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.
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 ):
v =   Ki
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.
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.
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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