Bureau Studies Ground Water Pumping, Land Subsidence

SOCORRO -- New calculations show that erosion by the Rio Grande during the last ice age may have reduced the potential for land subsidence in the Albuquerque area as a consequence of heavy groundwater pumping. The results will be presented by William Haneberg, an engineering geologist and assistant director of the New Mexico Bureau of Mines and Mineral Resources, at the 1997 Fall Meeting of the American Geophysical Union in San Francisco on Friday, Dec. 12.

The title of his presentation is "Calculated effects of valley incision on the state of stress in the Santa Fe Group aquifer system, Albuquerque Basin, New Mexico."

During the last ice age, known as the Pleistocene Epoch, the Rio Grande carved a valley about 450 feet deep, which reduced the stress on the underlying aquifer. Large scale land subsidence is not expected to become a problem unless the stress imposed by heavy groundwater pumping exceeds the stress removed from the aquifer when the valley was cut.

Haneberg estimates that the water table will have to drop more than 335 feet from its pre-development levels in order for subsidence to begin.

Studies by the U.S. Geological Survey have shown that water levels beneath the eastern portion of Albuquerque had dropped as much as 160 feet by 1992.

"The calculations should not alleviate concerns about subsidence," said Haneberg. "They simply tell us how much breathing room we have."

According to Haneberg, once the threshold is exceeded, the ground surface may subside from a few inches to nearly a foot for every ten feet that the water table drops, which may damage roads, utility lines, and buildings.

Land subsidence as a result of groundwater pumping has already caused damage in Houston, Phoenix, the San Joaquin Valley, El Paso, and Deming, New Mexico.

Although the Albuquerque water use plan calls for reduced groundwater use to ensure that the threshold is not exceeded, Haneberg cautions that adequate laboratory tests of the aquifer material have not been conducted and that it is dangerous to rely solely upon computer models.

For further information, contact Dr. William C. Haneberg, New Mexico Bureau of Mines & Mineral Resources, 2808 Central Avenue SE, Albuquerque NM 87106, (505) 262-2774, haneberg@nmt.edu.

-NMT-

George Zamora