Sandra J. Owen-Joyce and C. K. Bell

For ease of discussion, the water-bearing rock units of the upper Verde River area are grouped into a regional aquifer. The aquifer comprises the alluvium along the Verde River, the Verde Formation, Coconino Sandstone, Supai Formation, Naco Formation, Redwall Limestone, Martin Formation, and Tapeats Sandstone (pl. 1). The rock units are hydraulically connected; water flows from one unit into the next as it moves downgradient, and one potentiometric surface now is common to all (pl. 2). Well productivity and chemical quality of ground water differ from place to place because of the contrasting lithologies and secondary permeabilities of the rock units that make up the aquifer. Other aquifers discrete from the regional aquifer are the volcanic rocks, alluvium, granitic rocks, Kaibab Limestone, and Toroweap Formation.

Ground-water development in the Verde Valley is concentrated mainly along the Verde River and Oak Creek where the regional aquifer is the principal source of public and domestic water. Development of water resources in the Plateau uplands and Black Hills is sparse in comparison to that in the Verde Valley, and the water is used mainly for domestic and livestock supply. One exception is a well field near Lower Lake Mary (pi. 2), which is a public water supply for the city of Flagstaff (fig. 1).

Regional Aquifer

Units of the regional aquifer underlie all the upper Verde River area except where Precambrian rocks crop out west of the Verde fault from Chasm Creek to Jerome (pl. 1). Northeast of the Mogollon Rim, the regional aquifer consists of the Coconino Sandstone, Supai Formation, Naco Formation, Redwall Limestone, Martin Formation, and Tapeats Sandstone. In the Verde Valley the regional aquifer includes alluvium along the Verde River, the Verde Formation and the underlying basalt flows, Supai Formation, and Redwall Limestone. On the east side of the valley, the Verde Formation is underlain by the Supai Formation at a depth of 210 ft as shown in well (A-16-4)21aac. West of Cottonwood and east of the Verde fault, wells obtain water from the Redwall Limestone beneath the Verde Formation. No known well has completely penetrated the Verde Formation in the central and southern part of the valley. In the Black Hills, the regional aquifer consists of the Redwall, Martin, and Tapeats north of Jerome, and locally, the Martin and Tapeats south of Chasm Creek.

Occurrence of Ground Water

In most of the area, ground water in the regional aquifer is unconfined (water-table conditions). In places, water in the Verde Formation, Supai Formation, and Redwall Limestone is confined (artesian conditions). Near Rimrock, Cottonwood, Cornville, and Page Springs, the potentiometric surface is above the land surface and some wells flow. Measurements at two wells, one near Cottonwood and one near Cornville, show the water level to be about 0.1 and 47 ft above the land surface, respectively. Northeast of the Mogollon Rim, the units that generally yield water to wells are the Coconino Sandstone and upper member of the Supai Formation. Well (A-18-7)27cbb near Munds Park is 1,500 ft deep and obtains water from the upper member of the Supai; the water level is 1,279 ft below the land surface (table 10). The Coconino is tapped by wells in Munds Park, near Upper and Lower Lake Mary, and in the southeast corner of the study area. Depth to water ranges from 275 to 791 ft below the land surface in wells that are from 400 to 1,480 ft deep (table 10).

The Supai Formation is the principal unit of the regional aquifer that provides water to wells near Sedona, Big Park, Oak Creek, Page Springs, and north of Rimrock. Most of the wells in the Sedona area tap the middle and lower members of the Supai. The upper member of the Supai is dry except along the downthrown side of Oak Creek fault and in the Red Rock area. Water is obtained from the sandstone beds of the Supai, and the depth to water in wells ranges from flowing at the land surface east of Rimrock and near Page Springs to 746 ft below the land surface near Grasshopper Flat. Well depths range from 90 to 3,203 ft; only one well is more than 1,405 ft deep (table 10). North of Bear Wallow Canyon fault and west of Grasshopper Flat in T. 18 N., R. 4 E., the Supai is above the regional water table and is drained except for locally perched zones in the sandstone beds. The water levels in perched zones are from 200 to 700 ft above the water level in the regional aquifer.

The Redwall Limestone yields water to wells west of Clarkdale and Cottonwood, near Sedona and Grasshopper Flat, north of Grasshopper Flat, and to a well southeast of Red Rock. Depth to water in wells ranges from flowing at the land surface to 733 ft below the land surface, and wells are from 225 to 822 ft deep (table 10). North of Bear Wallow Canyon fault and west of Grasshopper Flat, deep-well data indicate that the Redwall is above the regional water table and drained of water (Levings, 1980).

The Martin Formation yields water to wells in the Sedona-Red Rock area, near the town of Drake, and in the Black Hills south-southwest of Perkinsville (pl. 1). Depth to water in wells ranges from 145 to 917 ft below the land surface, and wells are from 200 to 1,215 ft deep (table 10). Wells generally obtain water from the Martin Formation or the Tapeats Sandstone, or both, north of Bear Wallow Canyon fault and west of Grasshopper Flat. The Tapeats Sandstone probably would yield water to wells in most of the area, but no wells are known to tap the unit.

