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Unsaturated Hydrogeologic Properties of Reclaimed Coal Strip Mines
Author(s) -
Diodato D. M.,
Parizek R. R.
Publication year - 1994
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1994.tb00618.x
Subject(s) - vadose zone , water content , hydraulic conductivity , borehole , bulk density , porosity , hydrogeology , soil science , moisture , geology , mineralogy , neutron probe , neutron , soil water , geotechnical engineering , materials science , neutron temperature , composite material , physics , quantum mechanics , neutron cross section
Two nuclear methods were used to quantify hydrogeologic parameters in the unsaturated zone of a reclaimed and revegetated coal strip mine in Clarion, Pennsylvania. Am‐Be (neutron) and Cs‐137 (gamma‐gamma) geophysical logging tools were used to quantify volumetric moisture content, bulk density, total porosity, and unsaturated hydraulic conductivity. An additional study at the same site used postsampling neutron activation analysis to determine concentrations of a bromide tracer in unsaturated zone water samples. Those additional data were used to independently calculate unsaturated hydraulic conductivity. Geophysical logging of six boreholes at the site was conducted on seven different dates. Temporal variations in volumetric moisture content versus depth were observed to be short‐lived, with the general shape of the volumetric moisture content profiles remaining spatially stable over the eight month period of investigation. Bulk density values ranged from less than 1.14 to 1.86 g/cm 3 , corresponding to total porosities of greater than 57% to 30.1%. Large void spaces were encountered during past and present drilling and observed at a measurement point. Unsaturated hydraulic conductivities were calculated using draining profile volumetric moisture content data as input to an explicit numerical solution of the unsaturated flow equation. Calculated values ranged from 2.4 × 10 −7 to 1.5 × 10 −3 cm/s. Examination of all of the geophysical log data together showed sharp increases in volumetric moisture content spatially coincident with zones where bulk density increases (and porosity decreases). The bulk density contrast appears to be of more influence than the magnitude of the material property. Increased unsaturated hydraulic conductivity associated with increased volumetric moisture content was seen in several boreholes. Bromide tracer‐labeled waters were collected from pressure‐suction lysimeters installed at depths of up to 18.1 m for a period of 16 months. Unsaturated hydraulic conductivities, calculated by interpreting concentration peaks as average arrival times of steadily infiltrating water through a uniformly porous media, ranged from 2.8 × 10 −6 to 7.2 × 10 −5 cm/s. However, a dual‐permeability mechanism is suggested by the observed behavior of the tracer. Analysis of the data suggests that fluid flow in this hydrogeologic setting is dominantly transient. Ground‐water recharge occurs in short‐lived pulses. The periodicity of acid mine drainage formation and flushing to the water table is expected to correspond to infiltration and recharge events.