Bioaugmentation and Propane Biosparging for In Situ Biodegradation of 1,4‐Dioxane

Propane biosparging and bioaugmentation were applied to promote in situ biodegradation of 1,4‐dioxane at Site 24, Vandenberg Air Force Base (VAFB), CA. Laboratory microcosm and enrichment culture testing demonstrated that although native propanotrophs appeared abundant in the shallow water‐bearing unit of the aquifer (8 to 23 ft below ground surface [bgs]), they were difficult to be enriched from a deeper water‐bearing unit (82 to 90 feet bgs). Bioaugmentation with the propanotroph Rhodococcus ruber ENV425, however, supported 1,4‐dioxane biodegradation in microcosms constructed with samples from the deep aquifer. For field testing, a propane‐biosparging system consisting of a single sparging well and four performance monitoring wells was constructed in the deep aquifer. 1,4‐dioxane biodegradation began immediately after bioaugmentation with R. ruber ENV425 (36 L; 4 × 10⁹cells/mL), and apparent first‐order decay rates for 1,4‐dioxane ranged from 0.021 day⁻¹to 0.036 day⁻¹. First‐order propane consumption rates increased from 0.01 to 0.05 min⁻¹during treatment. 1,4‐dioxane concentrations in the sparging well and two of the performance monitoring wells were reduced from as high as 1090 µg/L to