United States
Environmental Protection
Agency
Office of Water
(4606)
EPA816-F-02-019
August 2002
&EPA 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.
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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).
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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.
Anti-icing chemical application.
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 anti-
icing 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
RWIS Unit ice ^ave 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
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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
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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 Storm water Manager's Resource Center,
http ://www. storm watercenter. 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
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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 lPage92.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 lPage423.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.eom/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/ro adsalt.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/roadshwvs.html
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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
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