If you are currently using a generator-powered bore pump where purge is controlled by frequency and you cannot slow the rate down to .5 or 1 L/min as recommended, what suggestions do you have to improve the quality of those results?

That is a challenge because if you can't get the flow rate down low enough to get the drawdown in the well to level off at some point, then obviously you need another approach. It's generally not a good idea to use a valve or some restriction at the surface in order to reduce the flow rate partly because, depending on the nature of the pump, it could affect the pump and you might get a pressure drop across the well that could cause the loss of volatiles. If you are using an electric powered pump that’s controlled by frequency and you can't get the flow rate down low enough, the only suggestion I have is to look for a pump that will. If you can't do that, the possibility of using a manual valve to reduce your flow could be used knowing it could affect the pump and you could potentially affect volatiles. Look into some of the pumps available such as water pumps and others that can be adjusted down to the flow rates that would match the well performance.