SITE INFORMATION AND CORRESPONDENCE

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Linda Turkette, REHS San Joaquin County PubV Health Services Environmental Health Division April 5, 1993 Page 2 evidenced in non-detect results)further substantiates the absence of any contaminated water movement toward the Tracy well site. The forgoing data will substantiate the logic that the Tracy well site is not in any jeopardy with respect to the minor amount of VOCs occurring in the stable plume on the BC&D site. Further, soil borings verify that the light level of contaminants have not invaded the clay stratum immediately beneath the perched water zone. Several hundred additional feet of predominantly clay soil zones further insulate the potable water supply from surface water intrusions (per Tracy well number 5 installation logs). The recent completion of MW-4 verifies the location of the contamination and establishes the fact that off-site migration has not occurred and that the contamination is isolated to the region of the former tank location. Original soil borings, numbered 2, 3 6 and 7 "Bracket" boring number 1 (the tank site) verify the problem zone. Further,groundwater data obtained from soil borings 1, 2, 3, 6 and 7 substantiate the soils data and confirm, again, the VOC local. In summary, the VOC's are in a known location, on site, and do not appear to be mobile as verified by repeated monitoring well data. All VOCs of concern detected in the 1987 report have decayed to acceptable levels or below with the exception of the benzene, which has a current level 2.1 PPB (as of November 13, 1992), and is declining in concentration through natural biodegradation. Please consider the following facts regarding the declining concentrations of the benzene. The Benzene declined in concentration from 24.6 PPB in 1987 to 4.4 PPB in 1990, a reduction of 550%. The Benzene concentration further declined from 4.4 PPB (January 11, 1990) to 3.9 PPB (July 23, 1990), at a rate of 0.078 PPB/month. The Benzene again declined in concentration from 3.9 PPB (July 23, 1990) to 2.1 PPB (November 13, 1992), at a rate of 0.064 PPB/month. Utilizing the more conservative value of 0.064 PPB/month,we can extrapolate that, at that rate, the Benzene concentration will decline to an acceptable level of 0.70 PPB (per Table 3 of Geological Technic's report of November 12, 1987) in 22.0 months. I submit that as per previous recommendations, and careful consideration of prevailing conditions, that the natural remediation process be allowed to