require that all data be submitted in a computer readable form. If the level of site

characterization necessary to design a RCRA ground water monitoring program is sufficient,

it will be possible to obtain the information listed in the last column of the table. This

information ultimately will be used to develop a conceptual model of the site prior to

designing the ground water monitoring system.

At a minimum, the site investigation should always include direct methods of

determining site hydrogeology (e.g., subsurface borings, water level elevation measurements,

textural analysis of soil samples). Indirect methods (e.g., aerial photography), especially

geophysical methods (e.g., resistivity and seismic surveys), may provide valuable information

for planning direct field measurements. Information obtained by indirect methods also can be

used in conjunction with information obtained by direct techniques to interpolate geologic

data between points where direct measurements are made. Information gathered by indirect

methods alone will not provide the detailed information necessary for complete

characterization of a site, however. Conclusions drawn from indirect site investigation

methods (e.g., geophysical surveys, aerial photography) should be confirmed by, and

correlated with, direct measurements. Lithologic data obtained from cone penetrometer (CPT)

surveys should be compared with lithologic information obtained from adjacent

conventionally drilled and sampled boreholes to verify the CPT results. When geophysical

surveys are used to characterize a site, information from geophysical surveys should be used

in conjunction with other physical data both to verify the initial interpretations of the

geophysical methods and to provide constraints to remove some of the non uniqueness of the

geophysical data.

A site investigation should include characterization of:

The subsurface materials below the owner/operator's hazardous waste facility,

including:

The lateral and vertical extent of the uppermost aquifer;

The lateral and vertical extents of upper and lower confining

units/layers;

The geology at the owner/operator's facility (e.g., stratigraphy,

lithology, structural setting); and

The chemical properties of the uppermost aquifer and its confining

layers relative to local ground water chemistry and hazardous wastes

managed at the facility, as it relates to the parameters specified in 40

CFR Part 265.

November 1992

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