Salt Monitoring Initiatives

FOSC is conducting two Salt Monitoring initiatives to assess the impact of road/sidewalk salt on Sligo Creek and its tributaries (Long Branch, Wheaton Branch, Takoma Branch and others). You may have read about how the use of road salt in the winter is hurting our waterways and, because salt isn’t removed by water treatment facilities, is ultimately affecting our drinking water. The Water Quality Committee has started to do something about it…with your help!

I. FOSC SaltWatch Monitoring in the Sligo Creek watershed

FOSC’s Winter Salt Monitoring Teams Find
Very High Salt Levels in the Creeks – Jan/Feb 2024

In January and February 2024, two winter storm events and a big thaw sent a tremendous amount of chloride into Sligo Creek, Long Branch, and their tributaries. Chloride (Cl) is a common element in the type of salts used to try to keep roads, parking lots, and sidewalks clear during snow, sleet, and ice storms.

These storm events saw brining and salting of roads and parking lots by a varied set of County, State, and local road crews. Many local schools, businesses, and residents added to the mix as they spread salt on their parking lots, sidewalks, driveways, and public spaces.

As the snows melted and the rains came, large amounts of chloride entered our waterways. At moderate and high concentrations, chloride can harm and even kill plant and animal life in freshwater streams. This winter, FOSC Salt Monitoring teams found very high chloride levels in both Sligo Creek and Long Branch, all the way from the headwaters of Sligo in Wheaton to the confluence of the two waterways just upstream of the PG County line. At most FOSC Salt Monitoring sites, these very high readings persisted in the streams for about two weeks, lasting considerably longer than either the brining/salting applications or the storms themselves. Across the watershed, chloride leveled off in March well above the baseline readings on 12/16/2023, perhaps reflecting the presence of salt in groundwater and soil.

Salt monitoring data by FOSC salt testing team volunteers. Subsequent testing with high concentration test strips found that the actual highs were double to triple the maximum reading the 750 mg/L “regular” salt testing strips display.

(Graph by Mimi Abdu, testing team member.)

The Long Branch graph, above, shows a typical salt “bump” from the storm in the first week of January. On Jan. 16th, the morning after region-wide salting was completed for the recent large storm, the chloride levels shot up and stayed up for 13 days straight, until Jan. 28th.

Within a few days of the storm, we realized that the salt levels exceeded the capacity of the regular test strips to report it. The protocol we follow (per the Izaak Walton League of America [IWLA], whose SaltWatch program supplied the regular test strips) called for an assumed maximum chloride level of 750 mg/L when using the regular low-concentration chloride test strips.

The FOSC WQ team quickly sought funding for high-salt test strips to determine the actual chloride levels during the remainder of this unexpected high salt spike. Thanks to a generous donation from a tester and from annual FOSC donors (thank you!), we were able to purchase them and make them available to our testers as soon as possible.

The January salt spike readings on Jan 17 - 27 show that the high concentration test strips readings of the actual salt levels were well over the 750 ppm limit of the regular test strips.

Use of high concentration test strips shows the actual salt levels were well over the 750 ppm limit of the regular test strips.

Salt levels were many times higher than the 230 mg/l chronic salt level considered toxic for fish and other aquatics. It also exceeded the acutely toxic level of 860 mg/l for several days from Jan 25-28. (FOSC data, graphed on

For the first few days after the snowstorm, the regular low-concentration test strip readings were capped at 750 mg/L chloride as this chart of chloride readings shows. When high-concentration chloride test strips were used from 1/25-1/28, the readings more accurately reflected the chloride levels at 1,000 mg/L and some as high as 2348 mg/L. Rain on 1/28 diluted the chloride levels.

FOSC year-round monthly testing team member Dean Tousley had a few high-salt strips on hand and captured the dramatic rise in salt levels in Section 1 starting on Jan. 16th. At its peak, the chloride levels were some 3 times the assumed 750 mg/L maximum. (see below)

In Section 1 of Sligo Creek this winter, salt levels peaked very high and stayed high for 2 weeks straight.

The use of high-concentration test strips revealed an actual salt level more than 3x the maximum reading of the “regular” test strips. (Graph by Mimi Abdu, FOSC testing team)

According to the EPA, chloride can be toxic to aquatic life, depending on the species, if it is present chronically at levels above 230 mg/L. A short exposure to chloride at 860 mg/L may also be lethal to some aquatics if it occurs more than twice in a three-year period. We hope that this recent salt spike was atypical and that the creeks haven’t been widely subject to salt levels of this magnitude and duration within the last 3 years.

Our testing in the two prior years did not reveal major salt events anywhere close to these levels.

In February 2021, however, the monthly Water Quality testing team did discover a fish and amphibian kill in Flora Lane creek involving more than 200 corpses, almost certainly caused by salting runoff from the Beltway and Georgia Ave.

