SITE INFORMATION AND CORRESPONDENCE_2004-2014

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Mr. Maurice Benson December 30, 2009 Page 3 calculated in a revised risk assessment and result included in an updated version of this Contingency Plan. 2.) Table 3-2, Page 3-5, PW050 & PW051; The table identifies that PW050 and PW051 sampling frequencies are to be reduced from annual and semi-annual to every five-years and no-sampling, respectively. The proposed guard well cluster for these wells is stated as MW535C. Reviewing the attached Figure 3-1 shows that PW051 and PW050 are cross-gradient and potentially up-gradient from MW535 questioning the level of warning or protectiveness the guard well cluster provides. Additionally, PW050 and PW051 screen intervals are not provided to know how they compare to MW535C and whether the wells are screened in the same lithologic formation. This is one example that further demonstrates the need for a critical analysis of guard well locations with respect to COC plumes and down-gradient potable wells in collaboration with the regulatory agencies to ensure that regulatory stakeholders concerns and input are received and incorporated as applicable. 3.) Page 4-1, section 4.1; The report should clarify that the Warning Level in most cases is identical to the federal maximum contaminant level (MCL) (Table ES-1). In the cases where the warning level is equivalent to the federal MCL, DTSC recommends reducing the warning level to one-half the MCL as a more stringent standard that would also create increased response efforts by DESJC and notification to the regulatory agencies. The Contingency Plan should provide rationale as to why the Public Health Goals were not considered as Warning Levels for DDJC-Sharpe CDCs. 4.) Page 4-1, section 4.1; Similar to comment #3, with five of the ten CDCs listed in Table 2-1 having an MCL equal to the warning level, one can easily confuse sections 4.1 and 4.2 as stating similar titles, even though the decision logic and response actions are different for each. The report should be revised to clarify this discrepancy. 5.) Page 4-1, section 4.2; The contingency plan proposes more stringent sampling for COC detections over the MCL which includes notification of the regulatory agencies. In the case of Tricholorethene the difference between notifications to the regulatory agencies could be the difference of 0.1 ug/L. DTSC requests that the report is modified to provide notification of the regulatory agencies even when COC detections do not exceed the MCL or warning levels. Regulatory notifications could be in the form of electronic mail and correspondence for relative convenience, speed, and economy.