Case Study 7: Watershed Management


Futurity, Inc.: NPSP (Non-Point Source Pollution Case Study)

5121 North Ravenswood Avenue

Chicago, IL 60640


Fax: 773-506-8921

When a native ecosystem is converted into a corn field or housing development, the hydrology of the area changes. Rain runs off compacted soils and pavement faster and in greater amounts than when it falls on vegetation and is absorbed by soil. Storm water runoff can carry pollutants such as sediment, pesticides, oil, and heavy metals and deposit them directly into open water. This type of pollution is known as non-point source pollution (NPSP). NPSP is now the leading cause of water pollution in the United States and has both short- and long-term consequences (1).

In 1999, the Environmental Protection Agency (EPA) declared over 20,000 bodies of water as polluted by sediments, nutrients, and harmful microorganisms. These waters encompass approximately 300,000 miles of river and shoreline, and 5 million acres of lakes (2).

The drainage area for a creek or lake is defined as a watershed. Watershed boundaries help determine where and how land-cover conditions degrade or promote water quality. Map 2 identifies NPSP risk for an entire watershed. Red represents areas which are most likely to contribute to NPSP due to land cover conditions and the proximity of water bodies (3).

Many pollutants affecting streams and lakes are produced by specific land use activities. NPSP risk maps can be refined to isolate the potential contribution of these individual activities.

Row crop agriculture

In the National Water Quality Inventory, the EPA identified agriculture as the leading contributor to water quality degradation (1). Many chemicals used in agriculture can have severe effects on water quality and pose a significant threat to aquatic species (4). Much of this chemical use is associated with row crop agriculture. The map on the left identifies NPSP risk for row crop agriculture.


Hydrocarbons, oil, heavy metals, salt, and fine solids are some of the numerous pollutants produced by the vehicle and maintenance activities associated with roads. The map on the left can be used to identify road segments that present a risk to water bodies.

Remote sensing techniques can identify areas of high NPSP risk. These areas can be isolated based on the source of the risk to determine effective pollution management practices. This approach allows various solutions to be coordinated to effectively address multiple sources of risk.

1. Environmental Protection Agency. 1996. The National Nonpoint Source Management Program: Pointer Number 1. Nonpoint Pointers, EPA-841-F-96-004A.

2. Environmental Protection Agency. 1999. Total Maximum Daily Load (TMDL) Program. TMDL Program Webpage:

3. Henderson, F.M., T.F. Hart, Jr., L. Orlando, B. Heaton, J. Portolese, and R. Chasen. 1998. Application of C-CAP Protocol Land-Cover Data to Non-point Source Water Pollution Potential Spatial Models in a Coastal Environment, Photogrammetric Engineering & Remote Sensing, Vol. 64, No. 10, pp. 1015-1020.

4. California State Water Resources Control Board, Division of Water Quality. 1994. Polluted Runoff: Watershed Solutions.

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