Term
| How can ARD generation be avoided? |
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Definition
-by minimizing ingredients available to the weathering stew
-cover tailings and waste rock to avoid ingress of gases and/or oxygen
-tailings: soil covers, water covers
-waste rock: soil covers
-carbonate dissolution can buffer acidic water, increasing the pH |
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Term
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Definition
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Term
| The main reservoirs where water is stored on Earth are...? |
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Definition
-Oceans (97.3%)
-Glaciers and polar ice (2.1%)
-Underground aquifers (that is groundwater) (0.6%) |
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Term
| What is infiltration or percolation? |
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Definition
| Surface water seeps into the pore spaces of soil or rock |
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Term
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Definition
| The portion of precipitation (rain plus snow) that does not infiltrate into the surface, but rather moves over the surface and eventually collects in streams or lakes |
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Term
| Hydrologic cycle and water balance |
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Definition
| Total flows between the various reservoirs approximately balance each other, that is FLOW IN = FLOW OUT |
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Term
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Definition
| Water that is present beneath the Earth's surface. Represents ~22% of the TOTAL FRESH water on Earth. |
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Term
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Definition
-when water is saturated within the rocks and sediments underground
-this surface roughly follows the topography of the landscape and can change seasonally |
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Term
Where does groundwater occur?
What controls its availability? |
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Definition
-stored in sediments and rocks underground
-porosity, permeability and sustainability |
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Term
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Definition
-symbol is n or Φ
-the percentage of the total volume of a rock, soil or sediment that is taken up by pore spaces. Can be either INTERGRANULAR or FRACTURE porosity
n = Vvoid/Vtotal |
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Term
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Definition
The capacity of a rock to transmit water (and other fluids)
-depends on grain size distribution and connectivity of pores
-permeable mean the voids are connected so water can pass through
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Term
| What is intrinsic permeability? |
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Definition
k = intrinsic permeability
A constant for material properties that influence fluid movement
Units: darcy or cm^2 |
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Term
| What is hydraulic conductivity? |
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Definition
k = [m/s] = Resistance to flow of water
K = k(ρg/μ)
Where:
k = intrinsic permeability
ρ = density of fluid
g = gravitational acceleration
μ = dynamic viscosity of fluid |
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Term
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Definition
A combined measure of the pressure and elevation relative to a specified datum (z=0) in an aquifer
h = Ψ + z (pressure head + elevation head) |
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Term
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Definition
Driving force for the movement or flow of groundwater (~slope)
WATER FLOWS FROM HIGH HEAD TO LOW HEAD |
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Term
| What is hydraulic gradient defined as? |
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Definition
Defined as the difference of the hydraulic heads at two measuring points divided by the distance L over which the water flows
i = (h1-h2)/L |
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Term
| Darcy's Law (flux) or specific discharge |
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Definition
Specific discharge or Darcy flux = q (m/s)
In a permeable medium the specific discharge q is:
-directly proportional to the head loss, and hydraulic conductivity
-inversely proportional to the length (distance)
q = Ki
q = K(h1-h2)/L
K = hydraulic conductivity |
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Term
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Definition
Volumetric flux [m^3/s]
-multiply q by cross sectional area
Q = KiA |
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Term
| Velocity in a porous medium |
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Definition
Specific discharge IS NOT velocity! This is because it does not take into account that in a porous medium not all of the volume of a flow path is available for water to travel; the rocks/sediments take up much of that space. So...
v = q/n
Therefore, while maintaining the same specific discharge and same total volume, velocity increases with decreasing porosity. |
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Term
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Definition
Areas where precipitation and infiltration occur.-
-usually topographically high areas, where hydraulic head is highest |
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Term
| What are discharge areas? |
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Definition
Areas where water seeps out of the ground as springs or enters rivers, lakes, or the ocean.
-usually topographically low areas, where hydraulic head is lowest |
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Term
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Definition
A geologic formation that can transmit significant quantities of water and which can be tapped by wells for a water supply
-sands, gravels, limestones, sandstones, basalts |
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Term
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Definition
A geologic formation that can store water, but can transmit it only slowly, and cannot provide sufficient quantities to sustain pumping wells
-clays, shales, tight crystalline rocks |
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Term
| Aquifers, Aquitards, and Aquicludes |
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Definition
- An aquiFER has the capability of transFERring water
- An aquiTARD reTARDS the movement of water
- An aquiCLUDE preCLUDES (or prevents) the movement of water |
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Term
| What is an unconfined aquifer? |
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Definition
| Unconfined aquifers or free water table aquifers are not confined by an overlying aquitard |
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Term
| What is a confined aquifer? |
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Definition
| Are confined ABOVE and BELOW by aquitards |
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Term
| What is an artesian aquifer? |
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Definition
| When the hydraulic head in a confined aquifer rises ABOVE the surface of the aquifer, it is called an artesian aquifer. Wells drilled into such an aquifer will flow freely and are called artesian wells. |
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Term
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Definition
Pumping water from an unconfined aquifer will cause the water table to decline locally and form a cone of depression
-water saturated pore space is drained
-ceasing pumping will eventually allow the depressed water table to rise to its original level
-the rate of recovery will depend on both the porosity and the permeability of the aquifer |
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Term
| Groundwater extraction from a confined aquifer |
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Definition
Confined aquifers remain completely saturated during pumping by wells.
Saturation of pores remain unchanged, but fluid pressure is reduced |
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Term
| Confined aquifer: Where does the pumped water come from? |
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Definition
Decrease in pressure
-Expansion of pore water to fill pore space
Increase in effective stress
-Compaction of sediment, decrease in pore space |
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Term
| Sustainability of Groundwater Resources |
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Definition
Although groundwater is a renewable resource, excessive withdrawal of subsurface water may lead to:
-depletion of groundwater (renewal by recharge may take 100's of years)
-degradation of water quality
-negative effects on surface water bodies (like wetlands, lakes, rivers)
-Subsidence due to overpumping |
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