Improving Dissolved Pollutant Removal in Permeable Friction Courses
Many DOTs are being required to retrofit existing highways to comply with TMDLs to improve the quality of runoff discharged from highways. This retrofit is a particular challenge given the limited ROW available in urban areas. Recent research sponsored by Caltrans, TxDOT, and NCDOT has documented substantially better runoff water quality from highways paved with Permeable Friction Course (PFC) and Open Graded Friction Course (OGFC), with up to a 90% reduction of the solids discharged in runoff. By incorporating stormwater treatment within the pavement itself, a number of difficulties related to highway retrofit can be overcome. No additional ROW is required for installation. No special maintenance is needed for the pavement to reduce pollutants over its structural life and many states already have standard specifications for PFC (or OGFC) and use it widely without recognition of its environmental benefit. Consequently, PFC is the one truly highway specific BMP. The processes that improve the quality of runoff within PFC appear to be primarily sedimentation and filtration. These are processes that remove sediment and the associated pollutants. The problem with retrofitting highways with PFC to address many TMDL requirements is that the constituents of concern are frequently dissolved. The three most common causes of impairment are pathogens, metals, and nutrients, accounting for about 27,000 listings. All three of these are difficult to remove in conventional BMPs, and metals and nutrients have a substantial dissolved phase, which makes treatment even more difficult. Consequently, what is needed now is research on additives to PFC to improve its pollutant removal for these problem constituents. Researchers have already demonstrated that addition of granular activated carbon to PFC reduces the concentration of total organic carbon in runoff. We also know already that there are a number of candidate materials that successfully remove bacteria, nutrients, and dissolved metals. For instance, iron oxides have demonstrated substantial removal of both dissolved metals and dissolved phosphorus. There are also a variety of commercial antimicrobial coatings available. The general goal of this research is to begin an investigation into how PFC could be modified to improve the removal of bacteria, nutrients, and dissolved metals. The objectives include identifying candidate materials for testing, incorporating these materials into PFC cores, and then dosing the cores with simulated highway runoff to determine removal efficiency. Task 1 – Literature Review and Background The main goal of the literature review is to identify materials that reduce the concentrations of bacteria, nutrient, and dissolved metals in runoff. The review will include a comprehensive analysis of published reports in peer-reviewed technical journals to determine the materials previous research suggests can remove the targeted constituents in highway runoff. Examples of these materials include metal oxides (dissolved metals and phosphorus removal) and titanium dioxide (a catalyst for reducing bacteria as well as ozone concentrations). Task 2 – Laboratory Evaluation The laboratory evaluation will determine the effectiveness of the materials identified in Task 1 for pollutant reduction. The candidate materials will be added to the cores, which will then be dosed with synthetic stormwater runoff at rates comparable to those observed during typical rainfall events. Influent and effluent concentrations will be recorded to determine the pollutant removal effectiveness. The most promising materials will be identified for a future field testing program as described in Task 3. Task 3 – Future Research A research plan will be developed describing a field prototype testing program. The research plan shall be developed to thoroughly investigate how to incorporate additives to PFC as both a stormwater quantity control and a water quality control best management practice that will be developed for further implementation by DOTs.
The benefits resulting from this research include: • Provide treatment within the pavement itself for the primary causes of receiving water impairment • Improving the removal of dissolved constituents in stormwater runoff • Eliminating the need for large, conventional BMPs that require additional ROW
June 2, 2020
- items posted in the last 7 days (30 days for TERI)