Saving the Potomac Aquifer

The SWIFT research center. Photo credit: Philip Shucet

by James A. Bacon

Broadly speaking, there are two approaches to dealing with increasingly stringent clean water regulations. One is to make incremental upgrades with the idea of deferring expensive capital outlays as long as possible, which is what most local governments do. The other is to go big and go bold — the option pursued by the Hampton Roads Sanitation District (HRSD) in its $1.2 billion Sustainable Water Initiative For Tomorrow (SWIFT) project.

As a regional sanitation district serving a population of 1.7 million, the HRSD has the size and resources to undertake projects of a magnitude that smaller municipal systems could only dream about. Under regulatory pressure to reduce algae bloom-causing nitrogen and phosphorus from wastewater released into the Chesapeake Bay, HRSD is implementing an ambitious scheme to treat the water and then pump it back into the Potomac aquifer. The hoped-for result is to slow the rate of land subsidence that contributes to increased flooding in the region.

HRSD’s ambitions are on display at a $25 million research center in Suffolk near the Monitor-Merrimac bridge tunnel. There, researchers are tweaking the process for cleaning about one million gallons daily — not only removing phosphorous, bacteria and viruses but breaking down organic chemicals found in medications tossed into sinks and toilets — to drinking water quality. By 2030, HRSD will apply the technology in five full-scale facilities capable of treating around 100 million gallons daily.

Jamie Mitchell. Photo credit: Philip Shucet

“Groundwater levels have dropped 200 feet in the last one hundred years,” says Jamie Mitchell, HRSD chief of technical services. “The U.S.G.S. (U.S. Geological Survey) estimates that half the relative sea level rise in Hampton Roads is due to subsidence. About half of that is due to withdrawal” from the Potomac aquifer. With the loss of offsetting pressure from the aquifer water, the land above sinks a few millimeters each year, adding up to a few inches over the decades.

With the potential to slow relative sea level rise by 25% or so, the SWIFT project will give the region more time to adapt to the inevitable increase in inundation and flooding. As a bonus, the project may address the water-shortage affecting major users like paper mills.

The geology underneath Hampton Roads is complex. Two thousand feet beneath the surface is bedrock. Above the bedrock are layers of impermeable clay and looser materials through which water can migrate. Three thin aquifers lie at relatively shallow depths under the surface, which residential property owners can tap with private wells, but the largest and deepest source of groundwater is the Potomac aquifer, a complex system which is fed by water infiltrating the ground around the fall line of the James River.

Schematic of the Potomac aquifer. Image credit: Hampton Roads Sanitation District

Municipal governments and manufacturing plants have tapped the Potomac aquifer for decades. But around a decade ago, the Department of Environmental Quality (DEQ) became concerned about the aquifer’s rapid rate of depletion. In the past natural pressure pushed the water to the surface. Now, pumping is required to extract it. Meanwhile, the loss of water pressure allows salt water intrusion from the Atlantic Ocean, which would ruin the aquifer for human consumption and industrial use.

In 2013 DEQ began scaling back permits for the rights to withdraw the groundwater, focusing on the 14 users biggest users. These users, which include James City County and the paper mills in Franklin and West Point, were allowed to withdraw no more than 145.6 million gallons per day. The price tag for developing alternative water supplies, such as piping water in from Lake Gaston on the Virginia-North Carolina border, building reverse-osmosis treatment facilities, and taking water from the Chickahominy River, would run into the hundreds of millions of dollars.

Meanwhile, another huge set of costs is looming. Local governments are under the gun for the nitrogen and phosphorus in stormwater runoff into the Chesapeake Bay and its tributaries. By going over and above conventional wastewater treatment process and reducing nitrogen and phosphorus content to 10% of untreated levels, SWIFT will generate nutrient credits that will help the region meet tighter TDMLs (Total Maximum Daily Loads) and spare localities the need to scrounge up roughly $1 billion for stormwater retrofits.

