Data modeling question on Cassandra DB

I'm trying to save events of a month for a user to my Cassandra DB instance. Each month the data will expire and will be removed. The data I try to model will contain user id, date of event and event id. I was planning to use the concat of userId, year and month as the row key (as I want to aggregate month of a user) and day as part of composite key. The composite key I plan is the concat and day because I will need the data ordered by day.

I'm open to your suggestions for modeling this data in Cassandra.