ARCHIVED REPORTS XR0000288 - Laserfiche WebLink

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O (DIPE), Methyl tertiary butyl ether(MTBE), and Tert-amyl methyl ether(TAME) greater than the analytical method reporting limit Analytical results are presented in Table 1 The constituent n-Propylbenzene was detected in SC-1-100' at a concentration of 13 pg/l The constituent tert-Butylbenzene was detected in SC-1-65' at a concentration of 0 6 µg/1 and 1,2,4-Tnmethylbenzene was detected in all groundwater samples at concentrations ranging between 2 9 and 4 4 pg/1 Laboratory analytical reports are included in Appendix C 3.4 Contaminant Mass Calculations The mass of contaminants was estimated at the site based on the data collected from CPT boring SC-1 and from plume data The plume data was based on monitoring data collected from on-site monitoring wells for first quarter 2002 The lithologic log from the CPT boring (Appendix B) was used to determine the depth and thickness of three high permeability zones The extent of each contaminant in each of the three zones was determined based on the CPT and monitoring well data The area between each contour was calculated and multiplied by the zone thickness and porosity to determine the volume of contaminated water The porosity was assumed to be 30 percent, which is within the range common to sands The concentration between each contour was assumed to be the average of the two isoconcentration contours defining the area The concentration inside the innermost contour was assumed to be the average of the isoconcentration contour defining the area and the highest concentration observed inside the contour The contaminant mass was calculated by summing the concentration multiplied by the volume for each area of the contaminant plume Based on the CPT data, Zone A includes a very stiff fined i<rained sand observed between 117 and 13 4 meters (38 5 and 44 feet) BGS, and again between 18 1 and 18 5 meters (59 5 and 61 feet) BGS Zone B includes a silty sand to sandy silt observed between 20 1 to 210 meters (66 to 69 feet) BGS and a very stiff fine grained sand observed between 210 and 25 0 meters (69 and 82 feet) BGS Chemical concentrations detected in the HydroPunch® sample collected at 27 4 meters (90 feet) BGS was applied to this zone Zone C includes very stiff fine-grained sand observed between 27 1 and 30 5 meters (89 and 100 feet) BGS The monitoring wells are completed to depths between 20 4 to 25 3 meters (67 to 83) feet BGS, which corresponds to zone B The monitoring data was applied to all three zones, unless the CPT data suggested otherwise The assumptions for each chemical constituent are discussed separately below The contaminant mass estimates are summarized in Table 2 M ftOP 0MPAAPJ8183S W7..2ab dw 3-2 &2r/02