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15 July 2002 <br />AGE -NC Project No 96-0232 <br />Page 18 of 21 <br />which then migrated through the First Zone and upper Second Zone to the former Rocky's <br />Restaurant domestic well, at which point it apparently migrated vertically to the Rocky's Upper, <br />Secondary Aquifer and Primary Aquifer Zones <br />Between December 2001 and June 2002, significant concentrations of dissolved MTBE were <br />detected from Second Zone well MW -8A (screened 40 to 50 feet bsg) However, intermediate well <br />MW -4, located between MW -8 and the UST area, continued to have no detection of MTBE, albeit <br />screened in the Fust Zone Since initiation of ground water extraction activities at the site, ground <br />water flow direction in the First Zone in the area of MW -8 has generally been inferred to be towards <br />the south-southwest, ground water flow direction in the Second Zone in the area of MW -8 has been <br />inferred towards a slight depression in the water table located between wells MW -6B and MW -9A, <br />it is not clear at this time why substantial MTBE is present in MW -8A after nine consecutive <br />quarters of being non -detect <br />Between March 2002 and June 2002, moderate to substantial MTBE decreases were reported from <br />wells MW -8A, MW -11A, MW -11B, EW -4 and EW -5, subtle MTBE decreases were reported in <br />extraction wells EW -6, EW -8 and EW -10 and monitoring wells MW -11D and MW -12A <br />Conversely, subtle MTBE increases were reported from monitoring wells MW -7, MW -13A and <br />Three B's Truck Plaza well MW -4 The data implies that the decreases may be due to the overall <br />MTBE mass reduction in First Zone water and possibly Second Zone (MW -11 A) and Upper Rocky's <br />Zone water (MW -11B), the subtle increases at MW -7 and Three B's Truck Plaza well MW -4 may <br />be due to the well abandonment of RDW -1, which may have caused a rebound effect due to <br />discontinued pumping activity at RDW -1 <br />AGE estimates the arithmetic average concentration of MTBE in ground water extracted between <br />27 March and 13 June 2002 was 27 4g11 During this time, the volume of water processed through <br />the ground water pump and treat system was recorded at 1,075,700 gallons (equivalent to 8,968,111 <br />pounds) of water extracted yields 0 22 pounds of MTBE (equivalent to 100 grams) removed from <br />the plume of impacted ground water (Appendix D), or approximately 1 5 grams per day <br />Analytical results from the June 2002 quarterly monitoring event indicates the most intense on-site <br />MTBE impact is in the First Zone near EW -4 (29 ,ug/1) and in the Second Zone near MW -8A (250 <br />µg/1), the most intense off site MTBE impact is in the First Zone near MW -7 and Three B's Truck <br />Plaza well MW -4 (49 1.ig/1 and 90 µg11, respectively), and in the Rocky's Upper Zone well MW -11B <br />(120 4g/1) It is not clear at this time why the Three B's Truck Plaza well MW -4 has consistently had <br />greater MTBE -impact than that of intermediate well MW -7 <br />Significant concentrations of TPH-mo and TPH-d were quantified west of the site in the area of <br />. MW -12A and MW -13A, which suggest the possibility of separate releases <br />Advanced GeoEnviranmentai, Ine- <br />