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.
