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Reducing Road Salt Usage

Photo Jennifer Latzgo

Insert presenter’s name and organization here

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Insert here information about your organization

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Agenda

Causes and impacts of winter salting
What you can do at home
Best management practices: municipalities and contractors

4. Questions

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Causes and Impacts of �Winter Salting

Photo: Jennifer Latzgo

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Road salt use has doubled in the past 50 years

Carey Institute

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Why the Increase?

Increased development = more roads, parking lots, impervious surfaces that need deicers in winter
Fear of liability for slips and falls
Change in expectations
Incorrect understanding of “right” amount of salt

Photo Jennifer Latzgo

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De-Icing Products

Sodium chloride (rock salt)
Magnesium chloride
Calcium chloride

All contain chloride

Photo: Jennifer Latzgo

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It only takes 1 teaspoon of salt to permanently pollute 5 gallons of water. A 50- pound bag of salt (which how salt is normally sold to the individual consumer) can permanently pollute 10,000 gallons of water, which is a typical residential pool size.

Notes

When 50 pounds of sodium chloride (NaCl) is dissolved in 10,000 gallons of water, the resulting chloride concentration would be about 360 mg/L chloride ( or 360 ppm chloride) in the water. This is about 50% higher than the current EPA criteria for aquatic life. So each 50 pound bag of salt can pollute a whole swimming pool of water.”

Assuming:

∙ 50 pounds NaCl = 22.68 kg = 22,680,000 mg NaCl

∙ Chloride is 60.66% of the mass of sodium chloride

∙ 10,000 gallons = 37,854 liters

Step 1. Calculate chloride mass

Step 2. Calculate concentration:

Result

So, if 50 pounds of sodium chloride (NaCl) were completely dissolved in 10,000 gallons of water, the resulting chloride concentration would be approximately:

363 mg/L chloride (363 ppm chloride)

For context:

∙ EPA's secondary drinking water standard for chloride is 250 mg/L.

∙ 363 mg/L is about 45% above that level.

∙ It is also well above the U.S. EPA chronic aquatic life criterion of 230 mg/L chloride, often used as a benchmark for freshwater protection.

Illustration: Nichola Latzgo

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Where the Salt Comes From

Chloride loads measured in Policy-Porcupine New Hampshire watershed region (Burak, et al., 2008)

Research from New Hampshire gives us a good picture of where chloride in a watershed comes from. As you can see, about 50% comes from parking lots, which are mostly maintained by private contractors. After that, municipal roads account for 27%, state roads for 9%, and salt piles for 7%. The remainder comes from a variety of smaller sources, such as water softeners, food waste, and atmospheric deposition.

In Pennsylvania, there are some additional sources of chloride that aren't represented on this graph. These include wastewater treatment plants and industrial processes, as well as mining and well-drilling activities in certain parts of the state.

References:

Data for graph from: Total Maximum Daily Load (TMDL) Study For Waterbodies in the Vicinity of the I-93 Corridor from Massachusetts to Manchester, NH: Policy-Porcupine Brook in Salem and Windham, NH

https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/2020-01/final-chloride-tmdl-report-policy-brook.pdf

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Where Does the Salt Go?

Runoff
Storm drains
Directly to streams: causes salt spikes
Infiltrates ground → groundwater (45%)

Photo Mary Rooney

So, where does all that salt go once it’s been spread? As snow melts or rain falls, the salt dissolves and is washed off roads and parking lots. Some of it enters storm drains, like the one you see here, while some travels across the ground as stormwater runoff and flows directly into streams. This can cause sharp spikes in chloride levels during the winter. It’s estimated that as much as 45% can soak into the ground and eventually reach the groundwater. And that creates a longer-term problem. Once chloride gets into groundwater, it can remain there for years and gradually accumulate, causing groundwater to become increasingly salty over time.

