Very high memory used by w3wp process

We have in a production setup a site for which the w3wp is taking up all available memory.
To see how far it would go we put in a server with more RAM, and it went up to 13GB before we took the server out again.
The obvious problem here would be a memory leak, but the site isn’t an ASP.NET site, and we have checked memory dump and found nothing. Also after disabling all possible caching settings it didn’t go away.
The site is written in Coldfusion running under Railo, using Boncode connector between Tomcat and IIS. But we think the issue is with our IIS setup.
The site has about 20 virtual directories set as application. These are used to redirect customer to international versions of the site.
Like this:
www.site.com/   is the normal version (which is UK),
www.site.com/us/   is the US version,
www.site.com/fr/   is the French version,
…
These virtual directories (us, fr, …) point back to the root of the site.
If www.site.com points to c:\inetpub\wwwroot\site, all the virtual directories also point to that folder.
We have put the virtual application onto a different application pool and it is that process that is taking up the memory. The process for the normal site always stays around 1.5GB.
A few simple tests showed that the memory quickly grows to over 1GB with the first 20 requests to various pages.
The complete size of the site is only 400MB, excluding product images, so what is IIS storing in memory?

Any insights into this would be greatly appreciated.
Thanks.

Peter De Ranter