SITE INFORMATION AND CORRESPONDENCE

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Sheldon Heckman, c/o Kama E. Herrigfeld -2 - 19 February 2002 Herum Crabtree Brown, Stockton Previous investigations reported maximum soil concentrations of 2300 mg/kg (TPH-g), 2000 mg/kg (TPH-d), 2300 mg/kg (TPH-ss) and methanol (VOCs) at 310 mg/kg. Previous maximum groundwater results include 120,000 µg/L(TPH-g), 330 µg/L (TPH-d), 120,000 µg/L(TPH-ss), 96 4g/L—72 µg/L— 1100 µg/L-760 µg/L(B-T-E-X, respectively). Tetrachloroethene (PCE)was detected in soil at a concentration of 68 µg/kg during a previous investigation. PCE was not detected in groundwater, although groundwater analysis detected its daughter product 1,2-dichloroethane (1,2-DCA), at 25 µg/L. The Work Plan also provides a schedule for field activities and the submittal of two reports (Problem Assessment Report and Final Remedial Plan). The Work Plan is approved provided the following comments are incorporated into the work scope. Comments: 1. The text states only that appropriate soil gas sample methods for TPH(-g, -d, -mo, -ss), BTEX, and VOCs will be performed for the SVE test. Please submit the specific soil vapor analytical methods, with their method detection limits, that will be used for TPH (-g, -d, -mo, -ss),BTEX, and VOCs. 2. Add, at a minimum, the following groundwater analyses to those specified in Section 3.7 Groundwater Sample Collection and Analysis in the Work Plan for the Natural Attenuation- Biodegradation Pilot Test: 1). dissolved oxygen (by field meter). This test is mentioned in Section 5.3. 2). oxidation/reduction potential (by field meter). This test is mentioned in Section 5.3. 3). pH(by field meter). Water sample pH may change in transit to the laboratory. Evaluate collection of other useful groundwater analyses for determining the existence of natural attenuation—biodegradation,including: ferrous iron, carbon dioxide, methane, and chloride. 3. Note that Table 7A (Proposed Upper Vadose Shallow Soil Vapor Extraction Pilot Test) also includes the Deep Soil Wells. Note that Table 7B (Proposed Lower Vadose Shallow Soil Vapor Extraction Pilot Test) also includes the Shallow Soil Wells and some groundwater monitoring wells. It appears that each SVE pilot test will be duplicated(upper and lower vadose zones), and one test(lower vadose zone SVE pilot test) will be measuring SVE response in groundwater monitoring wells. The text in Section 5.2 Soil Vapor Extraction Pilot Test states that each test will focus on one depth-specific vadose zone per test, without groundwater monitoring wells. Please submit corrected the tables, if applicable. 4. The Work Plan specifies clean water or tap water for the final rinse, when decontaminating equipment. De-ionized or distilled water should be used for the final rinse, whenever there is a possibility for cross-contamination of groundwater samples (e.g., water level meter).