The 41-year-old Republican was pulled over about 12:15 a.m. by a state highway patrol officer who allegedly noticed "a poor driving pattern," the Deseret News reported. Police said he failed a field sobriety test and then refused to breathe into a portable breath tester, the newspaper said.
"I could smell the odor of alcohol coming from the subject's breath," a trooper wrote in a probable cause statement.
Killpack issued a statement in which he said he is "deeply sorry for the impact this incident will have on those who support and trust me -- my colleagues in the Senate, my constituents and, most importantly, my family."
He added he is "prepared to accept all personal, legal and political consequences for my actions."
After Killpack was arrested, his car was impounded and he was booked into the Salt Lake County Jail on suspicion of DUI. Highway patrol officials obtained a warrant to allow them to take his blood. Results could take two to four weeks to obtain.
Senate President Michael Waddoups said Killpack's father was killed by a drunken driver when Killpack was a teenager. He also said he didn't know Killpack, who is a member of the Mormon Church, which frowns on drinking, was a drinker, the newspaper said.