Walt Whitman Bridge DC
Looking downriver toward the Walt Whitman Bridge, with Philadelphia on your right, Camden on your left. This is the urban corridor that needs work to be cleaner. PHOTO BY MEG MCGUIRE

Ta-DA! First big step in getting the Delaware River cleaner

| May 12, 2022

Where are the fireworks? Marching bands?

The scientific and engineering work that could well give us a significantly cleaner Delaware River — from Trenton, N.J., on south — has been completed.

Those scientists and engineers have been building a model that could capture all the important processes in the estuary (that bit below Trenton) and use that to calibrate what has to be done where to improve the river and bay, specifically with regard to dissolved oxygen in the water.

The sore spot is the urban corridor of the river approximately from Philadelphia to Wilmington. That is the exact spot where the focus on the river is growing, especially using the river for recreation.

One of the ways you can assess how healthy a river is: Find out how the native fish populations are doing. For the Delaware, that could be a number of species, but it’s sturgeon that are in the spotlight because, as an endangered species, we are required to do what we can to foster their propagation.

They, like us, need oxygen to thrive. We have it in the air, they have it dissolved in the water. And in that 38 miles of river, oxygen is often lower than what’s necessary, especially for young sturgeon. That lack of oxygen is called an oxygen sag and it’s pronounced in the urban corridor, especially in the summer when the warmer water is less saturated with oxygen.

So, how do you get more oxygen in the river?

That’s the million-dollar question that this model will be answering. Scientists and engineers from the Delaware River Basin Commission have been working on it since 2017, when the commissioners (the governors of the four border states and the U S. Army Corps of Engineers — the federal representative) unanimously voted for resolution 2017-4. Here’s the resolution .

Here’s what needs to be done from a slide shown at a recent Water Quality Advisory Committee meeting:

What needs to be done before rulemaking

There has been concern expressed by some that this process is taking too long — but Thomas Amidon, the DRBC’s manager in charge of modeling, pointed out that a similar model for the Chesapeake Bay took 15 years.

In fact, though there’s a broad consensus that ammonia IS the problem and that the wastewater treatments plants are the source, the DRBC’s plan allows for each facility to know exactly what its part of the problem is so each municipality can address it and defend it to the taxpayers who might have to foot some of the bill. With any luck, the recent federal funding for infrastructure work will ease some of that local burden.

Ages ago when the river was much dirtier than it is now (and smellier), there really wasn’t much processing of waste entering the river. The compact that created the Delaware River Basin Commission 60-plus years ago was the beginning of finding solutions to that problem. The commission enacted regulations that required municipalities to treat their wastewater, but the regs back then focused on the biggest problem — which was carbon from our poop. 

The solutions have worked and that section of the river is much cleaner, but not clean enough to support sturgeon — or really humans splashing around in the river water. (There’s a whole other problem for the river from water treatment plants that use a Combined Sewer Overflow, but that’s a different question that also needs to be addressed, outside of this work.)

The biggest driver of the DO sag is the work that the river itself has to do to process the excess ammonia that comes into the river from various wastewater treatment plants. Putting it bluntly, that ammonia is our pee.

If someone were to wave a magic wand and reduce the population of this part of the river by, say, half, the river would likely be able to process that amount of ammonia through nitrification without depleting dissolved oxygen. When the amount of ammonia grows to current proportions and the wastewater treatment plants empty the treated (for carbon) wastewater into the river (all legally, by the way) the river can’t handle it and the dissolved oxygen gets reduced — because the natural processes can’t keep up with it — and the sturgeon suffer.

So back in 2017, that resolution directed DRBC scientists and engineers to develop this just-completed model so that the commissioners could decide on what, if any, new regs to approve to make the river cleaner.

And that resolution hit on another important aspect of the work — that implementing new regs that would affect the dissolved oxygen in the river would likely mean really, really big bills for the wastewater treatment plants — and remember these are municipal plants. And nobody wants to pay more for their water. More about those million-dollar costs here.

So the goal for the model is to create a working tool that could help everyone see exactly how much each wastewater treatment plant needs to do to reduce the DO sag.

Then, there’s the possibility that new regulations could be forthcoming that will set new attainability standards for the river, especially in this troubled area.

The work would target so-called top-tier plants:

There are 12 wastewater treatment plants in the Tier 1 category — all municipal wastewater treatment plants:

  • PA Philadelphia Water Department, Southwest
  • PA Philadelphia Water Department, Northeast
  • PA Philadelphia Water Department, Southeast
  • PA Lower Bucks County Joint Municipal Authority
  • PA DELCORA (Delaware County Regional Water Quality Control Authority) DELCORA is in the middle of a battle over its purchase by Aqua Pennsylvania, which would make it the largest wastewater treatment plant in the watershed not operated by its municipality.)
  • PA Morrisville Borough Municipal Authority
  • NJ Camden County Municipal Utilities Authority
  • NJ Gloucester County Utilities Authority
  • NJ Hamilton Township (Mercer County) Water Pollution Control Facility
  • NJ Trenton Sewer Utility
  • NJ Willingboro Municipal Utilities Authority
  • DEL City of Wilmington Department of Public Works

Since 2017, these plants have been working with the DRBC to supply data to finely tune the model and make it “work.”

