Road Salt
Heavy salt application on roads is damaging the Watershed
NY State leads the nation in use of road salt and our watersheds are paying the price. Road salt, which is the mineral halite (NaCl), is probably one of the most widely dispersed contaminants in the Mohawk Watershed. It is liberally and freely applied as a de-icer on roads and highways, but the fate of that salt in the watershed is a major concern. Since the early 1950s, chloride levels in the river have increase by over 300% and this is year round, not just in the winter.
The increase in salt use in the last few decades is significant. There are two principal sources and pathways for concern: surface water and groundwater. NY State purchases and stores over a million tons of salt annually, and most of that salt is applied to road and highways. But salt dissolves and enters surface streams and rivers, or percolates into groundwater. Thus we need to be concerned about storage facilities and local groundwater contamination below these facilities, in addition to contamination of regional groundwater and surface waters.
Rock salt on Touareuna Road in the Mohawk Watershed in January 2020 (Photo: JI Garver).
Road salt use and the resulting salinization of streams and rivers has been in the news recently, led in part by a detailed piece by Kyle Bagenstose at USA Today (1). The news cycle was partly related to reporting by the US Geological Survey (USGS) of total road salt use, which apparently is now about 20 million tons per year in the US (2).
The Annual Survey of Winter Maintenance data from ClearRoads (3) released in April 2019 show that in the last full winter (ending in 2018), NY ranks third in the nation in total salt per mile (28.8 tons), behind only Rhode Island (44.4 tons) and Massachusetts (29.5 tons). These figures exclude salt brine application, which is high in Massachusetts, but not in NY. The figures also do not include local, private, and commercial use.
To handle all this salt, NY State has 257 storage facilities for rock salt and 207 storage facilities for liquid brines. While application of salt can vary from year to year, four-year averages reveal primary trends in usage and salt application. ClearRoads provides reports from annual surveys to states using rock salt. They report that NY State DOT currently applies an average of 1.01 million tons a salt annually – the highest reported application rate in the United States. NY is followed by Pennsylvania (0.844 million tons), Ohio (0.77 million tons), and Virginia (0.71 million tons). These are reported State figures (mainly DOT), and they do not include local, municipal, private, and commercial use, which is significant. American Rock Salt, the largest salt mine in the US, estimated in SEC filings (10-k forms) that the total market in NY State annually is 3.2 million pounds, which includes State, County, and local use (25).
NY also leads the nation in spending for snow removal (3). The data show that NY spent $370 m annually for snow removal, which includes labor, equipment, and materials (mainly rock salt) in the 2015-16 window highlighted in the 2019 report. Snow removal costs in NY State are the highest in the nation, by far. NY snow removal costs are followed by Pennsylvania ($246 m), Virginia ($215 m), and Minnesota ($102 m). The vast majority of these costs are equipment and labor with raw materials (salt) accounting for less than 20% of that total annual spending for these states. Obviously there are big differences here between total lane miles, areas treated in urban areas, and weather conditions, but regardless, NY purchases, stores, and then broadcasts that salt in our watersheds.
Salt is cheap
One of the reasons we can dump tons of salt on our roads is because it is relatively inexpensive and we have a built infrastructure for mining and distribution that is excellent. The most expensive way to buy salt is pre-packaged in a shaker and cylindrical box from the grocery store. For example, a 26 oz cardboard cylinder of Morton Salt is about $0.95 (~3.7 cents per oz), and you’d pay more than double (~$2.60 – ~10 cents per oz) for the same amount of Morton “Sea Salt” (both iodized). Sea salt is produced from the evaporation of marine water or saline lake water, and there has been some concern that this modern salt contains microplastics (see this article in Nature for an example – see 4).
Regular salt is mined from salt deposits (some layers and some salt domes), and there is no shortage of these rocks in the US. In NY, the Salina Group contains “sea salt” except the sea evaporated about 425 million years ago. Ultimately all salt is from the ocean, it’s just a matter of when. According the Mayo clinic, sea salt and mined table salt are the same with slight differences in additives to prevent clumping and iodine (5). The Mayo clinic provides us this health tip: “Whichever type of salt you enjoy, do so in moderation.” The same could be said for of our watersheds.
Salt is so cheap that you are really buying packaging and shipping, so if you want to feel good about your purchase, buy the package and consider the salt to be free (a clever marketing strategy might be “Free salt in every package” instead of “When it rains it pours”). If you decide to buy bags of salt from a big box store, it is even cheaper: you may pay about $6-9 for a 50 lb bag (800 oz for about 1 cent per oz). If you need more than a few bags for the driveway, you can buy bulk rock salt from an outfit like Rock Salt USA where you can get a reasonable deal of about $100 per ton (2000 lb), with a 22-ton minimum (FOB – not delivered) (6). This would be about 0.3 cents per ounce.
