Hydrogeology

Step 1: Understand the porosity formula.
Porosity is the fraction of the rock's volume that is void space, and it can be calculated using the following formula: The volume of voids is the difference between the saturated mass and the dry mass, divided by the density of water.

Step 2: Calculate the volume of voids.
The mass of the rock when saturated is 325 g, and the mass when dry is 300 g. The volume of voids is:

Step 3: Calculate the porosity.
The total volume of the rock is 100 cm³, so the porosity is:

Step 4: Conclusion.
The computed porosity of the rock is 25.0%.

Step 1: Understand the equation for Darcian flow.
The volumetric flow rate through the aquifer can be calculated using Darcy's law: where: - is the hydraulic conductivity (2 m/s), - is the cross-sectional area (7 m²), - is the hydraulic gradient (3.2).

Step 2: Substituting the values into Darcy's law.
Substituting the known values into the equation:

Step 3: Conclusion.
The volumetric flow rate through the aquifer is 44.8 m³/s.

Step 1: Understand Darcy's Law.
Darcy’s law relates the discharge through an aquifer to the hydraulic conductivity (permeability), the cross-sectional area, and the hydraulic gradient. It is given by: where: - is the discharge (m /day), - is the coefficient of permeability (m/day), - is the cross-sectional area of flow (m ), - is the hydraulic gradient, where is the difference in water surface elevations and is the distance between the wells. Step 2: Rearranging Darcy’s Law.
We are given the discharge per unit area ( m/day), so we can solve for : Step 3: Substituting the given values.
We know: - m/day, - m, - m. Substituting into the equation: Step 4: Conclusion.
The coefficient of permeability is 0.4 m/day.

Step 1: Understanding Subsurface Water.
- Vadose water occurs in the zone above the water table, in the unsaturated zone or zone of aeration (B is correct).
- Groundwater underflow occurs in permeable media, such as sand and gravel, where water can move easily (C is correct).
- A perched water table is a localized water table above the regional water table, often due to an impermeable layer (A is incorrect).
- When the water table intersects the surface, it forms springs, where groundwater flows to the surface (D is correct).
Step 2: Conclusion.
The correct answer is (B), (C), and (D).

Step 1: Understanding water classifications.
- Juvenile water: Magmatic origin — derived directly from Earth's mantle, not from sedimentary or surface processes.
- Connate water: Trapped in sedimentary rocks during deposition.
- Meteoric water: Derived from precipitation.
Step 2: Evaluating statements.
(A) True — A perched water table occurs above the main water table within the zone of aeration.
(B) False — Juvenile water originates from magma, not diagenesis.
(C) True — The zone of aeration lies above the saturated zone.
(D) True — Both aquiclude and aquifuge are impermeable.
Step 3: Conclusion.
The false statement is (B) Juvenile water is derived from sediment diagenesis.

Step 1: Given data.
Discharge in 2 hours = .
Length Head Diameter
Area
Step 2: Using Darcy’s Law.
Step 3: Substitution.
Step 4: Conversion to ×10^–6.
. Step 5: Conclusion.
Coefficient of permeability = 2.36 ×10^–6 cm/s.