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Quiz & test questions Grade 9 Science

Cindermill's Next Water Source: Supply Gap, Reuse, and Cost per MGD

A 40-point grade 9 quiz on a fictional city's water supply gap, mixing multiple choice, computation, and short answer across reuse, wells, energy, and cost per MGD.

Objectives

  1. Students will calculate a city's supply deficit and convert it between MGD and gpm.
  2. Students will compute the energy and annual electricity cost of a proposed water reuse project.
  3. Students will compare two supply options on cost per MGD and identify a non-cost constraint.

Vocabulary

Indirect potable reuse
Recycling water into drinking water with a natural stop along the way. Highly cleaned water is put into the ground or a reservoir, then drawn back out later and treated again for drinking.

Also: safe yield, supply deficit, cost per MGD

Teacher overview

This quiz is worth 40 points and runs about one class period. It combines two multiple-choice items, nine computation items, and three short-answer items around a single scenario: a fictional inland city deciding where its next water will come from. Students calculate a supply deficit, size a reuse project against it, price the electricity that project would need, and compare two options on cost per million gallons per day. The final items ask for reasoning rather than arithmetic, so partial credit should follow the quality of the evidence a student cites rather than the conclusion they reach.

Cindermill's Next Water Source: Supply Gap, Reuse, and Cost per MGD — Grade 9 Science
Name: ____________________________ Date: ______________

Assessment

Use this information for every item. The fictional city of Cindermill sits in the Rill Valley and has 62,000 residents. The city uses 6.2 MGD of water. Its only local source is a groundwater basin with a safe yield of 4.5 MGD. The wastewater plant receives 3.0 MGD, and a proposed reuse project would recover 75 percent of that flow and return it to the drinking water aquifer. The reuse plant would use 2.6 kWh per 1,000 gallons treated, and electricity costs $0.10 per kWh. The reuse project would cost $46 million to build. A new well field farther up the valley would cost $28 million and supply 1.2 MGD. Use 694 gpm per MGD.

  1. (2 points) Which statement best defines the safe yield of a groundwater basin?
    A. The largest amount the wells can physically pump in a single day.
    B. The amount that can be withdrawn year after year without drawing the aquifer down over the long term.
    C. The amount of water the city is permitted to sell to customers.
    D. The amount of water left after treatment losses are subtracted.
  2. (3 points) Cindermill uses 6.2 MGD for 62,000 residents. Find the average use in gallons per person per day.
  3. (3 points) Find the gap between the city's use of 6.2 MGD and the basin's safe yield of 4.5 MGD.
  4. (3 points) Convert the gap from item 3 into gallons per minute, using 694 gpm per MGD. Round to the nearest tenth.
  5. (3 points) The wastewater plant receives 3.0 MGD, and the reuse project would recover 75 percent of that flow. How much water would the project return, in MGD?
  6. (2 points) How much larger is the reuse project's yield from item 5 than the gap you found in item 3?
  7. (4 points) The reuse plant would use 2.6 kWh for every 1,000 gallons it treats. Using your answer from item 5, find its daily electricity use in kWh.
  8. (4 points) Electricity costs $0.10 per kWh. Using your answer from item 7, find the plant's electricity cost for a 365-day year.
  9. (2 points) Cindermill's engineers report that conventional treatment and delivery uses about 1 to 2 kWh per 1,000 gallons, seawater reverse osmosis uses about 11 to 15 kWh per 1,000 gallons, and the proposed reuse plant would use 2.6 kWh per 1,000 gallons. Which statement is best supported?
    A. The reuse plant would use less electricity per 1,000 gallons than conventional treatment.
    B. The reuse plant would use more electricity per 1,000 gallons than conventional treatment and less than seawater reverse osmosis.
    C. The reuse plant and seawater reverse osmosis would use about the same electricity per 1,000 gallons.
    D. All three use about the same electricity per 1,000 gallons.
  10. (3 points) Groundwater is the only local source in the Rill Valley. Using the numbers in this scenario, explain how the limits of that basin have shaped how large Cindermill could grow and what the city can build next.
  11. (3 points) The reuse project would cost $46 million and supply the yield you found in item 5. Find its cost per MGD of new supply, in millions of dollars. Round to the nearest tenth.
  12. (3 points) The new well field would cost $28 million and supply 1.2 MGD. Find its cost per MGD of new supply, in millions of dollars. Round to the nearest tenth.
  13. (2 points) Based on items 11 and 12, which option delivers new water at the lower cost per MGD?
  14. (3 points) Name one constraint other than construction cost that Cindermill should weigh before approving the reuse project, and explain why it matters.

