Permeable Asphalt: A New Tool to Reduce Road Salt Contamination of Groundwater in Urban Areas

Abstract

Chloride contamination of groundwater in urban areas due to deicing is a well-documented phenomenon in northern climates. The objective of this study was to evaluate the effects of permeable pavement on degraded urban groundwater. Although low impact development practices have been shown to improve stormwater quality, no infiltration practice has been found to prevent road salt chlorides from entering groundwater. The few studies that have investigated chlorides in permeable asphalt have involved sampling directly beneath the asphalt; no research has looked more broadly at surrounding groundwater conditions. Monitoring wells were installed upgradient and downgradient of an 860 m permeable asphalt parking lot at the University of Connecticut (Storrs, Connecticut). Water level and specific conductance were measured continuously, and biweekly samples were analyzed for chloride. Samples were also analyzed for sodium (Na), calcium (Ca), and magnesium (Mg). Analysis of variance analysis indicated a significantly (p < 0.001) lower geometric mean Cl concentration downgradient (303.7 mg/L) as compared to upgradient (1280 mg/L). Concentrations of all alkali metals increased upgradient and downgradient during the winter months as compared to nonwinter months, indicating that cation exchange likely occurred. Despite the frequent high peaks of chloride in the winter months as well as the increases in alkali metals observed, monitoring revealed lower Cl concentrations downgradient than upgradient for the majority of the year. These results suggest that the use of permeable asphalt in impacted urban environments with high ambient chloride concentrations can be beneficial to shallow groundwater quality, although these results may not be generalizable to areas with low ambient chloride concentrations.

Impacts of Road Salting on Water Quality in Fractured Crystalline Bedrock

“…A 300-mg L −1 chloride standard was run after every 10th sample and after the last sample to verify the calibration curve. Measurements from this study, combined with samples from Dietz et al (2016), established the following relationship (r 2 = 0.97):…”

“…The persistence in chloride residing in the glacial till overburden (Cassanelli, 2011; Dietz et al, 2016) and in the bedrock indicate that resulting chloride concentrations in the wellbore may be influenced by chloride stored in both the overburden and bedrock aquifers, with contributions from each varying seasonally. Figure 4 shows a conceptual model with three flow paths that may contribute water to the wellbore.…”

“…5a). Throughout the spring, as water levels increase, chloride concentrations in the saturated zone in the overburden become diluted (Cassanelli, 2011; Dietz et al, 2016) (flow path B in Fig. 4).…”

“…1) undergo salting for deicing. Investigations in the glacial till overburden (Cassanelli, 2011) and below nearby permeable pavement (Dietz et al, 2016) have demonstrated that salt application on campus results in increased chloride concentrations that persist beyond the winter months. The purpose of this study was to investigate the impacts of road salting in the fractured crystalline bedrock from 2003 to 2016, with consideration for persistent concentrations in the overburden, and with particular emphasis on impacts associated with the change in deicing practices at the university.…”

“…On average, the university receives 76.7 cm (30.2 inches) of snow between November and April (National Climatic Data Center, 2011). Dietz et al (2016) estimated salt applications of 0.077 kg m −2 per salt treatment on university paved surfaces, averaging three salt applications per storm. Therefore, the amount of salt applied annually varies depending on the severity of the winter.…”