HARRISON — Two tests on the Harrison Elementary School well water have come back positive for coliform bacteria, Oxford Hills School District Facilities Manager Dave Marshall said.

“Two were positive; one was negative. We’ll have to shock the well,” Marshall said Friday. The procedure using bleach or chlorine is expected to take place over the weekend.

Two tests last week also came back negative for coliform bacteria. The state requires five negative tests for the water to be considered contaminant free, Marshall said.

Students at the school have been drinking bottled water as a precautionary measure since the start of school. Coliform bacteria was found in four of five water samples tested on Aug. 24.

The state did not require a “boil water” or “do not drink” order, but school officials decided to bring in bottled water, donated by Poland Springs, as a precautionary measure.

Marshall said it appeared the coliform bacteria contaminant has to do with the source — the water in the well — and not an outside factor such as a crack in the well casing that might have allowed contaminants to leach in through the ground.

Roger Crouse of the Maine Center for Disease Control said usually systems such as the one at the Harrison school are contaminated with coliform bacteria because there is something wrong with the system — either a well is improperly constructed or perhaps there has been a change in plumbing and a contaminant has been introduced.

“There are very few cases where the groundwater is contaminated,” he said.

Whenever coliform is present in the water, a subsequent analysis is done to see if E. coli is present. If that test comes back positive, Crouse said a “boil water” order is issued immediately because the test indicates the presence of fecal matter in the water. That was not the case in Harrison.

“Surface contamination is not an imminent risk to public health,” Crouse said. The presence of E. coli would be considered an immediate threat.

However, the acceptable standard for coliform bacteria is zero, he said. “You need to get it out.” If it can be determined how the contaminant is getting into the system, it can be fixed; otherwise the system is shocked with bleach or chlorine.

“We’re shocking the whole water system,” Crouse said. “It goes through all the tabs; you let it sit, then you flush it out. Maybe the well water doesn’t have (the contaminant) but the plumbing could.”

In September 2008, the quarterly testing of the Harrison school water supply showed the presence of coliform, and although the contaminant was ousted with bleach, further testing showed the presence of uranium. Officials at the time said uranium is commonly found in drilled wells in this part of the state.

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