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Thread: Salt water

  1. #1
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    Default Salt water

    A complex threat touches southern SC coast: underground saltwater

    By Chloe Johnson

    HILTON HEAD — On a winding road nestled inside one of this barrier island’s gated communities, past a bay of idle lawnmowers that trim manicured golf courses, sits a cutting edge piece of technology.

    To look at it, you might just see a pipe mounted parallel to a concrete pad, painted a faded blue with a motor at the end. But it’s actually a complex piece of machinery that helps ensure thousands of customers on the island’s north end will have water to drink year-round.

    This well is just one way in which officials on Hilton Head have adapted to a difficult situation: the intrusion of salt into the aquifer under the island. If a supply is tainted with just 1 percent seawater, it makes typically pristine reserves mostly unusable.

    So the machinery injects up to 260 million gallons of treated water from the Savannah River underground, during the winter months when water demand on Hilton Head is low. Then, this water is slowly withdrawn in Hilton Head’s hotter months, when irrigation of yards and gardens sends demand soaring.

    Water wars and scarcity might normally be associated with the arid West. In South Carolina, abundant water defines the coast, laced with a complex matrix of streams, bays and marshes. Yet what’s going on underground here is a different story, one that threatens the availability of drinking water in a region where rapid population growth puts more and more pressure on natural resources. It poses a warning for the rest of the state’s coast, which is threatened by the same rising sea.

    “I think the whole coastal plain eventually will be dealing with these issues,” said Kelley Ferda, general manager of the utility on the southern end of Hilton Head.

    Salt is an expensive problem once it infiltrates a water supply. Take the example of Tampa Bay Water, a utility that serves roughly 2.5 million residents along the Gulf Coast of Florida. That system dealt with its salty groundwater in part by building a $158 million plant that could turn seawater fresh.

    In Beaufort County, the slow march of chlorides has been happening for decades. Water systems are also using creative fixes here. On the south side of Hilton Head Island, one utility dug a well so deep it punctures a layer of sediment last at the surface during the Cretaceous period, at least 65 million years ago. Managers jokingly call the liquid that comes up their “dino water.”

    But what is less clear is how this region will adapt more as sea level rise pushes salt further inland, in both surface water and in the vast reservoirs underground. A U.S. Geological Survey study published in 2010 suggested underground salt plumes could expand substantially by the end of the century. But the study’s most aggressive scenario only included 2 more feet of sea level rise; according to a 2017 federal report, the upper limit for potential global sea rise by 2100 is actually slightly more than 8 feet.

    It’s a sign of trouble for the coast at large, where salt is already spotted regularly in many wells near the ocean.

    Meanwhile, the S.C. Department of Health and Environmental Control recently released a report that combined decades’ worth of collected data on how salt has permeated underground supplies below Beaufort County. It described in detail 11 different plumes of salt in the aquifer at the southern coast, including seven that were previously unknown. Salt drifted 2 miles inland over roughly 50 years, the technical paper said.

    But it does not make a single mention of sea level rise or climate change. DHEC also does not take future sea level rise into account when evaluating proposals to suck up groundwater.

    “The aquifers that support drinking water along the coast, in general, are very deep and less likely to be directly impacted by sea level rise,” DHEC spokeswoman Laura Renwick wrote in an email. “However, changes in our climate paired with continued population growth could have potential impacts on water resources.”

    An ancient aquifer
    The underground aquifer system under the southern reaches of South Carolina’s coast, the Floridan Aquifer, is a valuable resource because the water from the highest layer needs little treatment.

    The limestone aquifer is separated into upper, middle and lower layers. Picture a type of geologic birthday cake: Porous limestone sections stacked on top of each other have plenty of open space for water to fill (the cake layers); dense, watertight layers of marl or clay in between mostly block water from passing from one zone to another (the frosting).

    Normally, the water in those layers flows in the same direction as water above ground — toward the ocean. But too many people sucking water out can change the direction of movement, pulling it toward a well site and disrupting that natural flow. On Hilton Head, that pressure differential also started pulling in salty groundwater that resides under the ocean.

    “Once that happens, it’s very hard to get out,” said Brooke Czwartacki, a hydrologist at the S.C. Department of Natural Resources who tracks water levels at 166 test wells across the coastal plain.

