From November, 2003 through November, 2004, Cemstone’s St. Bonifacius, Minn. plant underwent major remodeling to improve both its operational and environmental practices. Because this site is located within the Minnehaha Creek Watershed District (half of its perimeter is surrounded by wetlands), Cemstone was especially committed to following positive environmental practices during construction.
The largest environmental concern at ready-mix facilities is generally how to handle both storm water and process water, which contains suspended solids with an elevated pH. Ideally, it is best to separate both so that no process water leaves the site. Originally, two ponds were located on the site for washing out trucks and collecting storm water. These ponds had to be constantly dredged out of solid materials to keep them from overflowing. The solution was to install a weir system that collects this process water and allows the solid particles to settle out for periodic dredging while the clearer water is pumped into a holding tank to be recycled. Approximately 2 million gallons of water is annually recycled and can be used to wash trucks as well as in the batching of concrete. Now only a small portion of the site is used to collect process water. Approximately three-quarters of the site could now be used to collect and transport only storm water. This water is conveyed through filtering ponds before discharging to the surrounding wetlands.
From the design of these ponds, Sunde Engineering and the Minnehaha Creek Watershed District were able to increase the phosphorus removal rate on site. This further improved the water quality of the site, as phosphorus plays a major factor in the eutrophication of lakes.