In situ multiphase fluidization ("upflow washing") for the remediation of hydrocarbon contaminated sands

A new in situ remediation method is described, "upflow washing," in which contaminants are flushed to the surface within an in situ fluidized zone produced by a jet inserted into a granular formation. The suitability of the method for LNAPL (light non-aqueous phase liquid) remediation is examined by experiments on diesel-contaminated soils within column and tank settings. The experiments indicate significant reductions in diesel levels (96-99.9%) may be achieved by fluidization with water and gas (gas-liquid upflow washing, GLUW) for a wide range of initial diesel concentrations (10 000 to 150 000 mg/kg) and for soil fines contents of 0 to at least 10%. Final diesel levels of <1000 mg/kg in a uniform fine sand and <200 mg/kg in clayey sands can be achieved. The efficiency is much higher than that of fixed bed flushing (simulated pump-and-treat), as the method overcomes the trapping of NAPL ganglia. Fludization with water alone (liquid upflow washing, LUW) is less effective than fixed bed flushing in the uniform sand, but approaches that of GLUW in clayey and silty sands. The results are explained by theoretical analysis of the removability of isolated NAPL droplets and mixed solid - NAPL particles from a fluidized bed due to buoyancy and elutriation, which may be represented using a "removability regime map" for the diesel-water-sand system.Key words: fluidization, in situ, remediation, NAPL, diesel.