Page 159 - Water and wastewater engineering

4-14 WATER AND WASTEWATER ENGINEERING

®
Although the solubility of HTH is about 215 g/L at 0 C, a more practical working solution
is at about one-third of this concentration, that is
215g/L
71 66 or 72g/L
.
3
The volume of stock solution is then

201 5 g
.
stock 2 799 or 2 8 . L
V
.
72 g/L

Structural Protection
Every well should be provided with an overlapping, tight fitting cover at the top of the casing
to prevent contaminated water from entering the well. In Figure 4-6 this is done with a concrete

pad 1.2 m in diameter. The concrete pad should slope away from the well head. The slab should
be poured separately from the grout seal and, where the threat of freezing exists, insulated
from it and the well casing by a plastic or mastic coating to prevent bonding of the concrete to
either.
The top of the well should be readily accessible for inspection, servicing, and testing.
This requires that any structure over the well be easily removable to provide full, unobstructed
access.

Well House. For municipal wells, a well house is a common means of providing structural
protection. Figure 4-7 is an example of a typical well house. In addition to the sanitary protection
features noted in Figure 4-6 , the following are typically specified:
• A removable roof or hatch to allow for access to the top of the pump by a crane. This will
make maintenance of motors, pumps, and screens much easier.
• Thermostatically controlled auxiliary heat in cold climates. This will prevent lines from
freezing when the pump is not running or when the heat from the pump cannot compensate
for excessively low temperatures.

• Ventilation with a thermostat controller. Although motors are designed to “run hot,” in
warm climates the introduction of ambient air is required to keep them operating within
their service range.

• Lightning protection. Valve type arresters are preferred. The arrester must be connected to
a good ground. Connecting the ground terminal of the arrester to a copper rod driven into
the ground does not provide a good ground. It should be connected to the motor frame of a
submersible pump or to a casing that reaches the groundwater when the pump motor is at
the ground surface.
• Security features. Typically these include the absence of windows, doors without windows,
keyed locks, intrusion alarms.