A Key Aspect of the Wet Weather Strategy
To achieve the required improvements, MSD’s Wet Weather Strategy focuses on storage and conveyance, treatment, and source control. The fi rst two approaches represent a more traditional approach to wet weather improvements, which entails collecting, conveying, and treating combined rainwater and sewage. The third approach—source control—is more strategic. It involves diverting rainwater from the sewer system, thereby eliminating the need to convey and treat essentially “clean” water.
Source control techniques use natural systems (such as forests, fields, ponds, and streams), or simulations of natural systems (such as green roofs, porous pavement, bioswales, and raingardens). These systems are designed to detain or drain stormwater into the soil or allow it to evaporate into the atmosphere. Sometimes, this type of infrastructure is called “green” or “sustainable” because it mimics the processes that nature uses to soak up rain.
The illustration above (click image for larger view) shows a variety of source control techniques being evaluated. Source control is the greatest leverage point for solving the CSO problem as required by the Consent Decree, because clean rainwater entering the sewer system is the primary cause of CSOs. If these types of solutions are installed at many locations within a watershed, they could radically reduce the amount of stormwater entering the sewer system during a rainstorm.
Aside from reducing CSOs, source control offers many other environmental and social benefits. When rainwater is removed, it frees up capacity in the sewer system for sanitary sewage flow and vastly reduces the number of overflows into local streams. This reduces the public health threat caused by the pollutants in the CSOs, improves water quality for recreation and aquatic life, and eliminates offensive odors and unsightly debris. It also lowers the operation and maintenance costs at wastewater treatment facilities. MSD’s program to support and investigate source control options follows three avenues, with the purpose of substantiating the technical, economic, social, and environmental costs and benefits of these techniques.
- Direct Implementation – Through Project Groundwork, MSD has begun the planning,
design, and implementation of sustainable CSO reduction projects. These projects are
funded and staffed by MSD. - Enabled Implementation – MSD has assisted project partners to construct
demonstration and early success projects. - Inform and Influence – MSD encourages other organizations to research and deploy
source control installations, by providing information and education.
MSD selected projects to demonstrate early successes and measure real impacts in terms of source control. The project examples (see Sustainable Infrastructure Table of Contents along right side of this page) feature the kind of sustainable solutions, community partnerships, and results that MSD is striving to achieve.