Water Resources Division Annual Report - Fiscal Year 2017-18 WaterResourcesAR-FY17_18 | Page 6

Local Water Supplies
For the past decade, the SFPUC has been implementing a Local Water Program. This Program provides
conservation assistance, promotes recycled water to meet the City’s most significant irrigation needs,
mandates non-potable supplies for toilet flushing in new developments and develops local groundwater to
enhance the City’s drinking water supply sustainably now and into the future.
GROUNDWATER MANAGEMENT PROGRAM
As surface water, such as rain, seeps into the ground,
it passes between soil particles and collects in
underground reservoirs called aquifers. An aquifer is
made up of sand, silt, or other permeable materials
that can readily yield water to springs or wells.
Our groundwater supply comes from the 45-square-
mile Westside Basin, a series of aquifers extending
from Golden Gate Park in San Francisco southward
through San Bruno. Well depths range from 270
to 700 feet below ground. Since groundwater is
stored deep underground, it has the dual benefits of
being less vulnerable than surface waters to direct
contamination and being naturally filtered through
layers of soil and rock.
The basin is a vital local resource for San Francisco
and neighboring communities in San Mateo
County. To make sure the SFPUC responsibly and
sustainably manages and protects the Westside
Basin, monitoring of the groundwater quality and
its water levels is one of our top priorities. A series
of monitoring wells were installed in 2004. We
collect data from these wells to assess how the
groundwater basin responds to our operations. This
allows us to adapt our groundwater pumping, if
necessary, in response to changes in the aquifer.
Groundwater is an essential part of the state
and nationwide water supply. Eighty percent
of Californians depend on groundwater for all
or part of their drinking water supply, and have
been doing so for generations. Our Groundwater
Program includes two projects: the San  Francisco
Groundwater Supply Project and the Regional
Groundwater Storage and Recovery Project.
Together, these projects increase our local and
regional water supply reliability, diversify our water
supply portfolio and reduce our dependence on a
single source, making us less vulnerable to disrupted
service from drought and natural disasters such as
earthquakes and other challenges.
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San Francisco Groundwater
Supply Project
The San  Francisco Groundwater Supply Project
is a forward-looking project that allows us to
supplement our drinking water sources by blending
a small amount of groundwater with water from the
Regional Water System.
The SFPUC has begun ramping up to blend an
average of up to 1 mgd of groundwater in the coming
year to our water supply. Over the next several years,
we will incrementally build up to an average of
4  mgd of groundwater in San  Francisco. For more
information about groundwater, or to view our water
quality reports, visit sfwater.org/sfgroundwater.
Regional Groundwater
Storage and Recovery Project
The Regional Groundwater Storage and Recovery
Project is a partnership between the SFPUC,
the California Water Service Company (serving
South San  Francisco and Colma), the City of
Daly City and the City of San Bruno. This project
is a sustainable, conjunctive use project that has
storage and recovery components. During years
of normal or heavy rainfall, the project will provide
additional surface water from the Regional Water
System to the partner agencies to reduce the
amount of groundwater pumped from the South
Westside Groundwater Basin. Over time, the
reduced groundwater pumping will result in natural
recharge and increased storage of up to 20 billion
gallons. The stored water will serve as an additional
water supply during a drought. Construction of
Phase  1 of the project, consisting of installation of
13 production wells, will be completed in 2019. The
project has been in a storage phase since May 2016,
and during this phase the groundwater levels have
increased by approximately 20 feet.