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7 - Understanding subsurface contamination using conceptual and mathematical models
- Edited by John A. Wiens
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- Book:
- Oil in the Environment
- Published online:
- 05 July 2013
- Print publication:
- 18 July 2013, pp 144-175
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Summary
Introduction
Petroleum spills and other sources of hydrocarbon contamination represent risks for society. Regardless of whether oil is stranded on a shoreline, spilled from a pipeline, or leaked from underground storage tanks, the same basic physical and chemical principles characterize exposure levels of contaminants. The purpose of this chapter is to explain and illustrate these principles. In particular, we use these principles to explain the apparent paradox of how oil residues persist at some shorelines of Prince William Sound (PWS) as isolated subsurface patches, but yet pose little if any exposure risk to the local ecology. We resolve this apparent paradox using well-established scientific and engineering tools.
One of the biggest challenges of any study of a contaminated site is identifying the most important questions and the most important observations and data needed to answer these questions. This challenge is discussed in this chapter in both a general way and for the PWS study in particular. One of the key lessons learned from this study was the need for experts in multiphase flow in contaminated sediments to be a central part of the team addressing these questions. Our goal is to convey a coherent understanding and perspective that brings all of the observations and measurements by various environmental experts of different scientific disciplines into a consistent explanation.
8 - Removal of oil from shorelines: biodegradation and bioremediation
- Edited by John A. Wiens
-
- Book:
- Oil in the Environment
- Published online:
- 05 July 2013
- Print publication:
- 18 July 2013, pp 176-197
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- Chapter
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Summary
Introduction
Many microorganisms have evolved the ability to feed on naturally occurring petroleum hydrocarbons, which they use as sources of carbon and energy to make new microbial cells. Most of the tens of thousands of chemical compounds that make up crude oil can be attacked by bacterial populations indigenous to marine ecosystems. A consortium of different bacterial species rather than any single species acts together to break hydrocarbons down into carbon dioxide, water, and inactive residues. Even toxic oil residues, including highly toxic polycyclic aromatic hydrocarbons (PAH), can be detoxified. Microorganisms do not accumulate hydrocarbons as they consume and degrade them, so they are not a conduit for transferring hydrocarbons into the food web. In fact, microorganisms grown on hydrocarbons can be a potential source of protein for animal and human food (Shennan, 1984).
For many years before the Exxon Valdez oil spill, the US Environmental Protection Agency (EPA), the National Oceanic and Atmospheric Administration (NOAA), and other governmental agencies had supported research on microbial degradation of oil in marine environments – biodegradation – and on ways to enhance and accelerate it – bioremediation. These studies showed that, while in many cases biodegradation can mitigate toxic impacts of spilled oil without causing ecological harm, environmental conditions for it to happen rapidly are not always ideal (Atlas, 1995). If water carrying sufficient amounts of oxygen and nutrients cannot reach the oil, rates of biodegradation will be severely limited: oil incorporated into, or on, sediment above the tidal zone, oil buried in low-permeability sediments (Chapter 7), and thick oil layers and tarballs that are not intimately in contact with flowing water are especially resistant to biodegradation.