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1� <br /> GEOMATRIX <br /> Mr. Robert D. Mihalovich <br /> Chevron Environmental Management Company <br /> August 24, 2000 <br /> Page 2 <br /> characterize downgradient groundwater quality. Grab groundwater sampling is appropriate <br /> because investigations conducted by Geomatrix at this and other similar sites show that <br /> groundwater conditions are stable as indicated by relatively consistent constituent <br /> concentrations at a given monitoring location over time. Given that the crude oil has likely <br /> been in the subsurface for at least 50 years, such stable groundwater conditions are to be <br /> expected. Therefore, a single sampling event (i.e., grab groundwater samples) will <br /> sufficiently characterize downgradient conditions. Samples will be collected and analyzed in <br /> accordance with the methods described in the June 29, 2000 work plan. <br /> Previously, the RWQCB has accepted the use of grab groundwater samples to characterize <br /> groundwater conditions at other CEMC sites. We believe that the use of grab samples is also <br /> appropriate at this site. As part of groundwater monitoring activities, Geomatrix will continue <br /> to monitor groundwater in monitoring wells MW-6 and MW-7. If concentrations of <br /> biodegradation byproducts (TPHd without silica gel preparation procedure) increase <br /> significantly in these wells, additional downgradient sampling using grab groundwater <br /> techniques or monitoring wells may be warranted. <br /> We appreciate the opportunity to provide CEMC with our professional environmental <br /> consulting services. <br /> Sincerely, <br /> GEOMATRIX CONSULTANTS, INC. <br /> Michael R. Keim Gary R. Foote, R.G. <br /> Project Scientist Senior Geologist <br /> MRK/GRF/pp <br /> \\st3\deptdata\Doc_Sefe\6000s\6447\Lyoth response lmdoc <br /> Attachment: Figure 1 <br />