Commerce Square Stormwater Pond Improvements

Construction Update:

The project is currently under construction. Please check back for further updates.


The area surrounding Williston Road in South Burlington was developed prior to management regulations requiring the treatment of stormwater runoff. As a result, the stormwater generated by the homes, businesses and roads in this area are collected by a closed pipe drainage system and discharged untreated to Potash Brook.


Williston Road and the surrounding development currently discharges directly to tributary 3 of Potash Brook. Stormwater from this area was collected in a closed pipe drainage system that emptied into Potash Brook at the end of Midas Drive, behind the Commerce Square commercial development.

Existing Commerce Square Detention Pond

The Commerce Square development had a separate stormwater drainage system that directed stormwater runoff generated on site to a small detention pond located at the back of the property. This detention pond was originally designed to reduce the risk of downstream flooding during large rain events, but was not designed to provide treatment of stormwater runoff during smaller, more frequent, rain events. The discharge pipe for this existing detention pond was within 50-feet of the pipe that discharged the stormwater runoff collected by the Williston Road drainage system.

The City worked with the private property owner at Commerce Square to design a new stormwater treatment system in place of the existing detention pond. This new system would combine the stormwater runoff collected from Williston Road and with that of Commerce Square. This combined runoff will be directed to an expanded detention pond where it will receive treatment. The new system includes a hydrodynamic swirl separator designed to remove sediment and other pollutants from the collected stormwater runoff during smaller rain events.


The reconstructed stormwater detention pond behind Commerce Square will now provide stormwater treatment for runoff associated with approximately 95.7 acres of developed land. This includes nearly 42 acres of impervious area. The overall reduction in sediment discharged to Potash Brook is expected to be nearly 19,000 pounds per year. In addition, the detention pond will reduce the rate at which stormwater is discharged to the stream. Modeling indicates that stormwater is currently discharged to Potash Brook at a rate of 17.5 cubic-feet per second during the 1-year, 24-hour storm event. Once the stormwater detention pond is reconstructed this discharge rate will be reduced to 1.3 cubic-feet per second.

Best Management Practices

Stormwater detention pond, stormwater pipe replacement, hydrodynamic swirl separator.


Reconstruction of the stormwater detention pond behind the Commerce Square development is scheduled to occur during the summer of 2017.

Total Project Value

Construction cost estimates for this are between $240,000 to $300,000.

Funding Sources

The South Burlington Stormwater Utility, Pomerleau Real Estate, and the Vermont Department of Environmental Conservation’s Ecosystem Restoration Program (ERP). The City also worked with the Lake Champlain Watershed Environmental Assistance Program managed by the U.S. Army Corp of Engineers during the design phase of the project.


Last Updated: 4/4/2017