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<br /> URS
<br /> Mr. Robert McClellon
<br /> April 29, 2011
<br /> Page 3
<br /> 23.3 percent. Results for each probe, each extraction well, and each passive vent are summarized in
<br /> Table 1.
<br /> Groundwater. An interpreted groundwater contour map was prepared using the data collected on
<br /> March 15,2011 (Figure 2). The groundwater flow direction is to the northeast at a gradient of 0.0024.
<br /> The groundwater flow direction results can be compared to the historical results. The predominant
<br /> groundwater flow direction of the previous quarterly monitoring events is shown to be in the southwest
<br /> to northeast or west-southwest to east-northeast direction but has varied from quarter to quarter.
<br /> The following seven metals were not detected above the analyses reporting limit: aluminum,cadmium,
<br /> lead, mercury, selenium, silver, and thallium. The highest detected concentration of the remaining
<br /> ten metals are 0.00691J milligrams per liter(mg/L) for arsenic(MW-1), 1.46 mg/L for barium (MW-2),
<br /> 0.00498J mg/L for chromium (MW-3), 0.00341J mg/L for cobalt(MW-1), 0.00212J mg/L for
<br /> copper(MW-1), 1.04 mg/L for iron(MW-2), 2.75 mg/L for manganese (MW-1), 0.00586.1 mg/L for
<br /> nickel (MW-1), 0.0196 mg/L for vanadium (MW-3), and 0.00834J mg/L for zinc (MW-2). The highest
<br /> TDS concentration of 1,710 mg/L was found in MW-2. The field measurements for pH ranged from
<br /> 6.13 to 6.85, and specific conductance ranged from 1,690 to 2,780 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,copper at 1.3 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 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, copper, iron, manganese, nickel,vanadium and zinc)and
<br /> TDS were detected above the analytical reporting limits in the groundwater samples collected on
<br /> March 15, 2011. Of these constituents, four(barium, iron, manganese, and TDS)were above their
<br /> respective established regulatory levels. Because three of the metal results and TDS were above their
<br /> respective established regulatory levels, URS plans to continue monitoring of these metals and TDS.
<br /> Because the results have not changed significantly since the start of the quarterly groundwater
<br /> monitoring of December 2006, URS recommends that monitoring continue on an annual basis.
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