The Verde Formation is the principal unit of the regional aquifer in the Verde Valley from north of Clarkdale to Cottonwood Basin (pl. 1). Depth to water in wells ranges from flowing at the land surface near Cornville and Rimrock to 489 ft below the land surface south of Cottonwood (table 10). Water is obtained mainly from the limestone and sandstone facies, although some water is obtained from the mudstone facies. Wells in the Verde Formation are from 30 to 1,625 ft deep (table 10).

In most places the alluvium along the Verde River between Clarkdale and Cottonwood Basin (pl. 1) is hydraulically connected to the Verde Formation and is part of the regional aquifer. Water levels are similar in altitude to those in wells that tap the Verde Formation near the Verde River, and water chemistry changes are the same. The alluvium generally is less than 50 ft thick, and water levels in wells are from 3 to 43 ft below the land surface; wells are from 28 to 110 ft deep (table 10). The deeper holes bottom in the Verde Formation, but the principal source of water is the alluvium.

Recharge, Movement, and Discharge of Ground Water

Ground water in the regional aquifer is derived from the infiltration of precipitation on permeable rock units and from surface water in streams and lakes. The main area of recharge is in the Plateau uplands part of the area where the greatest amount of precipitation occurs and where permeable sandstone, limestone, and fractured volcanic rocks crop out at the surface. A smaller amount of recharge occurs in the Central highlands part because the annual precipitation is less and the exposed rocks are less permeable than those exposed in the Plateau uplands. Along the eastern flank of the Black Hills, the rock units are highly faulted and fractured. Water infiltrates along the fractures in the Redwall Limestone, Martin Formation, and Tapeats Sandstone.

Underflow that crosses the study area boundary into the upper Verde River area is assumed to be negligible. Most of the boundaries of the study area approximate ground-water divides as implied by a few wells and the geology. Because data are scarce, the ground-water divides are not accurately known except along the eastern divide (pl. 2). A likely source of underflow is from Chino Valley (fig. 1). The only known rock units of the regional aquifer in Chino Valley exist as erosional remnants (Krieger, 1965); water occurs in the valley-fill deposits that contain interbedded volcanic rocks. Near Sullivan Lake where this ground water would flow into the upper Verde River area, only a thin section of regional aquifer is present to transmit underflow. About 4.5 mi downstream from the point at which the Verde River enters the study area, massive Precambrian granitic rocks crop out. The granitic rocks are nearly impermeable and probably do not transmit significant quantities of ground water. If significant quantities of ground water were moving into the area as underflow through the aquifer, the water probably would be discharged to the Verde River at the constriction caused by the granitic rocks. However, discharge measurements made in December 1979 when evapotranspiration would have been small show no measurable gain in streamflow in this reach. Any water moving through the granitic rocks would have to be moving along faults or fractures and be of a negligible quantity.

When the infiltrating water reaches the water table, it moves downgradient toward the Verde River. The altitude and configuration of the potentiometric surface are depicted by the contour lines on plate 2. In the part of the Plateau uplands province within the study area, ground water moves southwestward from a ground-water divide toward the Mogollon Rim and into the Central highlands province. In the Central highlands province, the ground water flows toward the Verde River and then parallel to the river. Near Upper and Lower Lake Mary and in the southeast corner, part of the ground water flows to the northeast and out of the study area. Ground water probably moves down the eastern flank of the Black Hills toward the Verde River, but owing to the lack of data in this area the direction of the movement is poorly defined.

Ground water in the regional aquifer is discharged to springs, streams, and wells. Springs that issue from the Verde Formation near Rimrock discharge from 15 to about 1,280 gal/min; Page Springs discharge about 13,900 gal/min (table 11). Springs in the Coconino Sandstone maintain the perennial flow in parts of Wet Beaver Creek, West Clear Creek, and Oak Creek. The springs discharge from 75 to more than 1,000 gal/min (table 11). Along Oak Creek upstream from the town of Page Springs, part of the perennial flow is derived from the Supai Formation (Levings, 1980). Springs that issue from the Supai along the Verde River south of Sycamore Creek and at Mormon Pocket discharge about 50 to 75 gal/min (table 11). Along Dry Beaver Creek, springs discharge 85 gal/min from the Supai (table 11). Fossil Springs issue from the Naco Formation along the north wall of Fossil Canyon and furnish 18,600 gal/min to Fossil Creek (table 11). Downstream from the springs, a dam diverts the water into a flume that carries it to generate electricity in plants at Irving and Childs (pl. 3). Springs issue from the Redwall Limestone along the southern reach of Sycamore Creek and discharge 15 to 2,700 gal/min (table 11). Along the eastern flank of the Black Hills, the major source of springs is the Martin Formation. Near Jerome, springs are estimated to discharge from 2 to 52 gal/min; Brown Spring, just north of Tule Mesa, discharges about 50 gal/min (table 11). In the Black Hills, springs issue from the Tapeats Sandstone in sec. 11, T. 15 N., R. 2 E. One spring discharges about 40 gal/min (table 11).