References:

Minnesota Stormwater Manual. (2011). Environmental Impacts of Road Salt and Other de-icing Chemicals - Minnesota Stormwater Manual. State.mn.us. https://stormwater.pca.state.mn.us/index.php/Environmental_impacts_of_road_salt_and_other_de-icing_chemicals

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

https://pubs.acs.org/doi/10.1021/es101333u

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Gaining Stream

Illustration courtesy of the Groundwater Project

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Effects in our Watershed

Place graph or table here showing chloride trends in your local watershed, if you have some data OR a map of results from your testing

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Effects on Stream Ecology

This Photo by Unknown Author is licensed under CC BY-SA

Mayflies, Stoneflies, Caddisflies

Ephemeroptera, Plecoptera, Trichoptera (EPT)

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Relationship of Chloride & EPT Organisms

EPA National Aquatic Resources Survey (NARS) and Stroud Water Research Center

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Chloride Toxicity Levels

Organization	Long-term (chronic) chloride toxicity criterion (mg/l)	Short-term (acute) chloride toxicity criterion (mg/l)
U.S. Environmental Protection Agency (and many states) (1988)	230	860
Canadian Council of Ministers of the Environment (2011)	120	640
Ohio EPA, Macroinvertibrate Hazard Concentration (2021)	52	--
Maryland Biological Stressor Identification Process, Chloride Threshold Level (2009)	50	--
Natural Range in Pennsylvania	5 – 20 mg/l

This chart shows toxicity levels that have been used over the years in other states to regulate chlorides. The top number of 230 mg/l is the EPA number from 1988. However, the Maryland number of 50 mg/l at the bottom correlates much better with more recent research.

Currently, Pennsylvania doesn’t have a long-term chloride toxicity standard. PA Code Title 25, Chapter 93 establishes a value of 250 mg/l as the water quality standard applicable to chlorides. This standard was created in 1967 and serves as the baseline to protect drinkable water from taste concerns. It applies at the intake to the supply.

Notes:

1. The EPA long term standard is a 4-day average. The short-term standard is a one-hour average.

2. PA Code Title 25, Chapter 93.7 Table 3 is exact reference for 250 mg/L standard. This section also sets the OsmoticPressure standard at a Maximum 50 milliosmoles per kilogram. This standard can be referenced to chlorides but limited available laboratory capabilities for analysis of osmotic pressure adversely affect compliance monitoring.

Sources:

The “Natural Range in PA” data comes from data collected and presented in the PA Water Quality Network as reviewed by Stroud Research Center

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Effects on Other Aquatic Wildlife

Impacts zooplankton
Causes increased deformities and mortality of wood frog tadpoles
Reduces rates of fish hatching, larval development & overall growth
Inhibits growth of aquatic plants

Photo by Jennifer Latzgo

Photo Jennifer Latzgo

So, we’ve talked about the effects of chloride on mayflies, caddisflies, and stoneflies, but unfortunately, the impacts extend to many other forms of aquatic life as well. Chloride can interfere with osmoregulation—the process aquatic organisms use to maintain the proper balance of water and salts in their bodies—and can also contribute to reduced oxygen levels in the water.

Elevated chloride levels can affect zooplankton, which are an important part of the aquatic food web. Studies of wood frog tadpoles have found increased deformities and mortality, while fish can experience reduced hatching success, impaired larval development, and slower growth. Together, these effects can have consequences that extend throughout the aquatic ecosystem.

References:

Górecka, A., Szklarek, S., Frankiewicz, P. et al. Does winter application of road salt affect zooplankton communities in urban ponds?. Aquat Sci 85, 111 (2023). https://doi.org/10.1007/s00027-023-01009-y

Effects of road de-icing salt (NaCl) on larval wood frogs (Rana sylvatica)

https://pubmed.ncbi.nlm.nih.gov/16159689/

Collins, S. J., & Russell, R. W. (2009). Toxicity of road salt to Nova Scotia amphibians. Environmental Pollution, 157(1), 320–324. https://doi.org/10.1016/j.envpol.2008.06.032

Environmental Hazards of Road Salt

https://extension.psu.edu/environmental-hazards-of-road-salt#:~:text=This%20exponential%20increase%20in%20road,amounts%20of%20impermeable%20land%20cover.

