She said she has been working at polling locations for eight years.
Early balloting and mail-in voting may be responsible for lower-than-average turnout, election officials said.
The office of Lt. Gov. Greg Bell reported Monday that 73,350 already voted in the primary, or 4.9 percent of registered voters. Of them, 48,639 voted by mail and another 24,711 voted early at polling places.
Republicans statewide are deciding whether to hand Sen. Orrin Hatch the party's nod for a shot at a seventh term or give former state Sen. Dan Liljenquist a stab at a first term in Washington.
The winner of Tuesday's primary will face the Democratic nominee, former state Sen. Scott Howell, in the fall.
In Salt Lake County, GOP voters are choosing between West Valley City Mayor Mike Winder and former County Councilman Mark Crockett in the mayor's race.
The victor will take on Democratic state Sen. Ben McAdams in November.
Oh, and then there is the presidential chase. Republican nominee-in-waiting Mitt Romney is expected to lock up a lopsided victory in the Beehive State's GOP primary.
Salt Lake City resident Judy Patten said she cast her vote for Romney and Hatch.
She said the choice was difficult between Hatch and Liljenquist, but she eventually opted for the incumbent.
"I don't think Liljenquist can beat the Democrats," she said.
Salt Lake City resident David May said he cast his vote for Ron Paul in the presidential primary and Liljenquist to "get rid of" Hatch.
He favors Paul's stances on foreign policy and limited government.
Crockett got Dennis Engle's vote in the Salt Lake County mayor's race, and Patten voted for Crockett, too, over Winder.
Engle, also of Salt Lake City, said the controversy surrounding Winder's alias affected his vote. He called the current West Valley City mayor "deceptive."
"He didn't represent himself well with how it all unfolded," Engle said.
Winder earlier this year used the pen name Richard Burwash to write pro-West Valley City articles for the Deseret News and other publications.
Other key races on Tuesday's ballot include Republican match-ups for attorney general and state auditor, a Democratic contest in the 1st Congressional District and a Constitution Party showdown for governor.
Utahns also are selecting nominees in a number of legislative, county and school board races.
Polls close at 8 p.m.
Lee Davidson contributed to this story.