Sunday, August 12, 2007
A Solution For N.M. Water Needs?
By John Fleck
Copyright © 2007 Albuquerque Journal; Journal Staff Writer
The discovery of brackish water isn't normally cause for celebration. You wouldn't want to drink it. About the only thing you can do with it is kill plants.
But when a drill rig west of Rio Rancho hit brackish water more than half a mile underground last month, you could almost hear the sound of a pending economic boom.
"The fact that we hit (water) makes the future of Rio Rancho, Bernalillo and Corrales much more prosperous," said Sandoval County Commissioner Jack Thomas.
Standing between brackish water and boom is "desalination," the technology needed to remove salt and minerals and make the water drinkable.
To many, desalination looks like an inevitable part of arid New Mexico's future. The reason: The state's fresh water supplies are pretty much tapped out. We have probably built our last dam, supplies of fresh groundwater are shrinking and the only fresh water option left is moving water from one use to another.
"New Mexico is a water-limited state," said Peggy Johnson, a hydrologist with the New Mexico Bureau of Geology. "We've probably outgrown what our fresh water resources can do for us in the long term."
Our neighbors to the south are embracing their brackish water. El Paso flipped the switch this month on the largest inland desalination plant in the country. It will use brackish water from El Paso-area aquifers, delivering a major portion of the city's water supply and weaning it from dwindling supplies of fresh groundwater.
No one knows how much brackish water lurks beneath the ground in New Mexico, but a number of water-strapped communities in New Mexico have begun looking at the possibility of using it.
Alamogordo is in the midst of a desalination study, and officials in the San Juan Basin of northwest New Mexico, Colfax County in northern New Mexico and Lea County in southeast New Mexico all are considering desalination as part of their long-range water plans.
But to turn brackish groundwater into water salvation, experts say, serious hurdles must be overcome:
Cost. Desalinated water is more expensive. El Paso Water Utilities estimates it costs more than three times as much as clean groundwater.
Waste. All the salt and other minerals taken out of the drinking water have to go somewhere.
Supply. Critics charge that a switch to relying on brackish groundwater merely repeats a mistake in the arid West basing our water future on an unsustainable supply.
"These salt brines are really old and are not being recharged," said Bruce Thomson, head of the University of New Mexico's Water Resources Program. "So maybe Rio Rancho will have a water supply for 100 years, during which time the community will grow to perhaps five times its current size. After that, they'll be out of water but with five times the current demand. Then what?"
Snowpack and rain
New Mexico's water supply comes in two basic types. Surface water generally begins as winter snowpack in the mountains or, to a lesser extent, rain. Groundwater is found beneath the ground in layers of rock, dirt and gravel. While some is recent, soaking down from the surface, most has been underground for thousands of years or longer.
New Mexico's cities currently rely largely on pumping groundwater to meet their needs. But growing populations and shrinking groundwater reserves have cities looking for alternative supplies to meet their long-term needs.
The most prominent "new" water supply for city use is river water. Albuquerque will begin tapping into river water next year through the San Juan-Chama Project.
Cities can get more by buying water rights from farmers, who have legal title to much of the state's surface water.
When Sandoval County and the developers of the proposed 30,000-home Rio West development west of Rio Rancho began looking around for a source of water, agricultural rights did not look like a viable option, according to Mike Springfield, the county's development director. "They're just not out there on the market," he said.
So this spring, Sandoval County and Rio West developer Recorp Partners gambled on brackish water, sinking a test well deep beneath the Rio Puerco, the main river drainage west of the Albuquerque metro area.
The difference between sweet clean groundwater you can just pump and use and its brackish neighbor is an accident of geology, said Richard Kottenstette, a scientist at Sandia National Laboratories.
As water soaks into the ground, it dissolves many of the minerals it finds along the way. If there aren't many along its route into the aquifer, you end up with drinkable groundwater. If the water encounters things like salt and magnesium on its way, you end up with brackish salt brine.
In addition, groundwater that began its life as oceans or inland seas is brackish to begin with.
The size of New Mexico's reserves of brackish groundwater is an open question. Available scientific studies are limited and generally old, but they suggest the amount of water available could be vast as much as three times larger than the total available fresh groundwater, according to a 2004 summary by the U.S. Geological Survey.
The problem, according to Kottenstette, is that, until you actually drill a well, you can't be sure how much water is there and how salty it is.
Where does salt go?
The basic techniques used for desalination are relatively mature, developed over many years for turning ocean water into drinking water. They are currently in widespread use, especially in the Middle East, where nations tend to be energy-rich and water-poor.
While the issues for treating ocean water and inland brackish groundwater are different, the technologies are basically the same. The most common technique, being used in El Paso, is called "reverse osmosis." Salty water is forced through a membrane that filters out the dissolved minerals. Fresh water comes out the other side, leaving a highly concentrated brine solution behind.
That briny waste is one of the biggest headaches for inland desalination. For oceanside plants, it is merely pumped back into the sea "no big deal," said UNM's Thomson, "because the ocean's already salty." Inland plants have to find a place to get rid of it.
One option is pumping it back into the ground, which is expensive, Thomson said. Spreading it out to evaporate before disposing of the resulting dried waste is another option, but that would take hundreds of acres of evaporation ponds that could be toxic to wildlife, according to Thomson.
El Paso, after extensive study, concluded that the best way to get rid of it was to pump it underground, far from the city and well away from the aquifers from which it was originally pumped, according to Bill Hutchison, water resources manager for the El Paso Water Utilities.
Including the waste disposal cost, desalination is a cost-effective option for El Paso, Hutchison said.
Sandoval County officials say it's too early to talk about how much their desalinated water might cost. Analysis of the amount of dissolved minerals a critical variable for determining treatment costs is under way, and a second well is being drilled to get more information about how much water is down there.
"We'll know more by the end of August," Sandoval County development director Springfield said.
The high price of water
The best comparisons between brackish water desalination and other sources of water come from El Paso Water Utilities, which just completed construction on the largest inland desalination plant in the Southwest. Costs per acre foot of water (enough for two typical Albuquerque families for a year):
Groundwater that does not require desalination: $150.
Rio Grande water costs: $250.
Desalinated groundwater: $530.
Treated sewage used for park and golf course irrigation: $700.
Imported groundwater, piped in from an aquifer 100 miles away: $1,400.