Module 12 Wet Detention Systems Quiz

Which characteristic most clearly distinguishes a retention practice from a detention practice?

Retention results in a substantial reduction in runoff volume through infiltration or evaporation, while detention releases the treated volume after a holding period.

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Detention results in permanent volume reduction, while retention releases stored water after a set period of time.

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Both retention and detention reduce runoff volume equally, but only detention receives pollutant removal credit.

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Retention relies solely on biological removal, while detention relies solely on physical settling.

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What is the primary role for water quality control of the permanent pool in a wet detention pond?

It promotes particle settling, and provides habitat for biological removal organisms.

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It stores the entire annual runoff volume above the control elevation for gradual release.

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It exclusively supports chemical co-precipitation by maintaining saturated soil conditions at the pond bottom.

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It prevents the formation of the littoral zone by keeping water levels consistently deep throughout the pond.

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If a wet detention pond is designed without a littoral zone, how must the calculated pollutant removal be adjusted?

The calculated removal must be divided by 1.1 to account for the approximately 10% reduction in efficiency.

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The calculated removal must be multiplied by 1.1 to compensate for the missing littoral zone contribution.

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The removal estimate is reduced by a flat 20% because littoral zones provide roughly one-fifth of total removal.

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No adjustment is required; regulatory design criteria make the littoral zone optional with no performance impact.

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What is identified as the primary physical removal process in wet detention ponds?

Gravity settling of suspended particles during quiescent periods between storms.

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Adsorption of dissolved pollutants onto submerged aquatic vegetation surfaces.

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Chemical co-precipitation of phosphorus by iron and aluminum oxides in the sediment.

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Biological uptake of nutrients by algae and microorganisms in the permanent pool.

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Which formula correctly expresses the Average Annual Residence Time (ART) for a wet detention pond?

ART (days) = [Permanent Pool Volume (ac-ft) / Annual Runoff (ac-ft/yr)] × 365

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ART (days) = Annual Runoff (ac-ft/yr) / Permanent Pool Volume (ac-ft) × 365

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ART (days) = Permanent Pool Volume (ac-ft) × Annual Runoff (ac-ft/yr) / 365

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ART (days) = [Annual Runoff (ac-ft/yr) × 365] − Permanent Pool Volume (ac-ft)

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Approximately what total phosphorus removal efficiency is achieved at the regulatory maximum design ART of 200 days?

Approximately 80% TP removal.

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Approximately 43% TP removal.

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Approximately 60% TP removal.

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Approximately 95% TP removal.

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What is the approximate maximum total nitrogen removal achievable in a wet detention pond at the 200-day ART limit?

Approximately 43%

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Approximately 80%

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Approximately 60%

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Approximately 25%

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Which three parameters are used as inputs in the regression equation to estimate the anoxic depth of a wet detention pond?

Secchi disk depth, chlorophyll-a concentration, and total phosphorus concentration.

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Permanent pool volume, annual runoff volume, and mean annual temperature.

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Total nitrogen concentration, turbidity, and dissolved oxygen level.

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Pond surface area, side slope ratio, and mean annual precipitation depth.

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What conversion factor is applied to transform the mean annual anoxic depth to the minimum monthly anoxic depth used in wet pond design?

0.892

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1.10

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0.75

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1.25

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What are the recommended irreducible concentrations for total nitrogen (TN) and total phosphorus (TP) in wet detention ponds?

400 µg/L for TN and 15 µg/L for TP.

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15 µg/L for TN and 400 µg/L for TP.

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200 µg/L for TN and 50 µg/L for TP.

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100 µg/L for TN and 5 µg/L for TP.

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Why do the standard TP and TN removal equations for wet detention ponds become invalid when the influent is pre-treated runoff?

Pre-treatment removes coarser particles and reduces concentrations, so the same ART produces less removal than the equations developed for untreated runoff would predict.

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Pre-treatment increases pollutant concentrations beyond the range for which the equations were calibrated.

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The equations are invalid because pre-treated runoff eliminates the permanent pool and makes ART calculation impossible.

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Pre-treatment changes the chemical composition of nutrients so that biological removal no longer occurs in the wet pond.

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Module 12 Wet Detention Systems Quiz

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