Westside Groundwater Basin Conjunctive Program:
This program involves the coordinated use of groundwater, imported surface water, recycled water and storm water in the Westside Groundwater Basin by the cities of Daly City and San Bruno, Cal Water (South San Francisco) and the SFPUC. In normal and wet years SFPUC surface water would be used “in-lieu,” or instead, of pumping groundwater. Reducing such pumping would increase the volume of groundwater in storage available during dry years or an extended drought. Total available aquifer storage is approximately 75,000 acre-feet. As originally scoped in 2002, the program only included funding for hydrogeologic feasibility studies. Hydrogeologic studies since 2002 indicate that the program is feasible. Thus, the program now also includes an approximate (ten) 10 new groundwater production wells, estimated to be 600 feet deep, in San Mateo County to allow for increased groundwater production during a drought or an emergency. Well pump stations, disinfection units, and piping are assumed. Additional funds are also to cover stormwater reinfiltration projects in Daly City and San Francisco that would increase basin yield and reduce flooding from the Vista Grande Canal to Lake Merced. Projects for stormwater reinfiltration that are being considered include (1) Realignment of the Vista Grande canal to provide additional flood capacity, promote stormwater infiltration and create wetland and riparian habitat as potential environmental impact mitigation for other WSIP Projects; (2) Stormwater Pretreatment (Continuous Deflection System); (3) Recharge of the Westside Groundwater Basin and maintenance of lake levels by routing a portion of Daly City/Vista Grande Stormwater into Impound Lake portion of Lake Merced; and (4) Construction of infiltration basins in Daly City. The SFPUC would contribute up to 50 percent for design and up to 80 percent of construction cost for projects that result in cost efficient recharge of the Westside Groundwater Basin. This project also supports the development of a groundwater basin computer model.
Local Groundwater Project:
The project will update and adopt the Groundwater Management Plan for North Westside Basin, including construction of groundwater wells that can be pumped as emergency and regular supply in the Sunset District and near the Lake Merced Pump Station; and installation of a groundwater monitoring well network in the Sunset District and along the Great Highway to assess baseline conditions prior to further groundwater development. This project provides for approximately six (6) new groundwater production wells. Well pump stations, disinfection units, and piping are assumed. In addition, this program includes development of supply wells in the Upper Islais Creek Basin/Alemany Area for irrigation, environmental restoration, and limited reduction in flooding.
Restore Lake Merced Water Levels:
This project will result in the restoration of Lake Merced water levels using a supplemental source(s) of water (treated storm water, recycled water, groundwater or SFPUC system water). An interim and long-term water level elevation range will be established. New tasks include: (1) Needed upgrades to the Lake Merced Pump Station to improve the method for adding dechlorinated system water and groundwater to the lake: (2) New instruments for measuring and reporting lake levels; (3) New bathymetry and shoreline surveying; and, (4) New studies at the Pacific Rod and Gun Club evaluating potential need for cleanup of residual lead shot prior to raising lake levels further.
Contact Suzanne Gautier at (415) 554-3204 or via email at sgautier@sfwater.org
The latest data on Lake Merced's groundwater and Lake levels are now available. The SFPUC has been measuring groundwater levels and Lake Merced water levels to better understand their interrelationship. Data are being collected for several reasons, including restoration of lake levels, future planned groundwater development in the Sunset District and to study a pilot groundwater banking project with the City of Daly City. Water levels are collected daily to weekly, depending on the location.
