Groundwater sampling in Feb. 2013, confirmed tetrachloroethene (PCE), Trichloroethene (TCE), Vinyl chloride (VC) and Cis-1,2-dicholoroethene (c-1,2-DCE) are not detected above the laboratory reporting limit of 0.5 micrograms per liter (µg/l) in any of the five wells sampled at the site.
Detected concentrations of PCE, TCE, VC and c-1,2-DCE have been below their respective Aquifer Water Quality Standard (AWQSs) since the June 2006 groundwater sampling event. Historical groundwater monitoring data suggests that monitored natural attenuation (MNA) achieved cleanup of the site to concentrations below AWQSs.
ADEQ has reviewed the remedy and determined that site completion criteria has been met and that cleanup levels have been achieved. On December 27, 2013, ADEQ issued a closeout Record of Decision (ROD) demonstrating that the site completion criteria used to evaluate the selected remedial action for volatile organic compound (VOC) contaminated groundwater at the site has been achieved. The decision in the closeout ROD is based upon previous activities and investigations conducted and performed for this site.
Contaminants of Concern
The current contaminants of concern in groundwater include tetrachloroethene (PCE) and trichloroethene (TCE). Contaminants of concern at the site may change as new data becomes available. No drinking water wells are threatened by this contamination plume.
Public Health Impact
The AWQS for PCE is 5.0 µg/l. As of the March 2008 groundwater sampling, all domestic wells in the site are currently below the AWQS. The Arizona Department of Health Services stated in their health consultation that “…use of the water for domestic purposes other than drinking was not likely to cause any adverse health effects.”
The aquifer beneath the site is in the Payson Granite. The hydrogeology of the Payson area has been defined in the site Hydrogeologic Conceptual Model (HCM) based on drilling and testing activities.
The HCM identified three primary hydrologic units in descending order in the Payson Granite: 1) Alluvium/Colluvium, 2) Decomposed Granite/Fractured Granite, and 3) Variably Fractured Granite/Competent Granite.
A Community Advisory Board (CAB) was formed for the site in conjunction with the Payson PCE site and met on a regular basis throughout the remedial investigation (RI) process. Their final meeting was held in November 2008 where ADEQ presented the final ROD for the site | View Payson PCE Site CAB History >