Natural Attenuation of Hydrocarbon Polluted Soils in Mexico
L.C. Fernández-Linares, N.G. Rojas-Avelizapa, T. Roldán-Carrillo, M. Islas-Ramírez
Instituto Politecnico Nacional UPIBI, MX
Keywords: natural attenuation, bioremediation, hydrocarbons
Abstract:This work intends to describe the results from the monitoring natural attenuation in two sites contaminated with petroleum hydrocarbons, this study consider three years of monitoring. Paredon 31 and Campo 10 were the two sites studied. For each site, 6 monitoring wells were set and 15 sampling locations were chosen, each one having three samples from variable depth. Physicochemical and biological parameters measured to soil and water included pH, soil texture, TPH´s, PAH’s, heavy metals, conductivity, aerobic and anaerobic, both heterotrophic and oil degrading bacteria, as well as toxicity and risk studies. Reduction of contaminated compounds (up to 2257 mg TPHs/kg ds/year), the risk assessment and microbial activity showed that the two studied sites could be treated by natural attenuation. Microbial activity in both sites was established by bacterial count, the soil holds natural anaerobic, aerobic, heterotrophic and oil degrading populations between 8.5 x 106 to 1 x 109 bacteria/gram of soil; microbial degradation was proved in situ by CO2, H2S and CH4 determination and laboratory biodegradation tests. Concentrations of TPH found in Paredon 31 were from 300 to 50,000 ppm, and 150,000 in Campo 10. In both cases, the surface soil (0-1.5 m) was the most contaminated layer; however the upper layers showed TPH´s decrease through the study time. A clay layer was found which may have impeded the hydrocarbon migration to the deepest soil layers, by forming a mechanical barrier. Only if land use turns out, then potential risk for metals will appear.