But if you are really serious about buying bulk and you can commit to a few million tons a year, you can get even better prices. NY State is serious about buying salt. The Office of General Services for NY State purchases salt through annual delivery contracts to American Rock Salt, Atlantic Salt, Cargill, and Morton Salt (7). The State commands an average price of about $60 per ton (about 0.19 cents per ounce), and they get to demand grain-size distribution, moisture content, and purity – all salt must be 95% NaCl, But to get this deal you’d need to buy, or agree to buy, over a million tons of salt annually. If somehow you could get the same price for the 26 oz container of Morton salt from the grocery store, the container would cost ~$0.05, but you would need to add your own iodine.
It is interesting to note the change of the negotiated price of bulk salt from east to west in the watershed because it is generally cheaper in the headwaters of the Mohawk (i.e., Oneida), which is closer to the Silurian source rocks to the west (mainly those in central NY). The NY Office of General Services has annual contracts for these counties – listed here from the confluence with the Hudson to the headwaters of the Mohawk: 1) Albany County (77,056 tons from American Rock Salt at $60.44 per ton); 2) Schenectady County (46,621 tons from American Rock salt at $59.77/ton); 3) Fulton and Montgomery Counties - combined (62,290 tons from Cargill at $60.62/ton); 4) Herkimer (46,668 ton from Cargill $54.36 per ton); 5) Oneida County (100,204 tons from Cargill at $53.21 per ton). These contract prices are delivered, so the farther from the mine, the greater cost (24). American Rock Salt has 1000 rail cars and 21 regional off-site stockpiles (24).
A recent mineral commodities report by the USGS indicates that production of salt in the US is 42,000,000 metric tons with an apparent reported consumption of 57,000,000 tons – imports account for 17,000,000 tons (8,23). Kansas, Louisiana, Michigan, NY, Ohio, Texas, and Utah account for 92% of total domestic production. Salt for road de-icing accounts for 43% of domestic consumption and almost all the rest is consumed by chemical industries and agriculture. NY ranks third in domestic production in the US and most of that salt is from both hard rock mining and solution mining of salt-bearing units of the Silurian Salina Group, which is exposed and underground in central and western NY State (9).
One of those mines, in NY, is the largest in the US. American Rock Salt produces between 10,000 and 18,000 tons of salt a day from the Hampton Corners Mine south of Rochester - the largest active producing salt mine in the United States. On average they produce about 3,000,000 tons per year and they have reported reserves for 80 years at this extraction rate (21). In 2018 the final environmental impact was approved by the NYS DEC for a 1700 acre expansion on this underground mine, and this adds to the currently permitted mine that is 9000 acres. (Take a tour of the American Rock Salt mine here on Youtube.)
So, this nearly inexhaustible supply of cheap salt is part of the problem for our watersheds.
Salt harms the Environment
All that salt is bound to cause harm in watersheds across NY State. A recently released study by the V.R. Kelly and colleagues at the Cary Institute (10) estimated that 90% of the salt in a watershed (NY in this case) comes from road salt, 6% is from sewage/septic (including water softeners), and the rest is natural input from bedrock. Salt in groundwater can be a major issue for aquatic organisms. Between 1986 and 2017 samples from the East Branch of Wappinger Creek (in the Hudson watershed) showed that salinity in the creek is highest in the late summer (August), when streamflow is lowest. This seems like a puzzling finding because most road salt application occurs between November and March. But this result means that groundwater is contaminated with salt, so that in the hot dry low-flow conditions of the late summer, salt concentrations are highest. This groundwater flow into streams in called baseflow, and it is what can keep streams flowing even when there is little or no precipitation. But this result means that during the hot summer with low flows, the salt from contaminated groundwater becomes a major stressor in the environment. They wrote:
“More worrisome are salinity concentrations in the summertime. Scientists believe that these elevated concentrations in surface water are from highly concentrated groundwater. During this period, when aquatic animals and plants are most active, streams can have elevated salinity levels that can last for days or even weeks. This sometimes results in average salt concentrations that are higher in summer than in winter.”
Salinization in the Mohawk watershed
The amount of sodium and chloride have increased dramatically in the Mohawk. Winter or summer, low flow or high flow: there has been a dramatic increase in the salinity of the river. For several decades we have known that road salt in the Mohawk Watershed is problematic. Two important papers over the years have revealed the scope of change over decadal timescales.
