--> Abstract: Hydrogeology of the Santa Teresa Sub-Basin, Santa Clara County, California, by J. A. Oberdorfer; #90958 (1995).

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Abstract: Hydrogeology of the Santa Teresa Sub-Basin, Santa Clara County, California

June A. Oberdorfer

The Santa Teresa sub-basin lies at the southern end of the northern Santa Clara Valley basin, in the city of San Jose. The sub-basin consists of a tectonic valley bounded to the east and west by low-permeability bedrock. The valley is filled with between 250 and 400 feet of alluvium, deposited primarily by Coyote Creek which flows in from the south. The local Canoas Creek and the Guadalupe River to the northwest have also contributed alluvial and fluvial sediments.

These heterogeneous alluvial deposits have been separated into at least five water-bearing zones which average 15 to 30 feet in thickness. Hydraulic conductivities for the main water-bearing zones range from 1,000 to 2,000 ft/d for the sandy and gravelly aquifer material, and well yields are from 200 to over 1,000 gpm. The A-aquifer is perched and unconfined, discontinuous, and considerably less transmissive. The B-aquifer varies spatially and temporally between confined and unconfined. The B-aquifer and deeper confined zones are hydraulically connected in spite of what appear to be laterally continuous clayey aquitards.

Recharge occurs primarily from underflow through Coyote Narrows to the south, from stream bed and artificial recharge pond seepage along Coyote Creek and the Guadalupe River, and from precipitation and applied water. Discharge is from underflow out at Edenvale Gap to the north, and from pumpage of groundwater for municipal supply and for cleanup of contaminant plumes. During the mid-1980's the basin was experiencing serious overdraft conditions. These were due to extensive pumpage as part of the cleanup at the IBM and Fairchild Superfund sites and due to reduced artificial recharge during extended pond maintenance. Significant reductions in pumpage and a return to use of the recharge ponds has reversed the falling water level trend, and water levels are currently close to where they w re at the beginning of the 1980's.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California