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NIBW Superfund Site: Central Groundwater Treatment Facility

NIBW Superfund Site: Central Groundwater Treatment Facility


The Central Groundwater Treatment Facility (CGTF) is located at Pima Park in South Scottsdale in the vicinity of Thomas and Pima Roads. The CGTF is owned and operated by the City of Scottsdale and provides drinking water to their municipal system. The City operates the treatment facility according to procedures approved by Environmental Protection Agency (EPA) and the Arizona Department of Environmental Quality (ADEQ). The costs to design, construct, and operate the CGTF are paid for by the NIBW Participating Companies.

The site connects four water supply wells that had been impacted by trichloroethylene (TCE) to a central treatment plant for removal of TCE via air stripping. The wells have a maximum combined extraction rate of around 8,000 gallons per minute (gpm) and are used to provide treated water to the City of Scottsdale drinking water system. Over the years, the groundwater extraction and treatment rate has averaged around 6,000 gpm.

TCE in groundwater is removed by packed tower aeration (air stripping treatment technology). The CGTF has three treatment towers, each with a packed column that can treat up to 3,150 gallons per minute of water. The water enters the column at the top of the packing material and flows by gravity downward to a sump. TCE is removed or stripped from the water as it flows over the packing material by air passing upward through the column. A blower pulls approximately 14,000 cubic feet per minute of air in counter-current flow through the column and passes it to the next stage of the process, known as vapor phase treatment system. From the sump, the treated water is disinfected with chlorine and enters one of two five million-gallon reservoirs.

The vapor phase treatment system removes TCE in the air from the packed tower aeration, if needed. The air from each column is preheated by a gas burner to reduce relative humidity and then passed through a 20,000-pound granular activated carbon filter. The carbon filter adsorbs the TCE in the air and the treated air is discharged to the atmosphere. The treated air is monitored regularly and the activated carbon is replaced as necessary to insure that the treated air meets local, state, and federal standards. Since the CGTF became operational in 1994, more than 47 billion gallons of groundwater have been treated and returned to beneficial use and over 42,000 pounds of TCE have been removed from the groundwater. The City of Scottsdale provides a summary of CGTF operational data in Quarterly Compliance Monitoring Reports to EPA.