<P> The community can also help monitor the groundwater quality . </P> <P> The development of land - use zoning maps has been implemented by several water authorities at different scales around the world . There are two types of zoning maps: aquifer vulnerability maps and source protection maps . </P> <P> It refers to the intrinsic (or natural) vulnerability of a groundwater system to pollution . Intrinsically, some aquifers are more vulnerable to pollution than other aquifers . Shallow unconfined aquifers are more at risk of pollution because there are fewer layers to filter out contaminants . </P> <P> The unsaturated zone can play an important role in retarding (and in some cases eliminating) pathogens and so must be considered when assessing aquifer vulnerability . The biological activity is greatest in the top soil layers where the attenuation of pathogens is generally most effective . </P>

Where are aquifers most likely to be contaminated
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