In August, road crews spent two weeks repairing a section of San Tan Boulevard in Queen Creek that was damaged when an earth fissure suddenly opened after a monsoon rainstorm. Likewise, during the past few years, the Arizona Department of Transportation has had to deal with numerous incidents of road damage--and hastily mitigate impending threats of road damage--due to fissures.
Two years ago, a fissure developed under a Queen Creek home, causing serious property damage, and in the 1980s, fissures destroyed a North Las Vegas subdivision, destroying dozens of homes and costing the city some $14 million.
Meanwhile, the Maricopa County Flood Control District found numerous earth fissures close to McMicken Dam, northwest of Phoenix. Although considered a "dry" dam with a primary purpose of protecting Luke Air Force Base and the growing city of Surprise from flooding, the dam's failure, when needed, could have had serious repercussions for 50,000 people living in the area. The presence of the fissures prompted the district to rebuild a segment of the dam.
While earth fissures in the Southwest have been witnessed since the early part of the 20th century, with the first one officially recorded near Picacho in 1927, fissure activity has increased substantially statewide in the last half-century, with several hundred now identified in the state. Originally noticed in agricultural areas near the bases of mountain ranges, for years, fissures and land subsidence (the gradual sinking of land) have wreaked havoc for farmers, injuring animals, disrupting farm operations and changing irrigation flows.
Yet, it wasn't until Arizona's ever-expanding cities began encroaching on those former agricultural regions that the property damage associated with fissures received significant attention from the state.
In recent years, Arizona officials have begun to address issues concerning fissures. Laws have been established requiring disclosure of earth fissures when selling property; new technologies have been developed to mitigate destruction to roads, dams and projects like the Central Arizona Project canal; and, in 2005, state funds were allocated for the mapping of the state's fissures, a project current being conducted by the Arizona Geological Survey (AZGS).
Yet, even with the attention fissures have drawn, a potentially more serious problem may lurk: the potential for groundwater pollution.
Land subsidence is a natural geological occurrence; however, it has been greatly accelerated by humans through excessive groundwater pumping, according to the UA Water Resources Research Center. Generally speaking, land subsidence occurs at accelerated rates when water is pumped from an aquifer faster than it is replenished; it can also occur due to oil pumping and mining operations.
In Arizona, groundwater pumping has been the culprit of land subsidence for decades, with some areas (such as places near Eloy), sinking more than 15 feet in the last 50 years.
Such declining aquifers often create subsidence that goes largely undetected when basins sink at an even rate. While uniform subsidence can cause problems, more significant is uneven subsidence. There are various reasons land subsidence can occur unevenly; however, Lee Allison, an AZGS state geologist, said it occurs primarily along the bases of mountains due to unique geological factors.
Much of Southwestern geology consists of basins and ranges--in other words, valleys of compacted sediment between mountains ranges. Mountains do not start at the surface, but rise from deep in the ground. Between these mountain ranges, basins are made of layers of alluvial sand, gravel and clay.
"As the water table drops in one of these areas, the sediments begin to compact, causing subsidence," Allison said. "In areas where the water was stored in clay near bedrock (as is sometimes the case near mountain ranges), the clay shrinks as it dries and pulls away from the rock leaving a gap. That gap, we believe, is what causes earth fissures, which gradually move toward the surface."
Allison said that as groundwater pumping continues, the problem will just get worse.
"With continued groundwater depletion, we will continue to see new fissures forming," he said, "and we cannot be sure exactly where they will form. Furthermore, it is unclear how many fissures may have already formed that have yet to surface. Even if we were able to recharge the aquifers, it could take decades, perhaps longer, before we stopped seeing new fissures."
Such fissures are called blind fissures, because they are not visible until they surface. "We have an idea of where we should expect them, often times in areas where fissures already exist, but we are not certain," Allison said.
The state-funded fissure-mapping project is designed in large part to help with the obvious problems associated with blind fissures. The maps are tools that can help city planners and developers assess the risks of constructing developments on top of fissures. But, Allison said, the maps aren't perfect. Until a fissure forms, one can only speculate whether they are present.
Furthermore, such maps do not prevent development on fissure-prone areas. Mary Utley, assistant commissioner of communications for the Arizona Department of Real Estate, said they have not seen any new developments built directly on known fissures, but there have been developments that had to disclose that fissures are in the surrounding area.
"Essentially, as long as a developer does everything ... to determine if fissures are on the property and disclose any findings concerning fissures, the burden will fall on the owner if something happens," Utley said.
When a fissure reaches the surface, Allison said, it is generally as a hairline crack, often less than an inch wide. It is after a rainstorm that the real problems emerge: As surface water flows into a fissure, it quickly expands into a giant crevasse, which could grow large enough to swallow a house. It is a process that can happen quite rapidly, Allison said.
While the destruction of property is of concern, perhaps more worrisome is a potential problem that Allison said has yet to be addressed--groundwater pollution due to fissures.
"All that water rushing through the fissures is going somewhere," Allison said.
It's believed that once a fissure reaches the surface, it provides a conduit directly to the aquifer, which means water bypasses the natural purification process.
The ramifications, as of yet, are unknown. Stanley Leake and Nick Melcher, of the U.S. Geological Survey Arizona Water Science Center, said those who study the mechanics of earth fissures do seem to agree that fissures form below the surface and can function as direct routes to the aquifer--but they have yet to see a concrete link between surface pollution and groundwater pollution.
"Theoretically, it seems reasonable fissures can contribute to groundwater pollution, especially in urban areas or from fissures that people have thrown garbage into," Leake said.
