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f - P <br /> UP WR�l <br /> Y <br /> 33 <br /> GOLDEN GRAIN COMPANY <br /> December 21, 1989 <br /> 202/799-5045.06 <br /> tank pit, has a well-defined zero line. The 2,500-ppmv contour <br /> extrapolated from data from the SVS results (Figure 5) is prob- <br /> abiv a fair indication of the boundaries of the affected area. <br /> Dissolved hydrocarbon concentrations in groundwater are very <br /> in June 1988; however, the number of <br /> similar to those found <br /> wells containing SPP has decreased from four to one. Part of the <br /> decrease may be due to the SPP-removal program in combination <br /> with changes in water levels at the site; some of it may also be <br /> a result of natural biodegradation. <br /> Although dissolved hydrocarbon concentrations are high imme- <br /> diately beneath the site, the extremely gentle groundwater <br /> hplume. This <br /> gradient at the site has reduced migration <br /> ndothe plumemapsshown <br /> low gradient, combined with SVS result <br /> in Figures 9 and 10, gives confidence that the lateral extent of <br /> the plume has been defined in all directions except to the <br /> northeast. Because no hydrocarbons were detected in soil samples <br /> collected near the water table in 1411-9, <br /> either with the PID or by <br /> 1 laboratory analysis, it is probable that dissolved hydrocarbons <br /> are at very low or nondetectable levels in the groundwater to the <br /> ill be made to salvage and sample <br /> northeast as well. An attempt w <br /> MW-9 to confirm this observation. <br /> Analyses o£ groundwater p <br /> ter sam les from MW-'7, screened at a <br /> " <br /> depth of 30 to 50 feet, show TPH-G bofaundrat123stof257feet ppb. <br /> (MW- <br /> These are well below the 110,000 pp hydrocarbon5fee <br /> 2) . This difference suggests that the dissolved <br /> plume may attenuate quickly with depth. <br /> `j'WIN01,06-1,INC. <br />