Dewatering and Reinjection System Design Prevents Ground Water Intrusion
Water intruded into the lower floors of the Ohlone College campus buildings in Fremont, California at various times of the year. Weiss noted several springs on campus suggesting that it was caused by a high ground water table. Weiss Associates conducted investigations of the hydrology of the campus to apply an engineered solution to the water intrusion problem. In the process of evaluating the hydrology, Weiss Associates prepared a monitoring plan, installed the necessary wells, and carried out monitoring over both wet and dry seasons. The information from the monitoring was combined with geophysical survey results to achieve a complete picture of the surface and ground water hydrology of the campus area. As part of the investigation, continuous core sampling and geophysical logging was conducted in wells in strategic parts of the campus. This information was combined with seismic p-wave and s-wave velocity data derived from four intersecting lines on the campus to produce a comprehensive understanding of both the hydrology and the governing geological features, including the location of the Mission Fault on campus and any effect it might have on ground water flow.
Weiss Associates developed a sustainable design that is effective in stopping the ground water intrusion. The resulting system uses solar panels for its power, and gravity siphoning to keep power requirements to a minimum. The control system uses a model of the hydrology to ensure the amount of water extracted will avoid flooding the buildings, but be as high as possible to maintain as close to traditional water table levels as possible. The water is re-introduced into the aquifer in the down slope part of the campus beyond any building foundations. The disruption to campus activities was kept to a minimum by using horizontal directional drilling. Over the years, the system has proven to be robust and cost-effective.
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