Nona wrote:

We recently made some repairs to our well. The pump gave out and was
replaced and the 6.25" steel casing was sleeved with a 4" PVC pipe to
attempt to reduce the amount of sediment and iron in the water. We
were told by the health department that we would need to shock
chlorinate the well after the repairs to destroy any bacteria. Since
there were no bacteria present prior to the repairs, we didn't think
we needed to do this.

Wrong - as you discovered. When you open the well, bacteria in the air and on
the material (pump, pipe & wiring) will contaminate the well.


We just got our water test results back and, sure enough, there is
coliform bacteria present in the water now (although fortunately no E.
coli).

Total Coliform is a tracer. Although not dangerous in itself, it's an indicator
that there could be other bacteria present that is dangerous. It's easier and
cheaper to test for total coliform.

We have been reading a lot about shock chlorination and the
instructions vary from site to site, with the chlorine to sit in the
system for anywhere from 12 to 48 hours. My first question is:

1) Is there any harm in leaving the chlorine in the system for 1 week
while we are on vacation and then flushing it when we return? Is 12
hours really long enough for this type of treatment?

No harm at all. The times quoted are minimums. The lower amounts are based on
ideal pH and temps. If you get outside the normal pH & temps, or if you have a
problem with iron, it takes longer to completely sanitize the well.