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Cone Penetrometer Testing and Monitoring Well Installation Work Plan CALIFORNIA STOP 2224 Manthey Road, Stockton, California 1.0. INTRODUCTION On behalf of Ms. Nhuan (Nancy) Le of California Stop,Advanced GeoEnvironmental, Inc. (AGE) has prepared the enclosed Cone Penetrometer Testing and Monitoring Well Installation Work Plan for the property located at 2224 Manthey Road, Stockton, California(the site). The scope of work includes the advancement of one paired cone penetrometer testing(CPT)soil boring and installation, development,and survey of three ground water monitoring wells for vertical and lateral delineations of shallow petroleum hydrocarbon-impacted soil and ground water in the area of the current underground storage tanks (USTs) and fuel dispensers. The location of the site is illustrated on Figure 1. A plan of the site, including former soil borings and proposed monitoring well locations, is illustrated on Figure 2. This work plan was prepared as required by the San Joaquin County Environmental Health Department(EHD)by letter dated 18 January 2006 for the investigation of an unauthorized release of petroleum hydrocarbons from a former UST system at the subject site. This work plan is in accordance with the Central Valley Regional Water Quality Control Board's (CVRWQCB's) Appendix A to Tri-Regional Recommendations - Reporting, dated 30 August 1991, for the investigation of UST sites. 2.0. BACKGROUND The site is located in a commercial/residential area of south Stockton, immediately west of Interstate 5 and south of West Eighth Street. The site is presently utilized as a gasoline station and convenience store. Three 10,000-gallon USTs and one dispenser island with four dispensers are located at the site. It is our understanding that the USTs were installed approximately in 1991. 2.1. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The site is situated within the Great Valley Geomorphic Province (GVGP) of California, a large, elongate, northwest-trending, asymmetric structural trough. The GVGP 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 Klamath Mountains in the north. The California Coast Range and the Sierra Nevada comprise the western and eastern boundaries of the province,respectively. The thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south central portion of the valley. Older deposits are primarily marine in origin, while the younger deposits are continental. Continental-derived sediments, originating in the surrounding mountain ranges, were typically deposited in lacustrine, fluvial, and alluvial environments (Olmsted and Davis, 1961). Rocks composing the basement Advanced GeoEnvironmental,Inc.