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URS <br /> ' Ms.Kathy Amam Page 7 of 9 <br /> Regional Water Quality Control Board—Central Valley Region <br /> ' April 30,2014 <br /> ' concentrations previously observed in MW-6-BP and MW-24-BP appear to be stabilizing or decreasing, <br /> indicating that any increase in these metals' concentrations is likely temporary. <br /> ' RECOMMENDATIONS <br /> Based on 1Q14 groundwater monitoring results and historical data,URS concludes the following: <br /> ' • Evaluate the benefit of performing a laboratory bench-scale test of emulsified oil or other electron <br /> donors.Consider conducting the test with and without buffering reagents and added bacteria,in <br /> ' anticipation of possible follow-on remediation in areas where contaminants of concern <br /> concentrations remain elevated and there is no indication of further reductive dechlorination. <br /> • Implement targeted follow-on injection of emulsified oil(or another electron donor).Future <br /> injections will be based on the continued findings of the pilot test and,if applicable,the bench- <br /> scale laboratory test. <br /> • In anticipation of the possible bench test and full-scale implementation,evaluate installation of <br /> ' new monitoring well or wells.No more than two wells are needed to effectively monitor the <br /> remedy. <br /> • Discontinue sampling for Cr(VI). Continual Cr(Vl)sampling does not appear to be warranted <br /> ' because(1)dissolved chromium results are very similar and can be used instead,(2)Cr(VI)is <br /> expected to decrease under reducing conditions,and(3)the 24-hour holding time for Cr(VI) <br /> poses a challenge for timely delivery of the samples to the laboratory. <br /> REFERENCES <br /> ' United States Environmental Protection Agency, 1988. Technical Protocol for Evaluating Natural <br /> Attenuation of Chlorinated Solvents in Ground Water. 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 Q � <br /> JNp D. lq�T <br /> No. 64825 a <br /> Edmund Tarter,PE Exp, <br /> Project Manager <br /> J'! CMS �1�Q <br /> OF <br /> CAUF�� <br /> H:\Wpro=\CD R\ el Vocations l aiwtm(B Pd)\ VI-BP-IQMR14 Repon.doc <br />