HR: 13:55h
AN: H12H-02    [PDF]
TI: Geoelectrical Evidence of Microbial Degradation of Diesel Contaminated Sediments
AU: * Werkema, D D
EM: werkema.d@epa.gov
AF: U.S. EPA, ORD, NERL, ESD, CMB, 944 E. Harmon Ave, Las Vegas, NV 89119 United States
AU: Atekwana, E A
EM: atekwana@umr.edu
AF: University of Missouri-Rolla, Department of Geology & Geophysics, Rolla, MO 65409 United States
AU: Atekwana, E A
EM: eliota@umr.edu
AF: University of Missouri-Rolla, Department of Geology & Geophysics, Rolla, MO 65409 United States
AU: Rossbach, S
EM: Silvia.Rossbach@wmich.edu
AF: Western Michigan University, Department of Biological Sciences, Kalamazoo, MI 49008 United States
AU: Sauck, W A
EM: sauck@wmich.edu
AF: Western Michigan University, Department of Geosciences, Kalamazoo, MI 49008 United States
AB: The alteration of physical properties by microbial activity in petroleum contaminated sediments was investigated using geophysical techniques in laboratory column experiments. Microbial population growth was determined by the Most Probable Number technique (MPN), community dynamics were determined by the rDNA intergenic spacer analysis (RISA), microbial mineralization of diesel fuel was assessed using dissolved inorganic carbon (DIC), enhanced mineral dissolution was determined by dissolved calcium, and the vertical geoelectrical profile was measured using DC resistivity (converted to conductivity). The columns simulated a saturation profile and contained sanitized, uniform sand with the following experimental treatments: diesel $+$ microbes, diesel, microbes, and no treatment. After 16 months, two important conclusions were drawn. First, the relative increase in magnitude of the parameters measured was highest in the diesel + microbe column (showing at least 110% increase), lower in the diesel column and lowest (actually showing a decrease) in the column with no treatment. Further, the diesel + microbe column showed the greatest increase in oil degrading microbial populations (135%) compared to the column with no treatment, which showed no changes. Secondly, the depth at which the conductivity reached the maximum occurred within and slightly above the diesel layer (which represents a depth that was originally water wet). It was further observed that the relative change in bulk conductivity below the saturated zone is of a lower magnitude than above ($<$10%). These results suggest the diesel layer, and the zone slightly above, were the most biologically active. Additionally, the diesel $+$ microbe column showed RISA fragments attributed to microbial succession typically observed in organic contaminant plumes. A simple Archie's Law analysis was used to estimate the pore water conductivities necessary to reproduce the bulk conductivity measured. This analysis shows that relative to the column with only microbes (selected as the control to be most representative of field conditions), the diesel column revealed a 2.3 fold increase and the diesel $+$ microbe column showed a 3 fold increase in pore water conductivity. This increase was located within the diesel layer above the water saturated zone. Within the saturated zone, the no treatment column showed a 0.81 fold increase, the diesel column a 1.28, and the diesel $+$ microbe column 1.45. We conclude from this study that microbial activity and the resultant biogeochemical changes played an important role in modifying the geoelectrical properties of aquifers and sediments rich in organic carbon and mineralized by bacteria by increasing the bulk conductivity. This conductive zone occurred within and immediately above the free-phase petroleum layer. In natural environments with high concentrations of organic compounds available as electron donors, geophysical techniques may potentially be used as indicators of microbial activity. Notice: This is an abstract of a proposed presentation and does not necessarily reflect the United States Environmental Protection Agency (EPA) policy. The actual presentation has not been peer reviewed by EPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
DE: 1832 Groundwater transport
DE: 1866 Soil moisture
DE: 5102 Acoustic properties
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
SC: Hydrology [H]
MN: 2003 Fall Meeting