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Ms. Lori Duncan July 26, 2006 Page 2 of 6 Site History On February 1, 1965, Chevron entered into a ground lease with Myron Zimmerman for the property located at 434 East Miner Avenue in Stockton, California. Chevron subsequently constructed a retail service station on the property. Mr. Zimmerman sold the property to Sutter Office Center on August 22, 1980. The ground lease was terminated effective November 30, 1980. Chevron agreed to remove all improvements above and below ground with the exception of the fence, light fixtures and poles, sign footings,concrete slabs at grade, paving, sidewalks,curbs,gutters,and planters. According to the San Joaquin County Assessors Office, a Chevron gasoline service station operated on the property from 1935 until 1941 (assumed address of 448 East Miner Avenue). A cab car service operated at the same address from 1942 until 1958. Continental American Bus Lines also operated a depot from 1950 until the late 1960s. Four 500-gallon underground storage tanks were used through 1960. The tanks were reportedly filled with sand and abandoned in place in the 1960s. Previous site investigation activities have included the advancement of ten soil borings (A through H), five CPT borings (CPT-1 through CPT-5) and installation of five groundwater monitoring wells, four shallow wells (MW-1 through MW-4) and one deep well (MW-5). Concentrations of total petroleum hydrocarbons as gasoline and diesel (TPH-G and TPH-D, respectively) and benzene, toluene, ethylbenzene, and xylenes (BTEX) have been detected in soil and groundwater samples collected from the site, primarily near MW-1,the location the four USTs reportedly abandoned in-place. Twelve groundwater monitoring events were conducted at the Site from September 2001 through December 2005. Groundwater samples were collected from monitoring wells MW-1 through MW-3 since September 2001 and monitoring wells MW-4 and MW-5 since September 2005. Samples were collected using a three-volume purging technique. Analytical results for quarterly groundwater monitoring are summarized as follows: r • TPH-G, TPH-D, and BTEX have not been detected in groundwater samples from monitoring wells MW-2, MW-3, MW-4,or MW-5. • TPH-G was detected in groundwater samples collected from MW-1 at a concentration of 7,000 pg/I in December 2005. Benzene, toluene,ethylbenzene,and xylenes were detected in December 2005 at concentrations of 230 micrograms per liter (gg/1), 17 µg/l, 2,400 pg/I, and 4,228 µgd, respectively. • Oxygenates have not been detected in groundwater samples collected since December 2004. 1,2- dichloroethane was detected at a concentration of 2.6 µg/1 in a groundwater sample collected from MW-1 during the December 2004 monitoring event. The results of grab groundwater samples collected and analyzed during the CPT investigation indicated dissolved petroleum hydrocarbon concentrations extended to depths of up to 185 feet below ground surface (bgs) at the site. In the letter dated May 25, 2006 (attached) the SJCEHD acknowledged that the results of the deep grab groundwater samples collected from the CPT borings are not confirmed by the groundwater samples collected from the deep monitoring well MW-5, which were non-detect for petroleum hydrocarbons during the third and fourth quarters of 2005. V J:\D0006\9-8227_00261022_2006 Work Plan.doc BLASLAND, BOUCK& LEE, INC. engineers,scientists,economists