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Review of the Draft Natural Attenuation Investigation Results <br /> Technical Memorandum, DDJC Sharpe <br /> Lathrop, California <br /> June 2006 <br /> GENERAL COMMENTS <br /> 1. This memorandum concludes that natural bioattenuation alone is not an adequate remedy <br /> to address contamination at the North Balloon Plume; however it is unclear why other <br /> natural attenuation mechanisms such as sorption or volatilization were not considered in <br /> this document. Also, although bioattenuation is not a suitable remedy, enhanced <br /> bioattenuation should be evaluated as a potential remedy for this plume. Please consider <br /> evaluating other attenuation mechanisms for remediation of this plume. <br /> 2. It would be helpful in evaluating the analytical data to include the field log sheets for the <br /> groundwater sampling and to include the specific criteria used for assessing stability of <br /> water quality parameters. Please provide log sheets and specify stability parameters <br /> required prior to sampling. <br /> 3. No site specific background information was provided in this memorandum. Information <br /> such as the site specific conceptual model relevant to the bioattenuation investigation <br /> would aid in the assessment of the results. Also, information on the source of <br /> contamination would be helpful in interpreting the plume map in Figure 1. The map <br /> appears to show two separate sources of contamination(one in the vicinity of monitoring <br /> well MW456 and one in the vicinity of EWNB1)that are merged together to form one <br /> plume. Additionally groundwater flow rates would be useful in assessing attenuation <br /> processes for this plume. Please provide site specific background information, including <br /> conceptual model of site contamination, source description and groundwater flow rates. <br /> SPECIFIC COMMENTS <br /> 1. Section 2, Field Activities,Page 1: In the first paragraph of Section 2 the C Zone (90 <br /> feet to 170 feet) and the D Zone (120 to 270 feet) of saturation appear to overlap. It is <br /> unclear if this overlap is a typographical error or if the overlap is significant to the <br /> conclusions regarding natural attenuation. Please provide more information about the <br /> overlap between the C and D zones of saturation. <br /> 2. Section 3.1, Background,Page 4: The first sentence of the last paragraph on page 4 is <br /> misleading in stating that analytical data should be collected"for all or some of the <br /> parameters" from the EPA protocol. The EPA protocol (Table 2) specifies which <br /> parameters are required and which are optional in support of the evaluation of monitored <br /> natural attenuation(NINA). Please be explicit in the text that certain parameters are <br /> required. <br /> 1 <br />