Ground water flow below the owner/operator's hazardous waste facility,

including:

The vertical and horizontal directions of ground water flow in the

uppermost aquifer;

The vertical and horizontal components of hydraulic gradient in the

uppermost aquifer;

The hydraulic conductivities of the materials that comprise the

uppermost aquifer and its confining units/layers; and

The average linear horizontal velocity of ground water flow in the

uppermost aquifer.

The following sections outline the basic steps of a site hydrogeologic characterization,

and detail methods for collecting and presenting data.

4.1

Preliminary Investigation

The preliminary investigation is a comprehensive review of the available information

relating to the site. The preliminary investigation has two purposes: (1) to allow the

owner/operator to formulate conceptual models of regional and site specific hydrogeology,

and (2) to provide a basis for designing field investigations that will be used to obtain data to

refine the conceptual model of the site. This investigation should be performed prior to

conducting a field investigation and designing and installing a ground water monitoring

system.

The owner/operator should review the available information about the hydrogeology of

the site and the surrounding region to gain an understanding of the stratigraphic distribution

of soil, unconsolidated materials, and rock, and of the surface and ground water systems. The

preliminary investigation should include the review of the following information, as available:

The waste management history of the site, including:

A chronological history of the site that includes a description of the

wastes and raw materials managed (treated, stored, or disposed) on site;

A summary of documented releases from waste, product, or materials

management/storage areas;

November 1992

4 5