Delaware • New Jersey • Pennsylvania
New York • United States of America
- Aquatic Life Designated Use Study
- Bacteria Monitoring
- Biomonitoring Program
- Chlorides Monitoring
- Contaminants of Emerging Concern
- Delaware Estuary Water Quality Monitoring Program
- Dissolved Oxygen and Nutrients
- Modeling
- Other Monitoring Programs & Studies (e.g., Fish Tissue, Microplastics, Metals)
- PCBs and PMPs
- Special Protection Waters (SPW)
- Water Resource Data Sets

- Introduction
- Resolution Approved September 2017: Study Begins
- Resolution Approved September 2020: Updates Schedule Set in 2017
- DRAFT Analysis of Attainability: September 2022
- NGO Petition & EPA Determination
- Archive: DRBC Study Reports
- Archive: DRBC Presentations
- Archive: DRBC Resolutions
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 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.
- View Resolution 2017-4 (pdf)
- View Comment and Response Document regarding Resolution 2017-4 (pdf)
- View News Release
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.
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Collecting water samples to look at light extinction data. |
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 productivity. |
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 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
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Input obtained from an Expert Panel on modeling the water quality impacts of nutrient loadings;
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Research on the dissolved oxygen requirements of key sensitive species completed;
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Ambient nutrient monitoring and primary productivity and algal speciation studies conducted to support model calibration;
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Development of a hydrodynamic and eutrophication model;
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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
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Evaluation of the physical, chemical, biological, social and economic factors affecting attainment of uses.
DRAFT Analysis of Attainability (AA) & Supporting Documents
- Analysis of Attainability: Improving Dissolved Oxygen and Aquatic Life Uses in the Delaware River Estuary (DRAFT; September 2022; pdf)
- Modeling Eutrophication Processes in the Delaware Estuary: Three-Dimensional Water Quality Model (DRAFT; September 2022; pdf) & Appendices A-H (DRAFT; September 2022; zip)
- Modeling Eutrophication Processes in the Delaware River Estuary: Three-Dimensional Hydrodynamics Model (DRAFT; December 2021) & Appendices A-N (DRAFT; December 2021; zip)
- Social and Economic Factors Affecting the Attainment of Aquatic Life Uses in the Delaware River Estuary (DRAFT; September 2022; pdf)
- Linking Aquatic Life Uses with Dissolved Oxygen Conditions in the Delaware River Estuary (DRAFT; November 2022; pdf)
- Nitrogen Reduction Cost Estimation Study: Final Summary Report (submitted to the DRBC by Kleinfelder, Inc.; January 2021; pdf)
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.
- View NGO Petition to the EPA (April 2022; pdf)
- View EPA response to the NGO Petition (May 2022; pdf)
- View DRBC letter to the EPA (October 2022; pdf)
- View EPA Administrator's Determination (December 2022; pdf)
- View EPA Response Letter to NGOs (December 2022; pdf)
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.
- Nitrogen Reduction Cost Estimation Study: Final Summary Report (pdf; this report was submitted to the DRBC by Kleinfelder, Inc., in January 2021)
- Report to DRBC on Concentrations of Nutrients and Chlorophyll-a and Rates of Respiration and Primary Production in Samples from the Delaware River Collected in May and July 2019 (pdf; this report was submitted to the DRBC by the Horn Point Laboratory, University of Maryland; revised Sept. 2020)
- Report to DRBC on Concentrations of Nutrients and Chlorophyll-a and Rates of Respiration and Primary Production in Samples from the Delaware River Collected in May and July 2018 (pdf; this report was submitted to the DRBC by the Horn Point Laboratory, University of Maryland; revised Feb. 2019)
