Are there any drawbacks to using flow rates of less than 100 mL per minute if they are required to limit drawdown?

There is no actual scientific drawback to using a flow rate that is 100 mL/min or less. There is a practical drawback because it will take a long time to purge the well and, in turn, a long time to fill the bottles. I have worked at sites where flow rates were as low as 50-80 mL/min in order to get samples from extremely low-yield wells. These are wells where extremely high turbidity in the samples is always a problem (anywhere from 500-1,000 NTU). However, if your only reason for using a very low pumping rate is because you have a regulatory limit on drawdown, contact QED. We may be able to provide information to your regulatory agency showing that the water level just needs to be stabilized, regardless if it is at .3 of a foot or 3 feet, in order to purge and sample a well properly.