ECOPROBE 5 - rs dynamics

• Although there is a water valve fitted to the probe, it is best to avoid inserting the probe into water that
may accumulate in a hole. If a probe is inadvertently inserted into a ‘wet’ hole, the reading will be close to
zero or much lower than expected, because the water valve does not allow vapor to be drawn in. The
position of the sampling probe has to be vertical. Do not tilt the probe since the water valve may cut off the
air as it is not designed to operate in an off vertical position. When surveying a potentially waterlogged
terrain, use a stick to test each hole for seepage water.
• If a delicate measurement is required, the probe may be eliminated. Use only plastic tubes with a dust filter,
in which case always ensure that there is no possibility of liquid being drawn into the instrument.
Heavily contaminated soil vapor may leave a hydrocarbon residue in the entire sampling system, and it is
therefore advisable that the probe and its connecting tube receive special care when being cleaned.
Cleaning the probe
The sampling probe must be cleaned from residual gas and condensation if contamination was found at a
station. Cleaning the probe should be carried out using fresh, non-polluted air. The higher the concentration
and the heavier the hydrocarbons at the measured station, the higher will be the volume of air needed for
cleaning. The probe cleaning can be minimized in the case of soil gas containing contaminants originally
present in a gas phase such as methane. On the contrary, soil gas containing abundant vapor of heavy oils
demands greater volume of cleaning air. Clean air can be blown through by means of a manual pumping
device such as that used for inflating rubber mattresses. It is important not to blow into the sampling probe
with your breath as this may cause moisture to enter the probe and may give incorrect measurements.
Attention needs to be paid to the sampling apertures at the bottom of the sampling probe, which has to be
cleaned of residual soil after removal from the hole.
At some contaminated localities there may be a floating contaminant layer at the ground water table. If the
sampling probe is inserted directly into the pollutant, the probe will be contaminated. In order to avoid false
readings afterwards, immediately clean out the entire probe and pumping inlet with a household dishwashing
detergent and then use clean water for rinsing. Never use organic based detergents since their vapor can
affect the measured values and cause incorrect results.
Connecting tubes
MEASURING – STANDARD GRID
Special care is needed with the plastic connecting tubes between the probe and apparatus. There is an effect
of diffusion of hydrocarbons into plastic. The quality of the plastic materials varies. For example, if a plastic
tube of average quality is used to measure a contaminant concentration higher than 10 000 ppm, the residual
contamination could contribute some tens or hundreds ppm towards the next measurement. The worst type,
however, is the soft white silicon tube, while the best is transparent colorless or blue or slightly green plastic
tubes intended for medical purposes. All black rubber tubes are to be avoided. Careful cleaning of the tubes
together with the sampling probe is recommended. When measuring a delicate locality with dramatic shifts
between very high and very low concentrations from one station to another, the best solution is to use a set of
tubes equal to the expected number of stations to be measured within one day. At each station a clean tube is
to be applied. Used tubes usually self-clean if placed on a room heater overnight. The next day they are ready
to be used again.
It is a good practice to set up a locality for “warming up” the instrument and for test measurements.
Before starting to measure, the IR unit needs to be stabilised. Measure three “warming up” stations
in the test locality to avoid any incorrect readings at the beginning of the day’s survey. Use this
locality also for checking if plastic tubing, dust filters etc. are contaminated.
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