ARCHIVED REPORTS XR0011739 - Laserfiche WebLink

Home Browse Search

Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 2 ft Following closure of the Olympian Service Station, the Navarras contracted with Dietz Irrigation, an experienced contractor holding a general engineering contractor's license with hazardous waste endorsement, to remove four registered underground fuel storage tanks that had been in use by the fueling station at the time it ceased operation. Those tanks were removed from the site on December 9, 1998 under the permit and oversight of the SJCPHS. r Work to remove the underground piping from the area of the tank pit and dispenser islands of the former filling station revealed the presence of an additional four abandoned, underground storage tanks of considerable age. Those four tanks were removed on December 28, 1998, also under the permit and oversight of the SJCPHS 1.4 Geology and Hydrogeology The subject property and the surrounding area are situated on level terrain on the distal, northern slope of an alluvial fan. The underlying alluvial sediments are of Quaternary to k . Recent age. The site and the immediately adjacent property along the south side of West Eleventh E Street and the west side of Chrisman Road have been extensively excavated and backfilled during prior filling station construction and remodeling, utility installation and highway expansion. The first several feet beneath the surface of the site is composed of multiple layers of < bituminous macadam, concrete slabs and random fill. Beneath the paving and fill the soils are composed of clays, silts and sands that are complexly inter-bedded. These materials have been deposited in a complex lenticular form composed of relatively low permeability clays and silty clays inter-bedded with permeable silts and sands. The sizes of individual permeable lenses vary from relatively large features having considerable areal extent to small, localized lenses of limited extent and thickness. These lenses may or may not merge into each other to form semi-continuous permeable strata within the less permeable clayey material. The depth to groundwater beneath the site varies seasonally between 8 and 11 ft. Regionally, the direction of groundwater flow is to the north toward the Old River anastomosic branch of the San Joaquin River, the closest tributary of which, the Tom h :l Paine Slough, is one and one-quarter miles north of the 7500 West Eleventh Street site. (U.S. Department of the Interior, Geological Survey 1978) However, locally, the shallow groundwater gradient tends to follow the topography, which, at the subject property, slopes gently to the north-northeast. (U.S. Department of the Interior, Geological Survey 1978, 1981) The local direction of groundwater flow can also be affected by the local sedimentary geology, particularly where continuous or semi-continuous sand strata provide flow channels in generally lower-permeability deposits of clayey materials. sic