Water: Liquid Assets
Liquid Assets 2000: Today's Challenges
Clean water is important to our health and our livelihood. Today's biggest threat to water quality is polluted runoff. During rainstorms or snowmelt, billions of pounds of dirt, manure, fertilizer, farm and lawn chemicals, oils and grease from city streets and parking lots, nutrient and toxic contaminants from the atmosphere, contaminants from tire and brake pad wear, contaminants from abandoned mines, and other pollutants are carried into the nation's waters. Runoff from sprawling developments, hydromodification, and some farming and forestry operations that lack conservation measures continue to contribute significantly to degraded conditions nationwide. According to the 1998 National Water Quality Inventory, states report that polluted runoff is the leading cause of water quality problems nationwide and pollution from agriculture, including cropland erosion, animal waste (e.g., chicken, hog, and beef farms), and fertilizers, is the leading cause of polluted runoff.
Some of today's other water quality threats include combined sewer overflows, sanitary sewer overflows, and stormwater system discharges. These discharges contribute to serious water quality problems, including beach closings, shellfish bed closures, and threats to groundwater and drinking water supplies.
Combined sewer overflows occur in older cities with "combined sewer systems," where the sewer system collects both storm water runoff and sanitary sewage in the same pipe. During rainfall or snowmelt, volume in the combined sewer system can exceed capacity, resulting in direct discharges to streams, rivers, lakes or estuaries. These overflows contain not only storm water, but untreated human and industrial waste, toxic materials and debris. They occur during wet weather in approximately 900 cities that have combined sewer systems.
Sanitary sewer overflows, meanwhile, are discharges of raw sewage from separate sanitary sewers, which are not designed to carry storm water runoff. Sanitary sewer overflows occur as a result of leaky, damaged, or blocked sewer pipes or when the volume of sewage flow exceeds the capacity of the sewer pipes or treatment plant, backing up into basements, onto city streets, and into our waters. Storm water runoff from urbanized areas, industrial sites, and construction sites is another major source of pollution.
Although some programs are in place to control sewer overflows and stormwater runoff, EPA is continuing to explore ways to control the environmental and public health threats posed by these "wet weather" sources of pollution. These and other emerging threats require continued vigilance as our infrastructure ages and populations increase.
While this report focuses primarily on water pollution, we face other problems. Air pollution, global warming and other challenges are important issues that we need to address and which contribute to water pollution as well.