Geology Reference
In-Depth Information
FIGURE 12.1
Types of primary (A-D) and secondary (E, F) porosity. A, well-sorted sedimentary deposit having high porosity; B, poorly
sorted sedimentary deposit having low porosity; C, well-sorted sedimentary deposit consisting of pebbles that are themselves porous,
so that the deposit as a whole has a very high porosity; D, well-sorted sedimentary deposit whose porosity has been diminished
by the deposition of mineral matter in the interstices; E, rock rendered porous by solution; F, rock rendered porous by fracturing
(Meinzer, 1923, p. 3).
TABLE 12.1 Range in Hydrologic Properties of Selected Geologic Materials
Material (rock or regolith)
Porosity (n) %
Effective Porosity (n
e
) (%)
Hydraulic Conductivity
(K)
(ft/day)
Gravel
25-40
15-30
100-10000
Sand
30-40
10-30
0.1-1500
10~
7
-10
Clay, silt
45-60
1-10
Till
10"
7
-0.1
20-40
6-16
10~
4
-1
Sandstone
10-30
5-15
8
-10
Shale
1-10
0.5-5
10
Limestone
1-20
10~
3
-10
4
0.5-5
10"
8
-10
Igneous rocks
0-40
0-30
10~
8
-10
Metamorphic rocks
0-40
0-30
FIGURE 12.2
Schematic diagram of artesian and water table aquifers. Horizontal lines show well screen.