In 1981 Norm Peters and Jon Turk published a paper titled “Increases in sodium and chloride in the Mohawk River, New York, from the 1950’s to the 1970’s attributed to road salt” in the Water Resources Bulletin (11). The data analyzed were from the USGS and both data sets were from water collected from the headrace at either the Vischer Ferry Dam or the Crescent Dam. They determined changes in major ion concentration in the Mohawk during this analytical window, and the results indicate that by the early 1970s there was a statistically significant increase in Na and Cl in river water. Their analysis indicates an increase in sodium of 72% and chloride of 145% since the early 1950s. Between 1952-53 and 1971-74, mean sodium increased from 6.4 ± 3 to 9.3± 4 mg/L (milligrams per liter), and chloride increased from 7.7 ± 4 to 13.5 ± 5 mg/L. Remember those numbers, especially the chloride.
Sodium and chloride can come from a number of sources, including sewage. Using a human excretion rate of 1.8 to 3.8 kg of salt per year, they calculate sewage treatment may be responsible for 10-11% of the change. This number is likely too high because they assumed excretion by all people living in the watershed ends up in treatment plants, which is not true for those who have a septic system. Using application estimates and purchase records from NY State, they suggest that 96% of Na, and 69% of Cl in the period can be attributed to a dramatic increase in road salt application.
The second important summary paper was published in 2003, when Godwin, Hafner, and Buff published: “Long-term trends in sodium and chloride in the Mohawk River, New York: the effect of fifty years of road-salt application” in the journal Environmental Pollution (12). This study built on the Peter and Turk study (11), but quantifies changes from 1952 to 1998. They show that the flux of sodium and chloride in the watershed increased by 130% and 243% in this interval (early 1950s to late 1990s). They note that at the time (1991) NY State had the second highest application rate in the nation, behind Massachusetts.
For the 1990-98 period, the average for sodium was 13.2 mg/l, double the value in 1952-53 (6.4 mg/L) and maximum values were 27 mg/L. Chloride was 20.4 mg/l in 1990-98, nearly three times the mean in 1952-53 (7.7 mg/L) but maximum values were as high as 47 mg/L.
Seven decades of measurements: a plot of chloride in waters of the Mohawk River (upper at Utica; lower at Cohoes) and two representative tributaries (Otsquago Creek and Schoharie Creek) from 1951 to 2020. The Cohoes site (blue) is near the confluence with the Hudson River so this water integrates the signal from the entire basin. Data are from the USGS for sites 01357500, 1351500, 1342602, 1349000 (as of 1/2020). Blue swath is the best fit line for all data (Cohoes), green is for a more urban setting (Utica), and orange is for a more rural setting (Schoharie Ck).
We need a new summary for the Mohawk. But the data so far indicate that the news is not getting better: in the last few years the average chloride values appear to be even higher (see plot above that I made from USGS data). A recent thesis by Connor Horan at Union College investigated water quality in a number of streams and rivers in and around the Mohawk Watershed (14). Connor and his advisor Mason Stahl sampled creeks and rivers at high- and low-flow conditions. Part of the strategy of this approach was to determine differences in the context of baseflow, which would be influenced by groundwater. In part, their study was aimed at understanding how baseflow (groundwater) has contributed to surface flow and how geochemistry can reveal the relative contributions to total flow.
A couple of important findings come from this work, some of which was focussed on small tributaries in the watershed. First, it looks as if sodium and chloride continue to increase in the Mohawk. Second, it appears that groundwater, which can provide baseflow to a stream during periods of low precipitation, is contaminated with sodium and chloride. Their measurements of Na and Cl are higher than historic measurements reported by the USGS from the same streams. As with previous studies, their data show increases in Na and Cl, but no increases in other solutes (Ca, Mg, K, etc), and thus loading due primarily to road salt is almost certain. Perhaps most importantly, their data show that elevated levels of Na and Cl at low flow conditions indicate pervasive contamination of groundwater by salt. I talked to Professor Stahl about this and he noted that even if we stopped using salt today, it would probably take decades before all the salt was washed out of the groundwater.
Corrosivity and Chloride
In 2017, USGS and US EPA researchers led by E.G. Stets published a paper titled “Increasing chloride in rivers of the conterminous U.S. and linkages to potential corrosivity and lead action level exceedances in drinking water.” Their work suggests that increasing chloride in water supplies – including groundwater – increases the corrosivity of water that can then affect pipes.
They suggest that this corrosion can have a secondary effect of corrosion of lead (Pb) and thus result in elevated lead in drinking water. Changes in chloride and water corrosivity have been greatest in urban sites and values of key corrosion factors have “greatly exceeded thresholds found to cause corrosion in water distribution systems.” There is a connection between the surface water chemistry - especially chloride - and corrosion in drinking water distribution systems. Thus, chloride causes corrosion that can lead to leaching of lead that ends up in drinking water.
