Thomas Kwader reminds us that monitoring well data are only important if the wells are in the proper locations and the data are being analyzed to assess the progress toward the goals of the program.
Before we can address how many wells are being monitored, we must know what the objective of the monitoring program is. Generally, we monitor ground water levels and chemical constituents to assess the movement or cleanup progress of a contaminant in the subsurface. The number of wells necessary to accomplish this is dictated by many factors, including the complexity of the site's hydrogeologic conditions; the rate, or ground water flow; how many source areas are present; the mobility of the site compound of concern, including the specific gravity or weight of the compounds, etc.