What is proper way to dispose after getting audit entries?

I'm cleaning up our audit logs exporting to a local disk for archiving. The logs are so big I can only export about a half a month at a time. The script I wrote works fine, but I'd like to automate the entire process for every month.

This command causes about 1.5gb to 3gb of memory to be used.

$site.Audit.GetEntries($query) > $outputFile

Currently, I have to close powershell and rerun the script for each month to free up memory on the server.

I've tried $site.dispose(), but this hasn't freed up any memory.