Fort Belvoir is a United States Army installation in Virginia founded during World War I, located approximately 20 miles south of Washington D.C. Fort Belvoir operated and maintained onsite wastewater treatment plants until the 1970’s and now discharges wastewater to Fairfax County in Virginia. The original wastewater system remains and one of the plants contains a rectangular settling basin constructed with conventionally reinforced concrete. It is 80’-0” long by 40’-0” wide and approximately 13’-0” in depth. After many years of operation, the settling basin was no longer needed and it was eventually abandoned in place.
In 2009, American Water Military Services took over operations at Fort Belvoir and evaluated the use of the existing settling basin for other purposes. After consideration, it was decided that the existing structure would be better served as a Combined Sewer Overflow (CSO) tank. American Water elected to issue a request for proposal for various options to rehabilitate and retrofit the tank. After reviewing all proposals submitted, DN Tanks was selected based on extensive experience in concrete tank modifications and rehabilitations.
Since the tank had been abandoned for many years, the inside of the tank was overgrown with vegetation and small trees. The first step was to completely clean out the interior of the basin and further evaluate the condition of the concrete structure. Structural repairs were needed on the overhead beams and interior wall. All deteriorated and spalled concrete were removed and replaced with high strength repair materials. In addition, to improve flow through the rectangular channels, a chamfer was installed at the floor wall connection throughout the basin using shotcrete (pneumatically applied mortar).
Once the tank was cleaned out and repairs were completed, the interior was prepared for the application of a high performance elastomeric coating to be applied over the floor and wall. The coating application will provide long-term protection from the wastewater liquid being stored in the tank. Lastly, to improve safety at the facility, a new OSHA compliant handrail system was installed around the perimeter of the tank.
American Water’s sustainable approach to this project effectively repurposed this tank by rehabilitating the existing structure in place and improving operations at the plant. The new CSO tank will serve Fort Belvoir effectively and reliably for many more years.