Microsparger Probe for Real-Time Measurement of Volatile Compounds in Groundwater
The Microsparger is a groundwater probe capable of measuring groundwater concentrations of volatile compounds in the field in real time and is designed to fit in standard groundwater monitoring wells (Gilmore and Cantrell, 2000). The principal of the Microsparger probe is to equilibrate the groundwater containing dissolved volatile compounds with a small volume of air. Equilibrium is promoted by continuously spraying (vaporizing) the groundwater through the volume of air (Figure 1). The volatile compound concentrations are measured in samples collected from the gas phase contained within the headspace of the device, using commercially available gas analyzers such as a photo-ionizing detector (PID), gas chromatograph (GC) or photoacoustic infrared spectrophotometer for analysis. The concentration of the VOC in the vapor can then be used to calculate the equilibrium concentration in the dissolved phase (Henry's Law). To calculate the equivalent concentration in water, the gas phase concentration, temperature and the Henry's law constant for the constituent must be known. The temperature is measured directly (with a thermocouple attached to the Microsparger) and the Henry's law constant can be obtained from reference sources. The probe has a simple, straightforward design, is inexpensive, and easy to operate in the field.
Laboratory and field testing in groundwater monitoring wells at Edwards AFB has been conducted by Pacific Northwest National Laboratory using TCE as a model compound. The Bruel and Kjaer (B&K) photoacoustic infrared spectrophotometer was used as the gas phase analyzer for this testing. The B&K was found to be both an accurate and robust instrument suitable for the field (EPA, 1998). Laboratory testing results for the Microsparger used in conjunction with a B&K gas analyzer indicate that TCE concentrations could be measured within 10% of the concentrations using a traditional laboratory gas chromatograph (GC) (EPA Method SW846 8260B).
Microsparger vapor analyzer*
Microsparger reactive well system*
Microsparger contaminant input*
Microsparger tubing emplacement with directional drilling*
Microsparger Ozone Generator*
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