Collaborative Research: Biogeochemical Influences on Geophysical Sigantures at Light Non-Aqueous Phase Liquids (LNAPL) Impacted Sites

Western Michigan University, Kalamazoo MI

Investigators

Abstract

0087795 Atekwana Introduction of pollutants in the soil environment such as Light Non-Aqueous Phase Liquids (LNAPLs) after the physical, chemical, and biological properties of the soil media. Initially, the alteration of the soil properties is primarily physical as the LNAPL occupies pores of the resident soils. With time, the LNAPL undergoes changes driven by microbial-mediated processes that alter soil properties. Geophysical methods are able to detect freshly released LNAPLs in soils because their higher electrical resistivity readily distinguishes from background pore and groundwater. Nevertheless, many resistivity measurements of aged LNAPL spills reveal a decrease and not the expected increase. Hence, the key hypothesis to be addressed in this study is that shifts in geoelectrical signatures from resistive in "fresh spills" to conductive in "aged" or biodegrading spills accompany biogeochemical modifications of LNAPL in the impacted media. The work is driven by the need to gain a basic understanding of the dynamics that interrelate biological, chemical, geological, and hydrological processes in LNAPL-impacted soils and how these interrelations translate into measurable changes in the geoelectrical response. The objective is to experimentally document important soil physical and chemical parameters that result from microbial degradation of LNAPL and their role in controlling the soil's geoelectrical properties. Our experiments use sterilized laboratory columns filled with sands from a field site impacted with LNAPL. Some of the columns are layered with LNAPL and inoculated with microbes from the field site. Positive and negative control columns are maintained. Geoelectrical measuremens are obtained using electrodes implanted in the columns. The experiments are designed to: Verify microbial LNAPL degradation by monitoring changes in microbial types, population and community structure, and changes in the presence of potential electron donors; and Document changes in soil physical (grain) properties and in pore fluid geochemistry. Integrating geophysics, geochemistry, and microbiology will: (i) document how microbial degradation of LNAPLs and subsequent biogeochemical modifications of the impact media influence soil geoelectrical responses; (ii) support development of geoelectrical models necessary to quantify these biogeochemical processes; and (iii) provide a basis for extending laboratory geophysical degradation models to field sites contaminated with organic chemicals.