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Lower Colorado River Water Supply - Groundwater, Effluent and Contamination Sites

Water supplies in the Lower Colorado River Planning Area include groundwater, surface water, Central Arizona Project (CAP) water and effluent.  As shown on Figure 7.0-13, most water used is surface water.  Colorado River water is the major supply in the Lower Gila, Parker and Yuma basins and CAP water is the largest supply in the Harquahala Basin. Gila River water combined with effluent discharge from the Phoenix AMA is an agricultural supply in the Gila Bend Basin.  Elsewhere, groundwater is the primary water supply.  Colorado River water is also used to meet environmental needs at the Imperial Wildlife Refuge in the Parker and Lower Gila basins. A discussion of Colorado River water entitlements and accounting is presented below.  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.

Figure 7.0-13 Average Annual Water Supply Utilized in the Lower Colorado River Planning Area, 2001-2005 (in acre-feet)

Figure 7.0-13


In basins without access to Colorado River or CAP water, groundwater is the primary water supply.  Groundwater is an abundant and dependable water supply throughout the planning area with relatively large volumes of groundwater in storage and high well yields in many basins.  Well yields typically exceed 1,000 gpm, and often exceed more than 2,000 gpm.  In groundwater dependent basins, estimates of water in storage are as high as 61 maf in the Gila Bend Basin, 15 maf in the McMullen Valley Basin and 27 maf in the Ranegras Plain Basin.  However, groundwater levels declined in many of these basins between 1990-‘91 and 2003-’04.  During this period, water levels declined by more than 30 feet in several wells in the northern part of the Gila Bend Basin, in wells near Salome-Wenden in the McMullen Valley Basin and in the central part of the Ranegras Plain Basin (see Figures 7.2-6, 7.5-5 and 7.7-5).  There are widespread occurances of fluoride and arsenic levels in groundwater that equal or exceed drinking water standards and high salinity levels in many agricultural areas.  As mentioned previously, importation of Colorado River water to areas in the Lower Gila and Yuma basins has locally raised groundwater levels and changed groundwater flow directions, requiring drainage wells and exportation of groundwater out of the basins.

In general, the Groundwater Transportation Act of 1991 restricts the transportation of groundwater from non-AMA groundwater basins to AMAs. However, there are three basins in the planning area from which groundwater may be withdrawn and transported outside of the basin: Butler Valley, Harquahala and McMullen Valley. General statutory provisions governing groundwater transportation from these basins are discussed below. Withdrawal and transportation of groundwater may cause groundwater level declines and impact the groundwater supply available for use within the basins.

Pursuant to A.R.S. § 45-553, groundwater may be withdrawn from the Butler Valley Basin and transferred to an initial AMA from State land or land owned by a political subdivision of the State (e.g. counties, cities and special districts). There are no limits on the volume of groundwater that may be transported from the basin. Groundwater may be withdrawn from historically irrigated lands in the McMullen Valley Basin that were owned by a city or person prior to January 1, 1988 and transported to the Phoenix AMA. (A.R.S. § 45-552) Qualified groundwater importers are cities, towns, private water companies and replenishment districts for their use or use by the AWBA. The City of Phoenix owns 14,000 acres of agricultural lands in the basin. The annual volume that may be withdrawn is limited to an average of 3 acre-feet per irrigated acre with a total limit of 6 maf. If this water is used for an assured water supply demonstration in an AMA, only water withdrawn above 1,000 feet below land surface (bls) at a rate not to exceed 10 feet per year over the 100 year period will be considered. In the Harquahala Basin, A.R.S. § 45-552 allows the transportation of groundwater pumped from historically irrigated lands owned by a political subdivision of the state and transported for its use in an AMA or use by the AWBA. The volumetric limit is 6 acre-feet per acre per year or 30 acre-feet per acre for any period of ten consecutive years. The director of ADWR may establish an alternative volume as long as it will not unreasonably increase damage to residents and other water users. Groundwater may not be withdrawn below 1,000 feet bls nor at a rate that cause declines of more than an average of ten feet per year during the one hundred year evaluation period. The City of Scottsdale has applied to the Department to export 3,645.24 acre-feet of groundwater per year from 1,215.08 acres of historically irrigated lands in the Harquahala Basin. This application is currently still under review.

Automated well

Automated well in the Harquahala Basin.

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 consists of over 42,000 records of wells and over 210,000 ground-water level records statewide. GWSI contains spatial and geographical data, owner information, well construction and well log 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, which can be searched and downloaded to access local information for planning, drought mitigation and other purposes.  Approximately 1,700 wells have are designated as Index Wells statewide out of over 43,700 GWSI sites. (GWSI sites are primarily well sites 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 ground water level fluctuations. Approximately 200 of the GWSI sites are designated as Automated Wells. These systems measure water levels 4 times daily and store the data electronically. Automated groundwater monitoring sites 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.

