Subsurface In-Suite Volatile Organic Contaminant (VOC) Sampling Using Multiple Sorbent Traps With Rapid On-Site/Off-Site Quantitative Speciation

Dakota Technologies, Inc. (DTI), has demonstrated successfully key technologies used in the operation of a miniature gas chromatograph (GC) that fits inside a push rod for field screening and quantification of subsurface volatile organic compounds (VOCs). The GC is soft-pushed (no percussion) into the earth and uses a heated microporous inlet membrane on the side of the probe to transfer VOCs from the soil formation to a sorbent trap. Based on previous success of adapting these technologies, DTI proposes the design, construction, and field testing of a novel trap and valve assembly (TVA) that fits into a similar narrow-bore push rod for direct, hard-push, percussion delivery. The TVA consists of a series of sorbent traps and three-way solenoid valves for gas flow control. The strategy for site characterization is based on trapping VOCs at multiple depths using the multiple sorbent traps. The TVA is easily removed from the push rod and can be connected to a miniature, fixed-setting GC analyzer that permits rapid (less than 5 minutes) identification and quantification of the ballistically desorbed and eluting species. This GC analyzer is small enough that analysis can take place in a mobile laboratory or at a later time in a standard analytical laboratory. The key advantage to this approach is the ability of the TVA to operate with percussion hammering of the rod assembly and the ability to gather multiple VOC samples at discrete, user-defined depths. DTI previously has constructed novel, fixed-setting, miniature GCs with 5-m columns that employ ballistic heating of a sorbent trap for desorption of VOCs. The GC analyzers employ either a halogen-specific detector for chlorinated species or a general-purpose photoionization detector that can detect chlorinated or fuel-related species. The GC analyzers occupy a footprint of less than 0.5 ft2 and can be controlled via microprocessors.