Executive Summary:
The primary focus of this
review is to assess the potential for release of radionuclides from the
mixed waste landfill (MWL) and their effect upon human health and the
environment. Towards this, a large volume of key documents (publicly available
documents) was reviewed. Particularly, the following reports that were
carefully evaluated are the following: i) Report of the Mixed Waste Landfill
Phase 1 and Phase 2 RCRA Facility Investigation Sandia National Laboratories
Albuquerque, New Mexico - September 1991 with appendix; (ii) Response
to this report by the Department of Energy (DOE) iii) Report of the Mixed
Waste Landfill Phase 2 Facility Investigation Sandia National Laboratories
(SNL) Albuquerque, New Mexico, September 1996; (iv) Data obtained from
New Mexico Department of Environment; (v) Complete uranium data for the
groundwater samples (obtained from SNL). Based on the evaluation of data
reported in these reports, it is found that some of the data are ambiguous
and high quality data are required to fully characterize the nature and
extent of radionuclide contamination. The major issue on the remediation
of this site critically hinges on the spatial extent of radionuclide contamination
of this site and hence as a top priority, the extent of contamination
needs to be characterized.
From a huge database on the radionuclide concentrations in the soil, water,
and air in and around the mixed-waste landfill, the following observations
have been made:
i) Based on the evaluation of all the data on the concentrations of
235U and 238U and activity ratios of 235U/238U in the groundwater samples,
the data appears to indicate that a significant portion of U in the
groundwater samples has a non-natural source (s).
ii) The activity ratios of 238Pu and 239,240Pu in the bore hole soil
samples collected below the MWL and analyzed by three different groups
indicate that there is some amount of Pu observed in the bore hole soil
samples and it is likely derived from non-global fallout sources.
iii) Based on the activity ratios of 238Pu and 239,240Pu in the aerosol
samples collected at the MWL, it appears that most of the Pu is derived
from non-global fallout sources.
iv) The tritium has migrated far and wide from the MWL and it continues
to migrate to adjoining areas.
v) Although modeling efforts predicted that the radionuclides will not
migrate more that 30-40 ft from the MWL, presence of non-natural U,
Pu and 90Sr at >100 ft below ground surface indicates that the models
are not well constrained.
vi) The concentrations of any of these nuclides are below the upper
tolerance limit and have not posed any serious threat to the environment
so far.
It must be made clear that the concentrations of these radionuclides in
the groundwater system at present do not pose any threat to the environment.
Due to the quality of the radiochemical data presented in the reports,
the uncertainties associated with measurements are unusually high and
it is not possible to unequivocally conclude if non-natural uranium or
Pu derived from the mixed waste landfill has reached the groundwater system.
High quality data on the uranium activity ratios in soil, water and air
samples from the MWLF will provide information on the sources of radionuclides.
The radon emanation rate measurements as well concentration of 222Rn in
the air samples show that there is no significant amount of radon input
from the daughter products of 238U buried in the MWLF.
Various multiple remediation scenarios have been evaluated. Those include:
i) No-action ii) Containment and iii) Some combination of retrieval, treatment,
storage, and disposal. For options ii) and iii), the relative merits of
the following techniques have been evaluated: a) Capping to prevent mobilization
of contaminants; b) In-situ treatment; c) Dynamic compaction; d) Soil
Grouting; In-situ vitrification; e) soil washing/chemical extraction and
any other methods that may be relevant to this site. Some information
on the costs involved for remediating this MWL have also been discussed.
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