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Mr. Robert McClellon
<br />April 29, 2010
<br />Page 3
<br />Groundwater. An interpreted groundwater contour map was prepared using the data collected on
<br />March 9, 2010 (Figure 2). The groundwater flow direction is to the northeast at a gradient of 0.0033. For
<br />comparison, the groundwater flow direction varies from the northeast to the southwest
<br />(September 29, 2006), from the east to west (June 10, 2008 and September 9, 2009), from the east-
<br />southeast to the west-northwest (September 10, 2008 and December 10, 2009), from southeast to the
<br />northwest (September 20, 2007), from the southwest to the northeast (June 29, 2006, December 15,
<br />2006, March 14, 2007, December 9, 2008, and March 11, 2009), from the west-southwest to the east-
<br />northeast (June 14, 2007, December 13, 2007, March 13, 2008, and June 10, 2009).
<br />The following metals were not detected above the analyses reporting limit: aluminum, cadmium, copper,
<br />mercury, selenium, silver and thallium. The highest detected concentration of the remaining 10 metals
<br />are 0.00703J milligrams per liter (mg/L) for arsenic (MW -1), 0.867 mg/L for barium (MW -2),
<br />0.00434J mg/L for chromium (MW -3), 0.00386J mg/L for cobalt (MW -1), 0.538 mg/L for iron (MW -2),
<br />0.00504J mg/L for lead (MW -2), 3.60 mg/L for manganese (MW -2), 0.0111 mg/L for nickel (MW -2),
<br />0.0176 mg/L for vanadium (MW -3) and 0.00956J mg/L for zinc (MW -3). The highest TDS
<br />concentration of 2,100 mg/L was found in MW -2. The field measurements for pH ranged from 6.69 to
<br />6.94, and specific conductance ranged from 1,870 to 3,310 micromhos (µmhos).
<br />Of the 10 reported metals constituents, primary maximum contaminant levels (MCLs) are established for
<br />5 constituents (arsenic at 0.01 mg/L by EPA and 0.05 mg/L by California Department of Health Services
<br />[DHS], barium at 2 mg/L by EPA and 1 mg/L by DHS, chromium [total] at 0.1 mg/L by EPA and
<br />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 five metal constituents, secondary MCLs are established for three (iron at 0.3 mg/L by EPA
<br />and DHS, manganese at 0.05 mg/L by EPA and DHS and zinc at 5 mg/L by EPA and DHS). For the two
<br />remaining constituents, the California State Action Level for Drinking Water is established for vanadium
<br />at 0.05 mg/L. For the remaining constituent, the Agricultural Water Quality Limits is established at
<br />0.05 mg/L for cobalt. Secondary MCLs are established for TDS at 500 mg/L by EPA and DHS and
<br />specific conductance at 900 µmhos by EPA. The dissolved metal results, TDS results, and the field
<br />measurements are summarized in Table 2.
<br />The analytical report is provided as Attachment 2.
<br />CONCLUSIONS AND RECOMMENDATIONS
<br />Ten metals (arsenic, barium, chromium, cobalt, iron, lead, manganese, nickel, vanadium and zinc) and
<br />TDS were detected above the analytical reporting limits in the groundwater samples collected on
<br />March 9, 2010. Of these constituents, three (iron, manganese, and TDS) were above their established
<br />regulatory levels. Because two of the metal results and TDS were above their established regulatory
<br />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 historically
<br />exceeded 5 percent by volume within the following probes: VW -4, VW -5S, VW -5D, VW -6S, and
<br />VW -6D. Since the passive soil vapor extraction trench installation in September 2006, the methane
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