Aquatic Life Designated Use Study

Historical Conditions

When the DRBC was created in 1961, little or no dissolved oxygen (DO) was present in the Delaware River Estuary from Wilmington to Philadelphia for periods of up to six months each year.

To combat this serious challenge, DRBC in 1967 established designated aquatic life uses and associated numerical water quality criteria necessary to protect those uses.

The aquatic life designated use in this part of the estuary was set as "maintenance" (survival) of resident fish and movement of migratory fish through these waters to and from spawning areas.

Significant improvements in DO levels have occurred throughout this stretch of river since 1967.

Conditions Today

Today, Delaware Estuary water quality is  much improved. DO levels in the Delaware River Estuary are supportive of resident and migratory fish populations.

But, we know that early life stages of estuarine fish species are generally more sensitive to DO levels than are the adults living in the river stretches or just passing through these waters to reach spawning areas. 

The Next Chapter

Can the water quality be improved in this section of the estuary to better support fish propagation (i.e., reproduction and juvenile development), as well as the endangered Atlantic sturgeon?

Resolution Approved September 2017: Study Begins

Resolution 2017-4

In September 2017, the DRBC unanimously approved a resolution recognizing the significant water quality improvements in the Delaware River Estuary that have occurred and affirming that continued improvement is an important goal.

The Resolution directed staff to:

  • Perform a study to determine the attainability of an improved aquatic life designated use of fish propagation (i.e., reproduction and juvenile development) in a 38-mile stretch of the Delaware River Estuary around Philadelphia, Camden & Wilmington

  • Initiate a formal public rulemaking process on a proposed revised designated use and water quality criteria to protect that use and an implementation strategy

The Resolution provided for scientific and technical studies to be performed for the following purposes:

  • To conduct additional field studies of the occurrence, spatial and temporal distribution of all life stages of important resident and migratory fish species that utilize the estuary;

  • To determine the DO requirements of these fish species and the oxygen-depleting nutrient loadings from point (end-of-pipe) and non-point (runoff) sources that can be discharged into the tidal river while maintaining the DO levels in the water;

  • To conduct an analysis to determine the attainability of DO requirements and water quality standards that would result in an upgrade in the designated aquatic life use in this 38-mile section of the river, including technical, social and economic factors; and

  • To identify and evaluate opportunities for early action to reduce discharges of oxygen-depleting wastes to this stretch of river in the short term.

Study Area

A 38-mile stretch of the Delaware River Estuary, from Wilmington, Del. to just above the Tacony-Palmyra Bridge (connecting Phila. and N.J.).

It includes DRBC Water Quality Zones 3, 4, and the upper portion of Zone 5.

Monitoring/Data Collection

To support these studies and the development of the eutrophication model, lots of monitoring was needed.

Ambient (surface water) nutrient monitoring, primary productivity and algal speciation studies were completed.

DRBC staff collect water samples to study light extinction. Photo by DRBC. DRBC staff collect water samples to monitor nutrient levels. Photo by DRBC. DRBC staff monitor nutrient levels in the Darby Creek, a Delaware Estuary tributary. Photo by DRBC. DRBC staff collect a water sample from the Schuylkill River to monitor nutrient levels. Photo by DRBC. DRBC staff collect water samples to monitor primary productivity. Photo by DRBC.
Collecting water samples
to look at light extinction
Nutrient monitoring at
the Calhoun St. Bridge
(Delaware River).
Nutrient monitoring at
Darby Creek, a Delaware
River tributary.
Nutrient monitoring at
the Falls Bridge
(Schuylkill River).
Collecting water samples
to study primary

Study Partners

The DRBC is leading this groundbreaking effort through a collaborative process informed by:

  • DRBC's Water Quality Advisory Committee, a group representing state and federal co-regulators, NGO's, academic institutions, municipal and industrial dischargers and water purveyors

  • Expert Panel of Scientists and Engineers

  • Representatives of DRBC's "co-regulators" - member state agencies and EPA Regions 2 and 3

  • Representatives of point-source dischargers in the estuary (a total 67 provided data for this study)
Resolution Approved September 2020: Updates Schedule Set in 2017

Resolution for the Minutes September 2020

On September 10, 2020, at their 3Q Business Meeting, the Commissioners approved a Resolution for the Minutes that modified the schedule adopted by Resolution 2017-4. The change to the schedule was necessary in light of COVID-19-related mitigation measures that affected monitoring efforts, as well as funding constraints.

2017-2020: Progress to Date

  • Input obtained from an Expert Panel on modeling the water quality impacts of nutrient loadings;

  • Research on the dissolved oxygen requirements of key sensitive species completed;

  • Ambient nutrient monitoring and primary productivity and algal speciation studies conducted to support model calibration;

  • Development of a hydrodynamic and eutrophication model;

  • Identification and evaluation of the capital and operating costs required for twelve wastewater treatment plants to implement technologies for achieving higher levels of dissolved oxygen; and

  • Evaluation of the physical, chemical, biological, social and economic factors affecting attainment of uses.

