PRELIMINARY RESULTS OF NAPL CONTAMINATION IN A DISUSED INDUSTRY IN THE CITY OF SAO PAULO, BRAZIL, BY RADON EVALUATION WITH CR-39 DETECTORS

摘要

Contaminated sites by NAPL (Non-Aqueous Phase-Liquids) may lead to safety risks to human health and to ecosystems, restrictions to urban development and decrease of real estate value. This work used the radon gas as an indicator for the analysis of subsurface soil gas, once this noble gas presents good solubility in a wide range of NAPL, being partially retained in the NAPL contamination. Therefore, a decrease of the activity of radon in the contaminated soil gas can be expected, due to the high capacity of partitioning of radon in NAPL, which allows that the NAPL retain part of the radon previously available in the soil pores. The survey was carried out at a disused industry, contaminated by low volatile NAPL, located at east of Sao Paulo city, in March/2015. Radon was evaluated by passive detection methodology with CR-39 solid state nuclear track detectors (SSNTD). Radon concentrations for the eight monitoring stations at non-contaminated locations in March/2015 varied from 16.4 ± 1.2 kBq.m~(-3) to 55 ± 4 kBq.m~(-3). For the two monitoring stations assumed as contaminated locations in March/2015, radon concentrations were 1.17 ± 0.08 kBq.m~(-3) and 4.2 ± 0.3 kBq.m~(-3), diminished in a range from 92% to 98% when compared with the results for the non-contaminated areas.