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Road Salt


Published online at Louisville, Kentucky USA -

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The U.S. Environmental Protection Agency (EPA) has

established water quality standards for chloride for the

protection of aquatic life.

Water bodies are considered “impaired” if these standards are violated.

The water quality standard for chronic exposures is a four-day average concentration of 230 mg/ L not to be exceeded more than once every three years. The water quality standard for acute exposures is 860 mg/L for a one-hour average with a similar three year recurrence interval.

Effect on the Environment

Aquatic Biota. Road-salt loadings in surface waters vary with regional climate conditions, season, and air temperature fluctuation. Snowmelt may proceed gradually overall, but it increases dramatically following application of road salt. Shock loads of salt to aquatic ecosystems might last less than a day following application, with concentration decreasing thereafter. Salt held in solution in snow or deposited on surface soil layers is readily dissolved by rain and can be transported to receiving waters in runoff. Prolonged retention of salt in streambeds or lakebeds decreases dissolved oxygen and can increase nutrient loading, which in turn promotes eutrophication.

Toxicity responses of aquatic organisms to NaCl vary. Laboratory studies report that the LC50 for six freshwater fish and crustacean species exposed to NaCl for one day ranged from 2,724 to 14,100 mg/l with a mean of 7,115 mg/l (Cowgill et al., 1990). These values decreased significantly as exposure time increased. The LC50 for 17 species of fish, amphibians, and crustaceans exposed to NaCl for seven days ranged from 1,440 to 6,031 mg/l with a mean of 3,345 mg/l (EC, 2000).

Reports of chloride concentrations in highway runoff run as high as 19,135 mg/l. Salt tolerance of fishes ranges from 400 to 30,000 mg/l, greater than the salt concentration of seawater. A seven-day exposure of 1,000 mg/l is lethal to rainbow trout (NRC, 1991). While an estimated 10% of aquatic species will exceed their critical tolerance values for chloride with prolonged exposure to concentrations above 220 mg/l, many of the macroinvertebrates upon which the more tolerant species feed might exhibit lower tolerances. Stream studies in northern New York revealed that benthic diversity decreases as salinity increases and dominance of salt-tolerant invertebrates is synchronous with periods of road-salt application. Salinity stresses the periphyton community upon which benthic grazers forage and inhibits microbial processing of leaf litter (EC, 2000). Reduction of primary productivity causes repercussions at the top of the food chain in addition to the stress salinity imposes on the organisms themselves. The presence of salt in aquatic ecosystems also releases toxic metals from sediment into the water column and impairs distribution and cycling of oxygen and nutrients.

New salt spreader trucks


A Fresh Look at Road Salt: Aquatic Toxicity and Water-Quality Impacts on Local, Regional, and National Scales

“Road-salt runoff poses an increasing threat to aquatic ecosystems that are influenced by urban land use and transportation corridors. Four broad issues suggest that roadsalt runoff is a serious and increasing threat to the nation’s receiving waters.

First, there is a multitude of historical evidence documenting detrimental effects of road salt on water chemistry and aquatic life . . .

Second, road salt usage in the United States has increased steadily beginning in the 1940s through the current decade . . .

Third, urban development is increasing each year (10), which increases the amount of impervious area on which winter deicing operations are conducted . . .

Fourth, chloride, and to a large degree sodium, the two primary ions in road salt, remain in solution, making it difficult with present-day technology to design effective management practices for reduction of road-salt loadings to receiving waters after application.

Currently, reduction in usage appears to be the only effective road-salt-runoff management strategy.”

Key Findings:

Nationally: During the winter, samples from fifty-five percent of northern streams in this study had chloride levels that exceeded USEPA chronic water-quality criteria, indicating potential toxicity. Samples from twenty-five percent of the streams exceeded acute water-quality criteria.

Regionally: In eastern and south-central Wisconsin, potential toxicity was found during winter at all urban streams studied, with lingering effects at some streams in the summer.

  1. During winter, 100 percent of the streams monitored had chloride levels that exceeded the USEPA chronic water quality criteria with fifty-five percent of samples exceeding acute water quality criteria.

  2. Chloride levels higher than 10,000 milligrams per liter were observed at times during winter de-icing periods—much greater than the chronic water-quality criteria of 230 milligrams per liter and the acute criteria of 860 milligrams per liter.

  3. Chloride levels increased as urbanization percentage in the watershed increased.

Locally: In Milwaukee, more than half of the samples collected from streams during winter de-icing periods were toxic.

  1. Samples from seven of 13 streams collected during 2007 de-icing periods were toxic in bioassay tests.

  2. Chloride levels in 12 out of these 13 streams exceeded USEPA chronic water quality criteria; eight of 13 exceeded acute criteria.

