The Washington Aqueduct has upgraded its continuous monitoring system at the Great Falls intake to provide early warning of both algal blooms and potential sewage spills in the Potomac River.

The data sonde, placed into service in February, initially monitored total algae, conductivity, temperature, pH, dissolved oxygen and turbidity. Its algae sensor tracks both green algae through chlorophyll a and blue-green algae through phycocyanin, allowing the Aqueduct to identify changing river conditions and adjust treatment operations.

The latest upgrade adds continuous monitoring for ammonium and ammonia. Because ammonia typically occurs only at trace concentrations in the Potomac River but is present at higher concentrations in raw sewage, a sudden increase at the intake could signal an upstream sewage spill and trigger the Aqueduct's rapid-response protocols.

The upgrade coincides with the planned rehabilitation of the Potomac Interceptor. The Aqueduct said the additional monitoring provides a way to identify a potentially unreported spill associated with the project before it reaches the treatment facility.

The Washington Aqueduct supplies drinking water to approximately 1 million people in the District of Columbia, Arlington County and Fairfax County.