CES Groundwater & Hydrogeology 2

Question 1

A dense non-aqueous phase liquid (DNAPL) released to the subsurface will most likely:

Accepted Answer

Sink through the saturated zone and pool at the top of an aquitard

Answer

Float on the water table as a separate phase lens

Answer

Dissolve completely in groundwater before reaching the saturated zone

Answer

Volatilize entirely in the vadose zone and never reach groundwater

Question 2

The retardation factor (R) for a contaminant in groundwater accounts for which process?

Accepted Answer

Sorption of the contaminant onto aquifer solids, slowing its migration relative to advective water flow

Answer

Radioactive decay reducing contaminant mass over time

Answer

Biodegradation converting the contaminant to non-toxic byproducts

Answer

Volatilization transferring the contaminant from groundwater to soil vapor

Question 3

Hydrodynamic dispersion in a groundwater contaminant plume consists of:

Accepted Answer

Mechanical dispersion caused by velocity variations and molecular diffusion

Answer

Advection driven by the hydraulic gradient alone

Answer

Sorption and retardation of hydrophobic compounds

Answer

Volatilization at the capillary fringe interface

Question 4

A cone of depression forms around a pumping well because:

Accepted Answer

Pumping removes water faster than the aquifer recharges locally, lowering the water table or potentiometric surface radially

Answer

The well casing blocks lateral groundwater flow, creating a stagnant zone

Answer

Volatilization of pumped water reduces aquifer pressure near the well

Answer

Dense contaminants accumulate near the well screen, reducing permeability

Question 5

The Theis equation is used in groundwater science primarily to:

Accepted Answer

Determine aquifer transmissivity and storativity from pumping test drawdown data

Answer

Calculate the hydraulic gradient between monitoring wells

Answer

Estimate recharge rates from precipitation data

Answer

Predict contaminant retardation in the saturated zone

Question 6

Specific yield (Sy) is an important parameter for which aquifer type, and what does it represent?

Accepted Answer

Unconfined aquifers; the volume of water released by gravity drainage per unit aquifer volume per unit head decline

Answer

Confined aquifers; the elastic compression of the aquifer matrix under reduced pressure

Answer

Fractured rock aquifers; the proportion of secondary porosity to total rock volume

Answer

Perched aquifers; the ratio of infiltration to evapotranspiration at the surface

Question 7

Which in-situ remediation technology is most appropriate for a LNAPL gasoline plume in a shallow unconfined aquifer?

Accepted Answer

Dual-phase extraction (soil vapor extraction combined with groundwater pump-and-treat)

Answer

Permeable reactive barrier using zero-valent iron

Answer

Air sparging beneath the contaminated zone to strip dissolved chlorinated solvents

Answer

Deep soil mixing with Portland cement to stabilize heavy metals