SITE INFORMATION AND CORRESPONDENCE FILE 1

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CLEARWATER G R O U P, S N C. E—iro-rentnf Srroiees evidenced by laboratory data. It seems that little benefit stands to be gained from such estimates. • PHS/EHD staff state that "The full extent of the vertical extent of the soil contamination has never been assessed." Staff did not indicate this position prior to the commencement of the feasibility testing, and as such the workplan for the recently completed tasks did not address any additional assessment of the extent of contamination. Additionally, the PHS/EHD comment regarding the range of contamination is somewhat vague. The areas felt by the agency to require additional evaluation are not identified. If the PHS/EHD feels that additional evaluation is necessary, these areas will need to be specified. • In the first paragraph on page 4 of the May 23 letter, PHS/EHD staff point out that the estimated radius of groundwater contamination (50 feet) is smaller than the estimated footprint of soil contamination. Although it was not clearly stated in the report, it was Clearwater's intention to use a radius of soil contamination that was larger than the measured radius of the irregular groundwater contaminant plume. The radius of soil contamination (70 feet) was chosen to provide for a conservative estimate of vadose zone contamination. • As noted by PHS/EHD, the sample collected from the water well in January, 1996 was not preserved in the field. The sample was preserved immediately upon delivery to the lab (on the same day as sampled), however, this does not change the unpreserved holding time of the sample (seven days). The lab did not flag this in the quality assurance section of their report, nor was it noticed by Clearwater staff personnel. The lab has indicated that they will issue a letter stating their error, if the PHS/EHD so desires. • The May 23 PHS/EHD letter makes reference to a lab report submitted in July, 1995. PHS/EHD states that the lab report notes the presence of 20 ppm TPH in the diesel range in a soil sample collected during drilling of the boring for RW-1. PHS/EHD states that "It is unclear whether this detection of diesel was to infer that there may also be a diesel contamination problem ...". Clearwater made no such inference. The hydrocarbon contamination detected in the diesel range is most likely a product of weathered gasoline. Table 1 in the February 21 report will be revised to include this information. • PHS/EHD noted that Table 2 of the February 21 report contained a transposition error and a data entry error (toluene reported at 2.0 ppb instead of the actual 2.3 ppb concentration). PHS/EHD also pointed out the mis-referencing of Figure 10