Introduction

The Pima Mine Road Recharge Project (PMRRP) is a direct recharge project located in Pima County, approximately 15 miles south of Tucson, Arizona and was developed in cooperation with the City of Tucson.

It is located on the Santa Cruz River flood plain and the facility has two operational components: The original pilot facility, which consists of a 2-mile delivery pipeline and two 7-acre spreading basins, and an expanded facility consisting of a 5,500 foot pipeline and three new spreading basins totaling 23 acres. The total facility has 37 acres of spreading basins.

Pilot testing was conducted from March 1997 to March 1999, under two Pilot Underground Facility Storage permits issued by the Arizona Department of Water Resources (ADWR). The pilot project was intended to assess the long-term feasibility of operating a larger full-scale recharge project. During the pilot phase, 20,000 acre-feet of CAP water were recharged. Full-scale operations began on September 8, 2000 using the pilot basin while construction of the expansion project was underway. The project expansion was constructed between May and December 2001. The completed facility provides a maximum permitted annual recharge capacity of 30,000 af. Full-scale operation of the expansion basins began December 2001.

Pima Mine Road Recharge Project at Sunset

Pima Mine Road Recharge Project Aerial View

Project Facts

  • Hydrologic feasibility assessments conducted for Pilot Facility 1991 thru 1998
  • Location: T16S, R14E, West ½ Section 30 and SW ¼ Section 19
  • Construction of Pilot Facility: completed March 1998
  • Completion of Pilot Testing Phase 1 (10,000 AF): April 1999
  • Completion of Pilot Testing Phase 2 (10,000 AF): March 2000
  • Hydrologic feasibility assessments conducted for Expansion Project: April 1999 thru December 1999
  • Project Expansion Construction: March 2001 to December 2001
  • Total Construction cost: $11 million
  • Completion date: December 2001
Facility Components

Pilot Facility

The Reach 6 portion of the CAP aqueduct provides water to the PMRRP facility. This section of the aqueduct consists of a 72-inch diameter pipeline from the Black Mountain Operating Reservoir to the aqueduct terminus. The Reach 6 pipeline system creates substantial hydraulic head to the recharge facility.

The pilot facility includes a 2-mile long, 36-inch diameter concrete coated, steel pipeline constructed from the CAP terminus to the pilot facility. Four turnouts constructed in subsurface concrete vaults divert water into each of the four basin quadrants. The delivery pipeline reduces to a 16-inch diameter line at the turnouts, then tees, where two 16-inch butterfly valve are used for basin delivery control. Pressure reducing valves were recently installed (July 2003) in each valve vault to reduce cavitation at the primary control valves.

The pilot facility has six acoustic flowmeters: one at the CAP turnout to the PMRRP pipeline, four at the pilot basin (one at each turnout), and one for the expansion basins located at the turnout from the pilot facility.

Pima Mine Road Layout Drawing
General Site Layout

The pilot facility consists of two 7-acre sub-basins that are separated by a rip-rapped berm. Both sub-basins are excavated 13 feet below ground surface into floodplain deposits of the Santa Cruz River. Deep basin excavation was necessary to intersect deeper, coarse-grained alluvium for optimum infiltration rates.

Rip-Rap at Pima Mine Road Recharge Project
Rip-Rap Placement on Divider Berm

Each sub-basin has 3-foot high perimeter and internal divider berms. Both are covered with rip-rap material to protect them from erosion by waves and surface water runoff.

Basins Evacuated at Pima Mine Road Recharge Project
Basins Excavated and Ready for Recharge

Expanded Facility

The Expanded Facility consists of a delivery pipeline and three new basins (Basins 1, 2 and 3) located north of the original pilot basin. The expansion basins were positioned where favorable coarse-grained deposits occur close to land surface. The basins were aligned linearly north to south, down slope of the pilot basin to comply with floodplain requirements.

Three Expansions Basin Pima Mine Road Recharge Project
Operation of Three New Expansion Basins Down Slope from the Original Pilot Basin

A 5,500 foot long, 36-inch diameter, steel delivery pipeline extends from the pilot basin north to the three new basins. Three 24-inch diameter turnouts equipped with pressure reducing valves and a 24-inch butterfly valve provide delivery control to each basin. One acoustic flow meter in the delivery pipeline measures combined flows to all three basins. An isolation valve at the turnout from the pilot facility allows maintenance on the expanded facility independent from recharge operations at the pilot facility.

Construction of Basin at Pima Mine Road Recharge Project
Construction of Basin 3

Expansion Basins 1 through 3 were not excavated as deep as the pilot basin to reduce excavation costs. Basin 1 was excavated 6 feet, and Basins 2 and 3 were excavated 10 feet. The basin inverts are just above coarse-grained alluvium having high infiltration rates. The perimeter of each basin is lined with 6 feet of rip-rap to protect the basin edges from erosion by wave action and from surface runoff.

Operations

Full-scale operations began in September 2000 using only the pilot basins since the expanded facility was under construction. Recharge at the three project expansion basins began in December 2001.

Recharge operations at the pilot facility have consisted of either sub-basin rotations, or continuous recharge using both sub-basins depending on delivery constrains, infiltration rates and planned future outages. Rotating between the two sub-basins has allowed relative continuous operations with minimum infiltration loss. The rotation duration has ranged from one week to several months depending on infiltration rates. Both sub-basins are used when maximum recharge volumes are needed prior to a planned delivery outage or schedule basin maintenance.

Lower infiltration rates at the expansion basins usually require continuous operations to meet management recharge goals; thus no basin rotations or wet/dry cycling is conducted. Infiltration rates at the pilot facility typically range from 1.9 to 5.8 feet/day, but are much higher initially after maintenance is conducted.

The expansion basins were not excavated as deep as the pilot basin and therefore infiltration rates are substantially lower. Infiltration rates range from 0.7 to 4.2 feet/day.

Pilot Facility
Recharge Operations at the Pilot Facility in March 1998

Maintenance

Maintenance is conducted during the course of routine operations. Typically basin scraping and ripping are performed to rejuvenate infiltration rates after wet/dry cycling become ineffective. Wet/dry cycling rotation of the two sub-basins is commonly used to rejuvenate infiltration at the pilot facility.

Deep basin ripping was performed shortly after construction of the expansion basins to reduce the compaction effects produced by heavy equipment. Annual basin scraping, followed by ripping to ensure maximum infiltration rates are maintained, is performed on each basin.

The PMMRP delivery system is under about 70 pounds per square inch (psi) pressure because of the elevation drop from the Black Mountain Operating Reservoir (BMOR) to the recharge project. The high pressure has caused cavitation damage at the control valves at the pilot and expansion facilities. Control valve replacement became routine from the ongoing cavitation problem. To mitigate the damage caused by cavitation, five 16-inch Pressure Reducing Valves (PRV) were installed in July 2003. Two were installed at the pilot facility and three were installed at the expansion basins. These valves have been very successful at controlling the cavitation and since their installation, no control valves have required replacement.

hard surface layer
Hard encrusted surface layer reduced infiltration rates.

basin scraping of hard layer
In December 2001, basin scraping was conducted for the first time at the pilot basin to remove the hard crust layer.

PRV valves
Maintenance crew fine tunes PRV valves that were installed in 2003