Interval Training Suggestions

Hi everyone! I’m training for my first half marathon coming up on October 12th. I have been running twice a week: one short run (3-5 miles) and one long run (currently at 9 miles). For this week’s “short run” I want to do some interval training that totals 4 miles for the session. I’ve looked up some things online but I’m still unsure about what to do and figured I’d reach out to the community for ideas/recs. Thanks in advance!!