SITE INFORMATION AND CORRESPONDENCE

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Mr. Ken Price - 4- 3 July 2003 Analytical Quantiation Limit Comment Table, con't Constituent Geomatrix RWQCB RWQCB Response Practical Analytical Quantitation Quantitation Limits Limit 2,4,5-T 0.1 to 1 ug/L 0.1 ug/L 2,4-D 0.5 to 5 ug/L 0.5 ug/L A note has been added to the Revised Groundwater Cleanup Criteria table acknowledging that matrix Dicamba 0.1 to 1 ug/L 0.1 ug/L interferences could result in higher quantitation limits. Dinoseb 0.25 to 2.5 ug/L 0.25 ug/L Total Kjeldahl 0.5 to 125 mg/L 0.5 mg/L Nitro en Geomatrix states that analytical laboratories occasionally are unable to achieve the stated quantitation limits due to matrix interferences resulting from elevated levels of other constituents. This has been observed at this site as well as others,but to date has not been an issue. If matrix interferences routinely elevate the detection limits and this becomes an issue between MSRM and Board staff, then MSRM should provide the laboratory analytical data sheets that will substantiate the interference. At this site, MSRM and previous Regional Board staff Mr. Joe Mello made an agreement that MSRM would provide analytical data in an electronic format and is not obligated to provide laboratory analytical data sheets. Water Quality Limits In its comment letter, Geomatrix states that shallow groundwater under the site is unlikely to be used for municipal or domestic water supply because it is in the eastern border of salt water intrusion from San Francisco Bay. Because this is unlikely to be used as municipal supply, MSRM requests that the 1997 Target Cleanup Levels (1997 Target Cleanup Levels, 1904 West Charter Way, Stockton prepared by Geomatrix Consultants) for three compounds be replaced with the Maximum Contaminant Level (MCL). These target cleanup levels identify the constituent concentration estimated to provide protection to the 1-in-10,000 cancer risk level and a Hazard Index of 1. The following table shows these constituents, the target cleanup level,the MCL, and the Range of Cleanup Levels identified in the Revised Groundwater Cleanup Criteria Table. Risk-Based Concentration Comment Table Chemical Cancer Risk Hazard Index MCL Range of Cleanup Levels (1-in-10,000) 1 Benzene 1.3 ug/L 2.6 ug/L 1 ug/L not identified as a constituent of concern DBCP 0.053 u 0.064 ug/L 0.02 u 0.0017—0.01 u 1,1,2,2- 0.97 ug/L No Significant 1 ug/L not identified as a tetrachloroethane Risk constituent of concern Of the three constituents, only DBCP is identified as a constituent of concern at this site. The cleanup goal ranges from the water quality limit,which is below the detection limit, to the detection limit of 0.01 ug/L. The MCL is not an appropriate cleanup level because it does not