DRAFT Analysis of Attainability: September 2022

DRAFT Analysis of Attainability (AA) & Supporting Documents

The draft AA:

  • Describes the results of studies performed with a state-of-the-art hydrodynamic and water quality model, showing the DO improvements to be achieved when ammonia effluent limits are reduced, and identifies the highest attainable dissolved oxygen condition, or HADO.

  • Determines that DO levels are most impacted by summer ammonia loads from nine point sources (Philadelphia Water Department's Southwest, Southeast and Northeast wastewater treatment plants and the plants operated by Camden County Municipal Utilities Authority, City of Wilmington, Gloucester County Utilities Authority, Hamilton Township, DELCORA and Lower Bucks County Joint Municipal Authority).

  • Summarizes the results of cost and affordability evaluations for reducing ammonia discharges to the Delaware River Estuary.

  • Recommends steps for achieving the HADO.

  • Recommends that the Commission initiate a rulemaking process, as outlined in Resolution No. 2017-4, to revise the designated aquatic life uses and develop water quality criteria to support those uses.

Next Steps

  • The draft AA and its supporting products will continue to be discussed at future WQAC meetings.

  • The DRBC will initiate a public rulemaking process on revised designated uses and associated water quality criteria and an implementation strategy. All stakeholders will have an opportunity to provide their input and perspectives.
NGO Petition & EPA Determination

In April 2022, a group of NGOs sent a petition to the EPA seeking to bypass ongoing DRBC processes and compel EPA to commence a separate action to revise water quality standards for the protection of aquatic life in the Delaware River Estuary. 

On December 1, 2022, EPA issued a determination that revising the water quality standards for a portion of the Delaware River Estuary is necessary to satisfy the requirements of the Clean Water Act. In doing so, EPA recognized the value of foundational science performed by the DRBC, including to demonstrate that propagation throughout the Estuary is attainable, and the commitment and ongoing work by DRBC and the Estuary states to update the standards.  

The DRBC issued the following statement (12/1/22):  

The Delaware River Basin Commission (DRBC) has received a copy of EPA's determination in response to a Petition filed by a group of non-governmental organizations. Staff is reviewing the EPA response with the Commission members and counsel.   

The Petition sought to bypass ongoing DRBC processes and compel EPA to commence a separate action to revise water quality standards for the protection of aquatic life in a portion of the Delaware River Estuary. Because of the significant progress DRBC has already made – working in close collaboration with EPA and state co-regulators – to update the Estuary aquatic life use standards, the Commission viewed the Petition as unnecessary. (See DRBC letter to EPA, October 2022; pdf) Nevertheless, DRBC respects the Administrator's determination and welcomes EPA's continued engagement with DRBC in this effort.  

EPA's response commends DRBC and its member state agencies for the significant water quality improvements realized in the Estuary.  EPA also recognizes the value of foundational science performed by DRBC, including to demonstrate that propagation throughout the Estuary is attainable, and the commitment by DRBC and the Estuary states to update the standards. EPA acknowledges that the timeline for establishing new standards will be accelerated by the "readily available information that DRBC and other stakeholders have generated." The EPA also makes clear it, "acknowledges and appreciates DRBC's and your states' commitment to updating the WQS for the specified zones of the Delaware River Estuary."

Priority actions by the DRBC to revise the Estuary water quality standards to meet Clean Water Act goals are well underway. By resolutions adopted unanimously by the Commission's member states and the United States, the Commission has committed substantial resources over several years to establish the scientific foundation and conduct rulemaking for new standards through a transparent and collaborative process. The body of scientific work that DRBC has delivered supports the inclusion of fish propagation (by multiple species, including the endangered Atlantic Sturgeon) as a designated aquatic life use throughout the Estuary. DRBC-led science also has established the foundation for the development of new dissolved oxygen criteria to support this use. A summary of DRBC's plan for revising the Estuary water quality standards, along with key technical support documents and procedural records, are available on this webpage. 

While EPA's decision has the potential to create a duplicative regulatory process, the DRBC is committed to continuing to work jointly with EPA and state co-regulator agencies in Delaware, New Jersey and Pennsylvania to develop water quality standards using sound science to meet the goals of the Clean Water Act and the Delaware River Basin Comprehensive Plan. DRBC is equally committed to doing so through a transparent process that engages all concerned stakeholders. The Commission has a successful 61-year history of working collaboratively and delivering regulatory policy to protect and significantly improve water quality in the interstate waters of the Delaware River Estuary and is committed to continuing this critical work.   

Archive: DRBC Study Reports
Archive: DRBC Presentations

View a video of the presentation, courtesy of the NJ-AWRA:

Archive: DRBC Resolutions

During public meetings from 2010 through 2020, the Commission adopted the numbered resolutions (subject to public hearing) and resolutions for the Minutes (not requiring public hearing) listed in chronological order below, results of which were used to support various aspects of the Aquatic Life Designated Use Study. All are pdfs.