Information about Chlorides
Cambridge Watershed Deicing Salt Overview
Background
Deicing salts have been a concern for the Cambridge Water Department (CWD) since the 1960s as road salting began replacing abrasives (sand & cinders) in winter treatment of watershed municipal and state roadways. In the 1980s, after sodium concentrations exceeded drinking water quality standards of 20mg/L, CWD and Massachusetts Department of Transportation (MassDOT, then Massachusetts Department of Public Works) jointly funded a study identifying the sources of and reduction strategies for watershed deicing salts. That study, conducted by Geotechnical Engineers Inc. in 1985, identified state roadway treatments as the largest input (72%) of deicing salts.
Sodium, chloride and other deicing salt constituents are of concern to CWD because they are not readily removed by current water treatment practices. Sodium is regulated in drinking water at 20 mg/L (MassDEP Drinking Water Guideline) to protect those with high blood pressure and renal failure. As drinking water typically adds a small amount of sodium to a person’s daily intake (less than 10%), deicing impacts today are less driven by sodium concentrations and more by chlorides. MassDEP’s Secondary Maximum Contaminant Level (aesthetic standard) for chloride in drinking water is 250 mg/L, above which water will have a salty taste. The US EPA interprets chlorides as chronically toxic to aquatic life at 230 mg/L and acutely toxic to aquatic life at 860 mg/L.
What We Do
The Water Department Watershed Division works in-house and with the United States Geological Survey (USGS) to collect and analyze water quality data to better characterize and understand deicing impacts in the water supply. We also work at state and local levels to educate the public on water quality impacts and recommend low salt strategies for watershed stakeholders.
USGS/CWD Joint Effort
CWD and the USGS have partnered since 1997 to quantify our water source and understand development threats and water quality impacts thereto. They maintain four reservoir, ten tributary, and four weather data collection stations serving publicly available real-time results on the internet. USGS has published three major interpretive reports and many other data collection reports that provide information on deicing salt constituents in the water supply.
MassDOT
CWD works with MassDOT staff at the state and district levels to discuss steps to reduce watershed salt use. CWD comments on Environmental Status and Planning Reports, urging prioritizing the Cambridge watershed area for piloting new strategies for salt-reducing deicing strategies. MassDOT has recently initiated a follow-up study to the 1985 GEI report. CWD will commit resources to developing an acceptable scope and steer the process to ensure adequate representation of interest.
Site Plan Review
CWD reviews plans for private developments within the watershed subject to the Wetlands Protection Act and Massachusetts Environmental Policy Act. CWD makes recommendations for deicing practices for inclusion on issued permits.
Please see related links for additional information
Massachusetts DEP Sodium in Drinking Water
Chlorides Environmental Fact Sheet
Chlorides 101