Match the following items between Column I and Column II with the most appropriate combinations:Column I Column II P Properties of confined and semi- confined aquifers 1 Perched aquifer Q Property of an unconfined aquifer 2 Coefficient of storage R Property of semi-confined aquifer 3 Specific yield S A special case of an unconfined aquifer 4 Leakage factor
Aquifer Properties Matching Explained
This question requires matching hydrogeological terms from Column I with their definitions or characteristics from Column II.
- P: Properties of confined and semi-confined aquifers relates to 2: Coefficient of storage. The coefficient of storage ($S$) is a fundamental property indicating the volume of water released from storage per unit surface area per unit decline in hydraulic head in confined and semi-confined aquifers.
- Q: Property of an unconfined aquifer relates to 3: Specific yield. Specific yield ($S_y$) measures the volume of water released from storage by an unconfined aquifer per unit surface area per unit decline of the water table.
- R: Property of semi-confined aquifer relates to 4: Leakage factor. The leakage factor is used to describe the hydraulic properties related to water movement through the semi-permeable layers bounding a semi-confined (leaky) aquifer.
- S: A special case of an unconfined aquifer relates to 1: Perched aquifer. A perched aquifer is a localized saturated zone above the main groundwater table, forming a distinct, isolated body of groundwater within the unsaturated zone.
Correct Combination Summary
The correct matching derived from the definitions is as follows:
| P | 2 | Coefficient of storage ($S$) |
| Q | 3 | Specific yield ($S_y$) |
| R | 4 | Leakage factor |
| S | 1 | Perched aquifer |
This combination corresponds to P-2, Q-3, R-4, S-1.
Important Questions from Groundwater Occurrence
An unconfined aquifer of areal extent $20 \text{ km} \times 20 \text{ km}$ has hydraulic conductivity of $4 \text{ m/day}$, porosity of $0.32$, and storage coefficient (specific yield) of $0.18$. If the initial saturated thickness of the aquifer is $30 \text{ m}$, and $4\times10^8 \text{ m}^3$ of water is extracted from the aquifer, then the decline in the saturated thickness is _____________ (rounded off to two decimal places) m.
An unconfined aquifer extends over an area of $1 \text{ km}^2$ and has hydraulic conductivity, total porosity and specific retention of $20 \text{ m per day}, 30\%$ and $10\%$, respectively. After pumping some groundwater from this aquifer, the water table dropped to a depth of $20 \text{ m}$ from the ground level. If the water table was initially at $14.5 \text{ m}$ below the ground level, the change in groundwater storage in million cubic meters would be_______
A fully penetrating well is installed in a homogenous and isotropic confined aquifer. The aquifer has uniform thickness of 16 m and hydraulic conductivity of 25 m/d. Water is being pumped out from the well at a constant rate of $0.1 \text{ } m^3/s$ till steady state condition is reached. If a drawdown of 3.5 m is observed at a distance of 75 m from the well then the drawdown at a distance of 150 m from the well will be________ (in m, rounded off to two decimal places).
- One of the key assumptions made by Dupuit-Forchheimer about the flow behavior in the porous medium towards subsurface drains is
An underground hazardous waste storage tank is leaking. The contaminant concentration directly beneath the site is 0.5 mg/L. The contaminant is travelling at an effective rate of 0.4 m per day towards a water well which is 2 km away.
Assume that the degradation of the contaminant follows a first order reaction, and the initial concentration of the contaminant becomes half in 10 years.
In this case, the contaminant concentration expected at the well under steady state conditions is ________ mg/L (rounded off to two decimal places).
