localized pinhole failures from apparent concrete outgassing along with failures at the support column drop panels. An evaluation of the RAS Pump Station No. 2 and the Sludge Storage Tank was performed and the recommended remedial measures for both structures was for rehabilitation of the concrete and installation of a 100% solids Fiber Reinforced epoxy topcoat. The rehabilitation of these structures included the removal of all deteriorated concrete and failed coatings by abrasive blasting. The existing concrete was then resurfaced with a cementitious repair mortar. The repair mortar was followed by a prime coat to reduce the potential for concrete outgassing. A surfacing epoxy was then applied to create a surface profile for the 100% solids Fiber-Reinforced Epoxy topcoat.