Environmental Engineering Flashcards

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

Answer: The deoxygenation rate equals the reaeration rate

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

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:

Answer: Tailing and rebound from matrix diffusion in low-permeability zones

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

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

Answer: Alum (aluminum sulfate)

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

The RCRA Subtitle C program regulates hazardous waste from:

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

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

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

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

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.

For an air stripping tower designed to remove VOCs from groundwater, Henry's Law constant (H) is critical. A contaminant with H < 10⁻⁵ atm·m³/mol is generally considered:

Answer: Difficult to air strip; another treatment technology should be considered

Low Henry's Law constants indicate low volatility from the aqueous phase, making air stripping ineffective for contaminants with H < 10⁻⁵ atm·m³/mol.

Under the National Environmental Policy Act (NEPA), which document requires the most thorough environmental review?

Answer: Environmental Impact Statement (EIS)

An Environmental Impact Statement (EIS) is the most comprehensive NEPA document, required for major federal actions significantly affecting the environment.