Memory usage after running a long job

I have a long process running (importing data from an XML file, it can run hours, the XML file size could be around 25-30MB), and after the end of this process I have a huge memory usage (that is not liberated after the end of the ran).

And I experienced some Exceptions like :

Could not load file or assembly 'EntityFramework' or one of its dependencies. Not enough storage is available to process this command. (Exception from HRESULT: 0x80070008)

Regarding to the answer here Not enough storage is available to process this command in VisualStudio 2008, It's because I don't have enough contiguous space virtual memory available

When I look to Task Manager, I see 875.1 MB used by my IIS Express, how can I profile that ? In my code I am manipulating document (images, pdf), but when I read them from disk I am always inside an using statement

I want to know/understand why IIS use 875.1 MB after the end of my job. There is any tools to analyse the memory use, specially a dump file postmortem ?