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Geo(a dTwhnics Znc. • • Page 2 George's Service Work Plan—Supplemental Data ' Project No.425.2 October 13,2000 The calculations were based on the following parameters: 1. Shallow Aquifer Zone ' From 10 to 25 ft bgs. This is the depth interval that contains the contamination. • K ranges from 0.10346 to 1.0346 ft/yr. • Porosity ranges from 37.3 %to 38.6 %. ' • Hydraulic gradient averages 0.0019 ft/ft. According to these parameters the average groundwater velocity in the shallow aquifer ranges from 5.09 x 104 to 5.27 x 10"3 ft/yr towards the N-NE. ' 2. Intermediate Aquifer Zone • From 30 to 50 ft bgs. This is the depth interval immediately below the zone that contains the contamination. ' K ranges from 620.79 to 20,692.91 ft/yr. • Porosity ranges from 27.2 %to 35.5 %. • Hydraulic gradient averages 0.0023 ft/ft. According to these parameters the average groundwater velocity in the intermediate aquifer zone ranges from 5.25 to 134 ft/yr towards the N-NE. 2. Soil and groundwater mass balance calculations Tables 1 & 2 contain soil and groundwater data compiled to date. The extent of TPH-G in soil, TPH-G in groundwater, and benzene in groundwater are illustrated in Figures 1, 5 and 6, respectively. Mass balance calculations for TPH-G in soil and groundwater are included in Table 3. MTBE is not a factor at this site. ' The average contaminant concentrations for soil zones 1 & 2, and groundwater zones 1 through 7 were derived by averaging data from within the zones (one half of the detection limit was used for ND values). The area of each zone was calculated by the CAD software program, which was utilized to draw the zones. Calculations for the amount of soil mass contaminant to be removed by the proposed excavation are included in Table 3. The estimated amount of TPH- G mass to be removed by ' excavation, 3098.75 kg, is approximately 58% of the total mass, 5372.68 kg, calculated for the site. The extent of the proposed excavation is illustrated in Figure 7. 1 The post-treatment contamination goals are to achieve levels below the MCLs or taste and odors thresholds for individual constituents of concern.