Concrete Cistern Repair
CommTank, Inc. was contracted by a cohousing development in Berlin, Massachusetts to perform an investigation and subsequent repairs on the interior of a leaking 40,000-gallon underground concrete cistern system.
The cistern contains freshwater used to support the fire suppression system for the complex. The owner believed the cistern system had been losing water for approximately 6 years.
To support the fire suppression system while the cistern was offline, CommTank placed a 21,000-gallon frac tank onsite, filled the frac tank from the cistern, and installed a Storz fitting on the frac tank to provide access to the water for the Berlin Fire Department. The client’s fire suppression contractor installed a portable fire pump and connected the portable fire pump to the frac tank.
The cistern system consists of a 10-section concrete box culvert cistern (approximately 77’7” long x 10’wide x 8’ high), a concrete pit (approximately 15’ deep x 3’ wide) under the pump house, and a pipe connection (approximately 3’ wide x 20’ long) between the two. The pipe connection is constructed of corrugated PVC, which is not the preferred material for this application. The cistern system was installed in 2008.
The initial objective was to stop water from leaking out of the cistern system. As the project progressed, it was discovered that groundwater was also leaking into the cistern system. CommTank technicians discovered after emptying the cistern that the water level inside the tank rose to match the groundwater level.
During the course of the project, CommTank consulted with a concrete cistern manufacturer and engaged the services of a remedial waterproofing engineer/contractor to assist.
Each potential or actual source of water infiltration and exfiltration identified had been either patched or replaced with a concrete repair patch (used on inactive sources) or injected with a chemical grout (used on active sources). At the completion of each infiltration repair, it was visually confirmed that water infiltration had not increased at other locations within the cistern system.
The potential and actual sources of infiltration/exfiltration identified included visible cracks, areas of deteriorating concrete and mortar at the penetration of the pipe connection into the cistern and the pit, and circular, patched “depressions/openings” in the wall of the pit, presumably created during the manufacturing process for future pipe penetrations.