SITE INFORMATION AND CORRESPONDENCE

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Ms. Linda Turkatte December 14, 1995 Page 2 On May 3-5, 1993, three soil borings (MW2, MW3, and MW4) were drilled by RESNA Industries, Inc. to depths of approximately 91 feet below grade. The borings were subsequently converted to groundwater monitoring wells. No petroleum hydrocarbon constituents were detected in any soil or groundwater samples collected from these wells. Topography, Geology, Hydrology The site is situated on level terrain. Soils at the site have been mapped by the U.S.D.A. Soil Conservation Service as Stockton Clay (adobe). Stockton Clay is a fine-textured, dark gray to black clay, deposited by quiescent or slow moving water. The parent material was of mixed origin, but primarily igneous rock. According to the survey some in-place development of this soil has occurred also. The development is a tight clay subsoil and is the result of transport and re-deposition of very fine particles from the top of the soil profile to the subsoil, resulting in a high colloidal clay content and impervious structure in the subsoil. Deeper lithology and site geology is related to the surface soils. The site is mapped by the U.S. Geological Survey as "basin deposits." Basin deposits have lithologic profiles dominated by fine- textured materials. However, intercalating layers of coarser textured materials are common and usually capable of freely releasing water. Municipal water wells drilled in the general area penetrate through alternating clays and sands to a depth of 250 feet or more before intentionally extracting water. The closest surface water to the site is Duck Creek, approximately 0.2 miles to the north. Mormon Slough is approximately 1.5 miles north of the site. The historic high piezometric level of groundwater beneath the site has been reported to be approximately 55 feet below grade (San Joaquin County Flood Control and Water Conservation District, 1986). The most recent groundwater monitoring data collected at the site (May 1995) show groundwater at approximately 72.5 feet below grade. Regional and local groundwater flow is to the north-northeast. Historical groundwater monitoring data are included in Attachment A. Municipal wells seal off the first 250 feet of sediments because the upper zones of saturation do not meet quality standards or do not provide sufficient quantity to be developed (Bulletin 146, California Department of Water Resources, 1967). Therefore, it is highly unlikely the fuel components at this site have affected or will affect drinking water supplies. Evaluation of Site Contaminants Site lithology is shown on Stratigraphic Cross Section A-A', Figure 3. Soil beneath the site consists of interbedded sands, silts, and clays to a depth of at least 91 feet, the maximum depth explored. Reported groundwater levels beneath the site have varied from approximately 55 feet below grade groundze\hendrix\phs1295.jp1