Ground water, which is discharged to springs along the Verde River and its tributaries, maintains the base flow of the streams. Part of the water that has reached the surface is lost by evaporation from soils and open water surfaces and through transpiration by riparian vegetation, and part is diverted and used for irrigation. Some water diverted for irrigation may infiltrate back into the aquifer. The resultant base flow left in the Verde River leaves the area as surface water. Groundwater flow is intercepted by wells pumped for public and domestic use, mainly in the Verde Valley (pl. 2).

The seepage investigation showed no major gain south of Beasley Flat; therefore, little or no ground-water discharges to the river even where the Verde Formation pinches out onto volcanic rocks near Cottonwood Basin (pl. 3). About halfway between Cottonwood Basin and Childs, the river flows on an outcrop of nearly impermeable massive metamorphosed volcanic rocks of Precambrian age. About 130 ft of Martin Formation and Tapeats Sandstone lies between the impermeable rocks and the Tertiary volcanic rocks (R. E. Lewis, California Institute of Technology, written commun., 1979). If underflow upgradient from this area were significant, part of it should discharge to the river upon reaching the constriction caused by the thinning of the aquifer. Concealed underflow would have to move along faults and fractures in the impermeable volcanic rocks. Because no significant gains in the base flow of the river were detected and because the quantity of underflow moving along faults or fractures would be small, underflow out of the area probably is negligible.

Vertical and lateral changes in lithology can act as impediments to the movement of ground water. Locally, mudstone and basalt flows interbedded in the Verde Formation confine ground water. Water moving through fractured volcanic rocks is confined by overlying ash or clay beds or perched by underlying ash or clay beds.

The Oak Creek fault (pl. 2) acts as an impediment to the lateral movement of ground water and as a conduit for flow. In the north half of Oak Creek Canyon, the less permeable upper member of the Supai Formation contacts the more permeable Coconino Sandstone and flow across the fault is impeded. Water flowing through the Coconino in a southwesterly direction cannot easily flow across the fault into the less permeable siltstone beds of the Supai. In this area, water moves along the fractured rock of the fault zone to discharge at springs along Oak Creek. A disruption in flow also occurs along the Bear Wallow Canyon fault (pl. 2).

Water-Yielding Characteristics of the Regional Aquifer

The water-yielding characteristics of the regional aquifer differ areally; fracturing and solution of the rock units locally increase the hydraulic conductivity of the aquifer.

Transmissivity.--The rate of downgradient movement of water from areas of inflow to areas of outflow and the potential rate of groundwater withdrawal are dependent on aquifer transmissivity. Values of transmissivity may be determined by aquifer tests or estimated by well tests, which consist of pumping a well at a constant rate and measuring the resultant decline and (or) recovery of the water levels in the pumped well and (or) observation wells. The test data are useful in determining the potential yield of wells and the effects of ground-water withdrawals.

Aquifer and well-test data show that transmissivity of the regional aquifer ranges from 20 to 16,000 ft2/d (table 1). This wide range in transmissivity is a result of areal and vertical changes in lithology and the effect of secondary hydraulic conductivity caused by faulting, fracturing, and solution channels in the rock units. The higher transmissivity values are in faulted and fractured rock units of the regional aquifer.

Table 1 --Water-yielding characteristics for selected wells penetrating the regional aquifer in the upper Verde River area


		Well		Average				Specific			Trans-
Local well	diameter,	discharge,	Drawdown,	capacity,	Duration of	missivity,	Principal water-
number		in inches	in gallons	in feet		in gallons	aquifer test,	in feet		contributing		Remarks
				per minute			per minute	in hours	squared		rock units
								per foot			per day


(A-14-05)17aac	10		45		33		1.3		24		880		Verde Formation		Twenter and Metzger, 1963;
																	reported as (A-14-05)17aaa2;
																	80 feet of perforations.

(A-15-04)12abb	10		70		66		1.0		14		50		Verde Formation		Levings, 1980; reported as
														and Supai		(A-15-04)12abd; perforated
														Formation		intervals 661-702 feet,
																	881-941 feet.

(A-16-04)27dcc	6.63		37		209		0.2		47		20		Verde Formation		Levings, 1980; perforated
																	intervals 60-80 feet, 240-
																	260 feet, 358-388 feet.

(A-16-04)34abb	8		40		121		0.3		48.		200		Verde Formation		U.S. Geological Survey files,
																	1977; 600 feet, total depth;
																	447 feet of open hole.

		6		470		42		11.3		15		14,100		Verde Formation		Arizona Water Commission
																	(written commun., 1979);
																	flowing well, 690 feet,
																	total depth; 260 feet of
																	perforations.

(A-17-05)19aaa	8		87		5		17.4		49		10,000		Supai Formation		Levings, 1980; 622 feet of
														and Redwall		open hole.
														Limestone

(A-17-05)33adal	8		708		43		16.5		29		16,000		Supai Formation		Levings, 1980; well finish is
														and Redwall		unknown.
														Limestone

(A-20-08)18bcc	20		600		431		1.4		5,400		1,070		Coconino Sand-		Harshbarger and Associates,
														stone and		1976; 521 feet of perfora-
														Supai For-		tions; data from aquifer
														mation			test on well field.