  3. In long-term testing of one Milwaukee stream between 1997 and 2008, seventy-two percent of 38 samples collected during the winter were toxic in bioassay tests.

This USGS report is published in the journal Environmental Science and Technology and is available as a free download online at

There are a variety of environmental tests that may be or have been specified for use with liquid or solid ice-control products. Many agencies, for example, limit the amount of various constituents to certain levels (typically expressed in allowable parts per million of the constituent). The PNS, for example, limits amounts of Arsenic, Barium, Cadmium, Chromium, Copper, Lead, Mercury, Selenium, Zinc, Phosphorus and Cyanide.

Tests for these are standard and if an agency is subject to limitations in regard to these or other constituents, then all suppliers should be required to provide proof that their product does indeed satisfy these limitations.

Kentucky uses 415,000 tons of road salt

with toxic anti-caking agents

Courier-Journal reported: Kentucky transportation cabinet orders more salt   January 31, 2011

“WPSD-TV in Paducah reports the Kentucky Transportation Cabinet will get another 15,000 tons of salt from Kansas City and will distribute it statewide.

Transportation Cabinet spokesman Keith Todd says the state has used more than 400,000 tons of salt so far this winter — about 24,000 tons more than was used all of last winter. Todd says the state orders salt periodically to match the amounts used for each snowstorm.”

Road salt uses cyanide compounds as an anti-caking agent. 415,000 tons of salt spilled on state roads will cause many fresh water streams to exceed 230 mg/L concentrations of chloride that has been adopted standard as protective of freshwater habitat. Fishermen, people that enjoy wild and rural Kentucky should oppose and complain about Kentucky's salt poisoning of freshwater streams and groundwater with 415,000 TONS of road salt. Don't scratch your head and wonder where the fish and birds went?

Salt concentrations build up over many years and remain high in the soil and groundwater. Groundwater seeping into streams often keeps water flowing during the driest periods, typically in summer. If the groundwater is salty, the stream will be salty. Increases in groundwater salinity have indeed been observed in the northeastern U.S. and Canada (11, 12). For example, a survey of 23 springs in the greater Toronto area found Cl concentrations topping 1,200 mg·liter-1 arising from road salt use (11). This groundwater salinity is the primary concern for long-term potable water supply. Once groundwater becomes salty, it typically will take decades to centuries for the salts to disappear, even when road salt use ends.

Many Urban Streams Harmful to Aquatic Life Following Winter Pavement De-Icing: 

The use of salt to de-ice pavement can leave urban streams toxic to aquatic life, according to a new U.S. Geological Survey study on the influence of winter runoff in northern U.S. cities, with a special focus on eastern Wisconsin and Milwaukee.

More than half of the Milwaukee streams included in this study had samples that were toxic during winter de-icing. In eastern and southern Wisconsin, all streams studied had potentially toxic chloride concentrations during winter, with lingering effects into the summer at some streams. Nationally, samples from fifty-five percent of streams studied in 13 northern cities were potentially toxic; twenty-five percent of the streams had samples that exceeded acute water quality criteria.

Toxicity was measured by direct testing of organisms in samples during the local study component; in the regional and the national study components, observed chloride levels were used to assess potential toxicity.

"While winter driving and walking safety are the priority in treating pavements, this study suggests the need for advancements that will reduce salt loads to surface waters without compromising safety," said Matthew C. Larsen, USGS Associate Director for Water.

"We expected to see elevated chloride levels in streams near northern cities during the winter months," said Steve Corsi of the USGS Wisconsin Water Science Center. "The surprise was the number of streams exceeding toxic levels and how high the concentrations were," said Corsi, who led the study.

"This study shows that chloride contamination of urban streams is a problem in many places; it's not just a Milwaukee problem," said Corsi.

While road de-icing accounts for a significant portion of salt applications, it is not the only source. Salt is also used by many public and private organizations and individuals to de-ice parking lots, walkways and driveways.

Corrosion of bridges

“The massive spreading of salt on roads and highways unfortunately has also some serious negative effects. Besides environmental concerns, one of the major criticisms of salt use for deicing is its contribution to corrosion of metal in steel bridges, road vehicles, reinforced concrete (bridge decks, parking garages), and any other metallic objects in close proximity to roads and highways (lampposts, statues, etc.).

Although another effective but less corrosive deicing agent is commercially available (calcium magnesium acetate or CMA), its price is apparently too high for wide usage. One ton of CMA costs $300-600 as opposed to $20-70 for rock salt. The use of CMA has thus been confined to areas where corrosion could cause critically important damage such as for airport winter maintenance. It can therefore be expected that the road environment will likely remain corrosive well into the future.”


