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URS
<br /> Mr. Robert McClellon
<br /> January 31, 2007
<br /> Page 4
<br /> the detected VOC analytes exceeded the above identified regulatory thresholds. The VOC analytical
<br /> results for each well are summarized in Table 2.
<br /> The following metals were not detected above the report limit of the analyses: cadmium, mercury, silver,
<br /> and thallium. The highest concentration of the remaining 13 metals are 0.277J milligrams per liter
<br /> (mg/L) for aluminum (MW-1), 0.0358 mg/L for arsenic (MW-1), 1.77 mg/L for barium (MW-2),
<br /> 0.00298 mg/L for chromium (MW-3), 0.0121 mg/L for cobalt (MW-1), 0.0043 mg/L for copper
<br /> (MW-1), 10.7 mg/L for iron (MW-2), 0.00987 mg/L for lead (MW-2), 7 mg/L for manganese (MW-1),
<br /> 0.0155 mg/L for nickel (MW-1), 0.00106 mg/L for selenium (MW-3), 0.0159 mg/L for vanadium
<br /> (MW-3), and 0.145 mg/L for zinc(MW-2). The dissolved metal results are summarized in Table 3.
<br /> The highest concentration of the following general mineral constituents and field measurements were
<br /> 359 mg/L for calcium (MW-2), 152 mg/L for magnesium (MW-1), 33.6 mg/L for potassium (MW-2),
<br /> 270 mg/L for sodium(MW-2), 112 mg/L for chloride(MW-2), 12 mg/L for nitrate (MW-3), 2,220 mg/L
<br /> for total dissolved solids (MW-2), 89 mg/L for sulfate (MW-3), pH ranging from 6.65 to 6.70, and
<br /> specific conductance ranging from 1,279 to 3,063 micromhos (µmhos). The general mineral and field
<br /> measurements are summarized in Table 4.
<br /> The analytical report is provided as Attachment 3.
<br /> CONCLUSIONS AND RECOMMENDATIONS
<br /> Five VOC constituents (methylene chloride at 0.5J µg/L [MW-1], acetone at 11 µg/L [MW-2], carbon
<br /> disulfide at 0.25J µg/L [MW-2], toluene at 3.9 µg/L [MW-2], and chloroform at 1.4 µg/L [MW-3])were
<br /> detected in the groundwater samples collected on December 29, 2006. When these values are compared
<br /> to the most conservative established levels (i.e., primary MCLs or TOT) identified above, all of the
<br /> detected constituents were less than these levels ranging, from approximately one order of magnitude to
<br /> more than three orders of magnitude less that the established level. To date,VOC results for the ground-
<br /> water sampling during the most recent three quarters were less than their respective established values. If
<br /> the VOC results during the next quarter are similar in magnitude, we will recommend that groundwater
<br /> sampling be suspended and the monitoring wells be properly abandoned.
<br /> Prior to the passive soil vapor extraction trench installation, the methane concentration has historically
<br /> exceeded 5%within VW-4, VW-5S, VW-513, VW-6S, and VW-6D. Since the installation of the passive
<br /> soil vapor extraction trench, the methane concentration has decreased within these probes when com-
<br /> pared to the pre-trench results, and the methane concentration within these probes appear to be generally
<br /> decreasing with time. During the past two rounds of landfill gas concentration measurements, methane
<br /> concentrations within these probes were less than 5 percent. Based on the most recent results from this
<br /> past quarter, the passive soil vapor extraction trench appears to be effective at controlling methane from
<br /> leaving the site. Since the passive soil vapor extraction trench appears to be effective at controlling
<br /> methane from leaving the site, we plan to continue monitoring the landfill gas concentrations within the
<br /> probes, extraction wells, and passive vents throughout the quarter on a monthly basis rather than on a bi-
<br /> weekly basis through the second quarter of 2007.
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