log4net permission issue to write to application event log when the user is not in admin group in Windows 2008 R2 and IIS 7

I am having log4net permission issue from ASP.Net 4.0 web application to write to application event log, when the user is not in administrator group in Windows 2008 R2 and IIS 7. We are using NT authentication and impersonation. Once I assign the user to admin group it works fine.
I tried with many permission settings like giving Authenticated Users full permission to Eventlog in registry etc. and none of them work. If any one can help that will be great.