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E �^ T - �,. _ 4. .',+r _ _ �.Ff4.="f. •� _ �i -�_s�,�¢'__rte_-- _�, -�.. _ _ �� r _ .� ON 74 -16 1 a File No. 2070-.2 19 September 1988 T 5. Environmental Sci,nces and Engineering (ESE) was contracted to investigate • the :,,ontamination found above. ESE's field investigation was conducted in two. phases. In the first phase, conducted during the week of 6 July 1987, one monitoring well (MW-1, 95 feet deep) was 7,,nInstructed. In the second phase, conducted September 1987, two additional monitor-ing wells were installed (MW-2 and r11-3, refer to site plan) During the construction of , each well, the soil profile was recorded, and soil samples were taken at 5 foot vertical intervals. The groundwater was also sampled. approximately, 36 .feet vvre recorded.) (Groundwater depths of 6. The soil and grou::Iwater samples taken by ESE were chemically analyzed by • Anlab La;-)oratory in Sacramento. The soil sample taken from MW-1 at 55 feet below ground surface was determined to contain elevated levels of TPH. Soil samples taken at 30 and 35 feet in MW-2 were determined to contain elevated levels of TPH and lead. Benzene, toluene, xylene, and TPH were detected in the groundwater sample tak:n from MW-1. However, laboratory analysis Of groundwater samples taken from MW-2 and MW-3 showed no detectable concentrations of these constituents. 7. The three monitoring wells installed by ESE were situated in 4 . nearly a straight ]_ine (resulting in a questionable determination _.' of the groundwater gradient) . In addition, the zero line of contamination had r,ut yet been determined (both up and downgradient) . Anderson Geotechnical .Consultants (AGC) took over the investigation in order to resolve these issues. 8. 1n January ,1988, ern:3erson Geotechnical Consultants installed two additional monito,ing wells (M11-4 and MW-5, both 55 feet deep. see Figure 1) . From the AGC groundwater elevation measurements, it was determined that . the groundwater gradient tended to the east, ;rather than to the northwest, as ESE had determined. Groundwater samples 'taken from MW-4 and MW-5 were analyzed by Califoriu a Analytical Labs, in West Sacramento. Benzene, toluene, and xylene were detected in the sample taken from MW-4. Low levels of toluene were detected in the sample taken from mW-5 (see Figure 1) , TII. . PRS}POSED WORK'fLLAm- 9. On 16 June 1988 representatives of AGC met with Mr. Gordon Lee Boggs of the Regional Water Quality Control Board to review the status of the invatstigation. Mr. Boggs concerns were: 1) the questionable gradient determination by ESE; 2) the contamination found in MW-4, which is upgradient of the removed L -2-