U.S. Geological Survey (USGS) scientists studying two subsurface crude-oil spill sites in Minnesota measured concentrations of oil breakdown products (metabolites) at greater concentrations than parent compound concentrations.
At sites where there have been crude-oil or petroleum hydrocarbon fuel spills and contaminants have entered groundwater, metabolites from the crude oil form primarily from biodegradation reactions. The metabolites are more soluble than the parent compounds and are transported from the original source, forming a groundwater plume.
Contaminants such as benzene, toluene, ethylbenzene, xylene (BTEX), and polycyclic aromatic hydrocarbons (PAHs) are commonly present in groundwater plumes from crude oil. The standard method for quantifying the concentration of a mixture of groundwater contaminants from crude oil involves extraction followed by analysis on a gas chromatograph. Individual concentrations of extracted compounds containing 10 to 28 carbons are added to obtain a total concentration known as diesel range organics (DROs) or total petroleum hydrocarbons in the diesel range (TPHd). Regulatory monitoring and reporting requirements in Minnesota and other states require analyses for concentrations of BTEX and DROs; however, because of limitations in the method, analyses for DROs do not reflect all of the organic compounds entering the groundwater from crude oil. A more comprehensive analysis is nonvolatile dissolved organic carbon (NVDOC), which accounts for all organic carbon remaining after purging the sample of volatile dissolved organic carbon. Metabolites produced during hydrocarbon biodegradation are contained in the NVDOC.
The focus of this study was on the occurrence and fate of NVDOC metabolites in existing contaminant plumes associated with two crude-oil spill sites in Minnesota. The first site is the Toxic Substances Hydrology Program's long-term research site in Bemidji, Minnesota. The second site is located at the South Cass Lake pumping station near the town of Cass Lake, Minnesota. The plume scale NVDOC data for Bemidji are from sampling campaigns in July 1988 (22 wells), 1995 (23 wells), and 2010 (23 wells). Samples for NVDOC were collected from contaminated wells at the Cass Lake site in June 2008 (15 wells) and one background well in August 2009.
Scientists compiled 20 years of monitoring data to understand the occurrence of NVDOC relative to other regulated crude-oil contaminants. Concentrations of DROs and extended range DROs compounds are one-third to one-half of the total concentration of NVDOC present in groundwater at the two crude-oil spill sites the scientists studied. NVDOC was measured at concentrations of 20–50 milligrams per liter in monitoring wells at the sites. These values were 10 times higher than benzene and two to three times higher than DROs in the same wells. Monitoring data from 1988 through 2015 at Bemidji indicate that the plume of NVDOC is expanding more rapidly than the BTEX plume toward a lakeshore located 335 meters (2,000 feet) from the source zone.
Environmental Health Considerations
The NVDOC metabolites in groundwater plumes at the two sites are not covered by regulatory monitoring and reporting requirements in Minnesota and other States; however, at study sites where residual product is present, the total concentration of transformation products can exceed BTEX concentrations by one to two orders of magnitude. In addition to possible concerns about toxicity, these plumes of metabolites consume the electron-accepting capacity of the contaminated aquifer, resulting in the slowing of biodegradation of other compounds in the contaminated plume. Together these results indicate that at oil spill sites where residual sources are present, monitoring of NVDOC may be an important part of an effective evaluation of the fate and effects of groundwater contaminant plumes.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology).
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Energy Integrated Science Team
Cyclical Mobilization and Attenuation of Naturally Occurring Arsenic in an Underground Petroleum Plume
Understanding Pathways of Unconventional Oil and Gas Produced Water Spills in the Environment
Crude Oil Contamination in the Shallow Subsurface
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Natural Breakdown of Petroleum Results in Arsenic Mobilization in Groundwater
Pipeline Crude Oil Spill Still a Cleanup Challenge after 30 Years
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Below are publications associated with this project.
Crude oil metabolites in groundwater at two spill sites
- Overview
U.S. Geological Survey (USGS) scientists studying two subsurface crude-oil spill sites in Minnesota measured concentrations of oil breakdown products (metabolites) at greater concentrations than parent compound concentrations.
At sites where there have been crude-oil or petroleum hydrocarbon fuel spills and contaminants have entered groundwater, metabolites from the crude oil form primarily from biodegradation reactions. The metabolites are more soluble than the parent compounds and are transported from the original source, forming a groundwater plume.
U.S. Geological Survey (USGS) scientists collecting a groundwater sample from a well at the USGS Bemidji Crude-Oil Spill Research Site, Minnesota. The scientists monitored in real time the dissolved oxygen, pH, specific conductance, and temperature of the water as the well is pumped so they can know when to collect representative sample. Contaminants such as benzene, toluene, ethylbenzene, xylene (BTEX), and polycyclic aromatic hydrocarbons (PAHs) are commonly present in groundwater plumes from crude oil. The standard method for quantifying the concentration of a mixture of groundwater contaminants from crude oil involves extraction followed by analysis on a gas chromatograph. Individual concentrations of extracted compounds containing 10 to 28 carbons are added to obtain a total concentration known as diesel range organics (DROs) or total petroleum hydrocarbons in the diesel range (TPHd). Regulatory monitoring and reporting requirements in Minnesota and other states require analyses for concentrations of BTEX and DROs; however, because of limitations in the method, analyses for DROs do not reflect all of the organic compounds entering the groundwater from crude oil. A more comprehensive analysis is nonvolatile dissolved organic carbon (NVDOC), which accounts for all organic carbon remaining after purging the sample of volatile dissolved organic carbon. Metabolites produced during hydrocarbon biodegradation are contained in the NVDOC.
