Pneumatic gas drive pumps operated by automated pump controllers are often chosen as the desired equipment for low flow purging and sampling; however, automating these samplers may not be the best approach.<\/p>\n

Automating the pumping rate or the drawdown is often not a good idea for wells with slow recharge. When the rate of recharge is slower than the pumping rate, an unwanted instantaneous purge can occur rather than a preferred slow and steady pumping rate that approximates the well\u2019s recovery rate. Rapid removal of water in low hydraulic conductivity <\/b>formations increases the velocity of water flowing back into a well, creating turbulence and turbidity as the well recharges.<\/p>\n

Some automated pumping control devices stop a drive cycle as soon as the water level goes below the sensor; the drive cycle is restarted after the sensor detects water again (the well has recovered). This may lead to incomplete drive cycles and inconsistent flow rates rather than the preferred slow gentle pumping rate.<\/p>\n

Suitable systems should allow the water to fall slowly to a maximum drawdown of less than 0.1 meter (or 1% of the standing column of water) while monitoring the entire pumping process.<\/p>\n