Chlorides Monitoring
A Water Quality Concern

Why Care about Chlorides?

  • Chlorides found in water and wastewater at elevated concentrations can impart a salty taste to drinking water and potentially impact public health. 

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

The DRBC has adopted criteria and monitors chlorides to ensure water quality remains suitable as a source of drinking water and protective of aquatic life.
The Salt Front

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.

Monitoring the Salt Front

DRBC's Hydrology/Flow Management Program focuses on controlling the upstream migration of salty water from the Delaware Bay during low-flow conditions to protect drinking water.

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's location fluctuates in the Delaware River Estuary as streamflows increase or decrease in response to changing inflows, which either dilute or concentrate chlorides in the river.

Climate Change

DRBC is studying the potential affects of sea level rise on chloride concentrations in the Delaware River Estuary and Bay.

Will sea level rise force the salt front upstream? Will more freshwater coming downstream be needed to repel the salt front? Will additional reservoir storage be needed for freshwater?

Staff are using rainfall-runoff models and the latest climate research to help plan for a sustainable water supply to meet future water demands in the basin.
Monitoring Chlorides in Special Protection Waters
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.
View larger (jpg).

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 were 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.

A report is forthcoming.

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 is meeting quarterly.

Looking Ahead

In 2024, for the second phase of this project, staff identified a subset of the 2021-2023 non-tidal chloride monitoring sites for further and more frequent monitoring. Twice monthly monitoring at 10-15 tributary locations will begin in October 2024 and go through winter. Monitoring will be done using continuous conductivity loggers, and grab water samples will be collected for chloride, magnesium, potassium, sodium and other ions. Additional components of this phase of the study include outreach to highlight areas of concern, troubleshoot probable causes of degradation and educate the public about the issue.

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.
Winter Chloride Monitoring in Tidal Delaware River

One of the applications on the DRBC's water quality dashboard pulls real-time USGS chloride data and compares it to water quality criteria for DRBC water quality zone 2. Data show that criteria exceedances do occur when winter storms are timed with periods of low flow.

During the winter months of 2024-2025, the DRBC is going to - when conditions warrant - monitor chloride data with grab samples from the Bristol Wharf (located in water quality zone 2). Samples will be collected once per day during the storm event and will end when exceedences are confirmed or deemed no longer likely.
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