ARCHIVED REPORTS XR0010977 - Laserfiche WebLink

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WESTERN GEO-ENGINEERS The focus of Western Geo-Engineers investigation was to delineate the extent of loll and ground water contamination on site and to ascertain if contamination had migrated off-site, to evaluate the degree of contamination and if remediation was warranted. A review of the chemical data generated from the current investigation indicates that the soil has been clean of contamination (excavation and aeration) and that limited (predominately north, MW 1, and within the confines of the present fuel tank area) ground water contamination exists as dissolved constituants of gasoline (see tables 2 & 3 and figures 14A & 1443). According to Tracy Water Works engineers the aquifer currently being monitored in this investigation is not considered a primary aquifer the only indicated use would be for irrigation and thier records show no known useage. South of the site is the Alden Park Assessment area. This is upgradient of the 9 Desert Petroleum site and has known k round water contamination. Verbal communications with David Brent of the RWQCB, Sacramento, indicates the contaminate is of a Crude-Bunker oil type. Its extent is floating on the shallow aquifer and thought to be retained on the site (south of the railroad tracks as show on figure 2 Oil Reservoir ano Oil Tanks ). 'i Based on the geology of the area, ground water flow direction should be to the north and northeast, however, the ground water flow direction observed at the site -; has treaded from a northeast direction to a northwest direction and back to the north. These fluctuations in the site ground water flow can be attributed to the open fuel tank excavation from April 19 through the and of May, 1988. During the firsts weeks the excavation was left open precipitation amounts where slightly over the normal and the excavation acted as a recharge area for the shallow aquifer. From May 10 through May 27, 1988 the weather changed from cool and moist to hot and dry and the excavation became an evaporation pond and an area of dicharge, drawing the shallow aquifer and associated contaminants into It. By June 1, 1988 the excavation had been filled with the new installed tanks and clean pea gravel thus slowing or stopping evaporation and the ground water flow direction was starting to trend back to the north, which is thought to be the true (natural) direction. "-i page 37