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New Hampshire Department of Environmental Services

Southern I-93 Corridor Chloride Impairment


Project Overview
Ambient chloride concentrations in Policy Brook are more than one hundred times higher than typical concentrations from the 1920s, before salt was used as a deicer.Streams in four watersheds, including parts of Salem, Windham, Derry, Londonderry, Auburn and Chester do not meet water quality standards for chlorides in particular segments during various times of the year. The largest source of chlorides in these watersheds is road salt. Water quality monitoring from 2002 through 2005, conducted jointly by the NH Department of Environmental Services, NH Department of Transportation, and the US Environmental Protection Agency, has documented violations of the water quality standards for chloride in Beaver Brook, Dinsmore Brook, the tributary to the western embayment of Canobie Lake, and Policy Brook. The violations triggered the need for a total maximum daily load (TMDL) study for chlorides on these watersheds. The TMDL, which recommends reduction in road salt use to mitigate the water quality violations, was conducted by NHDES and funded by DOT. In addition to the TMDL, NHDES has issued a 401 Water Quality Certification Adobe Acrobat Reader Symbolfor construction activities to expand I-93 to eight lanes. The certification contains conditions requiring DOT to implement a number of water quality protection programs. On June 26, 2006 NHDES and DOT entered into a Memorandum of Agreement Adobe Acrobat Reader Symbolto clarify the roles of both agencies with regard to the TMDL and the 401 Water Quality Certification.

What is a Chloride Total Maximum Daily Load?
The term “total maximum daily load,” or TMDL, refers to the calculation of the maximum amount of a pollutant that a waterbody can receive and attain or maintain water quality standards for its designated use.

The purpose of the chloride TMDL is to estimate chloride loads from all sources that lead to the water quality violations, determine the capacity of the water bodies to assimilate chloride without violating the standards, and to develop an implementation plan to reduce chloride loads in order to meet the water quality standards.

Southern I-93 Corridor Chloride TMDL
The Southern I-93 Corridor Chloride TMDL is a study conducted in four small watersheds in the I-93 expansion corridor. The TMDL included the watersheds for Policy-Porcupine Brook, Dinsmore Brook, and the North tributary to Canobie Lake in Salem and Windham, and the Beaver Brook watershed in Derry, Londonderry, Chester and Auburn.

The study found that road salt accounted for approximately 90 percent of the salt imported to the watersheds. The water quality violations primarily occurred during low flow periods in both the summer and the winter, indicating groundwater contamination.The TMDL quantified the amount of salt imported into and exported from the watersheds, while simultaneously documenting the timing and conditions when water quality violations occurred. In each watershed, NHDES installed instruments to measure conductivity (a surrogate for salt) every 15 minutes for a year. The US Geological Survey was contracted to measure stream flow at these stations. The combination of the conductivity and stream flow records was used to identify critical season and flow conditions for water quality violations. The export of salt from the watershed was also calculated from this data set. NHDES quantified the salt imported to the watershed from data supplied by DOT, municipalities, and research on parking lot salt application rates from Plymouth State University Adobe Acrobat Reader Symbol. The percent reduction in salt loading was calculated using load duration curves. This method was used for another road salt TMDL in Minnesota.

The TMDL in the I-93 corridor found that road salt accounted for approximately 90 percent of the salt imported to the watersheds. In some watersheds the chloride concentrations were higher than the water quality standards 24 percent of the year. The water quality violations primarily occurred during low flow periods in both summer and the winter. Salt imports need to be decreased from 2007 levels by 24 to 40 percent in order to meet water quality standards. Ambient chloride concentrations in Policy Brook are more than one hundred times higher than typical concentrations from the 1920s, before salt was used as a deicer.

Working Group and Steering Committee Meetings
In coordination with the TMDL, DOT and NHDES established a Salt Reduction Working Group comprised of local selectmen and municipal public works directors, private winter road maintenance contractors, state environmental organizations, regional planning commissions, University of New Hampshire representatives, Federal Highway Administration (FHWA) as well as DOT, NHDES and EPA representatives. A steering committee comprised of representatives of the DOT, EPA, NHDES and FHWA coordinates the working group and implements their recommendations.

The purpose of the working group is to advise NHDES and DOT during preparation of the TMDL report and implementation plan on a broad range of issues associated with salt use in the watershed. In addition, the members of the working group, through consensus building activities are determining how to distribute federally earmarked funds allocated to assist with TMDL implementation. The working group will then continue to assist NHDES, DOT and each other with implementation of anticipated salt load reductions specified by the TMDL.

The federal earmark funds, totaling $4.1 million, were authorized to prepare and implement the chloride TMDLs. In addition to regional efforts focused on private sector salt reduction and driver safety, $2.5 million was set aside for municipal salt reduction.

Working Group Meeting Minutes

Potential Solutions Report
Jeffery H. Taylor & Associates and the Center for the Environment Plymouth State University were contracted to create a report on Potential Solutions for Reducing Road Salt in New Hampshire Adobe Acrobat Reader Symbolto be used as a framework for the implementation plans. Social research for the report was designed to identify approaches that could potentially reduce the use of chlorides and the negative impacts associated with their use in the I-93 corridor. A one-on-one survey effort, working group meetings and discussions, literature and internet research, and focus groups were used to identify: specific best management practices to reduce salt application to roadways and parking lots; behavior changes needed by the driving public, safety personnel, elected officials, and road and maintenance staff to support chloride reductions; optimal outreach, education, and technical assistance to facilitate attitude and behavior changes; potential regulatory approaches, and a strategy for evaluating and documenting success.

Chloride Implementation Plans
Implementation plans for chloride reduction are being developed based on chloride allocations set within the TMDLs for the four watersheds. Elevated chloride levels within these waterbodies is a direct result of road salt use during the winter months. Road salt is applied to keep roads, parking lots and sidewalks safe for the traveling public. The DOT, the towns of Salem, Windham, Derry, Londonderry, Auburn and Chester and the private contractors who maintain parking lots and driveways will be required to follow the implementation plans through certain federal and state permits. The best management practice activities identified are acceptable methods for chloride reduction that increase the level of service and safety to the traveling public within the impaired areas along the I-93 expansion corridor in southern New Hampshire. Although the implementation plans address chloride reduction within the southern I-93 corridor, BMPs and other recommendations within the plans can be utilized in other areas of New Hampshire.
Chloride Implementation Plan For Dinsmore Brook Watershed, Windham, NH Adobe Acrobat Reader Symbol
NHDOT Implementation Plan to Increase the Efficiency and Effectiveness of Road Salt Use to Meet TMDL – Sept, 2009 Adobe Acrobat Reader Symbol



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