Water Well Disinfection

PURPOSE
Agricultural Labor Camps in Michigan are operated on a seasonal basis. The water supply systems at camps are often dismantled or drained when not in use. These practices increase the possibility of bacterial contamination entering the water system. New water systems can also be contaminated during the drill and construction process.

In response to these problems, the Michigan Safe Drinking Water Act requires water systems that fall into the above categories be disinfected before the system is placed in service. Further, a safe bacteria water sample must be obtained after disinfection (Rule 1110 [4], Act 399, Public Acts of 1976).

The simple low cost disinfection procedures below will eliminate bacteria contamination in water systems. Systems using centrifugal or shallow well jet pumps can usually be disinfected by the owner. Systems using other types of pumps, those with certain types of construction, and those with persistent contaminated water sample results should be disinfected by a licensed well driller or pump installer.

DISINFECTION INSTRUCTIONS

  1. The well should be pumped to waste until the water is as clear and free from turbidity as possible, as suspended matter in the well will reduce the amount of free chlorine available for disinfection purposes.

  2. Using Table 1, determine the amount of chlorine (liquid, tablet, or granular) required for disinfection. Add the chlorine to five (5) gallons of water.

  3. Slowly pour the chlorine solution into the top of the well. Allow a contact time of at least two hours.

  4. After this contact period, start the pump and discharge the chlorine solution throughout the household piping system. Starting with the tap closest to the well and working to the point furthest away from it, turn on each tap one at a time until the odor of chlorine can be detected, then turn off the tap. When all taps have been completed, the entire distribution system will contain chlorinated water. Leave the solution in the distribution system overnight if possible, but for at least two hours.

  5. Connect a hose to a tap and pump water back into the well casing. Wash the interior of the casing down thoroughly for approximately one hour. This circulates chlorinated water from the well to the pump, drop pipe, well discharge line, and distribution system, and back.

  6. After Step 5 is complete, pump to waste until the water is free of chlorine odor. Do not flush the water into a stream, river, or lake. A sample should then be collected from a tap near the well for bacteriological analysis.

TABLE 1

Casing Diameter

(Inches)

Depth of Water in Well

5 ¼% Unscented Bleach (Cups)

65% Hypochlorite

Gallons of Water Required**

Tablets*

Granules (Ounces)

1 ¼

50

½

2

½

3

2

50

1 ½

6

1

9

3

50

3 ¼

12

2

18

4

50

5 ¼

20

3a

32

5

50

8 ¼

28

4b

50

6

50

10

40

6b

75

*Based on 100 tablets per pound of hypochlorite compound.

**Gallons of water required for chlorine-water solution per 50 feet of water depth.