PRELIMINARY SEDIMENT SAMPLING AT THE BIG LOST RIVER SINKS:
RESULTS AND RECOMMENDATIONS

Christopher Martin, Douglas Halford, Dr. Richard Marty
August 2004
STOLLER-ESER-59

ABSTRACT
The objective of this project was to determine whether radiological and/or conventional contaminants have been transported downstream by the Big Lost River system and subsequently deposited in the area of Big Lost River Sinks. The objective was met through the collection and analysis of sediment samples from selected depositional environments within the area of the Sinks, concentrating on the areas of primary sedimentation. Analysis for Resource Conservation and Recovery Act (RCRA) metals and gross radionuclides were performed. Statistical analyses of the various contaminants measured were carried out using nonparametric methods, specifically the Kruskal-Wallace Analysis of Variance for comparisons of multiple sample groups and the Mann-Whitney U test for paired comparisons. Statistical analysis showed that the concentrations of the radionuclides and metals measured in this initial assessment were statistically the same or lower than the background values used, with the exception of aluminum, barium, and chromium.

Certain limitations must be placed on the data presented in this report as this was an initial assessment. These limitations include a small number of biased sample locations (21) given the area of the sinks (approximately 4 mi²) which does not rule out the potential for contamination to occur at other unsampled locations, analysis of only the upper 30 centimeters of soil, which does not preclude the possibility that contamination from earlier site operations may occur at deeper levels, and statistical comparisons of data being made to similar and composite soil types.

Sampling locations were selected to cover the largest number of different depositional environments. While contamination did not show any relation to depositional environment (i.e., channel versus overbank deposits), there was a clear correlation between grain size and contaminant concentration. It is recommended that additional areas of fine-grained material in the Sinks are, particularly in the south playa, be sampled to assure that preferential deposition in that area has not occurred.

Equally as important is the fact that there is a very real possibility that contaminants associated with early site operations may lie deeper in the sediment profile. For this reason it is recommended that additional sample analyses be performed on the next deeper set of samples (30 – 60 cm) to determine if older buried sediments may contain elevated concentrations of the contaminants of concern. Also, since there is no information on sedimentation rates at the Sinks, it is recommended that information on sedimentation rates at the Sinks be collected so that horizons associated with early operations can be targeted. Further recommendations include additional physical analysis be done on all samples submitted, such as mineralogy, grain size, and percent organic matter. Such physical analysis would provide numerical values of grain size that can be directly related to constituent concentration, and provenance for those grains. Furthermore, if additional sample collection is performed to further identify contaminant concentrations in the Sinks area grain size data may allow for collection and analysis of only a specific fraction of the soils.

As mentioned above, there is a clear correlation between grain size and contaminant concentration. While the comparison of data from the Sinks to similar or composite soils is reasonable, it limits the amount of background data available for comparison, particularly the large Environmental Surveillance, Education and Research Program database cannot be used due to very different soil types than the Sinks. Since the background soil types were not an exact match to the sediments of the Sinks, and should have exhibited lower concentrations, there does not appear to be any further justification for analyses of matching soil types for most of the contaminants measured. However, the concentrations of aluminum, barium, and chromium must be evaluated further to determine if they do in fact reflect contamination of sediments at the Sinks.

In addition to the above statistical analysis a point of interest arose from the plot of ⁴⁰K versus aluminum concentration. This plot showed the samples from the Sinks to be deficient in potassium. This is a consistent problem with ⁴⁰K values at the INL and may indicate a problem of underestimation of other radionuclide concentrations. A recommended approach to this issue would be to analyze for total potassium in the samples, then look at the ratio of total to ⁴⁰K to determine were any problems may lie.
 

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This report was prepared for the
U.S. Department of Energy Idaho Operations Office
Under Contract DE-AC07-00ID13658
By the S. M. Stoller Corporation
Environmental Surveillance, Education and Research Program
1780 First Street
Idaho Falls, ID 83401