We investigated the effects of soil particle size on the geochemical and microbial dynamics during remediation of subsurface diesel contamination by in-situ soil flushing. The study site is located in a coastal region of S. Korea contaminated over a 10 year period by a leaking diesel fuel tank. We employed an in-situ sampler containing diesel-contaminated soils separated into two size fractions (&lt; 0.063 and &lt; 2 mm) in two monitoring wells, DH1 and DH2. DH1 is close to the injection and extraction wells for in-situ soil flushing, and thus is expected to be directly influenced by the transport of leaked diesel, while DH2 is located outside of sheet piles which block the transport of leaked diesel. We periodically monitored the total petroleum hydrocarbon (TPH) concentrations and geochemical properties in both soil and groundwater for 6 months. 16S DNA analysis was used to monitor changes in the microbial communities.<br/>TPH concentrations in the &lt; 0.063 mm size fraction were ~ 2 times higher than those in the fraction with particle sizes &lt; 2 mm in both DH1 and DH2, suggesting that the soil micro-particles were the major sink for TPH. Increases in soil TPH of DH1 were consistent with the expected outcomes following well pumping and surfactant injection to enhance TPH extraction. However, the number of diesel oil-degrading microorganisms decreased after surfactant injection. In addition, a shift in the groundwater type from Ca-HCO3 to Na-Cl occurred, likely because of seawater intrusion during the intense pumping. The results suggest that the soil flushing with the surfactant enhanced TPH extraction, but negatively impacted in-situ biodegradation of diesel as well as groundwater salinity.<br/>Bacterial phyla with high relative abundances in all samples included Proteobacteria, Bacteriodetes, Actinobacteria, Firmicutes, Acidobacteria, and Chloroflexi. The particle size distribution and diesel contamination significantly impacted microbial community composition and diversity. The relative abundance of Proteobacteria decreased, but that of Firmicutes increased in both DH1 and DH2 soils (&lt;0.063 mm) suggesting the phylum Firmicutes correlated with the presence of diesel contamination.<br/>Shifts in TPH concentration, groundwater type, and microbial community composition together in this study suggest that a thorough understanding of subsurface environmental conditions is essential to develop cost-effective and efficient solutions for successful remediation of contaminated sites.

Geochemical and microbiological dynamics in a diesel-contaminated subsurface environment during in-situ soil flushing

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.