Chain Wall Installation at Wastewater Treatment Plant
Our staff got an opportunity to tackle a new type of fuel storage tank installation for the Town of Hull in Massachusetts this fall. The town’s concern about protecting the backup generator system from rising sea levels and coastal flooding prompted them to replace the 40-year-old underground storage tank with an aboveground storage tank mounted on a chain wall. A chain wall is an elevated foundation that helps to keep structures above flood level. The chain wall is also known as a stem-wall foundation and was purchased as a pre-cast concrete form. In 2013, the plant had seen an abnormally high volume of water enter the basement which ultimately resulted in taking the treatment plant off-line. As part of a planned upgrade the town hired CommTank to install the new flood resistant system. The scope of the project included providing a temporary tank, fuel filtering, excavation, cleaning and removal of UST, installation of chainwall and AST, upgraded piping between the AST and day tank, upgrades to day tank and addition of overflow tank.
This video summary shows the installation of the chainwall and tank.
CommTank started the project by installing a temporary 3,000-gallon aboveground storage tank (AST). The temp tank was installed to provide fuel while the underground storage tank (UST) was being replaced with a permanent above ground tank. Piping was installed and insulated. Fuel was filtered and transferred from the UST to the AST. When the fuel transfer was complete, the UST was entered and cleaned. CommTank crews excavated and exposed the UST. The UST, groundwater monitoring well, vent, fill port and the pad at grade were removed and properly disposed of.
The project required the compaction of the excavation and testing by a geotechnical technician. When the compaction levels were confirmed, CommTank crews placed 2” of crushed stone on top of the fill. The compaction of the backfill material was very important as this area was the planned site of the permanent aboveground fuel storage tank and its associated slab. A crane was used to install the double-wall Fireguard aboveground tank on to the chain wall and crews secured it with steel straps to concrete anchors.
CommTank crews installed supply piping from the new Fireguard tank to the existing 100-gallon day tank. We also installed a new overflow tank that included a pump. The overflow tank was needed because the day tank did not have a return pump. It was required because the level of the underground tank was below the day tank. Since the new Fireguard tank sits higher than the day tank, an overflow tank will now pump any fuel not used by the generator to the Fireguard tank. All external piping was primed, painted and covered with fiberglass insulation. The 100-gallon day tank was cleaned, inspected and tested before being placed back in service. Fuel from temporary tank was transferred into the 3,000-gallon AST and the generator maintenance vendor tested the system at startup.