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Title: Feasibility Study: Applicability of geochronologic methods involving radiocarbon and other nuclides to the groundwater hydrology of the Rustler Formation, southeastern New Mexico

Technical Report ·
OSTI ID:5746120

Radiocarbon, tritium, and /sup 36/Cl were measured in groundwaters from the dolomite aquifers of the Rustler Formation in the northern Delaware Basin of southeastern New Mexico to determine the feasibility of using these nuclides in dating the groundwater at and near the Waste Isolation Pilot Plant, a facility for geological disposal of Radioactive waste. No measurable /sup 36/Cl was found in any of these groundwaters, which derive their dissolved chloride from Permian evaporites. Demonstrably uncontaminated groundwaters contained no significant amounts of tritium (<0.2 TU). Percent modern carbon (PMC) correlates linearly and directly with bicarbonate concentration, indicating mixing of a high-PMC/high-bicarbonate reservoir with a low-PMC/low-bicarbonate reservoir. This relationship together with the history of development of the wells sampling the groundwaters, indicates contamination by anthropogenic modern carbon rather than simple dilution by dissolving rock carbonate. /delta//sup 13/C does not linearly correlate with bicarbonate, indicating no single source of contaminant radiocarbon. Values of PMC and /delta//sup 13/C for groundwaters were used to calculate apparent radiocarbon ages according to an interpretive model that accounts for water/rock interactions in carbonate aquifers. All but six pairs of values give significant negative ages (/minus/1,000 to /minus/7,000 years). This suggests that in contaminated samples the model over-adjusts (based on /delta//sup 13/C) for radiocarbon loss due to dilution and isotopic exchange with the rock. 52 refs., 10 figs., 6 tabs.

Research Organization:
Sandia National Labs., Albuquerque, NM (USA)
DOE Contract Number:
AC04-76DP00789
OSTI ID:
5746120
Report Number(s):
SAND-86-1054; ON: DE89016927
Resource Relation:
Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English