Water Resources and Environmental Engineering Flashcards

In the Streeter-Phelps dissolved oxygen sag curve, the critical point is where:

Answer: The deoxygenation rate equals the reaeration rate

At the critical point, the DO deficit is at its maximum because oxygen consumption and reaeration are balanced.

The NPDES permit program for point-source discharges to US waters was created under which law?

Answer: Clean Water Act

Section 402 of the Clean Water Act created the National Pollutant Discharge Elimination System.

Which federal law governs 'cradle-to-grave' management of hazardous waste?

Answer: RCRA

The Resource Conservation and Recovery Act regulates hazardous waste from generation through disposal.

During the stable methanogenic phase of a municipal solid waste landfill, landfill gas is mostly made up of:

Answer: Methane and carbon dioxide in roughly equal parts

Mature landfill gas is typically about 50–60% CH₄ and 40–50% CO₂.

In Gaussian plume modeling, raising the effective stack height generally makes the maximum ground-level concentration:

Answer: Decrease

A higher effective release height allows more dispersion before the plume reaches the ground, which lowers peak concentrations.

A river flowing at 10 cfs with 2 mg/L of a pollutant receives a 5 cfs discharge at 20 mg/L. What is the fully mixed concentration?

Answer: 8 mg/L

C = (10×2 + 5×20)/(10+5) = 120/15 = 8 mg/L.

A unit hydrograph is the direct runoff hydrograph produced by:

Answer: One unit (e.g., 1 inch) of excess rainfall spread evenly over the watershed for a specified duration

A unit hydrograph shows the watershed response to a unit depth of effective rainfall over a set duration.