Purging

with the waterra inertial pump

Purging, in the groundwater context, is the removal of volumes of well water. One may want to purge to remove the stagnant standing water from the well and allow fresh formation water to fill the well prior to sampling. Numerous clients report that they purge the equivalent of three well volumes prior to sampling, but protocols vary.

The other major purging reason is to draw down the well and hence the water table so as to establish a hydraulic gradient towards the well. This is typical in a recovery type situation where contaminants are encouraged to flow towards the well. Here, the purging is typically done over longer periods of time. This purge and recover type of application is described under the section entitled Well Development.

suggested solution

The Waterra Inertial Pumping System is widely used for purge and sampling applications as it is a cost efficient, effective way of purging and then sampling using the same equipment. The system is best in 2 inch (5 cm) wells and smaller, although in shallow four inch wells (10 cm) it can be a good system as well.

To purge a 2 inch (5 cm) well, the usual arrangement would require either the Standard Flow System or the High Flow System, each of which consists of a foot valve, tubing and a drive mechanism to reciprocate the tubing and valve up and down.

 

standard flow system

The Standard Flow System usually consists of:

• a D-25 Foot valve
  
• a length of Standard Flow Tubing
  
• and a drive mechanism: either the manually operated Lever Pump, the electric Hydrolift-2, or the gas driven PowerPump-2

high flow system

The High Flow System usually consists of:

• a D-32 Foot valve,
  
• a length of High Flow Tubing
  
• and a drive mechanism: either the manually operated Lever Pump, the electric Hydrolift-2, or the gas driven PowerPump-2

procedure

The valve is securely threaded into the tubing. The tubing is then inserted into the well, valve first. The tubing is fed down to the depth of the screened interval and then cut about six feet (2m) above the top of the well. The drive mechanism should be affixed to the well head and the tubing connected to drive mechanism at both the reciprocating arm and the fixed discharge on the drive mechanism. Pumping is initiated by turning on the drive mechanism or pumping by hand at the rate corresponding to the desired flow. The advantage of the mechanized drive systems is the fact that whilst purging, the field person is available to do other tasks.

note

Four inch (10 cm) wells and larger hold a lot of water, especially if they are deep, and are usually best purged with high volume electric submersible pumps.

As always, a Waterra technician would be happy to help configure a system to your specific application.