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u ( =pf go Stewart's Beacon Project No-01-17.1 June 10,1991 Page 1 Stockviled Soil The stockpiled soil was spread out and allowed to aerate. Laboratory analysis indicated that there were small amounts of gasoline, BTEX and diesel in the soil. The gasoline and BTEX quickly evaporated, however the diesel remained and in fact the lab data shows that it has increased. The recent testing in May 1991 shows that there is some motor oil in the soil also. It is unclear why the TEPH compounds have increased over time. One possible explanation is that during field operations, the tractor used to rotate the soil may have dislodged small bits of asphalt and mixed them in with the soil. If this is the case, then the contaminants are not mobile and would not adversely impact ground water quality. This soil has been put into the underground storage tank excavation pit to help fill it and reduce the liability of an accident. The City of Tracy requested that the excavation be filled. Ground Water Monitoring At the time of excavation in January 1990, a round of samples were collected from the three monitoring wells and a second round in September 1990. A significant decrease in petroleum hydrocarbon content was observed during those 9 months. It is recommended that samples be collected this month to evaluate the current condition of the site. The decrease observed in 1990 may have been an artifact of the dewatering or from natural degradation or from ground water migration. Recommendations Geological Technics Inc. recommends that the tank water be disposed of as soon as possible and the tank removed. Geological Technics Inc. also recommends that no further site assessment or mitigation wore: be performed until there is sufficient funds to bring the job to completion without undue delays in an orderly and cost effective manner. if i -