Open-File Report 2006–1058

Open-File Report 2006–1058

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The Black Mesa study area includes about 5,400 mi2 in northeastern Arizona (fig. 1) and has a diverse topography that includes flat plains, mesas, and incised drainages. Black Mesa is about 2,000 mi2, is bounded by 2,000-foot cliffs on the north and northeast sides, and slopes gradually down in elevation to the south and southwest. Availability of water is an important issue in the study area because of continued ground-water withdrawals, a growing population, and precipitation that averages about 6 to 14 in./yr (U.S. Department of Agriculture, 1999). The N aquifer is the major source of water for industrial and municipal uses in the Black Mesa area. It consists of three formations—the Navajo Sandstone, the Kayenta Formation, and the Lukachukai Member of the Wingate Sandstone—that are hydraulically connected and function as a single aquifer (fig. 2).

Within the Black Mesa study area, Peabody Western Coal Company (PWCC) is the principal industrial water user, and the Navajo Nation and Hopi Tribe are the principal domestic and municipal water users. Withdrawals from the N aquifer in the Black Mesa area have been increasing during the last 34  years (table 1 and fig. 3). PWCC began operating a strip mine in the northern part of the mesa in 1968. The quantity of water pumped by PWCC increased from about 100 acre-ft in 1968 to a maximum of 4,740 acre-ft in 1982. About 4,370 acre-ft of water was pumped in 2004 by PWCC. Withdrawals for municipal use from the N aquifer increased from an estimated 250 acre-ft in 1968 to 2,840 acre-ft in 2004. The period before appreciable ground-water withdrawals began for mining or municipal purposes (about 1965) is referred to in this report as the prestress period.

The Navajo Nation and the Hopi Tribe have been concerned about the long-term effects of withdrawals from the N aquifer on available water supplies, on stream and spring discharge, and on ground-water chemistry. In 1971, these concerns led to the establishment of a monitoring program of the water resources in the Black Mesa area by the U.S. Geological Survey (USGS) in cooperation with the Arizona Department of Water Resources (ADWR). In 1983, the Bureau of Indian Affairs (BIA) joined the cooperative effort. Since 1983, the Navajo Tribal Utility Authority (NTUA); PWCC; the Hopi Tribe; and the Western Navajo Agency, the Chinle Agency, and the Hopi Agency of the BIA have assisted in the collection of hydrologic data.

Purpose and Scope

This report presents results of ground-water, surface-water, and water-chemistry monitoring in the Black Mesa area from January 2004 to September 2005. The monitoring is designed to determine the effects of industrial and municipal pumpage from the N aquifer on ground-water levels, stream and spring discharge, and ground-water chemistry. Continuous and periodic data are collected for ground water and surface water. Ground-water data include pumpage, water levels, spring discharges, and water chemistry. Surface-water data include discharges at four continuous-record streamflow-gaging stations.

Previous Investigations

Twenty-two progress reports on the monitoring program for the Black Mesa area have been prepared by the USGS (U.S. Geological Survey, 1978; G.W. Hill, Hydrologist, written commun., 1982, 1983; Hill, 1985; Hill and Whetten, 1986; Hill and Sottilare, 1987; Hart and Sottilare, 1988, 1989; Sottilare, 1992; Littin, 1992, 1993; Littin and Monroe, 1995a, 1995b, 1996, 1997; Littin and others, 1999; Truini and others, 2000; Thomas and Truini, 2000; Thomas, 2002a, 2002b; Truini and Thomas, 2004; and Truini and others, 2005). Most of the data from the monitoring program are contained in these reports. Stream-discharge and periodic water-quality data from Moenkopi Wash collected before the 1982 water year were published by the USGS (1963–64a, b; 1965–74a, b; and 1976–83). Stream-discharge data from water years 1983 to 2003 for Moenkopi Wash and other streams in the Black Mesa area were published in White and Garrett (1984, 1986, 1987, and 1988), Wilson and Garrett (1988, 1989), Boner and others (1989, 1990, 1991, 1992), Smith and others (1993, 1994, 1995, 1996, 1997), Tadayon and others (1998, 1999, 2000, 2001), McCormack and others (2002, 2003), Fisk and others (2004, 2005). Before the monitoring program, a large data-collection effort in the 1950s resulted in a compilation of well and spring data for the Navajo and Hopi Indian Reservations (Davis and others, 1963).

Many interpretive studies have been done in the Black Mesa area. Cooley and others (1969) made the first comprehensive evaluation of the regional hydrogeology of the Black Mesa area. Eychaner (1983) developed a two-dimensional numerical model of ground-water flow in the N aquifer. Brown and Eychaner (1988) recalibrated the model using a finer grid and revised estimates of selected aquifer characteristics. GeoTrans (1987) also developed a two-dimensional model of the N aquifer in the 1980s. In the late 1990s, HSIGeoTrans and Waterstone Environmental Hydrology and Engineering (1999) developed a detailed three-dimensional numerical model of the D and N aquifers.

Kister and Hatchett (1963) made the first comprehensive evaluation of the chemistry of water from wells and springs in the Black Mesa area. HSIGeoTrans (1993) evaluated the major-ion and isotopic chemistry of the D and N aquifers. Lopes and Hoffmann (1997) analyzed ground-water ages, recharge, and hydraulic conductivity of the N aquifer using geochemical techniques. Zhu and others (1998) estimated ground-water recharge using isotopic data and flow estimates from the model developed by GeoTrans (1987). Zhu (2000) estimated recharge again using the same isotopic data, but added numerical flow and transport modeling to the method. Truini and Longsworth (2003) described the hydrogeology of the D aquifer and movement and ages of ground water using geochemical and isotopic analyses.

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For more information about USGS activities in Arizona, visit the USGS Arizona Water Science Center home page.

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