VOC’s are carbon-containing chemicals that readily evaporate at normal air temperature and pressure. They are contained in 

many commercial products such as gasoline, paints, adhesives, 

solvents, wood preservatives, dry-cleaning agents, pesticides, 

cosmetics, correction fluid, and refrigerants. Approximately 15 

million pounds of VOC’s were released to the atmosphere in the 

focused study area (fig. 1) in 1992 by facilities registered with the 

U.S. Environmental Protection Agency. Millions of additional 

pounds of VOC’s are emitted to the atmosphere and to land and 

water by smaller unregistered users of these compounds in the 

focused study area. 

Exposure to VOC’s in the air we breathe and the water we 

drink is a human-health issue. Some VOC’s are suspected carcinogens (benzene, trichloroethene, tetrachloroethene, and 1,1-

dichloroethene). In high concentrations, many VOC’s can also be 

toxic to humans or wildlife.

As part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program, water-quality data from rivers and wells sampled from 1978 to 1994 were summarized to 

provide a general assessment of water quality in the focused 

study area. Data from rivers were from Federal and state agencies, which used similar sample collection and analytical methods. Ground-water-quality data were collected by Federal and 

state agencies from domestic and public water-supply wells.

Because of their volatility, VOC’s are not likely to be detected 

in rivers, except immediately downstream from points of VOC 

discharges. Most river samples did not contain VOC’s. VOC’s 

that were detected in a few water samples from the Mississippi 
October 1996 Fact Sheet FS-095-96, 2nd edition

River included trichloroethene, benzene, toluene, 1,2-dichloroethane, ethylbenzene, xylenes; 1,1,1-trichloroethane, ethylbenzene, 

chloroethene, and acrylonitrile. The Mississippi River is the primary source of water supplies to the cities of Minneapolis, St. 

Paul, and St. Cloud (fig. 2).

VOC’s are more likely to be detected in ground water than in 

rivers. Volatilization of VOC’s from ground water is not rapid 

because most ground water is not in direct contact with the atmosphere. VOC’s can be absorbed by clays or organic materials, or 

can be broken down by bacteria and other microbes in soils or in 

underlying aquifers. The highest concentrations of VOC’s in 

ground water are usually near sites of spills or leaks of these compounds. Several reports released by the Minnesota Department of 

Health indicated increased frequencies of detection of VOC’s in 

water from domestic and public-supply wells within a mile of 

VOC sources such as landfills.

For wells distributed throughout the focused study area, 

VOC’s were generally detected in less than five percent of water 

samples analyzed for those compounds (fig. 3). The most frequently detected VOC’s in ground water were commonly used 

solvents or gasoline components, including: trichloroethene, 

benzene, toluene, tetrachloroethene; 1,2-dichloroethene, ethylbenzene, meta+para- and ortho-xylene; 1,1,1-trichloroethane, 

and 1,1-dichloroethane. Except for trichloroethane, less than one 

percent of the water samples from wells exceeded health-based 

Maximum Contaminant Levels established by the U.S. Environmental Protection Agency. Most of the wells producing water 

with detectable concentrations of VOC’s were located in the 

Minneapolis-St. Paul metropolitan area or along river corridors 

(fig. 3), where factories, landfills, and other emission sites of 

VOC’s are concentrated.

The Upper Mississippi River Basin is 1 of 15 on-going study 

units started in 1994 as part of the U.S. Geological Survey’s 

NAWQA Program. The purpose of the program is to assess the 

quality of a large, representative part of the nation’s water 

resources. Retrospective analyses of water-quality data summarized in this fact sheet and in Andrews and others (1995) is the 

first stage of activity for each study unit. In subsequent years 

samples from widespread networks of surface-water sites, ecological sites, and wells will be analyzed for hundreds of constituents to evaluate the quality of water resources in the basin and 

the effects of natural and human factors on water quality.

Andrews, W.J., Fallon, J.D., and Kroening, S.E., 1995, Waterquality assessment of part of the Upper Mississippi River 

Basin, Minnesota and Wisconsin—Volatile organic compounds 

in surface and ground water: U.S. Geological Survey WaterResources Investigations Report 95-4216, 39 p.

Minnesota Department of Health, 1989, Water supply 

monitoring near metropolitan solid waste disposal facilities, 

Report to the Legislative Commission on Minnesota 

Resources: Minnesota Department of Health, Section of 

Water Supply and Engineering, Minneapolis, 34 p.

Stark, J.R., 1994, National Water-Quality Assessment 

Program—the Upper Mississippi River Basin: U.S. 

Geological Survey Open-File Report 94-101, 1 p.

U.S. Environmental Protection Agency, 1994, 1992 Toxic 

Release Inventory, Public Data Release: U.S. Environmental 

Protection Agency, EPA745-R-94-001, 372 p.

Prepared by William J. Andrews

For more information, contact:

Upper Mississippi River Basin NAWQA Coordinator

U.S. Geological Survey

2280 Woodale Drive

Mounds View, Minnesota 55112

Phone (612) 783-3100

World-wide Web home page:

http://wwwmn.cr.usgs.gov/umis
October 1996 Fact Sheet FS-095-96, 2nd edition