EPA Reports on CSO, SSO Discharges
The Environmental Protection Agency has released a report to Congress on the extent of human health and environmental impacts ...
The Environmental Protection Agency has released a report to Congress on the extent of human health and environmental impacts caused by municipal combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs), including the location of discharges, the volume of pollutants discharged, the constituents discharged, the resources spent by municipalities to address these impacts, and the technologies used.
This is the second of two reports that Congress requested on the impact of CSO and SSOs. The first report was sent to Congress in December 2001 as Report to Congress – Implementation and Enforcement of the Combined Sewer Overflow Control Policy.
In its new report, EPA estimates that the annual CSO volume is approximately 850 billion gallons, down from over 1 trillion gallons prior to the CSO Control Policy. EPA also estimates that the number of CSO events has dropped from approximately 60,000 prior to the CSO Control Policy, to around 43,000, or a reduction of 28 percent since the issuance of the CSO Control Policy.
The EPA report demonstrates that the nation's clean water agencies are working hard to improve public health and the environment, according to Ken Kirk, Executive Director of the Association of Metropolitan Sewerage Agencies.
"Clean water facilities have done an outstanding job in reducing sewer overflows but federal funding is needed to address the $88 billion and $50.6 billion EPA-estimated cost to fully control SSOs and CSOs, respectively, over the next 20 years," Kirk said. "It is imperative that EPA also develop a flexible SSO policy that incorporates watershed planning principles and allows communities to direct resources to those areas that will best improve public health and the environment."
This second study, "Report to Congress on the Impacts and Control of CSOs and SSOs" is organized into sections addressing both CSOs and SSOs:
• Environmental impacts
• Human health impacts
• Control technologies
• Resources spent
The following article provides a synopsis of each section and is based on the Report's Executive Summary. A full copy of the report is available on the Internet at http://www.epa.gov/ npdes/csossoreport2004.
Currently, 828 NPDES permits authorize discharges from 9,348 CSO outfalls in 32 states (including the District of Columbia). Most Combined Sewer Systems (CSSs) are located in the Northeast and Great Lakes regions.
The estimated volume of CSO discharged nationwide is 850 billion gallons per year. The number of CSSs and CSO permits has decreased slightly since publication of EPA's 2001 Report to Congress. Further, the percentage of CSO long-term control plans (LTCPs) that have been submitted to permitting authorities has increased from 34 to 59 percent.
EPA's 2000 Clean Watersheds Needs Survey (CWNS) Report to Congress reported 15,582 municipal Separate Sewer Systems (SSSs) with wastewater treatment facilities. An additional 4,846 satellite SSSs collect and transport wastewater flows to regional wastewater treatment facilities.
EPA estimates that between 23,000 and 75,000 SSO events occur per year in the United States, discharging a total volume of three to 10 billion gallons per year. This estimate does not account for discharges occurring after the headworks of the treatment plant or backups into buildings caused by problems in the publicly-owned portion of an SSS.
The majority of SSO events are caused by sewer blockages that can occur at any time. The majority of SSO volume appears to be related to events caused by wet weather and excessive inflow and infiltration.
CSOs and SSOs contain untreated wastewater, and therefore the pollutant concentration depends on the service population, the characteristics of the sewer system, weather conditions, any treatment provided, and other factors.
The principal pollutants present in CSOs and SSOs are:
• Microbial pathogens
• Oxygen depleting substances
• Total suspended solids (TSS)
• Floatables and trash
Pollutant concentrations in CSOs and SSOs vary substantially, not only from community to community and event to event, but also within a given event. CSOs and SSOs contribute pollutant loadings to waterbodies where discharges occur. It is important to note that waterbodies also receive pollutants of the types found in CSOs and SSOs from other sources such as storm water runoff.
Pollutant concentrations in CSOs and SSOs may be sufficient to cause a violation of water quality standards, precluding the attainment of one or more of the designated uses (e.g., swimming, boating, fishing) for the waterbody.
CSOs and wet weather SSOs discharge simultaneously with storm water runoff and other nonpoint sources of pollution. EPA recognizes that this can make it difficult to identify and assign specific cause-and-effect relationships between CSOs, SSOs, and observed water quality problems. In addition, EPA found that the identification and quantification of environmental impacts caused by CSOs and SSOs at the national level is difficult because there is no comprehensive national data system for tracking the occurrence and impacts of CSOs and SSOs.
Nevertheless, CSOs and SSOs can by themselves affect the attainment of designated uses and cause water quality standards violations. Average bacteria concentrations in CSOs and SSOs may be several thousand times greater than water quality standard criteria, and waterbodies that receive CSO and SSO discharges may lack sufficient dilution or assimilative capacity.
Based on modeling analysis conducted by EPA, water quality standards are projected to be violated frequently, even in the absence of other sources of fecal coliform pollution, where discharges from SSO events include more concentrated wastewater (e.g., SSOs with limited I/I) or when SSOs discharge to smaller receiving waters such as a stream or small tributary.