- A Review of Dissolved Oxygen Requirements for Key Sensitive Species in the Delaware Estuary (pdf; this report was submitted to the DRBC by the Academy of Natural Sciences in November 2018)
- A Methodology for Evaluating Dissolved Oxygen Requirements of Species in the Delaware Estuary (pdf; this report was submitted to the DRBC by the Academy of Natural Sciences in March 2018)
- Existing Use Evaluation for Zones 3, 4, & 5 of the Delaware Estuary Based on Spawning and Rearing of Resident and Anadromous Fishes (pdf; September 2015)
- Report to DRBC on Concentrations of Nutrients and Chlorophyll-a and Rates of Respiration and Primary Production in Samples from Delaware Bay Collected in May and July 2014 (pdf; this report was submitted to the DRBC by the Horn Point Laboratory, University of Maryland in May 2015; revised Jan. 2019)
- Improving Dissolved Oxygen and Aquatic Life Uses in the Delaware River Estuary (pdf; given at the NJ-AWRA Watershed Leadership Forum, March 2023)
View a video of the presentation, courtesy of the NJ-AWRA:
- Status of WQS-ALU Co-Regulator Workgroup (pdf; given to the Water Quality Advisory Committee, March 2023)
- Status of the DRBC Draft AA Reports (pdf; given to the Water Quality Advisory Committee, March 2023)
- Improving Dissolved Oxygen and Aquatic Life Uses in the Delaware River Estuary (as part of the Delaware Estuary Science & Environmental Summit, DRBC staff gave seven presentations and two posters on this topic, January 2023)
- Review of Aquatic Life Uses: Progress Update (pdf; given to the Water Quality Advisory Committee, November 2022)
- Analysis of Attainability (AA) Preview (pdf; given to the Water Quality Advisory Committee, September 2022)
- Analysis of Attainability (AA) Progress Update (pdf; given to the Water Quality Advisory Committee, August 2022)
- Analysis of Attainability (AA) Progress Update (pdf; given to the Water Quality Advisory Committee, July 2022)
- Point Discharge Monitoring Results and Summary (pdf; given to the Water Quality Advisory Committee, June 2022)
- Analysis of Attainability (AA) Progress Update (pdf; given to the Water Quality Advisory Committee, June 2022)
- DO Relative Stress Index: Comparison Tool for Different Model Scenarios (pdf; given to the Water Quality Advisory Committee, June 2022)
- Analysis of Attainability: Methodology Discussion (pdf; given to the Water Quality Advisory Committee, May 2022)
- Status Update on DRBC's Socio Economic Evaluation (pdf; given to the Water Quality Advisory Committee, May 2022)
- Estuary Eutrophication Model: Final Calibration Results and Intro to Analysis of Attainability Elements (pdf; given to the Water Quality Advisory Committee, April 2022)
- Status Update: Aquatic Life Designated Use Program (pdf; given to the Water Quality Advisory Committee, Nov. 2021)
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DRBC Expert Panel Update for the Water Quality Advisory Committee (pdf; given to the Water Quality Advisory Committee, Nov. 2021)
- Application of Eutrophication Modeling to Understand the Potential to Expand Designated Aquatic Life Uses in the Delaware River Estuary (pdf; given at the AWRA Mid-Atlantic Conference, Oct. 2021)
- Designated Use for Aquatic Life in Delaware River (pdf; given at the ICWP Annual Meeting; Oct. 2021)
- Restoring Water Quality in the Main Stem Delaware River: Programs, Policies and Strategies (pdf: given by DRBC staff at the 9th Annual Delaware River Watershed Forum, Sept. 2021)
- Socio Economic Evaluation in Support of Highest Attainable Designated Use (pdf; given to the Water Quality Advisory Committee, April 2021)
- Analysis of Attainability Part I: A Strategy to Determine Potential Designated Uses in the Delaware Estuary (pdf; given at the PDE Science and Environmental Summit, March 2021)
- Analysis of Attainability Part II: Linking Aquatic Life Uses with Dissolved Oxygen Condition in the Delaware River Estuary (pdf; given at the PDE Science and Environmental Summit, March 2021)
- DRBC Resolution for the Minutes: Sept. 2020 - Revised Schedule for Aquatic Life Designated Use Project (pdf; given at the joint WQAC/Expert Panel Meeting, Oct. 2020)
- Expert Panel Report to DRBC's WQAC (pdf; given at the joint WQAC/Expert Panel Meeting, Oct. 2020)
- Studies to Determine the Attainability of Aquatic Life Uses and Associated DO Conditions in the Urbanized Portion of the Delaware Estuary (pdf; given at the Delaware Watershed Research Conference, Oct. 2020)
