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1 <br /> LMSMILL-MERUEMMO", IMC, <br /> FINDINGS AND COHCLtI5I0NS <br /> 1 . The soil types encountered at the site consist of primarily clay. The <br /> clays varied from brown to gray and were primarily lean clays. The former <br /> excavation is filled with a clean sand to a depth of 9 to II feet and is <br /> covered with a layer of asphalt. <br /> ' 2. Groundwater was encountered at a depth of 37 feet below the ground surface <br /> in a sandy clay layer, beneath a confining fat clay layer. Once this <br /> confining layer was penetrated, groundwater quickly rose to a <br /> potentiometric level of approximately 33 feet below ground surface. <br /> Groundwater appears to be flowing in an easterly direction at a relatively <br /> flat gradient of approximately 0.28 percent. <br /> j 3. As evidenced by a 20-foot head differential and a significant difference <br /> in TOS concentrations, the groundwater aquifer beneath the site does not <br /> appear to be hydraulically connected to the adjacent Stockton Channel . <br /> 4. Petroleum hydrocarbon soil contamination exists in the center to eastern <br /> side of the former UST excavation to a depth of at least 36.5 feet. Some <br /> of this contamination appears to have migrated laterally off-site in a <br /> northerly direction within a sand layer located at a depth of <br /> approximately 16.5 feet to 23 feet. The lateral off-site migration, if <br /> • any, should be investigated further and based on the analytical data, <br /> these soils may also require remediation. The depth of contamination <br /> found in the soils below the former UST excavation indicates that the <br /> petroleum hydrocarbon contamination in the former UST excavation has also <br /> migrated vertically and has impacted the groundwater. <br /> 5. Petroleum hydrocarbon is present in the groundwater beneath the site. The <br /> highest concentrations of contamination were present in monitoring well <br /> MW3 which is down gradient of the former UST excavation. Contamination <br /> was also present in MWI and MW2, but at much lower levels than MW3. This <br /> indicates that the source of groundwater contamination is apparently the <br /> former USTs. The lateral off-site migration to the east, if any, should <br /> be investigated further and the groundwater should be remediated. <br /> 6. Although the existing waste oil tank at the site failed a precision tank <br /> test, this investigation has found no indication of soil contamination <br /> adjacent to the waste oil tank. It is possible, however, that soil <br /> contamination could be present directly beneath the tank and/or between <br /> the tank and the existing building. The tank will need to be formally <br /> closed by removal and soil samples will need to be obtained from beneath <br /> the tank to determine if leakage, and subsequent contamination, has <br /> occurred. <br /> 90829-12.=w/292(m) <br /> 26 <br />