HRSD will cover the $1.2 billion SWIFT cost by deferring work required by the Environmental Protection Agency to address sewer overflow. The EPA encourages local governments to prioritize investments to accomplish projects with the most significant environmental benefits first, and SWIFT looks like the best of the options. The benefit that comes from slowing the rate of subsidence and relative sea level rise is a big extra. (SWIFT will not affect subsidence that occurs from a gradual shifting of tectonic plates.)

“We can’t quantify the value of halting or slowing subsidence,” says Mitchell. “But it should buy time [for Hampton Roads] to adapt and innovate.”

The experimental SWIFT facility, designed and built by Charlotte, N.C.-based Crowder Constructors, Inc., is highly automated and requires the periodic presence of only three HRSD employees daily. As a research facility, it also hosts six to eight researchers, typically employed by Virginia universities, investigating ways to cut process costs and improve public health.

Interior of SWIFT water processing plant. Photo credit: Philip Shucet

Currently, HRSD treats wastewater to state and federal standards and releases it into Virginia waterways. SWIFT takes the wastewater through several additional steps. One stage in the treatment process injects ozone into the water — ozone is a highly reactive molecule consisting of three oxygen atoms — that inactivates pathogens such as protozoa and viruses by breaking them down into organic materials, which microbes embedded in a carbon medium can absorb in a biofiltration process. To kill off any surviving pathogens, SWIFT zaps the water with ultraviolet light.

Photo credit: Philip Shucet

At this point the wastewater is clean enough for human consumption — and SWIFT tour guides invite visitors to drink it from a fountain. But the water must be subject to further treatment before being put back into the aquifer. The goal, says Mitchell, is to match the “native groundwater chemistry” as closely as possible, which means matching concentrations of salt, manganese, fluoride and other chemicals found naturally in the groundwater.

Mitchell quickly dispenses with the idea that “fresh” aquifer water resembles the water that comes out of a sparkling mountain spring. All groundwater absorbs chemicals from the material through which it flows. The Potomac aquifer is notable for its high level of fluoride — a level that was so high that the City of Suffolk had to shut down several private wells. It is important to match the background aquifer water, she says, because a different chemical composition could react with clays and other materials in ways that would alter the aquifer’s natural functioning.

These pumps push treated water back into the Potomac aquifer. Photo credit: Philip Shucet

In the final stage, SWIFT delivers the treated water back into the aquifer through a well dug to a depth of about 1,500, and it has set up sensors in the main well and nearby test wells to study what happens to it. After several months in operation, the 140 million gallons injected so far have migrated only a few dozen yards. It takes a couple hundred years for water in the Potomac aquifer to travel a mile, which is an indication of the aeons of time it would take to replenish the entire aquifer naturally.

SWIFT is not a magic bullet that will solve all of Hampton Roads’ water shortages or subsidence issues. The region will have to explore many avenues, including water conservation, exploitation of surface water sources, and perhaps even desalination. But by putting 100 million gallons per day back into the Potomac aquifer, the project will buy the region time. And time may be the scarcest resource of all right now.

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8 responses to “Saving the Potomac Aquifer

  1. There are problems with the concept with respect to drug hormones that are execreted by folks taking the drugs – and to this point in time – as far as I know – there are no processes for removing them nor any standards for levels and concentrations.

    Right now, the “solution” is “dilution” – the wastewater is just released into the environment. I’m surprised that they invite folks to drink it because in the environment – it affects fish and other critters – so that we have intersex fish:

    ” Why Are These Male Fish Growing Eggs?
    Fish in wildlife refuges are feminized, probably by hormone-skewing pollution. What does this portend for the health of all creatures—and people?

    Scientists from the U.S. Fish and Wildlife Service and the U.S. Geological Survey studied fish in 19 national wildlife refuges in the U.S. Northeast, including Missisquoi. Their conclusion: An astonishing 60 to 100 percent of all the male smallmouth bass they examined had female egg cells growing in their testes.

    Scientists call this condition intersex, and while its exact causes are unknown, it’s been linked to manmade, environmental chemicals that mimic or block sex hormones.

    Over the past decade, feminized male fish have been discovered in 37 species in lakes and rivers throughout North America, Europe, and other parts of the world. Experts say the new discovery in protected wildlife refuges is worrisome because it suggests that pollution may be even more pervasive than previously thought.

