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u � Y W Du Pont 131UsN,,tCJ17s Page 35 August 10, 1989 Job No, 211-71-6 2. Benzene concentrations have increased in monitoring wells MW-1 (37 ppb to 67 ppb), MW-15 (0.5 ppb to 3.4 ppb), hf W-21 (2.7 ppb to 22 ppb), and MW-24 (non-detected to 3.2 ppb). The benzene levels have decreased in monitoring wells MW-16(0,63 ppb to non- detected), MW-23 (74 ppb to 66 ppb), and MW-25 (3.1 ppb to 2.5 ppb). Benzene in monitoring wells MW-18 and MW-20 has remained non-detected. 3. Free-floating product is present in monitoring wells MW-8, MW-10, and MW-17. The free product in these wells is being removed on a regular basis and the recovered product _ s being manifested for recycling by Alviso Independent Oil Company, REMEDIATION ALTERNATIVES The Regional Water Quality Control Hoard-Central Valley Region is recommending the following cleanup action levels: Material Analyte Limits Sna TPHg 1 Water ppm W TPHg non-detected Water Benzene 0.7 ppb k:y Water Toluene 100 ppb Water Xylenes 620 ppb t` Water Ethylbenzene 650 ppb We understand,through conversations with representatives of the Regional Water Quality Control Board,that the action levels listed above represent an idealistic ultimate goal,however,actual clean- up limits are negotiable based on site spec--irc conditions. Ground water in most of the monitoring wells at the Douglas Gas Station site exceeds some or all of the analyte limits listed above. Water in monitoring well MW-20 contains non-detectable amounts of TPHg and BTXE and monitoring wells MW-18, MW-19, MW-21, MW-24, and MW-25 have iow concentrations, considered from a practical standpoint to be at or near background levels. Significant so': contamination was encountered in monitoring wells MW-17,MW-22,and MW-23 and exploratory borings B-1 through B-6 and B-9. -- Soil -We have considered the,following soil reediation methods: ]. Excavation and a. Transport to a Class I disposal facility, Jb. On-site treatment (e.g. aeration)