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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 255-3000 Sacramento, CA 95827-3098 CAL.NET. 8-494-3000 To: Wendy L. Cohen FR M: Joel M. Weiss Senior Engineer Engineering Geologist-- DATE: 16 February 1994 SIGNATURE: SUBJECT: PETROLEUM CONTANICINATEI) SOILS AT BELCONTE NORTH SUBDIVISION, TRACY, SAN JOAQUIN COUNTY Background In 1988, petroleum-contaminated soils were found along Byron Road during the installation of a City of Tracy pipeline. The excavation occurred on the south side of the road and affected soils were found down to 18 feet below the ground surface (b s). A line of nine soil borings were drilled 125 feet south of Byron Road, and subsequent analyses ealed no contamination. Borings also were drilled 28 and 53 feet south of the road. These sar iples; also were free of contamination. One sample taken 11 feet south of the road at a depth of six I=t did contain petroleum contamination. A field surveillance discovered petroleum-affected.soils alo g the railroad right-of--way (adjacent to.a petroleum pipeline) north,-'of Byron Road. In 1989, Levine-Fricke drilled a line of 13 soil borings 18 to 54 feet south of Byron Road. Petroleum hydrocarbons were detected in five samples from three of the borings within 25 feet of the road. The petroleum was characterized as a "tar-like petroleum distillate with a degraded lighter fuel component which may be a diesel #2....a relatively heavy molecular structure and an extremely low solubility in water at the site". Concentrations rang from 81 to 1,100 ppm. The 1989 Levine-Fricke report is not in the Board's files. In May 1990, four ground water monitoring wells were installed at the site. Ground water depth is approximately seven feet bgs. Based upon a single gaug event which occurred on the same day as purging, the gradient is to the southwest, away from a road and pipeline, and towards the proposed development. Two soil samples were taken fr m each well and sampled for total petroleum hydrocarbons (T H) and benzene, toluene, a ylbenzene, & xylene (BTEX): Toluene was the only constituent found, at concentrations ranging from 15 to 180 gg/kg. Toluene was also found in one of the water samples at a concentration of 0.33 µg/1. RESNA submitted a work plan for soil remediation dated, 25 November 1992. They proposed to excavate, bioremediate and then utilize the soil around the proposed subdivision.