Roof Replacement for 1 Million Gallon Tank at the City of Williamsburg Water Treatment Plant
Location: Williamsburg, VA
Owner: Mount Carmel Municipal Authority
Engineer: TAM Consultants
Project Duration: 5 months
Daily, people use water without thinking twice about the infrastructure needed to provide the clean water supply that flows from their faucets. The City of Williamsburg, Virginia operates and maintains its own water and sewer system, providing water and sewer service to the entire City of Williamsburg as well as water service to parts of York and James City Counties.
The Williamsburg Filtration Plant is part of the City of Williamsburg’s water system infrastructure. The Filtration Plant is located north of the City in a wooded area off Waller Mill Road (Rt. 713). The Waller Mill Reservoir, a park enjoyed by many for recreation and fishing, is located nearby.
Originally constructed in 1982, the tank is a rectangular poured in placed, reinforced concrete structure approximately 104 feet x 114 feet x 15 feet tall, with a precast pre-stressed concrete double tee roof. Approximately 10 to 12 feet of the tank is below grade. There is a concrete bearing wall down the center of the tank, giving two spans approximately 51 feet long. The wall is discontinuous at each end to provide for water flow. Along the length of the tank are 14 double tees, each 8 feet wide by 25 inches high.
The tank was taken out of service in December 2014 due to failure of the roof membrane as well as deterioration of the original precast concrete roof structure, particularly severe cracking of the double tees along the stems. On a number of the tees, the bottom pre-stressing strands were corroded to the point that they were broken and draped down. Pieces of the concrete stems and debris were lying on the floor at the bottom of the tank. Deterioration of the roof membrane and resulting damage to the concrete roof resulted in a system that could no longer provide potable water to the community.
Since this tank was taken out of service, the City had been using an adjacent water tank to meet their needs. However, due to an increase in water demand, there was a need to put the 1 million gallon tank back into service. City of Williamsburg staff working with a local consulting firm developed a project scope that addressed the repairs needed to place this tank back into operation.
The project scope included the following: