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Western Plateau Planning Area Hydrology - Groundwater (Continued)

Skip to groundwater hydrology of the Coconino Plateau, Grand Wash, Paria, Shivwits Plateau or Virgin River basins.

Kanab Plateau Basin

The Kanab Plateau Basin is characterized by high plateaus, plains and incised canyons.  The basin contains a flat-lying to gently sloping sequence of alternating sandstones, limestones and shales.  Groundwater is found in several aquifers composed of these sedimentary rocks, which are generally isolated and not hydraulically connected.  Water bearing units in the vicinity of Pipe Spring National Monument include alluvium, Navajo Sandstone, the Kayenta and Moenave formations, and the Shinarump Formation (Truini and others, 2004).  Groundwater also occurs in recent stream alluvium, including the Cane Beds area west of Moccasin. 

Within the sedimentary rock aquifers, faults act as conduits for vertical and lateral groundwater movement.  Major faults include the Toroweap and Sevier faults.  Regional groundwater flow direction, annual natural recharge rate and groundwater storage data are not available for the basin. The median well yield reported for ten large diameter (>10gpm) wells was 70 gpm.  Hydrographs are available for two basin wells - one completed in the Kayenta Formation at Moccasin, with a recent water level of 87 feet bls, and a second completed in “sedimentary rock” south of Fredonia with a recent water level of 611 feet bls (Figure 6.3-7). Elevated levels of TDS and lead have been measured at some well and spring sites (Table 6.3-7) although water quality is generally good for most uses.

Kanab Plateau Marble Canyon Cliffs

Vermilion Cliffs outside of the Town of Marble Canyon.

Paria Basin

The geologic structure of the Paria Basin is typical of the Colorado Plateau with a gently-sloping sequence of limestone, sandstone and shale formations. The principal aquifer is the N-aquifer composed of Navajo Sandstone and the Kayenta and Moenave formations.  In places on the Paria Plateau, precipitation collects in sand deposits in limited quantities and may be recovered from shallow wells (Bush and Lane, 1980).  Groundwater movement is generally from south to north with discharge at springs in Paria River Canyon.  Some groundwater moves south toward the Vermilion Cliffs, which form the southern basin boundary.  An annual natural recharge rate is not available for the basin. Groundwater in storage is estimated at 1.5 maf.

Little groundwater development has occurred with only 12 wells registered in the basin.  Department data indicate well yields ranging from 30 to 1,400 gpm with a median well yield of 520 gpm for three large diameter (>10gpm) wells. The two largest yields come from wells completed in sedimentary rocks.  Water levels in basin wells are relatively deep, ranging from about 480 feet to 1,500 feet bls.  Arsenic concentrations above the drinking water standard have been measured at a number of wells in the Wahweap area (see Table 6.3-5).

Mt Trumbell Road

Mt Trumbell Road, Shivwits Plateau Basin.  The basin contains an alternating sequence of limestones, sandstones and shales with alluvial sands and gravels along larger washes and canyons.

Shivwits Plateau Basin

Most of the Shivwits Plateau Basin is high plateau with elevations of 4,000 to 6,000 feet.  The basin contains an alternating sequence of limestones, sandstones and shales with alluvial sands and gravels along larger washes and canyons.  Figure 6.0-6 shows a cross section of the geology in the Shivwits Plateau, Kanab Plateau and the western portion of the Coconino Plateau basins.  The cross section begins in the west-central portion of the Shivwits Plateau Basin (T33N, R12W) and follows a southeastern diagonal across the Shivwits Plateau and Kanab Plateau basins, ending just across the Colorado River in the Aubrey Cliffs in the Coconino Plateau Basin (T32N, R7W).  The cross section provides the general location of the water bearing units beneath the region and their depth and thickness in particular areas. The diagram also shows the impact of the Hurricane Fault on the cross section occurrence of the geologic units.

Stream alluvium is the major aquifer in the basin but well yields are relatively low. A number of dry wells have reportedly been drilled into the sedimentary rocks but some encountered water in faults and fractures.  Groundwater recharge occurs from infiltration of rainfall and snowmelt.  Data on groundwater flow direction, annual natural recharge rate and groundwater in storage is not available for the basin.

Figure 6.0-6 Geologic cross section of the Shivwits Plateau, Kanab Plateau and Coconino Plateau Basins

(modified from Billingsley and Welmeyer, 2003)

Click to view Figure 6.0-6

There are only 18 registered wells in the basin.  Department data indicate well yields ranging from 0 to 45 gpm with a median well yield of 5 gpm for 17 large diameter (>10gpm) wells. Recent water levels in wells range from 10 feet bls to over 960 feet bls (see Figure 6.5-6).  Water from springs and seeps is generally of better quality than well water, although the arsenic level at one spring exceeded the drinking water standard (Table 6.5-4).

Virgin River Basin

Located in the northwestern corner of Arizona, the Virgin River Basin contains a broad alluvial valley in the western half and the relatively high elevation Beaver Dam and Virgin Mountains in the south and east.  Principal aquifers are basin fill in the Virgin River Valley and Beaver Dam Wash, and the Muddy Creek Formation.  The mountainous portions of the basin are underlain by sedimentary and igneous rocks with little groundwater development.

The basin-fill aquifers are composed of a younger floodplain unit and an older underlying unit of semi-consolidated silts, sands, gravels and boulders. In the Virgin River Valley, the basin-fill aquifer contains floodplain and terrace alluvium southwest of Littlefield and includes alluvial-fan deposits from the Virgin Mountains.  Groundwater is unconfined and flows toward the southwest.  In Beaver Dam Wash, the basin-fill aquifer is largely isolated from other water bearing units in the basin and is also unconfined.  Groundwater flow is toward the Virgin River Valley. 

The Muddy Creek Formation consists of a series of siltstones, sandstones and conglomerates that is utilized as a water supply in the western part of the basin and by the City of Mesquite, Nevada adjacent to the basin along Interstate 15 (Black and Rascona, 1991).   It is several thousand feet thick in places and covers the land surface over much of the basin north of the Virgin River. The Muddy Creek Formation is underlain by saturated Paleozoic carbonate rocks.  South of the Virgin River, alluvial deposits from the Virgin Mountains overlie the Muddy Creek Formation. Fault and fracture zones in the formation control groundwater movement and may have groundwater development potential (Dixon and Katzer, 2002).

Virgin River Mountains

Virgin River Valley

Between Littlefield and the Virgin River Mountains and south of the Virgin River, a shallow, basin-fill aquifer overlies a limestone formation known locally as the Littlefield Formation.  Few wells are completed in the shallow aquifer but a number of springs emanate from groundwater flowing over or through the Littlefield Formation (Black and Rascona, 1991).

Natural recharge is estimated at less than 30,000 AFA. Groundwater in storage is estimated to total 1.7 maf. Well yields range widely in the basin, as listed on Table 6.6-6, from a reported 10 gpm in the Virgin River basin-fill aquifer to over 5,000 gpm during a pump test in the Beaver Dam Wash basin-fill aquifer (Black and Rascona, 1991).  The median of well yields reported from 53 large diameter (>10 inch) wells completed in the basin is 650 gpm.  Water quality ranges from very good to poor, the latter due to elevated concentrations of arsenic, chloride, sulfate and total dissolved solids.  Salt concentrations in groundwater increase downstream in the floodplain area along the Virgin River. Water quality data collected between 1997 and 2002 listed in Table 6.6-7 show elevated concentrations of arsenic, nitrate and radionuclides.

 

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