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This report describes a work plan for a project to study the relative effectiveness of specially designed highway drainage features in preventing contamination of ground water by highway-deicing salts with a solute-balance approach. Four different highway drainage designs along a new highway in southeastern Massachusetts will be compared. In one system, no attempt is made to channel runoff from the highway away from the edge of the road, and no attempt is made to prevent percolation of that water into the ground. In a second system, catch basins and drainage pipes conduct highway runoff away from the site for discharge elsewhere. The other two systems use drainage pipes and partial or complete snow berms in which subsurface impermeable layers constructed on the median and shoulders of the roadway prevent percolation of water into the ground. Two approaches will be used to determine the relative effectiveness of each type of drainage system in preventing salt from entering ground water adjacent to the highway. In the first, a solute-balance approach will be used to quantify the amount of salt applied to the highway with the amount that enters ground water at that site or leaves the highway in surface-drainage outlets at the closed-drainage sites. In the second, or modified solute-balance approach, the quantity of salt in ground water at each site will be compared to the quantity of salt in the ground at a control, the opendrainage site, to determine the capture efficiency of each drainage system. This method assumes that salt is applied to the highway at the same rate per mile of highway at all four highway drainage sites. This method also assumes that the capture efficiency of the open-drainage system in preventing salt from entering the ground water approaches 0 percent. The amount, or load, of salt in ground water at each of the four test sites will be estimated from the concentration of salt in the water and the volume of water in the aquifer. The concentration of salt will be determined by chemical analysis of water samples from a network of wells adjacent to the highway. The network will be designed so that each well will yield water samples representative of a prescribed volume, or block, of the aquifer. The volume of water within each block will be calculated from the block dimensions and the aquifer porosity as measured from neutron porosity logs and estimated from lithologic samples. The quantities of chloride in all the blocks will be added to determine the quantity of salt entering ground water at each site. Background data at each test site will be collected for at least 1 year before the highway is opened. After five salting seasons, the capture efficiency of each drainage system will be determined by comparing the salt load spread on the highway with the salt load in ground water and, where possible, in surface drainage. INTRODUCTION Background This article describes a work plan for a joint research project by the Survey (U.S. Geological Survey) and the MDPW (Massachusetts Department of Public Works). The objective of this study is to determine the relative effectiveness of different types of highway drainage systems in preventing highway-deicing salts (sodium chloride and calcium chloride) from getting into ground water adjacent to highways. This research is based on a previous highway salting/runoff study conducted by the Survey and the MDPW (Frost and others, 1981a, 1981b). One conclusion of that study was that highway drainage systems are a major influence in determining where and how much salt enters ground water. In the current research project, test sites representative of four different types of highway drainage systems have been selected along State Route 25, which is under construction in southeastern Massachusetts (figs. 1 and 2). Data collection will begin at least 1 year before the highway is open and will continue until Route 25 has been open for 5 years. It is anticipated that Route 25 will open during 1986. The Massachusetts Department of Environmental Quality Engineering requires that public water suppliers warn their customers if water which they deliver contains 20 mg/L (milligrams per liter) or more of sodium because of potential dangers of sodium to people with hypertension or heart disease. Also, the U.S. Environmental Protection Agency (1975) has recommended a 250 mg/L limit for chloride in drinking water. Where public-supply wells have been contaminated by deicing chemicals from highways, reconstruction projects have included special drainage systems designed to minimize future contamination of these wells. In addition, special highway drainage systems to prevent contamination of public and private ground-water supplies are being designed and constructed on new highways to restrict dispersal of highway-deicing chemicals. These chemicals consist of salt (sodium chloride) with as much as 20 percent calcium chloride. Each special drainage system costs between $750,000 and $3,000,000, but the effectiveness of these systems in preventing sodium and chloride from contaminating ground water has not yet been proven. An evaluation of the effectiveness of various highway drainage systems is needed for State agencies responsible for highway design and protection of public health and water supplies, and consultants who design highways and prepare environmental impact statements. Figure 1. Location of study area in Massachusetts.

water-resources investigations report

Effectiveness of highway drainage systems in preventing salt contamination of ground water, Route 25 from Wareham to the Cape Code Canal, Massachusetts