Jack Lavelle, Arizona Department of Water Resources public information officer, said they are also concerned with the potential of groundwater pollution due to earth fissures. The problem, he said, is there is no scientific evidence yet to document the issue. "I suspect it would take a large spill or some sort of long-term contamination stream flowing into a series of fissures before scientists would notice the pollution and be able to trace it back to its source," Lavelle said.
Kristine Uhlman, UA Water Resources Research Center assistant area extension agent, said contaminates like asbestos from brake pads and metals are some of the more likely pollutants that could be carried into the aquifer. "There are all kinds of containments in the environment," she said. "For example, it has been well documented that pollutants such as mercury, originating from smokestacks in China, have been deposited across the Untied States."
Yet, Uhlman said, such contaminates would not be her main worry: Uhlman said the illegal dumping of toxic waste into fissures and the potential for structural damage to "stacked" aquifers are greater concerns.
Mimi Diaz, an AZGS geologist who has been mapping fissures in Maricopa and Pinal Counties since the project began, said she is appalled by what she has found in fissures. "People see a large hole in the ground and think, 'That's a good place to dump,'" she said. "I have seen old cars, pharmaceuticals, used solvents and appliances in fissures ... everything you can imagine."
The pollution concern recently grabbed the attention of the Arizona Department of Environmental Quality. On Aug. 24, Diaz gave a presentation to ADEQ explaining the potential risks of groundwater pollution due to fissures. It was a meeting that captured the attention of ADEQ employees, who were previously unaware of the problem, and sparked discussions about an ADEQ/AZGS collaborative project to learn more about the issue.
"But everything is still in an embryonic phase," Diaz said. "Contamination due to fissures is a very new issue, and the truth is, little is known about it."
When asked about the potential of groundwater pollution via earth fissures, Mitch Basefsky, public information officer for Tucson Water, said he was unaware of fissures as a source of aquifer pollution.
"I have never even heard of it," he said. "What I can tell you is we are not detecting an increase in pollution at the moment."
As of now, no fissures have been identified as functioning conduits into the aquifers Tucson Water is pumping out of--nor have any been identified elsewhere in the state. Considering that Tucson has experienced less subsidence than other parts of the state, Allison said he is not convinced fissuring in the Tucson region will increase like it has in other areas.
"If the groundwater were to be overpumped to the extent it has been further north, then, yes, the Tucson area could be more prone to subsidence and resulting earth fissures," he said.
Basefsky said Tucson Water has seen improvement in the well fields they have shut down and began recharging, but he also said that on average, Tucson's aquifer levels continue to decline.
In Queen Creek, an area southeast of Phoenix that's rife with earth fissures, Paul Gardner, president of Queen Creek Water, is well aware of the problems fissures present. As of now, Gardner said, he is not aware of any pollution having entered the aquifer, and he questions the probability of it happening.
"I don't want to pretend there is not a problem, but also don't want to play Chicken Little," he said.
Gardner said that considering the structure of the aquifers in Queen Creek--which has three vertically "stacked" aquifers--it is likely a fissure would come from the top aquifer, which is already polluted. "It wouldn't be a huge problem, because we don't pump from that aquifer; we pump from the middle and lower aquifers," he said.
However, Uhlman said it is possible an earth fissure could form that would connect the aquifers, allowing contaminated water from the top aquifer to enter the aquifers below.
What is the probability of that happening? At the moment, nobody knows.
If such a fissure were to form, Gardner conceded it would create massive problems, though not irresolvable ones. "Essentially, if something like that were to occur, we would need to find new ways to treat water, perhaps treating groundwater like surface water," he said.
Gardner said he thinks the solution is first to identify where fissures are and then ensure that water doesn't enter them and open them up. The problem, he said, is new developments in areas "upstream" of old fissures have rerouted drainage systems and are diverting water into old fissures, allowing them to reopen. "For example, the fissure that recently trapped the horse in Chandler Heights was from the 1950s," he said.
Beyond that, Gardner said that communities need to ensure that an equal amount of water is being recharged into aquifers so future subsidence can be prevented. Gardner said that in contrast to many of the state's aquifers, their area's aquifers are rising, and that most of the fissuring occurring in the area is a product of unregulated aquifer depletion that took place a half-century ago.
While many old fissures have re-opened due to the rerouting of water, as Gardner said, Diaz said she is seeing new fissures surface on a regular basis. Furthermore, Diaz, like Allison, thinks even with aquifer recharging, new fissures will continue to surface for several decades.
Assuming problems with groundwater pollution due to fissures could be mitigated as Gardner thinks, he said Arizonans need to realize the state will eventually need more water. "In the future, will we be paying for California to build desalination plants on the coast so we can have their water rights?"
This leads to the crux of the problem, according to Allison: "As Arizona's population continues to grow, demand for water will increase, which means more aquifer depletion. And that equals more subsidence and more earth fissures."
While land subsidence and earth fissures have been detected in other states, Arizona has the largest concentration of them. In fact, the region of southcentral Arizona--which includes both Phoenix and Tucson--has the highest concentrations of known earth fissures in the country, perhaps even in the world, according to a UA Water Resources Research Center publication. Since the AZGS released the first set of fissure maps in June, Allison said, the agency has received hundreds of calls reporting potential new fissures.
More earth fissures obviously mean more destruction, especially as developments continue to expand into areas where fissuring is likely to occur. More fissures also mean more opportunities for contamination.
"There is a lot yet to be learned about fissures, but essentially, right now, we suspect any type of pollutant we deal with in the state has the potential to enter the water table," Allison said.