Impact of salinization on lake stratification and spring mixing:

https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lol2.10215

Hintz, W. D., & Relyea, R. A. (2017). Impacts of road deicing salts on the early-life growth and development of a stream salmonid: Salt type matters. Environmental Pollution (Barking, Essex : 1987), 223, 409–415. https://doi.org/10.1016/j.envpol.2017.01.040

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Effects on Ponds and Lakes

Road salt increases the density of water and reduces oxygen levels
Dense water sinks to bottom of ponds and lakes
Creates “dead zone”
Interferes with natural mixing (turnover)

Photo: Jennifer Latzgo

Road salt can also have significant effects on ponds and lakes. When salt enters these waterbodies, it makes the water denser. That heavier, saltier water tends to sink and collect near the bottom.

Normally, deeper lakes and ponds undergo seasonal turnover, when water from the surface and bottom mix. This mixing is extremely important because it helps replenish oxygen in deeper water. But when dense, salty water remains trapped at the bottom, it can interfere with that natural mixing process.

As a result, oxygen levels near the bottom can become very low, potentially creating what we sometimes call a “dead zone.” These low-oxygen conditions can make the habitat unsuitable for fish and other aquatic organisms and disrupt the overall health of the ecosystem.

References:

Sibert, R. J., Koretsky, C. M., & Wyman, D. A. (2015). Cultural meromixis: Effects of road salt on the chemical stratification of an urban kettle lake. Chemical Geology, 395, 126–137. https://doi.org/10.1016/j.chemgeo.2014.12.010

Norrstrom, A., & Bergstedt, E. (2001). The Impacts of Road De-Icing Salts (NaCl) on Colloid Dispersion and Base Cation Pools in Roadside Soils, Water, Air, &Salt Pollution [Review of The Impacts of Road De-Icing Salts (NaCl) on Colloid Dispersion and Base Cation Pools in Roadside Soils, Water, Air, &Salt Pollution]. Springer Nature Link, 27, 281–289. https://link.springer.com/article/10.1023/A:1005221314856#citeas

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Effects on Soil and Plantings

Road salt can travel 10 meters off road edge via “bounce and scatter”

Heavy traffic & wind – 300 feet

Chemicals in road salt:

Reduce soil permeability and fertility
Increase alkalinity and density
Impact soil microbes: reduction in activity, biomass, community structure

Photo: Mary Rooney

Salt also affects the soil and plantings. This picture shows grass that has been killed alongside a heavily salted path. Studies have shown that with bounce and scatter, road salt often travels as far as 10 meters from the edge of the road. If there is heavy traffic that grinds it into finer particles, and a lot of wind, it can be blown as far as 300 feet. Once in the soil, the chemicals in salt can reduce soil permeability and fertility while increasing its alkalinity and density. They can also reduce the activity, biomass, and community structure of soil microbes.

References:

UMass Extension: The Impact of Salts on Plants and How to Reduce Plant Injury form Winter Salt Applications:

https://ag.umass.edu/landscape/fact-sheets/impact-of-salts-on-plants-how-to-reduce-plant-injury-from-winter-salt

Special Report 235. Highway Deicing. Comparing Salt and Magnesium Acetate. Transportation Research Board:

https://onlinepubs.trb.org/onlinepubs/sr/sr235.html

Minnesota Stormwater Manual:

https://onlinepubs.trb.org/onlinepubs/sr/sr235.html

Yan, N., Marschner, P., Cao, W., Zuo, C., & Qin, W. (2015). Influence of salinity and water content on soil microorganisms. International Soil and Water Conservation Research, 3(4), 316–323. https://doi.org/10.1016/j.iswcr.2015.11.003

