EFFECTIVENESS OF HIGHWAY DRAINAGE SYSTEMS IN PREVENTING ROAD-SALT CONTAMINATION OF GROUNDWATER: PRELIMINARY FINDINGS

Abstract

A study to determine the relative effectiveness of four highway drainage designs in preventing the contamination of groundwater by road salt is being conducted by the U.S. Geological Survey in cooperation with the Massachusetts Highway Department and FHWA. Four test sites, each representing a specific highway drainage design, are located along a 5-km section of Route 25 in southeastern Massachusetts. The drainage designs being tested are open drainage, closed drainage, closed drainage with snow berm, and full-snow-berm drainage. Preliminary comparisons of the effectiveness of the highway drainage systems are based on computations of chloride loads from road salt in groundwater and chloride loads from road salt discharged through the highway-drainage monitoring stations at each test site. A comparison of monthly chloride loads from November 1990 through May 1992 shows that chloride loads in groundwater at the closed drainage site, the closed drainage site with snow berm, and the full-snow-berm site are about 40, 50, and 20%, respectively, of the chloride load in groundwater at the open drainage site. The chloride load discharged through the full-snow-berm drainage site, and thus prevented from entering groundwater, is twice that discharged from the closed drainage site and from the closed drainage site with snow berm. Evaluation of the effectiveness of these drainage systems will be refined as additional data are collected and analyzed. Results from this study should also be applicable to the transport of other conservative chemical constituents in highway runoff.