Cargill website on deicing salts


Deicing Salt – Recognizing The Corrosion Threat

File Format: PDF/Adobe Acrobat

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Concrete damage


Wang, K., D. E. Nelsen, and W.A. Nixon, (2006). “Damaging Effects of Deicing

Chemicals on Concrete Materials,” Journal of Cement and Concrete Composites, vol.

28, issue 2, pp. 173-188, February, 2006.

The damaging impact of various deicing chemicals and exposure conditions on concrete materials was investigated. Five deicing chemicals (sodium chloride, calcium chloride with and without a corrosion inhibitor, potassium acetate, and an agricultural product) were studied. Freezing-thawing (F-T) and wetting-drying (W-D) exposure conditions were considered. Mass loss, scaling, compressive strength, chemical penetration, and micro-structure of the paste and concrete subjected to these deicing chemicals and exposure conditions were evaluated. Results indicated that the various deicing chemicals penetrated at different rates into a given paste and concrete, resulting in different degrees of damage. Among the deicing chemicals tested, two calcium chloride solutions caused the most damage. Addition of a corrosion inhibitor into the calcium chloride solution delayed the onset of damage, but it did not reduce the ultimate damage. Chloride-related deicing chemicals often brought about leaching of calcium hydroxide, as well as chemical alterations in concrete. Potassium acetate caused minor scaling, associated with alkali carbonation of the surface layer of concrete. Although producing a considerable number of micro-pores on the surface of the samples, the agricultural deicing product resulted in the least chemical penetration and scaling damage of paste and concrete.

Usage of rock salt for deicing in the U.S. in thousands of tons.

(Data from the Salt Institute


This graph of national salt usage since 1940

A clear alarm bell is ringing for water pollution caused by deicing salt --Metro politicians are not listening

Despite clear, scientific evidence that we are polluting our groundwater resources by spreading road salt, the business is just too lucrative to stop. State and municipal politicians are helpless to shut down the busy marketplace buying, selling, moving, storing and using road salt in the millions of tons. The industry is powerfully protected by lobbying firms hired by the major trade associations. Below are scenes from the Louisville Metro area showing heavy use of road salt. No serious discussion of the long term impacts of road salt use on Louisville groundwater resources has been held by Metro Council or the Mayor. Major salt suppliers enjoy a lucrative market in Louisville and the state. Millions of dollars of corrosion damage to our roads and bridges is caused by deicing salt application. In KIPDA’s auto-centric Horizon 2030 Transportation Plan, long term use of millions of tons of deicing salt is integrated without any challenge.  Mass transit projects using fixed rail would reduce the use of road salt. None are planned.  

“ The perception that the damage is as bad as it is likely to get once in equilibrium is simply foolish. The Toronto study proved how devastating the present levels of chloride and sodium could become. Each area has distinctive hydrogeologic conditions, and these should also be taken into account. The question administrators now need to consider is, "Will present benefits of road salt use outweigh the eventual costs to drinking water?"


Below: Pictures of ice trucks in winter 2010 in Louisville and showing wastage by over application due to crude mechanical spreaders. Salt tends to accumulate on the rotating plate and be deposited in a clump when spreading starts. Large piles of salt delivered by rail and barge await winter use. Corroded rusting hulks of salt truck beds. 

KYTC District Five Deicing Operations Cost           2010 --   $ 7,233,729
A clear alarm bell is ringing . . .

“Chloride concentrations are increasing at a rate that threatens the availability of fresh water in the northeastern United States. Increases in roadways and deicer use are now salinizing fresh waters, degrading habitat for aquatic organisms, and impacting large supplies of drinking water for humans throughout the region. 

We observed chloride concentrations of up to 25% of the concentration of seawater in streams of Maryland, New York, and New Hampshire during winters, and chloride concentrations remaining up to 100 times greater than unimpacted forest streams during summers. 

 Our analysis shows that if salinity were to continue to increase at its present rate due to changes in impervious surface coverage and current management practices, many surface waters in the northeastern United States would not be potable for human consumption and would become toxic to freshwater life within the next century.”

Increased salinization of fresh water in the northeastern United States
Sujay S. Kaushal et al   See it     HERE
“The use of rock salt (NaCl) on U.S. roads has skyrocketed in the last 65 years, and chloride (Cl) concentrations in waters of the northeast have risen as a consequence. 

The mobility of salt in water leads to its potential problems in the environment. These problems include toxicity to plants and fish, groundwater contamination, and human health interactions, particularly salt intake and hypertension. In consequence, researchers have been monitoring increased salt concentrations in streams and groundwater for decades.

Even more importantly, if results are extrapolated into the next century, the data suggest that many rural streams in the Northeast will have baseline salt concentrations >250 mg/liter, the generally accepted cutoff for potable water and a level at which chronic toxicity occurs for many freshwater species.”

