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1 <br /> wells MW-6 and MW-10, on the perimeter of the plume, were also significantly reduced <br /> between September and December 1994 <br />' 5.2 Hydrocarbon Impacted Soil <br />' Since the final assessment at the site (March 1993) concentrations of petroleum <br /> hydrocarbons in the soil has shown a dramatic decrease Figure 15 represents cross-section <br /> A - A' extending from boring P-5 through borings P-4 and P-3 At the south end of the <br />' impacted soil plume, hydrocarbons are present in a very narrow zone from depths of <br /> approximately 25 to 30 feet The impacted soil is comprised mostly of silts and clays <br />' At the north end of the site, near VW-5, the impacted soil zone is somewhat wider, <br /> extending from depths of approximately 25 to 48 feet However, throughout the site, as <br /> indicated from borings P-1 through P-5, hydrocarbon concentrations in the soil have been <br />' reduced by as much as 90 percent Furthermore, the remaining hydrocarbons seem to be <br /> limited to silty and clayey soils <br />' Comparison of the microbiological and soil vapor data collected at the site with the analysis <br /> of the soil samples from borings P-1 through P-5 indicates that the addition of hydrocarbon- <br /> degrading bacteria has had a positive influence on the reduction of hydrocarbon <br /> concentrations in the soil Since no additional nutrients were added to the soil, elevated <br /> concentrations of nitrites, nitrates and phosphates were not detected The pH of the soil <br /> (approximately 8 4) remains within a normal range for the region <br /> During the assessment phases at the site h Jdrocai bons were detected at depths between 15 <br /> and 60 feet However, since 1994, hydrocarbons have only been detected in soil samples <br /> from very limited "zones" Similac ly, it appears that hydrocarbon concentrations at the site <br /> have decreased from a range of 1,000 to 7,000 ppm to less than 500 ppm <br /> 53 Recommendations <br /> i <br /> It appeals that the concentrations of hydrocarbons in both soil and groundwater at the site <br /> have decreased significantly over the past quarter All data collected from the site seems <br /> to indicate that the addition of the bacterial inoculum is successfully reducing hydrocarbon <br /> Iconcentrations at the site <br /> We recommend that one soil boring each be placed between VW-1 and VW-7, VW-1 and <br /> VW-4 and VW-5 and VW-6 A fouith boring should be dxflled east of EW-1 The soil <br /> borings are tentatively scheduled to be dulled in February 1995 At this time, we <br /> recommend no changes to the groundwater program However, if hydrocarbon <br /> I concentt ations in MW-9 do not continue to show a reduction, reinoculation will be <br /> considezed <br /> C-65-1 Aud 1 Srry9 <br /> nra Inc n <br /> Q..Ocdy R P.,Vj^San 33 GEWQM6 <br />