|
Front Range mountains generally are steep. Recharge K_ is aquifer hydraulic conductivity in the
<br /> to the fractured crystalline-rock aquifer has been esti- z-direction (L1)/T),
<br /> mated to range from 0 to 21 percent of precipitation b is aquifer saturated thickness (L),
<br /> with an average of 3.2 percent (Hofstra and Hall, h is hydraulic head(L),
<br /> 1975)to 10 percent (Mueller, 1979). S is storage coefficient (dimensionless),
<br /> In the Colorado Front Range,rock quarries typi- W is volumetric flux per unit area from a hydrologic
<br /> cally are mined dry(Langer, 2001). Although quarries source or sink as a function of location and
<br /> may penetrate the water table, the discharge rate to time (L/T),
<br /> quarries commonly is less than the rate of evaporation, x,y,z are Cartesian coordinates,and
<br /> and active dewatering measures are not needed. The t is time (T).
<br /> quarry may drain freely. To produce aggregate, the
<br /> rock is first drilled and blasted. Blasting commonly This equation assumes compressible fluid of
<br /> breaks the rock into pieces suitable for crushing, and constant density is flowing through a heterogeneous
<br /> the blasted material is extracted using conventional anisotropic aquifer according to Darcy's law (Fetter,
<br /> earth-moving equipment such as bulldozers, front 1994). It also assumes the principal axes of the
<br /> loaders, and track hoes. Material is transported, either hydraulic conductivity tensor are aligned with'the x,v,
<br /> by truck or conveyor, from the mining face to the and z coordinate axes,respectively (McDonald and
<br /> processing plant where it is crushed, washed, and Harbaugh, 1988). Additional details of the ground-
<br /> sorted by size. water flow equation and its derivation can be found in
<br /> numerous texts and reports (Freeze and Cherry, 1979;
<br /> Lohman, 1979; Huyakorn and Pinder, 1983;
<br /> GROUND-WATER HYDRAULICS McDonald and Harbaugh, 1988; Domenico and
<br /> AND METHODS MATHEMATICAL ETH Schwartz, 1990;Anderson and Woessner, 1992;Fetter,
<br /> C M
<br /> 1994).
<br /> To evaluate the effects of aggregate mining on The ground-water flow equation can be solved
<br /> the surrounding water table, ground-water flow was for the dependent variable head (h)by analytical or
<br /> simulated with analytical and numerical solutions to numerical methods. Analytical solutions use algebraic
<br /> the ground-water flow equation. A general form of the methods to derive closed-form solutions to the ground-
<br /> equation describing transient(time-varying)three- water flow equation, whereas numerical solutions use
<br /> dimensional ground-water flow can be written as finite-difference or finite-element numerical methods
<br /> (Konikow and Grove, 1977;McDonald and Harbaugh, to solve the ground-water flow equation. Analytical
<br /> 1988): solutions to the ground-water flow equation are most
<br /> useful for evaluating simplified ground-water systems
<br /> and often assume a homogeneous and isotropic
<br /> ah) hydraulic-conductivity distribution, horizontal flow,
<br /> a(bK a(bK,ah) and infinite horizontal extent or limited boundary
<br /> r ax + ay conditions. Analytical methods can be useful for esti-
<br /> ax ay (1) mating mine inflows and drawdowns during initial
<br /> stages of mine planning when site-specific data may
<br /> a(bK_ az> ah not yet be available(Marinelli and Niccoli,2000). The
<br /> + =S—+W(x,y,z,t) applicability of an analytical solution depends on the
<br /> az at extent to which the real problem under consideration is
<br /> consistent with the simplifying assumptions of the
<br /> where analytical solution. Analytical solutions that assume
<br /> infinite horizontal extent can be useful in predicting
<br /> drawdown in real aquifers of finite extent when aquifer
<br /> KY is aquifer hydraulic conductivity in the boundaries lie beyond the cone of depression in the
<br /> x-direction (L`/T), water table(area of influence)caused by the pit.When
<br /> Kv is aquifer hydraulic conductivity in the boundaries lie outside the area of influence,the aquifer
<br /> y-direction (L2/T), within the area of influence responds as though it were
<br /> 6 Analytical and Numerical Simulation of the Steady-State Hydrologic Effects of Mining Aggregate in Hypothetical Sand-and-Gravel
<br /> and Fractured Crystalline-Ronk AnijifP_rs
<br />
|