The MIP is a screening tool with semi-quantitative capabilities acting as an interface between the contaminates in the subsurface and gas phase detectors at the surface. The downhole, permeable membrane serves as an interface to a detector at the surface. Volatiles in the subsurface diffuse across the membrane and partition into a stream of carrier gas where they can be swept to the detector. The membrane is heated so that travel by VOCs across this thin film is almost instantaneous. MIP acquisition software logs detector signal with depth. The ability to detect a contaminant is determined by the type of detectors being used. Detectors used by ASC include photo ionization detector (PID), electron capture detector (ECD) and the flame ionization detector (FID). Each detector is designed for sensitivity to a group or type of contaminant. The ECD is used for chlorinated (TCE, PCE) contaminant detection, PID is best used for the detection of aromatic hydrocarbons (BTEX compounds), and the FID is best used for straight chained hydrocarbons (methane, butane). These detector signals, in conjunction with the time in which a contaminant takes to return to the surface, are graphed versus depth.

The detector information and the electrical conductivity of the soil are logged and graphed in the field by the FC5000 field instrument. This allows the ASC operator to determine the location of the contaminant, the relative concentration of the contaminant and the soil in which the contaminant is located. The MIP log can be used to determine the depth at which a monitoring well should be placed, at what depth samples need to be collected, and/or the interval for injection of remediation materials.

ASC has custom designed field vehicles with pre-strung dual rod strings to minimize down time from broken probes or saturated trunk lines, the ability to implement the MIP through dual wall casing to prevent cross contamination, integrated low-noise generator, internet access, air conditioned, high end laptop and printer capable of generating 3-D imaging in the field.

The benefits of MIP over traditional sampling:
  • Real time data allows site characterization location decisions to be made without waiting for soil or groundwater sample analysis
  • Better vertical delineation: 20 samples per foot vs. 1 sample every 5 feet for soil or one sample per monitoring well
  • Measures total contaminant mass versus just soil, soil vapor, or groundwater
  • Locates contaminant mass interface at unique lithologic zones
  • Lower halogen detection limits than hand held PID
  • PID and FID co-detection for petroleum hydrocarbons
  • Digital output allows for easy mapping of mass vs lithology.
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