Monday, December 29, 2014

Cost/Benefit Analysis of CSO Control Utilizing Green Infrastructure

The overflow of sewers that transport both stormwater and human waste is the bane of municipalities throughout the United States and elsewhere in the world. Traditional methods (so-called grey infrastructure) of controlling combined sewer overflows, such as huge containment tunnels, are extremely expensive.  

In recent years, municipalities, state agencies and the U.S. Environmental Protection Agency (EPA) have been studying and implementing green infrastructure (GI), sometimes referred to as low impact development (LID), as an alternative means of controlling sewer overflows.

An August 2013 study by EPA identifies instances of economic benefit derived from such alternative means, as well as methods of evaluating those benefits.

“The case studies were selected to represent a variety of analysis methods in different geographic areas of the United States, for different types of municipal programs. The case studies highlight locations where LID/GI applications, in combination with grey infrastructure, were found to be economically beneficial...”

“...Those entities that have begun to analyze their green infrastructure programs and practices
in order to ascertain the cost effectiveness of green infrastructure in comparison to 
grey infrastructure or hybrid systems have used different types of economic analyses, depending upon their objectives, resources, or other considerations.”

For example, the Philadelphia Water Department refers to its study “ ‘triple-bottom-line’ (TBL) analysis, a term that has become recognized in municipal asset management to emphasize the financial-social-environmental aspects of a complete benefit-cost analysis, rather than only the financial.”

This is a long, comprehensive document.  With the appendix, it runs well over one hundred pages. Nevertheless, political leaders in southeast Michigan and appointees to the new Great Lakes Water Authority would be well advised to study it closely.

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