CSOs were responsible for 1 percent of reported advisories and closings, and 2 percent of advisories and closings that had a known cause during the 2002 swimming season. SSOs were reported to be responsible for 6 percent of reported advisories and closings, and 12 percent of advisories and closings having a known cause. Studies also identify CSOs and SSOs as a cause of shellfish harvesting prohibitions and restrictions in classified shellfish growing areas.
The environmental impacts of CSOs and SSOs are most apparent at the local level, and as the result of large or recurrent discharges.
Human Health Impacts
Although it is clear that CSOs and SSOs contain disease-causing pathogens and other pollutants, EPA has limited information on actual human health impacts occurring as a result of CSO and SSO events. Further, CSOs and wet weather SSOs also tend to occur at times (e.g., storm events) when exposure potential may be lower.
Identification and quantification of human health impacts caused by CSOs and SSOs at the national level is difficult due to a number of factors, including under-reporting and incomplete tracking of waterborne illness, contributions of pollutants from other sources, and the lack of a comprehensive national data system for tracking the occurrence and impacts of CSOs and SSOs.
As an alternative to direct data on human health impacts, EPA modeled the annual number of gastroenteritis cases potentially occurring as a result of exposure to water contaminated by CSOs and SSOs at BEACH survey beaches. EPA found that CSOs and SSOs are estimated to cause between 3,448 and 5,576 illnesses annually at the subset of recreational areas included in the analysis.
Technologies Used to Reduce Impacts
Municipalities employ a wide variety of technologies and operating practices to maintain existing infrastructure, minimize the introduction of unnecessary waste and flow into the sewer system, increase capture and treatment of wet weather flow reaching the sewer system, and minimize the impact of any subsequent discharges on the environment and human health. For this Report to Congress, technologies used to address CSOs and SSOs have been grouped into five broad categories:
• Operation and maintenance practices
• Collection system controls
• Storage facilities
• Treatment technologies
• Low-impact development techniques
EPA, states, and municipalities have made progress in developing tools and strategies for reducing the frequency and volume of CSOs and SSOs.
Much remains to be done, however, to fully realize the objectives of the Clean Water Act and the CSO Control Policy. Municipalities have suggested that limited resources prevent them from acquiring and implementing technologies as quickly as they and regulatory agencies would prefer, EPA reported.
Municipal resources used to address CSOs and SSOs are documented in different ways. EPA's estimates of municipal CSO expenditures rely on requests for Clean Water State Revolving Loan Fund (CWSRF) loans and on documents submitted to EPA's CWNS, which include CSO LTCPs and other facility planning documents. In addition, EPA uses a cost curve methodology to estimate costs for communities with CSSs that do not submit documentation.
In communities served by SSSs, SSO control expenditures are generally a combination of general operation and maintenance (O&M) and capital expenditures.
In total, EPA documented expenditures of more than $6 billion on CSO control (through 2002) and at least $4 billion on SSO control (1998-2002). EPA's 2000 CWNS estimated that at least an additional $50.6 billion is required to capture no less than 85 percent of the CSO by volume, and an additional $88.8 billion is required to control SSOs over the next 20 years.
In its preparation of its report, EPA found that:
— Maintaining and improving the integrity of the nation's wastewater infrastructure will protect the high level of environmental quality and public health enjoyed in the United States.
— Proper O&M of the nation's sewers is integral to ensuring that wastewater is collected, transported, and treated at POTWs; and to reducing the volume and frequency of CSO and SSO discharges.
— Many existing structural and non-structural technologies are well suited for CSO and SSO control.
— Emerging technologies and innovative practices hold promise for even greater reductions in pollution.
— Municipal owners and operators of sewer systems and wastewater treatment facilities need to manage their assets effectively and implement new controls, where necessary, as this infrastructure continues to age.
— The impacts of CSOs and SSOs are a concern at the local watershed level.
CSOs and SSOs are two among many sources of pollutants that contribute to urban water quality problems. The watershed approach is central to water quality assessments and the identification of control strategies must include all sources of pollution affecting water quality. The presence of sewer systems in most developed watersheds nationwide underscores the importance of considering potential SSOs impacts on water quality. Similarly, the presence of CSOs in 32 states places them in many watersheds across the country.
EPA, states, and municipalities should strive toward better integration of wet weather programs with other NPDES, compliance assistance, and enforcement activities. Better integration of programs and activities at the watershed level will provide economies of scale with respect to monitoring and reporting, protecting water quality, and reducing the impacts of CSOs and SSOs.
— Improved monitoring and reporting programs would provide better data for decision-makers on CSO and SSO control.
Better tracking of environmental impacts and the incidence of waterborne disease would increase national understanding of the environmental and human health impacts associated with CSOs, SSOs, and other sources of pollution. Use of standardized reporting formats for information on the occurrence and control of CSOs and SSOs would enable EPA, states, and others to track pollutant loads and the performance of controls.
Recent EPA efforts such as WATERS (Watershed Assessment, Tracking, and Environmental Results) work to unite national water quality information that was previously available only from several independent and unconnected databases. EPA will continue to work to improve the information available. WW