SITE INFORMATION AND CORRESPONDENCE

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1 Mr. Maurice Benson • - 2 - 0 19 March 2008 Defense Logistics Agency I Aquifer Cleanup Level (ACL) wells: a well used to determine if a VOC ACL or the dieldrin ACL in the sanitary sewer dieldrin plume has been achieved is called an ACL Compliance Well; a well used to determine if the dieldrin ACL in the northwest corner plume has been achieved is called an ACL Attenuation Well. At this time, there is no need for the term Attenuation Well and therefore, no need for a separate dieldrin chart. 2. Site-specific monitoring requirements are established in the April 1998 Site-Wide Comprehensive Record of Decision (ROD). Section 9.1.2 identifies the Well Monitoring Program and provides for annual review to ensure that the well locations, monitoring frequency, water level measurements, and analytes are optimized for the long term at each site recommended for further action. The ROD requires that monitoring wells at each of these sites be monitored for ROD- specified analytes for no less than three years after soil and groundwater cleanup standards have been attained. To this end, each proposed revision to the Well Monitoring Program Decision Logic must meet this ROD requirement. The Final Report must demonstrate that the monitoring well network for each of the sites with ROD-specified remedies complies with this requirement. 3. There are three key components to the proposed Decision Logic: well type, sampling frequency for each type, and an introduced variable titled preferred well. a. Well Type. A well type is defined by its position in relation to the plumes of contaminants of concern (CDCs), whether or not it is new, or by reference to monitoring requirements specified in the ROD. Regional Water Board staff has no objections to the following proposed well types on Figure 6.3-1: New Well, Compliance Well, and Guard Well for the proposed VOC Decision Logic, provided the requirements of the ROD Section 9.1 Monitoring Program, including Table 9-2, are satisfied. As discussed in Comment 1 above, Regional Water Board staff sees no need for the term Attenuation Well and therefore, no need for the separate dieldrin chart shown on Figure 6.3-2. b. Sampling Frequency. DESJC is proposing significant reductions in the frequencies that various well types would be sampled. However, the Draft Report does not present justification for reducing the frequency of groundwater sampling. For consistency and Remedial Program Manager consensus, a valid scientific approach needs to be defined, utilized, and presented in the Final Report. The approach should consider the rate of COC concentration changes and the magnitude of concentration variability observed. c. Preferred Well. The Draft Report references `preferred well'in Section 6.3.2 on page 6-3, and in Table 6.3-1 on pages 6-5 through 6-30. In Section 6.3.2, the Draft Report states the following: