The Hanover Water Works Company claims two months of reorganization and monitoring have cleaned up the water supply since coliform bacteria were discovered in the water supply in July.
Hanover Water supplies water to much of the Hanover area -- including Dartmouth. Every month, the company sends a sample of its water to the New Hampshire Department of Environmental Services.
Samples tested in early August again showed a presence of bacteria.
Rick Skarinka, a sanitary engineer with the DES, said coliform bacteria is not harmful to humans, but its presence in the water supply may indicate that more harmful bacteria are in the system.
Carl Long, president of Hanover Water, said the company responded to the bacteria supply by flushing modified disinfectant through their distribution system.
The bacteria resurfaced after an initial flushing in July, but all the following samples -- taken in August, early September and mid-September-- showed no signs of bacteria, Long said.
Long said the company will send in their October sample next week and expects the water to be clean.
Skarinka said Hanover Water worked hard to correct the bacteria problem but the DES is still uncertain as to the cause of the problem.
"The issue with the bacteria, we're not convinced it's completely solved," he said. "There was no clear pattern or indication to point us towards a specific solution or a specific source of the problem."
The contact tank, which is the source of the water, contains no bacteria. The bacteria appeared after the water traveled thorough the distribution pipes, Long said.
"It must be picking up the bacteria somewhere in between but we don't know where, why or how," he said.
Skarinka said the DES also did not believe that the bacteria was related to the water source.
Hanover Water has a waiver that allows it not to have a filtration system at its water source, Skarinka said.
Instead, it cleans its water with a chlorine dioxide disinfecting system that adds chemicals to the water.
"If there was a problem with the source, the waiver would be in jeopardy," Skarinka said.
Long said tubercles, rust-like deposits that accumulate on pipes, may be sites of bacteria deposits.
"Some pipe was initially four inches [in diameter] and growth has extended an inch from the walls reducing it to two inches," Long said.
Skarinka said he believed the distribution piping was the cause of the bacteria growth.
"Hanover has quite a bit of distribution piping," he said. "Over the years, 50 to 100 years for some of those piping, on the inside you get deposits that have settled there over the years."
Coliform bacteria is tasteless and colorless, Skarinka said.
"If the water was discolored, you might be concerned there was a problem but with the bacteria, you cannot see or taste the difference," he said.
"It is the same as if you went out to a mountain spring: it is crystal clear and ice cold, but could have a substantial amount of bacteria in it," he added.
Long said the company tests for e. coli bacteria in addition to coliform bacteria.
"The one harmful bacteria that can raise Cain with the system is e. coli," Long said. "There have been some outbreaks of e. coli in other places but none in Hanover."
To address problems with the water distribution system, Hanover Water hired an engineering consultant who developed a report with many recommendations -- some that the company implemented, Skarinka said.
"It's a preventative maintenance program that they are implementing," he said.
Dartmouth pays about $55,000 every term for water, Long said. The College uses about 25 percent of the water distributed by Hanover Water.
