AQR Colorimetric Soil Gas Analysis Method

1

• AQR Colorimetric Soil Gas Analysis Method
• Shallow soil gas sampling is accomplished by
  driving a small-diameter steel probe into the
  subsurface soil to the desired sampling depth and
  purging a small volume of soil gas to be analyzed
  using a colorimetric detector tube. This
  direct-analysis method of soil gas sampling known
  as active soil gas sampling offers low level
  detection of compounds suspended in the
  unsaturated soil matrix near the sampling point.
  Multiple sampling points are used to provide wide
  sampling coverage to quickly locate shallow
  source areas and hot spots. The AQR soil gas
  analysis method provides fast, easy, and low cost
  collection and analysis of soil gas samples to
  depths up to 40-inches below ground surface.
• The method is easily modified to collect deeper
  soil gas samples when used in conjunction with
  direct push sampling rigs. Once the soil gas
  sampling/analysis results have identified areas
  of concern, soil matrix samples may be collected
  to confirm and quantify the impacts to soil. At
  sites with shallow water tables, contaminant
  vapor released from contaminated groundwater is
  often detectable in the overlying unsaturated
  soils using the AQR soil gas analysis method.

2

• Soil Gas Sampling Probe
• The probe consists of a ¼-inch OD stainless steel
  tube with a T bar positioned near one end to
  allow for pulling. A steel rod fits inside the
  steel tube to provide a drive point that allows
  the steel sampling tube to be driven to any depth
  up to 36-inches below ground surface. The inner
  rod also is fitted with a T bar used to extract
  the inner rod from the tube when the sampling
  depth is reached.

3

• Driving the Probe
• The probe assembly is driven to the desired depth
  by tapping the drive cap of the inner rod with a
  hammer until the base of the sampling tube
  reaches the desired sampling depth. The inner rod
  gives firmness and stability to the sampling tube
  during the driving process.

4

• Pulling the Inner Rod
• At the desired sampling depth, the inner drive
  rod is removed from the sampling tube while the
  sampling tube remains in place. The tip of
  drive rod is pointed for easier driving and
  extends 4 inches beyond the base of the sampling
  tube to provide an open space in the soil column
  for gas to enter once the inner rod is removed.
  Once the inner rod is removed, a 4-inch open
  sampling interval remains just below the base of
  the steel sampling tube.

5

• Attach Tubing and Syringe to Purge Soil Gas
• Soil gas is purged by attaching a disposable
  vinyl tubing assembly to the top of the steel
  sampling tube and using the 60 CC syringe to
  evacuate soil gas from the tube. A scissor clamp
  is used to pinch-seal the vinyl tubing between
  syringe extractions until the desired volume is
  purged (180 CCs is the recommended purge volume).

6

• Analyze Soil Gas Sample Using Colorimetric Tube
  and Hand-Held Piston Pump
• Once the appropriate volume has been purged, a
  colorimetric detector tube is attached to the
  vinyl tubing assembly and a hand-held piston pump
  is used to pull a sample of soil gas through the
  colorimetric tube to analyze.