Black Mesa Monitoring Program

Science Center Objects

The U.S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information about the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. The monitoring program includes measuring potential recovery in the N aquifer as a result of the reduction in industrial pumpage by Peabody Western Coal Company.

Black Mesa Interactive Data Map

The Navajo Nation and Hopi Tribe live in the Black Mesa area, and they depend on groundwater from the N aquifer to meet municipal, domestic, livestock, and irrigation needs. In addition, the springs and streams fed by groundwater discharge are an important part of their culture. The N aquifer is the major source of water for industrial and municipal users in the 5,400 square-mile Black Mesa area of northeastern Arizona. The aquifer consists of three rock formations-the Navajo Sandstone, Kayenta Formation, and Wingate Sandstone, which are hydraulically connected and function as a single aquifer.

The Navajo Nation and Hopi Tribe have been concerned about the effects of pumping on long-term water supply, discharge in streams and springs, and quality of groundwater. This concern led to the establishment of a long-term program to monitor groundwater levels, groundwater discharge, groundwater quality, and surface-water discharge. The U.S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information about the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. The monitoring program includes measuring potential recovery in the N aquifer as a result of the reduction in industrial pumpage by Peabody Western Coal Company.

Map showing location of Black Mesa study area, northeastern Arizona

Location of Black Mesa study area, northeastern Arizona

Peabody Energy began operating a strip mine in the northern part of Black Mesa in 1968 and used N aquifer water to slurry coal 273 miles away to a electric power plant in Laughlin, Nevada. Annual withdrawals from the N aquifer for industrial and municipal use increased from about 70 acre-ft in 1965, to 7,330 acre-ft in 2005. On January 1, 2006 Peabody Energy discontinued use of the coal slurry pipeline, which in turn reduced industrial water use by about 70 percent. Withdrawals by Peabody Energy had accounted for about 70-75 percent of the total withdrawals to the mid-1980's and have been about 60 percent of the total withdrawals from the mid-1980's to 2005. After 2005 Peabody’s water use only accounts for about 30 percent of the total water use and now municipal users account for 70 percent of the water use.

Figure of stratigraphic section showing rock formations and hydrogeologic units of the Black Mesa area, northeastern Arizona.

Stratigraphic section showing rock formations and hydrogeologic units of the Black Mesa area, northeastern Arizona (not to scale). The N aquifer is approximately 1,000 feet thick.

OBJECTIVE

To collect hydrologic data in a monitoring network that is designed to determine the long-term effects of industrial and municipal groundwater withdrawals on the N aquifer.

APPROACH

A long-term monitoring program has been established to collect hydrologic data in the Black Mesa area. Data are collected that describe the groundwater system, surface-water flow, and groundwater quality. Continuous measurements of groundwater levels have been made in six wells since 1972. Continuous data describing streamflow have been collected for more than 40 years in Moenkopi Wash, and for more than 15 years in three other streams. Once a year, groundwater levels are measured in about 34 wells, discharge is measured from 4 springs, and water-quality data are collected from a minimum of 4 springs. Annual groundwater withdrawal data are collected from about 28 municipal well systems. Peabody Energy and the Navajo Tribal Utility Authority provide annual groundwater withdrawal data for municipal and industrial use.

These hydrologic data are entered into a computer data base. A report is prepared every 1 to 2 years of the program. The report contains the data collected each year, and it shows comparisons of annual and long-term changes in groundwater levels, groundwater discharge, surface-water flow, and water quality. Long-term water-level changes in the six continuous-observation wells show that water levels in confined areas have declined about 80 to 130 feet and water levels in unconfined areas have not changed.

RELEVANCE AND BENEFITS

The long-term available supply of water in the Black Mesa area is critical to many parties. The Hopi Tribe and Navajo Nation use water to meet their needs for public supply, irrigation, and livestock. In addition, sustained springflow and streamflow are important to their culture. The hydrologic data collected in this monitoring program are needed to understand the available water supply and the effects of past industrial and current municipal groundwater withdrawals.

The U.S. Geological Survey has a commitment to provide data and information to Indian Tribes and other Interior Department Agencies. The Office of Surface Mining of the Interior Department uses the data from this program to facilitate their oversight and regulation of the coal mining operations of Peabody Western Coal Company.

The long-term groundwater, surface-water, and water-quality data collected for this program provides an important opportunity to investigate and gain a better understanding of a hydrologic system of bedrock geology in an arid climate in which there are many competing water-use interests.