TCF Bank Stadium

The stormwater system under the half-acre landscaped plaza beside TCF Bank Stadium, the University of Minnesota's 50,000-seat stadium. It opened in 2009 as the first college or professional football stadium to earn LEED New Construction Silver from the U.S. Green Building Council.

Space was tight on the built-up East Bank campus. The usual answer would have been a stormwater holding pond, which takes up land and does nothing else. The green space that was left also has to carry broadcast trucks, emergency vehicles, maintenance vehicles and staging on game days. The water leaving it drains to the Mississippi River.

RESI dug a flat, laser-levelled basin with sides rising at 3:1 and 4:1. About 100,000 sq ft of 45-mil Firestone EPDM went down in 20 ft by 100 ft panels, overlapped by 6 in, primed and sealed with QuickSeam tape. A four-person crew laid it in about five days. On the liner sit 589 EPIC chambers, one per 40 sq ft, then fine aggregate, the sand profile and sod. ReFlex polypropylene mesh is mixed into the top 8 in of soil to carry vehicles and resist rutting.

The system is unpressurised and runs by gravity, draining, treating and irrigating at the same time, so no holding pond is needed. Its 0.54 acre footprint is one seventh of the 3.75 acre area it drains. Published capacities are more than 60,000 gallons below ground, equal to a 0.50 in rainfall, and more than 72,000 gallons above ground. The published removal capability, given by Dave Muellner of RESI in Storm Water Solutions (July/August 2010), is more than 85% of phosphorus, 90% of total suspended solids and 60% of nitrates.