Chlorides Monitoring
A Water Quality Concern


Why Care about Chlorides?

  • The Delaware River is undammed its entire length, allowing for the movement of salt from the ocean into the Delaware River Estuary.

  • Delaware River Basin roadways are routinely treated with road salt and other de-icing agents during the winter, which enter our waterways.

  • Salt is not easily removed from water during treatment. Chlorides found in surface water and wastewater at elevated concentrations can impart a salty taste to drinking water and potentially impact public health.

  • Dissolved salts can accumulate in groundwater and slowly release into surface waters, compounding the problem over time.

  • Salinity levels also affect aquatic life and other living resources.


DRBC Management of Chlorides
Chlorides in the Delaware River Estuary

In the Delaware River Estuary, salt water mixes with freshwater.  

Higher chloride concentrations indicate the degree to which ocean derived saltwater has moved into the freshwater portion of the upper estuary, near Philadelphia and Camden, where drinking water intakes are located.

In addition to impacting treatment costs for public water suppliers, salty water increases corrosion control costs for other surface water users, for example, industry.


Water Quality Criteria: Chlorides

  • DRBC has adopted criteria for chlorides and sodium and monitors chlorides to ensure water quality remains suitable as a source of drinking water and protective of aquatic life.

    • See the data! Visit https://drbc.net/Sky/waterq.htm (scroll down ~halfway) to view a current comparison of estimated chloride concentrations to criteria for water quality zones 2 and 3 (map of zones; pdf).

    • Data show that criteria exceedances do occur in Zone 2 (Trenton, N.J. to Palmyra, N.J.) when winter storms are timed with periods of low flow.


Monitoring the Salt Front

The DRBC's Hydrology/Flow Management Program focuses on freshwater releases to control the upstream migration of salty water from the Delaware Bay during low-flow conditions.

One important metric that is monitored is the seven-day average location of the salt front, the 250 mg/L chloride concentration based on drinking water quality standards. The salt front indicates water that is too salty to be used for drinking water.

The salt front's location fluctuates in the Delaware River Estuary with the tide and with increases or decreases of freshwater streamflow, which either dilute or concentrate chlorides in the river.
Increasing Chlorides in the Non-Tidal Delaware River
This graph shows the increase in chlorides at the Delaware River at Trenton, N.J. Graphic by DRBC.
This graph shows the increase in chlorides at the
Delaware River at Trenton, N.J. Graphic by DRBC.

In the non-tidal Delaware River, salinity levels are primarily influenced by natural factors such as geology, precipitation and evaporation. However, human activities such as agricultural runoff, de-icing salt applications, wastewater discharges and mining processes also contribute to increasing salinity levels, leading to freshwater salinization.


Monitoring Chlorides in Special Protection Waters

Elevated chloride concentrations are also a concern in the non-tidal Delaware River, which are protected under DRBC's Special Protection Waters(SPW) regulations.

Over the past several years, instream monitoring of the non-tidal river has shown an upward trend in chloride concentrations. While concentrations are still below criteria for drinking water and aquatic life use, the DRBC is watching this trend closely. 

This trend is not just seen in the Delaware River's freshwater, it is becoming commonplace in areas of the U.S. with significant roadway de-icing activity. Studies suggest that chloride concentrations in winter are as much as a hundred-fold over summertime levels. Also, higher chloride concentrations increase as a function of impervious surface.

Additional monitoring and investigation into sources, mitigation measures and de-icing alternatives to salt and brine are needed.


Study: 2021-2023

From 2021 - 2023, the DRBC performed a two-year study to monitor chlorides, other ions and TDS concentrations in the non-tidal Delaware River watershed.

A mix of mainstem and tributary locations was chosen, for a total of 27 sites.

  • View Map of Monitoring Locations

  • Monitored Ions included: chlorides, TDS, nitrate, calcium, magnesium, sodium, potassium, sulfate, total silica, total alkalinity, total suspended solids and total phosphorus

At seven tributary sites, DRBC deployed continuous specific conductance and temperature loggers; the remaining sites already have continuous data being collected.  

To complement the continuous data collection, staff sampled each site once monthly for conductivity and temperature. The loggers were maintained regularly throughout the study period.

Data show increasing chlorides trends, but still below criteria for aquatic life and drinking water. A report is forthcoming.


Looking Ahead

In 2024, staff focused on analyzing the data collected from 2021 through 2023. The second phase of this project - as funding allows - could include targeting a subset of the 2021-2023 non-tidal chloride monitoring sites for further and more frequent monitoring during winter months. Monitoring would be done with continuous conductivity loggers and grab water samples for chloride, magnesium, potassium, sodium and other ions. This phase could also include outreach to highlight areas of concern, troubleshoot probable causes of degradation and educate the public about the issue. Please stay tuned for additional information.

DRBC staff prepare to collect a water quality sample from the Delaware River at Smithfield Beach. Photo by DRBC. DRBC staff carry a continuous logger set-up to where it is going to be placed in the creek. Photo by DRBC. The continuous data logger is secured in the creek. Staff collect real-time water quality readings via a probe in the water. Photo by DRBC.
DRBC staff prepares to collect a water
quality sample from the Delaware
River at Smithfield Beach.
Photo by DRBC.		 DRBC staff carries a continuous data logger set-up to where it is going to be placed in the creek. Photo by DRBC. The continuous data logger is secured in the creek. Staff collects real-time water quality readings via a probe in the water. Photo by DRBC.
DRBC staff prepare the water quality probe before deployed into the creek. For many sites, sampling occurs from a bridge, with equipment lowered over the side. Photo by DRBC. The water quality probe is connected to a tablet, where staff can read and save the data real-time. Photo by DRBC. DRBC staff collect a water sample from the Lehigh River to monitor chlorides concentrations. Photo by DRBC.
DRBC staff prepares the water quality probe before deployed into the creek. For many sites, sampling occurs from a bridge, with equipment lowered over the side. Photo by DRBC. The water quality probe is connected to a tablet, where staff can read and save the data real-time. Photo by DRBC. DRBC staff collects a water sample from the Lehigh River to monitor chlorides concentrations. Photo by DRBC.
DRBC staff collects flow measurements at Pohatcong Creek, one of the chlorides study sites. Photo by DRBC.
 In the Fall 2021, DRBC staff performed maintenance on the loggers, updating their appearance to blend in better (bottom of pic). Photo by DRBC. A logger with its updated encasement. Photo by DRBC.
DRBC staff collects flow measurements at Pohatcong Creek, one of the chlorides study sites. Photo by DRBC.
 In the Fall 2021, DRBC staff performed maintenance on the loggers, updating their appearance to blend in better (bottom of pic). Photo by DRBC. A logger with its updated encasement. Photo by DRBC.
Salinity Impacts Freshwater Toxicity (SIFT) Workgroup


SIFT Workgroup

In 2022, the DRBC formed the Salinity Impacts Freshwater Toxicity (SIFT) Workgroup to collaboratively sift through the escalating issue of freshwater salinization and increasing chlorides in rivers and streams and discuss regulatory and road salt management options. The workgroup is made up of DRBC partner agencies, ngos and a few consulting groups and meets quarterly.
Additional Resources


DRBC Presentations/Information


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