Dissolved Oxygen & Delaware River Water Quality

Looking out over the Delaware River from Camden, NJ, on a beautiful day, the Philadelphia skyline shines between a mostly blue sky and the shimmering river. The tents, crowds, and an ice cream truck for Delaware River Fest 2022 are visible on Penn's Landing.

What you should know

  • EPA’s proposed regulation seeks to improve dissolved oxygen in the Delaware River by imposing large-scale reduction of ammonia at PWD’s three Water Pollution Control Plants.
  • EPA claims these changes will help the Atlantic sturgeon population, but this theory is unproven and not supported by available juvenile and adult sturgeon monitoring data.
  • If finalized, the $3.6 billion price tag for PWD to meet this regulation could increase household water bills by an estimated $265 per year, with no guarantee of benefits to fish, humans, or the environment.
  • PWD is committed to improving water quality in the Delaware River at a scale and pace that does not significantly increase water customer bills. Our planned $74 million sidestream project is an example of this approach.
  • PWD supports revising existing dissolved oxygen regulations in the Delaware River, recognizing that Atlantic sturgeon are propagating and growing in the river. However, as currently drafted, EPA’s proposed regulation is overly stringent, not developed with sound science, and could significantly increase customer bills.
  • PWD is a nonprofit, City-owned water utility that acts in the best interests of our customers and the environment of Philadelphia. There is no profit motive for PWD.


In December 2023, the Environmental Protection Agency proposed a change to water quality standards in the Philadelphia portion of the Delaware River. These new rules aim to increase the levels of dissolved oxygen to protect the Atlantic sturgeon, an endangered species of fish that swim up the Delaware River to spawn and lay their eggs. The regulation, if adopted, would require significant new investment by PWD in its wastewater treatment facilities.

Dissolved oxygen levels in the river are affected by the discharge of Philadelphia’s three wastewater treatment plants. Ammonia – a component of treated wastewater – depletes oxygen in the water, and PWD is the largest contributor to the Delaware River as the provider of wastewater services to more than 2 million people. In order to reduce the ammonia coming from our treatment plants and meet the proposed dissolved oxygen standards, Philadelphia will be required to spend an estimated $3.6 billion for new construction projects at our wastewater facilities. While these investments may improve conditions for some fish, they would not reduce bacteria levels in the Delaware River or make public recreation safer.

PWD is committed to improving water quality in the Delaware River and the protection of the Atlantic sturgeon. In summer 2024, PWD begins construction on a new $74 million treatment facility that will reduce oxygen-depleting ammonia on an efficient scale and at a reasonable price. However, further spending requires examination of the costs to Philadelphia water customers and the benefits to aquatic life. PWD has not found definitive scientific evidence that dissolved oxygen levels are limiting sturgeon populations. Additionally, the construction of new wastewater treatment facilities will greatly increase energy usage and nearly double the emission of greenhouse gases.

Atlantic sturgeon swimming. Credit: NOAA Fisheries

Frequently Asked Questions

What is the EPA proposing for the Delaware River?

The EPA is proposing more stringent dissolved oxygen (DO) criteria that would apply to the Delaware River from Philadelphia to Wilmington. The EPA is proposing this regulation based on the theory that existing DO conditions in the Delaware River are not sufficient to protect reproduction and health of fish species that inhabit the river, including the endangered Atlantic sturgeon.

How is the EPA proposing to improve dissolved oxygen concentrations in the Delaware River?

To increase DO in the river, the EPA is proposing large-scale reduction of ammonia in the discharges from municipal wastewater treatment facilities on the Pennsylvania and New Jersey sides of the Delaware River. Ammonia is a natural component of human waste, and when wastewater enters the river, it reduces oxygen levels in the water. Wastewater treatment plants are the primary source of ammonia to the Delaware River. There are currently no major industrial dischargers of ammonia in the river.

How much is this going to cost?

To build and indefinitely operate the treatment technologies necessary to meet the level of ammonia removal required by the EPA’s proposed regulation, PWD estimates $3.6 billion in capital costs and annual operation and maintenance costs of $36 million per year.

How could Philadelphians’ water bills be impacted by the EPA’s proposed regulation?

PWD estimates the EPA’s proposed regulation will cost customers an additional $22.17 per month on water bills—not $1.50 per month as calculated by the EPA. That amounts to more than $265 per year in new costs for PWD customers.

How did PWD calculate estimated impacts on customer water bills?

PWD identified average watewater and stormwater fees in residential water bills, and then factored in the new costs (capital, operations, and maintenance) required for PWD to design, build, and indefinitely operate advanced ammonia removal processes at its three Water Pollution Control Plants.

Why are PWD estimates for the impact on residential water bills so much higher than those suggested by the EPA?

The EPA affordability assessment of Philadelphia is deeply flawed and does not correctly forecast the increased financial burden of the proposed rule. EPA’s cost of compliance estimate is $2.5 billion less than PWD’s estimate. This is due to discrepancies between the EPA Economic Analysis assumptions and PWD’s own understanding of its facilities, costs, operations, and billing practices. 

For example, EPA incorrectly calculates its estimate of the residential share of wastewater costs. The EPA estimate is 15%, while PWD estimates the residential share of annual wastewater costs is 51.6%. PWD reached this estimate based on its FY24 cost of service analysis.   

For more detail, see comments 22-32 in the PWD Comments on Draft EPA Rulemaking document submitted to the EPA.

Why can’t PWD use federal funding to pay for ammonia removal instead of raising customers’ water bills?

