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Mr. Scott Hilyard - 2 - 6 February 2007 2. Soil samples collected during the investigation and removal actions at the potential tear gas canister and copper sulfate disposal area have elevated concentrations of some metals. In particular, arsenic exceeds the US EPA Preliminary Remediation Goal for Industrial Soil in every sample. Regional Water Board staff agrees that the elevated concentrations of arsenic may fall within the range of local background, but CA ARNG needs to support this conclusion by assessing local background concentrations of arsenic. Revise the Draft Addendum to include background sampling and analysis for arsenic. The Final Addendum should include a figure showing the proposed locations of background samples. Specific Comments on Draft Addendum 1. Page 2-1, Section 2.1: It is unclear from the general description of activities in this section if a UXO team will be involved in all intrusive activities conducted under the Draft Addendum. If so, revise this section to state qualified personnel trained in the UXO identification, avoidance, and removal will be involved in all intrusive activities. If not, CA ARNG needs to explain how they determined these measures are not necessary for the proposed intrusive activities. 2. Page 2-2, Section 2.2.3: This section refers to proposed borings that are not shown on a figure. Add these proposed boring locations to Figure 4. Also, CA ARNG needs to provide the rationale for collecting samples at a depth of 10 to 15 feet below ground surface (bgs). 3. Page 2-3, Section 2.3.3: Define the objective or objectives referred to in the last sentence of the first paragraph. The second paragraph states "the excavation will be backfilled with suitable clean material from a local source". There are areas of residual soil contamination at the CA ARNG facility, so Regional Water Board staff assumes this means the backfill will come from an off-site source that has been shown to be clean through analytical testing by a laboratory certified by the California Department of Health Services. Revise this paragraph to clearly describe the source of the backfill and any information that can demonstrate that the proposed source will provide clean backfill. 4. Appendix C, Field Sampling Plan Addendum, Section 3: Analysis for polychlorinated biphenvls (PCBs) is included in the pre-characterization sampling in Table 1, but not the confirmation sampling in Table 2. Add analysis for PCBs to Table 2. 5. Appendix C, Field Sampling Plan Addendum, Section 4: The sampling program described in this section is not consistent with the description of characterization sampling activities in Section 2.2.3. Revise the Draft Addendum to clearly describe the sampling activities proposed by CA ARNG. If you have any questions, please contact me at(916) 464-4733 (mpierce@waterboards.ca.gov).