(A-20-08)19aba	20		701		342		2.0		5,400		800		Coconino Sand-		Harshbarger and Associates,
														stone and		1976; 480 feet of perfora-
														Supai For-		tions, 45 feet of open hole;
														mation			data from aquifer test on
																	well field.

(A-20-08)20dbc	20		1,000		182		5.5		98		800		Coconino Sand-		Harshbarger and Associates,
														stone and		1976; 675 feet of perfora-
														Supai For-		tions.
														mation

Specific capacity is roughly proportional to the transmissivity but differs from well to well because of the differences in well construction and development. Most of the data available to calculate specific capacities are from short-term tests, which may differ from those calculated on the basis of longer term pumping at a constant rate. The specific capacity of most wells producing from the regional aquifer ranged from 0.1 to 118.0 (gal/min)/ft (table 1).

Well yields.--Well yields are a function of the lithology and fracturing of the geologic units, thickness of the aquifer penetrated, well construction and development, and aquifer transmissivity. Well-yield data were obtained from drillers' reports, normal pumping operations, and well-test data. Well yields ranged from less than 10 to 1,600 gal/min, but these values may not represent the maximum yields obtainable.

Wells that obtain water from the Paleozoic rock units (pl. 1) show a wide range in yields (table 2) owing to the different lithologies of the units and secondary features, which increase the hydraulic conductivity. The higher yields in the Coconino Sandstone and Supai Formation occur in areas of fracturing and faulting. Near Rimrock and Page Springs, flowing wells that tap the Supai yield from 2 to 70 gal/min. In addition to fracturing and faulting, solution cavities along fractures improve the yields from the Redwall Limestone and Martin Formation.

Wells that produce from the Verde Formation are generally similar in size and construction characteristics. The yields (table 2) differ mainly owing to areal and vertical changes in lithology of the rock units making up the formation and the lenticular nature of the deposits. Higher yields occur where the limestone facies contain solution channels and joints.

Table 2 -- Well-yield data for rock units in the regional aquifer

			Number		Well yields, in gallons per minute
Rock unit		of wells	min.	max.	median

Alluvium (1)		18		12	300	32
Verde Formation		138		2	1,600	30
Coconino Sandstone	14		10	1,000	150
Supai Formation		74		1	225	25
Redwall Limestone	13		0.4	1,078	92
Martin Formation			2	10	10	10

(1) Along the channel and flood plain of the Verde River

Wells that produce from the alluvium along the channel and flood plain of the Verde River generally yield less than 50 gal/min (table 2). The hydraulic conductivity of the alluvium depends on the amount of fine-grained matrix present in the sand, gravel, and boulders. The saturated thickness of the alluvium generally is less than 20 ft, and in some places the alluvium is dry.

Chemical Quality of Ground Water

Ground water in the regional aquifer generally is suitable for most uses. Water obtained from the Verde Formation and alluvium near Camp Verde, however, may exceed the drinking-water standards for dissolved solids, sulfate, and some minor elements. The maximum contaminant level for dissolved solids in public water supplies is 500 mg/L (milligrams per liter), as proposed in the secondary drinking-water regulations of the U.S. Environmental Protection Agency (1977b, p. 17146). Water that contains a larger dissolved-solids concentration is used when better water is not available. The chemical composition and quality differ areally depending on which rock unit is tapped (table 3). The major ions in the water obtained from the Coconino Sandstone, Supai Formation, Redwall Limestone, and Martin Formation are calcium, magnesium, and bicarbonate. Dissolved-solids concentrations range from 134 to 1,480 mg/L. Four samples out of 158 exceeded the maximum contaminant level of 500 mg/L (table 13). Three of these samples were from storage tanks at the wells, and the dissolved-solids concentrations are 503, 506, and 585 mg/L. The first two wells probably tap the Supai and Redwall, and the latter one taps the Supai, Redwall, and Martin. Water from the fourth well, (A-17-6)6dca, had a dissolved-solids concentration of 1,480 mg/L before the well was plugged back. This well was originally drilled to Precambrian granite and tapped the Supai, Redwall, and Martin. After plugging, the well was perforated only in the Supai, and a specific conductance measurement showed a marked decrease in dissolved solids. In general, the Redwall and Martin yield water with a larger dissolved-solids concentration than the overlying Supai or Coconino.

The most noticeable changes in composition and quality of the ground water occur in the Verde Formation. The chemical composition of water changes as it flows from the northern sections of the Verde Valley toward the southern outflow point (table 4). The major ions in the ground water in the areas of Cottonwood, Cornville, and Lake Montezuma are calcium, magnesium, sodium, and bicarbonate. Near Middle Verde, the major ions are calcium, magnesium, sodium, sulfate, and bicarbonate. At Camp Verde, the major ions are calcium, magnesium, sodium, chloride, sulfate, and bicarbonate. The major ions in water from three wells southeast of Camp Verde are sodium, magnesium, and sulfate. The dissolved solids increase from north to south in the Verde Valley; only 8 percent of the samples exceed the 500 mg/L limit at Cottonwood, whereas 96 percent exceed the limit at and southeast of Camp Verde. The composition changes are due mainly to the rock type through which the water flows.

