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15 February 2005 - AGE-NC Project No. 02709501 Page 2 of Z UST location. The vertical migration of soil contamination appears to be slowed by the clay layer encountered from 29 to 36 feet bsg except_ at the Iocation of boring B3, where significant concentrations are detected at this-depth. Significant petroleum hydrocarbon-impact to soil in the'vadose and smear zone is present in borings B1 and B2, in the area of the former USTs-(Figure 2)..Total petroleum.hydrocarbons quantified as gasoline and diesel(TPH-g,TPH-d)and benzene are present at maximum concentrations of 22,000 mg/kg,7,500 mg/kg and 1:1 mg/kg,respectively,all from sample B2-15.Most of the contamination appears to reside above the top of the clay layer, at.approximately 29 to 36 feet bsg, except at B3, where TPH-g was detected at 35 feet bsg at a concentration of 900 mg/kg. Contamination in ground water was present in all four soil boring locations and in the up-gradient well MW-2; the ground water sample from B4, collected between 53 feet and 57 feet bsg, in the second sand .unit, indicated elevated amounts of contamination-at a-depth- of 57 feet bsg. Concentrations have not been detected in down-gradient well MW-1 and cross-gradient well MW-3 only had one very small detection of toluene and:xylene (January,2004), both below State of California Department of Health Services.(DHS)Maximum Contaminant Levels(MCL)for drinking water. Lateral hydrocarbon-impact to soil is not defined toward the north, southeast and southwest of the former UST. The vertical extent of soil contamination does not appear to exceed 40 feet bsg, with the exception of B3 at 35 feet bsg,and the low concentrations of hydrocarbons detected in samples collected at 35 feet from borings Bl; B2 and MW=2. The lateral extent of ground water contamination is not defined toward the north,.southeast and southwest of the former UST, and is not defined vertically, as contaminationis present'in the location of B4 at a depth of 57 feet bsg. 3.0. SCOPE OF WORK Based on analytical data from previous investigations at the-site, additional soil and ground water- investigation was required by the EHD to define the lateral and vertical extent of hydrocarbon impacted soil and ground water. The proposed scope-of work will include the following tasks: Permitting and pre-field work activities; • Advancement of CPT.boring; • Advancement of soil borings; • Collection of soil and ground water samples; • Laboratory analysis of samples; and Advanced GeoEnvironmental,Inc.