Multiple well installations of selected casing materials (i.e., polytetrafluoroethylene (PTFE), 304 stainless steel (SS), and polyvinyl chloride (PVC)) were constructed and sampled to determine if well purging and construction procedures would significantly bias chemical constituent determinations in ground water. Water quality results from six monthly sampling dates indicate that proper purging of stagnant water from monitoring wells and isolation of cement seals are essential for the collection of representative chemical data. Significant differences in purged samples taken from PTFE, SS, or PVC wells were observed for total organic carbon and volatile halocarbons, which may be linked to the materials' interaction with ground water. The well casing interferences were not predictably high or low for any of the materials. (Copyright (c) 1986 by the America Chemical Society.)