Brackish groundwater resources could play a pivotal role in water-stressed areas of the United States.
By Mike Price
The U.S. Geological Survey released in April its first nationwide assessment of brackish groundwater in more than 50 years.
The report found the amount of brackish groundwater underlying the country is more than 800 times the amount currently used each year. Brackish groundwater, which is about three to 30 times less salty than the ocean, was evaluated by the USGS down to 3000 feet in the country’s 60 major aquifers.
The report concluded every state has brackish groundwater save for New Hampshire and Rhode Island.
With drought, groundwater depletion, dwindling freshwater supplies, and demand for groundwater expected to continue to rise—understanding brackish groundwater supplies can help determine whether they can supplement or replace taxed freshwater sources in water-stressed areas.
“There is a large amount of brackish groundwater, but the issue is how much can be accessed and extracted in a way that is cost effective and environmentally friendly and that ensures high water quality,” says Bill Alley, Ph.D., director of science and technology for the National Ground Water Association, in the May issue of Municipal Water Leader. “There is a limited amount of information available on brackish water, so the recent USGS national study on brackish groundwater resources
was timely and needed.”
The lead hydrologist of the study, USGS hydrologist Jennifer Stanton, says the report is only the beginning for more detailed local analyses. The report, which can be accessed at https://pubs.usgs.gov/pp/1833/pp1833.pdf, contains key graphics such as minimum depth to brackish groundwater and dissolved-solids concentrations of 1000, 3000, and 10,000 milligrams per liter for depths 500, 1500, and 3000 feet below land surface in the 48 conterminous states of the United
States. It shows the deeper one goes, the saltier the water gets.
“This assessment lays the foundation for building a deeper understanding of brackish groundwater resources and how they might be used to better ensure our water security,” Stanton says.
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In states like Texas and New Mexico, desalination of brackish groundwater is common. The largest inland desalination plant in the world is in the Texas city of El Paso.
El Paso taps an aquifer called the Hueco Bolson, which it shares with the state of New Mexico and the country of Mexico. The city’s portion contains 7 million acre-feet of freshwater, but 35 million acre-feet of brackish water. (An acre-foot measures about 325,851 gallons.) The plant produces up to an extra 27 million gallons of water per day for the city.
Interestingly, NGWA’s Alley says operators are exploring the use of solar-powered desalination facilities to save on energy consumption. The Carlsbad facility in California is linked to a power plant and is using some of the heat generated by the plant to assist in the desalination of the water.
When constructing a brackish water production well, the choice of construction material is an extremely critical consideration in saline formations. In Texas, water quality and heat are also major factors as the average temperature of brackish water is 106°F. The average depth of a brackish well in Texas is 1200
“Looking at the materials of construction—a drop pipe (production casing) for a pump, set at any considerable depth, you’ve got a combination of sodium chloride, the strain of the string weight plus the elevated temperature—it’s a triple jeopardy for trying to keep equipmet in the hole,” so sums up Pat Goodson, PG, owner of Geoprojects International Inc. in Austin, Texas.
“I’m not a corrosion engineer, but I’ve had conversations with several, and it’s just really a tough spot.”
The stainless steel submersible motors that fail are not overheating, Goodson says, as they’re operating within the manufacturer’s recommended temperature range. Rather, the high heat combined with the corrosive environment of sodium chloride make the use of an all-stainless pump and submersible
motor a requirement.
Goodson, who serves on the Texas Ground Water Association Groundwater Science Board of Directors, shares his company learned through trial and error which material works best for production casing. They went through carbon steel and stainless steel before landing on epoxy coated carbon steel pipe,
which is a technique used in the oil field. The use of fiberglass was discussed, but Goodson’s firm ultimately passed due to concerns regarding workability issues.
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According to the Texas Water Development Board, virtually all municipal groundwater wells in Texas are constructed with carbon steel, polyvinyl chloride (PVC), or stainless steel casing.
The state agency says, overwhelmingly, stainless steel is the well construction material of choice for brackish water wells because of its corrosion resistance, strength, and widespread availability. PVC casing is common in lower-capacity wells because it is relatively inexpensive and provides excellent resistance to corrosion; however, there are significant strength limitations associated with PVC that generally preclude its use in deep and/or large diameter wells.
A guidance manual published by the Texas Water Development Board in 2013 looked at the potential of fiberglass as the material for casing. The manual, Fiberglass Casing Use in Texas Public Supply Wells, states fiberglass well casing provides an alternative to stainless steel and PVC where strength and
corrosion resistance are needed to ensure long-term well integrity in brackish groundwater and corrosive environments. Fiberglass-cased wells have been used in the oil industry for decades and have been used in other states in water well applications for the last 30 years.
