SITE INFORMATION AND CORRESPONDENCE

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t Environmental Consultants • 6761 Sierra 415 829-0661 Suite D FAX 415 829-5493 Dublin, CA 94568 SCS ENGINEERSA February 19, 1991 File No. 0389019.01 1INN Mr. Robert Evans California Regional Water Quality Control Board f� -.rO " 3443 Routier Road, Suite AE��lRot B 2 Sacramento, California 95827-3098 pCR tl'1CAlT It, Subject: Installation of Vadose Zone Monitoring Wells at the Land Treatment Site for Contaminated Soil in Traev. California Dear Mr. Evans: Following our discussion with Regional Water Quality Control Board (CRWQCB) on February 6, 1991, SCS Engineers (SCS) is enclosing a work plan for installing 3 additional vadose zone wells at the subject site. As discussed, these vadose zone wells will be installed in lieu of the groundwater monitoring wells as originally proposed. On January 29, 1991, SCS utilizing HEW Drilling Company attempted to install the groundwater monitoring wells at the site as outlined in the original work plan (see Figure 1). After drilling to a depth of 30 feet we did not encounter groundwater. Later based on discussion with the neighboring farmer, Mr. Lester Huck, and personnel with the U.S. Bureau of Reclamation (USBR) familiar with the area, we learned that the first groundwater bearing strata in the site area is at a depth of at least 130-150 feet. The units encountered during the drilling are between 5 ft and 6.5 ft dark brown organic silt and light brown silty to sandy gravel. Loose and dry brown sandy gravel was found between the depths 10 to 11.5 ft, and 15 to 16.5 ft. At 20 to 21.5 ft deep, a reddish brown silty sand was encountered. Because the water level is so deep, it is SCS' opinion that the possibility of groundwater contamination resulting from this treatment process is very remote. It was also apparent that groundwater monitoring would not be useful tool for assessing any possible contamination resulting from the bioremediation activities. Therefore SCS proposes to monitor the vadose zone for organic contaminants during the duration of the bioremediation process. To establish a baseline for groundwater quality, SCS will be taking water samples from an existing well of Mr. Lester Huck located about 1500 feet east (downgradient) of the subject site. The water sample will be analyzed by Cincinnoti Columbus Kansas City Los Angeles New York Norfolk Phoenix Son Francisco Seattle Tampa Washington, D.C.