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Classroom activity Grade 9 Careers & CTE

Sallowford Pretreatment Inspectors: A Discharge Permit Role-Play

A grade 9 careers role-play where three-person teams inspect three fictional industries, compute each discharge load in pounds per day, and decide the permit action.

Objectives

  1. Students will convert a discharge flow from gallons per day to million gallons per day.
  2. Students will calculate a pollutant load in pounds per day from a concentration and a flow.
  3. Students will decide whether a sampled discharge meets a stated local limit.

Vocabulary

Key words: pretreatment, local limit, discharge permit, loading, surcharge, notice of violation

Teacher overview

A wastewater utility does not only treat what arrives at the plant; it also writes and enforces permits for the factories, bakeries, and shops that send it strong waste. In this role-play, teams of three staff the pretreatment program of the fictional Sallowford Water Reclamation District and work three industrial files in turn, with the inspector, sampling technician, and permit writer roles rotating each round. The rotation mirrors the actual sequence of the job, because a permit decision cannot be made until the sample result and the flow have been combined into a load. The common misconception this role-play corrects is that a discharge is judged by its concentration alone; a small flow carrying a high concentration and a large flow carrying a lower one deliver very different pounds to the plant, which is why a district tracks both.

Activity Directions

  1. Before class, print the three industry file cards (one per round, copied from that round's section of the Student Handout), three role cards for each team (one role description from step 2 on each), and one Student Handout per student. Post the fictional Sallowford local limits where every team can see them: zinc at 2.0 mg/L, oil and grease at 100 mg/L, and a high-strength surcharge on any BOD above 300 mg/L at a rate of $0.24 per pound of excess per day.
  2. Open by naming the three roles. The inspector visits the site and describes the process, the sampling technician records the flow and the laboratory result, and the permit writer states the district's action. Explain that all three are real jobs inside a pretreatment program.
  3. Form teams of three and assign the first set of roles. Every student keeps a handout and answers every question, though the team works each file together.
  4. Round 1 covers Quillmore Metal Finishing, a fictional plating shop. Hand out its file card, set a twelve-minute timer, and have teams work Questions 1 through 4.
  5. Rotate roles clockwise within each team, then run Round 2 on Larkmead Bakery, a fictional wholesale bakery whose rinse water is high in organic material. Teams work Questions 5 through 8 in twelve minutes.
  6. Rotate roles a final time and run Round 3 on Ivyburn Truck Wash, a fictional washing bay, with Questions 9 and 10 in eight minutes.
  7. End the role-play when all three files are closed and each team has written one sentence of action for each industry: in compliance, notice of violation, or surcharge invoice.
  8. Close with a ten-minute debrief. Ask why the fictional Sallowford district writes a limit for zinc in milligrams per liter but bills the bakery in pounds per day, and ask which of the two numbers tells the plant operator more about the load arriving at the headworks.
Sallowford Pretreatment Inspectors: A Discharge Permit Role-Play — Grade 9 Careers & CTE
Name: ____________________________ Date: ______________

Student Handout

Every flow, concentration, and limit below belongs to the fictional Sallowford Water Reclamation District. Pounds per day equals concentration in mg/L times flow in MGD times 8.34.

Round 1: Quillmore Metal Finishing

  1. Quillmore discharges 6,000 gallons per day to the sewer. Write that flow in million gallons per day.
  2. The zinc result for Quillmore is 3.4 mg/L at a flow of 0.006 MGD. How many pounds of zinc per day is that, rounded to two decimal places?
  3. The fictional Sallowford local limit for zinc is 2.0 mg/L, and the Quillmore sample reads 3.4 mg/L. By how many mg/L does the sample exceed the limit?
  4. Does the Quillmore discharge meet the 2.0 mg/L local limit for zinc?

Round 2: Larkmead Bakery

  1. Larkmead discharges 22,000 gallons per day with a BOD of 1,450 mg/L. Write the flow in million gallons per day, then find the BOD load in pounds per day, rounded to the nearest pound.
  2. The fictional district applies its high-strength surcharge to BOD above 300 mg/L. The Larkmead sample reads 1,450 mg/L. How many mg/L above the surcharge threshold is that?
  3. At the same flow of 22,000 gallons per day, how many pounds per day does the 1,150 mg/L of excess BOD represent, rounded to the nearest pound?
  4. The fictional surcharge rate is $0.24 for each pound of excess BOD per day. Using the 211 pounds per day from Question 7, what is one day of surcharge for Larkmead?

Round 3: Ivyburn Truck Wash

  1. Ivyburn discharges 4,800 gallons per day with 92 mg/L of oil and grease. How many pounds of oil and grease per day is that, rounded to two decimal places?
  2. The fictional Sallowford local limit for oil and grease is 100 mg/L, and the Ivyburn sample reads 92 mg/L. Does this discharge meet the limit?

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: 0.006 MGD.
    A flow of 6,000 gallons per day divided by 1,000,000 is 0.006 million gallons per day.
  2. Answer: 0.17 lbs/day.
    The product of 3.4 and 0.006 is 0.0204, and 0.0204 times 8.34 is 0.1701, which rounds to 0.17.
  3. Answer: 1.4 mg/L.
    The sample of 3.4 mg/L minus the fictional limit of 2.0 mg/L leaves 1.4 mg/L.
  4. Answer: No.
    At 3.4 mg/L the discharge sits above the 2.0 mg/L limit, so the permit writer issues a notice of violation.
  5. Answer: 266 lbs/day.
    The flow is 0.022 MGD, the product of 1,450 and 0.022 is 31.9, and 31.9 times 8.34 is 266.05, which rounds to 266.
  6. Answer: 1,150 mg/L.
    The sample of 1,450 mg/L minus the fictional threshold of 300 mg/L leaves 1,150 mg/L of excess.
  7. Answer: 211 lbs/day.
    The product of 1,150 and 0.022 is 25.3, and 25.3 times 8.34 is 211.00, which rounds to 211.
  8. Answer: $50.64.
    The 211 pounds per day times the fictional rate of $0.24 per pound gives $50.64 for one day.
  9. Answer: 3.68 lbs/day.
    The flow is 0.0048 MGD, the product of 92 and 0.0048 is 0.4416, and 0.4416 times 8.34 is 3.6829, which rounds to 3.68.
  10. Answer: Yes.
    At 92 mg/L the discharge sits below the fictional limit of 100 mg/L, so the file closes in compliance.

Differentiation

Support

Give these teams a conversion strip showing 6,000 gallons per day written as 0.006 MGD, and let them keep it for all three rounds of the fictional Sallowford files. Assign the sampling technician role first so the student begins by reading numbers rather than assembling a formula.

Extension

Ask these students what happens to the fictional Larkmead surcharge if the bakery installs a screen that cuts its BOD to 600 mg/L at the same flow, and whether the saving would be worth a monthly maintenance cost the team proposes.

ELL supports

Pre-teach pretreatment, local limit, load, and surcharge with a simple diagram showing one factory pipe joining a sewer main that reaches the plant. Provide a sentence frame for the permit writer: "This discharge is in compliance or in violation because the result of ___ is below or above the limit of ___."

Extensions

Ask a pretreatment coordinator from a nearby district to describe how a real inspection is scheduled and what an inspector looks for inside a building. Teams that finish early can draft a fourth file card for a fictional Sallowford dairy processor, choosing a flow and a concentration that place it just inside the local limit.