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Mr Harlin KnoII . Environmental 9 December 1999 Resources Page 2 Management from MW-4 in October to confirm the results, however, the laboratory discarded the sample before it could be re-analyzed The groundwater samples collected from MW-4 during this sampling event were analyzed for TPH-g (EPA Method 8015), BTEX (EPA Method 8020), and methyl tertiary butyl ether (MTBE) (EPA Method 8020) However, due to the previous inconsistent results in this well, the analytical laboratory (AN/EN of Marina, California) recommended that the samples be centrifuged prior to analysis By centrifuging the samples, any soil particles in the ground water sample are separated from the water such that a true ground water sample can be extracted for analysis The groundwater sample analytical results are summarized in Table 1 (Attachment A), along with the results of previous samples collected at this location Copies of the laboratory analytical results and well sampling data are included as Attachments B and C, respectively As shown in Table 1, the results for this sampling event are "in line" with . the expected downward trend since ORC injection was applied and suggests the result obtained from the 28 October 1999 sampling event was not representative of the true water quality conditions at the MW-4 location The concentrations of TPH-g and BTEX obtained from samples collected during this sampling event were also the lowest observed in this well to date In general, the results of this sampling event were less than, but consistent with, the results obtained during the 22 April 1999 (pre-ORC injection) and 2 September 1999 sampling events Based on the results of this sampling event, ERM believes that the fluctuation of concentrations in MW-4 samples is due to the presence of fine-grained soils in the ground water samples This is confirmed by not only the lower sampling results observed during this sampling event, but also the reproducibility of the results (i e , the duplicate sample results were nearly identical to the original sample) Finally, the turbidity noted in field logs during previous sampling events indicates that soil particles have been present in samples collected at this location To further confirm the results obtained during this sampling event, ERM intends to perform a round of groundwater sampling at all the wells at the site in late December 1999 For samples collected during the . December 1999 sampling event, ERM intends to have the laboratory centrifuge the samples prior to analysis for all the wells at the site The results will be compared to previous analytical results to determine if