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-rr 20 October 1999 AGE-NC Project No. 99-0645 Page 2 of 5 the soil collected at the southern and northern end of the former Tank#1 excavation indicates that an undetermined mass of MTBE remains at the site. The scope of work is based on the detection of this mass of MTBE and other petroleum hydrocarbons. The removal of soil from these areas would reduce the documented MTBE mass, if sufficient soil is removed from the impacted areas. Approximately 150 yards of soil were excavated during removal of the USTs, sampled and then replaced into the excavation. 2.3. SITE HYDROGEOLOGIC CONDITIONS The closest surface water feature to the site is the Calaveras River (Diverting Canal) is located approximately 10,500 feet Southwest of the site. Water from drains into the San Joaquin River Deep Water Channel and is primarily used for commercial, agricultural and recreational boating. Based upon well information obtained from nearby sites and well data collected from San Joaquin County, ground water flow direction is northeasterly and is currently estimated to occur at a depth of approximately 90 to 100 feet below surface grade (bsg). 2.4. REGIONAL GEOLOGIC CONDITIONS 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. 3.0. SCOPE OF WORK Based on the laboratory analysis of soil samples collected and field observations noted during UST removal, petroleum hydrocarbon impacts to soil were located in the former TK41 UST area. The proposed interim soil remediation scope of work will include the following tasks: Advanced GcoEnN ironmenial,Inc.