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J. '4 kLE1 N FELD ER & ASSN SATES CHNICAL CONSULTANTS • MATE ,u! ESTING _ LAND & WATER RESOURCES RECEIVED i E Z 8 2825 EAST MYRTLE STREET STOCKTON, CA 95205.4794 .2091 948-1 34 5 File No. S-1773-8/12 July 11, 1985 Dave Tagliarenie Post Office Box 876 Rio Vista, CA 94571 Subject: SOIL BORINGS AND MONITORING WELL INSTALLATION EXISTING CHEVRON FACILITY STOCKTON, CALIFORNIA Gentlemen: As requested on May 31, 1985, representatives of our firm drilled and obtained several soil samples at previous and existing buried tank locations on the subject site. The locations were indicated to our representatives in the field. In addition, a groundwater monitoring well was drilled and installed at a location requested on the site. The test borings and monitoring well were drilled using a truck-mounted drill rig equipped with 6-inch diameter continuous-flight auger. Soil samples were obtained by driving a 2-inch inside diameter sampler into the soils using 140-pound hammer falling approximately 30 inches. The soil samples were covered with aluminum foil, capped and stored in a cooler until delivered to the lab for testing. We note that at the time of installation, if was our understanding that the purpose of the monitoring well was for groundwater measurements. Therefore, the well was not constructed according to Subchapter 15 requirements.' However, it was requested that a water sample be obtained from this well for gasoline content and oil and grease sampling. In general, the soil conditions encountered consisted of approximately 8 feet of recently placed tank backfill in Borings 1 and 2. In Boring 3, approxi- mately 4 feet of sandy clay and silt fill materials were encountered overlying black clay soils, which extended to a depth of approximately 7-1/2 feet. At the monitoring well location, approximately 7 feet of clayey and silty gravelly debris fill was encountered. Below approximately 7 to 8 feet in all the borings, relatively hard native sandy clay and silt soils were encountered to the maximum depths explored of from 16 to 45 feet below existing ground surface. Free groundwater was encountered in the monitoring well boring at a depth of approximately 33 feet. However, it is possible that groundwater conditions could vary at the site due to rainfall, construction activities, groundwater withdrawal, or other factors not apparent at the time of our field explorations. We note that gas odors were detected in the soils of Borings 1 and the moni- toring well. OTHER OFFICES: -, Walnut Creek • San Ramon • Sacramento • Fresno + Fairheid • Merced • Rohnert Park • Loi Anv, �e, erne Las Vegas • St.George,Utah + Oenver