North Peninsula cities rethink use of groundwater

For years, cities between San Bruno and Daly City have used groundwater to supplement the drinking water they get from the Hetch Hetchy system.

For some customers, it’s a crucial source — San Bruno gets about half its water supply from the aquifer.

Now, several cities in northern San Mateo County are considering a new strategy for managing the Westside Basin, the huge underground aquifer stretching from Golden Gate Park to Burlingame that supplies drinking water, along with irrigation water for golf courses and cemeteries in the area and the water in Lake Merced.

Under a proposal from the San Francisco Public Utilities Commission, cities would reduce their groundwater pumping in wet years to allow the basin to recharge. The cities would get an extra allotment of surface water from the Hetch Hetchy system, which is owned and operated by San Francisco, to make up the ­difference.

Then in dry years, the cities would pump extra groundwater from the aquifer with the help of 16 new wells built by the utility, part of a $4.6 billion upgrade to the Hetch Hetchy system.

Eventually, the reduced pumping would allow the aquifer to store 20 billion gallons of water — more than the entire Crystal Springs Reservoir — and allow up to 7.2 million gallons to be used per day for more than seven years during a dry spell, SFPUC spokesman Tyrone Jue said.

Officials say shifting how the groundwater is used — along with other efforts such as conservation and using recycled water — will help diversify the region’s sources, making it less reliant on water from the Sierra Nevada.

“I think that’s in everybody’s interest to maintain it as a viable resource moving forward,” said Patrick Sweetland, the water and wastewater resources director for Daly City.

To guide the management of the aquifer, the cities and other agencies have begun developing a formal groundwater management plan.

Officials are hoping to produce a final report later this year.

Retaining water

Groundwater from the Westside Basin makes up a large percentage of the water supply for some cities in northern San Mateo County:

San Bruno: 50 percent
Daly City: 40 percent
South S.F., Colma and Broadmoor: 15 percent

For more information, visit www.southwestsideplan.com

sbishop@sfexaminer.com

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