| This issue of Franklin Aid discusses
chlorination of water wells only in the context of possible adverse
effects to submersible motors if caution is not exercised. This issue
is not meant to serve as an all-inclusive procedure for chlorinating
wells. This would be impossible since specific requirements and regulations
vary by state and locality. For additional information on correct
chlorination procedures, please contact your local health department
or your State Department of Natural Resources.
Chlorination of new and existing water wells is
a common practice in our water systems industry. Chlorination disinfects
water supplies and kills bacteria, which may be present in the well
or was introduced into the well during normal drilling and casing
operations. Ideally a water well should be chlorinated without a
submersible water system installed, but this is not always practical.
When chlorine solutions are introduced into a water
well, hypochlorus acid (HClO) and hypochorite ions (ClO-) are formed.
These two oxidizing agents perform the disinfecting process. Unfortunately,
these two agents are very corrosive and can cause corrosion damage
to submersible motors, pumps, metal piping and metal casings if
these components are left in contact with the chlorine solution
for very long.
The amount of chlorine solution required to disinfect
water wells is normally quite small, ranging from one to six parts
per million. As an example, if a 5.25% chlorine solution, as described
below, were used at a rate at one part per million, one gallon of
solution would treat about 50,000 gallons of water. Also, the actual
time of exposure required is normally very short. Once the chlorine
solution is fully circulated throughout the water well, it completes
its disinfecting job in a matter of minutes.
Local health department requirements and guidelines
should always be followed, and consideration should be given as
to how much chlorine solution is really required to disinfect the
well.
The following lists the types of
chlorine solutions normally used in disinfecting water wells and
the suggested maximum exposure time for each:
1) Sodium Hypochlorite (NaClO): Normally
sold as a water and chlorine solution and commonly used for laundry
bleaches. Sodium hypochlorites are typically available in two strengths,
“domestic” and “commercial”.
- a) Domestic: This is common, ordinary
household bleach and is available in stores under names like “Clorox”,
“Purex”, and others. It typically consists of a 5.25%
chlorine solution. Exposure time for submersible motors to these
agents should be limited to 2 – 3 days.
- b) Commercial: These bleaches are generally
available from chemical wholesalers and/or some hardware stores
and consist of 10% to 19% chlorine solutions (15% is very common).
Since the concentration levels are higher than household bleaches,
smaller amounts can be used to accom- plish the same task. Exposure
time for submers- ible motors to these agents should be limited
to 1 – 2 days.
2) Calcium Hypochorite (Ca(ClO)2):
This form of chlorine is normally sold as powders or tablets
and is available from chemical wholesalers or dairy supply houses
under names such as: “H.T.H.”, “Perchloron”,
among others.
They consist of 30% to 75% active chlorine by weight
with 65% mixtures being common. If these types of chlorine are merely
dumped into the well, they will probably come in contact with a
submersible motor before they dissolve. If they adhere to the motor
or merely collect in the bottom of the well they are likely to cause
corrosion damage as they dissolve. Powder or tablet forms of
chlorine should always be dissolved at approximately 1 part product
to 10 parts water before being introduced into the well. Exposure
times for submersible motors to these agents should be limited to
1 – 2 days.
In some cases, hydrochloric acid (HCl) is added
with chlorine solutions to lower the overall pH level and speed
the disinfecting process.
This practice is unnecessary and is not recommend
because the hydrochloric acid makes for a much more corrosive
mixture.
In all cases, the exposure time is much more important
than the type or amount of chlorine mixture used. These solutions
should never be left in contact with submersible motors any longer
than required and certainly not more than a few days. Extended contact
could start corrosion of the stainless steel outer materials, especially
in the welded seams. Once this corrosion starts, it can continue
even after the chlorine has been pumped off and can contribute to
early motor failures.
If these guidelines are followed, chlorinating a
well should have no adverse affects on your submersible motor.
|
