Flushing water mains to rid water of manganese probably removes many other contaminants, including aluminum, lead, arsenic and nickel, a new Madison Water Utility report suggests.

The utility received the report Thursday from engineering consultant Abigail Cantor. It analyzes data from samples taken from six hydrants in March, when the city began flushing the mains.

Though some of the readings were above advisory levels, that's not necessarily worrisome because the concentrated matter stripped from pipes during high-pressure flushing is expected to have high levels of such pollutants, said David Denig-Chakroff, general manager of the utility.

The manganese levels in the flushed water, for example, were hundreds of times higher than those found in recent months in tap water.

The utility soon will test tap water for the other contaminants in parts of the city that have had manganese problems, Denig-Chakroff said.

Such testing, which hasn't been done before in Madison, would indicate whether the water people drink has elevated levels of these substances, Denig-Chakroff said.

"It's part of our whole effort to learn as much as we possibly can about the water system," he said.

What the city learned from the samples taken in March is that hydrants with the highest manganese levels tend to have the highest levels of the other contaminants. That is likely because the contaminants bind to manganese in the residue left on pipes, Denig-Chakroff said.

The residue "acts as a 'water treatment' system to remove leached chemicals from the water," wrote Cantor, of Process Research Solutions in Madison.

Two hydrants were tested from each of the three wells that have had manganese problems: No. 3 on the east side of the Isthmus, No. 10 in the Nakoma area and No. 29 on the Far East Side.

At least one hydrant from each well tested above the health advisory standard for arsenic.

Both hydrants from well No. 10 and one from well No. 3 tested above the "action level" for lead, meaning action would be recommended if such levels were found at the tap.

The hydrants from well No. 10 were above the lifetime health advisory level for nickel.

One hydrant from well No. 10 had an aluminum level exceeding the aesthetic standard, meaning such water might taste bad or be discolored at the tap.

Denig-Chakroff stressed that the findings from the hydrants are a guide for utility workers to better understand the effect of the flushing, not signs that the water residents drink definitely contains the contaminants.

"They don't have any correlation to what you might find at the tap," he said.