An isotopic investigation of groundwater in the Central San Juan Basin, New Mexico: Carbon 14 dating as a basis for numerical flow modeling

Abstract

Carbon 14 dating of groundwater can be used to help determine the transmissivity distributions of aquifers. This method may offer significant advantages, in certain respects, over traditional aquifer pumping test techniques. We have applied 14C dating to a hydraulic analysis of a multilayer aquifer system in the central San Juan Basin of New Mexico. After corrections for geochemical evolution of the solutes, the influence of dispersive processes on the 14C distribution was investigated. A model incorporating stochastic dispersion theory indicated that macroscopic dispersion exerted only a small influence on the measured 14C activities. The •4C-derived transmissivity distribution was used to construct a numerical flow model which was applied to an analysis of interaquifer leakage. The model showed that even though vertical flow between aquifers was significant, in this case it did not cause the 14C distribution to differ significantly from that predicted by a simple piston flow model. Carbon 14 can be used as a basis for detailed hydraulic evaluations of groundwater flow in areas where traditional well hydraulics methods are not practical. PHILLIPS ET AL..' ISOTOPIC INVESTIGATION OF GROUNDWATER Study Area ß Albuquerque New Mexico 108øW 107øW

Noble gas tracing of groundwater/coalbed methane interaction in the San Juan Basin, USA

“…The underpressured San Juan Basin coalbed methane show a systematic increase in age with distance from recharge, with 4 He ages ranging from 23.3 kyr to 106 kyr for 6 -35 km distance from recharge and show a similar, if slightly older, association of age with distance to recharge to 14 C dates derived from the Ojo Aquifer, which overlies the Kirtland Shale ( Fig. 2) (Philips et al, 1989). In contrast, 4 He ages of groundwater associated with the overpressured methane show more scatter and range from 70.5 kyr to 484 kyr, again increasing with distance to recharge (5-25 km).…”

Comparison of ground-water flow model particle-tracking results and isotopic data in the Mojave River ground-water basin, southern California, USA

“…The stable isotopes of oxygen and hydrogen have been extensively used to identify sources of recharge, delineate aquifers, and delineate flow paths within aquifers (Verhagen et al, 1991;Adar and Leibundgut, 1995). Carbon-14 has received considerable attention from model developers because of the potential for estimating hydrologic properties over large areas on the basis of carbon-14 data (Phillips et al, 1989). Phillips et al (1989) used carbon-14 dating as a basis for estimating aquifer transmissivity as part of numerical model development in the San Juan Basin of New Mexico.…”

“…Carbon-14 has received considerable attention from model developers because of the potential for estimating hydrologic properties over large areas on the basis of carbon-14 data (Phillips et al, 1989). Phillips et al (1989) used carbon-14 dating as a basis for estimating aquifer transmissivity as part of numerical model development in the San Juan Basin of New Mexico. Robertson (1992) used carbon-14 data to estimate ground-water ages, direction of ground-water flow, and ground-water velocity in the San Pedro basin in Arizona prior to flow-model development.…”

An Overview of 14C Analysis in the Study of Groundwater

“…Geyh and Backhaus 1979;Pearson et al 1983;Wigely et al 1984;Phillips et al 1989;Verhagen et al 1991). The regionally valid hydraulic information derived via this approach is often superior to the local information obtained from pumping tests.…”