Automated system for miscible displacement through soil of multiple volatile organic compounds

A novel, automated, miscible displacement system has been developed to study the fate and transport of volatile chemicals within soil. This system presents advantages over existing systems that utilize fraction collection, head space analysis, or single flow-through UV detectors because there is no volatilization, there is high chemical resolution, and there is simultaneous detection of multiple chemicals. This paper presents the design of the system and demonstrates its capabilities. The system's now rate and chemical concentration detection stability were tested through time, as was its ability to detect multiple compounds. For a chemical detection stability test of 2.7 days, the pump was able to supply 10 mg L-1 of toluene and measure its absorbency every 10 min with a coefficient of variation (CV) of 1.55%, The CV of the pumping rate was less than 1% for continuous now over a 9-day period of time, during which the pressure more than tripled. A toluene breakthrough curve through an Ottawa sand resulted in 99.99% mass recovery of toluene, indicating no volatilization or sorption to the equipment. Finally, the system's ability to measure multiple compounds was demonstrated with simultaneous breakthrough curves of three chlorinated hydrocarbons through sand. This system makes possible a wide variety of experiments that previously could not be performed with acceptable precision on volatile organic compounds.