Nonradioactive Dangerous Waste Landfill
The Nonradioactive Dangerous Waste Landfill and the associated Solid Waste Landfill located between
the Central Plateau and the Wye Barricade also are candidates for early action. These sites are among
the farthest sites outside the exclusive waste management area and may continue to release these
organic substances for quite sometime. Although not considered high- risk sites, these sites have
released volatile organic solvents to the groundwater at concentrations that exceed water quality
standards.
"Natural attenuation" refers to the ability of groundwater to rid itself of contamination
resulting from a spill or disposal of hazardous waste. Tests have demonstrated that it is
an effective form of remediation at sites with aquifers composed of granular sediment.
The basic concept of natural attenuation is not new. Bacteria that naturally inhabit
groundwater are able to break down chemicals that were once thought to be
non-biodegradable. For example, components of gasoline such as benzene, toluene,
xylene, and ethylbenzene are now known to biodegrade in groundwater to carbon dioxide
and water. Other contaminants, including chlorinated solvents (e.g., dry-cleaning
solvents), can also biodegrade under certain conditions. In some cases, natural
biodegradation may break down contaminants in groundwater faster than they can be
removed by engineered systems. DOE is using monitored natural attenuation in
conjunction with other technologies to remediate groundwater on the Hanford Site.
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Use of monitored natural attenuation may be a viable choice for remediation at the Nonradioactive
Dangerous Waste Landfill and other areas on the Hanford Site. Using natural attenuation is sometimes
a preferred remedy because it does not transfer contamination from one location to another. Rather,
the contamination is broken down in place and converted usually to non-toxic products. Monitored
natural attenuation has been previously used at Hanford to meet remedial action objectives to
restore groundwater. For example, the plume of organic solvents beneath the former Horn Rapids
Landfill in the 1100 Area is being addressed through natural attenuation. A CERCLA review determined
that monitored natural attenuation complied with the remedial action objectives for the Horn Rapids
Landfill. (Note: Although long-term monitoring will be required at the former Horn Rapids Landfill,
it was removed from the national Priorities List in 1996.)
In addition, the remedial actions of the Nonradioactive Dangerous Waste Landfill could include the
emplacement of a RCRA Subtitle C design surface barrier similar to those proposed for the cribs and trenches within
the 200 Areas. The adjacent Solid Waste Landfill and Central Landfill should not require an
infiltration barrier and could likely be closed with a standard Subtitle D
Solid Waste Landfill cover. These landfills are currently scheduled for remediation by 2026.
This strategy accelerates the activities so the work could be completed in 2007.
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