    This issue is made worse by geology. Ancient rivers and streams carved over present-day Beaufort County 18,000 years ago when the sea was around 300 feet lower. Those waterways weakened the earthen layer protecting the underground reservoirs, creating passageways for salt to sneak in today.

    That’s what has happened in Hilton Head; the Public Service District on the north end of the island once relied on 12 wells punched into the Upper Floridan, between 120 and 200 feet deep. Now, only two of those wells are regularly used, because the salt content is too high in the rest.

    It’s not entirely the island’s fault. About two-thirds of the problem comes from the city of Savannah, said Camille Ransom III, a retired hydrogeologist who led investigations of underground salt infiltration for years at DHEC. Savannah relies on groundwater for all of its municipal water, and it’s also an attractive resource for local industries.

    So for about the past century, pumping has been the main driver of salt infiltration in the region. But over the same time period, the ocean has risen about a foot, according to readings at a Charleston tidal gauge operated by the federal government. And a rising ocean also contributes to the pressure imbalance that lets salt sneak underground, slowly pushing it inland into formerly fresh areas.

    Pumping from Hilton Head and Savannah peaked in the 1990s, and in both areas, there are now limits on how much water can be withdrawn. But the studies are clear: If all the wells were capped tomorrow, the salt plume in the highest layer of the Floridan aquifer wouldn’t completely disappear.

    Hilton Head PSD withdraws at most about 2 million gallons a day from that aquifer layer. Eventually, the salt will reach those two remaining wells.

    “You don’t look at it as your future development,” said Pete Nardi, general manager for the Hilton Head Island PSD.


    So the water managers on this island were pushed to develop other sources. The crucial resource supports about 40,000 year-round residents, and as many as 2.6 million visitors a year on the tourism-dependent island.

    One option is to come above ground, using surface water from the Beaufort-Jasper Water and Sewer Authority. The Authority has its roots in the salt problem; it was created in 1954 to serve areas like the Parris Island Marine Corps installation, which had already lost several wells, over several decades, to advancing salt.

    This Beaufort-Jasper water is what Hilton Head PSD injects underground in the winter and slowly withdraws in the summer. But it doesn’t meet the entire demand. So the PSD also drilled three wells that penetrate further into the Middle Floridan. That water is lightly salty already. It’s filtered in a reverse osmosis plant, where pressurized water is spun through nylon membranes to remove salt.

    The plant and the three wells that feed it cost $11 million in 2009, Nardi said.

    On the south side of the island, farther from the invading underground plume, water managers have taken a different approach. For now, 13 Upper Floridan wells provide just over half of the utility’s water. Two others have been lost to salt.

    The remaining supply is coming from a different, and even deeper, source.

    The South Island’ PSD’s “Cretaceous well,” reaching an underground layer that’s 65 million years old, extends 3,832 feet deep, said Ferda, the general manager.

    Ferda said the well took a year to drill and is lined with a special high-gauge steel. The water that comes up is under so much pressure it naturally flows at 1,700 gallons a minute. It’s also scorching, at 118 degrees Fahrenheit. It has to be run through a cooling system before filtering out the magnesium and calcium that comes up with the ancient water.

    The original Cretaceous well cost $1 million to drill in 2001, Ferda said. She expects the next one to cost more than five times as much. That’s the supply the utility will rely on as some of its 13 shallow wells, as expected, are made useless by the advancing underground salt plume.

    “It’s quite an endeavor to drill that deep,” Ferda said.

    Utility managers have figured out the supply, but on the demand side of the equation some progress has been made, too.

    All golf courses on Hilton Head now use treated wastewater for irrigation instead of potable drinking water, Nardi said. But he said there are still gains to be made in conservation, especially with landscaping that doesn’t include so much water-hungry turf grass.

    Right now, state regulators don’t factor in sea level rise when making water withdrawal decisions near the coast. Policy is focused on making sure that companies or utilities don’t use the resource faster than it’s replenished and create a “cone of depression,” or a region with lowered underground water levels, as has happened in the Charleston region, under Mount Pleasant.

    Questions about how much water can be used before an aquifer is depleted led the state to deny some of Mount Pleasant’s recent requests for larger withdrawals. Tech giant Google also caused controversy as it asked for groundwater to cool a massive server farm in Berkeley County, though the company later struck a deal with environmentalists to only use that supply for emergencies.

