Page 39 - Water Engineering Hydraulics, Distribution and Treatment

Removable cover
Drainage
diversion ditch
Valve
Screened
stem
overflow
25 ft
or more
Rock drain
Water-bearing
sand or gravel
Screen
Screened 1.11 Individual Water Systems 17
Valve drain
Impervious stratum
Figure 1.11 Water supply from spring
Supply line (After US Public Health Service).
to storage
Conversion factor: 1 ft = 0.3048 m.
1.11 INDIVIDUAL WATER SYSTEMS
Because of the natural purifying capacity and protection of
the soil, individual and rural water supplies are generally
1˝ minimum Pump
drawn from springs, infiltration galleries, and wells. Where above base
groundwater is highly mineralized or unavailable, rainwater Manhole
5˝
is next best in general safety and quality. Only in uninhabited
and well-protected upland areas should ponds and streams 9˝
be tapped without purifying the waters drawn. 6˝
Some of the safeguards for groundwater works are illus- 20˝ square
trated in Figs. 1.11, 1.12, and 1.13. They share the following 1´–6˝
features in common:
1. Diversion of surface water from intake structures
2. Drainage of overflow or spillage waters away from 10´–0˝ minimum Cemented
joints
intake structures
3. Water tightness of intake works for at least l0 ft (3 m)
below the ground surface and, if necessary, until the
Concrete
aquifer is reached
36˝ diam
4. Prevention of backflow into intakes; where there is
no electric power, water is pumped by hand, wind,
water, or gasoline engines
Gravel
Individual and rural water supplies are not without
their purification problems. Gravity and pressure filters are
employed to improve waters of doubtful purity, and zeo-
Stone or
lite softeners and other ion-exchange units are used for the coarse gravel
removal of unwanted hardness. Iron-bearing groundwaters
that issue from their source sparklingly clear but become
rusty on exposure to air (by oxidation and precipitation of
iron) are best treated in manganese cation exchange units.
Hexametaphosphates may keep iron from precipitating, but Figure 1.12 Water supply from dug well (After US Department
′
this requires skillful management. It may be advisable to seek of Agriculture). Conversion factors: 1 = 1ft = 0.3048 m;
′′
an iron-free source instead. 1 = 1in. = 2.54 cm.