The Highland Basins include the Salt River, Tonto Creek and Verde River basins, and the northern half of the Agua Fria Basin. Basin-fill aquifers in the highlands are limited in areal extent and are hydrologically connected with stream alluvium. Consolidated rock aquifers surround and underlie the basin-fill aquifers and contribute underflow. Basin-fill aquifers also receive inflow from stream infiltration and mountain front recharge. Where the basin-fill aquifers are discontinuous, underflow between them may be restricted (Anderson, et al., 1992).
Agua Fria Basin (northern half)
Groundwater occurs in four geologic units in the Agua Fria Basin: basin-fill sands and gravels, volcanic rocks, conglomerates and igneous and metamorphic rocks. Groundwater occurs in volcanic rocks in the northeastern section of the basin that yield relatively small volumes of water. Conglomerates are found throughout the basin and contain the largest volumes of groundwater of any of the rock units. Due to faulting, this unit is separated into smaller discrete basins separated by low permeability crystalline rocks.
Groundwater flow in the northern part of the basin is from the basin margins toward the Agua Fria River drainage and then south (Figure 5.1-7). The estimated volume of groundwater recharge for the entire basin is 9,000 AFA. Groundwater storage estimates for the basin vary from 620,000 acre-feet to 3.5 million acre-feet (maf) (Table 5.1-6). The median well yield reported on registration forms for large (>10-inch) diameter wells in the basin is 300 gpm with relatively low yields found in the vicinity of Meyer and at other locations. Water levels in basin wells measured between 1990-’91 and 2003-’04 were less than 100 feet bls. Water levels in several wells increased by as much as 15 feet during this period, but declined in wells near Cordes Junction (Figure 5.1-7). Water quality in the basin is generally good. In the northern part of the basin, arsenic was the drinking water parameter most frequently exceeded in measured wells and springs (Table 5.1-7).
The southern half of the Agua Fria Basin was categorized by Anderson, Freethey and Tucci (1992) as a “Central Basin”. Central basins are characterized by deep alluvial sediments with small to moderate amounts of mountain front recharge and streamflow infiltration.
Agua Fria Basin (southern half)
The principal aquifers in the Agua Fria Basin are upper basin fill, which occurs under unconfined conditions, and sedimentary rock (conglomerate), which is found throughout the basin and contains the largest volume of groundwater. Water level data are sparse in this portion of the basin. A domestic well located in unconsolidated sediments near Black Canyon City had a measured water level of 43 feet bls in 2003-‘04 (Figure 5.1-7). Well yields in the unconsolidated sediments may be as high as 1,000 gpm or more although most are less than 500 gpm (Figure 5.1-9). In Black Canyon City the Water Improvement District obtains water from wells completed in precambrian schist. The wells yield less than 20 gpm and have water levels ranging from 21 to 23 feet below ground surface (Black Canyon City, 2006). Arsenic and fluoride concentrations at levels that equal or exceed drinking water standards have been detected in springs and wells near Black Canyon City and at Castle Hot Springs.