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Chemical feed and solutions: California D3 water distribution operator math

Solution strength, specific gravity, dilution, blending, feeders, jar tests, chemical cost.

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 0.5 MGD system doses dry alum at 22 mg/L. It costs $0.41 per lb. What is the chemical cost per day?

  1. A) $224 per day
  2. B) $75.2 per day
  3. C) $91.7 per day
  4. D) $37.6 per day
Show the answer and worked solution

Answer: D) $37.6 per day

1. lbs/day = MGD × mg/L × 8.34 (the sheet's "ppm or mg/L" line solved for lbs) [Sheet p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"] = 0.5 × 22 × 8.34 = 91.74 lbs/day. 2. Cost/Day = Lbs/Day × Cost/lb [Sheet p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"] = 91.74 × $0.41 = $37.6134 per day. 3. Answer: $37.6 per day (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"; p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"

Example 2. A 4.5 MGD system doses dry hydrated lime at 12 mg/L. It costs $0.16 per lb. What is the chemical cost per day?

  1. A) $450 per day
  2. B) $64.6 per day
  3. C) $72.1 per day
  4. D) $8.64 per day
Show the answer and worked solution

Answer: C) $72.1 per day

1. lbs/day = MGD × mg/L × 8.34 (the sheet's "ppm or mg/L" line solved for lbs) [Sheet p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"] = 4.5 × 12 × 8.34 = 450.36 lbs/day. 2. Cost/Day = Lbs/Day × Cost/lb [Sheet p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"] = 450.36 × $0.16 = $72.0576 per day. 3. Answer: $72.1 per day (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"; p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"

Example 3. A 9.9 MGD system doses dry soda ash at 30 mg/L. It costs $0.41 per lb. What is the chemical cost per day?

  1. A) $2,480 per day
  2. B) $911 per day
  3. C) $122 per day
  4. D) $1,020 per day
Show the answer and worked solution

Answer: D) $1,020 per day

1. lbs/day = MGD × mg/L × 8.34 (the sheet's "ppm or mg/L" line solved for lbs) [Sheet p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"] = 9.9 × 30 × 8.34 = 2,476.98 lbs/day. 2. Cost/Day = Lbs/Day × Cost/lb [Sheet p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"] = 2,476.98 × $0.41 = $1,016 per day. 3. Answer: $1,020 per day (rounded to 3 significant figures).

Source: CA Exam Conversion Sheet (Revised 4/30/2026), p.2, Chemical Dosage Calculations: "ppm or mg/L = lbs / (MG x 8.34)"; p.1, Other: "Cost/Day ($) = Lbs/Day x Cost/lb ($)"

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