Assessment of deicing salt storage and distribution as a salinization point source: the influence of permitting standards on water quality

摘要

Background Road deicing salts are impacting freshwater ecosystems in snowy regions worldwide. Rock salt (typically sodium chloride) is transported to and stored in regional facilities that operate year-round and are continuous potential sources of chloride discharge to adjacent water bodies, resulting in different impacts to aquatic ecosystems than chloride pollution from spatially diffuse road networks. The regulatory tools and associated monitoring regimes used by state and federal agencies related to permitting of these facilities is inconsistent. Selection of the regulatory standards and monitoring location in the receiving water body (and how the definition of ‘receiving water body’ is applied) can have a significant influence on the measured or modeled impact of a facility on aquatic ecosystems. Additionally, selection of the monitored media (surface water, soil pore water, shallow ground water, or vegetation) can further influence findings, resulting in inconsistent conclusions of environmental impact and potentially allow exceedances of regulatory thresholds of chloride. This study evaluates chloride pollution from salt loading over two years from a state-permitted salt storage and transport facility in Shelburne, Vermont, USA to an adjacent wetland and river that drains to Lake Champlain. Water quality results and modeled assumptions made by the permittee were compared to monitoring data at two discharge points from the site including a drainage channel downstream of the site’s stormwater pond and at a shallow ground water seep below the rail car unloading area. Results Results indicate elevated chloride concentrations (average of 243 and 643?mg?L~(?1)) at the discharge points to the receiving water body, in conflict with findings from annual permittee assessments. Soil cores taken in the wetland in the vicinity of the control and two discharge points also indicate elevated Cl~(?)(p?≤?0.035) and Na~(+)(p?≤?0.0006). Samples of Tsuga canadensis at the discharge points and at the control site indicate elevated chloride in plant tissues. Conclusions Determination of exceedances of chronic and acute standards vary based on the sampling location and medium, indicating a need for consistency and outcome-based monitoring point selection criteria and a move away from reliance on self-reporting by permittees.