The purpose of well development is to remove the residues of drilling fluids and fine particles of filter packs so that subsequent sampling is representative of the groundwater. The development should be performed as soon as possible after the well is installed and the annular seal is cured.
Development methods include bailing, overpumping, air surging, and high-velocity jetting. In bailing, a bailer is dropped and retrieved in and out of the well causing an outward surge of water through the well screen and filter pack. Such surging forces the loosely bound fine particles through the screen and into the well where they can be removed by the bailer. Bailing has the advantage of being a simple technique which does not introduce new fluids into the aquifer. However, bailing is time consuming and ineffective in unproductive wells.
In overpumping, a submersible pump is lowered into the well and alternatively turned on and off, usually at a slightly higher rate than what the formation can deliver. This action, along with the repeated raising and lowering of the pump into the well, causes the water to move back and forth through the well screen, moving fine particles and drilling fluids into the well where they can be removed. Overpumping is convenient for small wells or poor aquifers; however, excessive pumping rates can cause well collapse, especially in deep wells.
Air surging consists of injecting compressed air in the well, causing the water column to lift almost to the surface, and shutting off the air supply to allow the column to fall back into the well. Repeated use of this technique causes an outward surging action in the well intake which forces the loosely bound fine particles through the screen and into the well where they can be removed. Environmental engineers must filter the injected air so that contaminants, such as lubricants of the compressor, are not introduced into the well.
High-velocity jetting uses nozzle devices to force a horizontal stream of water against the well screen opening. Engineers can remove the material that enters the screen in the backwash of the jet stream by pumping or bailing. High-velocity jetting is effective in removing the mud cake and breaking the bridges in the filter pack. However, this technique can introduce potential air and water contaminants to the aquifer.
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