groundwater exam 1

hydrology

the study of water and its effects on and in the earth and in the atmosphere

hydrogeology

The study of the interrelationships of geologic materials and processes with water, especially groundwater.

hydrologic cycle

the movement of water through the biosphere

zone of saturation

zone where all open spaces in sediment and rock are completely filled with water

water table

top of zone of saturation

porosity

The percentage of the total volume of a rock or sediment that consists of open spaces.

uniformity coefficient

ratio of the particle size at 60% passing to that at 10% passing

effective grain size

Size corresponding to the 10% line on the grain size curve

specific yield

the ratio of volume of water that drains from a saturated rock via gravity to the total volume of rock

pendular water

water that clings to rocks from surface tension

intrinsic permeability

a measure of how easily a fluid (such as water) can move through a porous material (such as soil or rock), regardless of the fluid’s properties. It depends only on the size, shape, and connectivity of the pores in the material.

Hazen method

estimate hydraulic conductivity of sandy sediments from grain size distribution curve

K=C(d10)^2

Constant Head Permeameter

a lab device used to measure the hydraulic conductivity (or permeability) of granular soils, like sand, under saturated flow conditions. It keeps a constant water level (head difference) between the inlet and outlet, allowing water to flow steadily through the soil sample. HIGH K

Falling head permeameter

a lab device used to measure the hydraulic conductivity of fine-grained soils (like silt and clay), where water flows more slowly compared to coarse soils. LOW K

limitations to darcys law

applies for Re=pvd/u

laminar flow: Re < 1 or 10

aquifer

a body of permeable rock that can contain or transmit groundwater.

confining layer

Geologic material with little or no permeability or hydraulic conductivity. Water does not pass through this layer or the rate of movement is extremely slow.

aquifuge

completely impermeable geological formation that does not allow any water to pass through it. Unlike an aquitard (which has very low permeability but can still transmit some water), an aquifuge totally prevents groundwater flow.

aquitard

layer of low permeability that can store ground water and also transmit it slowly from one aquifer to another (leaky confining layer)

unconfined aquifer

a groundwater storage layer that is not trapped by an impermeable layer on top, meaning it is directly connected to the surface and can be easily recharged by rainwater or surface water.

confined aquifer

is a groundwater storage layer that is trapped between two impermeable or low-permeability layers

leaky confined layer

a semi-permeable layer that partially restricts water flow between two aquifers but still allows some water to pass through.

perched aquifer

a small, isolated groundwater zone that sits above the main water table due to the presence of a localized impermeable layer

transmissivity

a measure of how much water can flow through an aquifer in response to a hydraulic gradient. It combines both the aquifer's permeability (hydraulic conductivity, K) and its thickness ( b ).

storativity

Volume of water an aquifer releases from or takes into storage per unit surface area of aquifer per unit change in head.

specific storage

the amount of water a unit volume of an aquifer releases or takes in per unit change in hydraulic head, due to compressibility of the water and the aquifer material.

isotropic

The same in all directions

anisotropic

having different properties in different directions

assumptions for groundwater flow equations

1) aquifer bounded on the bottom by a confining layer

2) initial piezometric surface horizontal and constant

3) no other effects on piezometric surface

4) all formations horizontal

5) homogenius and isotropic

6) all flow is radical toward well

7) constant density/viscosity

8) pumping well is fully penetrating and screening over entire thickness of aquifer

9) pumping well has an infinitesimal (very small) diameter

radial flow

flow of water in an aquifer toward a vertically oriented well

Cooper-Jacob Method

confined aquifers, applies for when u<0.01

Theis equation

drawdown in a confined aquifer

interpolation

W(u')=W(u1)+(ΔWu/Δu)(u'-u1)

radius of influence

the maximum distance from a pumping well where the water table (in an unconfined aquifer) or potentiometric surface (in a confined aquifer) is affected by pumping.

dupuit equation

steady state unconfined flow

nonequilibrium radial flow

groundwater flow toward a pumping well where drawdown changes over time, meaning the system has not yet reached steady-state conditions.

completely confined aquifer flow

Q=2pirbK(dh/dr)

flow in a leaky confined aquifer

Hantush Jacob formula

flow in an unconfined aquifer

Neumans formula

steady state confined aquifer with 2 observation wells

Thiem equation, S does not impact ho-h

steady state unconfined aquifer with two observation wells

Dupuit equation

nonequilibrium flow: confined aquifer

Theis or cooper jacobs

nonequilibrium flow: leaky confined aquifer

Hantush Jacob formula

nonequilibrium radial flow (confined)

Cooper Jacobs S and T equations

nonequilibrium radial flow (unconfined)

Theis equation (sub W(u) with W(ua, ub, T)

slug test

a quick aquifer test used to determine hydraulic conductivity (or transmissivity) by suddenly changing the water level in a well and observing how it recovers over time.

Hvoslev Slug Test

a simple analytical approach used to determine the hydraulic conductivity (K) of an aquifer by analyzing water level recovery in a well after a sudden disturbance.

Bouwer and Rice Slug Method

a widely used approach for analyzing slug tests in unconfined aquifers to determine hydraulic conductivity (K).

CBP Slug method

a slug test analysis method used to determine the hydraulic conductivity (K) of confined or semi-confined aquifers.

superposition

a mathematical principle used to analyze groundwater flow when multiple wells, boundary conditions, or time-dependent effects influence an aquifer. It assumes that the total drawdown at any point is the sum of individual drawdowns from each source.

why do we use imaginary wells during superposition/determining groundwater flow

to simulate the effects of boundaries (like rivers, faults, or impermeable barriers) using the principle of superposition. Since real-world boundaries alter groundwater flow, imaginary wells help us mathematically represent these effects without changing the original well's pumping conditions.

well interfearence

can use CJ and steady state thiem/depiuit eq

Qi>0

pumping water up, hobs down

Qi<0

injecting water into the well, hobs up

no flow boundary

a boundary in an aquifer where groundwater cannot pass through, meaning the flow velocity across the boundary is zero. This happens when the boundary is impermeable due to geological or structural conditions.

constant head boundary

a boundary in an aquifer where the water level (or potentiometric surface) remains constant across the boundary, meaning that groundwater flow is determined by the fixed hydraulic head at that boundary. a river is a constant head boundary

partial penetrating flow

a well that does not extend through the full thickness of an aquifer, meaning it only penetrates part of the aquifer's vertical extent. As a result, groundwater flow is restricted to the portion of the aquifer that the well intersects.

step drawdown

a method used in pumping tests to assess the performance and capacity of a well by observing the change in drawdown at different pumping rates over time. It is primarily used to determine the well's efficiency and the relationship between flow rate and drawdown in the well.

recovery test

type of pumping test used to measure how an aquifer recovers after pumping has stopped.

B (recovery test)

y axis of line of best fit

C (recovery test)

slope of line of best fit