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B EMIDJI C RUDE O IL S PILL Darren Cartwright Stephen Toone.

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Presentation on theme: "B EMIDJI C RUDE O IL S PILL Darren Cartwright Stephen Toone."— Presentation transcript:

1 B EMIDJI C RUDE O IL S PILL Darren Cartwright Stephen Toone

2 Background In 1979, crude oil from a pipeline rupture contaminated a shallow aquifer in Bemidji, Minnesota After initial clean-up, 400’000 litres of oil remained in the unsaturated zone and near the water table This continues to be a source of contaminants to a shallow outwash aquifer Results of research collected on this site have provided fundamental knowledge that has been used to remediate similar sites worldwide

3 Aerial View of Site

4 Description and History of Site Land surface and shallow sub-surface were contaminated when the pipeline burst spilling 1’700’000 litres of crude oil onto a glacial outwash deposit Crude oil also sprayed southwest covering 7’500 m 2 of land After initial clean-up some crude oil had percolated through the unsaturated zone to the water table near the rupture site Some of this oil flowed over the surface towards a small wetland forming a second area of significant oil infiltration

5 Features of the Research Site

6 The Project A long-term, interdisciplinary research project sponsored by the USGS Toxic Substances Hydrology Program began in 1983 The research is directed towards understanding the physical, chemical and biological processes controlling the mitigation and fate of hydrocarbon contaminants in the subsurface The goal is to provide information and methods to help evaluate the potential for enhanced bioremediation of hydrocarbon contamination worldwide As of 1998, over 370 wells and test holes have been installed

7 Research Results The fate, transport and multiphase flow of hydrocarbons depends on geochemical processes and on processes of volatilisation, dissolution, biodegradation, transport and sorption, which occur as shown on the next slide Multi-phase flow modelling was used to study oil flow after the spill Transport and biodegradation modelling was used to simulate the evolution of the plume, evaluate factors limiting biodegradation and develop a mass-balance for contaminants This could be used to evaluate the amount and rate of removal of hydrocarbons by biodegradation

8 Geochemical Processes

9 Research Results – Oil Phase As of 1996, leading edge of oil plume had moved 40m downstream Degradation of oil product has resulted in selective loss of soluble and volatile compounds through dissolution and volatilisation Total loss of oil estimated at 11% between 1979-89

10 Research Results – Aqueous Phase Although geochemical processes that were predicted have occurred, the plume has not moved as far as predicted considering groundwater flow velocities and sorption constants As of 1996, the contaminant plume had moved 200m compared with the groundwater that had moved 500m The primary reason for this was that the hydrocarbons have degraded under aerobic/anaerobic conditions This lead to the view that the rate of removal of organic contaminants by natural attenuation and the factors that affect rates of biodegradation are important considerations in making decisions concerning clean-up of contaminated groundwater

11 Research Results – Vapour Phase Distribution of gases in the North Oil Pool has changed considerably: 1985 – leading plume 150m downstream 1997 – leading plume 75m downstream This is also due to aerobic degradation

12 Geochemical Zones in North Oil Pool Zone 1 – Oxygenated uncontaminated native groundwater Zone 2 – Low oxygen concentrations, high concentrations of DOC Zone 3 – Anaerobic plume of groundwater Zone 4 – Low concentrations of hydrocarbons due to aerobic degradation Zone 5 – Oxygenated water

13 Research Results Biodegradation of petroleum derived hydrocarbons in aerobic conditions is generally considered to be more efficient than anaerobic conditions Although anaerobic conditions can still remove substantial amounts of contaminant The next slide shows the microbial geochemistry of the oil plume

14 Contaminant Plume’s Microbial Geochemistry

15 Contributions of Research Provided a comprehensive documentation of natural attenuation of hydrocarbons in a contaminated aquifer under both aerobic and anaerobic conditions, promoting a widespread adoption of this procedure to remediate other contaminated sites This research may result in less expensive remedial actions on similar sites New methods were developed in testing saturated soils such as the ‘Freezing Drive Shoe’ A two-dimensional, multispecies solute-transport model code with biodegradation (BIOMOC) was developed to quantify natural rates of biodegradation; this code can be readily applied to other (similar) sites

16 Conclusion This was the first and best example of intrinsic bioremediation – where contaminated ground is remediated without human intervention and is now widely used Toxic chemicals leaching from crude oil can be rapidly degraded by natural microbial populations It was shown that plumes of contaminated groundwater stop enlarging as microbial degradation came into balance with rates of contaminant leaching


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