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r ' <br /> Ms Vicki McCartney Protect No 880-040 1A 02010000 <br /> August 30, 2004 <br /> Page 3 <br /> using U S Environmental Protection Agency (EPA) Methods 8015GRO/8021B and / <br /> t8260B 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 /> i <br /> I <br /> Third Quarter Groundwater Monitoring Results j <br /> Groundwater elevation at the site decreased an average of 0 49 feet since the previous <br /> sampling event conducted on June 22, 2004 During the third quarter, groundwater flow <br />' was to the east-northeast at an average gradient of 0 001, 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 August 12, 2004, data is shown on <br /> Figure i <br /> TPHg range hydrocarbons were reported in wells MW-1, MW-3, and MW-5 at <br /> concentrations up to 1,100 micrograms per liter (µg fl Benzene was reported in all <br /> wells except MW-2 at concentrations of up to 86 µg/L MTBE was reported in all wells <br /> sampled at concentrations ranging from 13 µg/L in well MW-3, to 2,500 µg/L in well <br />' MW-2 TBA was reported in all wells except MW-3 at concentrations of up to 3,200 <br /> µg/L. Groundwater analytical data are presented in Table 1 TPHg, benzene, and <br /> MTBE concentrations on August 12, 2004, are shown on Figure 2 <br /> DISCUSSION <br /> Groundwater levels have decreased an average of 0 49 feet since the second quarter <br /> 2004 sampling event Groundwater analytical data for the third quarter 2004 sampling <br /> event are generally consistent with historical data Since groundwater monitoring began <br /> in September 2000, MTBE concentrations have declined in all wells, while TBA A � <br /> concentrations have concurrently increased in some wells (MW-4 and MW-5)MTBE <br /> concentrations reported in wells MW-1, MW-3, MW-4, and MW-5 are historic lows <br /> This reciprocal relationship between MTBE and TBA concentrations may indicate �i t� l <br /> S <br /> intrinsic degradation of MTBShaw recommends continued monitoring of the existing <br /> five wells (MW-1 through MW to further evaluate the dissolved hydrocarbon plume <br /> at the site , <br /> 31 <br /> � 1'1'tiw <br /> Shaw Environmental,Inc <br /> N 1sacDM0041Pg18W8800401 A 4ac doc <br />