permeability or fracture identified from drilling logs should be considered when evaluating

hydraulic conductivity. Information from boring logs can be used to refine the data generated

by single or multiple well tests, and a comparison with existing data from nearby localities

that are in a similar geologic setting also can be useful.

4.3.5

Determining Ground Water Flow Rate

The calculation of average ground water flow rate (average linear velocity of ground 

water flow), or seepage velocity, is discussed in detail in USEPA (1989c), in Freeze and

Cherry (1979), and in Kruseman and deRidder (1989). The average linear velocity of ground 

water flow (v) is a function of hydraulic conductivity (K), hydraulic gradient (i), and effective

porosity (n ):

e

v =   Ki

n

e

Methods for determining hydraulic gradient and hydraulic conductivity are presented

in Sections 4.3.3 and 4.3.4 of this Manual. Effective porosity, the percentage of the total

volume of a given mass of soil, unconsolidated material, or rock that consists of

interconnected pores through which water can flow, should be estimated from laboratory tests

or estimated from values cited in the literature. (Fetter (1980) provides a good discussion of

effective porosity. Barari and Hedges (1985) provide default values for effective porosity.)

USEPA (1989c) provides methods for determining flow rates in heterogeneous and/or

anisotropic systems and should be consulted prior to calculating flow rates.

4.4

Interpreting and Presenting Data

The following sections offer guidance on interpreting and presenting hydrogeologic

data collected during the site characterization process. Graphical representations of data, such

as cross sections and maps, are typically extremely helpful both when evaluating data and

when presenting data to interested individuals.

4.4.1

Interpreting Hydrogeologic Data

Once the site characterization data have been collected, the following tasks should be

undertaken to support and develop the interpretation of site hydrogeologic data:

Review borehole and well logs to identify major rock, unconsolidated material,

and soil types and establish their horizontal and vertical extent and distribution;

From borehole and well log (and outcrop, where available) data, construct a

minimum of two representative cross sections for each hazardous waste

November 1992

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