On January 2, 2003, the Central Arizona Project (CAP) began delivering water to the Hieroglyphic Mountains Recharge Project (HMRP). The direct recharge facility is located in the West Salt River Sub-basin of the Phoenix AMA, west of the intersection of 163rd Avenue and the CAP canal. The project has an annual permitted recharge capacity of 35,000 acre-feet (AF) per year. The project was developed and constructed using State Demonstration Project funds.

HMRP consists of three basins that cover approximately 38 acres along a one-mile stretch of the CAP right-of-way. The basins are divided into a total of seven cells with each cell capable of being operated individually. Water is diverted from the CAP canal to the project through a pump station. The pump station consists of four electric turbine pumps that can deliver up to 25 cubic feet per second (cfs) each. The flow is measured by an acoustic flow meter with an accuracy of +/- 0.5%.

Initial deliveries to the project hieroglyphic mountains
Initial deliveries to the project, January 2, 2003 (Basin 2B)

Currently water is being stored for the Arizona Water Banking Authority and the Central Arizona Groundwater Replenishment District. The cities of Goodyear and Peoria have entered into water storage agreements at this facility for the future.

Project Facts

  • Permit Capacity: 35,000 AF per year for 20 years
  • Cost: $5.47 million
  • Volume Stored Through April 2004: 30,208 AF
  • Basins: Three basins, divided into 7 cells, totaling 38 acres
  • Location: T5N, R2W, Section 23 and 24 South ½
  • Project Operational: January 2003
  • Operational Delivery Capacity: 50 cfs

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 Facility Components

HMRP is composed of three basins, divided into seven individual cells. The cells range in size from 1.8 to 8.4 acres, for a total of approximately 38 acres of recharge basins. The water is pumped from the CAP canal using four electric turbine pumps rated at 25 cfs each. The deliveries average 40 to 45 cfs; therefore, only two pumps are used for deliveries with the other two ready as back-ups. The pumps are housed in individual sound reducing cabinets to protect the nearby neighbors.

Image of Pump station at HMRP Facility
Pump station at HMRP

The pumps are manifolded into a 42-inch pipeline with an acoustic flowmeter recording the flows every 15 minutes. Water is delivered to each basin through an upturned pipe with an apron of riprap to act as an energy dissipater. Flows to the individual cells are not measured. Pressure transducers installed in stilling wells record the water level in each cell. The normal operating level is less than 2 feet.

Image of Inlet pipe
Inlet pipe with riprap and the basin stilling

Data is collected for the amount of water pumped, water levels in each basin, and pump status for each pump. Geomation Measurement and Control Systems provide remote monitoring and control for the facility. The data is relayed to CAP Headquarters through the existing fiber optic line where it is displayed in real time.


HMRP is located southwest of the Hieroglyphic Mountains in the West Salt River Valley Sub-Basin of the Phoenix AMA. The mountains are composed of Tertiary and Cretaceous intrusive and Proterozoic metamorphic rocks, with minor Tertiary volcanics. The project is located in the Basin and Range Physiographic province.

The surficial geology maps prepared by the Arizona Geological Survey classify the site as alluvial fan deposits of Holocene age. The surface deposits form a broad and gently sloping plain with a dendritic drainage pattern. HMRP is unique within the CAP recharge facilities in that it is not built near a stream channel; rather it is constructed on alluvial fan deposits near the margin of the Salt River Valley alluvial basin.

 alluvial fan image
View of the alluvial fan with the Hieroglyphic
Mountains in the background

The subsurface hydrogeology in the West Salt River Basin has been subdivided into three hydrogeologic units: Upper Alluvial Unit (UAU), Middle Alluvial Unit (MAU), and the Lower Alluvial Unit (LAU). The UAU consists of unconsolidated interbedded clay, sand, and gravel typical of basin fill material. Underneath HMRP, the UAU is approximately 265 feet thick and is dry. The MAU is predominately clay with interbedded sand and gravel lenses. Beneath the site, the MAU extends to a depth of approximately 510 feet. The LAU is semi-consolidated to consolidated sand and gravel and is the principal aquifer for the region. The groundwater is under semi-confined conditions with water levels at approximately 480 feet below ground level prior to beginning recharge operations.

Groundwater flow is from northeast to southwest in the vicinity of HMRP. Trenching and drilling at the site show interbedded sandy silt, silty sand, clayey gravel, and weakly cemented gravel zones. In general, the unsaturated zone beneath the basins (UAU and MAU) is dominated by silty sand and gravel.

Monitoring and Reporting

The underground storage facility permit issued by the ADWR requires that each project operator monitor responses from the recharge operations on the regional water table and potential perched conditions as well as water quality. The HMRP has ten piezometers and two monitor wells to measure the impacts of the recharge operations. In addition, each of the seven basin cells has a pressure transducer installed in a stilling well to measure water levels.

