July2008:ES&E
7/15/08
5:13 PM
Page 35
Wastewater ations and maintenance cost savings vis-Ă -vis mechanical treatment systems, especially for systems that have to operate over long periods of time. Engineered wetland systems, through their complex assemblages of plants and natural bacteria, can provide a robust treatment system for both domestic wastewater and recalcitrant, difficult-todegrade synthetic compounds. Often, these two effective treatment approaches are used together in community system or cluster applications. The cluster wastewater system approach, employing engineered wetlands designed with subsurface chambers, is a viable alternative that allows for the preservation of community open space. These systems allow communities and developers to meet treatment requirements and economic goals. Cluster wastewater systems can easily be integrated into the landscape to preserve open space viewsheds. Community system To preserve open space and to protect the rural character of the community, Lake Elmo, Minnesota, refused to connect to the regional sewer. This conflicted with growth plans created by the regional planning agency, the Metropolitan Council, and a legal battle ensued that went all the way to the State of Minnesota Supreme Court. As a result, Lake Elmo was forced to accept regional sewer along the Interstate 94 corridor and limited use elsewhere. The remaining areas of the community, however, were able to retain their current wastewater systems. In 1995, a local developer, Robert Engstrom, proposed a development near the “Old Villageâ€?, the central area of Lake Elmo. His plan, called The Fields of St. Croix, was to mirror the Old Village with large tracts of open space surrounding a cluster of homes to be served by a decentralized water and sewer system. No ordinances were in existence to accommodate such a request and wastewater treatment was a concern. After months of work with the City and State, the development was able to proceed with the first state-permitted subsurface flow engineered wetland in Minnesota. This was the beginning of open space developments using decentralized wastewater technology within the community of Lake Elmo. There are now eight cluswww.esemag.com
ter treatment systems in the area, treating a combined flow in excess of 118,000 gallons per day. These systems employ both horizontal subsurface flow and vertical subsurface flow engineered wetland wastewater treatment systems. Subsurface infiltration chambers are used for treated wastewater disposal using infiltration beds and trenches. The chambers are engineered to increase the surface area available for infiltration of treated wastewater to the subsurface.
Performance testing and predictive tools increase in importance Testing infiltration chambers in the field is integral to obtaining accurate results regarding chamber performance characteristics. This in situ testing allows real-world conditions to be replicated including such factors as the impact of the weight of the soil on different infiltration chamber products. A 2004 field study by the Clemson continued overleaf...
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