Abstract: Aquifer Recharge Studies in the Albuquerque Basin: Relating Grainsize Distributions to Hydraulic Conductivity

Daniel M. Detmer

As part of an aquifer recharge study of the Albuquerque basin, central New Mexico, grainsize distributions were used to infer hydraulic conductivities of the lithofacies present. Samples were taken from outcrops throughout the basin. Surface exposures of the middle and upper members of the Santa Fe Group, ancestral Rio Grande deposits, eolian sands, tributary arroyos, and

the Sandia piedmont plain were analyzed. A weighted log diagram that considers the spacing between sieves and the weight retained on each sieve was employed, which allows rapid comparison among distributions. Sieves ranging from 2 to .045 mm were used. Specific facies among the deposits were sampled, and characteristic grainsize distributions were determined for each. Permeabilities of specific facies were measured prior to sampling with a portable air permeameter. This device measures the air-flow rate through the deposit, which is correlated to a hydraulic conductivity. These measurements were also compared to empirical permeability calculations based on a representative grainsize. This technique is appropriate on the small scale, but heterogeneity and interconnectedness of the faci s is of critical importance. Grainsize analysis of well cuttings is somewhat problematic due to the possibility of abrupt facies changes over small vertical distances. Better results are achieved when core samples are available. This technique offers an alternative to expensive drawdown tests, which may contain inaccuracies due to the screening of the wells and interfering cones of depression.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994