Continue to develop and refine a conceptual model of the site based on the
field investigations. The conceptual model will form the basis for the design of
the ground water monitoring system. The conceptual model should be based
on information of sufficient amount and quality to ensure that the monitoring
system will fulfill the established regulatory requirements and technical
objectives. The quantity of data required will vary with the hydrogeologic
complexity of the site. Facilities located in complex hydrogeologic settings
require more hydrogeologic data than facilities located in less complex settings.
Design a detection monitoring system consisting of both downgradient
monitoring wells that intercept and monitor the potential pathways of
contaminant migration, and background (e.g., upgradient) monitoring wells that
provide representative samples of background ground water quality (Chapter
Install downgradient monitoring wells and background (e.g., upgradient)
monitoring wells (Chapter Six).
Collect and analyze ground water samples from downgradient and background
monitoring wells (and from springs or the vadose zone, when appropriate) at
the frequency specified in the facility permit (Chapter Seven).
Evaluate the ground water monitoring system with respect to the regulatory
requirements, the technical objectives, and the accuracy of the conceptual
model. Refine the ground water monitoring system, if necessary (Chapter Six).
Each of the steps presented in Figure 1 is discussed in detail in the sections of the
Manual noted. The Manual does not discuss the statistical evaluation of ground water
monitoring data. Guidance for the statistical evaluation of ground water monitoring data is
presented in EPA's April 1989 publication entitled "Statistical Analysis of Ground Water
Monitoring Data at RCRA Facilities Interim Final Guidance" (USEPA, 1989a) and any
subsequent addenda to this publication.
The approach described above relies heavily on the development and refinement of
conceptual models. A conceptual model is an understanding of the hydrogeologic
characteristics of a site, and of how the hydrogeologic characteristics are integrated into a
hydrogeologic system that contains interacting and dynamic components. The Agency
strongly emphasizes that the process of developing a conceptual model of a site is ongoing.
After a ground water monitoring system has been installed and numerous ground water
samples have been collected, the conceptual model for a site may be further refined.