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Ms Vicki McCartney Project No 880-040 IA <br /> July 9, 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 /> Second Quarter Groundwater Monitoring Results <br /> Groundwater elevation at the site increased an average of 0 25 feet since the previous <br /> sampling event conducted on January 12, 2004 During the second quarter, groundwater <br /> flow was to the east at an average gradient of 0 001, which is consistent with previous <br /> sampling events Groundwater elevation data are presented inable 1 A groundwater <br /> Vie+v <br /> elevation contour map based on the June 22, 2004, data is shown on figure Y'4gla ay <br /> �► b t ,4fpork- Vnt <br /> TPHg range hydrocarbons were reported in all wells except MW-2 at concentrations up "'t <br />' to 4,200 micrograms per liter(gg/L) Benzene was reported in wells MW-1, MW-3, and <br /> MW-4 at concentrations of up to 910 gg/L MTBE was reported in all wells sampled at <br /> concentrations ranging from 13 gg/L in well MW-3, to 2,000 gg/L in well MW-2 TBA <br /> was reported in all wells except MW-2 at concentrations up to 9,800 gg/L. Groundwater <br /> analytical data are presented i Table TPHg, benzene, and MTBE concentrations on <br /> June 22, 2004, are shown on figure 2 - !Ge_Z;✓A-. $13/0A/ <br /> DISCUSSION <br /> Groundwater levels have increased an average of 0 25 feet since the first quarter 2004 <br /> sampling event Groundwater analytical data for the second quarter 2004 sampling <br /> event are generally consistent with historical data Since groundwater monitoring began <br /> jin 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 wells MW-1, MW-3, MW-4, and MW-5 are historic lows <br /> This reciprocal relationship between MTBE and TBA concentrations may indicate <br /> intrinsic degradation of MTBE Shaw recommends continued monitoring of the existing <br /> five wells (MW-1 through MW-5) to further evaluate the dissolved hydrocarbon plume <br /> at the site <br /> Shaw Environmental,Inc <br /> N\sac DP120041Prj188018800401 A 4ab doc <br />