Enhanced In Situ Co-Metabolic Biodegradation of 1,4-Dioxane in Weathered Bedrock via Propane Biosparging
In September 2016 a propane biosparge pilot test was initiated at the RACER Trust site in Lansing, MI. Air and propane were injected into contaminated weathered bedrock at 3 cubic feet per minute and up to 35 percent of the lower explosive limit (LEL) for 11 to 12 hours per day into each of two sparge wells. The propane concentration was increased from 15 to 35 percent LEL during the test to evaluate any change in the rate of biodegradation. Bioaugmentation with a propanotrophic culture was conducted, alongside nutrient addition of diammonium phosphate.
After four months of operation, 1,4-dioxane concentrations decreased up to 98 percent at monitoring locations within the test area. Higher reductions were observed at locations that were better connected with the sparge well and had increased dissolved oxygen (greater than 3 milligrams per liter) and propane (greater than 100 micrograms per liter). It was also concluded that increasing the propane from 15 to 35 percent of the LEL did not increase the rate at which 1,4-dioxane was degraded. Providing distribution of the gas mixture within the weathered bedrock will therefore be the key to making biosparging a viable remedy for the site.