The effect of steam treatment on subsurface aerobic and anaerobic microbial communities was investigated using multiple microbial assays. Soil samples were gathered and analyzed prior to, one month after, and eight months after a five-month field pilot test of steam injection and extraction. Aerobic soil samples were analyzed by respirometry, plate counts, and direct microscopic counts. Anaerobic microbial activity was examined by monitoring methane generation in anaerobic microcosms with gas chromatography. Respirometry showed pre-steam CO2 production was consistent with natural attenuation, post-steam (one month) CO2 production was below detection, and post-steam (eight months) CO2 production was about half of pre-steam. Post-steam (one and eight month) plate counts were one to four orders of magnitude lower than the pre-steam samples. Direct microscopic counts showed post-steam (one and eight month) cell numbers were higher than the pre-steam counts, but based on plate counts these cells were mostly non-viable. Significant amounts of methane and hydrogen were generated from pre-steam anaerobic microcosms, but post-steam microcosms had no detectable methane, and only trace amounts of hydrogen. Terminal restriction fragment (TRF) analysis was performed to determine the diversity of the microbial community before and after steam treatment. Pre-steam TRF analysis showed distinct differences in the microbial communities above and below the smear zone. Post-steam TRF analyses were not possible because insufficient DNA could be extracted from the soil.
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