Who put the arsenic in our water?

Shawn Benner, PhD

Today I attended an interesting illustrated lecture about arsenic in ground water in Canyon County, where I live in Idaho. The speaker was Shawn Benner, Ph.D., assistant professor for the Department of Geosciences at Boise State University.

The maps he projected on the screen were compelling. In the area bounded by the Snake River, the Boise River, and the line between Canyon and Ada Counties, colored marks indicated arsenic pollution spread out over the whole area but especially the area immediately to the west of Caldwell.

In 1999 the highest level of arsenic acceptable in our drinking water was lowered from 50 parts per billion to 10 parts per billion. The levels were set because of observations linking an increased risk of cancer among people to their exposure to higher levels of arsenic. This brought dozens of wells in this part of the Boise basin into non-compliance with the Environmental Protection Agency.

Actually, Dr. Benner said, the evidence is overwhelming that it should be even lower, but the heightened risk was weighed against the cost of compliance, and the standard remains at 10 ppb.

How does arsenic get into our water?

Scientists don't know. They know that contamination is widespread throughout the area. They also know that it is "naturally" occurring and not the result of "dumping" or "mixing" arsenic compounds into our groundwater. Analysis indicates that arsenic levels are highest in the shallowest wells.

But where does it come from?

Dr. Benner and a formidable team of scientists and students are digging out the facts. They suspect that "surficial sediments" are a major source of arsenic in its mobile form. Arsenic that readily mobilizes is also common in shallow oxide-rich layers of soil and gravel.

So now I'm thinking...Maybe I should just write a book for the ordinary person about arsenic!

I've written to Dr. Benner expressing an interest in the subject. We'll see...