Pennell, K.D., N.L. Capiro, S. Gaeth, T. Marcet, F.E. Loeffler, and Y. Yang.
SERDP Project ER-2129, 163 pp, 2017

To study the potential of combined remedies, the project evaluated the impacts of in situ thermal treatment and in situ anaerobic bioremediation on groundwater quality and relevant subsurface processes. Specific objectives were to identify potential electron donors released following thermal treatment and assess the ability of these substrates to support microbial contaminant degradation; to characterize the extent of metal sulfide precipitation and impacts on aquifer permeability; and to quantify impacts of pH reduction on bioremediation performance and microbial community structure. Results show that (1) thermal treatment of soils resulted in electron donors and fermentable substrates (formate, acetate, propionate, and butyrate) that were able to support microbial reductive dechlorination of PCE to ethene, (2) reductions in permeability (up to 80%) due to the formation of iron (II) sulfide precipitates restricted or blocked pore throats and caused preferential flow, and (3) dechlorination of PCE to ethene was possible at pH 5.5 in microcosms but was not observed in sediment-free enrichment cultures. These findings provide new information about the impacts of combining thermal treatment and biostimulation on groundwater quality and biogeochemistry. https://www.serdp-estcp.org/content/download/47278/451071/file/ER-2129%20Final%20Report.pdf