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Disinfecting Your Drilled Well
There are a number of reasons why bacteria may be present in your well water. Disinfecting the water system will kill bacteria that have entered the system due to new well construction, installation or replacement of the well pump, or plumbing repairs.
Chlorinating the well will not provide a permanent solution to an ongoing contamination problem. This process only destroys existing bacteria. If bacteria are detected after chlorination, that is evidence that contamination continues to enter the system, and that some problem exists with the ground water, well, storage, or plumbing. If bacterial contamination persists after repeated disinfection of the well, repair or replacement of the well may be required. To properly disinfect your well, follow these steps:
Quantities of Disinfectant Required for Water Well Disinfection
(COMAR 26.04.04N (5))
Chlorine is available in both liquid (household or commercial bleach) or solid (available where pool supplies are found) forms. Liquid bleach tends to “float” in a well, granular solid chlorine may dissolve before reaching the bottom of the well, and chlorine tablets may sit on the bottom of the well and slowly dissolve, making it difficult to flush the chlorine out of the system. The most effective chlorination technique uses both liquid and solid forms. Use half of the quantity of solid chlorine shown plus half of the liquid volume shown for the depth of your well.
Well Depth |
4” Diameter |
6” Diameter |
8” Diameter |
20’ |
A 1T |
A 3T |
A 4T |
B 1C |
B 1C |
B 2C |
|
30’ |
A 2T |
A 4T |
A 4T |
B 1C |
B 2C |
B 4C |
|
40’ |
A 2T |
A 6T |
A 8T |
B 1C |
B 2C |
B 1Q |
|
60’ |
A 3T |
A 8T |
A 4oz |
B 2C |
B 1Q |
B 2Q |
|
80’ |
A 4T |
A 9T |
A 5oz |
B 2C |
B 1Q |
B 2Q |
|
100’ |
A 5T |
A 4oz |
A 7oz |
B 2C |
B 1Q |
B 2 ½Q |
|
150’ |
A 8T |
A 6oz |
A 10oz |
B 4C |
B 2Q |
B 4Q |
T = tablespoons, oz = ounces (by weight), C = cups, Q = quarts,
Rows A are amounts of calcium hypochlorite (Solid Chlorine, Granular or Tablets) (70%)
Rows B are amounts of liquid household bleach (5.25%)
Maryland Department of the Environment, Water Supply Program
1800 Washington Blvd, STE 450 · Baltimore MD 21230-1708
(410) 537-3729, (800) 633-6101 (in Maryland)