Monitoring Road Salt Pollution and Taking Action at Home

"Salt Snapshot" or Synoptic Salt Sampling Study

In 2023, members of the Little Lehigh Watershed Stewards heard about the issues related to road salt pollution and decided to study its effects in our watershed.

This map shows the area where we did our studies. The Little Lehigh Watershed is composed of the Little Lehigh Creek to the south and east of Allentown and the Jordan Creek, which is to the north and feeds into the Little Lehigh in Allentown right before it flows into the Lehigh River. (See map) The area has a variety of land use, including mountain areas to the north and south, agricultural areas, warehouse and industrial areas, suburban housing developments, and dense urban areas in Allentown.

With the help of Stroud Water Research Center, we designed a "salt snapshot" or synoptic sampling protocol, which we used to perform two studies in the summers of 2023 and 2024.

Selecting the Sampling Sites

We chose sampling sites that have a variety of land use and that were upstream and downstream of any sites like warehouses or housing developments that might cause salt pollution. (See diagram) We made sure to include sites at headwater areas that are heavily forested to represent what are most likely the least contaminated conditions in the study region. We also selected sites just upstream from the confluence of two tributaries to determine the effects of each tributary. An important criterion for site selection was accessibility and safety for our volunteers, so most of the sites were in spots where there are publically owned bridges over the creek where it is possible to collect samples without needing to go onto private property.

Timing of Testing

Our testing was done during the summer when most of the water in the streams was from groundwater, called base-flow conditions. They were done at this time of year because, during the winter, there frequently are major temporary spikes in the amount of chloride in streams as a result of salty runoff events, which can last anywhere from a few hours to several days. While these fluctuations can be very harmful to aquatic wildlife, testing at these times does not give an accurate picture of how much chloride is in the groundwater and streams year-round. Summertime testing, on the other hand, gives very compelling evidence of the year-round effects of salt pollution.

It is also important to do testing when the streams are at base-flow so that water samples are not diluted by rain. In our area, we have some automated USGS stream monitoring stations that we utilized for stream flow data. Another way to avoid rainfall influences is to wait 48 hours after the most recent rain event and then perform a visual inspection of local creeks.

Testing Day

On the day of testing, we had teams of two volunteers go out and collect the water samples during a three-hour time period. Each team had a driver and a navigator who also collected the water samples.

The volunteers brought the water samples back to a central location, where they were later tested for chloride and conductivity.

Our Findings

In 2023, we tested 45 sites in the Little Lehigh Creek, and the following year, we added 45 more sites on the Jordan Creek. (See map above.)

In 2024, on the Little Lehigh, 28% of our samples were above 50 mg/l (the level for chronic toxicity threshold value for macroinvertebrates). As expected, the levels of chloride increased as the streams flowed through the more developed areas of the watershed, resulting in higher levels in Allentown and the warehouse district.

The Jordan Creek area is less developed, so as we suspected, we saw just 7% of samples that were over 50 mg/l. 

As a result of this study, we determined that there is chloride pollution in our watershed, and we identified problem areas where we need to focus our advocacy in the future.

If you would like to perform a salt snapshot study in your watershed, read more about our protocol: Salt Snapshot Protocol Guidance Manual.

What You Can Do to Reduce Road Salt Pollution at Home

Here are some steps you can take:

• Shovel frequently so snow does not accumulate and turn to ice.
• Salt works best on a thin layer of ice; always shovel any excess snow/ice before applying it.
• Using more salt does not make snow and ice melt faster; it's not necessary to feel the crunch underfoot for the salt to be effective: one 12-ounce coffee mug of salt is sufficient for a 20-foot driveway or 10 sidewalk paving squares. The grains of salt should be about 3 inches apart.
• Only apply salt in places where it is necessary.
• After the storm, sweep up any excess salt and use it for the next time it snows.
• You can also use alternatives to rock salt, such as sand, kitty litter, or birdseed.
• If bad weather is forecast, cover small areas, such as steps, with a tarp to prevent snow accumulation.
• Remember that it only takes one teaspoon of salt to pollute five gallons of water!

If you live in a controlled development that uses a private contractor, pay attention to how much road salt is being used, and if it appears to be excessive, bring it to the attention of your homeowners' association.

Next month's article will be about best management practices and local and statewide advocacy for road salt reduction.