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15 July 1999 AGE-NC Project No. 98-0504 Page 2 of 5 up to 190 mg/kg. Analytical results of soil samples collected during the UST removal are summarized on Table 1. 2.2. REGIONAL GEOLOGIC AND HYDROGEOLOGIC SETTING The site is situated within the Great Valley Geomorphic Province of California, a large, elongate northwest tending, asymmetric structural trough. The Great Valley Province has been filled with thick sequences of sediment ranging in age from Jurassic to Recent, creating a nearly flat lying alluvial plain, which extends from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively. Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origin. The Great Valley Province has been subdivided into two major divisions identified as the Sacramento and San Joaquin Valleys. The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. The estimated depth to ground water at the site is 40 feet below surface grade (bsg) based on information from Lines of Equal Depth of Water Wells Fall 1996, published by the San Joaquin County Flood Control District and Water Conservation District (FCD&WCD). The map shows the site to be in an area where ground water flows toward the northeast, but this may be modified by changing recharge and discharge patterns. Ground water is currently encountered at 23 feet bsg in ground water monitoring wells located approximately 350 feet west of the site. The ground water flow direction is toward the northeast and the site elevation is approximately 5 feet lower than the subject site. 3.0. SCOPE OF WORK AGE proposed re-excavation of the UST area to remove the initial overburden material and a limited volume of soil as part of an over-excavation procedure for the installation of two new USTs on the site and to allow for the remediation of the petroleum hydrocarbon-impacted soil at the western end of the site. Advanced GcoEnv ironmental,Inc.