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URS <br /> ' Mr. Durin Linderholm Page 8 of 10 <br /> Regional Water Quality Control Board—Central Valley Region <br /> ' October 30, 2014 <br /> • Perform a limited field investigation to characterize contaminant of concern concentrations <br /> downgradient of the remediation area (specifically downgradient of MW-24-BP) (see Focused <br /> Passive Soil Gas and Groundwater Investigation and Well Installation Work Plan [URS, 2014]). <br /> ' • As needed, implement targeted follow-on injection of emulsified oil (or another electron donor). <br /> Future injections will be based on the continued findings of the pilot test and, if applicable, the <br /> field characterization effort. <br /> ' • In anticipation of possible follow-on injections, evaluateinstallation of new monitoring well or <br /> wells. No more than two wells are needed to effectively monitor the remedy. <br /> • Discontinue sampling for Cr(VI)and all metals with the exception of dissolved iron, dissolved <br /> arsenic and dissolved manganese. Continued Cr(VI) sampling is not warranted because Cr(VI)is <br /> expected to decrease under reducing conditions and the 24-hour holding time for Cr(VI)poses a <br /> challenge for timely delivery of the samples to the laboratory. Continued sampling for metals <br /> other than the three listed is not warranted because, as shown by the pilot test results,most metals <br /> are not expected to be affected by the proposed injections. <br /> ' REFERENCES <br /> United States Environmental Protection Agency, 1988. Technical Protocol for Evaluating Natural <br /> Attenuation of Chlorinated Solvents in Ground Water. September. <br /> ' URS Corporation Americas, 2014. Focused Passive Soil Gas and Groundwater Investigation and Well <br /> Installation Work Plan, September. <br /> ' If you have any questions or require additional information, please contact Mr. Ed Tarter at <br /> ' (916) 679-2055. <br /> Sincerely, <br /> URS Corporation Americas QR�FESS�ON� <br /> ' No. 64825 ^ <br /> Edmund Tarter, PE gyp, 6 3o S <br /> Project Manager <br /> CMS <br /> Attachments: -9 OF CA1�FOe` <br /> Table 1 Groundwater Flow Direction and Gradient <br /> Table 2 Groundwater Elevation and Analytical Data <br /> Table 3 Injection Analytical Results <br /> Figure 1 Site Location Map <br /> Figure 2 Groundwater Analytical Summary <br /> Figure 3 Groundwater Elevation Contours <br /> \VSACDATA0100ciplivli\Wpmc=\CDCR\Dwd Vocations Insdwdm(Bum Pit)DVI-BP-3QM1 14 Re m.doc <br /> 1 <br />