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Western Plateau Planning Area Water Supply - Groundwater

Figure 6.0-

Figure 6.0-15  Average Annual Water Supply Utilized in the Western Plateau Planning Area, 2001-2005 (in acre-feet)

Water supplies in the Western Plateau Planning Area include groundwater, surface water and effluent.  As shown on Figure 6.0-15, groundwater is the primary water supply, accounting for about 63% of the demand.  Surface water is used for agricultural irrigation in the Virgin River and Kanab Plateau basins and for municipal use in the Coconino Plateau and Kanab Plateau basins.  It is estimated that about 34% of the total water demand is met with surface water.  Effluent is utilized for golf course irrigation and for landscape irrigation, toilet flushing and other uses in the Coconino Plateau Basin, contributing 3% of the planning area’s water supply. For purposes of the Atlas, water diverted from a watercourse or spring is considered surface water and if it is pumped from wells, it is accounted for as groundwater.  This is reflected in the cultural water demand tables in each basin section. 


Groundwater is the principal water supply for municipal, industrial and agricultural users in the planning area where it is pumped from relatively shallow local aquifers or from deep regional aquifers.  Groundwater pumpage averaged about 6,000 AFA during the period 2001 to 2005. Aquifer depth is a significant factor in groundwater availability in the area since it is both expensive to drill wells and to pump water to the surface. Groundwater is pumped from depths exceeding 2,000 feet bls at Tusayan and Williams.  In addition, well yields from sedimentary rocks of the deep regional aquifers are generally low unless fractures or faults are encountered.  The median well yield of 16 large diameter (>10 inch) wells in the Coconino Plateau Basin completed in sedimentary rock aquifers is about 45 gpm.

Areas of unconsolidated sediments are relatively limited as shown on the groundwater conditions maps for each basin in sections 6.1-6.6.  Extensive areas of unconsolidated sediments that comprise basin-fill aquifers are found only in the western portions of the Virgin River and Grand Wash basins.  Other basin-fill aquifers in the planning area are generally narrow and bordered by low water yielding consolidated rocks.  Areas of relatively high well yield include basin-fill deposits and the Muddy Creek Formation in the Virgin River Basin with a median well yield of 650 gpm based on data from 53 wells (Table 6.6-6).

Few hydrologic studies have been conducted in the planning area and as a result, there is uncertainty regarding groundwater resources including recharge rates and groundwater in storage.  Estimates of aquifer recharge are only available for the Virgin River Basin and estimates of groundwater in storage are only available for the Coconino Plateau, Paria and Virgin River basins.

Well data provide information on local groundwater conditions. The Department’s Groundwater Site Inventory (GWSI) database, the main repository for statewide groundwater well data, is available on the Department’s website.  The GWSI database contains over 42,000 records of wells and over 210,000 groundwater level records statewide. GWSI contains spatial and geographical data, owner information, well construction and geologic data and historic groundwater data including water level, water quality, well lift and pumpage records. Included are hydrographs for statewide Index Wells and Automated Groundwater Monitoring Sites (Automated Wells), which can be searched and downloaded to access local information for planning, drought mitigation and other purposes.

Approximately 1,700 wells are designated as Index Wells statewide out of over 43,700 GWSI sites (GWSI sites are primarily wells but include other types of sites such as springs and drains). Typically, Index Wells are visited once each year by the Department’s field staff to obtain a long-term record of groundwater level fluctuations. Approximately 200 of the GWSI sites are designated as Automated Wells. These systems measure water levels four times daily and store the data electronically. Automated wells are established to better understand the water supply situation in areas of the state where data are lacking.  These devices are located based on areas of growth, subsidence, type of land use, proximity to river/stream channels, proximity to water contamination sites or areas affected by drought.

Automated well in the Virgin River Basin

Automated well in the Virgin River Basin. 

Volume 1 of the Atlas shows the location of Index Wells and Automated Wells as of January 2009.  At that time there were 14 Index Wells in the planning area, primarily in the Virgin River Basin.  Of these, one is an Automated Well located west of Littlefield. Updated maps showing the location of Index and Automated wells may be viewed at the Department’s website.

Most large communities in the planning area rely on groundwater supplies.  Although groundwater may be difficult to access in many parts of the planning area, it is more reliable than the limited surface water supplies, particularly during drought.  Since 1999, the City of Williams has drilled four wells, three of which have static water levels greater than 2,700 feet bls, as a backup to their surface water supplies.  Some of the well drilling attempts have been unsuccessful.  As of 2002, Williams had spent about seven million dollars to drill six wells, three of which are producing (Pinkham and Davis, 2002). The City currently has four operational wells but one yields only 40 gpm, and another has poor water quality with elevated concentrations of dissolved oxygen, metals and arsenic. Tusayan relies on two 3,000-foot deep wells in the Redwall-Muav Aquifer as its primary water supply but also maintains a fleet of semi-tankers for emergency trucking of water if necessary (HydroResources, 2007).  Groundwater is also a supply for two industrial golf courses in the Virgin River Basin.

Pasture in Beaver Dam

Pasture in the Beaver Dam area, Virgin River Basin.

Groundwater is an agricultural water supply in the Beaver Dam area in the Virgin River Basin and in the Kanab Plateau Basin at Colorado City, Fredonia, and Moccasin/Kaibab.  Groundwater use for agricultural irrigation is declining in the planning area.

Information on major aquifers, well yields, estimated natural recharge, estimated water in storage, aquifer flow direction and water level changes are found in groundwater data tables, groundwater conditions maps, hydrographs and well yield maps for each basin in the Water Resource Characteristics sections.


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