ES Projects

Status Updates

• January, April, July, & October
  The City conducts quarterly landfill gas monitoring at perimeter probes during these months every year to monitor for methane migration at the property boundary.

• May & November
  The City monitors the groundwater quality semiannually at site wells and a downgradient private production well. Monitoring reports are prepared documenting the results.

• April & October
  The City conducts closed landfill site inspections during these months. A report documenting site conditions will be prepared after the inspections.

• December 2015
  The groundwater pump and treat system was shut down as VOC concentrations have been below regulatory standards since 2013. The groundwater is monitored quarterly at select wells. Should concentrations rebound, the system will be turned back on.

• February 2014
  The Arizona Department of Environmental Quality (ADEQ) provides approval to turning-off the groundwater treatment system. The remediation system has successfully cleaned-up the groundwater for tetrachloroethene (PCE) and trichloroethene (TCE) to concentrations below regulatory standards. The city will develop a work plan prior to shutting down the system for continued monitoring of the groundwater. Should concentrations in the groundwater rebound, the system can be turned back on.

• May 2011
  The city installed the new downgradient groundwater well HLM-550 along Wingate Road. The well is monitored quarterly and all VOC results are below the AWQS.

• January 2005
  An existing groundwater monitoring well was converted to an extraction well to better contain the plume.

• June 2001
  Groundwater pump and treat system began operation. The sytem is designed to remove and treat groundwater impacted with volatile organic compounds (VOCs), primarily tetrachloroethene (PCE) and trichloroethene (TCE). The treatment system consists of two 4,500 pound granular activited carbon (GAC) vessels. The treated water is re-injected into the groundwater.

• 1999-2002 & 2005-2006
  Operation of the deep SVE and air injection system (AI) began in order to remove and treat VOCs from the deep soil vapor. The system removed and treated 18,034 pounds of VOCs. This system is currently not operating, but the City monitors the vapor wells periodically and will return the system to operation if needed.

• 1999-2000
  The City acquired land rights and installed groundwater extraction wells, monitoring wells, injection wells, infrastructure and piping for the groundwater extraction and treatment system.

• 1999
  ADEQ Solid Waste Unit approved the use of an SVE system to remove the source of the contamination, and a groundwater extraction and treatment system to contain and clean up the PCE plume.

• 1998
  A landfill gas extraction and flare system was installed and is still in operation today. From 1995-1998 a temporary emergency flare was in operation.

• October 1998
  The City closed the landfill according to Federal and State regulations. Closure included construction of the landfill cover for the landfill, including a graded earthen cap and landscaping to prevent erosion. This date marks the beginning of the 30-year post-closure monitoring and management period.

• 1997
  The City stopped accepting waste at the Harrison Landfill.

• July 1996
  Groundwater investigation completed to characterize the aquifer properties and extent of the contamination.

• 1995-1998
  The City installed shallow landfill gas monitor probes to monitor methane concentrations between the landfill and nearby homes and businesses and began routine monitoring.

• 1988-1995
  Groundwater contamination of PCE was first discovered in monitoring wells that were not used to provide drinking water supply. Additional groundwater monitoring wells were installed to characterize the extent and migration rate of the contamination. The City commissioned studies to determine the best method of groundwater remediation.