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02 May 1996 AGE Project No. 95-0108 Page 2 of 7 2.3. APPLICATION OF BACTERIAL INOCULUM On 03 March 1992, Mr. Eric Trevena, of the PHS-EHD observed that a remedial action was being conducted at the site without the authority of the local regulatory agency: the former UST excavation was filled with water and a bacterial inoculum was then placed into the excavation. The intent of the procedure was to inoculate the soil surrounding the fomer UST excavation with hydrocarbon- degrading bacteria to remediate the area. A Notice To Abate, dated 03 March 1992, issued to Mr. Les Calkins from the PHS-EHD, indicated that Section 2722(b) of the California Underground Storage Tank Regulations states that prior to any corrective action at a UST site, the responsible party shall notify the regulatory agency of the proposed remedial action and comply with any requirements that the regulatory agency sets. The PHS-EHD directed that any unauthorized remedial action be ceased immediately. The PHS-EHD further indicted that the unauthorized corrective action could cause the vertical movement of existing hydrocarbons towards ground water at the site. In response, the bacteria-supplemented water was drained from the former UST excavation. 2.4. GROUND WATER DEPTH AND FLOW DIRECTION Based on the San Joaquin County Flood Control and Water Conservation District map entitled Lines of Equal Elevation in Water Wells, Fall 1993, ground water depth at the site is approximately 55 feet below surface grade (bsg). Regional flow direction in the area of the site is west to southwest. However, flow direction can vary locally and with seasonal changes of ground water depth. 2.5. REGIONAL GEOLOGICAL AND HYDROGEOLOGICAL SETTING The subject site is located in the central portion of the Great Valley geomorphic province of California. The valley is a nearly flat, elongate trough trending northwest and southeast for approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada Mountains on the east and the sedimentary and metamorphic Franciscan Coast Range on the west. The surficial and upper several thousand feet of subsurface layers consist primarily of unconsolidated and consolidated alluvial and floodplain sheet deposits (predominantly sand, silt and clay) of Quaternary age, which is derived from the Sierra Nevada Mountains. Beneath the upper sedimentary deposits lies a thick sequence of marine deposits of Mesozoic age, which in turn are underlain by a pre-Jurassic complex of igneous and metamorphic rock.