Several months ago, the Arizona Geological Survey's phones started ringing, but the calls weren't from energy and mining companies. Instead, real estate agents, spurred by the resurgence of the Phoenix-area market, wanted to know whether the land their clients were thinking of buying might be riddled with cracks or weak spots that could damage a building, or worse. They had good reason to worry: After heavy summer rains in 2007, a 15-foot-wide fissure opened southeast of Phoenix and swallowed a horse.
People have mined southern Arizona's aquifers for more than a century -- pumping groundwater faster than precipitation can seep back underground to replenish it. As a result, land in more than a dozen spots has buckled and subsided. It's one of 40 cases of groundwater pumping detailed in a recent U.S. Geological Survey report that shows how people are draining the nation's aquifers, often at accelerating rates. Between 1900 and 2008, the U.S. has lost enough underground water to fill Lake Erie twice. That volume jumped by 25 percent after 2000.
As the West continues to grow, with ever more people and industries vying for the same shrinking resources, the days of water policies that treat aquifers as infinite resources seem numbered. "At some point, the problems are going to be more and more frequent in more and more places -- and people may not notice until it's really severe," says Leonard Konikow, the USGS hydrologist who assembled the data. Here are some of the report's highlights (or see the data as a map or graph):
Central Valley, California
The Central Valley holds about one-sixth of the nation's irrigated land and produces 250 different crops. Farming has contributed to what the USGS calls "one of the single largest alterations of the land surface attributed to humankind." By 1970, 5,200 square miles of ground had sunk more than a foot -- up to 28 feet in places.
The sinking has slowed since use of surface water delivered from the Bay Delta to the north, surpassed pumping in 1971, but droughts in the late '70s, late '80s and early '90s, plus occasional surface water shutdowns to protect endangered fish, periodically forced farmers back to groundwater.
Some now gird for drought by flooding fields in wet years so water can soak back into the ground. Kern County has more than a dozen water banks; as of 2011, the largest one had returned more than 1.7 million acre-feet to the aquifer.
Las Vegas Valley, Nevada
Despite its reputation for excess, Sin City's conservation plan fines local water wasters, prohibits new turf in front yards, and offers coupons for water-recycling car washes. Between 2002 and 2011, southern Nevada cut per-person use by 29 percent, likely helped by the recession.
Vegas is well aware of its limited groundwater, and in 1987 began using part of its share of Colorado River water, drawn from Lake Mead, to recharge the aquifer that fed its early growth. But Mead has dropped more than 100 feet since 2000, and the Bureau of Reclamation recently projected that water levels could plunge enough to come close to triggering a federal shortage declaration by next autumn -- meaning potential cutbacks. To secure future supplies, the Southern Nevada Water Authority is pushing for a groundwater pipeline from rural east-central Nevada, despite its possible impacts on springs and creeks used by ranchers and wildlife.
Arizona alluvial aquifers
In Arizona, tighter groundwater management, starting in 1980, and the 1985 Central Arizona Project, which transports Colorado River water to Tucson and Phoenix, have helped ease the pressure on aquifers.
But the state still doesn't legally recognize that groundwater and surface water are connected, and draining the desert water table has transformed rivers like Tucson's Santa Cruz from verdant waterways lined with cottonwoods and mesquite into sand-filled valleys. Now, state-approved wells from a 7,000-unit housing development threaten to de-water the San Pedro, one of the healthiest remaining Southwest rivers and an oasis for migrating birds and other wildlife.
Snake River Plain, Idaho
This aquifer, which underlies a large agricultural area in southern Idaho, was recharged through the '70s, as river water from flood irrigation seeped back underground. But when agriculture expanded, more farmers began pumping groundwater. And as more efficient sprinkler systems became popular, less water was returned to the aquifer.
The combination reduced Snake River flows, provoking bitter battles between surface and groundwater users. In 2008, the state approved a water-supply plan to ensure sustainable use of 10 different Idaho aquifers for 50 years, but the process has been underfunded. The first plan underway, for Boise's Treasure Valley aquifer, includes conservation measures, promotes leasing or renting unused water rights, and encourages new subdivisions on former farmland to use surface water instead of wells. However, the state water board won't submit it to lawmakers until 2014.
Denver Basin, Colorado
Beneath the Denver Basin, the shallow aquifers that irrigators rely on have begun to drain more slowly. That's because the state now regulates that supply, recognizing its connection to carefully divvied-up surface water, and because wet years in the '80s and '90s helped slow water loss. But the depletion of unregulated deep aquifers has sped up as the region grows, since new subdivisions often lack surface-water rights and thus must drill for a source. New subdivisions exploded in the early 2000s, just as the latest drought began, further increasing the drawdown.
The suburb of Castle Rock, where well production has flagged by 7 to 10 percent each summer since the mid-2000s, recently joined nine other South Denver water providers in a pact with Denver and Aurora to pipe water from the South Platte River.
High Plains (Ogallala)
The High Plains, or Ogallala, aquifer -- which stretches from South Dakota to Texas -- accounts for about 34 percent of all U.S. groundwater depletion since 1900. A whopping 24 percent of that loss occurred between 2001 to 2008, likely helped by decreased rainfall and increased pumping for larger corn plantings, spurred by higher corn prices.
Irrigators are already seeing the consequences in Texas and Kansas, where the aquifer replenishes much more slowly than up north. Dried-up wells are now pumping up sand along with dwindling well water, and drought-stricken farmers have been forced to fallow their fields. According to a 2012 study in the Proceedings of the National Academy of Sciences, 35 percent of the southern High Plains will be unable to support irrigation within the next 30 years if current pumping rates continue. "There's so much talk about making things sustainable," says study author Bridget Scanlon. "Some things can't be sustainable."