Tucson Ajo Detention Basin

Pima County, AZ

Stronghold Engineering, Inc. served as the prime contractor for this ecosystem restoration project for construction, repair and renovation of Tucson Ajo Detention Basin in Pima County, Ariz., under the U.S. Army Corps of Engineers’ Section 1135 program. The 120-acre basin was originally designed to capture water from a 17.7-square mile watershed whose sources are from surrounding areas, including Davis-Monthan Air Force Base.

The scope of work included bollard installation; road construction; paving, fencing, clearing, grubbing; and excavation and extensive re-grading of more than 700,000 cubic yards of dirt to create mesquite bosques, riparian stream courses, ephemeral cienegas, emergent wetlands, and open water ponds that established a variety of wildlife habitats. Work was performed using in-house heavy equipment and resources.

Approximately 850,000 sq. ft. of 40 mil HDPE liner was installed within the pond areas. The ponds are fed by an elaborate water distribution system consisting of 30 inch epoxy-coated steel cylinder piping within a concrete encasement at a depth of 65 ft., surrounded by 3:1 side slopes. Four submersible pumps were installed to recirculate water from the depths of the large storm-water reservoir to different points throughout the basin. Numerous preparatory meetings were held between Stronghold and subcontractors to ensure that all aspects of the installation were discussed and application methods were defined to eliminate any uncertainty during construction of this complex lining system.

Record rainfall during the project necessitated massive pumping. Strict schedule adherence was observed to ensure completion of key project phases prior to seasonal desert monsoons. During 885 days of construction with multiple teams on site, not a single safety violation or incident occurred. The project was completed on schedule, within budget, and received an outstanding performance evaluation. This project also won the 2006 Chief of Engineers Award of Excellence for Environmental projects.