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r URS Mr.Robert McClellon April 30, 2007 Page 4 and specific conductance ranged from 1,524 to 3,209 µmhos/L. The general mineral results and the field measurements are summarized in Table 4. The analytical report is provided as Attachment 2. CONCLUSIONS AND RECOMMENDATIONS Two VOC constituents(acetone at 6.1Jµg/L [MW-2] and chloroform at 1.3 µg/L [MW-3])were detected in the groundwater samples collected on March 14, 2007.When these values are compared to the most conservative established levels(i.e.,primary MCL, or TOT)identified above,all of the detected constituents were less than these levels ranging, from approximately one order of magnitude to more than three orders of magnitude less than the established level.To date,the VOC re6ults of the groundwater sampling during the past four quarters were less than their respective established values. Since the VOC results are similar in magnitude during the four quarters and these results are less that their respective established levels,we recommend that groundwater sampling for VOC analysis be suspended. Ten metals(arsenic,barium chromium,cobalt, copper,iron,manganese,nickel,vanadium, and zinc) were detected above the reporting limits of the analyses in the groundwater samples collected on March 14,2007. Of these constituents,three(arsenic,barium, and nickel)were above their established levels. Since three of the metal results were above their established levels,we plan to continue quarterly monitoring of the metals and TDS. Prior to the passive soil vapor extraction trench installation,the methane concentration has historically exceeded 5 percent within VW-4,VW-5S,VW-513,VW-6S, and VW-61). Since the installation of the passive soil vapor extraction trench,the methane concentration has decreased within these probes to less than 5 percent.The methane concentrations measured within all of the probes during the first quarter of 2007 were less than 5%.Based on these results during this quarter,the passive soil vapor extraction trench appears to be effective at controlling methane from leaving the site.Because of these results,we recommend that the monitoring activities for measuring the landfill gas concentrations within the probes, extraction wells, and passive vents be continued monthly,during the next quarter.If the methane concentrations within all of the probes are less than 5 percent during this next quarter,we recommend that the monitoring activities for measuring the landfill gas concentrations within the probes,extraction wells,and passive vents be continued quarterly.