This spring, the MPCA found seven potential violations, which may prompt thousands in fines.
The University of Minnesota may face tens of thousands of dollars in fines after dirty water from the Gopher stadium construction site was dumped into the Mississippi River earlier this year.
The Minnesota Pollution Control Agency inspected the construction site in April and issued an "enforcement letter of warning" that identified seven potential environmental violations, including a "sediment plume with a chemical odor" observed in the Mississippi River on May 3.
Other potential violations included dirt in the streets near the construction site and inadequate filters to stop water containing silt and possible contaminants from going into the stormwater system.
University officials said that the problems associated with the laying of a sewer line were corrected immediately and that they have heard nothing from state pollution control officials for months.
"Based on everything our consultant showed us and testing of discharge water that was done, I do not believe there was any problem with what was going into the river," said Brian Swanson, University of Minnesota stadium project coordinator.
State pollution control officials would not comment on the severity of the river pollution or their investigation.
"All I can say about this case is that there's pending civil legal action and that's why the case is not public," said Katie Koelfgen, MPCA compliance coordinator for the construction stormwater program.
The location of the $288 million, 50,000-seat open-air stadium is northeast of Mariucci and Williams arenas on the Minneapolis campus, in an area now filled mostly by parking lots. It is scheduled to open in September 2009.
Swanson said the water was pumped into the Mississippi as part of the installation of a major new sewer pipe at the site by the Metropolitan Council's division of environmental services.
Excavation for the pipe was below the water table, which meant that groundwater needed to be pumped out.
The university's construction stormwater permit requires that any water pumped from the site must be filtered to capture sediment and contaminants before they enter street drains.
Those drains also collect rainwater and other runoff and route all of the stormwater into the Mississippi River.
MPCA's Koelfgen said that stormwater construction permits are required to prevent dirt and possible contaminants such as oil from being flushed into lakes or rivers, and that contractors are typically required to cover piles of excavated dirt to prevent erosion and install filter fences, sediment traps or sediment ponds.
Failure to do so has resulted in fines that have varied from $5,000 to "tens of thousands of dollars," Koelfgen said, depending upon the number and severity of alleged violations, size of the project and impact of the pollution.
The university's general contractor, Thomas & Sons Construction Inc., apparently did not have all of those devices in place when the MPCA inspected the site on April 26.
A May 10 letter from the agency identified the seven alleged violations and said the university should immediately stop discharging groundwater to the storm sewer because of pollution observed in the Mississippi River.
Swanson said that rather than dispute whether the university was the source of the problem, he complied with the state's request and told contractors to pump discharge water to the sanitary sewer system where it could be treated.
That ended on July 20, he said, when the sewer pipe installation was finished.