When establishing the locations of wells that will be used to monitor ground water in

hydrogeologic settings characterized by ground water flow in porous media, the following

should be documented:

Ground water flow rate should be based on accurate measurements of hydraulic

conductivity and hydraulic gradient, and accurate measurements or estimates of

effective porosity;

The horizontal and vertical components of flow should be accurately depicted

in flow nets and based on valid data; and

Any seasonal or temporal variations in the water table or potentiometric

surface, and in vertical flow components, should be determined.

Once an understanding of horizontal and vertical ground water flow has been

established, it is possible to estimate where monitoring wells will most likely intercept

contaminant flow.

4.4.2

Presenting Hydrogeologic Data

Subsequent to the generation and interpretation of site specific geologic data, the data

should be presented in geologic cross sections, topographic maps, geologic maps, and soil

maps. The Agency suggests that owners/operators obtain or prepare and review topographic,

geologic, and soil maps of the facility, in addition to site maps of the facility and waste

management units. In cases where suitable maps are not available, or where the information

contained on available maps is not complete or accurate, detailed mapping of the site should

be performed by qualified and experienced individuals. An aerial photograph and a

topographic map of the site should be included as part of the presentation of hydrogeologic

data and should meet the requirements of   270.13(h) and 270.14(b)(19), respectively. The

topographic map should be constructed under the supervision of a qualified surveyor and

should provide contours at a maximum of two foot intervals, as shown in Figure 7. Aerial

photographs with acetate overlays, the use of geologic data bases, or Geographic Information

Systems (GIS) may be suitable methods for presenting some data.

Geologic and soil maps should be based on rock, unconsolidated material, and soil

identifications gathered from borings and outcrops. The maps should use colors or symbols

to represent each soil, unconsolidated material, and rock type that outcrops on the surface.

The maps also should show locations of all borings and outcrops placed during the site

characterization. Geologic and soil maps are important because they can provide interpretive

information describing how site geology fits into the local and regional geologic setting.

November 1992

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