What different approaches are required for open bedrock wells?

A fractured rock system will have a different type of flow than a granular medium. So, unfortunately, not all of the guidelines of well purging and sampling will apply the same way. In general, if you have an open bedrock borehole with relatively well-fractured rock along its length and no real knowledge of where there are specific high flow rates from one fracture or another, I will generally install the pump within the open borehole and then just purge it as if it were a well screen. If we have some specific knowledge about fracture flow then you want to make sure that the pump is located between fractures where water may be entering and exiting. There are some specific guidelines in the 1996 US EPA Puls and Barcelona paper.