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I ' Site Background Information FORMER FISCO 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. The site is bounded on the north and east by the Stockton Diverting Channel, 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/HYDROGEOLOGIC SETTING ' 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- I lying alluvial plain,extending 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 metamorphic and igneous origin. The northern and southern portions of the Great Valley Province have been designated the Sacramento and San Joaquin Valleys,respectively. The Modesto,Riverbank,Turlock Lake Formations and overlying recent alluvium are therinci al P p 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 propertyis the Stockton Diverting Canal located approximately 300 feet north of the site. The Stockton Diverting Canal usually contains little water and has not appeared to have a significant effect upon ground water depth or flow direction in the area; however the canal could be the cause of the significant fluctuation in ground water flow direction and depth at the site. HYDROGEOLOGICAL MODEL Based on the CPT results, AGE has developed a preliminary subsurface model of the site soil stratigraphy comprised of four informal zones, a vadose (unsaturated) zone and three hydrological I units. Hydrological units may be defined as significant vertical intervals of soil having significant lateral extent and having similar hydrologic characteristics (i.e. hydraulic conductivity, transmissivity, etc.) over its vertical and horizontal extent. 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 migration of large contaminant masses over great distances. IAdvanced GeoEnvironmental,Inc I !