Chloride and corrosiveness

Abstract

My research examines dimensions of freshwater salinization at the local and statewide scale and the capacity for public agency response. This study grows knowledge of this phenomenon by considering secondary effects such as metal mobilization. Primary and secondary water quality data sources and in-depth interviews compare chloride concentrations, copper, zinc and three corrosiveness indexes to assess local conditions and determine long-term statewide trends from 2001-2010. A series of in-depth interview transcripts were analyzed for patterns in themes, terminology and identify key factors in management decision-making. Results indicate local, urban chloride concentrations exist well above what is considered background conditions for Iowa streams. Pulses of maximum chloride concentrations exceed both acute and chronic toxicity, with runoff from roadway surfaces at one quarter the ionic strength of sea water. Meanwhile, long-term trends measured in larger-order streams indicate chloride concentrations are declining, possibly due to increased base flow. Potential for promoting galvanic corrosion is increasing over time, but likely as a function of sulfate, not chloride. When groundwater is present, carbonate ions likely sequester any mobilized metals. However, higher proportions of impervious surfaces in urban areas reduce the ability for groundwater and carbonate geology to sequester ions due to more surface water influencing local hydrology. Metals will then potentially mobilize when salts are present. Management of freshwater salinization is evolving, based on interview transcript details. Regulation tends to occur primarily for drinking water protection, and accounts for both household and industrial chloride sources. Feedback from public agency managers indicate managers tasked with snow and ice removal tend to view chloride as a tool, whereas scientists and regulated agencies consider it a pollutant of concern. This divide likely spurs inconsistent patterns in decisionvi making and prioritization. Salt is an important resource for managers and comprises a significant proportion of operating budgets and schedules. The role of salt in public works suggests industrial suppliers as key stakeholders. The salt industry has a unique opportunity to play a major role in solving what may ultimately become one of the most challenging water quality problems of the 21st Century.