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: B. Safe yield is the withdrawal a basin can sustain year after year without long-term drawdown. Choice A describes pumping capacity, which is usually larger, and choices C and D describe permits and treatment losses rather than the behavior of the aquifer.
  2. Answer: 100 gallons per person per day. 6.2 MGD is 6,200,000 gallons per day, and 6,200,000 divided by 62,000 residents equals 100 gallons per person per day.
  3. Answer: 1.7 MGD. 6.2 MGD minus 4.5 MGD equals a 1.7 MGD gap between use and safe yield.
  4. Answer: 1,179.8 gpm. 1.7 MGD times 694 gpm per MGD equals 1,179.8 gpm.
  5. Answer: 2.25 MGD. 3.0 MGD times 0.75 equals 2.25 MGD returned to the aquifer.
  6. Answer: 0.55 MGD. 2.25 MGD minus 1.7 MGD equals 0.55 MGD more than the gap requires.
  7. Answer: 5,850 kWh per day. 2.25 MGD is 2,250,000 gallons per day, which is 2,250 units of 1,000 gallons, and 2,250 times 2.6 kWh equals 5,850 kWh per day.
  8. Answer: $213,525. 5,850 kWh per day times $0.10 per kWh equals $585 per day, and $585 times 365 days equals $213,525.
  9. Answer: B. At 2.6 kWh per 1,000 gallons the reuse plant sits above the 1 to 2 kWh range for conventional treatment and below the 11 to 15 kWh range for seawater reverse osmosis, which rules out the other three choices.
  10. Answer: Accept any explanation supported by the scenario numbers. A full-credit response notes that the basin can supply only 4.5 MGD year after year while the city uses 6.2 MGD, so Cindermill has already grown past its sustainable local source by 1.7 MGD. Because there is no river or import available in the valley, any further growth depends on reusing water the city already has or on reaching farther up the valley for new wells, and both options cost tens of millions of dollars. Award partial credit for answers that cite the safe yield and the gap without connecting them to the choice ahead.
  11. Answer: $20.4 million per MGD. $46 million divided by 2.25 MGD equals 20.44, which rounds to $20.4 million per MGD.
  12. Answer: $23.3 million per MGD. $28 million divided by 1.2 MGD equals 23.33, which rounds to $23.3 million per MGD.
  13. Answer: The reuse project. At about $20.4 million per MGD it delivers new supply for roughly $2.9 million per MGD less than the well field at about $23.3 million per MGD.
  14. Answer: Accept any reasonable constraint with an explanation. Examples include the electricity the reuse plant would need, since it adds about $213,525 a year to operating costs; public acceptance of recycled water; the permits and monitoring a state requires for indirect potable reuse; the reliability of the wastewater flow itself, which falls when the city conserves; and the operator staffing and training the new process would require.

Differentiation

Support

Provide the scenario data as a labeled table rather than a paragraph, with the units written beside each value, and allow students to use a printed conversion card for the MGD-to-gpm conversion. Reduce the assigned set to items 1 through 8 and item 14 for students who need a shorter assessment.

Extension

Ask students to find the reuse project's total annual cost per million gallons delivered, combining the electricity cost from item 8 with the construction cost spread over 30 years, and to state which assumption in that calculation is most likely to be wrong.

ELL supports

Pre-teach yield, deficit, recover, and constraint using a simple diagram of the fictional city's supply, showing water in from the aquifer and water out to customers. Provide a sentence frame for items 10 and 14: "Cindermill cannot ___ because ___, so the city must ___."