Perhaps the most straightforward approach would be to install DebugDiag 1.2, and enable the LeakTrack functionality.
After launching DebugDiag, select the Processes tab, right-click the desired w3wp.exe process, and select "Monitor for leaks".
You may use the Rules tab to create a trigger to collect the information:
After the user dump files have been generated, you can then use the Advanced Analysis tab, and run the Memory Pressure Analyzer, which will inspect the dump files and generate a report.
From the documentation:
"The memory leak monitoring feature is designed to track memory allocations for a process. This feature should be used when a process on the system continues to grow in memory until the system becomes unstable, or the process stops functioning correctly. The debug tool will inject a DLL into the specified process and monitor memory allocations over time. A dump is then generated, and the dump is analyzed to determine what allocations are not being freed and most likely causing the memory leak. Allocations generally fall into 3 groups: caching, short term allocations that will be freed later, and memory leaks. All three allocation methods have very distinct allocation patterns when measured over time. The leak tracking feature calculates a leak probability using a formula that is based on these allocation patterns as measured over a specific time period. "
Debug Diagnostic Tool v1.2