skip to main content

Title: Characterization of contaminant transport using naturally-occurring U-series disequilibria. 1998 annual progress report

'The goal of the research is to study the migratory behavior of contaminants in subsurface fractured systems using naturally occurring uranium- and thorium-series radionuclides as tracers under in-situ physico-chemical and hydrogeologic conditions. Naturally occurring U- and Th-series disequilibria can provide information on the rates of adsorption-desorption and transport of contaminants as well as on fluid transport and rock dissolution in a natural setting. The authors are developing a realistic model of contaminant migration in the Snake River Plain Aquifer beneath the INEEL by evaluating the retardation processes involved in the rock/water interaction. The major tasks are to: (1) determine the natural distribution of U, Th, Pa and Ra isotopes in the groundwater as well as in rock minerals and sorbed phases, and (2) study rock/water interaction processes using U/Th series disequilibria and a statistical analysis-based model code for the calculation of in-situ retardation factors of radionuclides and rock/water interaction time scales. This study will also provide an improved understanding of the hydrogeologic features of the site and their impact on the migration of contaminants. This report summarizes results after 20 months of a 36-month project. Studies performed at LANL include analysis of the long-lived nuclides {sup 238}U, {sup 235}U, {supmore » 234}U, {sup 230}Th, {sup 226}Ra, {sup 232}Th, and {sup 231}Pa by thermal ionization mass spectrometry (TIMS). Studies performed at the Univ. of Southern California include the measurement of short-lived naturally occurring radionuclides by decay-counting techniques and the development of models to predict the migration behavior of these radionuclides. Initial efforts began with analysis of 31, 0.5L water samples obtained through routine sampling by USGS and INEEL personnel. One significant observation from these data is that {sup 234}U/{sup 238}U activity ratios are highest in waters that emanate from local recharge areas to the northwest of the INEEL and they decrease in the direction of groundwater flow. Contours of high {sup 234}U/{sup 238}U ratios delineate preferential flow paths extending southward from the local recharge areas. The uranium data have allowed delineation of these preferential flow pathways in greater detail than obtained by other methods. The contour map of {sup 234}U/{sup 238}U ratios also identifies isolated pockets with low {sup 234}U/{sup 238} U ratios. These are suspected to represent groundwater which has undergone more extensive water/rock interaction as a result of either longer residence times of faster reaction rates. These results are important for understanding the hydrologic context of the site and crucial for interpreting the complete data sets for the U and Th decay chains.'« less
Authors:
 [1] ;  [2]
  1. Los Alamos National Lab., NM (US)
  2. Univ. of Southern California, Los Angeles, CA (US)
Publication Date:
OSTI Identifier:
13527
Report Number(s):
EMSP-54741-98
ON: DE00013527
Resource Type:
Technical Report
Research Org:
Los Alamos National Lab., NM (US); Univ. of Southern California, Los Angeles, CA (US)
Sponsoring Org:
USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
Country of Publication:
United States
Language:
English
Subject:
40; 54; 05; Progress Report; Sorption; Desorption; Remedial Action; High-Level Radioactive Wastes; PROGRESS REPORT; SORPTION; DESORPTION; REMEDIAL ACTION; HIGH-LEVEL RADIOACTIVE WASTES