PUBLIC WORKS COMMISSION DATE: December 10, 2012 REPORT NO. PW2012-073 TO: FROM: CHAIR AND MEMBERS COMMITTEE OF THE WHOLE OPERATIONS AND ADMINISTRATION GEOFF RAE, MBA, P.ENG. GENERAL MANAGER, PUBLIC WORKS COMMISSION 1.0 TYPE OF REPORT CONSENT ITEM [ X ] ITEM FOR CONSIDERATION [ ] 2.0 TOPIC: Permeable Asphalt and Concrete Products for Future Parking Lot Resurfacing Projects 3.0 RECOMMENDATION A. THAT a requirement for permeable pavement or concrete systems NOT BE CONSIDERED as a primary means to improve parking lot site run-off to minimize dependence on existing storm sewer infrastructure, and; B. THAT staff CONTINUE to monitor advances in the design and development of permeable pavement and concrete pavers, and; C. THAT, where practical, staff PROPOSE site layouts and designs that utilize existing natural vegetation and landscaped islands as a means to encourage groundwater infiltration and minimize dependence on existing storm sewer infrastructure in municipal parking lots. D. THAT staff CONTINUE TO REVIEW AND EVALUATE the feasibility of using alternative surface technologies such as permeable surfaces on a project by project basis where practical and cost-effective. 4.0 PURPOSE To provide Council with a response to a Council Resolution requesting that City staff research alternate surface materials for parking lots that will reduce local temperatures, as well as allow greater rain water infiltration.
Date: December 10, 2012 Page 2 5.0 BACKGROUND At the City of Brantford Council Meeting on August 15, 2011 the following resolution was passed: Ground Solution Options WHEREAS weather patterns throughout North America are changing and the Province of Ontario has just experienced the warmest July temperatures on record and significant drought like conditions; and WHEREAS large paved areas have an impact on localized temperatures, as well as permeability; BE IT THEREFORE RESOLVED THAT City staff BE ASKED to research alternate surface materials for parking areas that will reduce local temperatures as well as allow greater rain water infiltration. 6.0 CORPORATE POLICY CONTEXT None 7.0 INPUT FROM OTHER SOURCES Staff consulted and obtained opinions from Halsall Associates and GD Vallee Consulting Engineers to verify estimated costs and feasibility of permeable asphalt and concrete technology. 8.0 ANALYSIS Conventional asphalt pavement is commonly composed of 5% asphalt cement and 95% aggregates (stone, sand and gravel). Traditionally, the air void content for asphalt suitable for vehicular traffic is in the range of 2% to 4%. Permeable asphalt and concrete typically have an air void content of 15%-25%. This permits water to penetrate down through the voids into the granular base, or drainage layer and wick away from the surface. A key component for shedding the water away when using permeable asphalt is the associated drainage system under the surface, comprised of filter fabrics, high performance bedding sand and a granular drainage layer with increased air content. Runoff water is captured within the granular material, gradually dissipating or infiltrating into the native soil. Capacity is determined on a case-by-case basis. There are several permeable pavement options, including porous asphalt, pervious concrete, and grass pavers. Porous asphalt and pervious concrete visually appear to be the same as traditional pavement from the surface, but are
Date: December 10, 2012 Page 3 manufactured without fine materials, and as stated, incorporate void spaces to allow water migration and infiltration. Pros and Cons of permeable pavement compared to traditional asphalt Permeable pavements seem to offer the greatest benefit to urban areas where existing stormwater management facilities are challenged to accommodate additional surface runoff. Municipal parking lots are the ideal location to install and evaluate the use of permeable pavement materials because for the most part, they re utilized by relatively light-weight vehicles. Pervious pavement is not recommended for high traffic areas because of the potential for clogging, nor is it recommended for stormwater hotspots which could generate contaminated runoff with a higher than usual concentration of pollutants. Areas of low soil permeability, seasonal high groundwater tables, and areas close to drinking water supply wells should also be avoided. Traditional asphalt and concrete pavements are non-porous (or impervious), rainwater cannot seep into them and instead runs off. As the water travels through and away from the surface, it may also collect oil, gasoline and other pollutants before it enters into neighboring streams and rivers. High volumes of runoff can also cause landscape erosion. In addition to the infiltration characteristics, permeable pavement does not tend to ice up as quickly in the winter as traditional pavements because melting snow and rainwater doesn t pool on its surface. In freezing temperatures, permeable pavements tend to be warmer due to the increased circulation of air within the pavement. While there are benefits to using this, some negative factors also exist. Since permeable surfaces require approximately 15-25% void content in the asphalt or concrete mix, these voids can easily become blocked with debris, road salts, sand and leaves, reducing the permeability of the pavement over