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In-situ alteration of minerals by acidic ground water resulting from mining activities: Preliminary evaluation of method

Journal of Geochemical Exploration

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, , and
DOI: 10.1016/S0375-6742(98)00039-9

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Abstract

The chemical composition of the Cu-mining-related acidic ground water (pH ~ 3.5 to near neutral) in Pinal Creek Basin, Arizona has been monitored since 1980. In-situ experiments are planned using alluvial sediments placed in the ground-water flow path to measure changes in mineral and chemical composition and changes in dissolution rates of subsurface alluvial sediments. The test results should help refine developed models of predicted chemical changes in ground-water composition and models of streamflow. For the preliminary test, sediment from the depth of the well screen of a newly drilled well was installed in three wells, the source well (pH 4.96) and two up-gradient wells (pHs 4.27 and 4.00). The sediment was placed in woven macrofilters, fastened in series to polyvinyl chloride (PVC) pipes, and hung at the screened level of each well. After interacting with the slowly moving ground water for 48 days, the test sediments were removed for analysis. There was no evidence that any of the materials used were biologically or chemically degraded or that the porosity of the filters was diminished by ferric hydroxide precipitation. These materials included 21-??m-pore (21PEMF) and 67-??m-pore polyester and the 174-??m-pore fluorocarbon Spectra/mesh macrofilters containing the in-situ sediment, the polypropylene (PP) macrofilter support structures, and the Nylon (NY) monofilament line used to attach the samples to the PVC pipe. Based on chemical and mineral composition and on particle-size distribution of the sediment before and after ground-water exposure, the 21PEMF macrofilter was chosen as the most suitable macrofilter for the long-term in-situ experiment. Tests also showed that the PP support structures and the NY monofilament line were sufficiently durable for this experiment.The chemical composition of the Cu-mining-related acidic ground water (pH approx. 3.5 to near neutral) in Pinal Creek Basin, Arizona has been monitored since 1980. In-situ experiments are planned using alluvial sediments placed in the ground-water flow path to measure changes in mineral and chemical composition and changes in dissolution rates of subsurface alluvial sediments. The test results should help refine developed models of predicted chemical changes in ground-water composition and models of streamflow. For the preliminary test, sediment from the depth of the well screen of a newly drilled well was installed in three wells, the source well (pH 4.96) and two up-gradient wells (pHs 4.27 and 4.00). The sediment was placed in woven macrofilters, fastened in series to polyvinyl chloride (PVC) pipes, and hung at the screened level of each well. After interacting with the slowly moving ground water for 48 days, the test sediments were removed for analysis. There was no evidence that any of the materials used were biologically or chemically degraded or that the porosity of the filters was diminished by ferric hydroxide precipitation. These materials included 21-??m-pore (21PEMF) and 67-??m-pore polyester and the 174-??m-pore fluorocarbon Spectra/mesh macrofilters containing the in-situ sediment, the polypropylene (PP) macrofilter support structures, and the Nylon (NY) monofilament line used to attach the samples to the PVC pipe. Based on chemical and mineral composition and on particle-size distribution of the sediment before and after ground-water exposure, the 21PEMF macrofilter was chosen as the most suitable macrofilter for the long-term in-situ experiment. Tests also showed that the PP support structures and the NY monofilament line were sufficiently durable for this experiment.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
In-situ alteration of minerals by acidic ground water resulting from mining activities: Preliminary evaluation of method
Series title:
Journal of Geochemical Exploration
DOI:
10.1016/S0375-6742(98)00039-9
Volume
64
Issue:
1-3 -3 pt 1
Year Published:
1999
Language:
English
Publisher:
Elsevier Sci B.V.
Publisher location:
Amsterdam, Netherlands
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geochemical Exploration
First page:
293
Last page:
305
Conference Title:
Proceedings of the 4th International Symposium on Environmental Geochemistry ISEG. Pt 1 (of 2)
Conference Location:
Vail, CO, USA
Conference Date:
5 October 1997 through 10 October 1997