Science of Water : Concepts and Applications

328 The Science of Water: Concepts and Applications
Example 10.5
Problem:
A well produces 260 gpm. If the drawdown for the well is 22 ft, what is the specifi c yield in gpm/ft of
drawdown?
Solution:
Example 10.6
well yield, gpm
Specific yield, gpm/ft
drawdown, ft
260 gpm
22 ft
118 gpm/ft
Problem:
The yield for a particular well is 310 gpm. If the drawdown for this well is 30 ft, what is the specifi c
yield in gpm/ft of drawdown?
Solution:
well yield, gpm
Specific yield, gpm/ft
drawdown, ft
310 gpm
30 ft
10. 3 gpm/ft
Well Casing Disinfection
A new, cleaned, or a repaired well normally contains contamination, which may remain for weeks
unless the well is thoroughly disinfected. This may be accomplished by ordinary bleach in 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:
Example 10.7
Chlorine, lb (chlorine, mg/L)(casing volume, MG)(8.34 lbgal) (10.4)
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-fi lled casing is 110 ft, how many pounds of chlorine will be required?
Solution:
First calculate the volume of the water-fi lled casing:
3
(0.785) ( 0.67) ( 0.67) ( 110 ft) ( 7.48 gal/ft )
290 gal