Highway-runoff quality from segments of open-graded friction course and dense-graded hot-mix asphalt pavement on Interstate 95, Massachusetts, 2018–21

Highway runoff is a source of sediment and associated constituents to downstream waterbodies that can be managed with the use of stormwater-control measures that reduce sediment loads. The use of open-graded friction course (OGFC) pavement has been identified as a method to reduce loads from highway runoff because it retains sediment in pavement voids; however, few datasets are available in New England to characterize runoff quality from OGFC pavement. To meet this data need, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Transportation, conducted a field study from October 2018 through September 2021 to monitor runoff from a section of traditional dense-graded hot-mix asphalt (HMA) and from a section of OGFC pavement on Interstate 95 near Needham, Massachusetts. A robust dataset that includes suspended sediment concentrations for nearly every runoff event during the study period was generated to compare runoff from the two 4,180-square-foot sections of highway pavement under identical traffic volume and maintenance characteristics.

Automatic-monitoring techniques were used to collect over 6,500 samples at each station to characterize all runoff-generating events during the study period (226 events for the HMA site and 168 events for the OGFC site). Suspended sediment concentrations were consistently lower in runoff from the OGFC pavement throughout the study period, with median event-mean concentrations for all runoff events of 29 and 15 milligrams per liter for the HMA and OGFC sites, respectively. The total load of sediment less than 6.0 millimeters in diameter from the HMA section (202 kilograms [kg]) was 41 percent greater than the load measured from the OGFC pavement (120 kg), and the total load of sediment less than 2.0 mm in diameter was 49 percent greater (168 kg and 85 kg from the HMA and OGFC sites, respectively). The greatest differences in loads between the two pavement segments were in the particle-size ranges less than 2.0 millimeters in diameter, indicating that these particles are retained by the voids in the OGFC pavement. The relative difference between annual sediment-load estimates at each site over the study period indicates that OGFC pavement became clogged, a condition that permeameter test results also reflected. Specifically, the average total load of sediment for the first 2 years of the study was 68 percent lower at the OGFC site than the HMA site, but the difference between the respective loads decreased to 19 percent in the third year of the study.

Study-period loads for most total-recoverable metals in runoff from each pavement type were between 7 and 64 percent higher from the HMA site, except for loads of arsenic, cadmium, and zinc, which were higher from the OGFC pavement. Study-period loads for total phosphorus were similar from each pavement type. Despite the same application rate of deicing chemicals, sodium and chloride loads in runoff were about two times greater from the OGFC section than from the HMA pavement during years with average snowfall amounts but were approximately equal at both sites during the mild winter in 2020.