171A

Hydrogeology

Groundwater

See also: 894164. 894180. 894181

amounts of water to more permeable units above and below. A method is proposed to estimate aquitard/aquitude vertical hydraulic diffusivity on the basis of water level measurements in piezometers placed both in the confining layers and neighbouring aquifers. It is used to study the phenomenon of aquifer leakage between an unconfined surface contaminated aquifer and the confined water supply aquifer below.

894014 Modifying the USGS solute transport computer model to predict high-density hydrocarbon migration Hossain, M A; Corapcioglu, M Y Ground Water V26. N6. Nov-Dec 1988, P717-723

Migration of high density hydrocarbons in an unconfined gravel aquifer, transport of an immiscible phase in a natural gradient gravity-driven system, is investigated. Density and viscosity effects are examined. The governing equations are solved by modifying the solute transport model developed by the USGS. Numerical results suggest high density, low viscos- ity immiscible pollutants travel deeper and further than lower density, more viscous compounds. Migration is dominated by gravity, largely uncoupled from the horizontal component until the aquifer lower boundary is reached.

894015 Ground-water flow model of drawdown and recovery near an underground mine Tora, L; Bradbury, K R Ground Water V26, N6, Nov-Dec 1988, P724-733

Zinc-lead mines near Shullsberg, Wisconsin, closed in 1979. The carbonate aquifer containing the orebodies was dewatered and sulphide minerals became oxidised during the period of operation, and sulphate contaminated the groundwater on cessation of mining. The USGS flow model was used to examine the hydrogeology of the mines and predict future flow patterns and contaminant migration. Results suggest pollution will persist for about l0 years. Because validation data before, during, and after mining is available, predictions can be made with greater knowledge of model limitations than is generally possible.

894016 'Testing' a limestone aquifer using water-table response to storm water discharged into sinkholes Michalski, A; Torlucci, J Ground Water V26, N6, Nov-Dec 1988, P751-760

Aquifer response to stormwater discharge at sinkholes was analysed as a large scale, natural aquifer injection test to esti- mate aquifer parameters, characterise flow type, and assess the performance of waste management facilities within a karstified aquifer. Water level data from observation wells suggested an isotropic nature and dominantly diffuse groundwater trans- mission within the aquifer. Water level response to natural stress is seen to be a useful exploration tool where traditional pumping/injection tests may be disturbed by natural events.

894017 Determination of aquitard]aquitude hydraulic properties from arbitrary water-level fluctuations by deconvolution Neuman, S P; Gardner, D A Ground Water V27, NI, Jan-Feb 1989, P66-76

Sedimentary aquifer systems usually contain low permeability confining layers which act as conduits for vertical migration of water and contaminants across them. Such layers may be com- pressible on aquifer drawdown and release substantial

894018 Present limitations and perspectives on modeling pollution problems in aquifers Konikow, L F Proc NA TO Advanced Research Workshop on Advances in Analytical and Numerical Groundwater Flow and Quality Modelling, Lisbon, 2-6 June 1987 P643-664. Publ Dordrecht: Reidel, 1987

Improved groundwater simulation models have been devel- oped in recent years. The basis of these models for ground. water flow and solute transport, and numerical methods are reviewed. [t is considered that major improvements will next arise from increased accuracy in characterising aquifer proper- ties and their variability rather than improved mathematical techniques. 58 refs.

Chemical and physical changes due to water

894019 Sinkhole development along 'untreated' highway ditchlines in East Tennessee Moore, H L Proc 2nd Maltidisciplinary Conference on Sinkholes and the Environmental Impacts of Karst, Orlando, 9-11 February 1987 PI15-119. Publ Rotterdam: A A Balkema, 1987

In some areas it is not possible to avoid roadway construction in karst prone areas. Where ditches are unlined, runoff water can accumulate and percolate downwards, resulting, ulti- mately, in above average concentration of sinkholes along ditchlines. They are treated in East Tennessee by excavation to stable bedrock, filling with non-degradable 'chunk rock', and final sealing of the surface to prevent reoccurrence. Effective planning minimises the danger of untreated ditches in karstic areas.

894020 Limestone quarrying and sinkhole development in the English Peak District Gunn, J; Gagen, P Proc 2nd Multidisciplinary Conference on Sinkholes and the Environmental Impacts of Karst, Orlando, 9-11 February 1987 P121-125. Publ Rotterdam: A A Balkema, 1987

Limestone has been quarried in the Peak District for many years and sinkholes have frequently occurred in the quarries after abandonment. Where modern blasting practices are used, conical regions of fractures are left along the stemming lines. These can collapse or act as preferred runoff paths and become embryonic sinkholes. Existing cavities may be exposed by extraction and infill material may be lost. Removal of over- burden before blasting, practiced in all quarrying, exposes nat- ural fractures, which may weather or erode to become potential sinkholes.

1989 Pergamon Press plc. Reproduction not permitted