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31 August 2005
<br /> +' AGE-NC Project No 96-0232
<br /> Page 13 of 30
<br /> Laboratory analysis of First Zone(between 10 and 35 feet)groundwater historically detected MTBE
<br /> from monitoring wells MW-1,MW-2,MW-4,MW-5,MW-6,MW-7,MW-12A,MW-13A,MW-16,
<br /> MW-19A and MW-20A,on-site,the greatest MTBE concentrations were detected from well MW-1
<br /> at concentrations as high as 5,700µg/l(June 2000),off-site,the greatest MTBE concentrations were
<br /> detected towards the west from well MW-13A (near Three B's Truck Plaza above ground storage
<br /> tank area) at concentrations as high as 2,500 pg/l (May 2000) and towards the north from well
<br /> MW-19A (Banner Avenue) at concentrations as high as 5,300 µgd (May 2004) The approximate
<br /> lateral extent of First Zone dissolved MTBE between July 1996 and 2005 are depicted on site maps
<br /> in Appendix H
<br /> Laboratory analysis of Second Zone (between 40 and 60 feet) ground water historically detected
<br /> MTBE from monitoring wells MW-6B,MW-8A,MW-9A,MW-1 IA,MW-12B,MW-13B,MW-14,
<br /> MW-17,MW-19B and MW-20B, on-site,the greatest MTBE concentrations were detected toward
<br /> the north from well MW-8A at concentrations as high as 900 µg/1 (March 2003), off-site towards
<br /> the west,the greatest MTBE concentrations were detected from well MW-11 A(near former Rocky's
<br /> Restaurant domestic water well)at concentrations as high as 810 µg/l (June 2000)and towards the
<br /> north from well MW-19B (Banner Avenue) at concentrations as high as 58 µg/l (May 2004) The
<br /> approximate lateral extent of Second Zone dissolved MTBE between March 2001 and March 2005
<br /> are depicted on site maps in Appendix I
<br /> Based on plots of MTBE and ground water elevations versus time (Appendix J), a definitive trend
<br /> of decreasing dissolved MTBE concentrations has been evident on-site from monitoring wells
<br /> MW-1, MW-2 and MW-4 between July 1996 and March 2005, additionally, a trend of declining
<br /> MTBE concentrations was evident from off-site wells MW-6A, MW-7, MW-11(A and B),
<br /> MW-12A,MW-13A and MW-19A However,between December 2004 and March 2005,increased
<br /> ground water elevations and increased dissolved MTBE concentrations were reported from First
<br /> Zone well MW-2,from Second Zone well MW-8A and from Rocky's Upper Zone well MW-15 No
<br /> other trends were determined from ground water monitoring wells MW-1 through MW-20
<br /> 25 SOIL PROPERTIES /HYDROSTRATIGRAPHY
<br /> Based on vertical soil profiles in soil-boring logs acquired during site assessment, supplemented by
<br /> cone penetrometer test data,the vertical soil profile at the Flag City Chevron site generally consisted
<br /> of combinations of laterally discontinuous silts, sandy clays, sandy silts and silty sands between
<br /> surface grade and 30 feet bsg Thereafter, less permeable, stiff to hard, sandy silts and sandy clays
<br /> were generally encountered at depths between 30 and 40 feet bsg, 50 and 70 feet and 80 to 90 feet
<br /> bsg Medium dense to dense, unconsolidated, poorly graded, silty, fine to medium sands were
<br /> generally encountered at depths between 40 and 50 feet bsg, 70 and 80 feet bsg, 90 and 110 feet bsg
<br /> and at depths greater than 120 feet bsg Boring logs are included in Appendix F General lithology
<br /> Advanced GeoEnvironmental,Inc
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