SITE INFORMATION AND CORRESPONDENCE 1991-1992

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T, .,a l Mr. Robert Doss, P.E. SEP 19 1W September 17, 1991 Page 2 5. Table 2-8 - Compounds exceeding water quality goals are shown shaded on Table 2-8 . Concentrations of antimony are above water quality goals and thus should also be shaded. 6. Page 2-22, 2nd paragraph - Compounds exceeding water quality goals are discussed on page 2-22 . Concentrations of antimony are above water quality goals and thus should also be discussed. 7 . Page 4-8, 3rd paragraph - Five offsite surface soil samples are proposed to characterize background concentrations. These soil samples should be collected and analyzed at various depths as a means to establish soil background concentrations. Furthermore, these sample locations must be in areas that could not have received contamination from the site, but that do have the same basic characteristics as the soil at the site. 8 . Chapter 4 . 1.21 Soil Investigation - Based on the historical review described in item #4 above, PG&E should propose a soil investigation plan for Area II. There is no record of an investigation of this area to show that contaminants do not exist. The investigation should include Parcel L which housed a gas holder and a street R.R. powerhouse. The two soil samples proposed in area III are well located to detect if a release of contaminants have migrated to the outside boundary of the former tank, but may not detect contaminants that may exist toward the center of the former tank location. PG&E should propose a third soil sample location toward the center of the former tank or between the two other borings if necessary. 9 . Chapter 4 . 1.3, Well Installation - The Department recommends the use of engineered £ilterpacks based on borings logs and sieve analysis for wells since the use of non-engineered types may be limited. The proposed screen slot size may be too large allowing too much sediment to be removed possibly leading to settlement of the surrounding soils. Filtering out the sediments from the water sample could result in distortion of analytical results which would not be acceptable. Furthermore, well construction details should include a discussion of the number and location of centralizers and the type and size of the sand pack to be used. Centralizers should be installed below and above the screen, then at intervals of 40 feet. The filter pack should be matched to the screen so as to not allow more than 10% of the filter pack through.