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Supplemental Indicator for Wastewater Progress

The Chesapeake Bay Program Partnership-approved Supplemental Wastewater Indicator is a load-based measure of average annual progress toward the 2025 planning targets for wastewater treatment plants and industrial sources.

Nitrogen and Phosphorus loads released into the bay from wastewater


Wastewater is the second-largest source of nutrient pollution in Maryland, accounting for approximately 25% of the nitrogen that the State contributes to the Chesapeake Bay. To address this pollution, Maryland has undertaken a major capital improvements program to upgrade all of its major municipal wastewater treatment plants to include state-of-the-art enhanced nutrient removal (ENR) technologies. Between 2010 and 2017, it is anticipated that these upgrades will reduce the State’s annual wastewater nitrogen load to the Bay by over 40%. Because wastewater plants are critical to Maryland’s nutrient reduction strategy, it is important to have a reliable metric for estimating the annual impact of these upgrades and other operational changes at plants across the State.

The Chesapeake Bay Program (CBP) currently provides estimates of annual pollution loads entering the Chesapeake Bay through the Nitrogen Loads and River Flows to the Bay Indicator. This indicator represents the best available estimate of actual pollution loadings to the Bay, and it shows significant year-to-year variability which is driven largely by changing weather conditions. Although this metric is a valuable tool for looking at water quality, the weather-induced swings in annual loads obscure the incremental impacts of local management activities.

Recognizing the need to estimate the effect of management activities apart from any weather-induced impacts, the CBP developed a separate metric that reflects an average-rainfall condition. The CBP uses this metric to report Bay restoration progress each year, because it reveals management impacts that would otherwise be masked by annual changes in the weather. This average-rainfall metric is used only to assess nonpoint source management actions and not wastewater (point source) management.

To help Maryland assess the impact of its annual management actions, the CBP has approved a separate annual measure for wastewater pollution that has the same intent as the long-standing metric used for nonpoint sources of pollution. This “Supplemental Indicator of Wastewater Progress” was developed to normalize for the “uncontrollable” load fluctuations in order to more accurately represent the effects of the State’s management decisions relating to wastewater. It covers discharges from every NPDES-permitted municipal treatment plant in Maryland, as well as from industrial and federal facilities. The indicator does not include pollution from sewer overflows. For details on how this indicator is calculated, please read the technical memorandum memo, Proposed supplemental indicator for reporting point source progress.

Contact Information

If you have any questions regarding the supplemental wastewater indicator, please contact Greg Busch at, or at 410-537-3901.