At a Glance
Updated stormwater management regulations required the City of Woodbury to improve runoff treatment across impervious surfaces. The city used recycled tires, repurposing 3 years’ worth of discarded tires, reducing cost, mitigating flooding and providing a sustainable solution to limited available green space.
With a rapidly developing and growing city such as Woodbury, it can be a challenge to meet the stormwater criteria due to various site constraints for both new construction and redevelopment projects. Redevelopment projects within a fully-developed site often present challenges when implementing new surface Best Management Practices due to limited available green space. Treating a site with minimal green space calls for new and innovative thinking to ensure stormwater is adequately managed on-site. The City of Woodbury is no stranger to innovation when it comes to implementing sustainable amenities within city facilities.
Due to site constraints, surface treatment was very limited. Therefore, the city looked toward subsurface features to collect, manage, and treat site-generated runoff.
The complexity of this project required a highly collective effort between HCM Architects, Bolton & Menk, Inc., and the City of Woodbury to synchronize the project’s various components to ensure complete cohesion. HCM Architects focused on approximately 97,000 square feet of building design while Bolton & Menk focused on civil site elements, including stormwater management, to help manage and treat a total of 10 acres of impervious surfaces on site.
Due to the significant extent of the project’s new and redeveloped impervious areas, several BMPs were integrated throughout the site in order to meet South Washington Watershed District (SWWD) and Ramsey Washington Metro Watershed District (RWMWD) stormwater management requirements. These BMPs include
• Infiltration basins
• Wet sedimentation basins for pretreatment
• Hydrodynamic separator
• Porous asphalt areas within facility parking lots with a Tire Derived Aggregate (TDA) subbase section
The City of Woodbury used/is using recycled tires to address this/these challenge(s).
Tire Derived Aggregate, also known simply as TDA, are recycled tires manufactured through a shredding process and re-purposed for a variety of “green” construction applications. Lightweight fill such as TDA is often used for road construction in instances where unsuitable soil are present, limiting the use of conventional aggregate. Generally, TDA is a fraction of the weight of many soils, is highly permeable which promotes a free drainage layer, insulates eight times better than gravel, and costs less than most sands and gravels, making it an obvious choice for road construction and reconstruction projects.
In total, the Public Works and Parks Maintenance Renovation and Expansion Project used approximately 210,000 tires within the underground infiltration system that would otherwise be stockpiled on the surface, repurposing approximately 3 years’ worth of discarded tires from the City of Woodbury alone. The city used their overabundance of tires as a usable resource for this stormwater application, making it better for the community and keeping environmental sustainability moving forward. In addition, there is a budgetary benefit to using TDA as opposed to traditional stone aggregate—TDA is significantly cheaper.
Integrating porous pavement into this project is also beneficial from a stormwater management aspect, allowing runoff to drain freely into the pavement, and into the TDA sections below the parking lot; similar to the way grassed areas infiltrate and soak up runoff from adjacent areas when it rains. By doing this, the features reduce the amount of runoff that is generated on-site, which helps mitigate flooding and transportation of pollutants (dirt, oil, gas, etc.) and also helps route stormwater into the TDA infiltration sections. The City of Woodbury recognizes the increased maintenance aspect that comes with integrating porous pavement throughout its facilities and is willing to make that sacrifice to improve water quality throughout the city.
Including TDA and porous pavement in a project of this magnitude does not come without public works consideration. For example, traditional snow removal and management practices, such as sanding, salting, and plowing, are detrimental to porous pavement sections, as sand particles will plug up the pavement voids, salt will potentially contaminate groundwater, and plowing damages the surface of these sections. Therefore, highly detailed, comprehensive operation and maintenance plans have been developed to ensure the longevity of these systems.
- The City of Woodbury was able to meet stormwater requirements while repurposing 3 years' worth of the city's discarded tires.
- A highly collaborative approach between an architecture firm, civil engineering firm and the City of Woodbury was essential in treating 10 acres of impervious surfaces.
- Recycled tires were used to replace traditional stone aggregate, and offered many benefits. It weighs less, is highly permeable, insulates better, and costs less than most sand and gravel.
- Integrating porous pavement reduced the amount of runoff, helping to mitigate flooding, transportation of pollutants and route stormwater into underground infiltration sections.
- This project highlights the importance of sustainable BMPs for a city's longevity.
- Sustainable solutions to stormwater management don't have to be expensive.
- Sub-surface improvements are a good option when trying to improve fully-developed sites with limited greenspace or room for expansion.
- Traditional snow removal and management practices can be detrimental to porous pavement. Using porous pavement in a large-scale project must include significant public works consideration.
- Integrating porous pavement increases a city’s maintenance aspect. However, the long-term sustainability and improvement of water quality is worth the investment.
Since 1988, TDA had been used for roadway bedding, embankment support, backfill material for septic systems, and more due to its insulation, load distribution, and low-density characteristics. It wasn't until recently that TDA was first considered for stormwater management, taking advantage of the aggregate's 50% void for maximized water retention, interlocking characteristics for better load distribution, and cost savings of nearly 40% over traditional methods.
Who Should Consider?
Cities looking to provide a sustainable and cost-saving solution to their stormwater management improvements without needing to expand or maximize on green space. Extra tires are a plus.