Cedar City » Since 1939, the Cedar Valley spreading west and north of Cedar City has dropped 100 feet and the only way to stop or slow the process is replenish the underlying aquifer with at least as much water as is being discharged through pumping.
That was one of the statistics the Utah Geological Survey delivered to the Central Iron County Water Conservancy District at its board meeting Thursday night in Cedar City.
William Lund, senior scientist with the agency's southern Utah office, said the practice of overpumping causes noticeable fissures in the ground that sink all the way to the water table and allow pollutants to seep into the water. Most of the water is now used for agriculture, but officials are concerned about polluting the water source should it be needed for other uses.
"They start as a hairline crack and fast erode into gullies," said Lund of the fissures.
He noted a fissure first noticed in 1960 northeast of Enoch has grown 2.25 miles long and has snaked its way into a subdivision where home construction was set to begin.
Although only one structure was built and affected by the fissure, it has disrupted the infrastructure that had already been completed, including cracking curbs and gutters, streets and the sewer system, which now runs backward.
Lund said it is the only location in Utah he is aware of that has been damaged by a fissure.
Lund's update is part of an $85,700 study the Geological Survey is conducting in conjunction with the conservancy district. The agency is nearing completion of its final report after nearly two years of study.
Geologist Paul Inkenbrandt said, in addition to its own surveys, the agency used information collected from historical sources, including logs from well drillers in the area.
Lund said fissures are a geologic hazard, but unlike an event like a landslide, they are human-caused, and therefore subject to control through management.
Failure to do anything about the subsidence issue could cause major problems like those in Arizona and Las Vegas, where the sinking ground forced 135 people to abandon their homes in a North Las Vegas subdivision.
Mike Lowe, also a geologist with the survey, said he is preparing recommendations for the district on how to handle the problems as they occur.
He said his recommendations will be largely based on what has been done in Las Vegas Valley. They may include reduced pumping, increased use of surface water, artificial recharge, creating hazard zones where construction could be prohibited or special building methods used.
Surface water from runoff could be used to recharge the aquifer, but because of the subsidence, the aquifer will never have the capacity it once had, Lund said.
Lowe even suggests a special district be created to monitor fissures and subsidence.
"Our goal is to give you a grab bag of tools," said Lowe.