URANIUM CONCENTRATION MAPPING OF SCHOOL SITES IN THE PALOS VERDES PENINSULA UNIFIED SCHOOL DISTRICT, PALOS VERDES ESTATES, CALIFORNIA

Previous studies have shown that several school sites in the Palos Verdes Peninsula Unified School District (PVPUSD) consistently support elevated indoor radon levels, and all of these radon-prone sites reside on uranium-rich outcroppings of the Altamira Shale or Valmonte Diatomite subunits of the Monterey Formation in Southern California. Because radon gas is ultimately derived from soil uranium, knowledge of the local underlying uranium content is one important factor in the assessment of indoor radon potential at a given site.

Preliminary ground measurements of the soil uranium concentrations from these two subunits displayed a large dynamic range of values from less than 2 ppm to greater than 12 ppm equivalent uranium (eU), and it was noted that large concentration changes could occur over distances as short as 20 feet. The 3.8 day half-life of radon combined with typical soil permeability allows radon to travel a few meters up to tens of meters before decaying into a solid product. Hence, traditional aerial eU measurements which necessarily average over large areas may not have adequate spatial resolution to address the localized variability of eU concentrations that could affect classroom indoor radon levels.

We present a high spatial resolution map of the soil eU concentrations from one school site in the PVPUSD that has demonstrated persistently high classroom radon levels. The localized eU measurements obtained with a gamma ray spectrometer are compared to the classroom radon values for different buildings on the school site, and the implications of rapidly changing eU concentrations at a single site are discussed.