Page 326 - Materials Chemistry, Second Edition

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The Sanitary Landfill 297

FIGURE 10.3 Installation of a layer of low-permeability clay. The clay is spread in two lifts and then
rolled. (Reproduced with kind permission of the Town of Bourne Department of Integrated Solid Waste
Management, MA).

TABLE 10.2
Categories of Common Clays and Some Important Chemical and Physical
Properties

Clay Substitution Interlayer Swelling Cation Total Surface
2
Component Exchange Area (m /g)
Capacity
(cmol/kg)
Kaolinite None None None 3–15 10–20
Illite T K None 15–40 65–100
Vermiculite T/Oc H O Moderate 100–200 600–700
2
Smectite Oc/T Cations, H O High 80–150 700–800
2
Chlorite — Mg(OH) 2 None 10–50 75–100
T tetrahedral layer; Oc octahedral layer.

Henri Darcy, a 19th century French engineer, developed one of the earliest descriptions of
groundwater flow. He observed a relationship between the volume of water flowing through sand
and properties of the sand, and formulated the equation

Q/t KA dH/dL (10.1)

where Q is the volume of flow per unit time t through a column of a given cross-sectional area of
flow A. The flow is under a pressure gradient dH/dL, and the change in water level over a given
length is L. K is the saturated hydraulic conductivity, a proportionality constant. The difference in
elevation of the water table, dH or (h -h ) over the length (L) is the slope of the water table or the
2
1
hydraulic gradient. Darcy’s law calculates the volumetric flow rate through a unit cross section of