Surge blocks. A surge block acts like a piston in the borehole 'cylinder'. It is

mounted on a drill stem and gently moved up and down. The surging action

draws fine material and any remaining drilling fluid from the aquifer. This debris

is removed intermittently with a bailer. The figure shows a typical surge block,

but any close fitting tool, such as a bailer, can also be used. Care should be exercised

when using a surge block as vigorous use can damage a lightweight screen.