Shock Chlorination
There is a chance of bacterial contamination any time
there is a new well or a water system fixture such as a pump is removed from
a well and replaced. Bacterial problems are most common in shallow wells
and areas with coarse textured soils and fractured bedrock or limestone. The
major source of contamination is surface water, or septic tanks or sewage lines located too close
to the well. Runoff or leaching from livestock operations can also contaminate
wells.
Shock chlorination procedure:
- Select a time when well water will not be used for at least 24 hours.
Store enough drinking water for this period or do the procedure before
leaving for a short trip
- Determine how much laundry bleach
or dry calcium hypochlorite tables are needed. This depends on the diameter
of the well and the height of standing water in the well. The height of
standing water is the difference between the well depth and the distance
from the top of the well down to the water level. Recommended amounts of laundry bleach are shown
within the table below.
If iron bacteria are
a problem, concentrations of 800 milligrams per liter may be necessary.
- Mix the proper amount of
chlorine with water in a 5-gallon or larger
container and pour the solution directly into the well.
- Turn on the outdoor faucet nearest the well and let the water run until a
strong odor of chlorine is detected.
- Turn the faucet off. Connect a garden hose to the faucet and attach a
spray nozzle to the end of the hose. Thoroughly wash down the entire inside
surface of the well casing with the spray nozzle for at least 15 minutes.
- After washing the inside of the well casing, turn on all outdoor and
indoor faucets one at a time until a strong chlorine odor is detected at
each location. Turn each faucet off when the chlorine odor is detected
- Let the chlorinated water stand in the well and plumbing for at least 24
hours. Do not drink the chlorinated water during this period. You may
flush the toilets, but try to minimize the number of flushes.
- After 24 hours, completely flush the system of chlorine by turning on all
outdoor faucets and running them until the chlorine odor is gone. Do not
run the indoor faucets until the odor dissipates to prevent damage to the
septic system. Caution: Do not
allow more than 100 gallons to flow from system faucets and drains into the
septic tank
- Finally, turn on the indoor faucets until the
chlorine odor is gone. You
may notice a slight chlorine taste or odor in the water for a few days.
Test the water for bacteria two weeks after shock chlorination to see if you
have a recurring problem. Contact your local Health Department for information
on water testing and well protection.
Shock chlorination can be done using ordinary
laundry bleach (containing approx. 5.25 percent sodium hypochlorite right out of
the jug) or calcium hypochlorite (containing 65%-75% available chlorine). The goal is to add
enough chlorine to raise the chlorine concentration in the well to about 200 milligrams
per liter to kill potentially harmful bacteria and viruses.
A thorough shock chlorination of
the well and water system may destroy all iron bacteria colonies. However,
if
iron bacteria have penetrated the water-bearing formation they will be
difficult to eliminate and will likely re-infest the system. In this
situation you will need to repeat chlorination treatment periodically.
|
DUG
WELL (3’ Diameter)
|
DRILLED
WELL (6” Diameter)
|
|
Water
Depth
|
Bleach
5%
|
Water
Depth
|
Bleach
5%
|
|
Feet
|
Metres
|
Quarts
|
Litres
|
Feet
|
Metres
|
Ounces
|
ml
|
|
5
|
1.5
|
1
|
1.1
|
25
|
7.6
|
5
|
140
|
|
10
|
3.0
|
2
|
2.2
|
50
|
15.0
|
10
|
280
|
|
15
|
4.5
|
3
|
3.3
|
75
|
22.8
|
15
|
420
|
|
20
|
6.0
|
4
|
4.4
|
100
|
30.0
|
20
|
560
|
|
25
|
7.5
|
5
|
5.5
|
125
|
38.0
|
25
|
700
|
|
30
|
9.0
|
6
|
6.6
|
150
|
45.0
|
30
|
840
|
|
35
|
10.5
|
7
|
7.5
|
175
|
53.0
|
35
|
980
|
|
40
|
12.0
|
8
|
8.8
|
200
|
61.0
|
40
|
1220
|
| 
