20th Street and Factor Avenue | Site History

2019: ADEQ implemented the remedy which included monitoring and maintenance of the existing asphalt cap, ISCO groundwater treatment, and MNA.

2018: The Record of Decision was signed.

2017: The Proposed Remedial Action Plan (PRAP) was completed in June 2017 and issued for public review and comment. The proposed remedy for the site is monitoring and maintenance of the engineered asphaltic concrete cap and in situ enhanced reductive de-chlorination (ERD) with monitored natural attenuation (MNA).

2016: A downgradient deep monitor well was installed in January. ADEQ completed one round of ground water monitoring and sampling at the site. Contaminant of concern concentrations and distribution in the aquifer remained relative constant. The FS report was completed in August.

2015: During March 2015, ADEQ completed one round of ground water monitoring at the site. PCE concentrations and distribution in the upper part of the aquifer remained relative constant with the highest PCE concentration detected at a concentration of 54 parts per billion. In the middle portion of the aquifer, PCE concentrations and distribution also remained relatively constant with the exception of one well where concentrations continued to rise and PCE was detected at 1000 parts per billion. The Arizona Aquifer Water Quality Standard for PCE is 5 parts per billion.

In the upper part of the aquifer, cyanide concentrations remain above the Aquifer Water Quality Standard of 200 parts per billion in one monitor well. In the middle part of the aquifer, cyanide is present at 200 parts per billion in one monitor well. Cyanide concentrations in the middle part of the aquifer continue to separate from the source area.

No contaminants were detected above standards in the deeper part of the aquifer. 

2014: During 2014 ADEQ installed seven additional soil vapor monitor wells at the site. A round of soil vapor sampling was also conducted. Soil vapor samples were analyzed for hydrogen cyanide and volatile organic compounds including PCE and TCE. No samples detected hydrogen cyanide. PCE and TCE were detected a concentrations below ADEQ’s suggested soil vapor screening levels. ADEQ completed the draft RI report, solicited comments on the draft RI and on the Proposed Remedial Objectives. ADEQ will release the final RI by October 30, 2014. Groundwater monitoring is normally conducted annually at the site.

2013: ADEQ completed the installation of a permanent asphalt based cap over the cyanide impacted soils. This cap will limit human access to these soils and limit further impacts to the groundwater beneath the site by minimizing the amount of cyanide leaching from cyanide contaminated soils. ADEQ installed three additional wells down gradient of the site and the horizontal and vertical definition of the plume is complete. ADEQ is finalizing the draft RI report. Groundwater monitoring is at a minimum conducted annually at the site.

2012: ADEQ continues to investigate the site to identify the extent and severity of the groundwater contamination. ADEQ finalized plans to install a permanent asphalt based cap over the cyanide impacted soils still remaining at the site below a depth of one foot. This cap will limit further impacts to the groundwater beneath the site by minimizing the amount of cyanide leaching from cyanide contaminated soils.

2009  2011: A soil vapor investigation was performed which included the installation of several permanent soil vapor monitor probes and a soil vapor survey in order to help identify potential source areas. Additional permanent soil vapor monitor probes were installed and groundwater samplings were conducted. ADEQ continued to investigate the site to identify the extent of the groundwater contamination. Groundwater sampling results indicate the PCE plume extends over 4,000 feet dowgradient from the site. 

2008: ADEQ installed one groundwater extraction well in the middle of the contaminant plume. An aquifer test was completed to determine aquifer characteristics. The last remaining septic system on the HIL property was taken out of service and replaced with a new system and leach field located away from contaminated soil. Additional information was gathered north of the HIL property to locate potential sources areas.