Adopted January 21, 1993, by the WEF Board of Trustees
Sewer overflows occur when combined storm and sanitary sewerage systems, which are prevalent in older cities, receive excessive stormwater flows from streets, roof drains, and other stormwater catchment systems. When the design capacity of these systems is exceeded, overflow structures direct untreated flow into receiving waters, thereby bypassing treatment facilities designed to protect water quality.
Combined sewer overflows (CSOs) differ from other point source discharges in that they occur only intermittently. The impacts of CSO discharges depend on such diverse factors as watershed characteristics; nature of the pollutants; variability of the stormwater flow reaching the sewer; condition, volume, and flow rate of the receiving water during the storm; location of the overflow; and use of the receiving water body. Each storm event may have a different impact on water quality than previous storm events.
A national strategy to address CSOs was released by the U.S. Environmental Protection Agency in 1989, and regulatory guidance to implement this strategy is now being developed. The Water Environment Federation believes this strategy essentially is sound, but legislation is needed to support the strategy with a wider regulatory framework.
The Water Environment Federation's legislative recommendations for CSOs are presented in terms of water quality standards, minimum techno
logy requirements, phasing and prioritization, and compliance and enforcement.
Water Quality Standards
Existing state water quality standards typically are inadequate for addressing wet weather conditions. New standards are needed under the authority of the Clean Water Act which recognize the intermittent nature of CSO events and the impacts that conditions in tributary areas have on wet weather stream conditions. Standards should reflect accurately the impact of discharges on receiving water during and immediately after a storm event or snowmelt. EPA should have primary responsibility for ensuring development of wet weather criteria, and should fund needed additional water quality research. Comprehensive watershed plans should allow for development of wet weather standards which reflect reasonable efforts to allow for intermittent and minimum deviations of stream criteria due to CSO and stormwater discharges so that the costs of control correspond with the water quality improvements attained.
Monitoring is needed to characterize CSO discharges and evaluate their impacts on water quality. Monitoring wet weather conditions is more difficult than normal effluent monitoring due to the varying conditions. Selected CSO control technologies and/or point of discharge measurements should be the basis for compliance monitoring until more reliable dynamic stream response models are developed and implemented. Appropriate characterizations at representative CSO discharge points that are contributing to water quality degradation are necessary in order to establish a baseline for measuring future progress in meeting abatement targets. Initial monitoring data should not be used as a basis for enforcement action.
Minimum Technology Requirements
WEF favors the establishment of technology-based standards. These standards should rely on best professional judgment and site-specific factors. At a minimum, such standards should lead to the following elements of CSO program implementation:
- proper operation and maintenance of CSO facilities
- effective use of existing facilities
- elimination of dry weather overflows
- control of settleable and floatable solids using best management practices
Additional CSO discharge controls should be developed and implemented on a site-specific basis to attain the applicable wet weather standards. National uniform technology-based standards are, in our judgment, not appropriate due to the variable nature of CSOs.
Watershed management and regulatory authorities should inventory all CSO discharge points. Completion of the inventory should be given high priority and should be used to develop an understanding of how overflows vary as wet weather conditions vary. Regional rainfall data, runoff models, receiving stream assimilation evaluations, and water use all should be factored into the development of technology-based CSO control programs.
Phasing and Prioritization for CSO Program Implementation
The Clean Water Act should authorize watershed management and regulatory authorities to establish a schedule for all control plans. Schedules should take into account the financial and personnel resources available within each state and municipality. Plans should be reviewed on a regular basis to ensure goals are being met.
Priorities for improving and maintaining water quality are best set on a watershed basis. Within a watershed, all actions to achieve water quality standards should be implemented in the most cost-effective and timely manner.
In order to ensure success, Congress should provide for federal and state financial assistance to CSO system operators. Resolving all CSO issues on a nationwide basis will be costly. Some estimates exceed $100 billion, which is a greater amount than the federal government has spent for Clean Water Act programs since its passage in 1972. For this reason, water quality problems within each watershed must be prioritized, leading to the adoption of those control programs that provide the most significant degree of water quality improvement.
Compliance and Enforcement
CSO programs should be implemented through the NPDES permit program under authority provided in the Clean Water Act. Flexibility to address individual or regional systems should be maintained within the present system. Emphasis should be placed on increased efforts to prevent pollution and reduce the need for treatment at the outfall. Municipalities should be urged to undertake public education programs directed toward reducing the introduction of hazardous residential and commercial materials into sanitary and storm systems, and Congress should provide EPA with the means to render technical assistance.
In cases where wet weather water quality standards are being violated, dischargers should be required to further control CSOs. Enforcement measures should be based on targeting appropriate technology to meet site- specific needs. In locations where combined sewer systems have been upgraded already, EPA should accept the improvements as an alternative to meeting new or differing standards unless a water resource is being significantly degraded.
Unless an appropriate amount of federal and state resources is devoted to this issue, local governments are going to be saddled with massive CSO financing needs which may result in significant rate payer and taxpayer resistance. Special efforts need to be made to educate the public on the impact of CSOs, on the rationale for this important program, and on the public's role in helping to abate a significant remaining source of water pollution.