Geophysical surveys.

STEP 5

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.

STEP 6

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

Five).

STEP 7

Install downgradient monitoring wells and background (e.g., upgradient)

monitoring wells (Chapter Six).

STEP 8

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).

STEP 9

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.

November 1992

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