Quiz & test questions Grade 6 Engineering & Design

Marne Water Plant Settling Basin Design Assessment

A grade 6 engineering assessment where students size a rectangular settling basin, find detention time and removal percent, and pick a design change to meet a goal.

Grade: Grade 6
Subject: Engineering & Design
Material: Quiz & test questions
Time: 30 min
Prep: No prep
Materials: None

Standards

6.G.A.2 Common Core Math

Find the volume of a right rectangular prism with fractional edge lengths by packing it with unit cubes of the appropriate unit fraction edge lengths, and apply the formulas V = l w h and V = b h to find volumes of right rectangular prisms with fractional edge lengths in the context of solving real-world and mathematical problems.

How this material aligns: Items 2 and 9 have students find the volume of a rectangular basin, including one with a fractional edge length of 10.5 feet, applying V = l w h as this standard requires.

All materials for 6.G.A.2 →

6.RP.A.3 Common Core Math

Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations, including finding a percent of a quantity and converting measurement units.

How this material aligns: Item 4 uses volume over flow as a rate to find detention time, and item 5 finds removal efficiency as a percent, the rate and percent reasoning this standard targets.

All materials for 6.RP.A.3 →

MS-ETS1-2 NGSS

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

How this material aligns: Items 6, 7, and 8 judge the sized basin against the stated 2-to-4-hour detention criterion and weigh candidate design changes, a bigger basin or a lower flow, using the volume-over-flow relationship; the remaining computation items are not part of this alignment.

All materials for MS-ETS1-2 →

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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 volume of a rectangular settling basin in cubic feet and gallons.
Students will find detention time and removal percent and select a design change to meet a goal.

Vocabulary

Detention time: Detention time is how long water stays inside a tank or basin before flowing out. Water must stay long enough for each treatment step, like settling or disinfecting, to finish its job.
Turbidity: Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.

Also: settling basin, removal efficiency

Teacher overview

This 30-minute assessment (30 points total) checks whether students can size a settling basin and reason about its performance. A settling basin is a large tank where heavy dirt sinks to the bottom before water moves on to the filters. The assessment mixes two multiple-choice items, two short-answer items, and five computation items built around a fictional town's water plant.

Marne Water Plant Settling Basin Design Assessment — Grade 6 Engineering & Design

Name: ____________________________ Date: ______________

Assessment

Use this scenario where an item refers to it. The town of Marne, a fictional town, is designing a rectangular settling basin. The basin is 40 feet long, 20 feet wide, and 10.5 feet deep.

(2 points) A settling basin cleans water mainly by letting heavy dirt do what?
- A) float to the top
- B) settle to the bottom
- C) evaporate away
- D) freeze solid
(4 points) Find the basin's volume in cubic feet. Use V = length x width x depth.
(4 points) Convert the basin's volume to gallons. One cubic foot holds 7.48 gallons.
(4 points) Water enters the basin at 16,000 gallons per hour. Detention time equals volume in gallons divided by flow. How many hours does water stay in the basin? Round to the nearest tenth.
(4 points) Raw water enters at 12 NTU of turbidity and leaves treatment at 0.3 NTU. Removal percent equals influent minus effluent, divided by influent, times 100. Find the removal percent.
(3 points) Real settling basins are designed for 2 to 4 hours of detention. Your answer to item 4 was about 3.9 hours. Is that within the typical range? Explain in one sentence.
(3 points) Which change would increase the basin's detention time, with everything else held the same?
- A) a higher flow into the basin
- B) a lower flow into the basin
- C) a smaller basin
- D) warmer water
(3 points) Marne wants water to stay in the basin longer so more dirt settles. Name one design change that would do this and explain why it works using the detention-time idea.
(3 points) A second, smaller basin is 30 feet long, 15 feet wide, and 8 feet deep. Find its volume in cubic feet.

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. Heavy dirt settles to the bottom of the basin, which is how a settling basin removes it before filtering.
Answer: 8,400 cubic feet. V = 40 x 20 x 10.5 = 8,400 cubic feet.
Answer: 62,832 gallons. 8,400 cubic feet x 7.48 gallons per cubic foot = 62,832 gallons.
Answer: 3.9 hours. 62,832 gallons / 16,000 gallons per hour = 3.927, which rounds to about 3.9 hours.
Answer: 97.5 percent. (12 - 0.3) / 12 x 100 = 11.7 / 12 x 100 = 97.5 percent removed.
Answer: Yes. About 3.9 hours falls between 2 and 4 hours, so the basin's detention time is within the typical design range.
Answer: B. Detention time equals volume divided by flow, so a lower flow makes the water stay in the basin longer.
Answer: Make the basin bigger or slow the flow. A larger volume or a smaller flow raises volume divided by flow, so detention time goes up and dirt has more time to settle. Accept either change with a matching reason.
Answer: 3,600 cubic feet. V = 30 x 15 x 8 = 3,600 cubic feet.

Differentiation

Support

Provide the volume formula and the gallons conversion on a reference strip, and set up item 2 as 40 x 20 x 10.5 so students only carry out the multiplication. Allow a calculator for every computation item.

Extension

Ask students to find the flow, in gallons per hour, that would give the 62,832-gallon basin exactly 3 hours of detention, then explain whether raising or lowering the flow from 16,000 gallons per hour gets there.

ELL supports

Provide a labeled sketch of a settling basin showing water in, dirt settling to the bottom, and cleaner water leaving. Pair "settle," "detention time," and "removal" with the picture, and give a sentence frame for item 6: "About 3.9 hours is ___ the typical range because ___."