INDOOR RADON ESTIMATES FOR SCHOOL DISTRICTS ON THE MIOCENE MONTEREY FORMATION IN SOUTHERN CALIFORNIA

The San Fernando Valley is a densely populated region covering approximately ninety square miles in northwestern Los Angeles County. Because radon is derived from the uranium decay process, the uranium-rich subunits of the Miocene Monterey Formation are primarily responsible for the recent “high radon potential” designation of this area. Over 30% of homes in some local neighborhoods are known to exceed the U.S. EPA indoor radon action level of 4 pCi/l, though virtually no data exists regarding classroom radon levels of schools in the San Fernando Valley.

Extensive classroom radon studies conducted in the Palos Verdes Peninsula Unified School District (PVPUSD), a southern Los Angeles County school district also on the Monterey Formation, have demonstrated that school site configuration in addition to surface uranium concentrations determine classroom radon levels. Although school construction is critical, a minimum concentration of uranium must be present in order for this factor to become relevant.

Three distinct categories of school configurations from this past study were used to classify each of the fourteen school sites in the Las Virgenes Unified School District (LVUSD), located in the western region of the San Fernando Valley. For each school, five gamma ray spectrometer measurements yielding the surface potassium, uranium, and thorium concentrations were taken in order to obtain an accurate representation of the radon source strength. Because no indoor radon data exists for the LVUSD, average surface uranium concentrations together with school configurations were used to predict the district radon potential. This district value was then compared to the state-wide average obtained from previous studies. Additional comparisons between predicted classroom radon levels and those of the local residences are also discussed for an independent assessment of the method utilized.