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NIBW SUPERFUND SITE: AREA 12

 

We are involved in remediation efforts at Area 12, a former Motorola Facility located at 8201 E. McDowell Road in Scottsdale (now a General Dynamics facility). Between 1996 and 1998, a soil vapor extraction system was used at Area 12 to successfully clean up soil impacts. Our cleanup efforts continue at the site using a groundwater extraction and treatment system (GWETS).

Groundwater extraction and treatment system at Area 12

We voluntarily implemented a groundwater extraction and treatment system at Area 12, in partnership with the Salt River Project (SRP), a local water and electricity provider.

The Area 12 system extracts TCE from the MAU groundwater at the former Motorola site that would otherwise migrate slowly to the City of Scottsdale extraction wells, where water is extracted and treated at the Central Groundwater Treatment Facility. The system supplies water for irrigation use by SRP.

The Area 12 groundwater extraction and treatment system consists of two large extraction wells connected to an air stripping tower located in the southeast portion of the former Motorola plant site.

SRP offered to assist with Area 12 groundwater remediation to assure availability of a long-term, reliable groundwater supply in the NIBW Site. SRP generously provided the groundwater treatment system that has been extensively upgraded and is now in use at Area 12. We relocated this groundwater treatment system from Mesa where it had been used by SRP to clean up volatile organic compound (VOC) impacts at one of the SRP production wells. We also provided treatment for an existing SRP production well located just east of the former Motorola facility, designated as SRP 23.6E-6N and also known as the SRP Granite Reef well. We installed a new groundwater extraction well on-site, designated as MEX-1, which is used for SRP water supply. Collectively, these two wells can pump up to 2,000 gallons per minute to the treatment system. Treated water is discharged to the SRP irrigation system, primarily for use in Phoenix.

Motorola implemented a number of upgrades before operating the system, including installing:

 • Higher efficiency tower packing

 • A new water distribution system

 • A VOC monitor on the air outlet

 • A comprehensive control system

As a voluntary remedial action program, Motorola initially obtained a National Pollution Discharge Elimination System Permit to regulate discharge of treated water and an Air Quality Permit to govern air emissions. To date, the system has functioned effectively to meet all operating permit conditions. Groundwater extraction and treatment at Area 12 has subsequently been folded in to the Amended Consent Decree executed in June 2003 as a required remedial action.

Since groundwater extraction began in February 1999, over 4.0 billion gallons of groundwater have been pumped and over 4,200 pounds of TCE have been removed by the treatment system.

Soil vapor extraction at Area 12

In 1996, Motorola installed a soil vapor extraction (SVE) system at Area 12. Until 1998, the system was used to remove TCE from soil vapor. The area of cleanup was determined through testing done by Motorola and the EPA.

To remove TCE from the soil, SVE wells were installed at six locations designated 12VE-3 through 12VE-8. At each of the six locations, a cluster of three SVE wells provided for vapor extraction at three intervals of between five and nearly 90 feet below ground. Pilot studies and actual site monitoring data indicated vapor extraction would be effective over a distance of at least 300 feet away from the SVE wells.

The SVE wells were connected by underground pipes to a central treatment system. Soil vapor from each well was extracted by vacuum blowers and treated by passing the vapor through three granular activated carbon (GAC) filters in series. The treatment system also included a liquid separator, particulate air filter and heat exchanger.

An estimated 946 pounds of VOCs were extracted from the soils at Area 12. Initially, the removal rates were estimated to be about 30 pounds per day but rapidly declined to an estimated 0.2 pounds per day after nine months of operation and several planned shutdown periods to allow for rebound.

As required by EPA, we assessed the impact of any remaining TCE soil gas concentrations at the end of the SVE program and determined there was no longer a potential threat to groundwater. The EPA acknowledged in a letter dated August 18, 2000, that the remedial efforts at Area 12 attained the required performance standards and approved discontinuation of SVE operations. Motorola has properly abandoned the SVE wells and removed the SVE equipment according to a plan approved by EPA.