ARCHIVED REPORTS XR0001451 - Laserfiche WebLink

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November 22, 1995 Page 8 ' pit was excavated to a final dimension of 24 feet long by 2 feet wide by 5 feet deep The southern end of two of the abandoned 1921 USTs (500-gallon tanks) and their associated fuel fill lines were exposed in the test pit at approximately 4 feet bgs ' (Figure 1) The USTs were of plate riveted single-walled steel construction The USTs are positioned beneath the existing sidewalk and appear to be the fuel storage ' tanks corresponding to the 1921 general arrangement plan (Figure 3) To determine if the tanks contained any fluid or material, the exposed end plates of each tank were tapped with a hammer Based on this evaluation method, the tanks appeared to be ' empty The western and eastern ends of TP-3 were extended approximately 5 feet beyond ' the two USTs in attempt to identify the third tank noted on the general arrangement plans No evidence of a UST was encountered Because the third UST was not located by the test pit, it is-presumed to have been removed during either the station tremodel, between 1938 and 1950, or during the station demolition in 1965 All test pits were backfilled with the excavated soils The soils were placed in approximate 1-foot lifts, and mechanically compacted using the backhoe bucket Compaction testing was not performed Following the backfill operation, the - surfaces of the test pits were re-asphalted to restore the parking area to an acceptable condition. CONCLUSIONS The purpose of this investigation was to assess soil and groundwater conditions beneath the former Unocal site The results of this investigation indicate that petroleum ' hydrocarbons have impacted sod and groundwater in the northwestern portion of the site in the vicinity of the first and second generation USTs, and beneath the former product islands Soil and groundwater near the former waste oil tank do not appear to have been impacted by petroleum hydrocarbons. However, chlorinated organics, PCE and TCE, detected in U- 3 may be related to the former waste oil tank or an off-site source The source of the hydrocarbons detected in soil and groundwater appears to be ' related to the former service station operations The primary source areas may have included the first and second generation USTs and the former product island The second generation USTs and product islands were removed during station ' demolition Two abandoned USTs are located beneath the sidewalk bordering the northern end of the site The most significant soil impact occurs at the groundwater interface at a depth of 10 feet bgs Soils in the unsaturated zone, above 10 feet, r 3100971A/REPORT2 - N^ I