[Mpls] CSO's & Rooftop Gardens

[Corrie Zoll]

I was excited to see this morning's Strib article about Minneapolis's Combined Sewer Overflow (CSO) problem (http://www.startribune.com/stories/462/1405414.html)  It's not the raw sewage pouring into the river that's exciting, but the idea that, this time, the problem might get fixed.   I sat in on a city council meeting last fall at which the 2002 Public Works budget was discussed.  CSOs and the separation of the city's storm and sanitary sewers were major discussion topics.  Evidently 2001 saw 6-8 CSO events during which the city's combined sewer system overflowed, dumping raw sewage into the river.   Minneapolis was progressive in separating its storm and sanitary sewer systems before most other cities.  Although this was a good move for Minneapolis, eventually two negative impacts developed: 1) Minneapolis paid for most of its own sewer separation while other cities did so with state requirements and assistance; and 2) Minneapolis did not separate its sewer systems as thoroughly as other cities did at a later time.   As the Strib article notes, one of the big problem is rooftop drains.  These drains often connect to a building's plumbing system and drain along with toilets and sinks into the city's sanitary sewer system.  Correcting the problem would involve major re-plumbing of large downtown buildings.   What the Strib article did not mention was that these buildings may not be adjacent to existing storm sewer lines.  And even if they are, the existing storm sewer lines may not be able to handle the increased volume that would come with storm water from rooftop drains.  New sewer lines will be needed and existing sewer lines will need replacement.  That's what makes correcting the problem such a massive infrastructure project.   I'd like the city to investigate whether rooftop gardens are a cost effective method for retaining rooftop stormwater.  Green rooftops can hold 70 - 100% of the stormwater that falls on them.  In addition, rooftop gardens increase building insulation, increase the lifespan of roofing materials, add green space, reduce the urban heat island, clean up urban air, and provide public recreation and even food.   Chicago's city hall has a new 20,000 square foot rooftop garden.  Studies will compare  this rooftop with the asphalt rooftop of an adjacent building to quantify the costs and benefits.   Green rooftops might entirely solve the CSO problem in Minneapolis by retaining and cleaning thousands of gallons of storm water on the rooftops where it falls.  At a minimum, green rooftops can be a significant part of the city's storm water management plan.   Corrie Zoll Phillips Neighborhood