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Emergency Remediation 2480 Tracy Blvd., Tracy, CA. Page 17 Each batch of soil removed from the stockpile was spread in a layer between 6 in. and 9 in. in thickness over the area of the site where it was to be treated. This transfer was made using the 4 cu. yd. front loader. The front loader and the excavator were also used to work the stockpile by inverting piles of soil and dribbling soil from the buckets. This was done to induce aeration of components of gasoline so that the remaining quantities to . be removed by the final treatment process would as little as possible and the time required to complete the treatment reduced to a practical minimum. The five soil spreads that were used to aerate the contaminated soil are shown on Figures 5 through 9. After each batch of soil was placed in its treatment area and spread, it was rototilled using a large rototiller powered by an agricultural tractor. This procedure encouraged natural aeration and volatilization of gasoline from the spread soil. The spreads of soil were rototilled at frequent intervals and from time to time they were picked up and turned over ' before being re-spread and rototilled again so as to ensure that components of gasoline had been thoroughly volatized from the full thickness of the spread material. ' As the soil treatment of a spread of soil progressed, it was checked from time to time for visual and olfactory indicators of gasoline. When none could be detected by an experienced observer treatment was terminated and the spread of soil was either consolidated in a stockpile or left in place for later use by the general construction contractor. Sampling and Analysis of Treated Soil Before a batch of the spread of treated soil was released to the general construction contractor for incorporation into the works, it was sampled by the technique that is described below and that follows the procedures established by the United States Environmental Protection Agency (EPA) for evaluating the attainment of cleanup standards of soil and solid media(Ref. 3). Six sampling points within each soil spread were selected randomly by throwing die to separately and randomly select a set of alphabetic and numeric identifiers associated with the 35 ft. square sub-area into which the site had been subdivided by previously-described 1 grid system. Alphanumeric character combinations read from the die that identified sub- areas not covered with the treated soil that had been placed in a given spread were ignored and the die thrown repeatedly until the requisite number of randomly-selected sub-areas that included the soil spread being sampled had been identified. The sub-areas selected for sampling in each of the five soil spreads are shown on Figures 5 through 9. (Note: Due to the limited size of those spreads, only two and three sub-areas, respectively, were selected for sampling in Soil Spreads No. 2 and No. 4.) Specific sampling location within the selected sub-areas were selected arbitrarily by tossing a sampling tube into the square without consideration for any zones of color change or other small-scale variation in the visual characteristics of the soil.