Relation between Road-Salt Application and Increasing Radium Concentrations in a Low-pH Aquifer, Southern New Jersey

Abstract

The Kirkwood–Cohansey aquifer in southern New Jersey is an important source of drinking-water supplies, but the availability of the resource is limited in some areas by high concentrations of radium, a potential carcinogen at elevated concentrations. Radium (226Ra plus 228Ra) concentrations from a network of 25 drinking-water wells showed a statistically significant increase over a decadal time scale (p < 0.05), with a median increase of 0.35 picocuries per liter. Increases in Ra are correlated with road-salt application rates, and we hypothesize that the correlation is causal. Geochemical processes associated with road-salt applications that can mobilize Ra into solution include competition by excess sodium for sorption sites and formation of chloride complexes (RaCl+ and RaCl2). The largest increases in Ra were in groundwater with low pH (≤5), which is an indirect surrogate for low cation-sorption capacity. Correlations with other potential anthropogenic causes for the increase in Ra were not observed, further suggesting a road-salt effect. Given the significant increase in Ra concentrations in this drinking-water source, the known carcinogenic risks from Ra, the direct link to road-salt application, and the likelihood for continued increases, additional monitoring is necessary in areas with similar hydrogeologic and geochemical settings.

Stormwater drives seasonal geochemical processes beneath an infiltration basin

“…However, as chloride is chemically conservative, continued deicer impact will increase salinity in the aquifer, as has been observed in some local water supply systems (Andres & McQuiggan 2019). Further, as several studies have noted the association between increased salinity and elevated Ra in groundwater in the region (Lindsey et al., 2021; Bolton, 2000; Andres & McQuiggan, 2019), we suspect that there will be increased incidence of Ra contamination of water supply wells. This may become a significant concern where new development constructs infiltration basins in and around agricultural areas, as phosphate‐based fertilizer may be a source material for Ra mobilization to groundwater (Szabo et al., 1997).…”

“…Given there is poor correlation between Ra and geologic unit at the site, there likely are Ra sources in both units. These correlations most likely reflect Ra desorption by competitive ion exchange with Na, and chloride complex formation (Lindsey et al., 2021). These processes would preferentially mobilize 228 Ra where it is enriched by alpha‐recoil in the adsorbed and mobile pool of Ra in shallow aquifers (Krishnaswami et al., 1982; Luo et al., 2000).…”

Gross Alpha-Particle Activity and High 226Ra Concentrations Do Not Correspond with High 210Po in the Atlantic and Gulf Coastal Plain Aquifers of the United States

“…The long-term freshening effects remain the primary characteristic controlling the geochemistry of the Atlantic and Gulf coastal aquifers of the United States, although with rising sea levels as an effect of climate change, it is possible that an increasing percentage of coastal aquifers may be affected by saltwater intrusion in the near future . Increasing salinity may facilitate mobilization of 226 Ra in affected zones through reverse cation exchange combined with formation of aqueous Ra–Cl complexes . More sample collection and geochemical modeling of analytical results are needed to better define 226 Ra and 210 Po occurrence patterns in these vulnerable aquifer areas.…”

“…The forward models start with evaporated rainwater reacted with the smallest amount of minerals (Table SI.8) to produce dilute groundwater that is simulated to have a high concentration of 226 Ra (on the order of 1 pCi/L), derived from surficial aquifer sources, because of inefficient adsorption of Ra at low pH as detailed elsewhere. − Model 1 (black curves) reacts the dilute groundwater with a high concentration of NaCl to simulate the influence of road-deicing salt leachate (Figures , SI.2, and SI.3F). The Na:Cl of about 1.0 for slightly acidic or near-neutral samples (Figure A) indicates mixing of dilute rainwater with saltwater aerosols, road salt, and wastewater. − Models 2, 3, and 4 (red, blue, and green curves, respectively) react the “dilute” groundwater with approximately 10-fold of additional minerals. Model 2 (red curves), without cation exchange, generally explains the compositions of samples having high 226 Ra in “hard” water with considerable Ca and near-neutral pH (samples B–D; 226 Ra 0.97–1.08 pCi/L; Figures , SI.3A–D,G, SI.4, and Table SI.4B; PC2 in Table SI.6).…”

“…78 Increasing salinity may facilitate mobilization of 226 Ra in affected zones through reverse cation exchange combined with formation of aqueous Ra−Cl complexes. 70 More sample collection and geochemical modeling of analytical results are needed to better define 226 Ra and 210 Po occurrence patterns in these vulnerable aquifer areas.…”