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

DNAPLs have densities greater than water (e.g., chlorinated solvents like PCE and TCE) and will migrate downward through both the vadose and saturated zones until they encounter an impermeable layer, forming a pooled source.

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

The retardation factor R = 1 + (ρb × Kd) / n describes how much slower a sorbing contaminant travels compared to the average groundwater velocity; sorption onto soil organic matter or minerals is the primary mechanism.

Question 3

Hydrodynamic dispersion in a groundwater contaminant plume consists of:

Accepted Answer

Mechanical dispersion caused by velocity variations and molecular diffusion

Answer

Hydrodynamic dispersion combines mechanical (advective) dispersion—due to heterogeneous pore-scale velocity variations—with molecular diffusion, together causing spreading and dilution of the contaminant plume.

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

Pumping creates a head gradient directed toward the well; as water is extracted, head declines radially outward from the well, forming a characteristic cone-shaped depression in the potentiometric surface.

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

The Theis (1935) equation describes transient drawdown around a pumping well in a confined aquifer; by matching observed drawdown-time data to the Theis type curve, T and S can be determined from a pumping test.

(CES) Certified Environmental Scientist Practice Test

(CES) Certified Environmental Scientist Practice Test

CES Groundwater & Hydrogeology 2