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moo <br /> �g00 <br /> B_ <br /> The concentrations of both total and hexa, lent chromium etected in soil <br /> borings SBI and SB2 were nearly identical a - ^ - ", -- F <br /> 'ngs <br /> L..-. C. 44. 41... Fume�•—,6llJ.�--�0�1 <br /> Resna is •mag that the percentage of hexavalent chromium detected in SB1 <br /> and SB2 are representative of background conditions. Based upon the <br /> illustrations and the projections of plume definitions in the area of former <br /> vault #8, Resna approximates 450 square feet of contamination of chromium <br /> exceeding background levels with the contamination extending to the depth of <br /> 75 - 80 fbg. <br /> Estimations are that hexavalent chromium are not detected 5 feet north of the <br /> vault at a depth of 60 fbg. Resna is postulating that the°highly acidic pH" <br /> Qly be responsible for a reduction of hexavalent chromium to the less toxic <br /> and less mobile trivalent form which is claimed to be a background level. <br /> However, based upon what has been presented in this report, the pH does not <br /> represent highly acidic levels bgt,.myooree neutral in nature. <br /> rOLesna advised against actively introducing remediation to the soils impacted <br /> because of the risk of incomplete recovery of mobilized contaminants which can <br /> be introduced into the groundwater from reducing immobility of flushing agents <br /> thereby increasing the groundwater degradation. <br /> Resna's recommendation is an additional 6 months of quarterly groundwater <br /> Imonitoring from monitoring well #3 which would bring us to July 1994. <br /> At that point it is my opinion, Resna will request for site closure.and-- <br /> c <br /> It will be necessary for me to discuss this site with E. Thayer for her <br /> expertise, but it is my feeling that perhaps Resna's impression of acidic pH <br /> may not be adequately represented and their justification that the chromium <br /> may be background. <br /> I addition, cross a on diagrams the soil bori Bl and SB2 a not <br /> p esen the a itio l soil seas nt report. It m be nec ssar to <br /> re ve addi ion represe ati to graph' all lustrate a of initio f <br /> an nese, tots and hexavalent chromium contamination. <br /> hu=4 �cl <br /> v"Y" 4 lg41 <br /> ,rasa G '-� Stay k., <br />