Evaluation of an In Situ, On-Line Purging System for the Cone Penetrometer

Abstract

Materials that will be used to construct an in situ, on-line purging system for the cone penetrometer were evaluated. Transfer efficiencies for volatile organic compounds (VOCs) through stainless steel, nickel, aluminum, and Teflon® tubings were determined using a gas-phase mixture of VOCs containing trichloromethane, tetrachloromethane, 1,1,1- trichloroethane, tetrachloroethene, hexane, benzene, toluene, and 1,2-dimethylbenzene. The water content of the gas stream had an insignificant effect on the quantitative transfer of VOCs through Teflon® tubing but was critical to efficiently transfer the compounds through metal tubing, particularly nickel. Transfer efficiencies for all eight analytes in moist gas streams through stainless steel were greater than 95%. Toluene, tetrachloroethene, and 1,2-dimethylbenzene were transferred with 93%, 81%, and 80% efficiency, respectively, when they were drawn through Teflon® PFA (perfluoroalkoxy) tubing. In general, the retention of the VOCs by Teflon® increases with decreasing aqueous solubility of the analyte. The efficiencies at which VOCs were purged from aqueous standards in Teflon® PFA, Type 304 stainless steel, and glass vessels were similar. Stainless steel was superior to nickel, aluminum, and the Teflon® polymers as a material for an in situ, on-line purging system for the cone penetrometer.

Development and preliminary evaluation of a cone penetrometer-based method forin situ determination of volatile organic compounds in groundwater

“…These conditions include rough handling by truck operators, severe vertical and horizontal stresses during pushes, high humidity, high concentrations of solids (i.e., silts and fines) in most samples, and transfer of analytes through tubings that can approach Therefore, with the use of the breadboard prototype, 50 m. we initially examined materials for the QVAC, including the purging vessel, a thermostated sample gas transfer line, and groundwater inlet frit. 34 For the transfer line, we found that stainless steel (grade 304 or 316) was superior to various Teflon polymers (PFA, PTFE, FEP) as well as aluminum and nickel. Stainless steel consistently transported a range of VOCs at ambient ( ) and elevated ( ) tem-25 ЊC 110 ЊC peratures and various humidities (0 -50%) quantitatively ( ).…”

“…In previous work, we described the results obtained from testing the probe and transfer line materials used in the QVAC system. 33,34 The development of the QVAC method, including the probe design, fabrication, laboratory testing, and initial field testing, is described herein.…”