time. It is generally recommended that parking lots be swept or vacuumed 2 to 4 times per year to clear the voids increasing the operating costs associated with the surface. Failure to conduct general maintenance significantly hinders the effectiveness of the material and reduces permeability. Over time the effective infiltration levels tend to have lower rates than newer installations. This reduces the life cycle of the asphalt / concrete as they lose their effectiveness. Once the surface fails, the only option for these surfaces is the complete replacement of the entire surface to restore the desired infiltration properties originally seen. In traditional systems, milling, shaving and patching can be completed to bring the surface back to standard. Based on staff research, case studies have indicated that permeable asphalt and concrete pavers were weaker during higher temperatures, which could render them more susceptible to damage from heavy loading. This would include
Date: December 10, 2012 Page 4 vehicles that frequently visit corporate facilities; Operation Lift, garbage disposal and vacuum trucks. Trends Whereas permeable pavements applications are more common in southern climates there does appear to be product and design improvements emerging and use in northern areas is increasing. Northern U.S. communities in New Hampshire and Minnesota are investigating permeable pavements in climates that are susceptible to freeze/thaw conditions and are seeing some success. The Ministry of Transportation of Ontario (MTO) has been evaluating permeable pavements at two installations, the first being a demonstration project at Guelph Line and Highway 401 and more recently on a parking lot in Brampton. According to the MTO, the material has its challenges and limitations and they have stated the importance of getting the right mix of materials to allow the rainwater to flow through. As part of its evaluation, the MTO is working with two universities. The University of Waterloo is analyzing different pervious concrete mixes, while the University of Guelph is conducting research that includes determining the correlation between the use of the concrete and water quality. City staff will continue to monitor the studies progress, product use and success rates through dialogue with consulting engineering firms, MTO, municipalities, contractors and trades. In the interim, staff currently designs and implements cost-effective infiltration alternatives on projects where practical utilizing natural drainage, grading, vegetation and landscaping to direct runoff to locations where natural infiltration into the subgrade occurs. Most recently these methods were effectively incorporated into the recent T.B. Costain parking lot renewal project. 9.0 FINANCIAL IMPLICATIONS Cost estimates for installing permeable pavements will vary depending on the specific material quantities, complexity of the site, and the time of year. The following costs are intended to provide a general guideline for budgetary purposes. The average cost to replace an asphalt parking lot with traditional and permeable surfaces is shown in the table below. The costs associated with using permeable surfaces range from 120% to over 200% higher than traditional asphalt.
Date: December 10, 2012 Page 5 Table 1 Cost Comparison Traditional versus Permeable Surfaces Traditional Asphalt Granular (400mm depth) from $19 - $24 per m2 Asphalt from $21- $49 per m2 Permeable Asphalt/Concrete Drainage Layer (600mm Depth) from $40 - $53 per m2 Permeable Asphalt/Concrete from $50 - $110 per m2 Total cost from $40 - $73 per m2 Total cost from $90 - $163 per m2 Permeable asphalt/concrete tends to be the most practical in applications where cost avoidance is achieved by not requiring the installation or replacement of a traditional buried stormwater management system. The effectiveness or capacity of utilizing natural drainage is determined on a case-by-case basis. 10.0 CONCLUSION Staff is aware that the Ministry of Transportation of Ontario (MTO) has been evaluating permeable pavements with a limited number of demonstration projects and is evaluating the effectiveness of permeable pavement through research with the University of Guelph and the University of Waterloo. With limited actual demonstration applications within our environment, staff proposes to monitor the development of permeable pavement products, application and trends within the local and regional industry utilizing the knowledge of qualified consultants and the experience of material suppliers and paving contractors. Staff recommends the feasibility of mandating permeable materials as an alternative or replacement product for future parking lot construction or reconstruction be deferred until more conclusive results are provided on current demonstration projects. Geoff Linschoten, CET Director, Facilities & Asset Management Geoff Rae, MBA, P.Eng., General Manager, Public Works Commission Jim Quin Manager, Facilities Management In adopting this report, is a by-law or agreement required? If so, it should be referenced in the recommendation section. By-law required [ ] yes [ X ] no Agreement(s) or other documents to be signed by Mayor and/or City Clerk [ ] yes [ X ] no Is the necessary by-law or agreement being sent concurrently to Council? [ ] yes [ X ] no