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res � r r r■� e r r r r TABLETS ESTIMATED MASS OF TAH-g AND BENZENE IN GROUNDWATER CALTRANS-SHOP 10 MAINTENANCE STATION,STOCKTON,CALIFORNIA FEBRUARY 2000 AREA,VOLUME,AND MASS OF CONTAMINANTS BASED ON ISOCONCENTRATION CONTOURS-GROUNDWATER Maximum Mass Based on Mass Based on Isoconcentration Observed Areal Impacted ISOconcentration Maximum Level Average Contour Concentration Extent(A,) Volume(V,) Contour(M,) Observed(M,) Mass Reference Contaminant Depth Interval(Zi) (C,) (C,) (m=) (L) (kg) (kg) (kg) Figure TPH-9 9 60 m sat thickness >100 pg1L 450 8385 2 8E+07 2 8 13 8 5 7A 9 60 m Sat thickness >1 000 4g/L 8 820 4459 1 1 5E+07 1 1 5 132 67 9 60 in sat thickness >10,000 pglL 18 200 1107 3 7E+06 037 68 34 VTpH,Total Total Total M,,„9Total= Total Volume and Mass Estimates 4 7E+07 4 7 213 109 Benzene 9 60 m sat thickness >1 0 g/L 10 8965 3 0E+07 003 003 003 5-7B 9 60 m sal thickness >10 0 pg1L 85 3326 1 1 E+07 Oil 095 053 9 60 in sat thickness >100 pq1L 100 1229 4 1 E+06 0 41 041 041 9 60 m sat thickness >1 000 pg1L 7 920 1259 4 2E+06 42 34 19 V,,..Total Total Total Me„„„,.Total= Total Volume and Mass Estimates 1 1 5 OE+071 48 1 35 1 20 Assumptions Isoconcentrabon contours presented in Figure 5-7 used as basis for calculation of volume and mass of impacted groundwater Areal extent-calculated using function within Autocad Impacted Volume-Assumed a 9 60-meter(31 511)saturated thickness used to calculate volume from area(i e 2=9 60 m for all cases) Mass Based on Isoconcentration Contour-The mass was calculated based on the assumption that all the groundwater within a given isoconcentration contour was impacted at that given concentration(i a the groundwater volume within the 1 000 Iig1L contour is all impacted at 1 000 pglL) Mass Based on Maximum Level Observed-The mass was calculated based on the assumption that all the groundwater within a given isoconcentration contour was impacted at the highest concentration observed within the said isoconcentration contour (i a the groundwater volume within the 1 000 pg1L is all impacted at 7 920 pg1L) Arithmetic Mean of Mass-Total mass based on arithmetic mean of mass estimated by isoconcentration contour and mass estimated by maximum detected concentration for the respective isoconcentration interval(I e, 10 0 mg1L to 1,000 mg/L,and>1 000 mg/L) I I I Page 1 of 2