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URS
<br />Mr. Robert McClellon
<br />October 31, 2006
<br />Page 4
<br />RESULTS
<br />Groundwater. VOC constituents were not detected above the analytical laboratory reporting limits in the
<br />groundwater sample collected from MW -1. The following VOC constituents were detected in the
<br />groundwater sample collected from MW -2: acetone at 6.9J micrograms per liter (gg/L) and toluene at
<br />0.67 J (estimated value) gg/L. Only chloroform was detected at 1.4 gg/L within the groundwater sample
<br />collected from MW -3. Acetone and chloroform are known to be common laboratory contaminants.
<br />Of the three reported VOC constituents, primary maximum contaminant levels (MCLS) are established
<br />for two (toluene at 1,000 gg/L by EPA and 150 gg/L by the California Department of Health Services
<br />[DHS] and chloroform at 80 gg/L by EPA and 100 gg/L by DHS). For the remaining constituent,
<br />acetone, the taste and odor threshold (TOT) value is established at 20,000 gg/L. Analytical results for
<br />each well are summarized in Table 1. The analytical report is provided as Attachment 2.
<br />Soil Vapor. The methane concentrations in VW -1, VW -2, VW -3, VW -7S, VW -7D, VW -8S, VW -8D,
<br />VW -9, and VW -10 were 0 percent. The methane concentrations in VW -4, VW -5S, V W -5D, VW -6S,
<br />VW -6D, EW -1, EW -2 PV -1, PV -2, PV -3, and PV -4 were 1.0%, 3.5%, 4.2%,1.5%, 4.0%,10.2%, 8.4%,
<br />7.7%, 9.7%, 10.1%, and 7.6%, respectively. Oxygen concentrations in all sample locations ranged from
<br />4.5% to 21.1%. Carbon dioxide concentrations in all sample locations ranged from 0.2% to 20.0%. The
<br />latest results for each probe, extraction well, and passive vent are summarized in Table 2. along with
<br />historical results.
<br />CONCLUSIONS AND RECOMMENDATIONS
<br />Three VOC constituents (acetone at 6.9J gg/L [MW -2]; toluene at 0.67J gg/L [MW -2]; and chloroform
<br />at 1.4 gg/l, [MW -3]) were detected in the groundwater samples collected on September 29, 2006. When
<br />these values are compared to the most conservative established levels (i.e., primary MCLS or TOT)
<br />identified above, all of the detected constituents were less than these levels, ranging from approximately
<br />one order of magnitude to more than three orders of magnitude less that the established level. Although
<br />the results of the groundwater sampling were less than the established values, we recommend that
<br />groundwater samples be collected for four consecutive quarters to confirm these contaminants are
<br />remaining at concentrations less than these regulatory values. If the results confirm that the contaminants
<br />and their concentrations remain less than the regulatory values during this period, we will then
<br />recommend that additional groundwater sampling be discontinued.
<br />Although methane was measured above 5.0% in EW -1, EW -2, PV -1, PV -2, PV -3, and PV -4, methane
<br />was not measured above 5% at any of the probes along the property boundary. Based on the most recent
<br />quarterly results, the passive soil vapor extraction trench appears to be effective at controlling methane
<br />from leaving the site. We plan to continue biweekly monitoring to measure the landfill gas
<br />concentrations
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