If the water level keeps dropping at 100 mL/minute, what do you do?
If the water level keeps dropping at 100 mL/minute, what do you do?
Low-yield wells present a unique sampling challenge. The water in the well may not accurately represent the formation water chemistry, but purging the well by evacuating the casing and sampling the recovered water results in very dramatic changes in the O2/CO2 gas balance of the water, affecting many target analytes, and the potential for significant loss of VOCs is great. So, sampling the water within the well often provides the best representation of formation water chemistry that can be obtained.
In low yield wells, attempt to purge at a steady low rate if possible to avoid well evacuation. However, if a well can't be purged at a practical limit of 100 mL/minute without continuous drawdown, then low-flow purging may not be the best means of obtaining a sample. In those cases, I recommend either purging 1-2 times the volume of the sampling system and then collecting samples or, if there is very little water in the well, taking a no-purge sample with one of several grab samplers.
Low-yield wells present a unique sampling challenge. The water in the well may not accurately represent the formation water chemistry, but purging the well by evacuating the casing and sampling the recovered water results in very dramatic changes in the O2/CO2 gas balance of the water, affecting many target analytes, and the potential for significant loss of VOCs is great. So, sampling the water within the well often provides the best representation of formation water chemistry that can be obtained.
In low yield wells, attempt to purge at a steady low rate if possible to avoid well evacuation. However, if a well can't be purged at a practical limit of 100 mL/minute without continuous drawdown, then low-flow purging may not be the best means of obtaining a sample. In those cases, I recommend either purging 1-2 times the volume of the sampling system and then collecting samples or, if there is very little water in the well, taking a no-purge sample with one of several grab samplers.