Table 3 --Summary of quality of water in rock units in the regional aquifer

[Analytical results in milligrams per liter except as indicated.
All samples may not contain values for all parameters]

			Alluvium along	Verde		Coconino	Supai		Redwall		Martin
Constituent		the Verde River	Formation	Sandstone	Formation	Limestone	Formation
			(7 samples)	(188 samples)	(15 samples)	(112 samples)	(24 samples)	(7 samples)

Calcium
	Minimum		43		21		23		17		25		44
	Maximum		150		560		73		95		100		320
	Median		63		68		43		48		72		58

Magnesium
	Minimum		32		8.6		10		7.7		11		17
	Maximum		210		4,450		52		90		58		170
	Median		83		34		22		21		24		40

Sodium(1)
	Minimum		30		8.7		2.0		2.0		0		6.0
	Maximum		980		24,300		18		29		58		38
	Median		150		34		5.1		8.5		9.0		20

Bicarbonate
	Minimum		290		52		147		100		151		210
	Maximum		590		980		450		532		439		1,840
	Median		559		350		240		258		310		330

Sulfate
	Minimum		47		<1.0		0.2		<1		<1.0		5.4
	Maximum		1,900		64,700		5.4		81		100		37
	Median		220		14		2.8		6.0		7.4		30

Chloride
	Minimum		17		4.5		1.1		1.0		2.0		3.4
	Maximum		360		3,530		7.0		90		114		43
	Median		66		27		4.0		6.0		8		22

Fluoride
	Minimum		0.3		0		0		0		<0.1		0.1
	Maximum		0.8		3.4		0.4		0.6		0.6		0.4
	Median		0.7		0.3		0.1		0.1		0.2		0.2

Dissolved solids
	Minimum		383		209		135		134		158		207
	Maximum		3,790		97,700		360		585		503		1,480
	Median		1,450		424		211		242		307		420

Arsenic, in
	micrograms
	per liter
	Minimum		11		1		3		<5		<5		6
	Maximum		30		240		6		30		<10		6
	Median		27		30		4		<10		<10		6


(1) includes sodium plus potassium values.

Table 4 --Summary of quality of water in the Verde Formation

[Analytical results in milligrams per liter except as indicated.
All samples may not contain values for all parameters]


							Lake
			Cottonwood	Cornville	Montezuma					Southeast of
Constituent		and		and		and		Middle Verde	Camp Verde	Camp Verde
			Clarkdale	Page Springs	Rimrock		(29 samples)	(21 samples)	(5 samples)
			(38 samples)	(52 samples)	(43 samples)


Calcium
	Minimum		21		30		32		32		28		69
	Maximum		212		170		148		185		150		560
	Median		52		64		80		59		78		125

Magnesium
	Minimum		12		8.6		18		20		12		35
	Maximum		98		69		55		401		280		4,450
	Median		29		30		32		48		53		100

Sodium(1)
	Minimum		9.0		8.7		13		20		40		9.4
	Maximum		74		110		116		1,100		300		24,300
	Median		20		36		40		27		88		38

Bicarbonate
	Minimum		208		52		290		260		316		226
	Maximum		530		980		775		410		540		336
	Median		297		380		441		330		450		320

Sulfate
	Minimum		<1.0		3.0		1.0		9.5		69		78
	Maximum		673		84		18		2,900		1,200		64,700
	Median		8.0		14		12		64		210		485
	Percentage of
	samples
	greater than
	250 mg/L2	3		0		36		36		67		75

Chloride
	Minimum		4.5		8.0		9.7		15		20		4.9
	Maximum		52		83		49		260		200		3,530
	Median		22		16		28		22		47		29
	Percentage of
	samples
	greater than
	250 mg/L2	0		0		36		9		0		25

Fluoride
	Minimum		0.1		0		0		0.2		0.4		0.2
	Maximum		0.6		1.9		0.6		3.4		2.9		0.5
	Median		0.2		0.3		0.3		0.8		1.0		0.4

Dissolved solids
	Minimum		210		209		283		321		513		378
	Maximum		1,260		987		730		4,810		2,080		97,700
	Median		312		388		452		416		831		986
	Percentage of
	samples
	greater than
	500 mg/L2	8		30		44		41		100		75

Arsenic, in
	micrograms
	per liter
	Minimum		3		1		1		14		9		3
	Maximum		30		92		130		240		120		62
	Median		14		27		36		46		43		14
	Percentage of
	samples
	greater than
	50 ug/L2	0		19		21		43		44		25

The alluvium along the channel and flood plain of the Verde River contains water that differs in composition depending on location. Data for five wells indicate a hydraulic connection between the alluvium and the Verde Formation. A well that taps alluvium south of Middle Verde yields water that contains dissolved solids of 383 mg/L, mainly magnesium, calcium, sodium, and bicarbonate. Southeast of Camp Verde, similar wells produce water with dissolved solids that range from 806 to 3,790 mg/L (table 13), mainly magnesium, sodium, calcium, and sulfate. The similarities in chemical composition and correlation of areas with large concentrations of dissolved solids in the alluvium and Verde Formation indicate a hydraulic connection. The water in the Verde Formation, which contains large concentrations of dissolved solids flows into the alluvium, and increases the dissolved-solids concentration in the water in the alluvium. Increasing sodium and sulfate correlate with increasing dissolved solids for water from the Verde Formation and alluvium (table 3).

