4.2.2

Laboratory Analyses of Soil, Unconsolidated Material, and Rock

Samples

In addition to the field descriptions outlined above, the owner/operator should conduct,

where necessary, laboratory analyses of each significant geologic unit and each soil zone in

the unsaturated and saturated zones. These analyses can provide the following information:

Mineralogy and chemistry of the aquifer and confining units or layers, as

determined by optical and analytical techniques (e.g., microscopic analysis and

other analyses such as cation exchange capacity, atomic absorption

spectroscopy, inductively coupled plasma atomic emission spectroscopy, and X 

ray diffraction). In some circumstances, such as where high concentrations of

solvents may come into contact with a clay confining layer, it is important to

characterize the clay mineralogy accurately;

Petrographic analysis of the confining layer and each unit above the confining

unit/layer to determine petrology and petrologic variation including:

composition and degree of cementation of the matrix,

composition, degree of sorting, size fraction, and textural variation in

the framework grains, and

existence of small scale structures that may affect fluid flow;

Moisture content and moisture variation of each significant soil zone and

geologic unit;

An estimate of hydraulic conductivity of each significant soil, unconsolidated

material or rock unit in the unsaturated zone as determined by constant head

and falling head laboratory permeability tests on core samples that have been

collected in a manner that minimizes sample disturbance. The results of

laboratory hydraulic conductivity tests should be evaluated and used carefully

because these tests may not quantify secondary permeability factors that are

important in contaminant migration;

General composition of the sample as determined by examination of

unconsolidated materials with a binocular microscope;

Particle size analyses of unconsolidated or poorly consolidated samples using

sieves and/or pipettes to determine gravel sand silt clay content and the size

range of sand and silt particles.

November 1992

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