VOC Sample Collection
After purging the well, approximately 7 feet of the VOC tubing is inserted inside the Standard Flow or High Flow pump’s tube, leaving about one foot protruding out the end of the pump’s tubing. Once the VOC tube has been inserted into the pump’s tube, the pump can be operated again. After a few moments of pumping, water will flow from both tubes and will continue as long as the pump is actuated. When pumping is stopped, the pump’s tubing will cease to produce water. However, the VOC tube will continue to flow, operating as a siphon, drawing water down to the level standing in the pump’s tubing. This siphon action can easily be used to collect small samples for volatile analysis as the flow from the narrow tube is steady, laminar and easily directed into a glass vial.
There is no loss of volatile organic compounds as is commonly associated with suction pumps, as the siphon action is generated by gravity flow. In addition, the sample is drawn from below the surface of the water level in the pump’s tubing, ensuring that it has not been aerated.
These VOC tubing accessories should be dedicated to the monitoring well where they are used or they should be disposed of in order to avoid decontamination.