Practical Measures for Managing Chloride-Based Deicers
Research Idea Scope
Chloride-based deicers continue to be the primary deicing chemical of choice due to the huge cost differential with non-chloride deicers, which generally cost 15 to 20 times more than regular road salt. Essentially there are no salt alternatives that are comparable in terms of low cost and effective performance. However, there has been a trend where more and more water bodies are being listed as impaired in the northern snowbelt states due to chloride levels exceeding the EPA’s recommended water quality standard for chloride established in 1988. EPA’s ambient aquatic life water quality criteria (EPA 440/5-88-001, 1988) for chloride needs to be revisited to account for hardness and the presence of sulofates in ambient waters, and because the criteria do not account for seasonal effects where organisms may be less susceptible to chloride toxicity during the winter period when their metabolic rates are low and feeding is at a minimum. Other important considerations are the size of the receiving water body, and the setback distance to the highway drainage discharge points. For example, to be effective for deicing, the brine concentration on a snowy highway must be at least 10,000 mg/l NaCl. Hence, the closer the sampling location is to the discharge point, the higher the chloride concentrations. However, as streams flow downstream, their flows tend to increase and, through dilution, their respective salt concentrations tend to concentrations below EPA’s MCLs. Developing more practical performance standards could prevent unnecessary expenditures for chloride mitigation, as well as reduce the need to protect intermittent streams that freeze in the winter and run dry during the summer. This is of particular importance given the recent development of chloride Total Maximum Daily Loadings (TMDLs) and the application of their respective chloride-reduction requirements, which can have unintended consequences and lead to the mismanagement of highway funds. This scenario occurred when the NH DOT built an additional travel lane along I-93, but the EPA prohibited its use due to the Waste Load Allocation prescribed by the Chloride TMDL Report. Administration of a TMDL for chlorides is more challenging than for other pollutants of concern. It requires constant salt management rather than a one-time installation of a BMP (for P reduction, let’s say). Establishing TMDL rates and Waste Load Allocations is entirely dependent on weather variability and winter severity. Also, rather than look for a nationwide MCL to be exceeded, there should be a demonstrated problem where water uses are not being met (e.g., macroinvertebrate mortality having ecological consequences). Moreover, if chlorides are deemed to be a toxic material, then all public agencies should consider whether salt applicators should be licensed and accountable for applying chlorides. In addition, DOTs are not the only source of salt in any given watershed – in fact many DOTs’ salt application programs are well-managed when compared to those of municipal and private sources (e.g., roads, sidewalks, parking lots, and driveways). Furthermore, the USGS has published a recent report, titled “Methods for evaluating potential sources of chloride in surface waters and groundwaters of the conterminous United States” (2015) which emphasizes that road salt is by no means the only source of salt to water resources, and that salt concentrations tend to increase wherever population and development is increasing.
Urgency and Payoff
An overall goal of this study is to develop a framework for how DOTs can best address chloride loading from winter deicing operations, with a thorough description of the constraints and limitations facing DOTs. The study will formulate reasonable chloride management measures as a balance to environmental regulators who simply want to require DOTs to unilaterally reduce their salt use, which is not an operable solution. This study will serve to support better government decision-making by preventing indeterminate water quality requirements from blocking the construction of highway projects designed to enhance safety and otherwise serve public needs. In short, the study will help keep DOTs from having to choose between permit compliance and highway safety. The study will provide policy suggestions to make the regulation of salt management more equitable amongst users and more practical to implement, rather than have DOTs be the presumptive primary source of salt and act as the lead party to coordinate and manage other salt users. The primary DOT goal would be to avoid over-salting its highways during any one storm and/or winter season. The study will explore the justification for granting leniency to: 1) sizable highways, with significant salt usage, next to low-flow streams; and 2) anomalous winters, with high Winter Severity Indices, where chloride concentrations are unusually high. The study will provide guidance to DOTs for employing practicable and proven salt mitigation measures (i.e., source control) as a way to minimize chloride impacts to streams.
Henry Barbaro MassDOT 857-368-8788