Storage facilities
All that salt needs to be shipped and stored before it can be loaded on trucks to de-ice roads. Godwin and colleagues also warned that storage facilities are clearly a concern because they have the potential to severely contaminate groundwater (12). In the 2003 publication, they wrote:
“A recent government publication (NYSDOT, 1999) has identified alarming groundwater concentrations within the counties that comprise the Mohawk River Basin; chloride concentrations found in wells and springs of six of the 14 contributing counties range from 0.2 to 10,800 mg/L, with a mean value of 62.12 mg/L (n=288). This same report suggests that persons on low sodium diets should not ingest water with sodium concentrations greater than 20 mg/L. Besides suggesting an additional impact of road-salt application, these results help to explain the disparity between mean daily yields and road-salt application.”
Salt storage for the department of public works in Glenville NY. The salt is under the dome-shaped building. However, the area where salt is mixed with sand (to left) is open, bare, and exposed, and thus leaching and loss of salt to groundwater and the adjacent wetlands is a major worry. This type of situation was the primary concern of a 1987 NY DEC salt storage memo (see below) (Photo: JI Garver, January 2020).
Back in 1987 the NYS DEC issued a memo to regional water engineers (and others) in the State addressing salt storage facilities. They were concerned that these sites may be point sources for groundwater contamination. Naturally these storage sites should be of concern because they hold thousands of tons of salt and any issues with rainwater and dissolution may have a major impact on groundwater. It turns out they were right to worry.
These storage facilities are widely distributed across the state and many are dome-shaped buildings for salt storage and adjacent loading facilities. The basic premise of the memo is that salt storage facilities are the biggest threat to water quality (an idea that may be challenged today given the situation with surface waters). Nonetheless, NYS DEC state in the memo:
“The identifiable threat to water quality posed by improper storage is considered more significant than the threat from spreading [on roads]. Storage typically involves stockpiling large amounts of the material at one defined location where, if it is not properly protected from precipitation and surface runoff, high concentrations of dissolved material leaching from the storage pile can subsequently be transported to underlying groundwater or nearby surface waters.”
There are probably a number of these sites across the State that have impaired groundwater. This issue recently emerged in the town of Vernon NY, where contamination of groundwater is thought to be related to a former NYS DOT salt storage facility. Barton & Loguidice Engineering conducted analyses of groundwater and determined that the chloride and sodium levels were 6,600 mg/L and 3,800 mg/L, which are 26 to 60 times the levels recommended by NYS Department of Heath. The severity of the contamination means residents drink bottled water provided by the State.
There is political pressure to address this groundwater contamination in Vernon. On 13 January 2020, US Congressman Anthony Brindisi toured the town of Vernon and subsequently released a statement, which called for accountability and transparency in efforts to address this groundwater contamination. He noted: “Clean, safe, and drinkable water should be a basic right for all Americans. Unfortunately, many residents in Vernon Center have been dealing with contaminated water for years. Last year, I visited with residents here and heard their stories: stories of hard, salty, drinking water; stories of low-quality water wearing on faucets and pipes.”
Regional Salinization
The picture that is emerging is that such widespread use of salt is harming surface water and groundwater. Salinization of our rivers and groundwater is not just a problem in NY. Sujay Kaushai from the University of Maryland and colleagues have been analyzing USGS water quality data from sites in the Northeast and across the nation. Their 2005 paper “Increased salinization of fresh water in the northeastern United States,” which was published by the National Academy of Sciences, focused on coastal streams and rivers in the mid-Atlantic states and New England (18). Their subsequent paper looked at the problem nationally. The 2018 paper, “Freshwater salinization syndrome on a continental scale,” was also published by the National Academy of Sciences (19). Both worth reading because they provide a regional view of the problem. The message from this important work is clear and profound.
In 2005 they stated: “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.”
Then in 2018, they coined a term “freshwater salinization syndrome” that links salinization and alkalinization, and it manifests in increases in specific conductance, pH, alkalinity, and base cations. They write:
“Although environmental impacts of the freshwater salinization syndrome are still poorly understood, symptoms can include: changes in biodiversity due to osmotic stress and desiccation, corrosion of infrastructure, increased contaminant mobilization, enhanced river carbonate transport, and impacts on coastal ocean acidification caused by increasingly alkaline river inputs.”
What cost?
