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It is a well-known fact that our nation’s infrastructure is in dire need of upgrading and our sewer systems are among the most needy. In particular, combined storm and sanitary sewer systems, most of which are in 772 of our nation’s oldest urban areas, can no longer handle the flow volumes of sewage and stormwater, resulting in overflows of untreated waste to waterways.
While it might seem that fewer than 1,000 communities is a small number, the truth is that combined sewer systems (CSSs) serve about 40 million people in the United States, since most are located in highly populated areas in the Northeast, the Great Lakes region, and the Pacific Northwest. As climate change causes more frequent and intense wet weather events, the need to find CSO solutions is fast becoming urgent.
To assist sewer authorities and municipalities, the EPA recently released a guidance document titled “Greening CS Plans: Planning and Modeling Green Infrastructure for Combined Sewer Overflow (CSO) Control.” But businesses large and small can also benefit from the document, which explains the fundamentals of green CSO infrastructure and the benefits of they offer in addition to controlling CSOs.
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According to the EPA, CSO controls are generally categorized as one of four different technologies:
- Operation and maintenance practices
- Collection system controls
-Conventional Approaches
-Green Infrastructure Approaches
-Retention
-Runoff Control - Storage facilities
- Treatment technologies
Most of these are traditional, capital-intensive controls with fairly high price tags, and they involve pipes, sewers, and other concrete and steel structures that do not necessarily compliment the natural hydrology of the area. Green infrastructure controls, however, are inherently designed to “mimic” the natural hydrology, can be implemented on a variety of scales, and cumulatively can have a substantial impact on combined sewer systems (CSSs) with much less investment.
Also unlike traditional controls are the added benefits green infrastructure offer, including on-site water reuse, flood mitigation, groundwater recharge via infiltration from natural and permeable surfaces, reduced urban heat island impacts, improved air and water quality, and in some cases increased recreational opportunities, improved wildlife habitat, and better biodiversity.
In late March, EPA Administrator Gina McCarthy and Assistant Secretary of the Army (Civil Works) Jo Ellen Darcy signed a proposed rule to “clarify” protections under the Clean Water Act for “streams and wetlands that form the foundation of the nation’s water resources.” Learn more..
When considering green infrastructure for CSO controls, the EPA has established nine minimum technology-based requirements:
1. Proper operation and regular maintenance programs for the sewer system and the CSOs
2. Maximum use of the collection system for storage
3. Review and modification of pretreatment requirements to assure CSO impacts are minimized
4. Maximization of flow to the publicly owned treatment works for treatment
5. Prohibition of CSOs during dry weather
6. Control of solid and floatable materials in CSOs
7. Pollution prevention
8. Public notification to ensure that the public receives adequate notification of CSO occurrences and CSO impacts
9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls
Most CSO communities are required to have Long Term Control Plans (LTCP) and must characterize the CSS and receiving waters and develop CSO control targets to meet water quality standards (WQSs). Control targets must be defined and adopted within the LTCP using either the demonstration or presumption approach that achieve Clean Water Act (CWA) compliance and a postconstruction compliance monitoring program must be implemented to adequately measure and evaluate the effectiveness of the controls, protect designated uses, and prove compliance.
When green infrastructure CSO controls are used, an adaptive management approach is also allowed during implementation, providing the opportunity to monitor and evaluate controls and practices as work takes place. This enables project plans and designs to be adapted and revised as lessons are learned, which the EPA says “can often be a more effective approach than adopting a monitoring program confined to the post-construction phase.”