Specific Conductance

What is SPECIFIC CONDUCTANCE?

Specific Conductance is the measurement of how well water conducts electricity through its content of ions and is measured in standard unit microSiemens per centimeter (µS/cm) at a water temperature of 25 degrees Celsius. Naturally occurring ions include calcium and magnesium, but urban streams and rivers are also subject to pollution from sewage overflows, industrial discharge, and stormwater runoff containing nitrate, phosphate, chloride, salt, and metals ions.

Why is SPECIFIC CONDUCTANCE important?

Elevated Specific Conductance can be an indicator of an unnatural or harmful imbalance of ion content in the water. Low levels of Specific Conductance may indicate a lack of elements essential for aquatic life, such as calcium and magnesium. A factor causing this can be pollution discharges containing noncharged ions, such as oil and phenols.

How do we measure SPECIFIC CONDUCTANCE?

Specific Conductance is measured at tidal sampling sites with an optical probe lowered from our Waterkeeper boat the R/V Muckraker, into the water at each station location. Specific Conductance readings are automatically collected at 0.25, 0.5 or 1.00 meter intervals from the water’s surface to just above the river bottom.  Specific Conductance at nontidal stations is measured by placing a YSI Probe into the water, completely submerging the sensor. We assess Specific Conductance data using a numeric pass/fail threshold of ≤100 µS/cm for tidal streams which was established by the Mid-Atlantic Tributary Assessment Coalition (MTAC) Sampling and data analysis protocols for Mid-Atlantic tidal tributary indictors. The State of Maryland has not established an assessment threshold for Specific Conductance in nontidal streams.