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Environmental Health - Toxic Substances

Toxics Program Remediation Activities

Oil Recovery Performance Monitoring

Type
  • Performance Monitoring
  • Natural Attenuation Evaluation
Location Bemidji, MN
Partners
  • Equillon Enterprises, Houston, TX
  • Lakehead Pipeline Company, Duluth, Minnesota
  • Enbridge Partners, Houston, TX
Technology
  • Pump and Test
  • Monitored Natural Attenuation
Contaminants Crude oil
Description

USGS scientists are monitoring the state-mandated remediation at the Bemidji crude-oil spill site. The monitoring provides an important opportunity to investigate the impact and efficacy of pump and treat remediation of ground-water contamination at a site that has been extensively characterized. The Lakehead Pipeline Company designed the remediation system at the site using USGS data that was collected as part of a long-term investigation of the natural attenuation of crude oil spilled in the subsurface. Skimmer pumps installed in several wells are being used to remove oil from the water table, to eliminate the source of contamination in the aquifer. The impact of the remediation is being monitored and documented in several ways.

  • USGS scientists are obtaining and analyzing sediment cores from the oil contaminated zone in the subsurface in order to directly measure changes in the amount and distribution of oil in the aquifer.

  • The USGS is monitoring the efficacy of the remediation by measuring changes in the thickness of oil present in monitoring wells as a function of time. Water-table elevations are measured continuously in order to monitor changes in water-flow patterns.

  • USGS scientists are measuring hydrocarbon vapors and other gases in the unsaturated zone during the remediation. The remediation will most likely affect the transport of gases above the floating oil, which constitutes an important component of the overall removal or degradation of hydrocarbons at the site.

  • USGS is also monitoring the effects of the remediation on the dissolved hydrocarbon plume. Before remediation began in 1999, the hydrocarbon plume had been largely stabilized by natural attenuation. Microbes in the aquifer were rapidly degrading almost all of the hydrocarbons that were dissolved in the water, which greatly slowed the expansion of the plume. Because a large amount of water is being pumped out of the aquifer during the remediation, the natural ground-water flow field has been altered. The environment within the plume is changing, which may or may not have a detrimental impact on the microbial populations that are responsible for the natural attenuation. Monitoring of contaminant concentrations, the microbial community, and biogeochemical conditions (redox) will allow for early detection of such impacts, if they occur.

In addition to the above work, the Bemidji research team is conducting long-term research on the processes that control the natural attenuation of contaminants in the unsaturated zone.

Overview of remediation plan: The goal of the remediation is to remove the crude oil that is presently floating on the water table. The crude oil is the source of dissolved hydrocarbons that are present in a large plume of contaminated ground water. The plan of the remediation is to pump water out of collection wells and thereby lower the water table inside the wells. The oil then flows into the well, forming a layer on top of the water. The oil in this layer is pumped out of the well with a skimmer pump and removed from the site. The water that is separated from the oil is reinjected into the aquifer.

More Information
Contact
  • Geoff Delin, USGS, Denver, Colo.
  • Bill Herkelrath, USGS, National Research Program, Menlo Park, Calif.,
Publications
Herkelrath, W.N., 1999,
Impacts of remediation at the Bemidji oil-spill site, in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999--Volume 3 of 3--Subsurface Contamination from Point Sources: U.S. Geological Survey Water-Resources Investigations Report 99-4018C, p. 195-200.
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Page Last Modified: Tuesday, 06-May-2014 14:37:04 EDT