When building this sort of model, Amidon cautioned with an adage known to the modeling community: “All models are wrong, some are useful.”

Perfection isn’t the aim of this model — usefulness is. The model has received the blessing of a model expert panel that has been guiding its development. This model expert panel includes:

Steve Chapra, Tufts University; Carl Cerco, U.S. Army Corps of Engineers (retired); Bob Chant, Rutgers University; and Tim Wool, U.S. Environmental Protection Agency, Region 4.

Here’s what they said (from a slide shown at a recent WQAC meeting):

Conclusions from model expert panel

“The model is an attempt,” said Amidon, “to synthesize all the various processes that affect dissolved oxygen,” including nutrients and organic matter.

The first step is to calculate the ways that oxygen enters the system. Principally there are two: from the atmosphere — called aeration, and photosynthesis — mostly from algae which are active all the time whenever light is present, especially in summer.

And at the same time, what are the ways that oxygen is depleted? There are several but nitrification is the most important. Amidon said it was the opinion of most of the scientists that it was likely this process — turning ammonia into nitrate — that created the oxygen sag. The model has proven that.

The process of nitrification occurs naturally in the system, but the system is so overwhelmed that it significantly depletes oxygen in the process. So a big question to answer is: If the wastewater treatment plants were to perform the nitrification as part of their treatment process, how much would that improve DO and allow more successful propagation of sturgeon?

The first step in finding that answer was to build a hydrodynamic model to figure out the effects of tides, water, salt, etc. 

Then the water quality (aka eutrophication) model is built on “top” of that. It incorporates a large set of historical and experimental data and knowledge, allowing scientists to “play” with variables to see what effect they have on the system as a whole.

As Amidon explained a model is not reality, and can never capture reality but it can, with what he called “an appropriate level of complexity,” provide a way to understand the system.

The model expert panel has agreed, and the specific terminology is “The model is corroborated for its intended use.”

One of the surprising findings from the work so far is that this estuary is a really high-energy estuary, compared, for example, to the Chesapeake. That was known before the model but the model emphasizes that the action of waves, tides, etc., has a significant impact on the estuary and means that creating the hydrodynamic model was an important first step.

The other surprising thing was the importance of light and its absence or presence. Light is an important driver of photosynthesis. It drives phytoplankton growth and that has a profound effect on dissolved oxygen.

So the question was: How much light can penetrate the water column? Because more light means more growth. When the water is clear, more growth can happen. In fact, the water of the Delaware is relatively dark and turbid. The color is largely because the water coming into the river from the tributaries is dark, not because of pollution, but because of its geography. The turbid nature is due to physics, the high energy tidal system.

The lack of light explains why there aren’t significant gross mats of algae, even though there can be temporary algae blooms on the river.

Amidon explained that light is attenuated as it hits particles in the water. Also, it will be attenuated when it hits color. (The relationship of light and color is what the whole Impressionist movement was all about!) In this case, less light equals less photosynthesis.

An enigma related to light presented itself: Why didn’t the model capture a phytoplankton bloom in the urban estuary from early June through July of 2019?

The concern was that the model was “missing” something. After the team exhausted all the possibilities, Amidon said a decision was made to move on, albeit reluctantly. Then, showing how valuable the expert panel was, Bob Chant from Rutgers remembered a paper a student had done on phytoplankton blooms in the upper river and what causes it, and voila, they discovered the answer.

Here’s the science: Periods of higher water clarity during the growing season in the upper tidal river result in transient blooms that propagate downstream and affect phytoplankton throughout the tidal river.

Those blooms keep seeding new blooms if the light allows.

Now, the process moves on in the Water Quality Advisory Committee, which will meet monthly during the summer to develop a draft analysis of attainability. In other words, with the help of the model, finding the right combination of variables that link cost, benefit, affordability and level of fish protection.

That analysis of attainability is the end result and it will be for the commissioners to decide what new standards are indicated to achieve that cleaner healthier river that we mentioned at the beginning.

Here’s the schedule:

Tentative schedule
Meg McGuire

Meg McGuire

Meg McGuire has been a journalist for 30 years in New York and Connecticut. She started in weekly newspapers and moved to full-time work in dailies 25 years ago. She knows about the tectonic changes in journalism firsthand, having been part of what was euphemistically called a "reduction in force" six years ago. Now she's working to find new ways to "do" the news as an independent online publisher of news about the Delaware River, its watershed and its people.

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