We have also researched Powell's connection to Cape Girardeau. Slight correction, he was a lieutenant in the 20th Illinois which was raised in NE Illinois, from Bloomington up to Rockford. German engineers Franz Kappner and Henry Flad laid out locations for the forts. Work on Fort A commenced first but on August 6, 1861 work began on Fort D. A soldier (Allen M. Geer) wrote that it was engineered by Powell, so we have a good idea that Powell at least did the layout of the fort, using a standard French design for a redan. After Grant took command in Cape, he put Powell in charge of finishing all the forts.

I have lots more information available. My wife and I are also Powell followers, having just been to the Powell Museum in Page, AZ...