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Mr Harlin Knoll <br /> SanJ q County oa Count Environmental Health Division N <br /> 24 October 2000 <br /> • Page 6 <br />' Mass (M,„1100) of impacted groundwater in pounds {lbs) <br /> where <br /> CW = 100 µg/I TPHg estimated concentration from (Figure 3) <br /> V, = 8,400ft3is the calculated volume <br /> 0 1mg 3 785L 7 48ga1)(8,400ft' lb3 0 052lbs <br /> MW1°0L gal ft3 454x10 mg <br /> Total Mass of Soil and Groundwater Impact <br /> The total residual mass in pounds remaining in the soil and groundwater is estimated by <br /> summing the calculated mass of the soil and groundwater <br />' Mass Total = MS +MW400 +MW100 =0 121bs+0 091bs+0 0521bs=0 26lbs <br />' Summary of the Site Monitoring Program <br /> lie As directed by the SJCEHD, BFS has complied with the agency request to collect an <br /> additional round of groundwater sampling at the site No significant changes were <br /> observed from the previous groundwater sampling results Analytical data from this effort <br /> compared to previous investigation results show the concentration of hydrocarbon <br /> constituents in the soils at the site are below regulatory goals or standards Groundwater <br /> monitoring wells were placed at locations agreed to by the agency to determine the extent <br /> of soil and groundwater impacts An estimate of contaminant mass in soil and <br /> groundwater is calculated at approximately 1/4 pound of gasoline constituents remaining at <br /> the site As presented above, soil and groundwater impacts from previous site operations <br /> are limited in extent and below regulatory objectives For the constituents found, <br />' degradation by natural attenuation from the bacterial action in moist, shallow soils is <br /> likely <br /> The site data were evaluated against the California Water Resources Control Board's <br /> (CWRCB's) guidance document, Guidelines for Investigation and Cleanup of MTBE and <br /> Other Ether-based Oxygenates, dated 27 March 2000 The site's MTBE concentrations <br /> below 8 µg/I in groundwater and its distance (greater than 2,000 feet) from a drinking <br /> water well indicates that a low risk site classification should be assigned Therefore, BFS <br />' believes that the site assessment objectives have been met and the site should be formally <br /> • approved as closed <br /> 5\BFS\STOCKTON\LTR\LTR005 DOC 10/24/00 <br />