Date of Award

12-2002

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

Dr. Estella Atekwana

Second Advisor

Dr. Eliot Atekwana

Third Advisor

Dr. R. V. Krishnamurthy

Fourth Advisor

Dr. William Sauck

Abstract

In-situ vertical resistivity probes (VRPs) deployed at a hydrocarboncontaminated site in SW Michigan showed high soil conductivities within the contaminated zone. Within this zone, different phases of hydrocarbon impact were recognized, namely, zones with residual and dissolved phase hydrocarbons (RDH) and zones where these phases coexist with free product (RDFH). Bulk soil conductivities were highest ( 12 to 30 mS/m) in the zone with RDFH compared to the RDH zone (10 to 25 mS/m). Groundwater chemistry and stable carbon isotope data from closely spaced vertical samples within the anomalous conductive zones were used to provide evidence for biodegradation and to investigate the role of mineral weathering in the aquifer as the source of ions responsible for the observed conductivities.

Depth distribution of TEAs and educts showed evidence of reduction of nitrate, iron, manganese, and sulfate across steep vertical gradients. Within the zone with RDH, the reduction of NO3, Fe (III), Mn(IV), and SO4were the major observed redox processes. This zone also exhibited the highest DIC. The δ13CDIC values of -16.9 to -9.5‰ suggest that DIC evolution in this zone is controlled by carbonate dissolution through enhanced CO2production related to microbial hydrocarbon degradation. Within the zone with RDFH, DIC was lower compared to the RDH location with an associated δ13CDICin the range of +6.5 to -4.4‰. Both the DIC and δ13CDIC suggest that methanogenesis is the dominant redox process.

The results also show higher concentrations of Na, Ca, and Mg associated with high soil conductivities in the contaminated portion of the aquifer compared to background that is consistent with the weathering of carbonate and Na and Ca feldspars, the dominant minerals in the aquifer. This ion enrichment translated to higher TDS at the contaminated locations as reflected in the conductivity measurements. The results suggest an interrelationship between redox processes, biomineralization of hydrocarbons, and high soil conductivities. Moreover, bulk conductivity measurements may be useful in assessing the potential for natural attenuation in contaminated, unconsolidated, sandy aquifers.

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Dissertation-Open Access

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