Video

Pervious Asphalt Water Application

East Bioretention Area

Project Photo Gallery

The purpose of this project was to reduce hydromodification and water quality impacts from polluted runoff by reducing impervious surface coverage and treating runoff using bioretention. This project entailed the construction of two bioretention areas, on pervious paver patio and pervious concrete.

The project is located on the Reservation lands of the Shakopee Mdewakanton Sioux Community (SMSC). The SMSC is located in Scott County, approximately 25 miles southwest of Minneapolis, MN. The major watershed, as identified by the United States Geological Survey, is located in Hydrologic Unit Code 07020012.

The watershed for this site is approximately 2.6 acres. Prior to the project the entire site was comprised of impervious asphalt and metal rooftops. Asphalt, concrete, brick, stone and metals seal surfaces, repel water and prevent precipitation and melt water from infiltrating soils. Research studies have shown that water quality decreases when the amount of impervious surface increases. This is due to the increased runoff and the high levels of pollutants associated with impervious surface. The effect is an alteration of the plant and wildlife communities and a general decrease in biodiversity.

Before this project the rooftops, asphalt and sidewalks drained to Wetland C-1L without treatment. Water sampling by the SMSC Land and Natural Resources Department found impacts from excessive runoff, oil and grease and elevated levels of deicing salts and metals from automobiles.

This project removed 1.7 acres of impervious surface and replaced it with features to improve water quality and allow the water to enter the wetland at a slower rate. The project goals were:

1. Improve runoff water quality
2. Reduce hydromodification
3. Improve awareness of alternative runoff treatment methodologies.

In order to accomplish these goals impervious asphalt was removed and replaced with two bioretention areas, a pervious asphalt section and a pervious paver patio. Since only a portion of the lot (17,000 ft2) was replaced with pervious asphalt a bioretention areas was constructed to treat a large portion of the remaining area. Additionally, a bioretention area was constructed to treat roof runoff and a pervious paver patio was built to handle overland runoff from the new landscaped areas.

Modeling completed prior to the project showed that runoff will decrease and water quality will be improved. Research indicates that little if any deicing other than plowing is needed for pervious pavement, so a reduction in chlorides should also be realized.

Project Issues
The primary issue with building a pervious area is preventing potential contaminant from entering the drainage layer or the pervious asphalt. This is especially problematic during construction but can also be an issue post-construction.

During Construction
This problem was solved by working closely with the engineers and maintaining constant communication with the contractor. Two preconstruction meetings were held; one with the engineers and one with the contractor and engineers. It was conveyed that soil or mulch was not to be carried over the pervious asphalt and the bioretention areas needed to be protected from silt. This was a difficult proposition because the pervious asphalt surrounded the landscaped areas and the order of operations was usually to complete the landscaping last. After some discussion it was determined that the contractor would work with the Land Department staff to construct from the building outward. While this did provide some inconveniences this did accomplish the goal of keeping the pervious section free from contaminants.

Post Construction
To minimize the contaminants entering the pervious asphalt drainage to the lot from external sources was minimized. This was done by capturing most of the runoff before it enters pervious asphalt. Most of the site drains to a pervious paver patio or a bioretention area. The entire site, with the exception of asphalt was planted and covered with mulch or seeded with buffalo grass and covered with erosion control blanket. All open soil was covered and any other project debris was removed from the site.

Collaborators
Shakopee Mdewakanton Sioux Community
United States Environmental Protection Agency

Contractor | Hentges, Inc.

Subcontractors | Black Diamond Landscaping, Keller Fencing, Choice Electrical

Videos
Articulated Concrete and East Side Bioretention
Installation and Rolling of Pervious Asphalt
Landscaping and Pervious Patio
Pervious Asphalt Water Application
Roof Runoff Treatment Using Bioretention

Links to Low Impact Development Sites
http://www.lowimpactdevelopment.org/
http://www.epa.gov/nps/lid/
http://www.lid-stormwater.net/background.htm
http://www.duluthstreams.org/stormwater/toolkit/paving.html