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�7 i Harding Lawson Associates 6.0 DISCUSSION 6.1 Realonal Hvdroaeoloav The site is on the valley floor, in the north-central portion of the San Joaquin Valley and groundwater .basin at an elevation of approximately 13 feet. This valley 1.� .forms the southern two thirds of the Great Valley Geomorphic Province of California, between the Coast Ranges on the west and the Sierra Nevada on the east. The Great Valley is a northwest-trending asymmetrical to the west synclinal trough filled with as 5 much as 6 vertical miles of Jurassic to Holocene age marine and continental rocks and sediments. This province was formed by the uplift of the Sierra Nevada, and the later uplift of the Coast Ranges, and the concurrent downwarping and subsidence of the sediments of the Great Valley (US GS, 1986). r Review of published geologic literature (USGS, 1959, 1964, 1986 and DWR, 1967), indicates the site is underlain by Quaternary age flood-basin deposits composed of unconsolidated clay, silt, sand, peat, muck, and other organic soils, generally less then 100 feet thick. These deposits are generally of low permeability and restrict the vertical movement of water and well yields. Continental rocks and deposits of Oligocene to Holocene age underlie the flood basin deposits to a depth of approximately 3500 feet. These rocks and deposits comprise primarily the Laguna, Mehrten, and Valley Springs Formations, consisting of a heterogeneous mix of generally poorly sorted clay, silt, sand, and gravel with some beds �{ of claystone, siltstone, sandstone, and conglomerate. These formations form the main a fresh groundwater body of the San Jonquil groundwater basin. Groundwater in these Lformations, in the north end of the basin, is generally of the calcium magnesium bicarbonate type, becoming a sodium chloride type near the topographic axial trough of the valley. T19461-H 13 of 20