Smart Chloride Mitigation System

Chloride has been identified as a stressor impairing stream water quality in Maine. Salt application due to winter maintenance of the impervious surfaces is the leading chloride source in the stream watersheds. Chloride is a challenging stormwater contaminant since: (1) Chloride cannot be removed from the stormwater by the existing treatment measures due its high solubility, (2) Unlike most stormwater contaminants, stormwater infiltration into soil is not a removal mechanism for chloride. Chloride stored in the soil column and shallow groundwater persistently contaminate the streams via baseflow: high chloride concentrations are commonly observed in the streams during summer months, (3) Chloride source control is proven to be difficult since public safety, level of service concerns often outweigh the benefits of reduced winter salt application. Considering the limitations of the current winter maintenance practices, new best management practices (BMPs) are desperately needed to alleviate the chloride pollution in the streams. Furthermore, MaineDOT is required to implement BMPs in seven chloride-impaired stream watersheds under the new Transportation Municipal Separate Storm Sewer System (MS4) General Permit issued by the Department of Environmental Protection (DEP). A Smart Chloride Mitigation System has potential to provide a more controlled BMP. The proposed desktop research will answer the following questions using specialized software in the order given below: (a) What will be the SCMS design criteria? “Continuous” stormwater models including snowmelt process (e.g. SWMM) will be used to develop the SCMS design criteria (e.g. detention volume criterion) and simulate SCMS performance as a function of logic control, salt application rate, and weather. (b) Where can SCMS be implemented? Potential locations in seven chloride-impaired urban stream watersheds will be evaluated using GIS for the pilot SCMS implementation. Major evaluation criteria are the paved area that can be treated by SCMS, the area available for SCMS, the grade availability for positive drainage.