Groundwater Water Quality Monitoring and Human Health Next consider the case of a high density NAPL, which we call a DNAPL.
High density NAPL
Well A Well C Well B
In this case, only the samples from the deeper well, Well C, will show signs of pollution.
NAPLs in general can vary in their concentration by several orders of magnitude over horizontal or vertical distances of a few feet; in other words, one sample located within a few feet of second sample could show 10 times more contamination! This obviously presents a huge monitoring challenge. This is why, given financial constraints, sampling many more sites at a screening level may be more important that taking a few very precise samples. Hot spots of contamination are likely to be detected only if sampling is conducted every few meters horizontally and every meter vertically.
Traditional approaches rarely do approach sampling this intensively. Newer, improved methods can be used to achieve this. It is also why it is so important to spend time and money up front to characterize a site well so that the sampling sites chosen are most likely to be representative. It’s important for citizen’s groups to understand this so that they can advocate for proper well siting, ideally with the help of an experienced consultant.
Traditionally, the most common practice for monitoring contaminants at a site was to install ground-water monitoring wells. Hundreds of thousands of such wells have been installed since the late 1970’s. Unfortunately, many of these wells were designed and installed by people who were not aware of appropriate monitoring design, and who did not conduct or
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