U.S.
GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4205
TOXIC SUBSTANCES HYDROLOGY PROGRAM
Characterization of Hydraulic Conductivity of the Alluvium and Basin Fill, Pinal Creek Basin near Globe, Arizona
ABSTRACT
Acidic waters containing elevated concentrations of dissolved metals have contaminated the regional aquifer in the Pinal Creek Basin, which is in Gila County, Arizona, about 100 kilometers east of Phoenix. The aquifer is made up of two geologic units: unconsolidated stream alluvium and consolidated basin fill. To better understand how contaminants are transported through these units, a better understanding of the distribution of hydraulic conductivity and processes that affect it within the aquifer is needed.
Slug
tests were done in September 1997 and October 1998 on 9 wells finished in the
basin fill and 14 wells finished in the stream alluvium. Data from the tests
were analyzed by using either the Bouwer and Rice (1976) method, or by using
an extension to the method developed by Springer and Gellhar (1991). Both methods
are applicable for unconfined aquifers and partially penetrating wells. The
results of the analyses show wide variability within and between the two geologic
units. Hydraulic conductivity estimates ranged from 0.5 to 250 meters per day
for the basin fill and from 3 to 200 meters per day for the stream alluvium.
Results of the slug tests also show a correlation coefficient of 0.83 between
the hydraulic conductivity and the pH of the ground water. The areas of highest
hydraulic conductivity coincide with the areas of lowest pH, and the areas of
lowest hydraulic conductivity coincide with the areas of highest pH, suggesting
that the acidic water is increasing the hydraulic conductivity of the aquifer
by dissolution of carbonate minerals.
Abstract
Introduction
Slug tests
Results and distribution of hydraulic conductivity
Summary
References cited
Appendix
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