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the ponds. One boring, to be located at the center of each pond, was recommended <br />in our past comments, provided that the GPR survey results are definitive. <br />27. The quartering technique to be used for surface soil samples is not adequately <br />described and may not result in sufficiently uniform duplicate samples. An alternative <br />and preferred method of providing duplicate samples is to homogenize the discrete - <br />depth samples (pg. 4-1, Section 4.1). <br />28. Discrete 15 -in samples should be analyzed instead of the composited samples proposed <br />by SHAD in Section 4.2 (pg. 4-1), because of the potential for false negative results <br />due to dilution, and because of the lower vertical resolution that results from <br />compositing. - <br />The proposed compositing method was used in previous soil sampling by SHAD (ESE, <br />1987b) at locations where high TCE soil gas results indicated that TCE was present <br />in the soil. Discrete samples were analyzed for TCE, while arsenic, selenium and <br />bromacil were analyzed in composited samples. Because TCE, rather than other waste <br />compounds, was targeted in that sampling effort, only if arsenic and bromacil were <br />associated with the disposal of TCE would they be expected to be found. There is <br />some evidence that arsenic levels above background are associated with areas of TCE <br />contamination, but the correlation is not systematic. <br />SHAD proposes to collect three samples from each boring. A preferred procedure for <br />collecting three samples from each boring would be to collect and analyze discrete <br />samples (for example, from the upper 0- to 15 -in of soil (beneath any asphalt or <br />gravel cover), at 45- to 60 -in, at 120- to 135 -in), and to archive additional samples <br />(for example, at 90- to 105 -in and at the bottom of the hole) for possible future <br />analysis. In most cases the initial three samples would provide adequate vertical <br />coverage. If further resolution of non -volatiles were required later, the archived <br />samples could be analyzed. <br />29. Field quality control samples should be included. <br />30. The supplemental soil <br />investigation plan <br />represents an <br />outline of <br />the rationales and <br />methods to be used in <br />the proposed soil <br />investigation <br />but is not <br />sufficiently detailed <br />10 <br />