MADISON, Wis. -- A troubled city well serving the Isthmus area has been completely shut down after a cancer-causing agent tested above an Environmental Protection Agency standard. The Madison Water Utility closed off Well 3 Tuesday -- the same day a test for carbon tetrachloride came back at 6.4 parts per billion.

The federal drinking water standard is 5 parts per billion.

Technically, there's no violation until three consecutive tests average above that standard, and officials said that's not the case right now.

But Water Utility officials said they were planning on shutting down the well for the winter anyway due to high manganese levels.

"So, we decided we would just shut it down now and take it out of service and then, over the winter, try to determine what can do to deal with that elevated tetrachloride levels," said David Denig-Chakaroff, manager at the Madison Water Utility.

The utility manager said three other wells -- Wells 8, 10 and 29 -- with higher manganese levels will also be shut down by the end of the month for the winter.

Options for Well 3 include drilling a new well, buying expensive treatment or permanently shutting it down.