Fish kill on Flora Lane in Feb. 2021. More than 200 fish and salamanders were found dead by FOSC testers along Flora tributary. An investigation by the MoCo Dept. of Environmental Protection found the cause was excessive salt runoff, very likely from the Beltway.

The County and State contend they are making concerted efforts to reduce the amount of brine and salt used for these storms. Nonetheless, in the three years of monitoring, the Salt Monitoring team has never recorded sustained chloride readings anywhere near this high before. It appears that more work needs to done with regard to best management practices and resetting driver expectations for the winter salting and brining of roads, parking lots, and sidewalks.

Through other monitoring programs, we will assess the impact of the high chloride levels on macroinvertebrates, fish and other aquatics living in these streams this Spring. Check the Water Quality pages on the FOSC website for more findings as they become available.

–Pat Ratkowski, WQ Committee chairperson

II. Reporting Excessive Road/Sidewalk Salt in the Sligo Watershed

To help reduce the amount of salt entering Sligo Creek, we’re continuing the FOSC reporting program for excessive road or sidewalk salt “piles” (such as the piles shown in the photos at the bottom of the page) in the Sligo watershed.

If you see an excessive amount of salt on a roadway, parking lot, or sidewalk, please email [email protected] with a photo and the day, time, and location of the salt pile. You should also report it directly to the County by calling 311.

We will follow up to ensure that the County, State or responsible party to remove excessive salt piles before they go into Sligo Creek. View examples of excessive salt use further down this page. The watershed map may be viewed on the Maps of Sligo Creek page.

III. Data Reporting for salt testing results

SaltWatch results 21/22 season for close-in Maryland, shown as a chart of different size circle. Sligo Creek is represented with the largest circle of any area downcounty.

Results for Sligo Creek and other local testing sites

Winter 21/22/23

In the Washington region overall, the Izaak Walton League reports that Salt Watch testing results from 2021/22 showed 34% of streams had chloride at levels considered toxic to wildlife, or 410 ppm. Across the eastern and midwest US, 18% tested at that level.

Along Sligo and Long Branch, the average chloride levels at 14 test sites ranged from 216ppm to 507ppm, though FOSC volunteers’ data show individual readings as high as 860ppm during winter of 21/22. In the 22/23 testing, readings ranged from 43 at Three Oaks Drive on Jan 8, to 187ppm at Maple Ave and at Elson St, both also on Jan 8th just before the storm. On average, the salt levels were significantly lower in 22/23 season due to fewer storm events and a lighter hand with salt spreading by the County than in 21/22.

IV. Advocate for Reduced Salt Use and Alternatives such as Brining of Roadways

Let County Executive Marc Elrich and Director of MCDOT Christopher Conklin know that you support brining of roadways. Brining is as effective as rock salt for deicing but, because of the way it is applied, uses ~60% less salt than a roadway treated with rock salt. It would help protect wildlife in the watershed and county-wide, and save money too.

Please view the letters that the FOSC Advocacy Committee has sent to MoCo DOT, the MD State DOT , and others on this issue, as well as their responses. We are continuing to follow up with these groups to press for better training, higher quality equipment standards for contract salt applicators, and other measures to reduce excessive salt use.

A massive amount of salt applied to Parkside Rd at Sunnyside Rd. in Silver Spring, winter 2024.


A mega-salt application - unencessary and damaging to the creek just downhill from this location.

The IWLA is providing the test kits for the FOSC salt monitoring initiative. Thank you, IWLA!

The Winter Salt Watch logo of the Izaak Walton League of America
A set of excessive salt piles at Dallas Ave. near Sligo Creek.

Excessive salt piles at Dallas Ave near Sligo Creek

Large salt piles in a Dallas Ave intersection close to Sligo Creek. DOT removed them shortly after the FOSC Section Steward reported them.

A local salt pile in the middle of an intersection

A local salt pile, courtesy of J. Galella at UMD

Road Salt spread unnecessarily on a cleared roadway

Road salt sprinkled on snow-cleared roadway

FOSC Advocates for More Responsible Salting Practices on Roadways

FOSC recently shared our strong concerns about the excessive salting in the watershed with the Montgomery County Dept. of Transportation, the Dept. of Environmental Protection, and the State Highway Admin, which maintains the numbered roadways (University Blvd, Colesville Rd, Georgia Ave, Piney Branch, etc.) The letter is posted under the Advocacy tab, Letters and Testimony page.

2023 MoCo DEP/WSSC
SaltWise Guidance

Be salt wise!

One mug of salt will treat a 20′ driveway or 10 sidewalk squares

A blue mug sitting on a large pile of salt in the Montgomery County salt depot. The mug is part of the awareness campaign to reduce use of salt in order to protect our waterways.

The FOSC Water Quality team has rounded up these three handy salt use resources:

  • For the status of salting/brining in your area, see the Montgomery County Winter Storm Information Portal – shows MCDOT’s latest storm management actions.

IWLA Salt Kit - Guidance for Volunteer Salt Monitoring V2