REMEDIATION OF AQUEOUS CHROMIUM BY POTTING SOIL AND SAND SUBSTRATES USING A MODIFIED COLUMN METHOD

Hexavalent chromium is harmful to humans as an aerosol, resulting in contact dermatitis and several forms of ulcers and cancers. In its aqueous form, it is a potential human carcinogen and a definite hazard to aquatic ecosystems. Coal ash spills can result in aqueous hexavalent chromium being released into soils, threatening groundwater and surface water systems. To test the ability of different substrates to remediate aqueous hexavalent chromium, a modified column method was used to mimic the passing of aqueous chromium through two soils. Potting soil and a sand substrate were chosen to mimic separate soil strata in the southeastern United States because significant coal ash spills have occurred in this region in recent years. Though the maximum contaminant level (MCL) for all (trivalent plus hexavalent) chromium is 0.1 ppm, coal ash leachates have been shown to reach levels over 0.25 ppm. The starting solutions for this experiment of 0.10 ppm and 0.25 ppm Cr(VI) were prepared from reagent grade Cr(VI) standard stock solution. The concentrations of the pre and post-filtered solutions were determined using flame atomic absorption spectroscopy. Additionally, the volume of solution retained by each substrate was recorded. The volume of solution retained by the potting soil was significantly higher than that retained by the sand substrate (p<0.05) for all replicates. However, the amount of effluent aqueous Cr(VI) was significantly higher for the sand substrate (p<0.05) for both concentrations studied. This research indicates that slower percolation rates and higher retention rates lead to better remediation of aqueous Cr(VI) which occurred in the potting soil substrate.