Well Drilling (C-57) · Lesson 5 of 6

Disinfecting a Well: Chlorine Dose from Table 6

"Disinfecting a Well: Chlorine Dose from Table 6" is lesson 5 of 6 in the Well Drilling (C-57) Learning Hub. It opens with "When Disinfection Is Required" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. When Disinfection Is Required
  2. The Dose: 50 mg/L or 100 mg/L
  3. Scale Table 6 to the Water Column
  4. The Disinfection Procedure
  5. Gravel and Lubricants

The worked example in the course applies this lesson to a realistic job in 7 steps.

What you'll be able to do

  • Explain the main idea of "Disinfecting a Well: Chlorine Dose from Table 6" in plain language you can use on the exam.
  • Apply this step with confidence: "Scale Table 6 to the Water Column".
  • Apply this step with confidence: "The Disinfection Procedure".
  • Apply this step with confidence: "Gravel and Lubricants".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Well Disinfection Dose from Table 6Ground surface8-in casingStatic level85 ftChlorinatedwaterWatercolumn240 ftTotal depth 325 ftWORKED EXAMPLE: PUMP REPLACEDTable 6, 8-in casing, per 100 ft at 50 mg/L:70% calcium hypochlorite: 3 oz5.25% sodium hypochlorite: 2-1/8 ptWater column = 325 - 85 = 240 ft = 2.4 x 100 ftAt 50 mg/L: 3 x 2.4 = 7.2 ozAt 50 mg/L: 2.125 x 2.4 = 5.1 ptPump work, 100 mg/L: double the amountsCalcium hypochlorite: 14.4 ozSodium hypochlorite: 10.2 pt (about 1.3 gal)Then: stand 24 h, pump to waste, lab sampleDose 14.4 oz of 70% calcium hypochlorite (or 10.2 pt of 5.25% bleach)Stand 24 h, pump to waste until no chlorine, then bacteriological sampleSource: DWR Well Standards (Bulletin 74-90/74-81), Sec. 11.A and Appendix D (Procedures for Disinfecting Wells), Table 6CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: When Disinfection Is Required

Section 11.A of the DWR Well Standards (Bulletin 74-81 as supplemented by Bulletin 74-90, Part II) says all wells producing water for domestic use, meaning drinking or food processing, shall be disinfected following construction, repair, or when work is done on the pump, before the well is placed in service. Appendix D (Suggested Procedures for Disinfecting Wells) calls disinfection the final act of construction or repair. For a new well it should follow development, yield testing, and pump installation.

Step 2: The Dose: 50 mg/L or 100 mg/L

Appendix D, step 1, requires a chlorine solution containing at least 50 mg/L (parts per million) of available chlorine added to the well. Table 6 lists the quantities of several chlorine compounds needed to dose 100 ft of water-filled casing at 50 mg/L, for casing diameters from 2 to 24 in. For a repaired well, or when a pump has been repaired or replaced and the well must return to service quickly, the solution should contain at least 100 mg/L, which you get by doubling the Table 6 amounts.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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