Water Source and Storage Calculations - Basic Mathematics for Water and Wastewater Operators - page 222

■ Example 15.6
Problem: The yield for a particular well is 310 gpm. If the drawdown for this well is
30 ft, what is the specific yield in gpm/ft?

Solution:

Specific yield = Well yield (gpm) ÷ Drawdown (ft) = 310 gpm ÷ 30 ft = 10.3 gpm/ft

W ell C asing d isinfeCtion
A new, cleaned, or a repaired well normally contains contamination that may remain
for weeks unless the well is thoroughly disinfected. This may be accomplished by
using ordinary bleach at a concentration of 100 parts per million (ppm) of chlorine.
The amount of disinfectant required is determined by the amount of water in the
well. The following equation is used to calculate the pounds of chlorine required for
disinfection:

Chlorine (lb) = Chlorine (mg/L) × Casing volume (MG) × 8.34 lb/gal (15.4)

■ Example 15.7
Problem: A new well is to be disinfected with chlorine at a dosage of 50 mg/L. If the
well casing diameter is 8 in. and the length of the water-filled casing is 110 ft, how
many pounds of chlorine will be required?

Solution: First calculate the volume of the water-filled casing:

0.785 × 0.67 × 67 × 110 ft × 7.48 gal l /f ft 3 = 290 gal

Then determine the pounds of chlorine required using the mg/L to lb equation:

Chlorine = Chlorine (mg/L) × Volume (MG) × 8.34 lb/gal

= 50 mg/L × 0.000290 MG × 8.34 lb/gal = 0.12 lb

d eep -W ell t urBine p uMp C alCulations
The deep-well turbine pump is used for high-capacity deep wells. The pump, con-
sisting usually of more than one stage of centrifugal pump, is fastened to a pipe
called the pump column ; the pump is located in the water. The pump is driven from
the surface through a shaft running inside the pump column. The water is discharged
from the pump up through the pump column to the surface. The pump may be driven
by a vertical shaft, electric motor at the top of the well, or some other power source,
usually through a right-angle gear drive located at the top of the well. A modern ver-
sion of the deep-well turbine pump is the submersible type of pump, where the pump
(as well as a close-coupled electric motor built as a single unit) is located below water
level in the well. The motor is built to operate submerged in water.