Roughly 20 percent of Zone 7’s water supply is available from
water that exists below your feet in what’s called a groundwater
basin. We are fortunate that sands and gravels deposited
millennia ago in our valley provide space between the rock
particles for water molecules to sit. If you’ve ever seen water
disappear into the soil, you have witnessed groundwater recharge.
Annual rainfall, as well as flow in local streams, help to
replenish the groundwater that has been used the previous year.
This replenishment is called “groundwater recharge.” Not all
soils are conducive to allowing water to infiltrate, which is why
you may see areas that pond water after a rain. Just because
water ponds does not mean there isn’t a groundwater basin below
an area. It simply means that surface water may not be able to
seep down to recharge lower layers in that area.
Many of the soils in the valley do allow water to seep down to
lower layers (called aquifers) and continue to filter down into
even lower levels of the groundwater basin. The groundwater basin
is made up of several aquifer layers. Once the water makes its
way down to these lower aquifer layers, wells can be drilled that
allow the water to be pumped out and used.
Prior to the 1960s, the Livermore Valley Groundwater Basin had
been overused and water had been significantly drained from the
aquifer layers. Agreements with the State Water Project (run by
the California Department of Water Resources) provide not only
surface water through the South Bay Aqueduct to our drinking
water treatment plants, but also provide turnouts from the
aqueduct that allow water to be routed into local streams to help
replenish the groundwater basin through the process of what we
call “artificial groundwater recharge.” Zone 7 has been actively
managing the groundwater basin since the agreement with the State
Water Project became effective.
The graphic below shows you that the basin was being pumped
heavily in the early part of the 20th century as population
growth and agricultural uses were happening in the valley. The
descending line shows that water levels in the basin were
dropping drastically (called “overdraft”) until Zone 7 started
importing water from the State Water Project to recharge the
basin and allow water levels to recover. For more information on
how the State Water Project imported water is used, see water reliability.
In addition to Zone 7’s use of the groundwater basin, two local
water retailers also have municipal wells that extract
groundwater for use. In order to maintain the more recent
operational range (shown in the gray box of the graphic), the
local water retailers have maintained a consistent, contractual
groundwater pumping quota (GPQ). This GPQ represents the amount
of water naturally stored in the groundwater basin from rainfall
that could be pumped for use in any given year. Retailers with
wells and those operated by Zone 7 aim to only pump water that is
naturally recharged from rainfall or has been “stored” as a part
of artificial recharge efforts. For more information on other
water banking programs see Banking for non-rainy
days.More detailed information about how Zone 7 sustainably
manages the groundwater basin is described in our Sustainable
Groundwater Management and SGMA section.
In 2014 California enacted the Sustainable Groundwater Management
Act (SGMA) where the legislation designated Zone 7 Water Agency
as the exclusive Groundwater Sustainability Agency (GSA) for
groundwater basins within its boundaries. Zone 7 has a role in
all or portions of three groundwater basins. The Livermore Valley Groundwater
Basin (DWR 2-10) spans the central part of the valley and
portions of the basin exist under the cities of Dublin,
Livermore and Pleasanton. The community of Sunol has a separate
groundwater basin (DWR 2-11), further described below. A smaller
corner of the San
Joaquin Valley basin (DWR 5-22.15)lies within the
northeastern edge of the Zone 7 boundary. In the San Joaquin
Valley Basin, Zone 7 has executed an MOU with the San Luis and
Delta-Mendota Water Authority (SLDMWA) to support SGMA
compliance, and a GSP for that basin is anticipated in January
Sunol Valley Groundwater Basin (DWR 2-11)
This water basin is designated as very low priority and is not
currently a part active SGMA planning; however, Zone 7 continues
to act as the basin’s manager and is gathering information for
the eventual groundwater sustainability plan for this basin.
The Sustainable Groundwater Management Act
(SGMA) of 2014 requires local and regional agencies to
develop and implement Groundwater Sustainability Plans (GSPs).
These plans are detailed roadmaps for how groundwater basins will
reach long-term sustainability to ensure these valuable resources
are available when we need them.