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Ms Vicki McCartney Project No - 880-040 1A 02010000 <br /> November 8, 2004 <br /> Page 3 <br /> using U S Environmental Protection Agency (EPA) Methods 8015GRO/8021B and <br /> 8260B Field and laboratory procedures are presented in Attachment A Certified <br /> analytical reports, chain-of-custody documentation, and field data sheets are presented in <br /> Attachment B ' <br /> Fourth Quarter Groundwater Monitoring Results <br /> Groundwater elevation at the site decreased an average of 0 21 feet since the previous <br /> sampling event conducted on August 12, 2004 During the fourth quarter, groundwater <br /> flow was to the northeast at an average gradient of 0 002, which is consistent with <br /> previous sampling events Groundwater elevation data are presented in Table 1 <br /> A groundwater elevation contour map based on the October 21, 2004, data is shown on <br /> Figure I <br /> TPHg range hydrocarbons were reported in wells MW-1 and MW-3 at concentrations of <br /> 5,400 and 210 micrograms per liter (pg/L), respectively Benzene was reported in wells <br /> MW-1 and MW-4 at concentrations of 780 and 1 1 pg/L, respectively MTBE was <br /> reported in all wells sampled at concentrations ranging from 13 µg/L in well MW-3, to <br /> 1,100 µg/L in well MW-2 TBA was reported in all wells at concentrations ranging <br /> from 20 pg/L in well MW-3, to 7,200 gg/L in well MW-1. Groundwater analytical <br /> data are presented in Table 1 TPHg, benzene, and MTBE concentrations on <br /> October 21, 2004, are shown on Figure 2 <br /> DISCUSSION <br /> Groundwater levels have decreased an average of 0 21{pfe t since the third quarter 2004 X31 ��05 <br /> sampling event Groundwater analytical data for the #&a quarter 2004 sampling event <br /> are generally consistent with historical data Since groundwater monitoring began in <br /> September 2000, MTBE concentrations have declined in all wells, while TBA <br /> concentrations have concurrently increased in some wells (MW-4 and MW-5) MTBE <br /> concentrations reported in well mW-1, MW-3, MW-4, and Mare historic lows <br /> This reciprocal relationship between MTBE and TBA concentrations may indicate <br /> intrinsic degradation of MTBE J <br /> r <br /> N 1sacDP120041Pry188018800401 A 4ae doe SHAW ENVIRONMENTAL,INC <br />