10:30 am - 11:30 am
849 General Services Building (GSB), General Services Building, University of Alberta, Edmonton AB
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Alison Murata. This seminar is open to the general public to attend.
Thesis Topic: Long term dynamics and potential remediation of fine textured soils and ground water contaminated with chlorinated organic compounds and salts
Seminar Abstract: Contamination of land, water, and air is a widespread concern often associated with anthropogenic activities. Remediation of contaminated sites is necessary to minimize negative impacts on human health and the environment and allow for safe, productive use of land. Although contaminated sites often have fine textured soils and/or multiple contaminants, research on remediation of such sites is lacking. Fine textured soils can make remediation more difficult by hindering movement of contaminants or amendments and by promoting anaerobic conditions. Contaminant mixtures can complicate remediation since each contaminant has unique characteristics to address and can hamper remediation of other contaminants.
The objective of this research was to characterize a contaminated site with fine textured soils and multiple contaminants and investigate the potential of various remediation techniques. The research site was the former Ellerslie Waste Management Facility which treated laboratory waste from 1972 to 2007 in Edmonton, Alberta. Prior to 1983, a waste water pond cracked and leaked. Contaminant dynamics over 30 years were characterized by identifying soil and ground water contaminants based on Alberta Tier 1 guidelines, identifying temporal trends with Mann Kendall analysis, and identifying spatial trends with two and three dimensional mapping. The potential of anaerobic biostimulation and bioaugmentation treatment of chloroform were investigated in microcosm experiments using soil from the Ellerslie site and a secondary contaminated site. Microcosms were amended with canola oil, acetate, lactate, nitrate, or sulfate. The soil microbial community was characterized by comparing bacterial and fungal communities from various soil depths in, up gradient, and down gradient of the pond. The potential of chemical reduction treatment of chloroform was investigated in an anaerobic bottle experiment using micro scale zero valent iron with and without soil. The potential of leaching treatment of salinity was investigated in soil column experiments using two soil composites of differing textures with and without calcium nitrate amendment.
Of the 18 soil and 37 ground water contaminants identified, chloroform, dichloromethane, and salinity were of greatest concern based on their frequency and magnitude of detection. Temporal contaminant trends were inconsistent, possibly due to heterogeneous contaminant distribution or movement. A clear spatial association with the pond was identified, as expected. There is some evidence of northward chloride and sodium movement with ground water flow. The bioremediation experiments did not yield any meaningful changes in microcosm headspace chloroform or formation of degradation products over time. Biostimulation and bioaugmentation with the inoculation microorganisms used in this research are not likely effective options for the Ellerslie site. This is supported by the lack of chlorinated methane degrading microorganisms enriched in the pond. However, the enrichment of Geobacter species in the pond indicated benzene biodegradation may be occurring. Bacterial richness and diversity were decreased in the pond, likely a result of contamination toxicity. The fungal community was more similar across the Ellerslie site than the bacterial community. Chemical reduction of nearly 2 g L-1 chloroform using zero valent iron was rapid and complete. Headspace chloroform was not detected after 0.5 and 2 days in the soil zero valent iron and zero valent iron treatments, respectively. Dichloromethane which formed during the degradation process was removed by day 2 in both treatments. The leaching experiments showed potential for treatment of fine textured soils. Soil electrical conductivity, sodium adsorption ratio, sodium, chloride, and sulfate were greatly reduced by eight rounds of leaching. Greatest salt removal occurred during the first leaching round. Calcium nitrate increased the saturated hydraulic conductivity of the finer textured soil from 4.12 ± 0.46 x 10-8 to 1.29 ± 0.14 x 10-7 m s-1.
The soil and ground water contaminant inventory and knowledge of their spatial distribution will aid in development and application of a site remediation plan. Potential remediation methods include chemical reduction with zero valent iron for chlorinated methanes and leaching for salinity. Zero valent iron treatment could be implemented with a permeable reactive barrier, in situ injection, or ex situ batch reactor. Leaching treatment could be implemented with an interceptor trench or ex situ soil washing. Contaminant maps will be important in guiding soil excavation or placement of in situ remediation infrastructure. Site characterization and remediation methods explored in this research can be applied to similar contaminated sites.
Alison Murata – PhD with Dr. M. Anne Naeth