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Soils (Operable Unit 1)

Operable Unit 1 (OU1) included soils contaminated with explosive compounds, mostly trinitrotoluene (TNT), trinitrobenzene (TNB), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The contamination was limited to drainage ditches and sumps in the load lines, and in isolated high concentration areas. A majority of the contaminated soil was found within 5 feet of the ground surface while some areas went to a depth of 30 feet. Remediation for OU1 was completed in 1999 with the excavation of soils and treatment through an on-site thermal treatment unit. As work on this Operable Unit is complete, no new information is available.

Groundwater (Operable Unit 2)

Operable Unit (OU) 2 includes contaminated groundwater, explosives contaminated soil not remediated during OU1 which could act as a source of explosives contamination of groundwater, and soil contaminated with volatile organic compounds. The major components of the selected remedy for OU2 include:

• Hydraulically contain contaminated groundwater exceeding the Final Target Groundwater Cleanup Goals;
• Focused extraction of groundwater in areas with relatively high concentrations of TCE and explosives;
• Treat all extracted groundwater using granular activated carbon adsorption, Advanced Oxidation Process, and air stripping, any of which may be applied individually or in combination;
• Dispose of the treated groundwater by beneficially reusing it or through surface discharge;
• Provide a potable water supply to local groundwater users whose water supply contains RDX exceeding the Health Advisory and/or TCE exceeding the    Maximum Contaminant Level;
• Monitor the groundwater elevations and water quality; and
• Excavate and treat explosives-contaminated soil which could act as a source of explosives contamination of groundwater and which does not meet the OU1 excavation criteria. 

Hydraulic Containment and Focused Extraction

In place at the site is a network of containment and focused extraction wells for remediation. Eight extraction wells are currently in operation to hydraulically contain contaminated groundwater exceeding the Final Target Groundwater Cleanup Goals and three extraction wells are currently in operation as focused extraction wells. One groundwater circulation well is also currently in operation to treat and area of relatively high TCE concentrations. Four extraction wells that no longer contributed to containment and/or may have impacted the direction of flow of groundwater were removed from the groundwater extraction system, but may be turned on at a later time if needed.

Groundwater Treatment and Disposal  

Four groundwater treatment plants are currently in operation at the site to treat extracted groundwater. Two of the treatment plants operate by air stripping, one operates by the Advanced Oxidation Process, and the other operates using granular activated carbon to remove contamination from the extracted groundwater. Extracted groundwater is treated at the plants and then properly discharged and, in some cases, made available for beneficial reuse.
Water Supply Well Sampling and Alternate Water Supplies.

A number of private residential water supply wells are sampled every year within one mile to the south or to the east of the former Nebraska Ordnance Plant groundwater contaminant plumes. A granular activated carbon unit and/or bottled water is provided to any local groundwater user whose water supply at any point contains TCE above 5 µg/L and/or RDX 2 µg/L. The results of the Water Supply Well Sampling Program determine if an alternate water supply will be provided to a user. Currently five residential water supply wells are included as part of the alternate water supply program.

Water Quality and Groundwater Elevation Monitoring

Monitoring well and surface water sampling is conducted quarterly as part of the Groundwater Monitoring Program. A network of over 300 active monitoring wells is present at the site and each year the Corps of Engineers along with the federal and state regulators determine which wells should be sampled. In addition, surface water samples are collected from three creeks adjacent to the site. Groundwater samples from monitoring wells and surface water are used to monitor and evaluate potential changes in the contaminant concentrations and monitor and evaluate the concentration of groundwater and surface water contamination. Groundwater data are also used to provide data for evaluating whether the plumes are being contained by the groundwater extraction well network.

Site water level measurements are collected periodically at wells prior to monitoring well sampling or during other investigation activities. Regional water level measurements are also collected semi-annually in conjunction with other agencies at over 500 wells located by the former Nebraska Ordnance Plant and surrounding area. The water level data are used to prepare maps that show groundwater flow direction across the area, update the groundwater flow model and identify abnormalities in water levels across the site, and help document capture and/or drawdown related to the extraction well network.

Soil Excavation and Treatment

The excavation and thermal treatment of explosives contaminated soil was completed for OU2 during the OU1 Remedial Action with a removal of approximately 13,607 cubic yards of contaminated soil, thus, reducing the potential for a continued source of explosives contamination migrating to groundwater. No further action for explosives-contaminated soil is required for OU2.

Miscellanous (Operable Unit 3)

OU3 includes a former on-site landfill and former unidentified waste disposal areas not previously identified. Contaminants evaluated include metals, explosives, volatiles and semi-volatiles. The only chemical contamination requiring remediation is the heavy metal antimony, which was found in localized areas related to painting operations.

 Areas that have been investigated throughout the history of the project are:

• Former Administration Are
• Former Atlas Missile Area
• Bermed Area Southwest of Load Line 1
• Clear Creek, Johnson Creek, and Silver Creek
• Former Demolition Ground
• Former Detonation Craters
• Former Ammonium Nitrate Plant
• Former NOP Landfill Area and Potential Landfill Area
• Former Raw Product Igloo Storage
• Former Tetryl Pelleting Area/ Bomb Booster Assembly
• Former Load Lines (1-4)
• Former Nike Missile Maintenance Area
• Former Burning Grounds (North and South)
• Northeast Boundary Area
• Natural Resources District Reservoir Area
• Former Proving Grounds
• Former Air Force Global Communications Area

The final supplemental investigation for OU3 was completed in 2011. A Proposed Plan was finalized in October 2012 after which a No Further Action Record of Decision was signed in April 2013. These documents can be viewed under 'Project Documents'.