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surface flow in the movement of the contaminants from point <br /> source to off-site surface water conveyances. <br /> OPERABLE UNITS <br /> 28 . The discussion on the "preliminary proposed OUs, " not agreed <br /> to by all parties, does not really belong in the Work Plan, <br /> a primary document, scheduled for finalization, and intended <br /> to be a part of the Administrative Record. Instead, DDRW- <br /> Tracy should follow the procedures in the Federal Facility <br /> Agreement, i.e. , Sections 4 . 2 and 8 .4 . DDRW-Tracy needs to <br /> discuss the OU options with EPA and the state. Once general <br /> agreement is achieved, DDRW-Tracy should formally propose <br /> the OUs in a separate letter, under DLA letterhead. Once <br /> all parties agree, DDRW-Tracy will propose a schedule in 21 <br /> days, per the terms of Section 8. 4 of the FFA. <br /> SPECIFIC COMMENTS <br /> 1. Page 1-4, Section 1.2 . 6 <br /> Explain how the 64 hazardous waste sites will be evaluated <br /> to determine the type and quantity of data required in order <br /> to adequately describe the extent of contamination. (See <br /> Also General Comment No. 17. ) <br /> 2 . Page 1-7, Section 1.4 . 1. 3 <br /> State that additional soil and groundwater investigations <br /> will place if the most hazardous constituents such as <br /> benzene, lead, or ethylene dibromide reach hazardous levels <br /> in the soils. <br /> 3 . Pages 1-11 through 1-15, Sections 1.4 .2 .3.2 through <br /> 1.4.2 .3. 10 <br /> Most of the discussion on random sampling refers to VOCs and <br /> sometimes SVOCs, both of which have low CVs, and background <br /> may be assumed to be below detectable limits (ND) . While <br /> most metals have CVs less than 100%, background <br /> concentration for some metals and for certain classes of <br /> pesticides are unlikely to be ND. (CVs for beryllium, <br /> cadmium and mercury may be greater than 100%; see also <br /> General Comment No. 14 . ) These background values need to be <br /> estimated. The human health risk at background levels will <br /> help to determine the minimum detectable relative difference <br /> that will be acceptable for these compounds. These <br /> determinations should be made on a case-by-case basis. <br /> 4 . Page 1-16, Section 1.4.2 .7 <br /> State if these methods for determining future impacts will <br /> include modeling to determine how much of the soil <br /> contamination will potentially leach into groundwater (or <br /> some other method of determination) . <br /> I-8 <br />