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KLEINFELDER ' 3 CONTAMINANT MASS ESTIMATES Based on the groundwater sample analytical results from the June 2004 sampling event and iso-concentration contour Interpretations, contaminant mass estimates have been ' calculated as requested in SJCEHD correspondence dated September 24, 2004 The contaminant mass calculation summary table has been presented in Table 8 31 CONTAMINANT MASS CALCULATIONS ' The calculations were performed by using the most recent vertical extent values as determined from the data collected during the June 2004 CPT boring of CPT-A as reported in the June 2004 Site Investigation Report The calculation also used the contoured concentration values from the October 2004 event ' Contaminant mass can be estimated based on a number of other estimatedp arameters using the following equation Contaminant mass in kilograms = Area (sq ft ) x Porosity x Thickness (ft) x Concentration (ug/kg) x (7 5 gal/cu ft x 3 8 Llgal x 1 E-9kglug) 3 2 CONTAMINANT MASS ESTIMATES The contaminant mass In groundwater calculations indicate that the total mass is 1 8 Kilograms (Kg) for benzene and 70 7 Kg for dissolved gasoline This represents a decrease in contaminant mass from the previous calculation as reported in the April 2003 Remedial Action Completion Report The calculated values differ in part, because the previous values were calculated using a vertical extent value of 50 feet bgs, where this current calculation is based on a vertical extent value of 90 feet bgs Therefore, the previous thickness values were normalized to the current values (using 90 feet) so that the comparison can be determined based solely on a concentration trend Upon normalizing the equation, the contaminant mass again appears to have decreased significantly C23-484517-B001SAC5R540 Page 9 of 14 August 11, 2005 Copyright 2005 Kleinfelder, Inc