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Work Plan Addendum -7- 21 September 1992 <br /> DDRW, Sharpe <br /> 8. The Work Plan Addendum states that the vertical extent of pesticide <br /> contamination has been adequately defined (page 3-12) . However, the figures <br /> presenting the data do not support this claim. Of particular concern, is that <br /> Figures 3-2 and 3-3 depict concentrations of chlordane at 55 mg/kg and 11 .8 <br /> mg/kg for the CHLOR 11 and CHLOR 10 samples, respectively. (However, the text <br /> and Table 3-1 show these concentrations to be in CHLOR 4 and CHLOR 11, <br /> respectively. CHLOR 4 was reported to be a composite sample and had 55 mg/kg <br /> of chlordane.) These concentrations far exceed the hazardous concentration of <br /> 2.5 mg/kg for chlordane. It is unclear whether these samples were collected at <br /> the surface or were from deeper samples (1.0 to 1.5 feet) . <br /> Pending clarification of the data, if hazardous concentrations of chlordane or <br /> other pesticides are found at the 1 .5 feet deep samples, then we cannot concur <br /> that the vertical extent of contamination has been defined. Deeper samples may <br /> need to be collected to define the vertical extent of contamination, <br /> particularly in the ditch were these very high concentrations of chlordane were <br /> detected. In order to define the vertical extent of contamintion, soil samples <br /> must be collected and analyzed until background concentrations are detected. <br /> 9. The Work Plan did not appear to discuss the extremely high concentrations of <br /> DDD, DDE and DDT. The hazardous concentration for these insecticides is 1 <br /> mg/kg. However, based on the data presented in Table 3-1, up to 217.11 mg/kg <br /> (CHLOR 16) were found in soil samples. This does not agree with the statement <br /> in the Work Plan addendum that the concentrations of DDD, DDE and DDT, as great <br /> as 8.56 mg/kg are present in the area north of Building T-40. Because these <br /> other reported concentrations of pesticides were not discussed in the Addendum, <br /> we question the findings regarding the distribution of the pesticides. <br /> Clarification of the data for the purposes of further definition and for <br /> confirmation is needed prior to selection of additional sampling locations. <br /> 10. The Work Plan Addendum does not recommend the installation of any monitor wells <br /> in the pesticide mix area because the existing data indicate that the <br /> contamination is confined to the very shallow soils (page 3-14) . The closest <br /> monitor well to the pesticide mix area is MW-414A, but this well is up gradient <br /> from this area. Before we concur with the recommendation not to install a <br /> monitor well in this area, Sharpe needs to clarify the data with respect to <br /> concentrations and sample depths. Because Sharpe did not sample the soils for <br /> all potential different types of pesticides and due to the wide spread presence <br /> of hazardous concentrations of pesticides in many of the soil samples, it is <br /> premature to state that a monitoring well is not needed in this area. <br /> 11. The Work Plan states that there are four monitor wells in the immediate area of <br /> WMU No. 26 where sand blasting wastes were dumped. Two of these wells, MW-420 <br /> and MW-432, are up gradient and two wells, MW-413 and MW-438, are down gradient <br /> (page 4-6) . Elevated concentrations of chromium and lead have been found in <br /> the soil samples from this area. It is unclear whether any of the existing <br /> soil samples were analyzed for metals other than chromium and lead. The <br /> Addendum proposes to sample the four existing monitor wells for chromium and <br /> lead (page 4-16) , but does not propose analysis for any other metals. <br /> WMU No. 26 is adjacent to UST No. 27 in the North Balloon Area. In MW-472A, <br /> elevated concentrations of chromium and nickel (above the Primary MCL) and zinc <br />