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� fk i B. GROUNDWATER S 4 , Groundwater occurs in the area due to the fact that the subject property is underlain by unconsolidated sediments of the Tulare formation of Tertiary and Quaternary aged deposits. The Tulare formation contains the fresh water bearing deposits and is the primary aquifer supplying fresh water to the San Joaquin Valley. This formation is composed of beds, lenses, and tongues of clay, sand andravel of both Coast Range and g g Sierra origins. A predominant diatomaceous clay bed is present within the Tulare f formation. This clay layer, known as the Corcoran Clay member or"blue clay," separates the aquifer into the so-called "confined zone" beneath the Corcoran Clay member and an unconfined or semi-confined zone above the Corcoran Clay layer (Hotchkiss and Balding, 1991). An approximate geologic cross-section extending across the western portion of the San Joaquin Valley from the Coast Range to the San Joaquin River is depicted in Figure 2 (Davis, et, al, 1959). As shown on the cross-section, Corcoran CIay extinguishes near Section 5 of Township 4 South, Range 6 East, indicating probable absence of the confining layer on the subject property. This conclusion is substantiated from the driller's log for the existing production well located on the subject property as indicated on Figure i 4 1. The geologic log prepared by the well driller is shown in Table 1. The well is _ perforated between 180 feet and 500 feet. Changes in groundwater conditions in the 1986 through 1994 period in western.;' San Joaquin County have been recently examined (Stoddard, 1995 . Thiseriod of time P covers the extended drought period between 1987 and 1992. Examination of the response of the groundwater basin provides insight into the sustainability of the groundwater basin, H I STODDARD&ASSOCIATES Assessment of Water Supply Impacts AUGUST 1995 PAGE 3 i