ARCHIVED REPORTS XR0012690 - Laserfiche WebLink

Home Browse Search

P - - d 21 fi — Wr G.r_ WESTERN GEO-ENGINEERS Ground water production in this region is predominately from the Tulare Formation a non-marine (continental) sediment deposit of Pilo-Pleistocene age, The Corcoran Clay Member of the Tulare Fm., represents a lacustrine (lake bottom) deposit of diatomaceous clay which divides the upper third of the Tulare Formation from the lower two thirds. Overlaying the Tulare Formation are the younger {pleistocene to Recent) flood basin, alluvial fan and stream channel deposits. f�nderlaying the Tulare Formation a sequence of older (Miocene thru Cretaceous) marine To the sedimentary deposits which contain conate water too brackish for any use• ar west, in the Coastal Range foothills, the Tulare Fm. outcrops against the older undifferentiated marine Cretaceous formations. This unconformity produced by the Coast Range uplift and subsequent subsidence of the San Joaquin Valley created the northwest trending Black Butte Fault, marking the boundary Ranges and the Great Malley provinces. of the Coastal Ground water recharge to to younger surface to near surface de above the Corcoran .. deposits an srts ' cls i A situated ua to red d downdip along the less permpeabenlayers. The Corcoran clay farms somewha ofeakage and lateral movem n a barriei to the sediment deposits found below it and recharge is presumably slower; by lateral movement downdip from the outcrop areas to the west and southwest along the Coastal Range foothills, by slow leakage from the above clay and by more rapid movement vertically beyond the limits of the clay. The direction of free ground water movement in this region ,tom northeast from the Coastal Ranges towards the San Joaquin River tote north and the east an the Sacramento - San Joaquin Delta to the north { see figure 5a ). Athe present intrusion of waters from the Delta has not occurred in the Tracy area as it has in Stockton area (see figure 5B), the z SECTION 3.1 r . LOCAL. GEOLOGY AND HYDROGEOLOGY The Tracy area is built upon flood plain/basin deposits of brown clayey slit. Intermixed with and underlying the flood plain deposits are stream channel deposits consisting of silty sand, sand, and sandy gravels with occasional clay layers and Clay lenses. The channel deposits do not seem to be continuous between wells in the area, indicating a braided and/or meander type deposition. A shallow aquifer exists at approximately 10 to 15 feet below the surface (12 feet below the surface of the site) in the Tracy area. Chloride ion and resistivity measureme,its of this aquifer (from the monitor wells on the site) indicate this water to be slightly brackish; chloride ion ranges between 350 and 500 ppm and resistivity values range from 5.39 to 6.61 ohms/meter 2/meter. l flow and gradients of this aquifer are influenced by recharge and d scharge €rromctions local irrigation and construction and/or leaks and breakage of the_local_water_and-sewer linas.__But,_the-general-flow-direction-shoLld-be-to fhg north with a relativel ------ ------------ gradient (see figures 5A and 5B). y flat page 9