Advances in Multilevel Well Technology
Several detailed field studies performed at research sites in the 1980’s and 1990’s suggest that most contaminant plumes exhibit large variations in concentration over small vertical distances. These variations are caused by spatial variations in the contaminant source zones and heterogeneity of the geologic materials. Conventional monitoring wells have been shown to be ineffective for accurately defining the distribution of contaminants in most aquifers because of the mixing that occurs in the wells when they are pumped. Nested or clustered monitoring wells (i.e., two or more individual wells installed to different depths in the same borehole) have been used at some sites. However their use is discouraged by many government regulatory agencies because of the difficulty in installing reliable seals between the various monitored zones.