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URS
<br />Mr. Robert McClellon
<br />October 17, 2008
<br />Page 3
<br />locations during the quarter ranged from 0% to 19.3%. Carbon dioxide concentrations measured at all
<br />sample locations during the quarter ranged from 0.7% to 26.0%. Results for each probe, each extraction
<br />well, and each passive vent are summarized in Table 1.
<br />Groundwater. An interpreted groundwater contour map was prepared using the data collected on
<br />September 10, 2008 (Figure 2). The groundwater flow direction is to the west-northwest at a gradient of
<br />0.0012. For comparison, the groundwater flow direction varies from the east to west (June 10, 2008),
<br />from southeast to the northwest (September 20, 2007), from the west-southwest to the east-northeast
<br />(June 14, 2007, December 13, 2007 and March 13. 2008), from the southwest to the northeast (June 29,
<br />2006, December 15, 2006 and March 14, 2007), and from the northeast to the southwest (September 29,
<br />2006).
<br />The following metals were not detected above the analyses reporting limit: aluminum, cadmium, copper,
<br />mercury, selenium, silver, thallium and zinc. The highest detected concentration of the remaining nine
<br />metals are 0.0334 milligrams per liter (mg/L) for arsenic (MW -1), 1.01 mg/L for barium (MW -2),
<br />0.00440J mg/L for chromium (MW -3), 0.00847J mg/L for cobalt (MW -1), 1.94 mg/L for iron (MW -1),
<br />0.00310J mg/L for lead (MW -2),4.25 mg/L for manganese (MW -1), 0.0105 mg/L for nickel (MW -1),
<br />and 0.0160 mg/L for vanadium (MW -3). The highest TDS concentration of 2,440 mg/L was found in
<br />MW -2. The field measurements for pH ranged from 6.65 to 6.75, and specific conductance ranged from
<br />1,840 to 3,400 micromhos (µmhos).
<br />Of the nine reported metals constituents, primary maximum contaminant levels (MCLs) are established
<br />for five 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, lead at 0.015 mg/L by EPA and DHS and nickel at 0.1 mg/L by DHS). For the
<br />remaining four metal constituents, secondary MCLs are established for two (iron at 0.3 mg/L by EPA and
<br />DHS and manganese at 0.05 mg/L by EPA and DHS). For one of the two remaining constituents, the
<br />California State Action Level for Drinking Water is established for vanadium at 0.05 mg/L. For the
<br />remaining constituent, the Agricultural Water Quality Limits is established at 0.05 mg/L for cobalt.
<br />Secondary MCLs are established for TDS at 500 mg/L by EPA and DHS and specific conductance at 900
<br />µmhos by EPA. The dissolved metal results, TDS results, and the field measurements are summarized in
<br />Table 2.
<br />The analytical report is provided as Attachment 2.
<br />CONCLUSIONS AND RECOMMENDATIONS
<br />Nine metals (arsenic, barium, chromium, cobalt, iron, lead, manganese, nickel and vanadium) and TDS
<br />were detected above the analytical reporting limits in the groundwater samples collected on September
<br />10, 2008. Of these constituents, five (arsenic, barium, iron, manganese and TDS) were above their
<br />established regulatory levels. Because four of the metal results and TDS were above their established
<br />regulatory levels, URS plans to continue quarterly monitoring of these metals and TDS.
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