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Groundwater supplies Zone 7's service area overlies the Livermore Valley Groundwater Basin which extends from Pleasanton Ridge east to the Altamont Hills and from the Livermore Uplands to the Tassajara Uplands. The portion of the Livermore Valley Groundwater Basin that contains the high-yielding aquifers and good quality groundwater is called the Main Basin which lies mostly beneath Pleasanton. The Main Basin has an estimated capacity of 254,000 AF (Acre Feet) and receives natural recharge through percolation of rainfall, natural stream flow, and irrigation waters, and inflow of subsurface waters. This natural recharge is considered the long-term natural sustainable yield of the basin. Zone 7 uses the Main Basin as a storage facility and not a source of long-term water supply because Zone 7 only pumps groundwater it has artificially recharged using surface water supplies. Zone 7's policy is to maintain groundwater levels above historical lows in the Main Basin through its artificial recharge operations. During high demands, groundwater is used to supplement water supply delivered. Ground water is also used when the State or Zone 7 are shut down and performing maintenance activities. The Main Basin is a key component of Zone 7's drought and emergency management efforts to manage water supplies locally. Finally Zone 7 pumps groundwater out during normal wet years to help reduce the salt loading in the Main Basin. Ground water is very important to Pleasanton as a supply and from a water quality perspective as it contains more salt than surface waters. Pleasanton also pumps groundwater from the basin as part of our allotment, 3,500 AC/Ft a year which is approximately 15 to 20% of our total demand. The graphs below provide a history of Main Basin groundwater capacity and storage. Page 5 of 10