Groundwater standards may also serve to define classifications of groundwater. The argument should be made that not all groundwater is potable and that drinking water standards need only apply to aquifers which produce potable groundwater. Furthermore, there is a tremendous difference between objectives and standards. Arguably, cleanup standards should be set at realistically achievable levels commensurate with the risk posed by the contamination and the designated use of the aquifer, while cleanup objectives should represent targets or goals which might be technically, practicably, and financially unachievable. In the case of stringent generic cleanup standards, there may be an opportunity to apply the concept of risk by extending the point of compliance beyond the point of release.
Many State codes allow for mixing zones.
Also, many States base their cleanup standards on drinking water MCLs. By strict interpretation of the federal definition, MCLs apply only at the tap and not to the aquifer. Following this interpretation would allow for some flexibility to apply the principles of RBCA to the remedial effort. Natural attenuation is one of many acceptable remediation options at UST sites. Please see the PIRI Issue Paper on natural attenuation for a discussion in greater detail.