Department of Water Resources
A daily compilation of significant news articles and comment
July 14, 2008
4. Water Quality –
Drilling deep wells for water faces myriad problems
The Antelope Valley
By Linda Lee, Staff Writer
But at what cost?
Sinking wells thousands of feet deep to reach the deepest water means higher pumping costs, and also draws up water more likely to be contaminated with naturally occurring arsenic and other substances.
In addition, pumping more groundwater than is replenished by rainfall or other sources can result in subsidence: a slow compaction and sinking of the earth's surface, which can damage buildings and roads and permanently reduce the water storage capacity in the Valley's aquifers - underground layers of rock and sand that hold water in their pores.
"There will always be water in the aquifer," said Adam Ariki, Los Angeles County Waterworks assistant deputy chief. "If we extract all of it ... the soil's going to crash on us and we're all going to sink."
However, water officials, farmers and others disagree about how much water can be safely pumped from wells without damaging the aquifers and leading to subsidence.
Estimates vary from 30,000 acre-feet to as high as 120,000 acre-feet, Ariki said, but most people seem to accept a range of 70,000 to 80,000 acre-feet.
(An acre-foot equals 325,851 gallons, enough to supply an average
If water districts, farmers and other well owners collectively agree to pump about 90,000 acre-feet per year, it will be equivalent to the amount returned to the groundwater basin from rain and manmade activities, Ariki said.
"Logically the amount should be equivalent to how much water is being put in the groundwater basin," he said.
But farmer Gene Nebeker, a former water-quality official, says: "Nobody really knows how safe the yield is, until we take better data over a period of time."
Since the 1920s, wells have pulled more water than has been naturally returned, dropping water levels by more than 200 feet in some areas and by at least 100 feet in most of the Valley. The overdraft was greatest when alfalfa fields covered much of the Valley: Studies show groundwater pumping grew from about 29,000 acre-feet in 1919 to a peak of about 400,000 acre-feet in the 1950s.
The shift from predominately agricultural water demands to municipal/industrial use began in the early 1960s and took hold in the 1990s. According to U.S. Geological Survey studies, during this time agricultural use dropped 80% while urban demands increased by more than 200%.
Meanwhile,
Well pumping is far less now than in the 1950s, but there is no agreed-upon amount: the estimates are being haggled over in a 9-year-old legal battle over groundwater rights.
Groundwater tables have stabilized in some areas with the use of more imported water. But groundwater levels, and changes in groundwater levels, are not uniform across the Valley: between 1975 and 1988, according to a 1998 report, groundwater level changes ranged from an increase of 84 feet to a decrease of 66 feet.
Nebeker, who formerly served on the State Water Quality Control Board for the Lahonton region, calculates that Valley wells can safely withdraw about 150,000 acre-feet of groundwater per year.
Nebeker's estimate of how much water returns to the basin each year is much higher than those estimated in the regional water plan adopted earlier this year by 11 agencies.
But Nebeker claims that past studies have not had reliable data on how much water farmers were using, and how much was being returned to the groundwater basin.
Nebeker said his calculations take into account natural recharge from rainfall and snowfall, coupled with farm irrigation water that soaks into the ground, plus water from lawns and other urban sources- which includes imported water.
Nebeker disagrees that subsidence poses a threat. He believes the subsidence that has already occurred - which includes a half-mile-long crack that opened in
"We can continue to pump at the current level and if we're off by a few hundred acre-feet, the basin won't see it," he said.
But other expects say even without the threat of subsidence, accessing water at deep levels could be economically prohibitive due to the amount of electricity needed to run the pumps, according to a 1995 study by Kennedy-Jenks Consultants.
And it may not be worth the trouble.
"The deeper the water, the poorer its quality," said Steven Phillips, a hydrologist with the U.S. Geological Survey. "Poor quality usually means high salinity, which usually precludes it for use in irrigation as well."
Arsenic is also one of the major problems in the deep aquifer in the
The Valley's wells are drilled generally to 600 or 800 feet, though the water can lie as deep as 5,000 feet, Ariki said.
Arsenic can be treated, but it is probably a more expensive option than if surface water is available from the California Aqueduct, said Curtis Paxton, interim manager of the Palmdale Water District.
Paxton said the amount of water available in the aquifer is a guess, claiming no one really knows where the bottom is.
Once the legal battle over water rights is concluded, the total amount of water available may not be as important an issue as what amounts to the safe yield of the basin, he said.
Palmdale City Engineer Michael Mischel calculated the 52 million acre-feet estimate based on studies provided by Kennedy-Jenks Consultants in 1995.
That study estimated a total storage available in the aquifer at 68 million acre feet, with about 13 million acre-feet remaining after decades of well pumping.
Well pumping
So the issue is how much water can safely be pumped from the groundwater basin without causing a problem.
While that safe yield is an important factor in protecting groundwater supplies, pumping extra during times of emergencies is a water supply management tool available to water districts, Ariki said.
In what is called conjunctive use, water districts take imported water when it is available and allow it to infiltrate into the ground and replenish the groundwater. The groundwater could be pumped out through wells when drought reduced the aqueduct supply.
Over the last five years, the county waterworks district in the
"And we did very, very well with that," Ariki said. "So now that we don't have as much available we're going to go and pump from the groundwater basin, not extensively, but more than we would have done otherwise."
But that will only meet existing demand.
"If next year I only get half of the water that I would get this year from AVEK for my existing customers, I have to go and look for deficit water somewhere else," he said.
Subsidence damage
More than six feet of subsidence has been documented in
The most visible evidence of subsidence was the half-mile long fissure that opened at Edwards in 1991. It led base officials to close two lakebed runways for a short time as a precaution. The fissure started 70 feet below the surface, but cracking was visible to a depth of about 12 feet. It repaired itself after rains and is no longer visible.
James Judkins, director of Edwards' Civil Engineer/Transportation Directorate, said some fissures remain on the southern portion of the base, but they do not hinder the base's mission.
"It's something that we're continuing to monitor over time," he said.
While subsidence is no longer a problem at Edwards, officials are studying the impact of well pumping and subsidence in anticipation of a problem that would impact the base's mission. In addition, Edwards has reduced its reliance on wells and now purchases about 50% of its water from AVEK. Total water consumption is down 13% over the last four years, officials said.
Phillips, the U.S. Geological Survey hydrologist, described pumping wells beyond the natural replenishment level "groundwater mining."
The cost of pumping water from wells, according to Phillips, doesn't reflect the cost to society in terms of the damage caused by subsidence.
One visible results of subsidence is flooding during heavy rains, he said.
"When it rains heavily in Lancaster, or Amargosa Creek floods, the water has nowhere to go because the natural gradient has been changed by land subsidence," Phillips said.#
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