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Damage to Infrastructure

$5 billion a year:

Roads
Bridges
Culverts
Concrete structures
Vehicles
Flooring

Photo: Avinash Kumar via Pixabay

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Damage to Drinking Water Infrastructure

Higher chloride levels can increase corrosion in water pipes
Can cause lead and toxic metals to leach into drinking water

DonnaMarie113. rusty PIPE DREAMS. Published April 22, 2012. Licensed under Creative Commons Attribution 3.0 (CC BY 3.0). Source: [image URL]. License: https://creativecommons.org/licenses/by/3.0/

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Green Infrastructure

Riparian buffers and rain gardens only slow infiltration by salt
Chloride is not retained by soil particles
Chloride can damage vegetation
Chloride alters microbial activity that helps manage other pollutants
Chemicals in salt degrade soil and makes riparian buffers less effective in soil stabilization

Photo : Tyler Groh

Many people wonder if green infrastructure, such as riparian buffers and rain gardens, is effective at mitigating salt pollution. Riparian buffers and rain gardens can help slow the movement of road salt and reduce the amount of salt-laden runoff that reaches streams and lakes. However, chloride is highly mobile and is not easily retained by soils, allowing it to move readily through the environment. This is because chloride ions are negatively charged and are generally not retained by soil particles, allowing them to move through soil and water. Chloride can also reduce the effectiveness of green infrastructure by damaging vegetation. It has also been found to alter microbial processes that help manage other pollutants. Additionally, chemicals in road salt can degrade soil conditions and reduce the ability of riparian buffers to stabilize soil and provide other environmental benefits

References:

Impacts of salt loading on nutrient and metal processing in stormwater bioretention.

https://cbtrust.org/wp-content/uploads/20231001_CBTfinalreport_McPhillips.pdf

Can Natural Buffers Help Mitigate Road Salt Pollution?

https://watersheds.ca/can-natural-buffers-help-mitigate-road-salt-pollution/#:~:text=Over%20time%20and%20with%20excessive,et%20al.%2C%202008).

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�Effects on Drinking Water

Drinking water comes from rivers and groundwater
Water treatment does not remove salt
Salty water is problematic for people with hypertension & people on dialysis
Reverse osmosis extremely costly

AI illustration: Jennifer Latzgo

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What You Can Do at Home

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Shovel first
Salt may not be necessary
12 oz coffee mug of salt sufficient for 20-foot driveway or 10 sidewalk paving squares
Crystals should be approx. 3” apart
Sweep up excess salt after storm
Cover small areas with tarps
More salt doesn’t melt ice faster – you don’t need to feel “crunch”

Photo courtesy of Izaak Walton League

First of all, shovel frequently so that any snow that falls does not turn to ice. In many situations, it’s not necessary to put salt down because the sun and the air can clear the remaining snow and moisture. If salt is needed, apply it sparingly.

If you look at the picture on the left, you can see the wrong and the right amount of salt. A 12-ounce coffee mug of salt is sufficient for a 20-foot driveway or 10 sidewalk squares. The salt particles should be about 3 inches apart like in the right-hand picture. After the storm, sweep up any excess salt and save it for the next time it snows. If you have small areas like steps, cover them with tarps before the snow comes. And remember that putting down more salt does not make the ice melt faster – you don’t need to feel that “crunch” underfoot for the salt to be effective.

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Best Management Practices (BMP’s): Municipalities and Contractors

Proven methods
Reduce road salt usage
Maintain safety

Photo: Courtesy Hilltip

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Calibrating Equipment

50% reduction in salt usage
Performed annually
Whenever deicing material changed
PennDOT: 100 – 300 lbs/lane mile

Photo Marilee Ebus

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Pre-Treatment and Pre-Wetting with Brine

Pre-treatment with brine:

23.3% solution salt and water
Applied before storm – prevents ice from bonding with road surface
50% reduction in salt use
Effective for parking lots and sidewalks

Pre-wetting salt – 30% reduction

Photo Jennifer Latzgo

Brining is another very effective way to reduce salt use. Pretreating roads with brine can reduce salt use by as much as 50%. Brine is a 23.3% solution of salt and water that is sprayed onto the pavement before a storm. This photo shows brine stripes on a city street in Allentown.

