A Little Less Salt, Please
Sunday, April 12, 2009
We know that too much salt in our diets is bad for our health. But few recognize the impact that excessive salt on our roads has on local waterways and our sources of drinking water. The end of winter presents an opportunity to plan for sensible salting and integration of new technologies to reduce road salt usage. Increased use of road salts allows commuters to drive more safely and reduces time lost to weather, but these benefits come at a cost to our drinking water sources. Icy roads can be tackled with less harmful chemicals and with better information on road conditions, allowing for precise application of salt.
Salt carried in runoff can cause peak chloride concentrations in some urban streams to approach 25 percent of the salt concentration of seawater. These levels can harm or destroy aquatic life, particularly in small streams. Chloride persists long after the last snowflake, as dissolved road salt infiltrates into groundwater and into local streams. This increased level can last through the summer, often at a level more than 100 times greater than in unaffected forest streams. Average annual chloride concentrations increase with the spread of impervious surfaces, making the concentrations found in suburban and urban watersheds extremely harmful to freshwater life.
In addition to environmental impacts, salt can also contaminate drinking water supplies. After winter storms, observations at water treatment intakes in the Potomac River and in adjacent water supply watersheds, such as the Washington Suburban Sanitary Commission's Patuxent basin, include increases in chloride, ammonia (to counter an increase in salt during the treatment process), sediment and total organic carbon. The highest annual levels of chloride in the Potomac River are detected after winter storms. Local water utilities have observed increased sodium levels in pre-treated Potomac River water during the past 12 years. Winter weather-related runoff can affect the taste of drinking water, corrode plumbing infrastructure, complicate treatment challenges and, potentially, increase costs.
Innovative alternatives are available. The Massachusetts Highway Department has adopted a reduced-salt application in areas where salt could harm the environment or drinking water supplies. Other departments have integrated road weather information systems (automatic weather stations that use embedded roadway sensors to measure surface temperature, wetness, and residual chemicals to more efficiently plan winter maintenance operations) that increase safety and reduce the use of de-icing chemicals.
Regionally, the Maryland State Highway Administration uses pavement sensors and other technologies to guide ice management decisions, the Virginia Department of Transportation is increasing pre-treatment (to reduce overall chemical usage), and the D.C. Department of Transportation uses naturally-derived beet juice products with brine mixtures to reduce chemical usage and corrosivity.
In addition, our expectations during winter weather bear examination. As long as we expect immediate access regardless of weather conditions, transportation agencies will salt roads before the first snowflake. Road safety is paramount, but if the harmful effects of increased salt in our drinking water sources are ignored, the costs will be evident in our water treatment costs and in the negative environmental effects.
The Potomac Drinking Water Source Protection Partnership, a group of water suppliers and government agencies focused on protecting drinking water sources, identified roadway de-icers as a priority concern, and encourages use of more environmentally friendly anti-icing chemicals and research.
The writer is executive director of the Interstate Commission on the Potomac River Basin (ICPRB). The ICPRB serves as coordinating agency for the Potomac River Drinking Water Source Protection Partnership.