The focus of this study was on the occurrence and fate of NVDOC metabolites in existing contaminant plumes associated with two crude-oil spill sites in Minnesota. The first site is the Toxic Substances Hydrology Program's long-term research site in Bemidji, Minnesota. The second site is located at the South Cass Lake pumping station near the town of Cass Lake, Minnesota. The plume scale NVDOC data for Bemidji are from sampling campaigns in July 1988 (22 wells), 1995 (23 wells), and 2010 (23 wells). Samples for NVDOC were collected from contaminated wells at the Cass Lake site in June 2008 (15 wells) and one background well in August 2009.
Scientists compiled 20 years of monitoring data to understand the occurrence of NVDOC relative to other regulated crude-oil contaminants. Concentrations of DROs and extended range DROs compounds are one-third to one-half of the total concentration of NVDOC present in groundwater at the two crude-oil spill sites the scientists studied. NVDOC was measured at concentrations of 20–50 milligrams per liter in monitoring wells at the sites. These values were 10 times higher than benzene and two to three times higher than DROs in the same wells. Monitoring data from 1988 through 2015 at Bemidji indicate that the plume of NVDOC is expanding more rapidly than the BTEX plume toward a lakeshore located 335 meters (2,000 feet) from the source zone.
Environmental Health Considerations
The NVDOC metabolites in groundwater plumes at the two sites are not covered by regulatory monitoring and reporting requirements in Minnesota and other States; however, at study sites where residual product is present, the total concentration of transformation products can exceed BTEX concentrations by one to two orders of magnitude. In addition to possible concerns about toxicity, these plumes of metabolites consume the electron-accepting capacity of the contaminated aquifer, resulting in the slowing of biodegradation of other compounds in the contaminated plume. Together these results indicate that at oil spill sites where residual sources are present, monitoring of NVDOC may be an important part of an effective evaluation of the fate and effects of groundwater contaminant plumes.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology).
- Science
Below are other science projects associated with this project.
Energy Integrated Science Team
The Energy Lifecycle Integrated Science Team focuses on the potential for contaminant exposures in the environment that might originate from energy resource activities including, extraction, production, transportation, storage, extraction, waste management and restoration. Perceived health risks to humans and other organisms will be distinguished from actual risks, if any. If actual risks are...Cyclical Mobilization and Attenuation of Naturally Occurring Arsenic in an Underground Petroleum Plume
Scientists found that naturally occurring arsenic in aquifer sediments was mobilized into groundwater and attenuated through reattachment to sediments within an underground petroleum plume. Understanding these patterns identifies anthropogenic factors that affect arsenic presence and magnitude in groundwater.Understanding Pathways of Unconventional Oil and Gas Produced Water Spills in the Environment
A new study measures the transport of chemicals associated with unconventional oil and gas (UOG) produced waters downstream from a pipeline leak in North Dakota. This work is part of a long-term study designed to understand chemical persistence in sediments and water and how those factors might be related to contaminant exposures and associated with adverse health effects, if any, on organisms.Crude Oil Contamination in the Shallow Subsurface
This investigation focuses on the long-term persistence in soils and groundwater of petroleum hydrocarbon spills, including crude oil and refined petroleum fuels. The study site near Bemidji, MN, is a laboratory for developing site assessment tools and understanding chemical changes affecting human and environmental health that occur during natural attenuation of petroleum hydrocarbons.Ethanol-Containing Fuel Spills Enhanced Natural Trace Element Release from Sediments in an Experimental Setting
Experimental field research simulating hydrocarbon spills by researchers from the U.S. Geological Survey (USGS), Virginia Tech, and the University of St. Thomas showed that mixed ethanol and petroleum-based fuels increased the rate by which arsenic and other natural trace elements are released from aquifer sediments to groundwater when compared to petroleum-based fuels alone.Natural Breakdown of Petroleum Results in Arsenic Mobilization in Groundwater
Changes in geochemistry from the natural breakdown of petroleum hydrocarbons in groundwater promote mobilization of naturally occurring arsenic from aquifer sediments into groundwater. This geochemical change can result in potentially significant and overlooked arsenic groundwater contamination. Arsenic is a toxin and carcinogen linked to numerous forms of skin, bladder, and lung cancer. Of...Pipeline Crude Oil Spill Still a Cleanup Challenge after 30 Years
Research at a 1979 crude oil spill from a ruptured pipeline has exposed and helped to overcome many challenges facing an effective, cost-efficient cleanup of crude oil, U.S. Geological Survey (USGS) scientists have found. The environmental release of crude oil occurred near Bemidji, Minnesota.Ground-Water Recharge Affects Fate of Petroleum Contaminant Plumes
U.S. Geological Survey (USGS) scientists have discovered that rainwater recharging the water table above petroleum contamination plumes affects how plumes grow and the rate that petroleum products (in this case crude oil) degrade and weather in ground water. The amount of recharge affects the migration of oil in the subsurface, how chemicals dissolve from the oil into ground water, and the... - Publications
Below are publications associated with this project.
Crude oil metabolites in groundwater at two spill sites
Two groundwater plumes in north central Minnesota with residual crude oil sources have 20 to 50 mg/L of nonvolatile dissolved organic carbon (NVDOC). These values are over 10 times higher than benzene and two to three times higher than Diesel Range Organics in the same wells. On the basis of previous work, most of the NVDOC consists of partial transformation products from the crude oil. MonitoringAuthorsBarbara A. Bekins, Isabelle M. Cozzarelli, Melinda L. Erickson, Ross Steenson, Kevin A. Thorn