Innovative techniques for collection of saturated and unsaturated subsurface basalts and sediments for microbiological characterization

Abstract

Basalt and sediment samples were cored from depths of up to 183 m at the Idaho National Engineering Laboratory (INEL) for evaluation of microbiol abundance and diversity in the subsurface. The overall goal of the research is to understand subsurface microbial ecology to effectively conduct in situ bioremediation. To minimize the impact of sampling on the biological and chemical integrity of subsurface strata, argon (Ar) was used as an inert drilling fluid. Upon retrieval, cores were placed into Ar-filled chambers for processing. Subsamples for microbiological analyses were pared by hydraulic splitting and milled to diameters of 0.1–0.5 cm and then aseptically packaged for distribution to investigators. Multiple tracers measured potential contamination which may have occurred during drilling or coring. Fluorescent microspheres and lithium bromide (Br −) served as downhole tracers while gaseous perfluorocarbon tracers (PFTs) were used to monitor intrusion of drilling fluids into the cored zone. Tracer concentrations in samples indicated that microsphere and Br − occurrence and quantity was not necessarily correlated to the type of material cored but possibly related to characteristics of individual cores such as presence of fractures or core length. Microsphere and Br − concentrations indicated that, in samples provided to the investigators, any contaminating microbes or chemicals introduced during the coring process would have been diluted to the extent that they would have been insignificant. PFTs indicated gaseous intrusion into sediments and basalts deeper than the drill bit-stratum interface and provided evidence of Ar intrusion into the sample and ahead of the drill bit. Tracer data provided evidence that the quality control techniques employed protected the integrity of the subsurface samples.