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Quiz & test questions Grade 9 Engineering & Design

Quennfield Plant Upgrade: A Design and Sizing Unit Test

A 35-point grade 9 unit test on a fictional plant upgrade, mixing criteria and constraint items with detention time, chemical feed, filter loading, and pressure math.

Objectives

  1. Students will distinguish design criteria from design constraints in a plant upgrade scope.
  2. Students will calculate basin volume, detention time, chemical feed, and filter loading rate.
  3. Students will compare a calculated value against a published design range and interpret the result.

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: loading rate, criterion, constraint

Teacher overview

This 35-point test closes a unit on sizing the pieces of a small surface water treatment plant. It runs on one fictional scenario, an upgrade at the Quennfield Water District, and mixes multiple choice, short answer, and multi-step computation so that recall and application are scored separately. Items 3 through 11 build on one another, so a student who misses an early conversion can still earn credit on later work if the method is shown. Allow calculators and expect about 50 minutes.

Quennfield Plant Upgrade: A Design and Sizing Unit Test — Grade 9 Engineering & Design
Name: ____________________________ Date: ______________

Assessment

The town of Quennfield and its water district are fictional. Use these conversions where needed: 1 MGD = 694 gpm, 1 cubic foot = 7.48 gallons, 1 foot of head = 0.433 psi, and pounds per day = concentration in mg/L x flow in MGD x 8.34.

  1. (2 points) Which statement below is a constraint rather than a criterion?
    A. Finished water must stay at or below 0.3 NTU in 95 percent of monthly samples.
    B. The upgraded plant must treat 1.8 MGD on the peak day.
    C. The new filter building must fit inside the existing 60-foot by 40-foot slab.
    D. The plant must hold a chlorine residual of at least 0.2 mg/L at the far end of town.

  2. (2 points) Under the EPA Surface Water Treatment Rules, a conventional filtration plant must keep finished-water turbidity at or below what value in 95 percent of its monthly samples?
    A. 0.1 NTU
    B. 0.3 NTU
    C. 1.0 NTU
    D. 5.0 NTU

  3. (3 points) The Quennfield plant treats 1.8 MGD. Convert that flow to gallons per minute.

  4. (3 points) The plant feeds chlorine at 2.2 mg/L into a flow of 1.8 MGD. How many pounds of chlorine does it feed each day? Round to the nearest hundredth.

  5. (3 points) The sedimentation basin is a rectangle 60 feet long, 20 feet wide, and 12 feet deep. How many gallons does it hold?

  6. (3 points) Using your basin volume from item 5 and the plant flow of 1,800,000 gallons per day, what is the detention time in hours? Round to the nearest hundredth.

  7. (2 points) Water typically spends about 2 to 4 hours in a sedimentation basin. Compare your answer from item 6 with that range. Is the basin inside it? Answer yes or no and state the reason in one sentence.

  8. (3 points) The district wants 2.0 hours of detention at the same 1,800,000 gallons per day and the same 60-foot by 20-foot footprint. How deep must the basin be? Round to the nearest hundredth of a foot.

  9. (3 points) The plant's filters have 180 square feet of total surface area. Using the flow in gallons per minute from item 3, what is the filter loading rate in gallons per minute per square foot? Round to the nearest hundredth.

  10. (2 points) Conventional filters typically run between 2 and 6 gallons per minute per square foot. Compare your answer from item 9 with that range. Is the loading rate inside it? Answer yes or no and state the reason in one sentence.

  11. (3 points) How many square feet of filter surface would the plant need to run at 5.0 gallons per minute per square foot at the same flow? Round to the nearest tenth.

  12. (4 points) The district can fund only one project this year: deepening the sedimentation basin or adding filter surface area. Choose one, and name two trade-offs your choice creates. Support your choice with a number from your own work on this test.

  13. (2 points) A storage tank's water surface sits 138 feet above a customer's meter. Using 1 foot of head = 0.433 psi, the pressure at that meter is closest to:
    A. 32 psi
    B. 60 psi
    C. 138 psi
    D. 319 psi

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

Answer Key

  1. Answer: C.
    The slab size bounds where the building may go without saying anything about how the water must perform, which makes it a constraint. Choices A, B, and D all state measurable performance the design must achieve, so each is a criterion.

