Pollution Prevention Fact Sheet: Bridge and Roadway Maintenance
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This management measure involves incorporating pollution prevention techniques to reduce or eliminate pollutant loads from existing road surfaces as part of routine operation and maintenance. Substantial amounts of sediment and pollutants are generated during daily roadway and bridge use and scheduled repair operations, and these pollutants can threaten local water quality by contributing heavy metals, hydrocarbons, sediment and debris to stormwater runoff. Table 1 shows some of the constituents that can be present in highway runoff and their primary sources.
|Table 1. Highway Runoff Constituents and Their Primary Sources (US EPA, 1993)|
|Particulates||Pavement wear, vehicles, atmosphere|
|Nitrogen, Phosphorus||Atmosphere, roadside fertilizer application|
|Lead||Tire wear, automobile exhaust|
|Zinc||Tire wear, motor oil, grease|
|Iron||Auto body rust, steel highway structures, moving engine parts|
|Copper||Metal plating, brake lining wear, moving engine parts, bearing and bushing wear, fungicides and insecticides|
|Cadmium||Tire wear, roadside insecticide application|
|Chromium||Metal plating, moving engine parts, brake lining wear|
|Nickel||Diesel fuel and gasoline, lubricating oil, metal plating, brake lining wear, asphalt paving|
|Manganese||Moving engine parts|
|Cyanide||Anticake compound used to keep deicing salt granular|
|Sodium, Calcium, Chloride||Deicing salts|
|Sulphate||Roadway beds, fuel, deicing salts|
|Petroleum||Spills, leaks, or blow-by of motor lubricants, antifreeze and hydraulic fluids, asphalt surface leachate|
As Table 1 demonstrates, there are numerous pathways for pollutant deposition on roadways and bridges that can influence the water quality of stormwater runoff. Routine performance of general maintenance activities such as sweeping, vegetation maintenance, and cleaning of runoff control structures can help alleviate the impacts of these pollutants. Modifications in roadway resurfacing practices and application techniques for salt and other deicers can also help reduce pollutant loads to stormwater runoff and protect the quality of receiving waters.
Roadway systems are a large part of the infrastructure of urban areas across the country, and require regular repairs and maintenance due to traffic use and climatic conditions. The level of pollutants found in road and bridge runoff is variable and is determined by a number of factors in addition to traffic volume and climate. Other factors affecting pollutant levels include surrounding land use, the design of the bridge or roadway, the presence of roadside vegetation, roadside application of pesticides and fertilizers, and the frequency of accidents and spills that can introduce hazardous chemicals. In colder climates, the amount of deicer applied to melt ice and snow can also influence the level of certain pollutants in road runoff and its impacts on local water quality (for more information, see Influence of Snowmelt Dynamics on Stormwater Runoff Quality, Article 3 in The Practice of Watershed Protection).
Road and bridge maintenance programs have a number of options for reducing the level of pollutants generated during the maintenance of existing road surfaces. Changes in the methods used for maintaining road surfaces, removing debris and sediment from roadways, and cleaning of runoff control structures can help improve the overall quality of stormwater discharges from roads and bridges.
Proper planning for road and bridge resurfacing operations is a simple but effective method to control pollution. There are a number of suggestions that can be implemented to control the impacts of this maintenance operation. First, paving operations using concrete, asphalt, or other sealers should be performed only in dry weather situations to prevent contamination of runoff. Second, use proper staging techniques to reduce the spillage of paving materials during the repair of potholes and worn pavement. This can include covering storm drain inlets and manholes during paving operations, using erosion and sediment control measures to decrease runoff from repair sites, and utilizing pollution prevention materials such as drip pans and absorbent material for all paving machines to limit leaks and spills of paving materials and fluids. Finally, resurfacing operations can employ porous asphalt for pothole repair and for shoulder areas to reduce the level of stormwater runoff from road systems. For more information on permeable road surface materials see the Assorted Tools Fact Sheet on Alternative Pavers.
Cleaning practices can help diminish impacts to stormwater runoff. Sweeping and vacuuming of heavily traveled roadways to remove sediment and debris can reduce the amount of pollutants in runoff. Street sweeping as a pollution source control is discussed more extensively in the Pollution Prevention Fact Sheet on Parking Lot and Street Cleaning. Regular cleaning of runoff control structures such as catch basins can help reduce sediment loads in runoff that will end up in local waterways. For more information, see the Pollution Prevention Fact Sheet on Catch Basins.
Proper application of road salt or other deicers also reduces stormwater pollution. By routinely calibrating spreaders, a program manager can prevent over-application of deicing materials. In addition to reducing the effects of these materials on the aquatic environment, a cost savings may be realized due to reductions in the purchase of deicing materials. Training for transportation employees in proper deicer application techniques, the timing of deicer application, and what type of deicer to apply will also alleviate impacts to water quality and aquatic habitat.
Maintenance practices for roadside vegetation also determine the storm water quality of road runoff. Restrictions on the use of herbicides and pesticides on roadside vegetation and training to ensure that employees understand the proper handling and application of pesticides and other chemicals can help prevent contamination of runoff. Selection of roadside vegetation with higher salt tolerances will also help to maintain vegetated swales that filter out runoff. For more information on vegetated stormwater practices, see the Fact Sheet on Filter Strips.
