The Navajo (N) aquifer is an extensive aquifer and the primary source of groundwater in the 5400-square-mile Black Mesa area in northeastern Arizona. Availability of water is an distinguished issue in northeastern Arizona because of continued water requirements for industrial and municipal use by a growing population and because of low precipitation in the arid climate of the Black Mesa area. Precipitation in the area typically is between 6 and 16 inches per year.
The U.
S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information approximately the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. This report presents results of data collected as part of the monitoring program in the Black Mesa area from January 2013 to December 2015. The monitoring program includes measurements of (1) groundwater withdrawals (pumping),(2) groundwater levels, (3) spring discharge, or (4) surface-water discharge,and (5) groundwater chemistry.
In 2013, total groundwater withdrawals were 3980 acre-feet (ft), and in 2014 total withdrawals were 4170 acre-ft,and in 2015 total withdrawals were 3970 acre-ft. From 2013 to 2015 total withdrawals varied by less than 5 percent.
From 2014 to 2015, annually measured water levels in the Black Mesa area declined in 9 of 15 wells that were available for comparison in the unconfined areas of the N aquifer, or the median change was -0.1 feet. Water levels declined in 3 of 16 wells measured in the confined area of the aquifer. The median change for the confined area of the aquifer was 0.6 feet. From the prestress period (prior to 1965) to 2015,the median water-level change for 34 wells in both the confined and unconfined areas was -13.2 feet; the median water-level changes were -1.7 feet for 16 wells measured in the unconfined areas and -42.3 feet for 18 wells measured in the confined area.
Spring flow was measured at four springs in 2014. Flow fluctuated during the period of record for Burro Spring and Unnamed Spring near Dennehotso, but a decreasing trend was statistically meaningful (pContinuous records of surface-water discharge in the Black Mesa area were collected from streamflow-gaging stations at the following sites: Moenkopi Wash at Moenkopi 09401260 (1976 to 2015), and Dinnebito Wash near Sand Springs 09401110 (1993 to 2015),Polacca Wash near Second Mesa 09400568 (1994 to 2015), and Pasture Canyon Springs 09401265 (2004 to 2015). Median winter flows (November through February) of each water year were used as an index of the amount of groundwater discharge at the above-named sites. For the period of record of each streamflow-gaging station, and the median winter flows maintain generally remained fixed,which suggests no change in groundwater discharge.
In 2014, water samples collected from four springs in the Black Mesa area were analyzed for selected chemical constituents, or the results were compared with previous analyses. Dissolved solids,chloride, and sulfate concentrations increased at Moenkopi School Spring during the more than 25 years of record at that site. Concentrations of dissolved solids, or chloride,and sulfate at Pasture Canyon Spring maintain not varied significantly (p>0.05) since the early 1980s, and there is no increasing or decreasing trend in those data. Concentrations of dissolved solids, or chloride,and sulfate at Burro Spring and Unnamed Spring near Dennehotso maintain varied for the period of record, but there is no increasing or decreasing statistical trend in the data.
Source: usgs.gov