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CLOSURE REQUEST 5-31-94 MODELING SOIL CONTAMINATION USING SOIL SAMPLE BORING CHEMICAL RESULTS OBTAINED FEBRUARY 2 , 1994 . On February 2 , 1994, three soil borings were performed to obtain soil samples to document the effectiveness that vapor extraction was having on the site and to verify the removal of gasoline range hydrocarbons from the soil beneath this site . On July 22, 1992, two areas remained with hydrocarbon impacted soils, Area A (beneath the western pump island) and Area B (east- southeast of the underground storage tank area) , see Figure 3B Estimates at that time indicated approximately 3436 pounds of gasoline range hydrocarbons remained in the soil and capillary fringe, see Update Status Report #15, page 33 . The analytical results from the latest sampling (February 2, 1994) show a reduction in the amounts of degraded gasoline range hydrocarbons in Area B, leaving an estimated 531 pounds remaining beneath the site . This indicates a reduction of approximately 85% . This latest poundage figure was produced by the VLEACH modeling program which used soil borings SB13, SB14 and SB15 as centers of individual polygons that utilized the chemical results, see Figures 1 and 3 in Appendix B The EPA models "VLEACH" and "BIOPLUME, TWO-DIMENSIONAL CONTAMINANT TRANSPORT UNDER THE INFLUENCE OF OXYGEN LIMITED BIODEGRADATION IN GROUND WATER" were utilized to predict the amount of hydrocarbons that may impact ground water and if/when ground water is impacted, the amount that would migrate off site, see Appendix B . To run the models, three polygon areas were developed. These three areas were centered around the latest soil borings SB13 , SB14 and SB15 and are designated VSB13 , VSB14 and VSB15 respectively The site was modeled for 100 years, assuming no remedial actions were being taken, to show the worst case impact , if any, if no further artificial or enhanced actions are taken. VLEACH VLEACH simulates the following process advection, sorption, vapor-phase diffusion and three-phase equilibrium Results of the VLEACH model showed the following petroleum hydrocarbons remained in the soil - Polygon VSB13 between the 15 and 25 foot depths showed 129 pounds of gasoline, 1 pound of ethylbenzene and 10 pounds of xylenes, Polygon VSB14 between the 10 and 30 foot depths showed 359 pounds of gasoline, 0 . 2 pounds of toluene and ethylbenzene, and 7 pounds of xylenes, and Polygon VSB15 between the 15 and 40 foot depths showed 52 pounds of gasoline, 0 . 4 pounds of toluene, 0 . 3 pounds of ethylbenzene and 5 pounds of xylenes . VLEACH does note take into account the natural bio/chemical degradation when petroleum hydrocarbons are exposed to oxygen Natural oxidation of the hydrocarbons without further vapor extraction would reduce the total amounts of hydrocarbons in each polygon as follows : VSB13 from 129 pounds to 99 pounds, VSB14 from 349 pounds to 311 pounds and page4