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' Site Background Information Former F1SCO WAREHOUSE (Howard Lenz Property) ' 1648 Shaw Road, Stockton, California ' The site is located in a commercial area of low topographic relief in east Stockton, California, at an approximate elevation of 25 feet above mean sea level (MSL). The site is bounded on the north and east by the Stockton Diverting Canal, on the west by State Highway 99, and on the south by Shaw ' Road. Golden West Irrigation, an agricultural irrigation supply and distributing facility, presently occupies the property. ' REGIONAL GEOLOGIC/HPDROG O OGE L ICSETTING ' The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, northwest-trending, 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 that extends from the Tehachapi Mountains in the south to the Klammath 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 origins. The northern and southern portions of the Great Valley Province have been designated the Sacramento and San Joaquin Valleys, respectively. The Modesto, Riverbank, and Turlock Lake Formations and overlying Recent alluvium are the ' principal source 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 nearest surface water feature in the vicinity of the property is the Stockton Diverting Canal, located ' approximately 300 feet north of the site. The canal could be the cause of the significant fluctuation in ground water flow direction and elevation at the site. ' HYDROGEOLOGIC MODEL ' Based on cone penetrometer(CPT) results,AGE has developed a preliminary subsurface model of the site soil stratigraphy consisting of four informal zones: a vadose (unsaturated) zone and three ' hydrologic units. Hydrologic units may be defined as significant vertical intervals of soil having broad lateral extents and similar hydrologic characteristics (i.e. hydraulic conductivity, transmissivity, etc.) over its vertical and horizontal expanses. A `flow unit' may be defined as a ' hydrologic unit, and is characterized by significantly greater hydraulic conductivity values than overlying and underlying units. A flow unit is capable of serving as a preferred migration route, and could potentially allow the migration of large contaminant masses over great distances. ' The model presented is interpretational and will be modified as more data is collected. The four . vertical zones identified are as follows (depths are approximate and can vary by several feet across 1 ,Advanced GeoEnvironmental,Inc I