The environmental cost of this regional salinization is profound. There is no question that road salt saves lives and reduces accidents (20). But the environmental cost appears to be enormous and I sense we are nearing a tipping point. The salinity of the Mohawk has increased significantly, and this increase is year-round, not just in the winter when salt is actively broadcast across the watershed. This salinity change is well documented through total salt purchases by counties, chemistry of surface waters, and groundwater chemistry.
Although these physical changes are well documented, the effects on aquatic organisms in the watershed have not yet been thoroughly studied, and we have a long way to go before we fully understand how this much salt will permanently change the ecosystem. It seems clear that we need to take a closer look at how road salt is affecting our environment. It also seems clear we need adopt some of the proven strategies aimed at reducing salt use for road de-icing. Perhaps we need to consider the advice of the Mayo Clinic: use “in moderation.”
This and other Notes from a Watershed are available at: https://mohawk.substack.com/
Further Reading
1) USA Today, 24 December 2019 - Heavy road salt use in winter is a growing problem, scientists say.
2) USGS annual Salt statistics and information, including production in the US
3) ClearRoads.org Survey. Clear Roads continues a multi-year project to gather, compile, and analyze state DOTs data related to snow removal. Participating State DOTs provide information about their winter resources, materials and costs for 2017 to 2018. These recent data are combined with data from 2014-2015, 2015-2016 and 2016-2017 winters.
4) Article in Nature concerning microplastics in Sea Salt (open access). Lee, H., Kunz, A., Shim, W.J. and Walther, B.A., 2019. Microplastic contamination of table salts from Taiwan, including a global review. Scientific reports, 9(1), pp.1-9.
5) Brief analysis by the Mayo Clinic and the differences between Sea Salt and regular Table Salt.
6) Bulk rock salt rates from Rock Salt USA
7) Office of General Services for NY State purchases of salt through annual delivery contracts to American Rock Salt, Atlantic Salt, Cargill, and Morton Salt Inc.
8) 2019 mineral commodities report by the US Geological Survey,
9) NY production of salt and location of salt mines
10) Kelly, V.R., Findlay, S.E.G., Weathers, K.C. 2019. Road Salt: The Problem, The Solution, and How To Get There. Cary Institute of Ecosystem Studies.
11) Increases in sodium and chloride in the Mohawk River, New York, from the 1950’s to the 1970’s attributed to road salt” Peters, N.E. and Turk, J.T., 1981. Increases in sodium and chloride in the Mohawk River, New York, from the 1950'S to the 1970'S attributed to road salt. JAWRA Journal of the American Water Resources Association, 17(4), pp.586-598. Link here - paywall.
12) Godwin, K.S., Hafner, S.D. and Buff, M.F., 2003. Long-term trends in sodium and chloride in the Mohawk River, New York: the effect of fifty years of road-salt application. Environmental pollution, 124(2), pp.273-281.
13) New York State Department of Transportation. 1999. NYSDOT guidance road-salt contamination: procedures to evaluate and resolve road-salt contamination complaints.
14) Horan, Connor, 2019 "Characterizing the Waters of 6 Rivers in Upstate New York With a Focus on Physical Hydrology and Controls on Water Quality" (2019). Honors Theses, Union College, Schenectady NY (link to Digital Works at Union)
15) “Increasing chloride in rivers of the conterminous U.S. and linkages to potential corrosivity and lead action level exceedances in drinking water” US Geological Survey and US EPA researchers lead by E.G. Stets.
16) NYS DEC MEMO on salt storage facilities
17) Jan 2020 letter by congressman Anthony Brindisi about high sodium in drinking water in Verona near a salt storage facility.
18) Kaushal, S.S., Groffman, P.M., Likens, G.E., Belt, K.T., Stack, W.P., Kelly, V.R., Band, L.E. and Fisher, G.T., 2005. Increased salinization of fresh water in the northeastern United States. Proceedings of the National Academy of Sciences, 102(38), pp.13517-13520. (Paper here, open access).
19) Kaushal, S.S., Likens, G.E., Pace, M.L., Utz, R.M., Haq, S., Gorman, J. and Grese, M., 2018. Freshwater salinization syndrome on a continental scale. Proceedings of the National Academy of Sciences, 115(4), pp.E574-E583. (Paper here, Open access)
20) Ontario salt safety study (reduction of accidents due to salt application - not peer reviewed)
22) Final Environmental Impact statement for the expansion of the American Rock Salt mine.
23) A metric tonne is 2000 kg, so it weighs 2205 pounds, slightly more than a regular US ton, which weighs 2000 pounds. See the details here.
24) SEC filing for American Rock Salt, CO, LLC. (Form 10-K). This interesting document has background, operations, and projections for the company filed with the SEC because the company is listed on the NYSE.
25) Form 10-K American Rock Salt Co Llc (2007)