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Tosco Corporation a subsidiary of Pluthps Petroleum Company 5 Tosco Station#1205 16470 Cambndge Street,Lathrop,CA - June 26,2002 total xylenes at a concentration of 720 ppb, and ethylbenzene at a concentration of 5 4 ppb Benzene, toluene, and MtBE were not detected above laboratory reporting limits Refer to Table 3 for groundwater analytical results required for disposal and Attachment A for the Certified Analytical Reports DPE MASS REMOVAL RATES The total mass of TPHg, benzene, and MtBE removed during the test were estimated using the influent air analytical results, an average well field flow rate, and the time duration of the test The calculated TPHg, benzene, and MtBE mass removed during the DPE test were approximately 304 84 pounds, 132 pounds, and 0 07 pounds, respectively (Table 5 and Figure 2) SOIL VAPOR RADIUS OF INFLUENCE The radius of influence was determined graphically by plotting the average lateral distance from the test well to the observation wells, versus the initial applied vacuum (inches of water) and the resulting induced vacuums (inches of water), from Table 1 The initial applied vacuum is derived by converting inches of mercury to inches of water by using 13 6 inches of water per one inch of mercury An induced vacuum of 0 1 inches H2O was used to represent the theoretical minimum induced vacuum defining "influence" from the applied vacuum The distance at which a "best fit" line formed by the data crosses 0 1 inches H2O is the estimated radius of vacuum influence for each test well During the DPE test for MW-6, two observation wells had an induced vacuum present For this test, an induced vacuum of 0 25 inches of water was observed in well MW-5 located approximately 50 feet from the extraction well and an induced vacuum of 0 02 inches of water was observed in well MW-7 located approximately 110 feet away from the extraction well Induced vacuums were not observed in wells MW-1, MW-2, and MW-4 located approximately 75 feet, 95 feet, and 150 feet away from the extraction well, respectively The lack of induced vacuums observed in wells MW-1 and MW-2 could be the result of the proximity of the former and current underground storage tanks between the extraction wells and observation wells causing a short circuit in the vacuum The lack of induced vacuums observed in well MW4 could be the distance between the observation well (MW-4) and the extraction well (MW-6) Based upon this data, the estimated radius of influence for test well MW-6 was 71 feet (Figure 3) The radius of influence was unable to be determined for test well MW-1, MW-2, MW-5, and MW-7 due to the lack of induced vacuum in observation wells In order to graphically represent the radius of influence, two or more observation wells would be required to have an induced vacuum. During the DPE test for MW-1, MW-2, MW-5, and MW-7,induced vacuums were only observed in one observation well In each of these tests, induced vacuum was observed in the well closest to the extraction well Based upon the data collected, an estimated radius of influence would be less than 71 feet, however, more observation points closer towards the extraction wells would be required to calculate an accurate radius of influence