United States Office of Water EPA 816-F-02-019

Environmental Protection (4606) August 2002

Agency

Source Water Protection

Practices Bulletin

Managing Highway Deicing to

Prevent Contamination of

Drinking Water

We depend on clear roads and highways for safe travel and the continual flow of goods and

services. Deicing chemicals are used to clear roads covered by snow and ice during winter

weather. The runoff associated with

highway deicing may contain various

chemicals and sediment which have the

potential to enter surface and ground

water sources. This bulletin focuses on

the management of highway deicing

chemicals. See the bulletin on storm

water runoff for additional management

measures.

USE OF HIGHWAY DEICING

CHEMICALS

Each winter, state, county, and local

transportation departments stock their arsenal with the tools necessary to face whatever winter

storms may bring. This arsenal includes a variety of chemicals to melt snow and ice. This

preparedness has a high price tag; in the U.S., an estimated $2 billion is spent each year on

chemicals, materials, labor, and equipment for winter road maintenance.

The most commonly used and economical deicer is sodium chloride, better known as salt;15

million tons of deicing salt are used in the U.S. each year. Salt is effective because it lowers the

freezing point of water, preventing ice and snow from bonding to the pavement and allowing

easy removal by plows. However, the use of salt is not without problems. Salt contributes to

the corrosion of vehicles and infrastructure, and can damage water bodies, ground water, and

roadside vegetation. These issues have led to the investigation and use of other chemicals as

substitutes for and supplements to salt. Other deicing chemicals include magnesium chloride,

potassium acetate, calcium chloride, calcium magnesium acetate, and potassium chloride (these

are described below). 

Abrasives such as sand are often used in conjunction with deicing chemicals to provide traction

for vehicles, particularly on corners, intersections, and steep grades. However, when sand is

overused, it often ends up in the environment, either as dust particles that contribute to air

pollution or in runoff to streams and rivers. 
WHY IS IT IMPORTANT TO MANAGE HIGHWAY DEICING NEAR THE

SOURCES OF YOUR DRINKING WATER?

Salt and other deicing chemicals can concentrate in runoff, which enters surface water or

percolates through soil to reach ground water sources. It is difficult to generalize and quantify a

deicer’s effect on water bodies on a national level due to the complexity of stream environments

and lack of detailed data. Furthermore, runoff is often diluted once it enters larger bodies of

water, though it may affect smaller streams and creeks along highways. Generally, reservoirs

and other drinking water supplies near treated highways and salt storage sites are susceptible to

contamination, therefore special consideration and best management practices (BMPs) are

needed to protect them.

Sodium is associated with general human health concerns. It can contribute to or affect

cardiovascular, kidney, and liver diseases, and has a direct link to high blood pressure. Elevated

sodium levels in sources of drinking water could prove dangerous, and dietary intake of sodium

should be restricted. There is no MCL or health advisory level for sodium; however, there is a

Drinking Water Equivalent Level of 20 mg/L, a non-enforceable guidance level considered

protective against non-carcinogenic adverse health effects. Sodium is one of the contaminants

EPA is considering for a regulatory determination.

Chloride, for which EPA has established a national secondary drinking water standard of 250

mg/L, adds a salty taste to water and corrodes pipes. The water quality standard for chloride is

230 mg/L, based on toxicity to aquatic life.

Anti-caking agents are often added to salt, the most common of which is sodium ferrocyanide. 

There is no evidence of toxicity in humans from sodium ferrocyanide, even at levels higher than

those employed for deicing. However, some studies have found that the resulting release of

cyanide ions is toxic to fish.

AVAILABLE PREVENTION MEASURES TO ADDRESS HIGHWAY DEICING

This section provides an overview of several management measures. The reference materials

below can provide additional resources and information. Please keep in mind that individual

prevention measures may or may not be adequate to prevent contamination of source waters. 

Most likely, individual measures should be combined in an overall prevention approach that

considers the nature of the potential source of contamination, the purpose, cost, operational, and

maintenance requirements of the measures, the vulnerability of the source water, the public’s

acceptance of the measures, and the community’s desired degree of risk reduction.

