Water Quality Study
What is a TMDL?
The term "total maximum daily load," or TMDL, refers to the calculation of the maximum amount of a pollutant that a water body can receive, and attain or maintain water quality standards for its designated use.
The one major unresolved issue identified following publication of the Draft Environmental Impact Statement (DEIS) relates to the application of road salt and the potential impairment of surface waters due to elevated chloride concentrations. From the winter of 2002/2003 through 2005, surface water quality monitoring in the I-93 corridor was conducted jointly by the New Hampshire Department of Environmental Services (DES) and the United States Environmental Protection Agency (EPA).
The monitoring indicated that, during various times of the year, chloride levels do not meet state water quality standards in four streams – Beaver Brook, Dinsmore Brook, an unnamed tributary to the western embayment of Canobie Lake, and Policy Brook – which triggered the requirement for a total maximum daily load (TMDL) study for chlorides. The study is being conducted by DES and funded by the New Hampshire Department of Transportation (DOT).
The largest source of chlorides in these watersheds is presumed to be road salt. However, winter road maintenance on I-93 may not be the primary source of chloride. Other chloride sources include deicing activities on other state, municipal and private roads and commercial parking lots, as well as the discharge from septic systems and water-softening systems. Therefore, in an effort to implement a regional solution, and in coordination with the TMDL study, DOT and DES have established a Salt Reduction Workgroup. Town Departments of Public Works and Highways, Regional Planning Commissions, the DOT, EPA, DES, Federal Highway Administration, University of New Hampshire and Plymouth State University were represented at the first meeting on September 26, 2006. Four additional meetings were then scheduled. Furthermore, the DOT and DES will be conducting a training/outreach program to promote the best practices for the storage and application of road salt.
While DES has been the lead agency in the TMDL study, the DOT, EPA, Plymouth State University, and the US Geological Survey have also contributed data. A draft report on the study was completed in late summer, 2007. The final report and implementation plan, which will define the actions state, municipal and private entities will be required to take to reduce chloride loadings, will be available September 30, 2008.
For more information regarding TMDL, please see the Chloride Surface Water Quality Fact Sheet or the Documents section.
