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-- r t 1 1 S, t i 17 December 1999 AGE'NC Project No 96-0235 ; 'i ' P —Page=9of1114 i1 J 1 4 AGE notes that the hydrocarbon masses calculated are not intended to be,pr`ecise, but are only ' estimates, based on the assumptions listed above and in Appendix F The mass calculations and formulas are presented in Appendix;F 4.0. SUMMARY AND CONCLUSIONS L Based'on the data collected from the former UST No 3 area, AGE finds ' • Petroleum hydrocarbons were detected in MW-1, MW-2 and MW-3, screened below the current ground water surface, at the,histoncal low ground water elevation Hydrocarbons were not detected in MW-6B and MW-8B, also screened near the historical low ground ' ' water elevation, defining the down-gradient lateral extent of impacted ground water at this depth toward the northwest and north MW-3 appears to be near the margin of the impacted deep ground water plume toward the west ' • Petroleum hydrocarbons were not detected in MW-4, MW-6A,MW77 or MW-8A, screened at the current ground water surface MW-5 was not accessible during the October 1999 monitoring event • Hydrocarbon concentrations decreased in three wells and remained below detection limits in the remaining six wells sampled during both the May and October 1999 sampling events ' Ground water in MW-1, MW-2, MW-6B and MW-8B does not appear to be in direct hydraulic communication with the ground water in MW-4, MW--5, MW-6A, MW-7 and MW-8A' Monitoring well MW-3,-screened,from 30 to 55 feet bsg may be to hydraulic - communication with all wells at thersrte • Impacted deeper ground water appears to be centered in the area near MW-2 and MW-1,, A ' migration toward the southwest to southeast may be possible Vertically, impacted ground ; water appears to be constrained to historic low ground water elevation of 40 to 50 feet bsg ' The impacted gr`oundmater plume does not appear to be migrating laterally or vertically •' The highest concentrations of hydrocarbons and organic vapor in soil were detected at depths _ of 40 to 45,feet bsg, corresponding"to known historical low ground water levels 1 r r E • Impacted soil appears`to extend vertically to a depth of approximately 55 feet bsg ' Impacted soil was not encountered in borings B13, MW-6 or MW-8, defining the western and northern extent of impacted soil Low`concentration's of hydrocarbons'were detected lin borings B 12, B 14, B 15,B 16 and B 1, indicating the approximate lateral margin of impacted ' soil_toward the south, east and northeast The approximate lateral extent of impacted `soil is r illustrated on Figure 4 Advanced GeoEnvironmental,Inc 5 '