Stormwater Retention for NPDES Permitting and Irrigation Re-use in an Earthquake Prone Area

A 10,000 gallon RainSpace Retention Chamber was installed under the driveway of an existing residence in Alameda, California to meet local stormwater management requirements and also collect stormwater for re-use for on-site irrigation. Alameda is a low-lying flat island on the eastern side of San Francisco Bay that is fully developed with commercial, industrial and residential properties. The area presents unique soil and water table issues as the tidal waters of San Francisco Bay create a very high, fluctuating water table level under the ground surface. Flood control, stormwater run off, basement flooding and water pumping present unique challenges for construction and development in the area. This RainSpace Retention Chamber was installed with a water table drain underneath the unit to eliminate any possibility of buoyancy during times of extreme high water table levels. The water table drain flows to a pump sump that also collects flood water from the basement and paved surface areas and delivers it to the RainSpace; rainwater is collected from the roof surfaces and also routed to the water retention chamber. The water stored in the RainSpace is used to irrigate the landscaping on the property. Other important considerations of the owner were the ability of the RainSpace Retention Chamber to carry the vehicle traffic and parking on the driveway and its earthquake proof characteristics to ensure an independent water supply in this seismically active area. The RainSpace installation was done by a general building contractor for his client.

Alameda, California