Open-File Report 2006–1058

Open-File Report 2006–1058

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The N aquifer is the major source of water for industrial and municipal users in the Black Mesa area of northeastern Arizona. Availability of water is an important issue in the Black Mesa area because of continued industrial and municipal use, a growing population, and precipitation of about 6 to 14 in. per year.

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 data for 2004–05 are compared with data for 2003–04 and with historical data from the 1950s to the present.

In 2004, total ground-water withdrawals were 7,210 acre-ft, industrial withdrawals were 4,370 acre-ft, and municipal withdrawals were 2,840 acre-ft. From 2003 to 2004, total withdrawals decreased by less than 1 percent, industrial withdrawals decreased by 2 percent, and municipal withdrawals increased by 2 percent.

From 2004 to 2005, annually measured ground-water levels declined in 14 of 25 wells. The median water-level change for the 25 wells was -0.4 ft. In unconfined areas, water levels declined in 6 of 13 annual wells, and the median change was -0.1 ft. In the confined area, water levels declined in 8 of 12 wells, and the median change was -1.2 ft. For wells in the confined area, the median water-level change was -1.7 ft, and there is no appreciable trend in the water-level changes from 1983 to 2005. For wells in unconfined areas, the median water-level change was 0.2 ft, and there is no appreciable trend from 1983 to 2005.

From the prestress period (prior to 1965) to 2005, the median water-level change in 33 wells was -9.0 ft. Water levels in the 16 wells in the unconfined areas of the aquifer had a median change of -0.6 ft, and the changes ranged from -33.2 ft to 15.0 ft. Water levels in the 17 wells in the confined area of the aquifer had a median change of -32.0 ft, and the changes ranged from -193.3 ft to 14.0 ft.

Discharges were measured annually at four springs in 2004 and 2005. Between 2004 and 2005, spring flow stayed the same at Burro Spring, increased by 71 percent at the unnamed spring near Dennehotso, decreased by 5 percent at Moenkopi School Spring, and increased by 8 percent at Pasture Canyon Spring. For about the past 12 years, discharges in the four springs have fluctuated; however, increasing or decreasing trends are not apparent.

Annual average discharges at four streamflow-gaging stations—Moenkopi Wash, Laguna Creek, Dinnebito Wash, and Polacca Wash—vary considerably during the periods of record. No trends are apparent in streamflow at the four gaging stations. Median flows for November, December, January, and February of each water year are used as an index of ground-water discharge to those streams. Since 1995, the median winter flows have decreased in Moenkopi Wash, Dinnebito Wash, and Polacca Wash. Since 1997, there is no increasing or decreasing trend apparent in the median winter flow in Laguna Creek.

In 2005, water samples were collected from 11 wells and analyzed for selected chemical constituents. Dissolved-solids concentrations ranged from 122 to 639 mg/L, and samples from 9 of the wells had dissolved-solids concentrations less than the SMCL (500 mg/L). There are some long-term trends in the chemistry of water samples from 7 wells with more than 10 years of data.

Samples from Rough Rock PM5 exceeded the SMCL for dissolved solids, samples from Keams Canyon PM2, Rough Rock PM5, and Second Mesa PM2 exceeded the MCL for arsenic (10 μg/L), and samples from 9 of the 11 wells exceeded the SMCL maximum for pH (8.5).

Dissolved-solids concentrations in water samples from the unnamed spring near Dennehotso, Pasture Canyon Spring, and Moenkopi School Spring ranged from 114 to 212 mg/L, and the dissolved-solids concentration in the water sample from Burro Spring was 357 mg/L. From the mid-1980s to 2005, long-term trends are not apparent in the concentrations of dissolved solids, chloride, and sulfate in water samples from the unnamed spring near Dennehotso and Pasture Canyon Spring. Increasing trends in concentrations of dissolved solids and chloride are evident in data from Burro Spring and Moenkopi School Spring, and an increasing trend in sulfate is evident in data from Moenkopi School Spring.

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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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