Pinal Creek Group Operates Numerous Remediation Facilities
Over the past few years the Pinal Creek Group has constructed and commissioned several new remediation facilities designed to capture and treat poor quality groundwater in Pinal Creek’s alluvial aquifer. Between 1998 and 2001, a wellfield (A) was constructed at Lower Pinal Creek to capture contaminated groundwater that threatened surface water quality in perennial Pinal Creek. The wellfield has a maximum capacity of 6,500 gallons per minute and is complimented by an underground barrier wall that is situated immediately downgradient from the wellfield. The barrier wall is approximately 1,200 feet long, 100 feet deep, and is 3-5 feet in width. The underground barrier wall is a low-permeability structure comprised of a soil-cement-bentonite-clay mixture, which ensures that contaminants do not migrate past the wellfield.
Water captured by the Lower Pinal Creek Wellfield and barrier wall is pumped to the Lower Pinal Creek Water Treatment Plant (B) located at Hicks Wash on old State Route 88. The plant utilizes a lime treatment process to neutralize influent water, precipitate metals, and clarify the water. The water is then pH adjusted, filtered, and discharged into perennial Pinal Creek. The precipitated metals, or process sludge, are delivered through a closed-circuit system to the Diamond H Pit (C) at the BHP Copper Cities mine for disposal. The plant has a maximum capacity of 6,500 gallons per minute, or about 9.4 million gallons per day. All of the water that is pumped from the Lower Pinal Creek Wellfield is treated at the Lower Pinal Creek Water Treatment Plant and is then released to perennial Pinal Creek.
The Kiser Basin Wellfield (D) is located at the confluence of Bloody Tanks Wash and Russell Gulch, near the intersection of Highways 60 and 188. This wellfield was expanded significantly in 2000 and has a maximum capacity of 4,200 gallons per minute. The wellfield captures poor quality groundwater migrating into Kiser Basin and forms a hydraulic barrier that allows inflows of clean water from Russell Gulch to bypass the system and flow into Pinal Creek via Miami Wash.
Water captured by the Kiser Basin Wellfield is pumped to the Diamond H Pit Neutralization Plant at Copper Cities, where it is neutralized prior to its discharge into the Diamond H Pit. This water is then managed at the Diamond H Pit for use throughout the mining district. The amount of water pumped and consumed by this system does not exceed the amount of water consumed historically by local mining companies in this area.
Due to pit slope degradation that occurred in the spring of 2004, PCG determined, in consultation with the Arizona Department of Environmental Quality, that it was prudent to install an interim plant and disassemble the existing Diamond H Pit Neutralization Plant. The Diamond H Pit Neutralization Plant will be re-configured, reconstructed and relocated at a new site farther from the pit’s edge in 2005. No offsite discharges occurred during the deconstruction project and, due to the drought and low flow conditions in the aquifer, the interim system is able to manage all poor quality water pumped from the Kiser Basin Wellfield.