The U.S. Environmental Protection Agency (1977a, b) has established national regulations and guidelines for the quality of water provided by public water systems. Primary drinking-water regulations govern contaminants in drinking water that have been shown to affect human health, such as fluoride and arsenic. Secondary drinking-water regulations apply to those contaminants that affect esthetic quality, such as dissolved solids, sodium, magnesium, sulfate, and chloride. The primary regulations are enforceable either by the Environmental Protection Agency or by the States; in contrast, the secondary regulations are not Federally enforceable but are intended as guidelines for the States.

In some wells in Middle Verde and Camp Verde, sulfate exceeds the maximum contaminant level of 250 mg/L (U.S. Environmental Protection Agency, 1977b, p. 17146). Large concentrations of sulfate occur in wells that obtain water from the Verde Formation and alluvium (table 3). Large concentrations of sulfate in the water are associated with solution of evaporate minerals in the Verde Formation. These evaporate minerals are mainly sodium sulfate salts and minor amounts of sodium chloride and gypsum (hydrous calcium sulfate), which are present in sufficient quantity to make mining economical. An active gypsum mine is in sec. 11, T. 13 N. ' R. 5 E., and an inactive salt mine is in sec. 1, T. 13 N., R. 4 E. (pl. 1).

Chloride occurs in water from the Verde Formation and alluvium (table 3). Two wells in the Verde Formation yield water in which the chloride concentration exceeds the maximum contaminant level of 250 mg/L (U.S. Environmental Protection Agency, 1977b, p. 17146). One well just south of Middle Verde yields water that contains a chloride concentration of 260 mg/L. The other well is the same well that contains anomalously large concentrations of dissolved solids, and the chloride concentration is 3,530 mg/L (table 13). Water from two wells in the alluvium in Camp Verde contains 290 and 360 mg/L of chloride, which exceeds the maximum contaminant level.

Selenium, iron, manganese, mercury, fluoride, and arsenic in drinking water and boron in irrigation water exceed the maximum contaminant level set by the U.S. Environmental Protection Agency (1977c) and the State of Arizona (Bureau of Water Quality Control, 1978). For all these constituents except fluoride and arsenic, the large concentrations occur at individual sites scattered throughout the area. Maximum contaminant levels for selected chemical constituents are given below. The maximum contaminant levels for metals and trace elements are given in total concentrations.

Constituent			Concentration
Iron (Fe)			300 micrograms/liter
Arsenic (As)			50 micrograms/liter
Manganese (Mn)			50 micrograms/liter
Selenium (Se)			10 micrograms/liter
Mercury (Hg)			2 micrograms/liter

Fluoride concentrations exceed the maximum contaminant level in some wells that derive their water from the Verde Formation (table 4). The maximum contaminant level for fluoride in public water supplies differs according to the annual average maximum daily air temperature (Bureau of Water Quality Control, 1978, p. 6). The amount of water consumed by humans, and therefore the amount of fluoride ingested, depends partly on air temperature. Listed below are the maximum contaminant levels for fluoride in drinking water for the indicated temperatures at weather stations in the upper Verde River area (Sellers and Hill, 1974).

						Average		Maximum
    			Altitude above		max. daily	contaminant level
			National Geodetic	air temp.,	for fluoride,
			Vertical Datum		in degrees	in milligrams
Station			of 1929, in feet	Fahrenheit	per liter
Beaver Cr. Ranger Sta.	3,820			76.6		1.6
Cottonwood		3,360			78.4		1.6
Flagstaff Airport	7,006			60.8		2.0
Jerome			5,245			69.2		1.8
Junipine		5,124			69.9		1.8
Montezuma Castle	3,180			80.2		1.4
Perkinsville		3,855			75.7		1.6
Sedona Ranger Sta.	4,320			74.7		1.6

Arsenic is found in water from the regional aquifer. In most of the study area, arsenic concentrations are less than 10 micrograms/liter except at Big Park and in the Verde Valley. At Big Park (pl. 1), concentrations in water from the Supai Formation range from 20 to 30 micrograms/liter. In the Verde Valley, concentrations in water from the Verde Formation are as much as 240 micrograms/liter. South of Camp Verde, concentrations in water from the alluvium range from 11 to 30 micrograms/liter. Arsenic concentrations that exceed the maximum contaminant level of 50 micrograms/liter (U.S. Environmental Protection Agency, 1977c) are found only in ground water obtained from the Verde Formation (table 3). Water from some wells near Cornville, Rimrock, Lake Montezuma, Middle Verde, and Camp Verde (fig. 3) (table 4) contain more than 50 micrograms/liter of arsenic. Arsenic concentrations range from 1 to 240 micrograms/liter in 125 samples of water from the Verde formation (table 13). In the southern half of the Verde Valley where large concentrations of arsenic occur, 31 percent of the 97 samples exceed the maximum contaminant level for arsenic.

