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Groundwater Extraction and Treatment at Area 7


Area 7 is a former Siemens electronics manufacturing site located at the southeast corner of 75th Street in Scottsdale, Arizona.  Siemens is the responsible party for Area 7, with Motorola Solutions overseeing operations and maintenance on behalf of Siemens.  Siemens installed the Area 7 Groundwater Extraction and Treatment System (GWETS) to enhance the NIBW groundwater remedy by extracting and treating MAU groundwater containing relatively higher VOC concentrations associated with the source area and by reducing VOC mass allowed to migrate to the CGTF extraction wells for removal and treatment.  Groundwater extraction is currently performed using MAU groundwater extraction wells designated as 7EX-3aMA, 7EX-4MA and 7EX-6MA.  The extracted groundwater is treated by ultraviolet oxidation (UV/OX) followed by air stripping.  Treated water is distributed to the UAU using two upgradient groundwater injection wells (7IN-1UA and 7IN-2UA). The Area 7 MAU source control program was initiated in 1999.

Soil Vapor Extraction and Treatment at Area 7

Soil Vapor Extraction (SVE) was used at Area 7 to remove TCE vapor from the soil. SVE at Area 7 has resulted in removal of approximately 7,000 pounds VOCs. 

The SVE system at Area 7 was installed in 1994 as required by the Operable Unit II Consent Decree. Following years of operation, followed by rebound and evaluation periods, a work plan was approved in 2008 to operate the Area 7 SVE system under a pulsing regime until December 2009. After the pulsing period, the Area 7 SVE system was shut down for a planned 3-year period to observe overall vapor rebound.  At the end of the 3-year period in December 2012, soil-vapor samples were collected from the soil-vapor monitoring wells.  The results of this sampling were input into a modeling program to determine whether or not the performance criteria had been met. Upon demonstration that the performance criteria had been met, in August 2013 the NIBW PCs requested that a certification of completion for the Area 7 SVE and Upper Alluvial Unit (UAU) groundwater extraction be granted by EPA and ADEQ.  In December 2013, Gilbane, on behalf of EPA, provided comments and conducted further analysis. Using conservative methodologies, Gilbane showed that even in a worst-case scenario, TCE concentrations would not exceed limits established by EPA.  Based on the model results by Gilbane, and the NIBWs PC’s model simulations, the agencies concluded that there is no threat posed to the UAU groundwater by minimal residual concentrations in the soils at Area 7.  In April 2014, the NIBW PC’s again requested certificate of completion and closure for the Area 7 SVE and UAU groundwater treatment systems.  EPA agreed in April 2015 that the SVE system had met performance criteria and issued a Letter of Determination requesting a decommissioning plan.  The NIBW PCs submitted a decommissioning plan in May 2015 for the proper disassembly, removal and/or abandonment of all on-site equipment when certification of completion is received.  EPA approved the Decommissioning Plan in June 2015, and the system was decommissioned in July and August 2015.  A final report will be prepared and submitted to EPA, and, once approved, EPA will certify closure of this component of the NIBW remedy.  This system is the final component of the active vadose zone (soils layer) remedy.