At the issuing of the guidance manual, fiberglass casing in Texas used in brackish groundwater public supply wells was relatively new because of the relative abundance of fresh groundwater supplies. But as reverse osmosis treatment costs have been reduced, brackish groundwater has become an attractive option for some public water supply operators.
Walter Skinner, owner of Skinner Well Service in Alpine, Texas, has installed fiberglass production casing but has yet to use fiberglass for well casing. He installed 2⅜-inch fiberglass production casing after pulling and replacing a 1-inch galvanized steel pipe. This solved the corrosion issue at a well site in 2008 in southwestern Texas near the Rio Grande.
“As far as well casing with fiberglass, I haven’t really thought of doing that but that’s an option we may need to check into ourselves and see if we couldn’t do that down there,” Skinner says, “because that would make it last a lot longer and that would stop our rust problem from our casing. Those wells would last a lot longer.”
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The drilling method used depends on the formation type and the level of salinity in the water-bearing formation.
Lee Gebbert, vice president of Geoprojects International who has drilled for nearly 40 years, says if mud rotary is chosen, sodium bentonite drilling mud most likely won’t work. Instead, a salt-based drilling mud or something similar should be used. When air drilling, the salinity will degrade the foaming agent
being used, so extra precaution is necessary when using drilling polymers.
“The higher the salt content is, the higher the effect on polymers,” Gebbert says, “and its properties may change completely. You need to check and double-check you’re not putting something in the hole that is going to plug it.”
A downside of installing and replacing the epoxy coated carbon steel pipe for production casing is the labor-intensive and time-consuming component, but according to Gebbert, the casing’s average life span is four to five years. All other options for production casing can last on average five to 10 years.
“If you put galvanized steel in there, within four years you’d swear it was in there for 15 to 20 years,” Gebbert says. “That’s how bad it is. I’m not sure if it’s a combination of the heat and minerals. Heat accelerates everything.”
A positive in southwestern Texas is due to its limestone formations—open hole completions are common, negating the need to install a well screen that could corrode. Despite the challenges that may come in constructing a brackish well, all signs point to it becoming more of a realistic option in water-stressed areas.
“It’s more cost-effective to treat brackish groundwater than it is to take ocean water and clean it, at least to my understanding,” Gebbert says. “I see it as the next best shot of increasing our public water supply.”
All the same, there are limitations to its use. “There is only so much brackish groundwater that can be
developed before factors such as pumping costs or environmental effects become limiting factors,” Alley says. “Thus, the challenge is to tap into the brackish water resource in a cost-effective and sustainable manner while minimizing adverse effects on nearby existing freshwater resources. Other considerations include the disposal of brine and energy consumed to process the brackish water.”
“More work is needed to fully understand the resource,” Stanton adds. “Although this assessment can’t answer all of the questions related to sustainable use, it represents a starting point for identifying the gaps in our knowledge and for directing research to locations where further study would be most
NGWA Sponsors Congressional Briefing on Brackish Groundwater
Congressional and federal agency staff assembled on Capitol Hill to hear a May 4 briefing on the U.S. Geological Survey brackish groundwater assessment—the first national assessment of brackish groundwater since 1965.
Three panelists who spoke at the briefing were Jennifer Stanton, U.S. Geological Survey; Katherine Dahm, Bureau of Reclamation; and Marty King, Nebraska Department of Environmental Quality.
The briefing highlighted the ways in which stakeholders outside of the government could use the report and was moderated by Chuck Job, NGWA’s manager of regulatory affairs.
Representatives Rob Wittman (R-Virginia) and Grace Napolitano (D-California) were the congressional sponsors of the event. Ryan Nichols, special assistant to the secretary in the Office of Water and Science at the Department of Interior, also provided introductory remarks to the group at the briefing.
The event represented an opportunity to highlight the importance of brackish groundwater as water resources continue to be constrained. It also served as a primer on brackish groundwater
to a number of new congressional staff and agency officials in attendance.
To view the USGS report, visit https://water.usgs.gov/ogw/gwrp/brackishgw.
NGWA has an information brief on this subject, which can be viewed under the Publications/Bookstore tab at www.NGWA.org.
Mike Price is the senior editor of Water Well Journal. In addition to his WWJ responsibilities, Price produces NGWA’s newsletter and contributes to the Association’s quarterly scientific publication. He can be reached at email@example.com.