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not been detected in the receptor area (for carbon tetrachloride) <br /> is not correct. Carbon tetrachloride has been detected in the <br /> receptor area, i.e. , at the Rose and Robertson wells. <br /> Corrective Action: Include text or a footnote which explains that <br /> carbon tetrachloride has been detected at two downgradient private <br /> wells. Delete the footnote from the carbon tetrachloride "row" <br /> which indicates that carbon tetrachloride has not been detected in <br /> the receptor area. <br /> C. The remedial decision rationale for arsenic states "risk value <br /> based on 1/2 the detection limit." While this statement is true <br /> for the risk assessment (for the August 1991 sampling round, i/2 <br /> of the detection limit was 2.5 mg/1) , the text does not mention <br /> that arsenic has been detected at LM-76 at 2 mg/l in prior rounds <br /> (e.g. , May 1991) . Without this additional information one might <br /> erroneously conclude that arsenic has not actually been detected. <br /> The addition of this text will support the use of 1/2 the August <br /> sampling round detection limit. <br /> Corrective Action: Add the supporting text which states that <br /> arsenic has been detected in prior sampling rounds at levels <br /> approximating this value. <br /> d. The text for both carbon tetrachloride and dieldrin states that <br /> these chemicals "could contribute significantly to human health <br /> risk." Actually, both of these chemicals do contribute <br /> significantly to the risks. <br /> Corrective Action: Revise the text to state accurately that these <br /> chemicals are significant contributors to risks. <br /> 10. Section 6.2.5.2 <br /> The text in the first bullet indicates that for arsenic and dieldrin <br /> states "risk value based on 1/2 the detection limit." While this <br /> statementis true for the risk assessment (for the August 1991 sampling <br /> round, i/2 of the detection limit was 2.5 mg/1) , the text does not <br /> mention that arsenic has been detected at LM-76 at 2 mg/l in prior <br /> rounds (e.g. , May 1991) . Without this additional information one might <br /> erroneously conclude that arsenic has not actually been detected. The <br /> addition of this text will support the use of 1/2 the August sampling <br /> round detection limit. <br /> Corrective Action: Add the supporting text which states that <br /> arsenic has been detected in prior sampling rounds at levels <br /> approximating this value. <br /> 11. Section 6.3.7 <br /> Despite EPA's previous questioning of the text in this section regarding <br /> dieldrin at the Base, the text continues to state "it is unlikely that <br /> the risk attributable to dieldrin usage at DDRW-Tracy constitutes a <br /> significant incremental risk when potential use of pesticides and <br /> herbicides in the vicinity of the base is considered." However, as EPA <br /> has questioned before, we do not know what study (or data) is being used <br /> to support this statement. Further, it is not clear that this statement <br /> has a purpose to this ROD which is setting aquifer cleanup standards for <br /> only TCE, PCE and DCE. <br /> Corrective Action: Delete this sentence. <br /> EPA/R9 July 28, 1993 3/7 <br />