The 2012 ARRA Radiological Survey of Santa Susana Field Laboratory specifically ONLY included Area IV at the insistence of the discharger, The Boeing Company, and Department of Energy. 

Despite years of spills, leaks, fires, and discharges to the surrounding environment, a toxic mix of chemicals and radionuclides. The public was told by California DTSC and USEPA that no radiological operations took place outside Area IV, with an outsized focus on the SRE Sodium Reactor Experiment and the partial meltdown that took place in 1959. Considering the 50 years of operational history that included the Apollo programs, rocket testing and in Area 1, chemical laser and other top secret work. USEPA  More: 

The $42 million dollar ARRA funded investigation of radiological impacts at Santa Susana was restricted to Area IV, because they said the work was restricted to that side of the Hill. Violations of illegally using unauthorized amounts of Tritium in an area not licensed for it.

"If we don't look where the contamination is, we are certain, never to find it."

Why it matters:

Unauthorized use of Tritium in Area 1, that included known violations, so why was the public told that no nuclear work took place outside of Area IV?