Date of this Version
Past disposal of industrial solvents into unregulated landfills is a significant source of groundwater contamination. In 2009, we began investigating a former unregulated landfill with known trichloroethene (TCE) contamination. Our objective was to pinpoint the location of the plume and treat the TCE using in situ chemical oxidation (ISCO). We accomplished this by using electrical resistivity imaging (ERI) to survey the landfill and map the subsurface lithology. We then used the ERI maps to guide direct push groundwater sampling. A TCE plume (100-600 µg L-1) was identified in a low permeable silty-clay aquifer (Kh = 0.5 m d-1) that was within 6 m of ground surface and underlain by an even lower permeable zone (Kh = 0.04 m d-1). Because injecting a liquid oxidant into the low permeable aquifer would have been difficult, we manufactured slow-release potassium permanganate candles (SRPCs) to treat the TCE. SRPCs were prepared by heating and mixing KMnO4 and paraffin wax at a 4.6 to 1 ratio (w/w), and then pouring the heated mixture into circular cardboard molds (91.4 cm long) that were either 5.1 cm (2 in) or 7.6 cm (3 in) in diameter. For comparison, we inserted equal masses of SRPCs (7.6-cm vs 5.1-cm diameter) into a low permeable aquifer (4.6 m vertical thickness) in staggered rows that intersected the TCE plume. The 5.1-cm diam candles were inserted directly into the formation using direct push hollow rods at 21 locations. The 7.6-cm SRPCs were encased in slotted containers and placed in 10 permanent wells. Pneumatic recirculators that emitted small air bubbles were placed below the 7.6-cm SRPCs in the second year to facilitate permanganate distribution. Results obtained prior to inserting recirculators showed a 64 to 82% reduction of TCE in the 7.6-cm candle treatment zone after 342 d and between 64 to 100% decrease in associated ethene degradates. These results support using slow-release permanganate candles as a means of treating chlorinated solvents in low permeable aquifers.
Advisor: Steve Comfort