Water Source and Storage Calculations - Basic Mathematics for Water and Wastewater Operators - page 220

Discharge

Static water level

Ground surface Pump

Drawdown

Cone of depression

Pump water level

Zone of inuence

FIGURE 15.1 Drawdown.

time to explore alternative sources, establish conservation measures, or obtain any
special funding that may be needed to get a new water source. Well drawdown is the
difference between the pumping water level and the static water level:

Drawdown (ft) = Pumping water level (ft) - Static water level (ft) (15.1)

■ Example 15.1
Problem: The static water level for a well is 70 ft. If the pumping water level is 90 ft,
what is the drawdown?

Solution:

Drawdown = Pumping water level (ft) - Static water level (ft) = 90 ft - 70 ft = 20 ft

■ Example 15.2
Problem: The static water level of a well is 122 ft. The pumping water level is deter-
mined using the sounding line. The air pressure applied to the sounding line is 4.0
psi, and the length of the sounding line is 180 ft. What is the drawdown?

Solution: Calculate the water depth in the sounding line and the pumping water level:

1. Water depth in sounding line = 4.0 psi × 2.31 ft/psi = 9.2 ft

2. Pumping water level = 180 ft - 9.2 ft = 170.8 ft

Then calculate drawdown as usual:

Drawdown = Pumping water level (ft) - Static water level (ft)

= 170.8 ft - 122 ft = 48.8 ft