NCEES Environmental Engineering 4

Question 1

In the Streeter-Phelps model for river oxygen sag, the critical point occurs where:

Accepted Answer

The deoxygenation rate equals the reaeration rate

Answer

At the critical point (minimum DO), deoxygenation and reaeration rates are equal, so the DO deficit is at its maximum.

Question 2

A groundwater plume contains TCE at 500 µg/L. The EPA MCL for TCE is 5 µg/L. A pump-and-treat system reduces the concentration to 10 µg/L after 5 years but stalls due to back-diffusion. This behavior is best described as:

Accepted Answer

Tailing and rebound from matrix diffusion in low-permeability zones

Answer

Back-diffusion from low-permeability matrix materials causes tailing (slow concentration decrease) and rebound after pumping, a well-documented limitation of pump-and-treat.

Question 3

Which coagulant is commonly used in water treatment and functions by forming aluminum hydroxide floc that sweeps particles from suspension?

Accepted Answer

Alum (aluminum sulfate)

Answer

Alum (Al₂(SO₄)₃) hydrolyzes to form Al(OH)₃ floc, which adsorbs and enmeshes suspended particles in a process called sweep flocculation.

Question 4

The RCRA Subtitle C program regulates hazardous waste from:

Accepted Answer

Cradle to grave — generation, transport, treatment, storage, and disposal

Answer

RCRA Subtitle C establishes a cradle-to-grave tracking system covering generation, transportation, treatment, storage, and disposal of hazardous waste.

Question 5

A municipal solid waste landfill uses a composite liner system. Which configuration meets the minimum RCRA Subtitle D requirements?

Accepted Answer

60-mil HDPE geomembrane overlying a 2-ft compacted clay layer with hydraulic conductivity ≤ 1×10⁻⁷ cm/s

Answer

RCRA Subtitle D requires a composite liner: a 60-mil HDPE geomembrane in direct contact with at least 2 ft of compacted soil with k ≤ 1×10⁻⁷ cm/s.

NCEES Practice Test

NCEES Practice Test

NCEES Environmental Engineering 4