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It is our opinion p nion that the soils in the vicinity of test boring <br /> TB-1 is contaminated with hydrocarbon. The exact extent of <br /> ' contamination can not be determined by a single test boring. <br /> However, we estimate the area of contamination is approximately <br /> twice the width of the original tank width or about 10 feet in <br /> radius. The vertical extent of contamination is likely within <br /> the upper 5 feet of subgrade soils. The location of test boring <br /> ' TB-1 as well as the approximate location of original tanks are <br /> shown in the "Boring Location Map", Plate 2 . The general area of <br /> test boring TB-3 is considered not contaminated by hydrocarbon. <br /> ' For underground g fuel storage tank removal, the CRWQCB guidelines <br /> ' (section 3 . 3 , figure 2 . 4) require contaminated soil with <br /> concentration level greater than 1000 ppm be removed from the <br /> site and no action is needed for concentration level less than <br /> ' 100 ppm. Since the concentration level In the area of test <br /> boring TB--1 as slightly higher than the minimum allowed by these <br /> guidelines but not quit as high as required to be removed, and <br /> with the fact that the contaminant is gasoline, it is our opinion <br /> that the concentration level of contaminated soils can be reduced <br /> to below regulation level by aeration. <br /> ' RZCONXENDATIONS <br /> It is recommended that the contaminated soils at the vicinity of <br /> ' test boring TB-1 be excavated and aerated to reduce: concentration <br /> level. The extent of such excavation should be at least 5 feet <br /> below the existing ground surface and at least twice the original <br /> ' underground tank plan dimensions (width and length) . <br /> ' The excavated soils should then be spread on-sate into thin layer <br /> no greater than one foot in thickness and be allowed to aerate. <br /> Prior to aeration process , local health agency and the Air <br /> ' Quality Control Board should be notified. Periodic measurements <br /> should be taken to verify the reduction of contamination level. <br /> Once the concentration level is below 1.00 ppm, the aeration <br /> process may be considered complete and the soils can be <br /> 5 <br />