CHARACTERIZING SITE HYDROGEOLOGY
The adequacy of a ground water monitoring program largely depends upon the
quantity and quality of the hydrogeologic data used in designing the program. Clearly, if the
design of the monitoring well system is based on incomplete or inaccurate data, the system
will not fulfill its intended purpose. Because of the complexity of site characterization and
ground water monitoring system design, owner/operators should discuss the intended approach
with the appropriate State or EPA Regional office prior to finalizing site characterization
When characterizing the hydrogeology of a site prior to designing a monitoring well
network, owner/operators should be concerned with questions relating to data quantity and
Has enough information been collected to identify and adequately characterize
the uppermost aquifer and potential contaminant migration pathways? Does the
information allow for the placement of monitoring wells that are capable of
immediately detecting releases from the regulated unit(s) to the uppermost
Have appropriate techniques been used to collect and interpret the information
that will be used to support the placement of monitoring wells, and is the
quality and the interpretation of the information satisfactory when measured
against the program's DQOs?
The answers to these questions will establish whether or not the site characterization is
adequate. The Agency recognizes that the quantity of site characterization information and
the appropriateness of investigation techniques vary according to site specific conditions.
Sites in complex geologic settings require more hydrogeologic data for ground water
monitoring system design than do sites in less complex settings. Likewise, investigatory
techniques that may be appropriate in one geologic setting or for one waste type, may be
inappropriate in another setting or for a different waste type.
This section identifies techniques that can be used to characterize a site prior to
installing a monitoring well network, and describes the factors that should be considered when
evaluating whether a particular method is appropriate in a specific case.
Table 1 lists a number of investigatory techniques commonly used to conduct
hydrogeologic investigations. Also listed are preferred methods for presenting the data
generated from a hydrogeologic investigation. Many States and Regions also may request or