Laboratory Evaluation of a Volatile Organic Compound Analysis System for the Site Characterization and Analysis Penetrometer System

Conventional subsurface contaminant mapping technology requiring borings and laboratory analysis of soil samples is time-consuming, expensive, and often results in inadequate descriptions of contaminant plumes. Adaptation of advanced chemical techniques to cone penetrometer technology provides a means for real time detection and mapping of contamination in the subsurface. An in situ volatile organic compound sampling system to detect ppb levels of BTEX compounds (benzene, toluene, ethylbenzene, and total xylenes) and trichloroethene has been developed for the site characterization and analysis penetrometer system. The sampler is pushed to a desired depth in the subsurface, an interior actuator rod is retracted to form a sampling chamber, and a measured volume of soil is sampled and purged in place. Volatilized compounds are transferred to the surface where they are trapped on tenax and desorbed into a portable gas chromatograph. The soil sample is expelled, and the penetrometer is pushed to a new depth where the process is repeated. Materials and system-operating conditions were optimized during laboratory tests. Stainless steel tubing heated to 100 deg C and a carrier gas flow rate of 40 ml per min yielded maximum recoveries (>90 percent) in a 30-min sampling period. Complete system tests yielded recoveries greater than 85 percent from soil spiked with BTEX and other chlorinated volatile compounds. These recoveries compared favorably with spike recovery data obtained from U.S. Environmental Protection Agency Method 8240 by gas chromatograph/mass spectrometer. Overall, the sampling system was able to successfully thermally desorb BTEX compounds from spiked soil and transport the volatilized compounds through 50 ft of heated transfer line into a tenax trap with recoveries greater than 85 percent. jg p5