Evaluation of Porous Pavements as a Watershed Chloride Source Reduction Strategy
Research Idea Scope
Porous pavements have been identified as a potential strategy for minimizing the use of deicing chemicals for winter maintenance. The use of porous pavements for parking lots is on the rise with the implementation of NPDES Phase II requirements. Chloride is an integral component of winter maintenance and safe usage of transportation surfaces. Anti-icing and deicing is routinely needed to control both ice development caused by the pooling and freezing of meltwater and the accumulation of compacted snow and ice not removed by standard winter plowing procedures. Chloride laden runoff from impervious surfaces threaten aquatic habitat and degrade drinking water supplies. As an example, transportation runoff has been identified in the northeast with chloride concentrations in excess of 5,000 mg/L over extended periods, greatly exceeding regulatory standards. Resultantly, state and federal environmental agencies have recently begun to regulate chloride usage through the implementation of Total Maximum Daily Loads (TMDLs) as part of permit conditions for highway infrastructure. Assessment of chloride loading sources for TMDLs have identified parking surfaces as the single largest source, in some instances contributing up to 50% of the total load. Watershed management entities including transportation agencies have been directed to reduce chloride usage within watersheds by as much as 40%. The difficulty is compounded in watersheds where chloride usage is expected to increase corresponding with population growth as TMDLs require loading reductions and do not provide for future growth. Future construction of additional roads, and parking lots in the TMDL watershed will therefore have to provide additional reductions.
No existing stormwater management technology is designed to reduce chloride, leaving source control or deicing substitutes as the only viable chloride best management practices. Deicing substitutes can often be cost prohibitive. Porous pavements have been identified as a potential strategy for minimizing the use of deicing chemicals for winter maintenance. Research indicates the potential for reduced salt application rates of up to 50-75% with equivalent performance for skid resistance and snow and ice cover as compared with traditional pavements. The reduction is substantial and within the range needed for TMDL compliance. It is important to note that these existing TMDLs do not provide for future growth and expansion of roads and parking. New growth such as the construction of park and rides, off ramps, and roadway widening, as well as reconstruction of public and private pavement surfaces will have to provide additional reductions not considered in the TMDL. For this reason, porous pavements present a real potential strategy for chloride reduction.
Urgency and Payoff
Products: Develop a study report providing recommendations for porous pavement selection, outlining winter recommended application rates specific to pavement type and condition, for road agents.
Changes: The cost benefits of the use of porous pavements may be substantial when compared with the usage of chloride substitutes and technology advancements for the efficient application of chloride. Porous pavements for new construction can be cost competitive with standard construction measures combined with advanced stormwater management. Additionally, a high level of winter performance for porous pavements with reduced maintenance demands can reduce costs associated with plowing and deicing applications.
Outcomes: Additional tools and guidance for DOT, Municipal, and Private entities for chloride TMDLs
Robert Roseen, PhD, PE, D.WRE, University of New Hampshire Stormwater Center