Event

The hydrogeologic characteristics of, and remedial actions at, the St. Louis, MO Formerly Utilized Sites Remedial Action Program (FUSRAP) sites will be discussed. These St. Louis sites’ investigations and remediations were complex, due to a long waste history at sites with the prior influences of man, varied geomorphic locations, and major influence from surface water and groundwater.
FUSRAP is a class of remediation projects for typically low-level radioactive wastes. FUSRAP sites remediated before 2000 were generally located in arid, western US locales. These arid western US sites allowed more simplified analyses of the waste source and transport before mitigation, because of their environs and typically little reworking of the waste. The waste sources were often surficial radiologic waste that was dominantly transported by wind with some groundwater and surface-water migration. Most characterization was accomplished before the acceptance of the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), which is a statistical assessment of the contaminant density. Eastern US sites may have: more developed depositional and erosional surfaces, higher precipitation (resulting in hydrogeologic complexities), longer use histories and greater anthropogenic site impacts, varied waste placement over differing time intervals, and varied physical placement and environmental transport of the waste.

The site geologic characterization, anthropogenic site modifications, and site contaminant history provide sufficient information to develop the understanding of the possible radiological contaminants’ transport. Radiological contaminants’ transport causes additional uncertainties that require a team of professionals to investigate the contaminant issues. Health physics, chemistry, specialized sampling and geostatistics each have roles in the solution of the transport of radiological contaminants. Radiological contaminants have a broad range of solubility, which may change (for an individual element) with varying water chemistry or in the company of other chemicals. Contaminants may be moved in the subsurface in preferential pathways formed naturally or caused by man.

The advantage of a conservative nonparametric (MARSSIM) approach may be challenged by the possible waste migration along channels or conduits. A linear route of waste migration along a now buried past stream channel or granular backfill of a utility corridor reduces the effectiveness of the surficial sampling. While a conduit truly has three dimensions, the lineation’s areal extent over a surface may be quite small. Adding to the difficulty are low-level wastes. Because of the foregoing issues, St. Louis District relied on historic, air photo, and geologic literature reviews, hydrogeologic assessments, multiple hypotheses for waste transport, and preferential pathway surveys of the final exposed surfaces.
The communication of the risk (hazard and vulnerability) from residual radioactive constituents to the public may be as difficult as the earlier investigations and remedial actions. Significant effort may be necessary to convince the public that the known and unknown risks are acceptable, and that the resolved remediation is detailed and proper.

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