I have IIS 7.0 installed on and there is a .net application with a .svc service there.
I would like to point a file in the virtual directory pointed by the application (
try this might help to resolve your issue
string apPath = System.Web.Hosting.HostingEnvironment.ApplicationPhysicalPath;
or
string apPath = System.Web.Hosting.HostingEnvironment.MapPath("~/folder/file");