Image of measuring water levels in the basin
Basin stilling well with pressure transducer mounted
inside to measure water levels in the basin (Basin 2B)

The ADWR requires weekly water level measurements in the piezometers and monitor wells and quarterly water quality sampling from the two monitor wells. After 2 years of operation, the operator can petition the ADWR to reduce the monitoring to monthly for the water level measurements and semi-annual for the water quality sampling.

The nested piezometers are constructed to monitor potential mounding beneath the basins. During the exploration phase of the siting study, two relatively shallow 4 to 8-foot thick, fine-grained layers were encountered at depths of approximately 40 and 90 feet below ground level. The observed mounding follows a similar pattern seen at the other recharge projects: at start-up of a basin, the recharged water forms a mound above the fine-grained unit then dissipates as the fine-grained becomes saturated.

Alert levels are established in the ADWR USF permit issued for the project. Water levels in the wells cannot be less than 20 feet below ground level and the water quality analytes cannot exceed the ADEQ NAWQS standards. CAP monitors water quality both in the groundwater and source water. CAP monitors inorganic constituents as well as organic constituents such as herbicides and pesticides. Since operations have begun, there have been no exceedences of any of the established alert levels.


Deliveries began on January 2, 2003 with water being stored primarily for the AWBA and the CAGRD. In December 2003, the City of Goodyear obtained a Water Storage Permit from the ADWR and plans to store water at the facility in 2004.

Water levels are measured in each basin with depths typically held at 2 feet or less. As water levels rise, basin rotations are utilized to dry each basin and rejuvenate the infiltration rates. Initial infiltration rates in the individual cells ranged from 3.1 to 6.8 feet per day and have remained over 3 feet per day for the project has a whole. At the end of 2003, infiltration rates dropped to less than 2 feet per day due to clogging and, in January 2004, the project was dried and ripped. Since the ripping, infiltration rates are again over 3 feet per day.

Image of Basin 2
Basin 2 with the northern cell wet and
the southern cell in a drying cycle

During normal operations, approximately 80% of the basin area is wetted with 20% in the drying mode. The basins are rotated approximately every two weeks to give the unused basins sufficient time to dry. Flows to the project average 40 to 45 cfs with two of the four pumps operating. The pumps are alternated monthly.


Maintenance is required to maintain good infiltration rates, ensure that the electrical and mechanical equipment operates properly, and to manage weed growth. Maintaining good infiltration rates is imperative with recharge projects and is accomplished through a combination of basin rotation and mechanical scraping and ripping. The physical attributes of the project, pumps, valves, remote data acquisition system, all require regular preventative maintenance (PM) to ensure reliable operations.

The basins are operated with approximately 80% of the basin area wet and 20% dry. By rotating the wet/dry cycle through the seven cells, algae growth is kept to a minimum. Since beginning operations in January 2003, only one mechanical ripping of the basins has been required to keep the infiltration rates over 3 feet per day.

HMRP basins
HMRP basins with the northern basin in the wet
cycle and the southern basin in the dry cycle

The pumping station has four electric turbine pumps that require regular PM's. The maintenance includes lubricating the pump shafts, inspecting the impellers, and monitoring the pump vibration. Also, the trash rack between the forebay and the canal requires regular cleaning. During periods of monsoons, tumbleweeds clog the intake to the pumps and require back flushing.

Electric pump
Electric pump at the HMRP turnout

HMRP turnout
Trashrack between the forebay and the canal at
the HMRP turnout with the tumbleweeds beginning to build up

In the past, weeds were controlled through the use of the chemical Rodeo. Starting in 2003, goats have been brought in twice a year to control weed growth. The goats are especially effective on controlling tamarisk. Also, starting in 2003, additional weed control will be managed with a truck-mounted burner.

Water Deliveries

Water deliveries to HMRP are measured at the turnout by an acoustic flowmeter at the pump station on the CAP canal. Deliveries to the individual basins are not measured. In 2003, water was stored for the AWBA and the CAGRD.

Water deliveries are tabulated daily for each basin and added up for the month. Evaporation losses are calculated using the 1970 Cooley Method that calculates a maximum daily evaporation dependent on the time of year and the number of wetted acres for that day. Average evaporation losses are less than 1% of the stored volume. The deliveries are reported to the ADWR each month and are used by CAP to bill the individual customers storing water at the project.

In 2003, 23,848 acre-feet of water was delivered to the project. Due to high customer demand, the project was left dry in May, and then in September the project was shut down for approximately 4 weeks due to storm damage to the CAP canal upstream of the project. The highest monthly total delivered to the project was 2,802 acre-feet in March 2003 with the average being approximately 2,500 acre-feet per month.