When complete, the $283-million Harry Tracy Water Treatment Plant (HTWTP) improvement project in San Bruno, Calif., will increase the utility's treatment capacity from 10 to 20 million gallons per day (MGD) to as much as 140 MGD -- enough water to supply San Francisco Public Utilities Commission (SFPUC) customers with double the amount of water typically needed.
A key part of the project is the replacement of the existing 6.5-million-gallon and 8-million-gallon treated water reservoirs with a new 11-million-gallon reservoir. Configured much like a donut with a double-wall construction, the new reservoir includes an exterior tank where chemicals are added to the water for final treatment, and an interior tank that stores the treated drinking water.
The interior tank must comply with NSF/ANSI Standard 61 to ensure there is no water infiltration or exfiltration between the two chambers through micro-cracks. Based on its waterproofing capabilities and cost effectiveness, crystalline technology from Xypex was selected by the city of San Francisco and its contractor to waterproof the inside of the 11-million-gallon tank.
Xypex Concentrate and Xypex Modified were applied to the floor, walls and columns of the large inner chamber to stop water migration due to hydrostatic pressure -- a total of approximately 100,000 square feet of concrete. A spray-applied waterproofing membrane was used for the walls of the outer chamber.
Unlike coatings and membranes that depend on their adhesion to the surface, Xypex crystalline waterproofing technology works within the concrete, plugging the pores, capillaries and micro-cracks of the structure with a non-soluble, highly resistant crystalline formation that remains a permanent, integral part of the concrete for the life of the structure.
The application of crystalline waterproofing was completed in September 2014. Construction of the reservoir is scheduled to be completed by February 2015. The reservoir is engineered to withstand earthquakes along the nearby San Andreas Fault. The reservoir must also prevent water intrusion for the length of its life -- a minimum of 50 years.
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