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1 <br /> I <br /> FINAL REMEDIATION PIAN <br /> 1399 East Yosemite Avenue Manteca California <br /> ' 2.5 Groundwater Level Measurements <br /> Groundwater level measurements have been collected from May 1989 to <br /> 1 December 21, 1991, from the five existing wells (MW-1 B, MW-2, MW-3, MW-4, and MW-5) <br /> on site All water level measurements were referenced to the surveyed wellhead <br /> elevations (top of casing) and measured to the nearest 0 01-foot Table 2 summarizes <br /> ' the groundwater elevation data <br /> Groundwater elevations ranged from 13 59 to 16 70 feet above mean sea level (MSL) <br /> during the observation period Calculated historical groundwater elevations have been <br /> plotted on Figure 5 As indicated by the data, the maximum groundwater elevation <br /> fluctuation is 3 11 feet This observation was used to evaluate design parameters of a <br /> remediation system <br /> The potentiometnc surface of the groundwater beneath the site on December 21, 1991, <br /> ' is shown on Figure 6 The direction of groundwater flow, since May 1989, has remained <br /> fairly consistent toward the west-northwest The calculated hydraulic gradient fluctuated <br /> from 0 002 to 0 0005 ft /ft during the observation period <br /> ' 2.6 m PetroleuHydrocarbons in r <br /> ._ _ y „ Groundwater <br /> Analytical results obtained during the site investigation indicate the groundwater beneath <br /> the site contains concentrations of BTEX and TPH, as gasoline Table 3 summarizes the <br /> ' groundwater analytical results collected to date Floating liquid hydrocarbons have not <br /> been observed in any of the wells Dissolved petroleum hydrocarbons have been <br /> detected consistently to well MW-113 and periodically in wells MW-2, MW-3, and MW-4 <br /> ' An inferred zero line of petroleum hydrocarbons in groundwater was included in Aegis' <br /> "Problem Assessment Report," dated November 12, 1991 <br /> r <br /> 3.0 VAPOR EXTRACTION PILOT TEST <br /> 4 <br /> A vapor extraction plot test was conducted at the site on September 12, 1991 The <br /> 1 , purpose of the test was to determine of it is possible to induce air to flow in the soil <br /> beneath the site, and to measure parameters associated with the air flow and volatilization <br /> of hydrocarbons present in the soil <br /> ' 90-098F RPT 4 <br />