U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division
Apache Nitrogen Products, Inc., Benson, AZ
Superfund NPL
 
 
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Wetland Design
Wetland Design
Wetlands Vegetation
Wetlands Vegetation
Groundwater Recirculation
Groundwater
Recirculation
Flow Measurements
Flow Measurements
Windmill Operations
Windmill Operations
Perched Water Treatment
Perched Water
Treatment
Exterior Building Controls
Exterior Building
Controls
Solar Canopy
Solar Canopy


Cleanup Objectives: Remediate soils and groundwater containing high concentrations of metals, nitrate-nitrogen, and explosives on 1,100 acres of a 9-mile2 property (formerly known as Apache Powder Company)

Green Remediation Strategy: Employ a hydraulically driven constructed wetland system, use native clay to cap contaminated soils, and capitalize on sources of onsite renewable energy to power cleanup equipment or offset grid electricity consumption

  • Installed a 4.5-acre, tiered engineered wetlands to treat contaminated groundwater in the site's northern half; this remedial approach avoided typical chemical usage, energy consumption, and waste generation associated with a traditional alternative involving a wastewater treatment plant
  • Capped ten contaminated evaporation ponds (in the site's southern half) with low-permeability covers made of native clay
  • Used onsite solar and wind energy to power auxiliary equipment instead of extending power lines to the wetlands system, which is located in a remote portion of the property; initial equipment included: (1) a 1.4-kW photovoltaic (PV) system equipped with a solar-powered centrifugal pump to re-circulate water between the wetland ponds, and (2) a mechanical windmill to de-water a perched groundwater zone underlying the capped areas
  • Maximized reinjection of wetlands-treated water directly into the alluvial aquifer rather than discharging all treated water to nearby surface water

Results:

  • Reduced electricity costs for groundwater recirculation and de-watering by approximately 66% over the expected project life, when compared to the expense of installing new power lines and purchasing the electricity
  • Operating the groundwater recirculation system only during daylight hours, which matches peak performance of contaminant degradation mechanisms occurring in the wetlands; sufficient PV-generated electricity is generated to re-circulate groundwater in the wetlands system (through 100 feet of 2-inch hosing elevated 10 feet from ground surface) at a rate of 5 gallons per minute
  • Replaced the windmill after five years of operation with a small PV system, to accelerate de-watering of perched groundwater below the caps
  • Expanded the use of onsite solar resources over recent years through small-scale PV applications that: (1) measure groundwater flow through the wetlands, and (2) operate lighting, motion detection, security camera, and gate control systems around the wetlands area
  • Treated over 550 million gallons of groundwater (removing over 563,000 pounds of nitrates) between 1997 wetlands installation and early 2011, at a rate averaging 180 gallons per minute
  • Continuing to achieve nitrate-nitrogen concentrations below the 10 µg/L drinking water standard, as compared to pre-remediation concentrations reaching 570 µg/L
  • Directly recharging the underlying aquifer with the majority of treated water exiting the wetlands, with the remainder flowing a distance of less than one mile to the San Pedro River
  • Providing a wetland habitat for wildlife such as deer, javelina, Gila monsters, bobcats, snakes, lizards, and amphibians, numerous bird species, and insect-consuming bats; wildlife-friendly fencing allows the animals access but denies entry by grazing livestock that can damage sensitive flora
  • Installed a 42-kW solar canopy for the site's administrative buildings in late 2010, which is expected to annually save $6,400 in electricity costs and avoid a carbon dioxide (equivalent) emission of nearly 35,000 pounds each year; nearly 100% of the PV capital costs were covered by federal/state tax credits and utility incentives, with system payback expected in six years
  • Recovering rainwater from the solar canopy for use in xeriscape landscaping in the site's desert environment; during heavy rain, a network of constructed rock-lined channels capture the runoff for gradual subsurface infiltration or release to the San Pedro River
  • Considering future large-scale solar energy development on the capped ponds, if financially viable; a preliminary solar energy assessment suggests that a 2-MW system would meet the peak daily energy demand of the site's current chemical processing operations

Property End Use: Continued industrial operations

Point of Contact: Andria Benner, U.S. EPA Region 9

Update: July 2011

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