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Chlorination and CT: California D1 water distribution operator math

Chlorine feed, demand and residual, hypochlorite, well and main disinfection, CT, chloramines.

Below are 3 worked examples. Each answer is computed with the formulas and constants on the CA Exam Conversion Sheet (revised 4/30/2026), and the solution names the line it uses.

Formulas from the sheet for this topic

Example 1. A well pumps 2,900 GPM around the clock. How many lbs/day of chlorine are needed for a dose of 0.8 mg/L?

  1. A) 55.8 lbs/day
  2. B) 34.9 lbs/day
  3. C) 27.9 lbs/day
  4. D) 43.1 lbs/day
Show the answer and worked solution

Answer: C) 27.9 lbs/day

1. Flow = 2,900 ÷ 694.4 = 4.176 MGD [Sheet p.1, Units and Conversion Factors, row 29: "1 MGD = 694.4 GPM"]. 2. Gas (lbs) = MG × mg/L × 8.34 [Sheet p.1, Chlorination: "Gas (lbs) = MG x mg/L x 8.34"] = 4.176 × 0.8 × 8.34 = 27.86 lbs/day. 3. Answer: 27.9 lbs/day (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.1, Units and Conversion Factors, row 29: "1 MGD = 694.4 GPM"; p.1, Chlorination: "Gas (lbs) = MG x mg/L x 8.34"

Example 2. A chlorinator fed 182 lbs of chlorine in one day to a flow of 10.9 MGD. What was the dose in mg/L?

  1. A) 16.7 mg/L
  2. B) 2.00 mg/L
  3. C) 139 mg/L
  4. D) 2.23 mg/L
Show the answer and worked solution

Answer: B) 2.00 mg/L

1. mg/L = lbs ÷ (MG × 8.34) [Sheet p.1, Solutions: "mg/L = lbs / (MG x 8.34)"] = 182 ÷ (10.9 × 8.34) = 182 ÷ 90.906 = 2.002 mg/L. 2. Answer: 2.00 mg/L (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.1, Solutions: "mg/L = lbs / (MG x 8.34)"

Example 3. A well pumps 3,325 GPM around the clock. How many lbs/day of chlorine are needed for a dose of 2.7 mg/L?

  1. A) 12.9 lbs/day
  2. B) 4.49 lbs/day
  3. C) 167 lbs/day
  4. D) 108 lbs/day
Show the answer and worked solution

Answer: D) 108 lbs/day

1. Flow = 3,325 ÷ 694.4 = 4.788 MGD [Sheet p.1, Units and Conversion Factors, row 29: "1 MGD = 694.4 GPM"]. 2. Gas (lbs) = MG × mg/L × 8.34 [Sheet p.1, Chlorination: "Gas (lbs) = MG x mg/L x 8.34"] = 4.788 × 2.7 × 8.34 = 107.8 lbs/day. 3. Answer: 108 lbs/day (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.1, Units and Conversion Factors, row 29: "1 MGD = 694.4 GPM"; p.1, Chlorination: "Gas (lbs) = MG x mg/L x 8.34"

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