    “I rarely hear folks talking about (sea level rise) in terms of water withdrawal planning and those types of things,” said Chris Foldesi, a hydrogeologist who consults for the Hilton Head Island PSD. “I’m not saying it doesn’t have an effect. It’s going to have an effect.”

    Scientists have known for years that sea rise will put additional pressure on the aquifer. Czwartacki, of DNR, said signs of salt already show up in monitoring wells in many areas east of U.S. Highway 17 in the Lowcountry. For now, the problem mostly affects private homeowners with individual wells.

    Ransom, the retired state hydrogeologist, built the gold-standard model that tracks water movement in the aquifer under Beaufort County — basically, a math equation to predict where the salt will seep and under what conditions. He said he could plug in different ocean heights into the model and see the effects, though that type of analysis has never been published.

    “If sea level rises another foot, we’re going to see significant impacts on the aquifer as well as surface water supplies along the coast,” Ransom said.

    The problem is that most scientific projections now peg sea rise by the year 2100 at far more than a foot.

    DHEC’s recently published technical report provides a partial answer. It shows salt spreading across a far broader area underground by 2050, using Ransom’s model. The plumes grow in size and salt concentration, blanketing the southern end of Hilton Head and beginning to encroach on nearby Daufuskie Island.

    But that modeling doesn’t account for sea rise at all. Now, there are just two wells left tracking the actual speed of saline assault underneath Beaufort County, one run by DNR and one run by the U.S. Geological Survey.

    Renwick, the DHEC spokeswoman, said the agency hasn’t run any wells there in four years because it gave the tracking program over to DNR. Czwartacki said DNR focused its scarce efforts elsewhere for now because of the long-term research that was already happening at the south end of the coast. She is the only staff member tasked with tracking and calibrating the rest of the monitoring wells on the coastal plain.

    Renwick also said DHEC’s withdrawal permitting, river basin planning by DNR and other research at Clemson University all contributed to “appropriately managing the state’s valuable water resources.”

    In the meantime, more people migrate to the area, demanding ever more water.

    Just 15 miles away from Hilton Head, the 3,000-home Latitude Margaritaville retirement community was awarded a groundwater permit in 2019. The development can suck up as many as 65 million gallons a day. Only a small portion can be taken from tightly-regulated upper layers. Mostly, the development is going lower — plunging six wells into the Middle Floridan.

    All of that water, according to the permit, would be used to water lawns and gardens.

    https://www.postandcourier.com/news/...b17428ace.html

  2. #2
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    Feb 2003
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    Maybe stop developing our coast like there's no tomorrow?

  3. #3
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    Quote Originally Posted by GMAC View Post
    Maybe stop developing our coast like there's no tomorrow?
    You mean government tell landowners what to do, nawh. If you want to persevere something buy it. But stop federal flood insurance, owners beware.

  4. #4
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    Quote Originally Posted by Bigtimber2 View Post
    You mean government tell landowners what to do, nawh. If you want to persevere something buy it. But stop federal flood insurance, owners beware.
    Bingo.

  5. #5
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    Nov 2002
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    FloVegas SC
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    Just read this post. It is amazing to me how this works. In Charleston/Mt P they use empty aquifers as storage tanks to both add capacity and as a cooler place to store water. They have such deep wells to get fresh water that by the time it reaches the surface and goes through the reverse osmosis system it is nearly at the boiling point. I am amazed and the smart people that figured this out. we cannot underestimate how quickly our society would evaporate (no pun intended) without fresh running water.

    Having said that I have still not tapped into our city water choosing to drink my well water. It is tested regularly and tastes as it should...like nothing. The middle east has figured out desalinization, I am sure that will be our long-term plan as well. MG
    Dum Spiro Spero

  6. #6
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    1700 gallons a minute is amazing

  7. #7
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    Feb 2003
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    Columbia
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    Why should I subsidize their developments? If they can't supply water for their developments on their own dime, fuck'em.

  8. #8
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    May 2008
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    East Cooper
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    They use the desalination of salt water in Gitmo. When I was going there in the early/mid 90’s we got to check it out.

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