ROAD SALT (NACL) RUNOFF INCREASES SOIL PH AND SIGNIFICANTLY ALTERS CATION EXCHANGE CHEMISTRY IN SOILS AND AQUIFERS

Application of halite (NaCl) as a de-icing salt has increased since the 1950s due to increases in population and impervious surface area as well as changing expectations about how quickly roads should be cleared. Numerous studies demonstrate that de-icing salt application significantly impacts surface and ground water chemistry, but many fewer studies have investigated the impact on soil or aquifers. We investigated soil and aquifer chemistry impacted by water from two stormwater management basins (SMBs) built circa 2000 in a suburban area near Baltimore, MD. To characterize changes resulting from de-icing salt application, we collected seven cores ranging from 3.5-7 feet in depth within and downgradient of the SMBs. The soil and aquifer materials are produced from schist weathering and are acidic (typically pH ~5). We found that soil pH increased to >6 in cores receiving runoff or groundwater flow with high Na⁺ concentrations ([Na⁺]). The exchangeable complex (EC) of unimpacted soils was 75-90% Ca²⁺ with Mg²⁺ comprising the bulk of the remaining EC. In contrast, the EC in cores impacted by water with high [Na⁺] shifted to 20-60% Na⁺ with 40-80% Ca²⁺ and nearly complete depletion of Mg²⁺. Our data demonstrate that 15 years of high [Na⁺] water from road salt runoff has dramatically changed soil and aquifer chemistry.