According to Clot :
Nona wrote:

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?

Absolutely none. A week should be good provided chlorinated to above 40
mg/l., I'd rather 100ppm - sorry mg/l. I am personally sceptical of only 12
hours soak dependent upon conditions. Take your vacation, enjoy, - and flush
on your return.

I'd say _probably_ none. While it's pretty darn dilute, chlorine does
attack copper and other metals. Very long dwell times may not be a good
idea, or at least, if you've guessed at the bleach amount, and put
in way too much.

The Ministry of Health of Ontario has the following detailed instructions
on how to shock a well:

http://www.health.gov.on.ca/english/...infection.html

The above says 12 hours. Previous iterations said 24 hours IIRC - they
must have had good reason to reduce it.

Ontario's MoH advisories of this type are pretty much on the ball, so I'd
trust the 12 hours given.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.