Disinfecting Dug Wells

Thanks for visiting this part of Maida New Hampshire & Massachusetts Home Inspection Services educational series on Disinfecting Dug Wells. Maida Services, Inc. does not provide well disinfection for private water supplies. However, we have provided the content below for your information.

How do I disinfect a bored or dug well?

Calculate the amount of disinfectant needed by using the calculation table provided below.

CHLORINE BLEACH FOR A BORED OR DUG WELL
Diameter of well (in feet)	Amount of 5.25% laundry bleach per foot of water	Amount of 70% chlorine granules per foot of water
3	1 1/2 cups	1 ounce
4	3 cups	2 ounce
5	4 1/2 cups	3 ounce
6	6 cups	4 ounce
7	9 cups	6 ounce
8	12 cups	8 ounce
10	18 cups	12 ounce

• Measure the diameter of the well, and round the measurement to the nearest foot.
  (Example: 5.3 feet = 5 feet; 5.7 feet = 6 feet)
• Find the amount of chlorine bleach needed to disinfect each foot of water for the diameter well that you have measured. For example, the amount for a 5-foot diameter well would be 4-1/2 cups per foot.
• Determine the depth of the well in feet.
• Multiply this measurement by the computed amount of bleach to use. For a 5 foot diameter, 40 foot deep well:
  1. Go to the chart that shows 4-1/2 cups of chlorine bleach per foot of water for a 5-foot diameter well.
  2. Next multiply the 4-1/2 cups of chlorine bleach by the 40-foot depth of the well.
  3. The total amount of chlorine bleach needed would be 4-1/2 times 40 or 180 cups of ?chlorine bleach. This is equal to 11.25 gallons using the conversion of 16 cups in one gallon.
• Use an appropriately sized, clean container and pour the measured volume of chlorine bleach into the well.
• While pouring the chlorine bleach, try to splash some around the wall or lining of the well.
• Seal the well top.
• Open all faucets and pump the water until a strong odor of bleach is noticeable at each faucet. Then stop the pump and allow the solution to remain in the well overnight.
• The next day, turn on all the faucets and run the pump until all of the chlorine odor disappears. Be sure to adjust the flow of the water faucets or fixtures to a level that avoids overloading the septic system.
• After 5 days of normal usage, test water for coliform.