There are preparations to make before beginning to sample a monitoring well.
If the well is purged by pumping from the screen or at the water level in the casing, water in the casing column will not be removed. Care should be taken not to sample this stagnant water. The standing water above the well screen should be removed by bailing or by pumping from the top of the water surface so that water is displaced upwards from the screen to the water table.