Sampling of Ground Water Monitoring Wells - Part 2
Hydrogeologic effects can confound sampling.
High pump rates also can yield false plume locations and higher-than-actual contaminant concentrations, especially when combined with the above long-screen scenarios. Figures 1 and 2 illustrate that wells with long screens can provide incorrect, low contaminant values but a potential overestimation of plume thickness. Figure 3 shows the potential for high pump rates to pull contaminated water into a zone where there previously was none. The figure depicts this occurrence via high-permeability sand, but fractured rock also could be very susceptible to such errors. This scenario results in overestimation of the natural extent of the plume as well as spreading of the contamination into uncontaminated zones. Although horizontally induced migration is depicted, field data has shown that vertically induced migration through the aquifer also is possible.