[development] Custom Webform Module

I have a module that creates a web form for users to fill out. I'd like to track different campaign that access the same web form using a different URL so I can track hits and conversion rates for each URL. For example www.mywebsite.com/myform?campaign=june www.mywebsite.com/myform?campaign=july How in the module can I capture the extension (after 'campaign=') and redirect the user to a unique confirmation page based on the extension? Thanks, Lynn