Coastal Plain Aquifer Synoptic - Chloride Network
Groundwater Resourses of the New Jersey Coastal Plain
A New Jersey Geonarrative
Chloride concentrations in groundwater are measured in select wells on a 5-year cycle, as an early warning indicator of saltwater intrusion, and for the definition of the 250 mg/L chloride concentration line within the principal aquifers of the New Jersey Coastal Plain.
Statement of problem:
Demand for potable water supplies in New Jersey has increased with the growing population. Saltwater intrusion into groundwater is a water-supply issue. Elevated concentrations of chloride is the commonly-used indicator of saltwater intrusion. In New Jersey, the areas of concern for chloride concentrations are in the confined aquifers in the southern and central parts of the State near Delaware Bay, areas near Raritan Bay, and in deeper-downdip areas of aquifers.
The principal sources of chloride in the major aquifers of New Jersey are from seeping in of modern marine or brackish bay waters, or from salty groundwater that has been locked within the aquifer on the scale of geologic time. Withdrawal of groundwater can increase chloride concentrations through the reduction of the flow of freshwater towards coastal areas or by causing saltwater to be drawn inland towards the freshwater zones of an aquifer. Chloride monitoring at select wells helps in the interpretation of trends and identify the areas with the greatest threat of contamination from saltwater intrusion.
Strategy and Approach:
The U.S. Geological Survey New Jersey Water Science Center maintains a network of about 100 wells that are part of a long-term cyclic sampling strategy. About 20-25 wells/year are sampled on a rotation of once every 3-5 (or more) years. In addition to chloride and major ions, samples are analyzed for select indicators of source and age of groundwaters, including stable isotopes. The chloride network data is supplemented by a substantial set of chloride data that purveyors provide to NJDEP.
Interpretation and analysis of the above data includes updates to chloride distribution maps, principally using the 250 mg/L chloride line as the threshold of most concern. Where data are sufficient, trends in increasing concentration can serve as an early warning system. Documenting and assessing all types of chloride interpretations has a high value for water purveyors, NJDEP, and local stakeholders, enabling informed decisions about withdrawal rates and the best management of the groundwater resource to ensure future viability.
Chloride concentrations in groundwater are measured in select wells on a 5-year cycle, as an early warning indicator of saltwater intrusion, and for the definition of the 250 mg/L chloride concentration line within the principal aquifers of the New Jersey Coastal Plain.
Statement of problem:
Demand for potable water supplies in New Jersey has increased with the growing population. Saltwater intrusion into groundwater is a water-supply issue. Elevated concentrations of chloride is the commonly-used indicator of saltwater intrusion. In New Jersey, the areas of concern for chloride concentrations are in the confined aquifers in the southern and central parts of the State near Delaware Bay, areas near Raritan Bay, and in deeper-downdip areas of aquifers.
The principal sources of chloride in the major aquifers of New Jersey are from seeping in of modern marine or brackish bay waters, or from salty groundwater that has been locked within the aquifer on the scale of geologic time. Withdrawal of groundwater can increase chloride concentrations through the reduction of the flow of freshwater towards coastal areas or by causing saltwater to be drawn inland towards the freshwater zones of an aquifer. Chloride monitoring at select wells helps in the interpretation of trends and identify the areas with the greatest threat of contamination from saltwater intrusion.
Strategy and Approach:
The U.S. Geological Survey New Jersey Water Science Center maintains a network of about 100 wells that are part of a long-term cyclic sampling strategy. About 20-25 wells/year are sampled on a rotation of once every 3-5 (or more) years. In addition to chloride and major ions, samples are analyzed for select indicators of source and age of groundwaters, including stable isotopes. The chloride network data is supplemented by a substantial set of chloride data that purveyors provide to NJDEP.
Interpretation and analysis of the above data includes updates to chloride distribution maps, principally using the 250 mg/L chloride line as the threshold of most concern. Where data are sufficient, trends in increasing concentration can serve as an early warning system. Documenting and assessing all types of chloride interpretations has a high value for water purveyors, NJDEP, and local stakeholders, enabling informed decisions about withdrawal rates and the best management of the groundwater resource to ensure future viability.