Question 8

Depth From Surface

Earth Material

Porosity

0 – 20 feet

Clay

50%

20 – 40 feet

Mixed silt, sand, gravel

25%

The table above is a section of a driller’s log that contains a description of the different earth materials that the driller encountered while drilling a borehole for a well from the ground down to 40 feet. The third column show the representative porosity value in percent for the earth materials listed in the log. The calculated weighted average porosity for the earth materials from the ground surface down to 40 feet is:

29.5%

32.5%

33.3%

37.5%