Math and Calculations Practice Questions for Washington Level I

1. Question 1

   A treatment plant receives 0.75 million gallons per day. What is the flow in gallons per day?

   1. 750 gallons per day
   2. 7,500 gallons per day
   3. 75,000 gallons per day
   4. 750,000 gallons per day
   Show the answer

   Answer: D. 750,000 gallons per day

   One million gallons equals 1,000,000 gallons, so 0.75 MGD equals 750,000 gallons per day. Calculation: 0.75 × 1,000,000 = 750,000 gallons per day.

2. Question 2

   Influent BOD is 200 mg/L and effluent BOD is 40 mg/L. What is the BOD removal?

   1. 20%
   2. 40%
   3. 80%
   4. 160%
   Show the answer

   Answer: C. 80%

   The plant removes 160 mg/L from an influent concentration of 200 mg/L. Dividing the amount removed by the influent concentration gives 0.80, or 80%. Calculation: ((200 − 40) ÷ 200) × 100% = 80%.

3. Question 3

   An aeration basin holds 500,000 gallons and receives a flow of 1.0 million gallons per day. What is the detention time in hours?

   1. 0.5 hours
   2. 12 hours
   3. 24 hours
   4. 48 hours
   Show the answer

   Answer: B. 12 hours

   Dividing basin volume by daily flow gives 0.5 day. Converting one-half day to hours gives 12 hours. Calculation: 500,000 gal ÷ 1,000,000 gal/day = 0.5 day; 0.5 day × 24 hr/day = 12 hours.

4. Question 4

   A plant treats 1.0 MGD with an influent BOD concentration of 150 mg/L. What is the BOD loading in pounds per day?

   1. 1,251 lb/day
   2. 150 lb/day
   3. 8.34 lb/day
   4. 12,510 lb/day
   Show the answer

   Answer: A. 1,251 lb/day

   The pounds formula combines flow in MGD, concentration in mg/L, and the 8.34 conversion factor to calculate the daily BOD mass loading. Calculation: 1.0 × 150 × 8.34 = 1,251 lb/day.

5. Question 5

   A plant flow is 1.44 MGD. What is the flow in gallons per minute?

   1. 1,440 gpm
   2. 10,000 gpm
   3. 1,000 gpm
   4. 694 gpm
   Show the answer

   Answer: C. 1,000 gpm

   Convert 1.44 million gallons to 1,440,000 gallons, then divide by 1,440 minutes per day to obtain 1,000 gallons per minute. Calculation: (1.44 × 1,000,000) ÷ 1,440 = 1,000 gpm.

Operator Master has 10 Level I math and calculations questions, free, with an explanation after every answer.

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