I think the statement "the naturally occurring release of arsenic from granite" in your article about the Deven's cleanup is an oversimplification that may mislead your readers. It sounds as though the arsenic was there all along, and we're forcing the Army to clean it up anyway. It also leads people with private wells -- like me -- to worry more than necessary.
After doing some research online, I found that most experts concur that some of the arsenic is naturally occurring, but it is only contaminating the water in large quantities because of the landfill's siting and operation. They also seem to think it quite possible that materials disposed of in the landfill, possibly from the tannery, are also leaching arsenic.
This is the most recent statement I found:
From ARSENIC SPECIATION AND GROUNDWATER CHEMISTRY AT SHEPLEY'S HILL LANDFILL, DEVENS, MASSACHUSETTS, March, 2012: https://gsa.confex.com/gsa/2012NE/finalprogram/abstract_199280.htm
"The primary source of arsenic has not yet been conclusively determined and likely involves a combination of the landfill waste material, the peat, and/or the underlying overburden sequence."
It appears to be a complex problem, and I understand that most of your audience isn't interested in "the assessment of geochemical changes along a gradient path..." but perhaps a bit more explanation would be appropriate.