The goal of these prevention measures is to minimize the loss of deicing chemicals due to

overuse and mishandling. Management of deicing chemicals focuses on reducing waste through

training and access to information on road conditions through the use of technology. Generally,

optimal strategies for keeping roads clear of ice and snow will depend on local climatic, site, and

traffic conditions, and should be tailored as such. Road maintenance workers should be trained

on these measures prior to the winter season. Personnel should also be made aware of areas

where careful management of deicing chemicals is particularly important, e.g., sensitive water

areas such as lakes, ponds, and rivers. Similarly, personnel should be aware of runoff concerns

from roadways that are near surface water bodies or that drain to either surface water or the

subsurface (e.g., through a dry well).
Anti-icing chemical application. 

RWIS Unit.

Alternative deicing chemicals include

calcium chloride and calcium

magnesium acetate (CMA). Another

alternative, sodium ferrocyanate,

should be avoided due to its toxicity to

fish. Although alternatives are usually

more expensive than salt, their use may

be warranted in some circumstances,

such as near habitats of endangered or

threatened species or in areas with

elevated levels of sodium in the

drinking water. Sensitive areas and

ecosystems along highways should be

mapped, and the use of deicing

alternatives should be targeted to those spots. Other considerations for using alternatives to salt

include traffic volume and extreme weather conditions. 

Each deicer works differently in various climatic and regional circumstances. For example, salt

is most effective at temperatures above 20° F. As an alternative, calcium chloride is effective

for temperatures that dip below 0° F and is fast acting, making it ideal for several areas of the

country. In New England, it is used as an alternative on roadways in areas with high sodium

concentrations in water. However, its high cost limits its use to these severe conditions. CMA

has had limited use on roadways because of its high cost and the fact that it is only effective

above 23° F; however, research shows few negative impacts on human health and the

environment. Combining deicers, such as mixing calcium chloride and salt, can be cost-effective

and safe if good information on weather conditions and road usage are available.

Road Weather Information Systems (RWIS) help maintenance centers determine current

weather conditions in a given location. Since the mid-1980’s,

increasing numbers of states are using this technology. 

Sensors collect data on air and pavement temperatures, levels

of precipitation, and the amount of deicing chemicals on the

pavement. The data are paired with weather forecast

information to predict pavement temperatures for a specific

area and determine the amount of chemicals needed in the

changing conditions. The strategically placed stations are 90

to 95 percent accurate. This information is also used for antiicing treatment (described below) to allow for chemicals to be

applied before the pavement freezes, reducing the amount of

deicing chemicals used. Several states are developing satellite

delivery of this information to maintenance workers. 

Anti-icing or pretreatment methods are increasingly being

used as a preventative tool. Anti-icing may require up to 90

percent less product than is needed for deicing after snow and

ice have settled on road surfaces. Deicing chemicals, often

liquid magnesium chloride, are applied to the pavement before

precipitation or at the start of a storm to lower the freezing point of water. Magnesium chloride

is effective in extreme cold temperatures (as low as -13° F) and is cost effective as well. 

Timing is everything in the process, and weather reports or RWIS data can assist highway

departments in determining the best time and place to apply chemicals. Anti-icing programs can

avoid over-application of deicing chemicals after a storm event because less ice and snow bonds

to the road. Several states reported improvements in traffic mobility and traction after using

anti-icing treatment techniques. The Pacific Northwest Snowfighters (PNS) Association

evaluates the safety, environmental preservation, and performance of winter road maintenance
products, including road deicers and anti-icers. PNS maintains, monitors, and updates a list of

approved products on its web site (see the section on additional information below).

Some states have installed fixed chemical spraying systems in highway trouble spots, such as on

curves and bridges, to prevent slippery roads. Chemicals are dispensed through spray nozzles

embedded in the pavement, curbs, barriers, or bridge decks. Using pavement temperature and

precipitation sensors, maintenance workers can monitor conditions and activate these fixed

maintenance systems. This technique saves materials and manpower and reduces deicing

operations during a storm. Though expensive to implement, these systems can be beneficial for

areas such as bridges that cross sensitive water bodies, because the risk of over-application is

reduced through the systems’ efficiency.

Spreading rates and the amount of deicer used are important considerations. Some studies

have shown that snow melts faster when salt is applied in narrow strips. In a technique known

as windrowing, spreading is concentrated in a four to eight foot strip along the centerline to melt

snow to expose the pavement, which in turn warms a greater portion of the road surface, and

causes more melting. This technique can be used on

lesser traveled roads. The amount used is important, since

too much deicer can be ineffective, as chemicals will be

dispersed (i.e., to the side of the road) where they cannot

melt snow and ice. If not enough deicer is used, the

chemical interaction with ice needed for melting will not

occur, wasting the application. Here is where knowledge

of the specific conditions of precipitation and the pavement

is needed. For example, shaded areas have lower

pavement temperatures and ice forms easier; therefore, more chemicals may be needed in these

spots. As a general rule, less chemicals should be used when the temperatures are rising, and

more should be used when they are falling.

