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Limited Environmental Investigation May 21, 1990 <br /> Proposed Unocal Station, Stockton, California AGS 30010-1 <br /> REGIONAL GEOLOGY AND HYDROGEOLOGY <br /> The site is underlain by the Lower Modesto Formation, which is composed of alluvial <br /> sediments that range in size from gravel to silt (Marchand and Allwardt, 1977). The <br /> Modesto Formation dips gently to the west (Wagner, D.L. and others, 1981). <br /> The site is in the northeastern San Joaquin County Ground-Water Basin (California <br />' Department of Water Resources, 1980). According to the San Joaquin Public Health <br /> Service (SJPHS), the regional ground-water gradient flow is to the southwest. The local <br /> ground-water gradient may be influenced, however, by pumping of nearby irrigation, <br /> I� <br /> domestic, and municipal wells. According to the SJPHS, data obtained from measuring <br /> ground-water levels in local wells in the Spring of 1989 indicate that ground water in the <br /> area is approximately 50 to 60 feet below grade. <br /> The site is approximately 1/2 mile north of the Calaveras River (Plate P-1). The <br />» Mokelumne Aqueduct is north of March Lane. The aqueduct is owned by East Bay <br /> Municipal Utility District (EBMUD). We understand from EBMUD that there are three <br /> separate steel pipes within the aqueduct; one is coated with tar and two are coated with <br /> N mortar. <br /> 4 <br /> Applied GeoSystems <br />