"While reading your June 23 article on the environmental monitoring being done in the Rogue River after the August 2010 removal of Gold Ray Dam, I saw no discussion about continuing studies of chromium-6. Are they still ongoing, or were they stopped as well?"

— John M., by email

The short answer, John, is kind of.

But before we get into that, let's refresh ourselves on what chromium-6, aka hexavalent chromium, is and why it popped up in one Gold Ray Dam study but not others.

Chromium-6 is an element found naturally in the western Cascade slopes but also the source of some industrial contamination elsewhere in the country.

It is found naturally in rocks, plants, soils and volcanic dust. Trace amounts have been found in rivers and streams of the western Cascades. It's sometimes also a byproduct of industrial waste and was the topic of the Erin Brockovich case in California and the ensuing movie about it.

In September 2010, an Environmental Protection Agency draft on chromium-6 effects on human health proposed classifying it as a likely cause of cancer in people when ingested over a lifetime.

Current studies are trying to determine a baseline threshold for what would be considered safe exposure levels, similar to other regulated carcinogens.

In recent years, concerns about chromium-6 levels have been raised at municipal water-treatment plants throughout the United States.

Before Gold Ray Dam was removed, Jackson County had the sediment in the reservoir upstream of the dam tested for several possible contaminants, including chromium. It was not specifically tested for chromium-6, but any chromium-6 would have shown up in the total chromium amount.

At that time, test results showed 0.8 micrograms/liter of total chromium, well below the federal standard of 100 micrograms per liter of total chromium, so no more testing was done, says John Vial, the county's roads and parks director.

Further testing of chromium, and chromium-6, was not paid for under the NOAA-Fisheries post dam-removal monitoring grant, Vial says. But the city of Grants Pass continues to test the Rogue water it takes in at its treatment plant and it provides Jackson County with that data, Vial says.

The highest level of chromium-6 measured there since the removal of Gold Ray Dam was 0.114 micrograms per liter, according to a March 2012 summary report on post-Gold Ray Dam monitoring.

Vial says there is no plan to monitor for it as part of the dam-removal studies. But as long as Grants Pass tests for it and supplies Jackson County with the data, it will be added to monitoring reports, Vial says.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by e-mail to [email protected]. We're sorry, but the volume of questions received prevents us from answering all of them.