Bridge runoff may require additional maintenance practices to eliminate stormwater runoff impacts. In addition to some of the roadway practices listed above, there are practices in bridge siting and design that can help reduce water quality impacts. One is to avoid using bridge scupper drains for any new bridges and to routinely clean existing ones to avoid sediment and debris buildup. Scupper drains can cause direct discharges to surface waters and have been found to carry relatively high concentrations of pollutants (CDM, 1993). Program managers should consider endorsing retrofits of scupper drains with catch basins or redirecting water from these drains to vegetated areas to provide treatment. Other techniques such as using suspended tarps, booms and vacuums to capture pollutants (e.g. paint, solvents, rust and paint scrapings) generated during bridge maintenance will also help reduce impacts to receiving waters. In addition, using deicers such as glycol, urea or Calcium Magnesium Acetate (CMA) reduces the corrosion of metal bridge supports that can occur when salt is used.
Generally speaking, limitations to instituting pollution prevention practices for road and bridge maintenance involve the cost for additional equipment and training. Since maintenance of roadways and bridges is already required in all communities, staffing is usually in place and alteration of current practices should not require additional staffing or administrative labor.
An area where limitations may arise is in location of new bridges. The availability and cost of land and other economic and political factors may dictate where the placement of a new bridge will occur. In that case, better design of the bridge to control runoff is required if it is being placed near sensitive waters. The practice of controlling pavement areas to limit impervious surface may also be restricted by community regulations on required widths for roadways and shoulders.
There is limited data available on the actual effectiveness of road and bridge maintenance practices at removing pollutants from stormwater runoff. Table 2 examines the effectiveness and cost of some of the operation and maintenance practices recommended for stormwater pollution control.
2. Road and Bridge Maintenance Management Practices: Cost and Effectiveness
(US EPA, 1993)
|Practice||Effectiveness (% Removal)||Cost|
|Maintaining Roadside Vegetation||Sediment
- 90% average
Phosphorus and Nitrogen - 40% average
COD, Pb, and Zn - 50% average
TSS - 60% average
succession allowed to occur
Reported Range: $50 -$200/acre/year
Street Frequent Cleaning:
TSS - 20%
COD - 5%
Pb - 25%
Street Infrequent Cleaning:
TSS - Not applicable
COD - Not applicable
Pb - 5%
Reported Range: $10 -$30/curb mile
|Litter Control||Not applicable||All are accepted as economical practices to control or prevent storm water impacts|
|General Maintenance||Not applicable|
|Minimizing Deicer Application||Not applicable|
While data may be limited on cost and effectiveness, preventative maintenance and strategic planning are time-proven and cost effective methods to limit contamination of stormwater runoff. It can be assumed that the management practices recommended will have a positive effect on stormwater quality by working to reduce pollutant loads and the quantity of runoff. Protecting and restoring roadside vegetation, removal of debris and sediment from roads and bridges, and directing runoff to vegetated areas are all effective ways to treat stormwater runoff. Other practices such as minimizing deicer application, litter control, and proper handling of fertilizers, pesticides and other toxic materials work to control some of the sources of stormwater pollution. Employing good road and bridge maintenance practices is an efficient and low cost means of eliminating some of the impacts of pollutants associated with road systems on local streams and waterways.
The maintenance of local roads and bridges is already a consideration of most community public works or transportation departments. Therefore, the cost of pollutant reducing management practices will involve the training and equipment required to implement these new practices. Cost data for some of the new practices that have been recommended is included in Table 2.
One area where costs may vary greatly is in the type of deicer selected for application. Table 3 includes a comparison of four different deicers and the cost for application. It should be noted that Calcium Magnesium Acetate (CMA) has a higher cost than the other deicers, but that reductions in corrosion to infrastructure, damage to roadside vegetation, and amount of material used may offset the higher cost.
Table 3. The Estimated Cost of Four Deicer Types (Caraco and Claytor, 1997)
|Deicer Type||Material Cost per Ton||Cost per Lane Mile per Season|
|Calcium Magnesium Acetate (CMA)||$650-$675||$12,960-$16,320|
|CG-90 Surface Saver||$185||$5,930-$6,150|
Bay Area Stormwater Management Agencies Association (BASMAA). 1995. Blueprint for a Clean Bay: Best Management Practices to Prevent Stormwater Pollution from Construction-Related Sites. Bay Area Stormwater Management Agencies Association. Oakland, CA.
Camp Dresser & McKee (CDM), et al. 1993. California Storm Water Municipal Best Management Practice Handbook. Stormwater Quality Task Force. Sacramento, CA.
Caraco, D. and R. Claytor. 1997. Stormwater BMP Design Supplement for Cold Climates. Center for Watershed Protection. Ellicott City, MD.
Ohrel, R. 1995. Rating Deicing Agents-Road Salt Stands Firm. Watershed Protection Techniques. 1(4): 217-220.
Ohrel, R. 1995. Choosing Appropriate Vegetation for Salt Impacted Roadways. Watershed Protection Techniques 1(4): 221-223.United States Environmental Protection Agency (US EPA). 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. US EPA, Office of Water. Washington, DC.