WRRC/Ike Wai Seminar

Fate of Petroleum Hydrocarbons in Groundwater: Lessons for Hawaii and Red Hill from a Terrestrial Oil Spill Study

Dr. Barbara Bekins

The oldest continuous study of a terrestrial oil spill in the world began in 1983 by the U.S. Geological Survey. In 1979, over 10,000 barrels of a light, paraffinic crude oil spilled from a pipeline rupture onto forested land on the outskirts of the town of Bemidji in northern Minnesota. The oil composition is dominated by saturated hydrocarbons (58–61%), with aromatics representing most of the remainder. Each of these compound classes has different fates. The aromatic fraction, most notably benzene, has traditionally been of greatest regulatory concern because of its toxicity and mobility. The aromatics dissolve into in the groundwater according to their relative solubilities, and migrate as a contaminant plume. Today benzene concentrations in the oil are 22 to 42% of those in freshly spilled oil, and concentrations entering the groundwater are decreasing. The saturated hydrocarbons are mostly poorly soluble alkanes that degrade within the oil body source zone to methane and CO2. Most of the produced methane migrates upward and is oxidized to CO2 and water, before reaching the surface. In the groundwater contaminant plume, benzene is biodegraded by iron-reducing bacteria, which utilize natural iron oxy-hydroxide coatings on the aquifer sediments. The largest organic carbon fraction in the contaminant plume consists of partial oxidation products of the oil compounds. Over 14,000 individual compounds are present in this largely unregulated fraction, but concentrations and toxicity decrease with distance from the oil source as oxygen contents increase through biotransformation. These results could have implications for use of monitored natural attenuation (MNA) as a remedial strategy at leaking underground storage sites in Hawaii, including the Navy’s Red Hill Bulk Storage Facility.

Barbara is a hydrologist with the U.S. Geological Survey, Water Resources Division. She studies biodegradation of crude oil and nitrate contamination in groundwater and specializes in integrating field and laboratory observations using computer models. She also studies the generation of fluid overpressures and their effect on fault strength.

Event Sponsor
Water Resources Research Center/Ike Wai, Mānoa Campus

More Information
(808) 956-3097, wrrc@hawaii.edu

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