    “There are no truly untouched areas. I think the take away here is that everything we do, everything we use or put on the land, ends up in the water at some point,” says Luke Iwanowicz, a U.S. Geological Survey fish researcher based in West Virginia who led the wildlife refuge study.

    so the question is – do you want this in the aquifer?

    Also – I’d like to know how much this process adds to a ratepayers bill.

    • Larry, you’ll be reassured to know that the HRSD people I talked to were not aware of any reports of girly-man fish in their service territory (the lower James River Basin). Their destruction of pharmaceutical compounds is just a precaution.

      • I was not aware there was a process for that… is it in your article?

        the hormones affect more than just sex in some fish – and to my knowledge, it’s in all wastewater these days unless HRSD has found a process to remove it … have they?

        ( it’s MORE than just “girly-fish” – it’s a harmone that affects wildlife – in different ways, still being studied.

  2. human drugs with harmones – loose in the environment via wastewater have the potential to do great harm. We just don’t know the potential impacts but things like crabs and oysters and other critters that make up the food web could be adversely affected.

    Over and Over, we do things and do not realize that we cause harm – then we have to back up and try to undo it but some of these things are not so easily undone. Something that took decades to happen, may well take decades to reverse and in some cases you cannot go back.

    I do not expect the Chesapeake Bay to revert to what it was like when John Smith sailed up it but we seem to have immense potential to do things that harm it then have to writes laws and regulations and spend billions of dollars to try to reverse it.

    The advent of human drug harmones is one of those things that we are just starting to understand the damage and while it’s tempting to talk about “girly” fishes – it won’t be near so funny is it results in the extinction of crabs or they morph into something so different that we no longer have the original crabs that we value.

    If Hampton Roads has figured out how to remove harmones from wastewater – it’s a tremendous achievement that will gravitate to other wastewater plants so I hope that it is true.

  3. I think there is more to this story:

    ” Supporters say the $1 billion project could provide all of those benefits without increasing costs for the district’s ratepayers beyond what’s currently projected — if the district is allowed to postpone some needed fixes to address sewer overflows.”

    then if you Google: ” hampton roads combined sewer overflows”

    you get a lot of links about the EPA, DEQ and consent decrees to fix their sewage overflows….

    In this blog post – we ae seeing HR folks viewpoints and not the other issues involving sewage overflows…and what they have done about them (or not).

    • Jim, thanks for this informative article.
      Larry, your concern about putting human hormones into the aquifer is a legitimate one. Based on a quick Google search, it seems there are methods to remove these hormones during water treatment. If HRSD is matching the chemistry of the aquifer to the extent possible, then I assume it using one of these methods.

  4. Gray water reuse (treated waste water) is a controversial topic, but obviously it represents a potential substitute for fresh water. When I lived in South Jersey years ago, they wanted to build a coal plant and give the coal plant the gray water for cooling. They were planning to use tons of chlorine to treat the water. But I wanted a nat gas power plant with air cooling (eg; NJ turnpike Exit 9 Linden Power Plant). Years later (after I moved to Va.) I won that battle – nat gas power plant was built- but I don’t know about the air cooling.

    Depletion of water flow from the river is a problem too.

    One idea NJ had was to put new water wells near the Delaware river, so basically you are getting mix of ground water and river water and reducing strain on both. This had to be upstream of the salt line, and also I think required some treatment.

  5. A fascinating post. Jim, the “hydrogeologic section” you show above has an interesting detail in it that’s worthy of special note: the notation “Chesapeake Bay Impact Crater” and the total absence of the Potomac Aquifer within the crater. This is what underlies much of Mathews County and eastern Gloucester and York, and part of the Eastern Shore. Drill a well down more than 200 feet within the crater walls and you hit: — not fresh water, but intense brine. And as you can see, this area of Virginia lies adjacent to (if not within) the HRSD area of responsibility. Long term water resources within the crater are extremely limited, and resources just outside that area must be shepherded especially carefully. I for one am very glad to hear that the use of the Potomac Aquifer, a scarce and extremely valuable groundwater resource, for, e.g., the paper mill in West Point, is being scaled back.

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