Chloride and corrosiveness: trends, indices, scales of measurement, and agency management capacity to address freshwater salinization

This study localizes dimensions of freshwater salinization by directly measuring chloride concentrations in ungauged urban streams, assessing the relationship between chloride, copper and zinc in sample data, measures statewide trends for Iowa, and considers the regulatory and cultural environment of managing winter roads. Chloride concentrations in local, urban streams generally persist at higher levels than what is typical of natural Iowa waters. Runoff from snow melt events violate water quality standards, with chloride concentrations more closely resembling sea water than freshwater. Meanwhile, long-term trends at the statewide scale suggest levels are decreasing over time. Dissolved ions in groundwater from limestone aquifers encourage chemical buffering. Surface runoff in urban areas does not contain groundwater but does contain a large amount of salt from roads and other sources. More salt present year-round in streams influenced by surface water hydrology likely increases the potential for storm sewers, bridge decks and other urban infrastructure to corrode. Public agencies take varied approaches to freshwater salinization and related concerns. Regulation focuses on drinking water protection, and accounts for both household and industrial chloride sources. Snow and ice “fighters” see chloride as a tool, whereas scientists and regulated agencies consider it a pollutant of concern. This split leads to inconsistent patterns in decision-making and prioritization. Salt is a commodity, generating billions of dollars for suppliers throughout North America. Industry can play a significant role in solving what may ultimately become one of the most challenging water quality problems of the 21st Century.