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I8 April 1997 <br /> AGE-NC Project No 95-0141 <br /> Page 2 of 5 <br /> I 1993 Evidence of petroleum hydrocarbon soil contamination was detected in soil samples collected <br /> at 40 and 45 feet bsg Furthermore, initial ground water samples detected TPH-g at concentrations <br /> as high as 6,800 pg/l and BTEX at concentrations as high as 1,400 pg/1 <br />' In May 1994, a fifth ground water monitoring well was advanced near the northeast corner of the site <br /> (downgradient of the former UST area) Petroleum hydrocarbons were not detected in selected soil <br /> I samples analyzed Initial ground water samples contained TPH-g concentrations as high as 93 ugll <br /> and BTEX at concentrations as high as 1 3 pg/l <br /> I23 REGIONAL GEOLOGIC SETTING <br /> IThe property is located within the Great Valley Geomorphic Province of California, a large, elongate <br /> northwest trending, asymmetric structural trough The Great Valley Province has been filled to its <br /> present elevation with thick sequences of sediment ranging in age from.Jurassic to Recent, creating <br /> a nearly flat lying alluvial plain, extending from the Tehachapi Mountains in the south to the Klamath <br /> Mountains in the north The western and eastern boundaries of this province are comprised of the <br /> California Coast Range and the Sierra Nevada Mountains, respectively Rocks composing the <br /> basement complex of the province have not been completely defined but are believed to be <br /> metamorphic and igneous in origin The Great Valley Province is subdivided into two major <br /> subdivisions designated the Sacramento and San Joaquin Valleys <br /> 2 4 GROUND WATER DEPTH AND GRADIENT <br /> Based upon review of Lines of Equal Depth of Water Wells - Fall 1993 (published by the San <br /> I Joaquin County Flood Control and Water Conservation District), the water-table surface beneath the <br /> site occurs at a depth of approximately 35 feet below surface grade (bsg) Recent ground water <br /> monitoring events have encountered ground water at approximately 23 feet bsg The uppermost <br /> ground water flows in an unconfined aquifer <br /> Based upon historical ground water monitoring events at the site, the prevailing ground water flow <br /> direction is toward the northwest <br /> I3.0. QUARTERLY MONITORING PROCEDURES <br /> 3 1 MONITORING WELL PURGE PROCEDURES <br /> On 20 February 1997, the depth to ground water in each monitoring well was measured to the nearest <br /> 0 01 foot utilizirig a Solinst water level meter The relative ground water elevations were calculated <br />