Iet. Iben et al., THERMAL BLANKET FOR IN-SITU REMEDIATION OF SURFICIAL CONTAMINATION - A PILOT TEST, Environmental science & technology, 30(11), 1996, pp. 3144-3154
Surficial PCB contamination has been successfully and safely removed f
rom soils in a field test at the site of a former dragstrip where oil-
containing PCBs had been sprayed to minimize airborne dust. Decontamin
ation was achieved by electrically heating a 9.3-m(2) area under a the
rmal blanket, and PCB concentrations were reduced from up to 2000 ppm
to less than 2 ppm in 24 h of heating. Initial PCB concentration in so
me of the more contaminated areas averaged 700 mg/kg from 0 to 7.5 cm
deep and 100 mg/kg from 7.5 to 15 cm, with maximum concentrations as h
igh as 2000 mg/kg at the surface. The thermal blanket was operated at
temperatures ranging from 815 to 925 degrees C. It took about 20-24 h
for a 15-cm depth to reach 200 degrees C, which was sufficient to redu
ce the total PCB concentration to below the mandated 2 mg/kg cleanup l
evels. The variation of times to reach the desired temperature is prin
cipally related to soil water content. A vapor stream was drawn by vac
uum from the thermal blanket at a rate of 550-1100 L(STP)/min. Vaporiz
ed groundwater constitutes from 40% to 70% of the vapor stream at the
beginning of each heating cycle and therefore displaces a significant
fraction of the air, but enough remains for oxidation of waste stream
hydrocarbons in an external thermal oxidizer. We also;tested 2.4 m x 6
m thermal blanket modules that could be assembled into large arrays t
o treat extensive areas. A full-scale thermal blanket system designed
to treat this site would consist of 20 modules assembled into 288 m(2)
thermal treatment systems, which require 1.8 MW of power and operate
on a three-part cycle: heat and treat soil cool, and move to a new tre
atment area. Emissions from the blanket consist of organics, which are
destroyed by passing through a flameless thermal oxidizer.