This document provides instructions on how to calculate the volume of a well. It discusses that the dimensions needed are the well diameter, total depth, and water depth. An example calculation is shown for a hand dug well that is 3 feet in diameter and 45 feet deep with 10 feet of water. The volume is calculated using the formula of pi times the diameter squared times the depth. Alternative methods for calculating plugging material needs are also described, such as using a table that lists the amount of cement or bentonite needed based on the well diameter.

1. How to Calculate the Volume
of a Well

2. Introduction
• Discuss which dimensions are needed.
• How to obtaining the dimensions.
• Example
• Alternative method

3. Goals of this Presentation
• Establish the importance of properly
calculating the volume of a well.
• Describe the dimensions that are needed
for the calculation and how to obtain them.
• Create a clear understanding of the
calculations through an example problem.
• Describe alternate methods to completing
the calculations.

4. Why is this important?
• The volume of the well is used to
determine the amount of plugging material
needed.
• The volume is also used to determine the
needed amount of disinfectant.
• Assuming the wrong volume of the well
could lead to many future problems.

5. According to the video what
dimensions are needed in order to
accurately calculate the volume of
a well?
• Well diameter
• Total depth
• Depth of the water

9. Obtaining Well Dimensions
• Diameter of the well – measured distance across
the inner lip of the well
• Total well depth – measured distance from top to
bottom of well.
• Water depth – measured distance of depth of
water in the well. (Tie a weight to some string
and drop it to the bottom of the well. Retrieve the
string and measure the portion of the string that
is wet.)

10. Hand Dug Well Example
• You have large hand dug well that is 3 feet
in diameter and is 45 feet deep. The
depth of water in the well is 10 feet.

11. Hand Dug Well Example
• The volume of the well is calculated by the
formula.
V = ((Π * D2)/ 4)* d
Where :
Π= 3.1416
D=diameter of well (feet)
d= depth of well (feet)

12. Hand Dug Well Example
• The volume of the well is
V= ((3.416* 32)/4) *45
V= 318.53 ft3
1 yd3 = 27 ft3
V= 11.79 yd3

13. Example
• An abandoned well is 6 inches in diameter,
100 feet in depth, and the water level is 40
feet.

14. Prior to groundwater sampling, the wells are purged because a freshwater
sample is needed to accurately assess groundwater quality. Typically,
purging monitoring well of three well volumes is considered sufficient to
obtain a valid sample.:
Well volume = π/4 × (Well diameter)² × (Total well depth - Static water
depth)
Where:
π - The mathematical constant, approximately equal to 3.14159.
The total volume of water a cylindrical well can hold is calculated as shown
below:
Total well volume = π/4 × (Well diameter)² × (Total well depth)
Calculating three times the well volume is as shown here:
Three well volumes = 3 * Well volume
Well Purge Volume Calculation

15. Well volume equation

16. Alternate Method
• Use Table 1 Plugging Material Calculation
Sheet.
• And the diameter of the well.

17. Well or Hole
Diameter
Cement Bentonite Chips
Inches Linear Feet Linear Feet
2 50.3 31.3
3 28.8 13.9
4 16.2 1.9
5 10.4 5
6 7.2 3.5
7 5.3 2.6
8 4 2
9 3.2 1.5
10 2.6 1.3
12 1.8 0.86
14 1.3 0.63
16 1 0.48
18 0.8 0.38
20 0.6 0.31
24 0.4 0.21
36 0.2 0.097
40 0.16 0.078
44 0.13 0.065
48 0.11 0.054

18. Alternative Method
• Bags of cement needed (94 lb per sack)
100 feet / 7.2 feet = 13.8 sacks
• Bags of Bentonite needed (50 lb per sack)
100 feet / 3.5 feet = 28.5 sacks

19. Conclusion
• Well depth, diameter, and depth of the
water are all needed in calculating the
volume of the well.
• How to obtain these dimensions.
• There are several ways to calculate the
amount of plugging material that is
needed.