EPA CSO Policy Overview

EPA's Combined Sewer Overflow Control Policy [PDF Format] is a national framework for control of CSOs through the National Pollutant Discharge Elimination System (NPDES) permitting program. The Policy resulted from negotiations among municipal organizations, environmental groups, and State agencies. It provides guidance to municipalities and State and Federal permitting authorities on how to meet the Clean Water Act's pollution control goals as flexibly and cost-effectively as possible. The CSO Policy was published April 19, 1994, at 59 Fed. Reg. 18688.

The Policy contains four fundamental principles to ensure that CSO controls are cost-effective and meet local environmental objectives:

Clear levels of control to meet health and environmental objectives

Flexibility to consider the site-specific nature of CSOs and find the most cost-effective way to control them

Phased implementation of CSO controls to accommodate a community's financial capability

Review and revision of water quality standards during the development of CSO control plans to reflect the site-specific wet weather impacts of CSOs

EPA continues to develop guidance and information to foster implementation of the CSO Policy. State and EPA NPDES permitting authorities are working with permittees to incorporate CSO conditions into NPDES permits and other enforceable mechanisms, such as administrative or judicial orders.

The first milestone under the CSO Policy was the January 1, 1997, deadline for implementing minimum technology-based controls (the "nine minimum controls.") The nine minimum controls are measures that can reduce the prevalence and impacts of CSOs and that are not expected to require significant engineering studies or major construction.

Communities with combined sewer systems are also expected to develop long-term CSO control plans that will ultimately provide for full compliance with the Clean Water Act, including attainment of water quality standards.

CSO communities are now in various stages of developing and implementing their long-term control plans, including characterizing their combined sewer systems, monitoring the impacts of CSOs on waterways, and discussing water quality and CSO control goals with permitting authorities, water quality standards authorities, and rate payers. EPA encourages municipalities to take advantage of the flexibility in the Policy as they embark on this process, particularly where opportunities exist to evaluate water pollution control needs on a watershed management basis and to coordinate CSO control efforts with other point and nonpoint source control activities.