NATURAL ATTENUATION OF DIESEL FUEL IN HEAVY CLAY SOIL

petroleum hydrocarbons in the extractable fraction decreased rapidly i n a heavy clay soil contaminated with diesel fuel at 5000 mg kg(-1) de monstrating natural attenuation. Natural attenuation rates for untille d soil were estimated using two distinct extraction and analysis metho ds, the Oil & Grease Content (O&G) (US EPA 418.1; ASTM D 95) and extra ctable organics (EO) (EPA 3520B; EPA 8000A). The time to 50% decrease (t(1/2)) in the fraction varied with extraction method, Oil & Grease C ontent (11 d) and Extractable Organics (26 d). Complete attenuation ap peared to have occurred after 74 d as Extractable Organic values for s oil extracts were below the detection limit (5 mu g g(-1)). An enzyme- linked immunosorbant assay (ELISA) was also used to monitor the hydroc arbons present in the soil. This also effectively demonstrated the nea r-complete disappearance of the hydrocarbons but was not quantitative. Soil microbial biomass carbon (chloroform fumigation-extraction) and surface CO2 flux measurements did not show any significant impact of d iesel contamination or tillage in the active microbial population. Thi s observation serves to demonstrate the applicability of natural atten uation as a remedial strategy for heavy clay soils contaminated with d iesel fuel of the type used in this study.