Timing of application is an important consideration, as the strategy of anti-icing indicates. It

takes time for the chemical reactions of salt and other deicers to become effective, after which

a plow can more easily remove the snow. Sand should not be applied to roadways if more snow

or ice is expected, as it will no longer be effective once covered. Traffic volume should also be

taken into consideration, as vehicles can disperse deicers and sand to the side of the road. The

timing of a second application is dictated by the road conditions. For example, while the snow is

slushy on the pavement, the salt or deicer is still effective. Once it stiffens, however, plowing

should be done to remove excess snow.

Application equipment aids in the proper distribution of deicer chemicals. Many trucks are

equipped with a spinning circular plate that throws the chemicals in a semi-circle onto the road. 

A chute is used to distribute in a windrow, typically near the centerline of the road. Modified

spreaders prevent the over-application of materials by calibration or by the speed of the truck

and should be used. Spreader calibration controls the amount of chemicals applied and allows

different chemicals to be distributed at different rates. Equipment can also be used to vary the

width of the deiced area. General equipment maintenance and checks should be conducted at

least once a year to ensure proper and accurate operation. 

Plowing and snow removal are chemical-free options to keep roads clear of snow and ice. 

With plowing, less chemicals are needed to melt the remaining snow and ice pack. For specific

weather conditions, specialized snow plows may be used. For example, various materials, such

as polymers and rubber, can be used on the blade.

Pre-wetting of sand or deicing chemicals such as salt is a widespread practice. The resulting

brine mixture can provide faster melting. Salt can be pre-wetted through a spray as it leaves the

spreader. Sand is often pre-wet with liquid deicing chemicals just prior to spreading. This is an
effective method for embedding the sand into the ice and snow on the pavement. This

technique can pay for itself through the savings in materials because less sand or salt bounces

off the pavement and is lost.

Street sweeping during or soon after the spring snow melt can prevent excess sand and deicing

residue from entering surface and ground waters. Many road departments sweep streets at

least once in the spring, with either a broom sweeping or vacuuming vehicle. The sweepings

can be added to sand piles for future reuse.

Proper salt storage is a key measure to prevent the introduction of potentially harmful

contaminant loads to nearby surface and ground waters. It is important to shelter salt piles from

moisture and wind, as unprotected piles can contribute large doses of sodium chloride to runoff. 

Salt should be stored inside a covered, waterproof structure, such as a dome or shed. Soil type,

hydrology, and topography must also be appropriate for the storage area. Any runoff should be

cleaned up immediately and the collected brine reused. Spills during loading and unloading

should be cleaned as soon as possible. Salt storage sites should also be located outside of

wellhead and source water protection areas, away from private wells, sole source aquifers

(where feasible), and public water supply intakes. These areas should be identified so

application in these areas can be controlled and storage precautions enforced.

Ground water quality monitoring near salt storage and application sites should be performed,

at minumum, annually. Site-specific water table maps that show the direction of groundwater

flow should be reviewed, and monitoring performed up gradient and down gradient of storage

and application sites to detect contamination.

FOR ADDITIONAL INFORMATION

These resources contain information on deicing chemicals, related studies, or BMPs. All of the

documents listed are available for free on the Internet. State departments of transportation,

whose contact information can be found on the Internet or in the phone book, are also good

sources of information.

Caraco D. and R. Claytor. (1997) Storm Water BMP Design Supplement for Cold Climates.

Center for Watershed Protection. Ellicott City, MD. http://www.cwp.org/cold-climates.htm

Center for Watershed Protection, 8391 Main Street, Ellicott City, MD, 21043

http://www.cwp.org. CWP also maintains the Stormwater Manager’s Resource Center,

http://www.stormwatercenter.net

Church, P. and P. Friesz. (1993) Effectiveness of Highway Drainage Systems in Preventing

Road-Salt Contamination of Ground Water: Preliminary Findings. Reprinted from:

Transportation Research Record. No. 1420. National Research Council.

http://www.nap.edu/books/NI000009/html/index.html 

Granato, G.E. and K.P. Smith. (1999) Estimating Concentrations of Road-Salt Constituents

in Highway-Runoff from Measurements of Specific Conductance. U.S. Department of the

Interior. U.S. Geological Survey. Water Resources Investigation Report 99-4077.

http://ma.water.usgs.gov/ggranato/WRIR99-4077.pdf

Iowa Institute of Hydraulic Research, College of Engineering, The University of Iowa. (2001) 

The Use of Abrasives in Winter Maintenance: Final Report of Project TR 434. Wilfrid A.

