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CLEARWATER G R O U P I N C • Environmental Services Groundwater Flow Direction and Gradient Static groundwater was measured at depths ranging from 24 52 (MW-2) to 29 34 (MW-5) feet below top of well casing Gauging data, combined with well elevation data, was used to calculate groundwater elevations in these wells, and to generate a groundwater elevation contour map for the upper water bearing zone The groundwater flow direction was calculated to be towards the northwest at an approximate gradient of 0 013 ft/ft(Figure 3) Groundwater Contaminant Analytical Results Gasoline range hydrocarbons were detected in water samples collected from wells MW-1, MW-2, and MW-5 Maximum concentrations of TPHg, benzene, and MTBE were 2,200 4g/L (MW-1), 9 3 pg/L (MW-1), ND in all wells, respectively Neither TPHg, BTEX nor MTBE was detected in concentrations exceeding the practical quantitation limit (PQL) in samples from the remaining wells (MW-3, MW-4, MW-6, MW-7 and MW-8) None of the fuel additives tested for were detected in concentrations exceeding the practical quantitation limit (PQL)in samples collected from any of the eight wells sampled Groundwater sample analytical results are summarized in Table 1 and presented ` graphically on Figure 4 Copies of the laboratory report and chain-of-custody form are included in Appendix C. Clearwater reviewed the groundwater quality trends over the course of the project fol using available data The groundwater quality data, which are primarily from quarterly sampling events and post well installation events, are compiled in Appendix D The observed trends for this site indicate that concentrations have significantly declined,or remain close to or below laboratory detection limits for all tested analytes in all eight monitoring wells Clearwater calculated the amount of residual dissolved phase hydrocarbons in the saturated zone using the groundwater data collected on December 10, 1998 The calculations are shown on Table 2 and the assumed areas used in the calculations are shown on Figure 4 Using this data Clearwater estimated the quantity of residual dissolved phase hydrocarbons remaining in the saturated zone to be 0 38 gallons Clearwater also compiled all of the historic soil,sampling data for this site This historic data is compiled I i I on Table 3 andis shown on'Figure 5 The soil,samples were collected during the excavation of the' borings used,to install,MW-1 through MW-8 Appendix E presents alliof the historic soil quality data collected for this site 1 These samples were collected and wells installed from 1991 to 1993 Using these results Clearwater calculated the amount of residual sorbed phase hydrocarbons as TPH-G in the vadose zone These calculations are shown on Table 4 and the areas used to estimate the volume of I I p ` ll [ I'' Page 4