Arsenic concentrations in water from the Verde Formation are shown in figure 3 and include total and dissolved concentrations. The maximum contaminant levels used by the Arizona Bureau of Water Quality Control are total concentrations. Water samples analyzed by the Arizona Department of Health Services give total trace-element concentrations, but those in this area analyzed by the U.S. Geological Survey laboratory prior to 1979 report dissolved concentrations. To compare the two methods of reporting concentrations, some water samples were analyzed for both total and dissolved arsenic. For most wells, the total and dissolved concentrations were equal, within the detection limits of the analysis. A difference between total and dissolved concentrations indicates suspended arsenic, which was found in some samples.

The wells that contained suspended arsenic were compared because the suspended form is uncommon in ground water. Similar conditions existed at each of the wells. All the sampled wells that contain suspended arsenic are under artesian conditions, and those with the highest suspended values flow at the land surface. I n most of these wells the water rises 200 ft or more above the depth where water was encountered during drilling. The artesian conditions can maintain vertical circulation in the wells and keep the clay particles in suspension, which increases the total arsenic concentration of a water sample. The largest number of water samples with suspended arsenic concentrations were from wells near Lake Montezuma where the red clay contains the largest arsenic concentrations of all the rock units sampled.

Arsenic occurs in the rocks of the Verde Formation. Drill cuttings and outcrop samples from the Verde Formation (fig. 3) contained from 7 to 88 micrograms/gram of arsenic (table 5) and indicate that arsenic is disseminated throughout the formation rather than occurring in a particular bed of the formation. The amount of arsenic present in different beds does differ with location. A sample of the salt deposits from the Camp Verde Salt Mine contained the least amount of arsenic, 7 micrograms/gram. The white lime beds contained from 7 to 43 micrograms/gram of arsenic and averaged 19 micrograms/gram. The blue clay beds contained from 16 to 73 micrograms/gram, and the blue lime beds contained from 24 to 75 micrograms/gram; both units averaged 54 micrograms/gram of arsenic. The largest concentrations of arsenic were contained in the red clay beds near Lake Montezuma where the values were 34 and 88 micrograms/gram and averaged 61 micrograms/gram. Arsenic probably is associated with clay where arsenic ions are in the matrix of the clay particles. Arsenic concentrations are lowest in the clean white limestone and salt beds where the clay content is low.

Other Aquifers

In places, ground water is present in the volcanic rocks, alluvium, granitic rocks, Kaibab Limestone, and Toroweap Formation. Although these units do not contain ground water over large areas, they do provide locally important sources of water where developing water from the underlying formations means deeper wells at added cost.

Volcanic Rocks

Several wells and springs obtain water from the volcanic rocks northeast of the Mogollon Rim and in the Black Hills. The ground water is contained in fractured basalt flows and cinder beds several hundred feet above the regional water table and generally is perched over underlying rocks of low hydraulic conductivity. Locally, the underlying rocks may include the siltstone and mudstone in the Moenkopi Formation, unfractured basalt flows, or clay and ash layers between two basalt flows. These nearly impermeable rocks retard the downward movement of water into underlying formations; where they are absent, the volcanic rocks are dry. Wells are from 40 to 800 ft deep, and water levels range from 2 to 752 ft below the land surface (table 10). Wells in volcanic rocks are reported to yield from 0.8 to 80 gal/min. Well (A-18-7)27cba penetrates 400 ft of volcanic rocks and the yield is reported to fluctuate seasonally. In sec. 10, T. 21 N., R. 2 E., and sec. 27, T. 18 N., R. 9 E., shallow wells-less than 130 ft deep-that penetrate the volcanic rocks are dry. Springs generally discharge less than 20 gal/min (table 11). Verde Hot Springs is in the extreme southern part of the area along the Verde River in a fault zone and discharges an estimated 10 gal/min. The temperature of water that issues from the basalt at this location is 39°C.