  2. Answer: B.
    The rule sets 0.3 NTU as the value that must not be exceeded in 95 percent of monthly samples, with a never-exceed value of 1 NTU. Students who choose C have named the never-exceed value rather than the 95 percent value.

  3. Answer: 1,249.2 gpm.
    1.8 MGD x 694 gpm per MGD = 1,249.2 gpm.

  4. Answer: 33.03 pounds per day.
    2.2 mg/L x 1.8 MGD = 3.96. Then 3.96 x 8.34 = 33.0264 pounds per day, which rounds to 33.03 pounds per day.

  5. Answer: 107,712 gallons.
    60 x 20 x 12 = 14,400 cubic feet. Then 14,400 x 7.48 = 107,712 gallons.

  6. Answer: 1.44 hours.
    107,712 gallons divided by 1,800,000 gallons per day = 0.05984 day. Then 0.05984 x 24 hours = 1.436 hours, which rounds to 1.44 hours.

  7. Answer: No, it is below the range.
    At 1.44 hours the basin holds water for less than the 2 to 4 hour range, so lighter, slower-settling floc has less time to settle and more solids reach the filters. Award full credit for a clear no with a reason tied to settling time.

  8. Answer: 16.71 feet.
    Two hours is 2 divided by 24, or one twelfth of a day, so the basin must hold 1,800,000 divided by 12 = 150,000 gallons. Convert: 150,000 divided by 7.48 = 20,053.5 cubic feet. The footprint is 60 x 20 = 1,200 square feet, so the depth is 20,053.5 divided by 1,200 = 16.71 feet. Many state design rules call for at least 4 hours in conventional basins, so a real design would be checked against the state standard.

  9. Answer: 6.94 gallons per minute per square foot.
    1,249.2 gpm divided by 180 square feet = 6.94 gallons per minute per square foot.

  10. Answer: No, it is above the range.
    At 6.94 the filters run faster than the usual 2 to 6 gallons per minute per square foot, which shortens filter runs and pushes turbidity through sooner. Award full credit for a clear no with a reason tied to filter performance.

  11. Answer: 249.8 square feet.
    1,249.2 gpm divided by 5.0 gallons per minute per square foot = 249.84 square feet, which rounds to 249.8 square feet. That is about 70 square feet more than the plant has today.

  12. Answer: Either choice, supported by a number and two trade-offs.
    Award full credit for a clear choice, one number drawn from items 6, 8, 9, or 11, and two genuine trade-offs. Strong answers for deepening the basin note that better settling sends less load to the filters, which lengthens filter runs even though the loading rate stays at 6.94, while excavation is costly and the basin must be taken offline. Strong answers for filter area note that only added filter area brings the 6.94 loading rate back inside the 2 to 6 range, while more filters take building space the slab may not have and add backwash water to handle. Deduct for a choice with no number attached.

  13. Answer: B.
    138 feet x 0.433 psi per foot = 59.75 psi, which is closest to 60 psi. Students who choose D multiplied by 2.31, which converts psi into feet rather than feet into psi.

Differentiation

Support

Give these students a formula sheet listing the four conversions with one worked example each, using numbers different from the test. Allow items 6 and 8 to be answered with the setup shown and the arithmetic completed by calculator without intermediate rounding. Provide a printed number line marked with the 2 to 4 hour range and the 2 to 6 loading range for items 7 and 10.

Extension

Ask these students to size the sedimentation basin at the fictional Quennfield plant for a future flow of 2.5 MGD while holding 2.0 hours of detention, and to report the footprint that would require if the depth is capped at 14 feet. Then have them write a paragraph on whether the district should build for today's flow or for the future flow, naming the cost of each choice.

ELL supports

Pre-teach detention time, loading rate, criterion, and constraint with a labeled plant diagram showing the basin, the filters, and the clearwell in order. Provide the sentence frame "The answer is ___ because the volume is ___ and the flow is ___" for item 6. Allow items 7 and 10 to be answered with yes or no plus a phrase rather than a full sentence.

Extensions

Have students turn items 6 through 11 of this fictional scenario into a one-page memo to a plant superintendent, stating which of the two findings is more urgent and why. Ask them to include one table showing the calculated value, the published design range, and the gap between them for both the basin and the filters. Students can then draft the single sentence they would put at the top of the memo so a busy reader learns the recommendation first.