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1. �ty f LEED$HILL•HEAKENHOFF.WC. f .. r FINDINGS AND CONCLUSIONS 1. The soil types encountered at the site consist of primarily clay. The clays varied from brown to gray and were primarily lean clays. The former excavation is filled with a cleans and to a depth of 9 to 11 feet and is covered with a layer of asphalt. 2. Groundwater was encountered at a depth of 37 feet below the ground surface in a sandy clay layer, beneath a confining fat clay layer. Once this confining layer was penetrated, groundwater quickly rose to a potentiometric level of approximately 33 feet below ground surface. Groundwater appears to be flowing in an easterly direction at a relatively flat gradient of approximately 0.2a percent. 3. As evidenced by a 20-foot head differential and a significant difference in TOS concentrations, the groundwater aquifer beneath the site does not appear to be hydraulically connected to the adjacent Stockton Channel. 4. petroleum hydrocarbon soil contamination exists in the center to eastern side of the former UST excavation to a depth of at least 36.5 feet. Some Of this contamination appears to have migrated laterally off-site in a northerly direction within a sand layer located at a depth of approximately 16.5 feet to 23 feet. :. The lateral off-site migration, if any, should be investigated further and based on the analytical data, these soils may also require remediation. The depth of contamination found- in the soils below the former UST excavation indicates that the Petroleum h;drocarbon contamination in -the former UST excavation has also migrated vertically and has impacted the groundwater. S. Petroleum hydrocarbon'i-s.present in the groundwater beneath the site. The highest concentrations OfContaminationwere present in monitoring well MW3 which is down gradient of the former UST excavation. Contamination was also present in MWI and MW2, but at much lower levels than MW3. This indicates that the source of groundwater contamination is apparently the former USTs. The lateral off-site migration to the east, if any, should be investigated further and the groundwater should be remediated. 6. Although the existing waste oil tank at the site failed a precision tank �- test, this investigation has found no indication of soil contamination adjacent to the waste oil .tank. It is possible, however, that soil contamination could be present directly beneath the tank and/or between the tank and the existina, building. The tank will need to be formally Closed by removal and soil samples will need to be obtained from beneath the tank to determine if leakage, and subsequent contamination, has m- •- -- — oc,:urred. 9W19.12.carl/z9z(m) 26