Table 5 --Arsenic concentrations in selected drill cuttings and outcrop
samples from the Verde Formation


		Drillers'			Arsenic
		description	Depth interval,	concentra-
Local number	of the		in feet below	tion, in
		rock samples(1)	land surface	micrograms
						per gram

(A-13-04)Oldac	Salt		Outcrop		7

(A-13-05)06dbc	Blue clay	19- 48		16
		Blue lime	85-140		66

(A-13-05)06dbd	White lime	15- 21		24
		Green lime	21- 40		48
		Blue lime	40- 48		64

(A-13-05)07cca	Blue clay	Outcrop		38

(A-13-05)08caal	Blue clay	24- 37		67

(A-13-05)09dbb	Brown clay	23- 77		28
		Blue clay	77-160		73
		Blue lime	160-210		75

(A-14-04)03bbc	White lime	57-120		9

(A-14-04)13bca2	Blue clay	20- 30		56
		Blue  lime	40- 50		47
		Blue  lime	90-100		43

(A-14-04)14dba	Blue  clay	40-105		73
		Blue  lime	105-220		24

(A-14-05)02aad	White lime	158-210		43
		Red clay	270-286		34

(A-14-05)02ada	Red clay	75-115,		88
				141-160

(A-14-05)18cba	Blue clay	Outcrop		54

(A-14-05)19bcc	Blue lime	42-150		58
		White lime	150-250		10

(A-14-05)32dcc	White lime	90-108		7
		Gray lime	123-130		20


(1)Drillers' logs for these wells appear in table 15.

The ground water in the volcanic rocks, with the exception of Verde Hot Springs, is generally of acceptable chemical quality according to the standards set for drinking water. Water samples from five wells and nine springs (table 13) indicate that the dominant ions in solution are calcium, magnesium, sodium, and bicarbonate. The dissolved solids range from 111 to 600 mg/L. Table Mountain Spring, (A-12-5)10a, is near the southern extent of the Verde Formation depositional area and issues at the contact of fractured basalt and a red tuff. The water contains 600 mg/L of dissolved solids, a larger concentration of sulfate than other springs that drain volcanic rocks, and 9 micrograms/liter of mercury. This sample is the only one that exceeds the maximum contaminant level for mercury. Arsenic analyses are available for two wells in the Black Hills, (A-13-6)29dbb and (A-16-2)24aab, that obtain water from volcanic rocks. Both contained arsenic, 14 and 50 micrograms/liter, respectively, and the latter amount was at the limit recommended in the standards.

Verde Hot Springs, (A-11-6)lla, contains larger concentrations of the major ions than other springs issuing from the volcanic rocks (table 13). The dissolved-solids concentration is 3,230 mg/L, mainly sodium and bicarbonate. Other constituents with large concentrations are arsenic, iron, and boron, which are 1,400, 870, and 9,100 micrograms/liter, respectively.

Alluvium

Local deposits of alluvium near Munds Park, Cherry, Mormon Lake, Bill Williams Mountain, and along Hackberry Creek and Oak Creek in secs. 7 and 19, T. 17 N., R. 6 E., yield water to wells and springs. The water supplies are perched above the regional aquifer and water levels may be influenced by the stage of nearby streams. In Munds Park, wells are from 19 to 388 ft deep, yield from 5 to 450 gal/min, and the depth to water ranges from 8 to 170 ft below the land surface (table 10). Near Cherry, the depth to water is from 15 to 35 ft below the land surface, and wells are 50 to 150 ft deep. Two springs discharge water from alluvium; (A-21-3)27bad discharges 0.7 gal/min, and (A-12-6)11d, which is along Hackberry Creek, discharges 2 gal/min but is reported to fluctuate seasonally (table 11). Three wells in T. 17 N., R. 6 E., obtain water from the alluvium along Oak Creek. Wells are from 18 to 25 ft deep, and depth to water ranges from 13 to 16 ft below the land surface. Water is perched by the underlying siltstone beds of the Supai Formation.

The major ions present in water from the alluvium are calcium and bicarbonate. Water-quality data are available for four wells in Munds Park (table 13). The dissolved-solids concentrations range from 134 to 388 mg/L and averaged 222 mg/L. Water from spring (A-12-6)lld, which issues from the alluvium along Hackberry Creek, had a dissolved-solids concentration of 311 mg/L and is similar in chemical makeup to the waters in the volcanic rocks (table 13).

Granitic Rocks

In the Black Hills a few wells and springs obtain water from fractured granitic rocks. Two wells that obtain water from granite are 60 and 111 ft deep, and depth to water is 12 and 68 ft below the land surface, respectively (table 10).

Water from one well and three springs contained from 325 to 390 mg/L of dissolved solids, mainly calcium and bicarbonate (table 13). A fourth spring, (A-13-5)29cca, contained 669 mg/L of dissolved solids, mainly calcium and bicarbonate, and contained higher percentages of magnesium and sulfate than the other samples. This spring issues from an abandoned mine shaft, and the water quality may be influenced by the mine workings.

Kaibab Limestone and Toroweap Formation

The Kaibab Limestone and Toroweap Formation are above the regional water table, and no wells are known to obtain water from these rocks. Several springs along tributaries to Oak Creek, along the northern reach of Sycamore Canyon, near Upper Lake Mary, and in the southeastern part of the study area, issue from these rocks. Ground water contained in the sandstone of the Toroweap or in fractures, solution fissures, and solution caverns in the limestone of the Kaibab is perched on underlying siltstone and mudstone in the Toroweap or on chert beds in the Kaibab. Discharges from these springs range from 0.12 to 20 gal/min (table 11). Water-quality data are not available for the springs that issue from the Toroweap Formation or Kaibab Limestone.