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David Wang, P.E. , Chief <br /> August 12, 1991 <br /> Page 5 <br /> Sharpe has proposed three possible explanations for the <br /> presence of arsenic. Those explanations are: <br /> a. the arsenic is anthropogenic and due to past activities <br /> at the site or surrounding area; <br /> b. the arsenic is naturally occurring; and <br /> C. the ground water geochemistry has increased the <br /> mobility of arsenic due to conditions unique to the San <br /> Joaquin Valley. <br /> No evaluations of the proposed explanations and no <br /> conclusive evidence to support that Sharpe did not dispose <br /> of arsenic at the site are provided. The Draft Final Ground <br /> Water FS provides an evaluation of the arsenic data, <br /> summarizes the data, and makes a terse conclusion regarding <br /> the arsenic issue. A majority of the arsenic data is <br /> presented as independent and unrelated information. It is <br /> recommended that the Final Ground Water FS be revised to <br /> bring a more cohesive closure to this issue. Text should be <br /> developed which summarizes and correlates the information. <br /> 5. The Draft Final Ground Water FS made many statements without <br /> adequate documentation/referencing. For example, on <br /> Page 1-102 concentration of arsenic in granite, basalt, and <br /> shale are specified without any acknowledgment of the data <br /> source. Better referencing and/or documentation should be <br /> provided throughout the Draft Final Ground Water FS. <br /> 6. The Draft Final Ground Water FS discusses the existence of <br /> high levels of nitrates in the ground water at the site. <br /> Although the presence of nitrates in the ground water may <br /> effect water quality, such contaminants are not a part of <br /> the CERCLA process, nor were they intended to be addressed <br /> within the Sharpe FFA. However, the Regional Water Quality <br /> Control Board may address this issue pursuant to separate <br /> authority. <br /> 7. CENTRAL AREA DESIGN - The Draft Final Ground Water FS <br /> include statements regarding the design of the Central Area <br /> remedial measure. The report should clearly identify that <br /> the design referenced in the Draft Final Ground Water FS is <br /> preliminary and was developed for the cost estimation <br /> purposes. Additionally, it should be clarified that the <br /> design is being developed and has not been submitted to the <br /> regulatory agencies for review. <br /> 8 . NORTH BALLOON SIX MONTH EVALUATION REPORT - Both the Draft <br /> Final Ground Water FS and the associated Remedial <br />