SITE INFORMATION AND CORRESPONDENCE

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Mr. Scott Hilyard - 2 - 27 July 2007 former 5,000-gallon USTs and fuel dispensers are needed to delineate potential groundwater contamination. Regional Water Board staff also recommends installing at least one monitoring well immediately north of all former UST and fuel dispensers to verify there is no groundwater impact from the former fueling operations and improve understanding of local groundwater flow. 3. In several sections of the Work Plan, CA ARNG implies that the 2004 investigation defined the lateral extent of soil contamination south and southeast of the former 5,000 USTs and 20,000-gallon USTs. The three borings (B-1, B-2, and B-28) advanced during this investigation provide information on potential leakage south and southeast of the former 20,000-gallon USTs, but are more than 100 feet from the former 5,000-gallon USTs. The 2004 investigation does not provide useful information on the lateral extent of contamination resulting from leakage from the former 5,000-gallon USTs. Revise these sections to clarify the 2004 investigation provides information on the lateral extent of contamination resulting from leakage from the former 20,000-gallon USTs only. 4. CA ARNG should sample the three existing monitoring wells as part of the investigation proposed in the Work Plan. These wells have only been sampled twice in past seven years and have not been sampled since March 2004. Specific Comments 1. Page 3, Section 1.4.2: It is misleading to conclude that the site groundwater table is flat. There is a measurable gradient of 0.004 foot/foot. Also, there are only 3 monitoring wells at the AAFS and these wells are closely spaced, so any conclusions drawn on local gradients should be qualified. Revise the Work Plan accordingly. The groundwater gradient was determined to flow north. The reference for this information is "Hilyard, 2007". The Work Plan should be revised to indicate this conclusion is based on the historical groundwater measurements collected by CA ARNG from the three AASF monitoring wells and reviewed by the author of the Work Plan (URS) rather than implying CA ARNG says groundwater flows north. 2. Page 4, Section 3.1.4: This section briefly describes the results of soil sampling during removal of the three former 5,000-gallon USTs, but does not provide a figure or table for these results nor indicate if there was any subsequent investigations or remedial actions to address the soil contamination detected in soil samples 1 and 4. Did the soil contamination pose a potential threat to groundwater quality? Add this information to the Work Plan. 3. Page 8, Section 6.3: This section states "a minimum of two soil samples" will be submitted for analysis per boring, but Table 6-1 and Section 6.7 indicate a maximum of 10 soil samples will submitted for analysis from the five borings. It will be pointless to advance any of the proposed step-out borings ("contingency borings") if the Work Plan does not allow collection of more than 10 soil samples for analysis. Regional Water Board staff believes the sampling plan should be modified to include contingencies to collect more than 10 total soil samples and more than 2 samples per boring if suspected contamination is encountered at multiple depths. The Work Plan should also indicate