verifying the use of specific conductance as a surrogate for chloride in seawater matrices
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Verifying the Use of Specific Conductance as a Surrogate for Chloride in Seawater Matrices. Rob Mooney Technical Marketing Manager In-Situ ® Inc. Abstract Summary. Coastal groundwater supplies are vulnerable to chloride contamination.

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verifying the use of specific conductance as a surrogate for chloride in seawater matrices

Verifying the Use of Specific Conductance as a Surrogate for Chloride in Seawater Matrices

Rob Mooney

Technical Marketing Manager

In-Situ® Inc.

abstract summary
Abstract Summary
  • Coastal groundwater supplies are vulnerable to chloride contamination.
  • Validate linear relationship of specific conductance (SC) to chloride concentration.
  • Advantages of using conductivity sensor for long-term field deployments.
goals of this study
Goals of This Study
  • Satisfy customer requests for a viable field technique to estimate chloride.
  • Provide a laboratory procedure that a field hydrologist can perform.
  • Minimize the amount of analytical costs and equipment needed to develop data.
saltwater intrusion inland
Saltwater Intrusion – Inland
  • Interior of U.S. – Deep saline water underlies fresh water. Withdrawing water from overlying aquifers increases potential for saltwater intrusion from below.
  • Road salt impacts – Shallow aquifers and surface waters near roads may be impacted.
chemically conservative parameters
Chemically Conservative Parameters
  • SC and chloride are chemically conservative or stable water quality indicators and tracers.
  • Chloride is least affected by movement away from the source and provides a true representation of contamination.
chloride retardation
Chloride Retardation

Chloride shows little to no retardation effect in various aquifer matrices.

current chloride measurement technologies
Current Chloride Measurement Technologies
  • Chloride ISEs – Sensitive to drift, fouling, and not designed for field deployments.
  • Titrimetric methods – Less precise and may use hazardous chemicals.
  • Ion chromatography – Very accurate but potentially expensive laboratory technique.
validating use of sc as a surrogate for chloride
Validating Use of SC as a Surrogate for Chloride
  • SC can be directly correlated to chloride concentration.
  • Balanced cost of ISE lab technique vs. reduced accuracy compared to IC.
methodology correlation testing
Methodology – Correlation Testing
  • OSIL Atlantic Seawater Standard (35.0 PSU) was diluted to 10 additional concentrations.
  • 11 concentrations brought to temperatures of 0, 10, 20, 30, 40, and 50° C.
  • Total of 66 samples stabilized in thermal bath for a minimum of 1 hour.
methodology correlation testing11
Methodology – Correlation Testing
  • Prior to sample analysis, chloride ISE was calibrated using a 3-point, bi-thermal calibration with NIST-traceable chloride standards and validated throughout testing.
  • Five replicate readings were taken at each of the 66 chloride/temperature test points.
methodology correlation testing12
Methodology – Correlation Testing
  • Five readings were averaged to determine the final response value for each test point.
  • Results were plotted to compare chloride and SC values.
methodology drift testing
Methodology – Drift Testing
  • SC values compared to chloride ISE values during a 7-day continuous test.
  • Hourly readings taken in a 17 PSU dilution of OSIL Atlantic Seawater Standard.
  • Secondary NIST-calibrated conductivity and Cl- sensors used to monitor test solution.
technology comparison
Technology Comparison

Accuracy

  • Chloride ISE: ± 15% of reading or 5 mg/L, whichever is greater. Accuracy can be maximized by performing a three-point,bi-thermal calibration.
  • Conductivity sensor: ±0.5% of reading
sc and chloride relationship17
SC and Chloride Relationship
  • Low chloride concentrations: Chloride concentration and SC values showed strong linearity (R2 = 0.9887)
  • Low to high chloride concentrations: Chloride concentration (x) and SC values (y) showed strong linearity (R2 = 0.9845)
drift results19
Drift Results
  • Chloride ISE drift over 7 days: 1,036 mg/L or 8.4% of the reading.
  • Conductivity sensor drift over 7 days: 25 µS/cm or 0.08% of the reading.
    • Equates to a drift of ≈15 mg/L chloride at this range.
conclusions
Conclusions
  • Strong correlation validates use of SC as a surrogate for chloride in this study.
  • Stability of conductivity sensor and strong linear correlation indicate advantage for using SC as a surrogate for chloride in situations that require real-time monitoring.
conclusions conductivity sensors
ConclusionsConductivity Sensors
  • Proven, stable method for measuring SC.
  • Much less susceptible to drift than ISEs.
  • Require less maintenance than ISEs.
  • Saves on analytical testing costs.
  • Recalibrate every 3 to 6 months depending on matrix vs. daily recalibration for ISE.
conclusions conductivity sensors22
ConclusionsConductivity Sensors
  • Ideal for field deployments and long-term monitoring to generate real-time data.
  • Develop more robust data sets.
  • Matrix-specific linear correlation to chloride.
  • Use correlation data to estimate chloride.
applications
Applications
  • Saltwater intrusion monitoring
  • Salt marsh and coastal wetlands research
  • Aquifer storage and recovery systems
additional resources
Additional Resources

Application and Technical Notes:

  • Conductivity Measurement Methodology
  • Controlling Saltwater Intrusion in CA
  • Hurricane Surge and Inland Saltwater Impacts
  • Tracking Saltwater Intrusion in Coastal Aquifers
  • Three-Point, Bi-Thermal Calibration of ISEs

White paper:

  • Verifying SC as a Surrogate for Chloride

www.in-situ.com

verifying the use of specific conductance as a surrogate for chloride in seawater matrices25

Verifying the Use of Specific Conductance as a Surrogate for Chloride in Seawater Matrices

Rob Mooney

Technical Marketing Manager

In-Situ® Inc.

970-498-1655

[email protected]

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