Stormwater Library
resources for stormwater professionalsCSO Tunnel Projects in United States
Across the country, large underground tunnels are commonly used to prevent combined sewer overflows. Some of the larger projects have been taken on in Chicago, Atlanta, Milwaukee, Austin, Boston, Cleveland, Houston, Detroit, Los Angeles, New York, Minneapolis, and San Francisco. A typical tunnel project ranges from 7 feet to 33 feet in diameter and from 2 miles to 33 miles in length. The Chicago Tunnel and Reservoir Plan (TARP) is considered the most successful application of this technology. It covers 109 miles and typical tunnel diameters reach 33 feet. Since 1984, when the first TARP tunnels were built, the number of fish species in the Calumet and Chicago River systems have nearly doubled from 33 to 63.
What needs to be put into perspective here is the cost. Combined sewer systems are an infrastructural relic – many dating back to the beginning part of the last century. The amount of new infrastructure to deal with this problem, while successful in reducing CSO discharges to our nation’s surface waters, is astronomical in size and cost. Take a smaller project like that in the City of Milwaukee. Over 2 billion dollars was spent on developing those CSO tunnels – more than half of that money was from federal grants. Another thing to consider is this, while the systems are typically able to successfully store and treat the overflows, the massive amounts of energy to make this happen begs quantification.
Is a massive concrete hole in the ground the answer? It is working, but is it the answer?
Compost-based BMPs – EPA Presentation
One of the better presentations that I have come across on the use of compost in stormwater BMPs was done by Chris Newman of the U.S. EPA. Mr. Newman provides some background into the EPA’s initiative to promote compost-based BMPs and points audience to its fact sheets database.
The presentation is a very nice primer on the benefits, effectiveness, and limitations of using compost blankets, compost filter socks, and compost filter berms. He also goes into some detail about the quality standards and certification required for the use of compost products.
Some of the key benefits highlighted in the presentation include:
- ability to prevent rill erosion
- runoff volume reduction
- promoting establishment of vegetation
- improving water quality through adsorption of nutrients and pollutants
A brief survey of some of the companies out there installing compost-based BMPs illustrated how creative designers can be with the products. Of particular note is the use of compost filter socks, traditionally used in the same manner as straw wattles, in the creation of permanent stream banks, or even as an alternative to rip-rap.
Stormwater Factoid: Combined Sewer Systems
There are approximately 770 combined sewer systems serving 40 million people in the United States. Most are concentrated in the Northeast, Great Lakes, and Pacific Northwest.
Source: U.S. EPA