- A Fishable, Swimmable (and Drinkable) Delaware River Estuary (pdf; given at the 8th Annual Delaware River Watershed Forum, Sept. 2020)
- Status Update: Aquatic Life Designated Use Program (pdf; given to the WQAC on 7/28/20)
- Nutrient Monitoring 2020 (pdf; given to the MACC on 5/12/20)
- "Analysis of Attainability": A Strategy to Determine Highest Attainable Dissolved Oxygen Condition (pdf; given to the WQAC on 4/30/20)
- Eutrophication Model Development Monitoring (pdf; given to the MACC on 12/18/19)
- Meeting of the Model Expert Panel with DRBC Staff (pdf; given to the WQAC on 12/5/19)
- Update given at the WQAC Meeting, November 2019 (pdf)
- Update on Engineering Evaluation and Cost Estimates Contracted Work (pdf; given at the Delaware Watershed Research Conference, November 2019)
- Modeling Eutrophication Processes in the Delaware Estuary to Link Watershed Efforts to Control Nutrient Impacts (pdf; given at the Delaware Watershed Research Conference, November 2019)
- Eutrophication Model Development Monitoring Updates 2019 (pdf; given to the MACC on 6/17/19)
- Tributary Ultimate BOD Monitoring (pdf; given to the MACC on 6/17/19)
- Other DRBC Monitoring Surveys (pdf; given to the MACC on 6/17/19; see light extinction and primary productivity slides)
- Update on Eutrophication Model Development (pdf; given to the WQAC on 5/14/19)
- Additional Review of Existing DO Data (pdf; given to the WQAC on 5/14/19)
- Meeting of the Model Expert Panel with DRBC Staff - A Report to the WQAC (pdf; given to the WQAC on 3/20/19)
- The Next Chapter in the Story of Restoring Clean Water to the Delaware River Estuary (pdf; given at the AWRA Annual Conference, November 2018)
- Dissolved Oxygen, Aquatic Life Uses, and the Delaware Estuary (pdf; given at the WRADRB Annual Fall Conference, November 2018)
- Updating Major Wastewater Treatment Infrastructure for Delaware Estuary Aquatic Life Uses: Technical, Economic, and Social Impacts (pdf; given at the Delaware Watershed Research Conference, November 2018)
- Modeling Eutrophication Processes in the Delaware Estuary to Link Watershed Efforts to Control Nutrient Impacts (pdf; given at the Delaware Watershed Research Conference, November 2018)
- Eutrophication Model Development Monitoring 2018 (pdf; given at the March 29, 2018, WQAC Meeting)
- Additional Monitoring Evaluation for Delaware Estuary Point Discharges (pdf; given at the August 2017 WQAC Meeting)
- DRBC to Review Aquatic Life Uses in Delaware River Estuary in Recognition of Improved Water Quality (pdf; given at the April 7, 2017 public hearing)
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.
- Resolution No. 2010-5: Nutrient monitoring of point source discharges to the Estuary and Bay
- Resolution No. 2012-7: Formation of Model Expert Panel
- Resolution No. 2013-6: Analysis of primary productivity by University of Maryland
- Resolution No. 2014-9: Study of effects of low DO and the presence of PCBs on the early life stages of the Atlantic sturgeon
- Resolution for the Minutes of March 15, 2017: Consultation services for model development from LimnoTech
- Resolution No. 2017-4: Initiates the Aquatic Life Designated Use Study
- Resolution No. 2017-5: Analysis of primary productivity by University of Maryland
- Resolution for the Minutes of Sept. 13, 2017: Monitoring of effluent from Estuary point source discharges for two years
- Resolution No. 2018-6: Feasibility and cost evaluation of effluent ammonia reduction from key point source dischargers by Kleinfelder
- Resolution for the Minutes of June 12, 2019: Consultation services for enhancement of source code for the hydrodynamic model (EFDC) from GHD
- Resolution for the Minutes of Dec. 11, 2019: Analytical services for algal composition from Academy of Natural Sciences, Drexel University
- Resolution for the Minutes of Sept. 10, 2020: Revision of project period due to COVID 19 and budget constraints
- Resolution 2021-5: Collection of additional information essential to the evaluation of social and economic factors
- Resolution for the Minutes of March 9, 2022: Authorizing agreement for professional services with the Environmental Finance Center at the University of Maryland
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