Nixon, Ph.D., P.E. IIHR Technical Report No. 416. March.

http://www.sicop.net/Abrasives%20report.pdf
Michigan Department of Transportation. (1993) The Use of Selected Deicing Materials on

Michigan Roads: Environmental and Economic Impacts. December.

http://www.mdot.state.mi.us/mappub/deicing/

New England Interstate Water Pollution Control Commission. (1996) Source Protection: a

Guidance Manual for Small Surface Water Supplies in New England. March.

New Hampshire Department of Environmental Services. Road Salt and Water Quality.

Environmental Fact Sheet WMB-4. 1996.

http://www.des.state.nh.us/factsheets/wmb/wmb-4.htm

Ohrel, R. (1995) Choosing Appropriate Vegetation for Salt-Impacted Roadways. Watershed

Protection Techniques. 1(4): 221-223. 

http://www.stormwatercenter.net/Database_Files/Publications_Database_1Page92.html

Ohrel, R. (1995) Rating Deicing Agents: Road Salt Stands Firm. Watershed Protection

Techniques. 1(4): 217-220.

http://www.stormwatercenter.net/Database_Files/Publications_Database_1Page423.html

Pacific Northwest Snowfighters Association. Website includes a monitored and updated list of

approved deicing products. http://www.wsdot.wa.gov/fossc/maint/pns/htm/resources.htm

Road Management Journal. (1997) Using Salt and Sand for Winter Road Maintenance.

[Information reproduced with permission from the Wisconsin Transportation Bulletin No. 6,

March 1996.] December. http://www.usroads.com/journals/p/rmj/9712/rm971202.htm

The Salt Institute, 700 N. Fairfax Street, Suite 600, Fairfax Plaza, Alexandria, VA 22314-2026

703.549.4648. Website contains useful information on salt storage and its Sensible Salting

Program. http://www.saltinstitute.org

Seawell, Charles and Newland Agbenowosi. (1998) Effects of Road Deicing Salts on

Groundwater Systems.

www.ce.vt.edu/program_areas/environmental/teach/gwprimer/roadsalt/roadsalt.html

Transportation Research Board, National Research Council. (1991) Highway Deicing:

Comparing Salt and Calcium Magnesium Acetate. Special Report 235.

http://gulliver.trb.org/publications/sr/sr235.html

U.S. Department of Transportation, Federal Highway Administration. (1996) Manual of

Practice for and Effective Anti-icing Program: A Guide for Highway Winter Maintenance

Personnel. Publication No. FHWA-RD-95-202. June.

http://www.fhwa.dot.gov/reports/mopeap/eapcov.htm

USEPA. (2001) Contaminant Candidate List Preliminary Regulatory Determination Support

Document for Sodium, EPA 815-R-01-014, United States Environmental Protection Agency,

Office of Water. http://www.epa.gov/safewater/ccl/pdf/sodium_final_rsd.pdf

USEPA. (No Date) Shallow Injection Wells (Class V ). Available at

http://www.epa.gov/safewater/uic/classv.html

USEPA links to sites on Roads, Highways, and Bridges:

http://www.epa.gov/owow/nps/roadshwys.html
USGS. (1999) An Overview of the Factors Involved in Evaluating the Geochemical Effects of

Highway Runoff on the Environment. Open-File Report 98-630. 

http://ma.water.usgs.gov/FHWA/products/ofr98-630.pdf

USGS. (no date) National Highway Runoff Water-Quality Data and Methodology Synthesis

State Transportation Agency Reports. http://ma.water.usgs.gov/FHWA/qw/state.htm

Warrington, P.D. (1998) Roadsalt and Winter Maintenance for British Columbia

Municipalities. Best Management Practices to Protect Water Quality. December. 

http://wlapwww.gov.bc.ca/wat/wq/bmps/roadsalt.html

Winter Maintenance Virtual Clearinghouse, Federal Highway Administration. U.S. Department

of Transportation. http://www.fhwa.dot.gov/winter