One advantage of brine is that it can be applied well in advance of a storm. Once it dries on the pavement, the salt remains in place until precipitation begins. It works by preventing snow and ice from bonding to the pavement, which makes plowing much easier and more effective. It also begins working more quickly than dry rock salt and can be very effective on parking lots and sidewalks.

Brine can also be used to pre-wet rock salt as it is being spread. The moisture helps the salt stick to the pavement instead of bouncing and scattering off the road, and it allows the salt to begin working more quickly. Pre-wetting can reduce salt use by around 30%.

References

Cary Institute of Ecosystem Studies: Road Salt The Problem, The Solution, and How to Get There.

https://www.caryinstitute.org/sites/default/files/downloads/report_road_salt.pdf

Snow and ice Management for Parking Lots and Sidewalks What do Property Managers Need to Know?

https://saltsmart.org/wp-content/uploads/2023/12/Salt_Smart_Property_Manager_Booklet_v4_compressed.pdf

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Segmented Snow Plows

Blade has short, spring-loaded sections
Cleaner scrape
30% reduction in salt usage

Photo courtesy Metal Pless

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Road Condition Information Systems

In-road, pole-mounted and truck-mounted sensors
Detailed real-time data on road conditions:

Surface temperature
Precipitation
Deicer
Amount of grip

Hyper-local weather forecasts
Better informed decisions
Significant reduction in salt use

Images: Permission Vailala

Municipalities can also use road condition information systems, which use different types of sensors to provide detailed, real-time information about road and weather conditions. The sensors shown in the top picture are embedded in the pavement, while those in the bottom picture are mounted on poles alongside the road. Sensors can also be mounted directly on maintenance vehicles.

These systems can provide information such as pavement temperature, precipitation type, the presence of deicing materials on the road, and the amount of grip or friction on the pavement. Data from sensors combined with hyper localized weather forecasts provide real-time information, which allows winter maintenance crews to make better decisions about when to treat roads, what materials to use, and how much to apply. This can reduce unnecessary salt use while also saving money on materials, fuel, and labor.

References:

Vaisala: Case Study – Innovation and automation cuts road salt use in half

https://www.vaisala.com/en/case/innovation-automation-cuts-road-salt-use-half

Xweather Article - https://www.xweather.com/blog/article/wx-horizon-x-cranberry

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Salt Storage

Under cover
Larger piles: roofed structures
Smaller piles: weighted tarps
Impervious surface
Inspected and maintained regularly

Photo: Jennifer Latzgo

Proper salt storage is also important because uncovered salt piles can become a significant source of chloride pollution. When rain or melting snow comes into contact with the pile, it dissolves the salt and can carry highly concentrated chloride into nearby soil, groundwater, and surface water.

Larger salt piles should be stored under permanent roofed structures, while smaller piles can be protected with securely weighted, waterproof tarps. Salt should also be stored on an impervious surface to prevent it from leaching into the ground. Finally, storage areas should be inspected regularly to make sure the salt remains properly covered and contained.

References:

Stormwater Best Management Practice, Deicing Material Application and Storage:

https://www.epa.gov/system/files/documents/2021-11/bmp-deicing-material-application-and-storage.pdf

Southwestern Water Resource Center, PennDOT: Quick Resource Guide for Winter Maintenance BMP’s

https://spcwater.org/wp-content/uploads/2020/01/WinterMaintGuidebook.pdf

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Staff Training

All staff trained annually
PennDOT Local Technical Assistance Program (LTAP)
Training for management and municipal employees

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More Information:

paroadsaltaction.org

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