---
title: "What is an aquifer"
subject: "Engineering Geology II"
chapter: 3
key: "semester_4/engineering_geology_ii:aquifer-definition"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/aquifer-definition
site: BCT Engineering
---

# What is an aquifer

Engineering Geology II · Chapter 3: Hydrogeology

- Asked in: 2075 Bhadra, 0.5 marks; 2079 Jestha, 2 marks; 2068 Magh, 1 marks (asked 3 times)
- Video: [What is an Aquifer?](https://www.youtube.com/watch?v=g7R0yLX0V9E) — GeoScience Videos
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/aquifer-definition
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-3

## Question

What is an aquifer?

## Short answer

An aquifer is a saturated geological formation with sufficient porosity and permeability to store and transmit usable groundwater to wells and springs. Examples include gravel, sand, fractured sandstone, and limestone. Types include unconfined, confined, semi-confined, and perched aquifers.

## Answer

An **aquifer** is a saturated geological formation (rock or sediment) that is sufficiently porous and permeable to store and transmit usable quantities of groundwater to wells and springs.

Examples: gravel, sand, fractured sandstone, cavernous limestone, fractured basalt.

#### Characteristics
- High porosity and, especially, high permeability.
- Gives economic yield to wells and springs.
- Has a recharge area and a discharge area.

#### Types
- **Unconfined aquifer** with a free water table.
- **Confined (artesian) aquifer** between impermeable beds, water under pressure.
- **Semi-confined (leaky) aquifer** and **perched aquifer** (small water body above an impermeable lens).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What defines an aquifer?
   A. Any wet soil
   B. A saturated formation porous and permeable enough to give usable water
   C. A dry rock layer
   D. A deep lake
   Answer: B. An aquifer stores and transmits usable quantities of water to wells and springs. (Key point: Definition)

2. Which property is especially important for an aquifer?
   A. High permeability
   B. High hardness
   C. Dark colour
   D. Low porosity
   Answer: A. Aquifers need high porosity and especially high permeability to yield water. (Key point: Key property)

3. What is a perched aquifer?
   A. A small water body held above the main water table by a local impermeable lens
   B. A confined deep aquifer
   C. A dry layer
   D. A karst cave only
   Answer: A. A local impermeable lens holds a small unconfined water body above the main table. (Key point: Perched aquifer)