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Mr. Robert McClellon
<br />July 22, 2009
<br />Page 3 of 4
<br />concentrations measured at all sample locations during the quarter ranged from 0.9% to 24.0%. Results
<br />for each probe, each extraction well, and each passive vent are summarized in Table 1.
<br />Groundwater. An interpreted groundwater contour map was prepared using the data collected on June
<br />10, 2009 (Figure 2). The groundwater flow direction is to the east-northeast at a gradient of 0.000096.
<br />For comparison, the groundwater flow direction varies from the east-southeast to the west-northwest
<br />(September 10, 2008), from the east to west (June 10, 2008), from southeast to the northwest
<br />(September 20, 2007), from the west-southwest to the east-northeast (June 14, 2007, December 13, 2007,
<br />and March 13, 2008), from the southwest to the northeast (June 29, 2006, December 15, 2006,
<br />March 14, 2007, December 9, 2008, and March 11, 2009), and from the northeast to the southwest
<br />(September 29, 2006).
<br />The following metals were not detected above the analyses reporting limit: aluminum, cadmium,
<br />mercury, selenium and silver. The highest detected concentration of the remaining 12 metals are
<br />0.0155 milligrams per liter (mg/L) for arsenic (MW -1), 0.908 mg/L for barium (MW -2), 0.00392J mg/L
<br />for chromium (MW -3), 0.00605J mg/L for cobalt (MW -1), 0.00274J mg/L for copper (MW -3),
<br />3.44 mg/L for iron (MW -2), 0.0154J mg/L for lead (MW -2), 3.66 mg/L for manganese (MW -1),
<br />0.00891J mg/L for nickel (MW -1), 0.00718J mg/L for thallium (MW -1), 0.0173 mg/L for vanadium
<br />(MW -3) and 0.0226 mg/L for zinc (MW -2). The highest TDS concentration of 2,330 mg/L was found in
<br />MW -2. The field measurements for pH ranged from 6.49 to 6.92, and specific conductance ranged from
<br />1,880 to 3,350 micromhos (µmhos).
<br />Of the 12 reported metals constituents, primary maximum contaminant levels (MCLS) are established for
<br />seven constituents (arsenic at 0.01 mg/L by EPA and 0.05 mg/L by 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, lead at 0.015 mg/L by EPA and DHS,
<br />nickel at 0.1 mg/L by DHS, and thallium at 0.002 mg/L by EPA and DHS). For the remaining five metal
<br />constituents, secondary MCLs are established for three (iron at 0.3 mg/L by EPA and DHS, manganese
<br />at 0.05 mg/L by EPA and DHS and zinc at 5 mg/L by EPA and DHS). For the two remaining
<br />constituents, the California State Action Level for Drinking Water is established for vanadium at
<br />0.05 mg/L. For the remaining constituent, the Agricultural Water Quality Limits is established at 0.05
<br />mg/L for cobalt. Secondary MCLs are established for TDS at 500 mg/L by EPA and DHS and specific
<br />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 />Twelve metals (arsenic, barium, chromium, cobalt, copper, iron, lead, manganese, nickel, thallium,
<br />vanadium and zinc) and TDS were detected above the analytical reporting limits in the groundwater
<br />samples collected on June 10, 2009. Of these constituents, five (arsenic, iron, lead, manganese and TDS)
<br />were above their established regulatory levels. Because four of the metal results and TDS were above
<br />their established regulatory levels, URS plans to continue quarterly monitoring of these metals and TDS.
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