Volume 1 of the Atlas shows the location of index wells and automatic water-level recording sites as of January 2009.  At that time there were a total of 167 index wells and 8 ADWR automatic water-level sites in the planning area located in the Butler Valley, Gila Bend, Harquahala, Lower Gila, McMullen Valley and Ranegras Plain basins. Index wells are located in all basins except for San Simon Wash, most of which is covered by the Tohono O’odham Indian Reservation. The most updated maps may be viewed at the Department’s website.

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 Sections 7.1-7.11.


Effluent, or reclaimed water, is a little used resource in the planning area with less than 700 acre-feet used annually as a partial water supply for six golf courses in the Yuma Basin and one golf course in the Parker Basin.  Golf course irrigation demand is higher in the summer, but effluent production is higher in the winter when the area population increases due to winter visitors.  The water supply at Foothills Executive, Foothills Par 3 and Las Barrancas Golf Courses is about 90% effluent in the winter and 90% groundwater in the summer (personal communication, T. Holyk, 11/07).  Effluent discharged to the Gila River from the Phoenix AMA is an agricultural water supply in the Gila Bend Basin, but the volume used is not quantified.

Approximately 16,300 acre-feet of effluent are treated in the planning area, and 79% of that (12,800 acre-feet) is generated in the Yuma Basin.  Approximately 153,000 people or 79% of the total planning area population is served by a sewer system.  Most of this potential water supply is discharged to evaporation ponds or to infiltration basins after treatment.  A number of basins including, Butler Valley, Harquahala, McMullen Valley, Ranegras Plain, and Tiger Wash, have no record of a wastewater treatment plant. Use of septic tanks appears to be widespread throughout the entire planning area.

Golf course in Yuma

Golf course in the Yuma Basin

Contamination Sites

Sites of environmental contamination may impact the use of some water supplies.  An inventory of Department of Defense (DOD), Resource Conservation and Recovery Act (RCRA), Superfund (Environmental Protection Agency designated sites), Water Quality Assurance Revolving Fund (state designated WQARF sites), Voluntary Remediation Program (VRP) and Leaking Underground Storage Tank (LUST) sites was conducted for the planning area.  Of these various contamination sites, LUST, DOD, Superfund, WQARF and VRP sites are found in the planning area.  Table 7.0-9 lists the contaminant and affected media and the basin location of all but the LUST sites.  The location of all contamination sites in the planning area is shown on Figure 7.0-16.

Click to view Figure 7.0-16

Seven active VRP sites are located in the planning area and all but one is in the Yuma Basin. All are primarily sites of organic compound contamination such as petroleum and pesticide products. The VRP is a state administered and funded voluntary cleanup program.  Any site that has soil and/or groundwater contamination, provided that the site is not subject to an enforcement action by another program, is eligible to participate.  To encourage participation, ADEQ provides an expedited process and a single point of contact for projects that involve more than one regulatory program (Environmental Law Institute, 2002).

Two WQARF sites and one Superfund site exist in the Yuma Basin.  All sites involve Trichloroethylene (TCE) or Tetrachloroethene (PCE) contamination.  The Tyson Wash WQARF Site is located between Tyson Wash and Highway 95 north of Business Route 10 in Quartzsite. Contamination was detected in 1993 and a groundwater monitoring program began in 1995 to further investigate the extent of contamination.  The upper aquifer, located about 42 to 65 feet bls, has been affected.  Water is being pumped and treated on site and injected back into the aquifer. (ADEQ, 2005)  The 20th Street and Factor WQARF Site is located in Yuma and has cyanide contamination.  Formerly the site of a motion picture laboratory and photo equipment manufacturer, wastewater was treated to recover silver and then discharged to a sump and disposal pond, to the ground, and used for landscape irrigation.  Remedial actions at this site include soil removal and investigations to define the extent of a groundwater contamination plume. (ADEQ, 2007a)  The Yuma Marine Corps Air Station (YMCAS) Superfund site, located at Yuma, involves multiple contaminants in groundwater as a result of disposal of materials related to military activities. Remedial actions include vertical recirculation of groundwater to contain and treat areas of relatively low contaminant concentrations, and air sparging/soil vapor extraction to treat the Area 1 Hot Spot (Source) Plume area (ADEQ, 2007b).

The Yuma Army Proving Ground Department of Defense Site is located northeast of Yuma and was first used as a military training facility during WWII.  Later it became a site for testing of equipment under desert conditions. Groundwater contamination has occurred from the possible release of half a million gallons of fuel and from other actions. Environmental investigations and cleanup activities are underway and most of the contaminated areas are fenced. (ADEQ, 2007c)

There are 213 active LUST sites in the planning area.  One hundred eight sites are located at Yuma, 22 at Gila Bend, 18 at Quartzsite, 13 each at Parker and Ehrenberg, and ten sites or less at Somerton, Vicksburg, Wellton, Salome, Lukeville, Tacna and Centennial Wash.


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