Terrafirma was contracted by Garney Construction to install the groundwater control system for the Buckeye WWTP Expansion project in Buckeye, AZ.
The Phase I construction of the expansion of the Buckeye WWTP, located just south of Irwin Road in Buckeye, Arizona, consisted of the construction of Anoxic Basins, a Booster Pump Station, a MLR Pump Station, a Sodium Bisulfate Facility, and associated yard piping. The depths of excavation for the structures varied from 0 to 16 feet below the current average ground elevation of 841. The associated Yard Piping was relatively shallow. The groundwater was reported to be approximately 834 msl; however, the groundwater surface was expected to vary greatly, depending on irrigation of the farm fields located to the north and west of the site. Groundwater levels had been known to come up to just 2 feet below the ground surface during irrigation season. For the purposes of design, the higher groundwater elevation was used. The Anoxic Basin excavation was open cut. The Booster Pump Station and Valve Vault excavations were vertical, with the excavation sides shored and braced. Fully penetrating deep wells were installed adjacent to these excavations penetrating the water table, and configured in a way to benefit anticipated future construction. Groundwater was lowered to a point 2 feet below the excavation bottom. Well discharge was directed to the southeast corner of the site to a settling tank. From the settling tank the discharge was allowed to over flow into the new 12” Relief Outfall.
The temporary dewatering system included a total of 10 wells: five located at and Anoxic Basin, two at the booster pump station, one at the valve vault, and two located to influence the yard piping and areas designated for future construction. Each well was equipped with a pumping unit ranging from 10-20 HP, producing a system pumping rate of approximately 3000 GPM.