2008 ACEC Minnesota Grand Award and National Finalist
Donohue & Associates, LHB Corporation, and the City of Chatfield, Minnesota, received a Grand Award in the 2008 ACEC Minnesota Engineering Excellence competition. The project, which was also a national finalist, saved the City nearly $5 million after Donohue/LHB reviewed their Facility Plan and recommended more cost effective improvements to meet permit limits.
The Facility Plan was prepared by another firm in 2003 in anticipation of new NPDES permit limits that would enforce ammonia, totals suspended solids, and phosphorus restrictions. The new permit set ammonia limits during warm weather; however, the Facility Plan recommended upgrades to achieve them year-round. Donohue/LHB recommended reducing the size of the oxidation ditches to allow for nitrification only during summer months. In addition, use of the three-ring oxidation ditch, as opposed to the Carousel-type ditch originally recommended, eliminates the need for primary clarifiers, freeing up space for a maintenance area and saving in operation and maintenance costs.