4.3.3.2

Establishing Horizontal Flow Direction and the Horizontal Component

of Hydraulic Gradient

After the water level data and measurement procedures are reviewed to determine that

they are accurate, the data should be used to:

Construct potentiometric surface maps and water table maps that are based on

the distribution of total head, such as the example in Figure 4. The data used

to develop water table maps should be from piezometers or wells screened

across the water table. The data used to develop potentiometric surface maps

should be from piezometers or wells screened at approximately the same

elevation in the same hydrostratigraphic unit;

Determine the horizontal direction(s) of ground water flow by drawing flow

lines on the potentiometric surface map or water table map (i.e., construct a

flow net); and

Calculate value(s) for the horizontal and vertical components of hydraulic

gradient.

Methods for constructing potentiometric surface and water table maps, constructing

flow nets, and determining the direction(s) of ground water flow, are given by USEPA

(1989c) and Freeze and Cherry (1979). Methods for calculating hydraulic gradient are

provided by Heath (1982) and USEPA (1989c).

A potentiometric surface or water table map will give an approximate idea of general

ground water flow directions; however, to locate monitoring wells properly, ground water

flow direction(s) and hydraulic gradient(s) should be established in both the horizontal and

vertical directions and over time at regular intervals (e.g., over a one year period at three 

month intervals).

4.3.3.3

Establishing Vertical Flow Direction and the Vertical Component of

Hydraulic Gradient

To adequately determine the ground water flow directions, the vertical component of

ground water flow should be evaluated directly. This generally requires the installation of

multiple piezometers or wells in clusters or nests, or the installation of multi level wells or

sampling devices. A piezometer or well nest is a closely spaced group of piezometers or

wells screened at different depths, whereas a multi level well is a single device. Both

piezometer/well nests and multi level wells allow for the measurement of vertical variations in

hydraulic head. To obtain reliable measurements, the following criteria should be considered

in the evaluation of data from piezometer/well nests and multi level wells:

November 1992

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