Federal funding opportunities such as the Bipartisan Infrastructure Law (BIL) do not provide enough funding to make PWD compliance with the EPA proposed rulemaking affordable. The BIL provides $44 billion over five years for wastewater, water, and water quality projects—or about $9 billion annually to be allocated among U.S. states, territories, and tribal governments. While $9 billion is certainly a big number, it’s important to consider how much Pennsylvania actually receives.

In the 2022 federal fiscal year, the BIL allocated $240 million to Pennsylvania for wastewater, water, and water quality projects. Of that $240 million, $74.2 million was designated for Clean Water Act related projects across Pennsylvania. It is not realistic to assume that PWD would obtain all of Pennsylvania’s wastewater funding from the BIL for all five years. Even if that assumption were true, such funds would only pay for 10.3% of the funding needed. PWD is recommending that the EPA work with Congress and other stakeholders to ensure adequate funding is made available for this rulemaking to be more affordable for PWD ratepayers, particularly those residing in environmental justice communities.

Will these potential rate increases result in more profit for PWD?

No. PWD is a public municipal utility operated by the City of Philadelphia and does not profit from rate increases. We only request the amount needed to cover the cost of services and to achieve compliance with state and federal regulations.

How could PWD’s electricity use and greenhouse gas emissions be affected by EPA’s proposed regulation?

Estimates from PWD’s wastewater plant evaluations indicate that the addition of ammonia removal treatment at each plant will result in a 147% increase in electricity use and a 99% increase in greenhouse gas emissions.

Isn’t the current DO standard of 3.5 mg/L in these zones too low?

PWD agrees that water quality standards need to be updated to reflect the fact that “propagation” of Atlantic sturgeon is occurring. The current DO standard of 3.5 mg/L as a daily average has not only been met, but has been greatly exceeded, with summer DO levels almost always above 5 mg/L or 60% saturation. PWD supports updating the DO standard based on scientific evidence for levels that protect spawning and growth of fish and other aquatic life in the Delaware River.

What is the status of the Atlantic sturgeon in the Delaware River and are current dissolved oxygen conditions a threat to their survival?

PWD compiled and analyzed more than 5,000 juvenile sturgeon collection records from the Delaware River between 2009-2022 and concluded that dissolved oxygen conditions support spawning and growth of juvenile sturgeon:

  • Total length measurements of young-of-year (YOY) Delaware River Atlantic sturgeon were found to be within the expected range for the species.
  • The average length of 4,593 YOY sturgeon collected from the Delaware River between 2009 and 2022 was 345 mm, or 13.5 inches long.
  • These rapid rates of juvenile sturgeon growth, which were measured consistently from year to year from thousands of fish collected and measured, would not be observed if sturgeon lacked adequate levels of dissolved oxygen.
  • PWD performed 560 statistical tests comparing sturgeon growth measurements with DO statistics for 2009-2022 and found no significant correlations between growth and DO.
  • Delaware River sturgeon also appear to be growing as well as similar age fish in upstate New York’s Hudson River, where dissolved oxygen levels are typically higher.

Does PWD care about improving water quality for Atlantic sturgeon and other fish species in the Delaware River?

Yes, absolutely! PWD shares the goals of ensuring that fish and other aquatic life can not only survive, but thrive, and rebuilding populations of our iconic native species such as Atlantic sturgeon, striped bass, and American shad. To move the ball forward, PWD anticipates completing construction of a $74 million sidestream treatment facility at our Southwest Water Pollution Control Plant by 2027, which would treat 10% of the existing municipal ammonia load to the Delaware River for a reasonable cost to our customers.

How could the EPA’s proposed regulation affect PWD’s other priorities?

PWD’s primary mission is to plan for, operate, and maintain both the infrastructure and the organization necessary to purvey high quality drinking water; to provide an adequate and reliable water supply for all household, commercial, and community needs; and to sustain and enhance the region’s watersheds and quality of life by managing wastewater and stormwater effectively. To keep water bills affordable for our customers, PWD has to be strategic in where, when, and how it invests its resources. The significant costs associated with removing ammonia would force PWD to devote fewer resources to issues that directly affect the public health and daily lives of Philadelphians such as flooding, pipe replacement, emerging contaminants, and combined sewer overflows (CSO).

Would the EPA’s proposed regulation improve recreational water quality in the Delaware River?

No. State and federal agencies measure bacteria (i.e., not ammonia) to determine if a waterway meets swimmable water quality. Bacteria in the Delaware River is attributed to combined sewer overflows, stormwater runoff, and animal sources. The ammonia removal processes needed to meet EPA’s proposed regulation would not reduce bacteria concentrations in the Delaware River and would compete with state and federal funding for CSO mitigation in Philadelphia.

Would the EPA’s proposed regulation improve drinking water quality in Philadelphia or anywhere else?

No. The EPA’s proposed regulation pertains to Philadelphia’s three wastewater treatment plants that discharge to the Delaware River downstream of Philadelphia’s drinking water intakes. There are no drinking water treatment plants located in close proximity to PWD’s wastewater treatment plants. Drinking water in Philadelphia would not benefit from this regulation.

What is PWD doing to voice its concerns to the EPA?

PWD provided oral testimony at the EPA’s Public Hearing on 2/7/2024 and submitted written comments to the EPA on 2/20/24, which focus on aquatic life use, treatment costs, affordability, and fish science. PWD also met with leadership from the EPA Office of Water on 12/14/23 to present PWD’s technical work and communicate concerns with the proposed regulation. We are continuing to engage with EPA and state officials to convey our concerns.

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