Stormwater on the UW-Green Bay Campus

Campus Stormwater Conveyance System

Most of the rainfall or snowmelt that flows over UW-Green Bay campus land either flows down slope into a ditch, or into a storm drain inlet and then into a storm sewer. Some of the runoff then flows through detention ponds, but all of the runoff leaving the UW-Green Bay campus flows untreated into the nearby waters of the bay of Green Bay or Mahon Creek. It does not go to a treatment plant as sanitary sewers do. Here on campus, the stormwater conveyance system consists of: Vegetated Infiltration; storm sewers and detention ponds. Grassed swales drain most of the non-curbed roadways on campus and can be seen adjacent to these roadways, such as South Circle Drive. Grassed swales have the ability to treat stormwater and allow for infiltration, whereas the alternative storm sewer system does not. Storm sewers drain sections of campus where storm drain inlets are present as well as the curbed roadways and parking lots on campus. Four campus ponds serve as detention ponds: Upahki, Teal, the large golf course pond and the detention pond serving the Kress Events Center. Of these four, only the detention pond serving the Kress Events Center is an engineered detention pond. Detention ponds are depressions in the ground surface with a permanent pool of standing water. During rainfall events, stormwater runoff from storm sewers or grassed swales enters the detention pond where some of the sediment in the runoff settles out before it flows downstream.

Regulatory Background

Since the 1990’s, new rules adopted by the U.S. Environmental Protection Agency (EPA) and Wisconsin Department of Natural Resources (WDNR) now affect the way the university must deal with stormwater discharges. WDNR ch. NR 216 requires municipalities to obtain stormwater discharge permits. Since the university campus lies within the urbanized area of the city of Green Bay, there was originally some question as to whether the university would be covered by the City’s permit or would be required to obtain its own permit. Because the university owns and operates its own storm sewer system, UW-Green Bay, along with all the other four year UW campuses, was required to obtain its own stormwater discharge permit from the WDNR. The university obtained its permit on September 1, 2007 and is required to comply with all requirements set forth in its permit as well as all stormwater regulations set forth in chs. NR 216 and 151.

The permit specifies that the campus comply with the following permit requirements:

• Public education and outreach plan for UW – Green Bay
• Public involvement and participation plan (included in Public education and outreach plan for UW-Green Bay)
• Illicit discharge detection and elimination program for UW – Green Bay
• Construction site pollution control
• Post-construction storm water management
• Pollution prevention program for UW – Green Bay

To comply with the requirements of NR 151 and the permit, Earth Tech/AECOM completed an analysis of annual sediment and phosphorus loadings for all storm sewer outfalls on campus. Their analysis found that the UW-Green Bay campus as a whole has met this requirement by achieving a 40.02% reduction in sediment. This is primarily because the campus has several existing best management practices in place. These practices are: 1) rooftop, parking and sidewalk disconnection, 2) swale drainage, and 3) wet detention ponds. Disconnection refers to impervious surfaces, such as rooftops or parking lots, which drain directly onto pervious (vegetated) surfaces and allow for some stormwater infiltration before runoff enters the conveyance system. Conversely, directly connected source areas are those impervious surfaces that drain into a stormwater conveyance system (such as a storm sewer) without passing over pervious surfaces. In spite of the fact that the campus as a whole has achieved its sediment reduction load requirements, there are some areas of the campus that have little to no sediment reduction control. Earth Tech/AECOM found that a large area of western and central campus which drains into a single storm sewer that empties directly into the bay of Green Bay, achieves only a 0.1% reduction in TSS.