By Mike Ekberg and Richard Stuck
Most of us know that too much salt is unhealthy for the body, raising blood pressure for example. Well, apparently it can be unhealthy for our water, too. As the saltiness or salinity of groundwater increases above naturally occurring levels, so does its potential to harm aquatic life and to damage drinking water infrastructure.
Unfortunately, it appears groundwater in many areas of the buried valley aquifer system is getting saltier by the decade. If the salinity in groundwater continues to rise, it may begin to pose a serious water quality challenge for the region.
Salinity of groundwater increasing
Groundwater is a precious and abundant natural resource in the Miami Valley, supplying drinking water to an estimated 2.3 million people. The quality of groundwater in the buried valley aquifer system is generally pretty good. A growing body of evidence, however, suggests the groundwater supply is getting saltier.
Salt (Halite) is a mineral largely composed of sodium chloride. As salt dissolves in water, the amount of sodium and chloride in the water increases, and the overall salinity of the water increases as well.
Four agencies and organizations in southwest Ohio actively monitor long-term trends of sodium and chloride levels in groundwater:
- The Hamilton to New Baltimore Groundwater Consortium (Consortium)
- Ohio Environmental Protection Agency (Ohio EPA)
- The Miami Conservancy District (MCD)
- The U.S. Geological Survey (USGS)
Together, the four organizations survey 70 wells, collecting and analyzing groundwater samples for sodium and chloride and other constituents. Of these 70 wells, 39 wells show increasing trends in sodium and chloride levels or at least periodic detections of elevated levels. The map below shows the locations of Ohio EPA and MCD monitoring wells—and which of those wells show increased salinity levels.
Twenty-two of the wells are included in Ohio EPA’s Groundwater Quality Characterization program. The surveys of sodium and chloride levels in groundwater for some of these sites dates back to the 1980s. The median sodium and chloride concentrations measured in groundwater has increased when compared with data collected over the past 20 years (see chart below).
Risks posed by increasing groundwater salinity
- Groundwater provides roughly 50 percent of the water that flows in the Great Miami River during a typical year. As the salinity of groundwater rises, so does the salinity of the water in the Great Miami River and its tributaries. Some of the aquatic plants, insects, and fish living in the river are very sensitive to changes in water salinity and may not tolerate higher amounts of dissolved salt in water. If water salinity in the Great Miami River continues to rise, aquatic life may begin to suffer.
- Rising groundwater salinity may—in the future—present a challenge for communities that supply safe drinking water. Groundwater becomes more corrosive to metals as the salinity rises. Corrosive groundwater can attack the insides of pipes, releasing high levels of metals such as lead from lead pipes into drinking water. The increased salinity can also decrease the lifespan of pumps and pipes.
Remember the news stories about the problems with drinking water in Flint, Michigan? Problems that arose with the presence of lead in the drinking water system in Flint were attributed, in part, when the city changed its source of water from the Detroit Water and Sewerage Department to the Flint River. Chloride samples in the Flint River were considerably higher than the water supplied by Detroit, contributing to increased corrosivity, ultimately resulting in the water becoming more corrosive to metals (Torrice, 2016). Locally, groundwater contamination from a salt pile near Camden in Preble County was so severe that, in 2009, the village was forced to abandon its wells.
Where is all the salt in groundwater coming from?
Salt in natural waters comes from natural and human sources. Natural sources include the atmosphere; weathering of rocks, minerals, and soils; and geologic deposits. Human sources include water softeners, which release saline water into municipal sewers or home sewage treatment systems; agricultural fertilizers; and road salt as a deicing agent.
Bromide is an impurity found in road salt. The ratio of chloride to bromide in road salt is higher than it is for other sources of salt in natural waters. In southwest Ohio, chloride-to-bromide ratios measured in groundwater by Ohio EPA and the Consortium point toward road salt as a major contributor to the increasing salinity of groundwater.
According to USGS, the United States’ use of salt for deicing highways accounts for a dramatic increase in salt consumption since the 1940s (see chart below). Just since 1975, salt use for deicing has grown from about 8 million metric tons to more than 20 million metric tons or more in recent years. Road salt use in Ohio during winter 2019-2020, alone, totaled nearly 385,000 metric tons.
No doubt modern roadway deicing practices have improved safety during winter- weather driving conditions. The impact on groundwater salinity, however, is becoming increasingly apparent.
What can be done?
According to a report on road salt by the Cary Institute of Ecosystem Studies, there are many ways for street departments to minimize the impact of road salt on groundwater quality:
- Implement best management practices that reduce the amount of salt needed to ensure safe driving conditions such as:
- Pre-treat roads with brine. Estimates suggest that road pre-treatment with brine can yield a 75-percent savings in total salt applied.
- Pre-wet the salt before application. Pre-wetting salt before roadway application can reduce salt infiltration to aquifers by 5 percent.
- Properly calibrate equipment, including automated spreader controls on salt trucks.
- Store salt properly. Store it under roof, on impervious surfaces with secondary containment that completely enclose the salt pile.
- Explore alternatives to road salt. Agro-based products such as fermentation byproducts, cheese and pickle brine, de-sugared molasses, and corn steepwater are mentioned as possible alternatives. They can be used alone or with salt applications to improve the efficiency of salt on the road and to reduce the corrosivity of salt solutions.
- Protect sensitive water resource areas.
- Reduce salt applications in designated areas.
- Eliminate salt applications altogether or perhaps use alternatives to road salt.
- An example of a no-salt zone might be the immediate area surrounding a public water supply wellfield that is not surrounded by high traffic roadways.
- All public water supplies in the Miami Valley have defined source water protection areas around their wellfields. The inner management zones for some of these source water protection areas might be good candidates for sensitive water resource designation and a reduction in salt applications.
A local example of best management practices
One group of groundwater users taking action is the Consortium, a group of public water utilities and businesses that use groundwater in Butler County. At one large parking area near a wellfield, the Consortium reviewed and significantly reduced the road salt application rate, balancing water-quality needs with deicing and public safety requirements.
In another instance, a previously uncovered road salt storage location close to public water supply wells was replaced with an enclosed salt storage facility with a roof and impervious bottom, further protecting sensitive groundwater resources in that area. Piles of salt that cities and businesses keep to melt ice off roads should be stored at least 300 feet from streams and wells, according to Ohio EPA.
If all Miami Valley communities were to implement a few simple measures such as these, it’s likely the upward trend in groundwater salinity could be halted.
Mike Ekberg, is manager of water resources monitoring and analysis at the Miami Conservancy District. He served on the Salt Storage Workgroup for the State of Ohio’s Ohio Water Resources Council and helped develop the “Recommendations for Salt Storage,” a guidance for protecting Ohio’s water resources.
Richard Stuck, P.G., is source water manager at Greater Cincinnati Water Works, a municipally owned public drinking water utility.
References
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, from URL https://www.caryinstitute.org/news-insights/road-salt-problem-solution-and-how-get-there-report, accessed September 20, 2021, HTML format.
Torrice, M. 2016. How Lead Ended Up in Flint’s Tap Water: Chemical and Engineering News, Volume 94, Issue 7, from URL https://cen.acs.org/articles/94/i7/Lead-Ended-Flints-Tap-Water.html, accessed September 23, 2021, HTML format.
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