Civil Enforcement

"Wet weather discharges" refers collectively to point source discharges that result from precipitation events, such as rainfall and snowmelt. Wet weather discharges include storm water runoff, combined sewer overflows (CSOs), wet weather sanitary sewer overflows (SSOs), and discharges from concentrated animal feeding operations (CAFOs). Storm water runoff accumulates pollutants such as oil and grease, chemicals, nutrients, metals, and bacteria as it travels across land. CSOs and wet weather SSOs contain a mixture of raw sewage (often containing high bacteria levels as well as disease-causing pathogens and viruses), industrial wastewater and storm water, and have resulted in beach closings, shellfish bed closings, and aesthetic problems. Runoff from CAFOs enters water bodies through poor maintenance of waste lagoons and improper storage of animal waste which can result in spills and leaks of manure laden water. Excessive and improper application of manure to cropland can be another major source of water pollution from CAFOs.

OECA has directed that compliance assistance, compliance monitoring and enforcement of wet weather compliance problems be prioritized by looking at regulated facilities contributing to the impairment of watersheds, beaches and shellfish beds, source water protection areas, environmental justice areas, and other sensitive areas. EPA has compliance assistance information on wet weather problems available through the National Agriculture Compliance Assistance Center. (Compliance Assistance Information) (Compliance Monitoring Information)

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EPA's compliance and enforcement efforts in the wet weather discharges areas are producing significant gains in the protection of human health and the environment. See the list of settled cases below.

Combined Sewer Overflows

Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and them discharged to a water body. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies.

These overflows, called combined sewer overflows (CSOs), contain not only storm water but also untreated human and industrial waste, toxic materials, and debris. They are a major water pollution concern for the approximately 772 cities in the U.S. that have combined sewer systems. EPA's CSO Control Policy, published April 19, 1994, is the national framework for control of CSOs. The Policy provides guidance on how communities with combined sewer systems can meet Clean Water Act goals in as flexible and cost-effective a manner as possible. EPA's Report to Congress on implementation of the CSO Control Policy assesses the progress made by EPA, states, and municipalities in implementing and enforcing the CSO Control Policy.

Concentated Animal Feeding Operations

Concentrated Animal Feeding Operations (CAFOs) are point sources subject to the National Pollutant Discharge Elimination System (NPDES) program. A CAFO is a livestock facility, or lot, that confines a prescribed number of animals for at least 45 days out of a calendar year, and does not sustain crops on any portion of the facility or lot in the normal growing season. CAFOs exist in all regions of the U.S. They are concentrated in the eastern seaboard, the plains and the west coast. The total number of CAFOs is unknown but is estimated to be in excess of 20,000.

Runoff from CAFOs enters water bodies through poor maintenance of waste lagoons and improper storage of animal waste which can result in spills and leaks of manure laden water. Excessive and improper application of manure to cropland can be another major source of water pollution from CAFOs.

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Sanitary Sewer Overflows

Properly designed, operated, and maintained sanitary sewer systems are meant to collect and transport all of the sewage that flows into them to a publicly owned treatment works (POTW). However, occasional discharges of raw sewage from municipal sanitary sewers occur in almost every system. These types of discharges are called sanitary sewer overflows (SSOs). SSOs have a variety of causes, including but not limited to severe weather, improper system operation and maintenance, and vandalism. EPA estimates that there are at least 40,000 SSOs each year. The untreated sewage from these overflows can contaminate our waters, causing serious water quality problems due to the presence of bacteria such as fecal coliform and other disease-causing pathogens and viruses.

Storm Water

Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events that often contain pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by an National Pollutant Discharge Elimination System (NPDES) permit. The primary method to control storm water discharges is through the use of best management practices.

The 1987 Amendments to the CWA included the addition of paragraph (p) under Section 402 which established phased NPDES permit requirements for municipal and industrial storm water discharges. Storm water discharges are nationwide occurrences. The total number of storm water dischargers is estimated at several hundred thousand. Storm water runoff poses a significant threat to public health and the environment, and remains a leading cause of water quality impairment. Pollutants in storm water discharges can cause a variety of diseases in humans, ranging from dysentery to hepatitis. They can also contaminate fish, shellfish, and drinking water sources, create harmful algal blooms, and impair water quality.

Additional Information

Wet Weather Discharges Reference Materials
This includes EPA documents relating specifically to wet weather discharges used in enforcement, a listing of the major settled cases that involve wet weather discharges, and links to other EPA information sources on wet weather discharges.

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