That ten-fold increase in drug arrests at George Mason University? The campus’s police chief pins it, in part, on an unusual culprit: A Grateful Dead spin-off band.

And Soundgarden.

Chief Mike Lynch says drug arrests at Patriot Center concerts are driving the upswing. The number of people being picked up for narcotics offenses in the Fairfax campus’s public spaces jumped from 11 in 2009 to 120 in 2011, according to a new report.

Lynch said there has not been an effort to crack down on drugs at the Patriot Center, but police step up enforcement during concerts they believe will draw more drug use.

And, he says, there were more of those type of shows in 2011.

One such concert was by Furthur, a band formed by former members of the Grateful Dead. Lynch said roughly 40 of those 120 arrests in 2011 came at the band’s Patriot Center show in March. Lynch said the Soundgarden concert in July also drew a significant number of arrests.

There is also another factor at work.

“We have a bigger residence population than ever before,” Lynch said.