Effectiveness of Highway Drainage Systems in Preventing Road Salt Contamination of Groundwater Preliminary Findings (1993) / Chapter Skim
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Effectiveness of Highway Drainage Systems in Preventing Road-Salt Contamination of Groundwater: Preliminary Findings
Effectiveness of Highway Drainage Systems in Preventing Road-Salt Contamination of Groundwater: Preliminary Findings
Pages 1-12
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Friesz Reprinted from TRANSPORTATION RESEARCH RECORD 1420 (1993) Transportation Research Board National Research Council Washington, D.C.
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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 highwaydrainage monitoring stations at each test site.
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The roadway surface at all test sites is crowned to allow highway runoff to flow toward the highway shoulders and the median strip. The top 2.5 cm of the highway pavement is composed of an open-graded friction coarse bituminous concrete, referred to as "popcorn pavement," to limit pending of water on the highway surface.
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Background chemical data at Site C are probably higher than at the other test sites because of the former presence of a pig farm approximately 0.8 km upgradient from the test site, which is now an unpaved lot where many used buses are stored. , , METHODOLOGY 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.
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Monthly chloride loads are then converted to chloride loads, in kilo grams per lane-kilometer of highway, for comparison between test sites. Monitoring Road-Salt Chloride Discharged from Highway Drainage Stations Highway-drainage monitoring stations were installed in the trunkline drainage pipes of the highway drainage systems at Sites B
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Monthly chloride loads are then converted to chloride loads, in kilograms per lane-kilometer of highway, for comparison between test sites. RESULTS AND DISCUSSION OF RESULTS Comparison of road-salt chloride loads in groundwater at each test site from November 1990 through May 1992 shows that the various highway drainage systems differ in effectiveness.
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Maximum loads occurred in March at the open drainage site, in May at the closed drainage site with snow berm, and in June at the closed drainage and fullsnow-berm drainage sites. Minimum chloride loads occurred in the late fall and early winter of 1991 at each test site.
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These elevated values, relative to those at the other drainage systems, are probably due to retention and slow release of salt-laden water from the approximately 1-m-thick layer of sand fill overlaying the snow berm. SUMMARY Four test sites, each representing a separate highway drainage system designed for a different amount of highway runoff control, were selected and instrumented to determine their relative effectiveness in preventing groundwater from becoming contaminated by road salt.
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TABLE 2 Monthly and Total Chloride Loads Discharged Through Highway-Drainage Systems, November 1990 Through May 1992 (kg/lane-km) Year/ Closed drainage Full-snow-berm month Closed drainage with snow berm ~ 990 drainage November 1 1 2 December 17 23 42 1991 January 270 190 250 February 100 140 250 March 220 300 540 April 27 17 73 May 16 5 June 5 1 July 6 5 August 5 7 September 9 7 October 9 7 39 November 3 2 24 December 110 56 200 1992 January 96 84 230 February 58 78 340 March 220 210 340 April 130 180 460 Stair 34 46 83 TOTAL 1,300 1,400 2,900 [data rounded to two significant figures; ~ denotes no data collected during this periodl
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From page 11... ...
Monthly chloride loads discharged through the highway drainage systems are computed by use of relations between stage and discharge and between specific conductance and chloride concentration. A comparison of accumulated monthly chloride loads in groundwater from November 1990 through May 1992 shows that chloride loads at the closed drainage site, the closed drainage with snow berm site, and the full-snow-berm drainage site are about 40, 50, and 20 percent, respectively, of the chloride load at the open drainage site.
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