From icy roads to salty streams       See it      HERE
Robert B. Jackson , Esteban G. Jobbágy



The chart above is taken from a 1993 Kentucky Geological Survey of Groundwater chloride concentrations in the KIPDA region of Kentucky and southern Indiana. The data below is 2006 -2008 data supplied by the Louisville Water Company in response to an Open Records Request and shows astronomical chloride poisoning of the groundwater in the vicinity of River Road and Zorn Avenue. Nearby, the giant salt pile of the River Road Terminal sits partially covered.

LWC Data - Test results at Zorn Avenue groundwater test wells ZMW-9A, 9B, 9C from 9-06 to 3-08

9-19-06        Na(mg/L)     Chloride (mg/L)

ZMW-9A         2900           4900

ZMW-9B        1700            2700

ZMW-9C        1600            2600

9-29-06        Na(mg/L)     Chloride (mg/L)

ZMW-9A         3700           5100

ZMW-9B        1700            2800

ZMW-9C        1500            2500

10-4-06        Na(mg/L)     Chloride (mg/L)

ZMW-9A         2800           5000

ZMW-9B        1800            3100

ZMW-9C        1600            2400

11-14-06        Na(mg/L)     Chloride (mg/L)

ZMW-9A         3200           5300

ZMW-9B        1600            2900

ZMW-9C        1300            2400

12-13-06        Na(mg/L)     Chloride (mg/L)

ZMW-9A         6900           5800

ZMW-9B        1600            2900

ZMW-9C        2800            2100

1-10-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         3500           6000

ZMW-9B        1900            3000

ZMW-9C        1100            1800

2-14-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         7400           6100

ZMW-9B         4300            2600

ZMW-9C        1600            2000

See a road salt barge terminal at:


Graph from--

From icy roads to salty streams       See it      HERE

Robert B. Jackson , Esteban G. Jobbágy

The U.S. Environmental Protection Agency (EPA) has

established water quality standards for chloride for the

protection of aquatic life.

Water bodies are considered “impaired” if these standards are violated.

The water quality standard for

chronic exposures is a four-day average concentration of 230 mg/ L not to be exceeded more than once every three years.

The water quality standard for

acute exposures is 860 mg/L for a one-hour average with a similar three year recurrence interval.*

3-13-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         3700           6800

ZMW-9B        1700            3000

ZMW-9C        1200            2100

4-10-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4000           7000

ZMW-9B        1800            3100

ZMW-9C        1300            2400

5-15-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4400           7500

ZMW-9B        1800            3000

ZMW-9C        1300            1800

6-13-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4700           7600

ZMW-9B        1900            3200

ZMW-9C        1000            1800

7-12-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4000           7100

ZMW-9B        2000            3000

ZMW-9C        1000            1700

8-14-07        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4300           7700

ZMW-9B           430           3600

ZMW-9C           210           1700


3-24-08        Na(mg/L)     Chloride (mg/L)

ZMW-9A         4900           8700

ZMW-9B         2400           4200

ZMW-9C        1600            3000

  1. *Relating Road Salt to Exceedances of the Water Quality Standard for Chloride in New Hampshire Streams

Philip R. Trowbridge*, J. Steve Kahl, Dari A. Sassan, Douglas L. Heath§ and Edward M. Walsh

Environ. Sci. Technol., 2010, 44 (13), pp 4903–4909



“According to the National Research Council (NRC), road-salt use in the United States ranges from 8 million to 12 million tons of NaCl per year. Massachusetts, New Hampshire, and New York report the highest annual road-salt loadings, with Massachusetts the highest at 19.94 tons/lane-mi./yr. New York’s annual road-salt loading averages 500,000 tons/yr. or 16.6 tons/lane-mi./yr. (NRC, 1991). The New York State Department of Transportation (NYSDOT) requires a road-salt application rate of 225 lb./lane-mi. for light snow and 270 lb./lane-mi. for each application during rapidly accumulating snow (NYSDOT, 1993).”

                            LOUISVILLE’S ROAD SALT ARMY


293 employees and 169 pieces of equipment

to clear 1,362 miles of road in Louisville

    - 23 brine distributors; each holds 1,600 gallons of brine

    - One brine maker, which produces 5,000 gallons of brine per hour

40,000 tons of salt available for treating roads:

    - 15,000 tons of salt on hand at 7 storage facilities, including 4 domes

    - 25,000 tons of salt stored underground for emergency reserve

    -3,000 tons of salt to be delivered later in the season

Welcome to©                                                   INDEX PAGE for all articles

Overpass on I-71 above the Butchertown Greenway showing deicer corrosion  of steel reinforcing and concrete disintegration

See related pages:

Sherman Minton Bridge corrosion from Roadsalt  Here

Gallery of infrastructure corrosion  Here

Related webpage 
Peaks of Conductivity