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Al Jesena - 7 - 1 March 2000 Draft RI for OU#3 NCTS, Stockton "(3) LI.VIITATIONS ON RESPONSE. —The President shall not provide for a removal or remedial action under this section in response to a release or threat of release— (.4) of a natural!#occurring substance in its unaltered form, or altered solely through naturally occurring processes or phenomena,from a location where it is naturally found; (B) from products which are part of the structure of, and result in exposure within, residential buildings or business or community structures; or (C) into public or private drinking water supplies due to deterioration of the system through ordinary use. 3. Please clarify what is meant by the statement on page B-28, 1st paragraph, "Therefore, some other measure must be established to identify contaminated areas or hot spots of pesticides, arsenic, lead, and chromium." The other measures that should be taken include representative soil and discrete groundwater sampling of the site, test COC using acceptable methods using the lowest detection limit, and then further delineate the impacts if CDCs are found to be above background screening levels. RI Management Approach for Radionuclides 1. Potential remedies include natural attenuation and dilution. We do not agree that there is enough of a soil column to provide attenuative capacity nor do we agree that dilution is the solution when groundwater contaminates surface water. The Navy should delete all references to natural attenuation and dilution in this regard. Additional comments on the adequacy of this section will be submitted under separate cover by DTSC. 2. The Navy should clarify at what depth they propose to sample "surface soils." We recommend that soil be sampled at measured intervals until ground water is encountered (i.e., 1-, 3-, 6-, 9-foot intervals). Samples should be compared to background concentrations once background levels have been approved by the State. 3. The Navy proposes to conduct statistical comparisons of background concentrations with downgradient water quality to evaluate the presence of a radionuclide release to groundwater. Often there are no"downgradient"wells available for this purpose and/or wells are more than 250 feet away from the soil sample in a more or less hydrogeologically stagnant environment. We recommend that discrete groundwater samples to taken in the same location that soil samples are taken during the initial investigation.