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<br /> URNS
<br /> Mr. Robert McClellon
<br /> October 31, 2007
<br /> Page 4
<br /> Groundwater.Interpreted groundwater contour map was prepared using the data collected on September
<br /> 20, 2007(Figure 2).The groundwater flow direction is to the northwest at a gradient of 0.00125. For
<br /> comparison,the groundwater flow direction varies from the west-southwest to the east-northeast(June
<br /> 14, 2007), from the southwest to the northeast(June 29,2006,December 15,2006, and March 14,2007),
<br /> from the northeast to the southwest(September 29,2006).
<br /> The following metals were not detected above the analyses reporting limit: aluminum, cadmium, lead,
<br /> mercury, selenium and silver.The highest detected concentration of the remaining 11 metals are
<br /> 0.0303 milligrams per liter(mg/L) for arsenic (MW-1), 0.928 mg/L for barium(MW-2), 0.00347J mg/L
<br /> for chromium(MW-3), 0.00995 mg/L for cobalt(MW-1), 0.00471)mg/L for copper(MW-2), 0.688
<br /> mg/L for iron(MW-2), 5.04 mg/L for manganese (MW-1),0.0117 mg/L for nickel(MW-1), 0.00577J
<br /> mg/L for thallium(MW-1),0.0169 mg/L for vanadium(MW-3), and 0.0199 mg/L for zinc(MW-2). The
<br /> highest TDS concentration of 2,320 mg/L was found in MW-2. The field measurements for pH ranged
<br /> from 6.43 to 6.68, and specific conductance ranged from 1,660 to 3,460 micromhos(µmhos).
<br /> Of the 11 reported metals constituents,primary maximum contaminant levels(MCLS)are established for
<br /> 6 constituents(arsenic at 0.01 mg/L by EPA and 0.05 mg/L by the California Department of Health
<br /> Services(DHS),barium at 2 mg/L by EPA and 1 mg/L by DHS, chromium [total] at 0.1 mg/L by EPA
<br /> and 0.05 mg/L by DHS, copper at 1.3 mg/L by EPA and DHS,nickel at 0.1 mg/L by DHS and thallium
<br /> at 0.002 mg/L by EPA and DHS). For the remaining five metal constituents,secondary MCLS are
<br /> established for three(iron at 0.3 mg/L by EPA and DHS,manganese at 0.05 mg/L by EPA and DHS, and
<br /> zinc at 5 mg/L by EPA and DHS). For one of the two remaining constituents,the California State Action
<br /> Level for Drinking Water is established for vanadium at 0.05 mg/L.For the remaining constituent,the
<br /> Agricultural Water Quality Limits is established at 0.05 mg/L for cobalt. Secondary MCLs are estab-
<br /> lished for TDS at 500 mg/L by EPA and DHS and specific conductance at 900 µmhos by EPA. The
<br /> dissolved metal results, general mineral results, and the field measurements are summarized in Table 2.
<br /> The analytical report is provided as Attachment 3.
<br /> CONCLUSIONS AND RECOMMENDATIONS
<br /> Eleven metals(arsenic,barium chromium, cobalt,copper, iron,manganese,nickel,vanadium,thallium
<br /> and zinc) and TDS were detected above the analytical reporting limits in the groundwater samples
<br /> collected on June 14, 2007.Of these constituents, six(arsenic,barium, iron,manganese,thallium, and
<br /> TDS)were above their established levels.Because five of the metal results and TDS were above their
<br /> established levels,URS plans to continue quarterly monitoring of these metals and TDS.
<br /> Prior to the installation of the passive soil vapor extraction trench,the methane concentration has
<br /> historically exceeded 5 percent by volume within VW-4,VW-5S,VW-5D,VW-6S, and VW-6D. Since
<br /> the passive soil vapor extraction trench installation,the methane concentration has decreased within
<br /> these probes to less than 5 percent by volume during the following quarter and has continued to be less
<br /> than 5 percent during the subsequent quarters.Methane concentrations measured within all probes during
<br /> the second quarter of 2007 were less than 5 percent by volume. Based on these results during this
<br /> K:\Wprocess\25532\WorldEnteiprise\Quarterly Rpt\2007\3Q07\103107.doc
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