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| Discrete Vadose Zone Sampling
Discrete Vadose Zone Vapor Sampling Devices
The Post-Run Tubing System (PRT)
The Post-Run Tubing System (PRT) is the most common way to recover vapor
samples. The PRT system consist of O-ring connections that enable the
PRT system to deliver a vacuum-tight seal to prevent sample contamination
from up hole. With the PRT system the sample can be drawn through the
point holder, adapter and into the sample tubing via a vacuum pump.
Sampling Purge Volumes
1 Volume = Volume of polytube 4.4647ML/ft
pointholder & 3" of rod pull back= 60ml
| Volume Purge/ML | 5'depth |
10'depth |
15'depth |
20'depth |
25'depth |
30'depth |
35'depth |
40'depth |
| Volume | 82.32ml |
104.65ml |
126.97ml |
149.29ml |
171.62ml |
193.94ml |
216.26ml |
238.59ml |
| Purge Volume 200cc/min | 24.7
sec |
31.4
sec |
38.1
sec |
44.8
sec |
51.5
sec |
58.2
sec |
64.9
sec |
71.6
sec |
V=
Volume
Tubing 0.25 in OD, 0.17in
H=Depth
r=Radius
Derived from fomula
Note: Please keep in mind that not every soil yields
soil gas. Some damp to moist, fine grated, well compacted plastic clays
(which have been slightly compressed by probe rod insertion) will not
yield soil gas to the tool string no matter how much vacuum is applied.
The solution to this problem consists of applying a vacuum and shutting
off the line valve and slowly retracting the probe rods until the tip
passes through a permeable zone. Soil gas will enter the system and
the gauge on the vacuum source will respond abruptly.
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