Quiz & test questions Grade 12 Engineering & Design

Grebe Point Lift Station: Wet Well and Force Main Test

A grade 12 quiz on a fictional lift station mixing multiple-choice and computation: wet well volume, fill and pump-down times, cycle time, and force main velocity.

Grade: Grade 12
Subject: Engineering & Design
Material: Quiz & test questions
Time: 35 min
Prep: No prep
Materials: Calculator

Standards

HSG-MG.A.3 Common Core Math

Apply geometric methods to solve design problems (e.g., designing an object or structure to satisfy physical constraints or minimize cost).

How this material aligns: Item 3 applies cylinder geometry to the wet well's operating band, using volume to satisfy the station's pump-control design.

All materials for HSG-MG.A.3 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Item 6 chains gallons per minute to cubic feet per second to feet per second through the force main's cross-sectional area, the unit path this standard targets.

All materials for HSN-Q.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will calculate the wet well volume between pump start and stop levels.
Students will compute fill time, pump-down time, and total cycle time from inflow and pump rates.
Students will determine force main velocity from flow and pipe diameter and evaluate it against a scouring minimum.

Vocabulary

Lift station: A lift station is a pumping setup that raises wastewater from a low spot so it can keep flowing toward the treatment plant. Sewers mostly flow downhill, so low areas need a lift.

Also: wet well, force main, cycle time, scouring velocity

Teacher overview

This 35-minute quiz, worth 30 points, checks whether students can carry lift-station design math from the wet well through the force main. It mixes two multiple-choice items, five computation items, and one short-answer item, all built on a single fictional station, so answers from early items feed the later ones the way a design check actually proceeds.

Grebe Point Lift Station: Wet Well and Force Main Test — Grade 12 Engineering & Design

Name: ____________________________ Date: ______________

Assessment

All items refer to the fictional Grebe Point lift station, which collects wastewater from a low-lying neighborhood and pumps it over a ridge to the gravity sewer beyond. Useful facts: Volume (cu ft) = 0.785 × Diameter² × depth; one cubic foot holds 7.48 gallons; one cfs equals 448.8 gpm.

(2 points) What is the primary job of a lift station in a collection system?
- A) Add chlorine to the wastewater before it reaches the plant
- B) Raise wastewater so it can continue flowing by gravity where the ground no longer slopes downhill
- C) Remove grit and debris from the wastewater
- D) Measure each neighborhood's flow for billing
(3 points) What normally signals the station's pumps to start?
- A) A timer that runs the pumps at fixed intervals all day
- B) The wet well level rising to the lead pump's start setpoint
- C) The treatment plant calling for more flow
- D) The force main's velocity dropping below its design value
(4 points) The wet well is a cylinder 12 feet in diameter. The pumps start when the level has risen 2.5 feet above the stop level. How many gallons enter the wet well between a pump stop and the next start? Round to the nearest whole gallon.
(4 points) During an average evening, wastewater flows into the wet well at 150 gpm with the pumps off. Using your answer from item 3, how many minutes pass between a pump stop and the next start? Round to the nearest tenth.
(4 points) The lead pump moves 400 gpm while inflow continues at 150 gpm. How many minutes does the pump need to remove the item 3 volume and pump the well back down to the stop level? Round to the nearest tenth.
(4 points) The force main is 6 inches (0.5 feet) in diameter. At the pump's 400 gpm, first convert flow to cfs, then use Q = A × V with the pipe's area (0.785 × 0.5²) to find the velocity in feet per second, to the nearest tenth.
(4 points) Using your answers from items 4 and 5, compute the station's full cycle time in minutes, and state about how many times per hour the lead pump starts.
(5 points) Short answer: engineers want force main velocity to stay near or above 2 feet per second at least once a day. Explain what that minimum velocity accomplishes inside the pipe, and name one design change that would raise the velocity if it came in too low.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: B) Raise wastewater so it can continue flowing by gravity where the ground no longer slopes downhill. Lift stations are installed where the ground stops sloping downhill far enough for gravity flow to continue, while treatment steps such as disinfection and grit removal happen at the plant rather than at the station.
Answer: B) The wet well level rising to the lead pump's start setpoint. Level controls, floats or transducers, cycle the pumps; timers would ignore how much wastewater has actually arrived.
Answer: 2,114 gallons. Volume = 0.785 × 12² × 2.5 = 0.785 × 144 × 2.5 = 282.6 cubic feet, and 282.6 × 7.48 = 2,113.8, about 2,114 gallons.
Answer: 14.1 minutes. 2,113.8 gallons ÷ 150 gpm = 14.09, about 14.1 minutes of filling between cycles.
Answer: 8.5 minutes. The pump gains on the well at 400 − 150 = 250 gpm net, so 2,113.8 ÷ 250 = 8.46, about 8.5 minutes to pump down.
Answer: 4.5 feet per second. 400 gpm ÷ 448.8 gpm per cfs = 0.891 cfs. Pipe area = 0.785 × 0.5² = 0.196 square feet. V = Q ÷ A = 0.891 ÷ 0.196 = 4.54, about 4.5 feet per second.
Answer: 22.6 minutes. Cycle = fill + pump-down = 14.1 + 8.5 = 22.6 minutes, so the lead pump starts about 60 ÷ 22.6 = 2.7 times per hour.
Answer: It keeps solids moving, scouring the pipe. At or above roughly 2 feet per second the flow resuspends grease and grit so they do not settle and build up in the force main. Acceptable design changes: use a smaller-diameter force main so the same flow moves faster, or select a higher-capacity pump; either raises velocity.

Differentiation

Support

Provide the three formulas printed at the top of the quiz with the wet well's 0.785 × 144 product already evaluated, and allow items 4, 5, and 7 to use the rounded 2,114-gallon value without penalty for the small difference it introduces.

Extension

Suppose a storm doubles the fictional station's inflow to 300 gpm. Have students recompute the fill time from item 4 and the net pump-down rate from item 5, then explain which of the two changes threatens the station first as inflow keeps climbing toward the pump's 400 gpm capacity. (Fill time drops to about 7.0 minutes; the net rate collapses to 100 gpm.)

ELL supports

Provide a labeled cutaway sketch of the station showing the wet well, the start and stop levels, the pumps, and the force main climbing the ridge, and let students annotate it during the quiz. Offer a sentence frame for item 8: "The velocity keeps ___ from settling in the pipe, and using a ___ pipe would make the water move faster."