Oil Recovery Performance Monitoring
- Performance Monitoring
- Natural Attenuation Evaluation
- Equillon Enterprises, Houston, TX
- Lakehead Pipeline Company, Duluth, Minnesota
- Enbridge Partners,
- Pump and Test
- Monitored Natural Attenuation
|| Crude oil
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
- 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.
- Geoff Delin, USGS, Minnesota District, Mounds View, MN,
- Bill Herkelrath, USGS, National Research Program, Menlo Park,
- Herkelrath, W.N., 1999,
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.
Toxics Hydrocarbon Remediation Projects
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