## Calculation Of A Pore Volume

To learn how to calculate pore volumes, let us use an example from the experiment by Vogeler et al. (2001). They studied phytoremediation of soil contaminated with copper using poplar. The lysimeter with the poplar is shown on the cover of the book edited by Iskandar and Kirkham (2001). FIG. 12.11 Tritium breakthrough curve for Yolo loamy sand at two different water contents. The bicolored circle shows where 0.5 pore volume would occur. (From Advanced Soil Physics by Kirkham, D., and Powers, W.L., p. 388, ©1972, John Wiley & Sons, Inc.: New York. This material is used by permission of John Wiley & Sons, Inc. and William L. Powers.)

FIG. 12.11 Tritium breakthrough curve for Yolo loamy sand at two different water contents. The bicolored circle shows where 0.5 pore volume would occur. (From Advanced Soil Physics by Kirkham, D., and Powers, W.L., p. 388, ©1972, John Wiley & Sons, Inc.: New York. This material is used by permission of John Wiley & Sons, Inc. and William L. Powers.)

A solution of copper in the form of Cu(NO3)2 was added to the surface of the soil (Manawatu fine sandy loam) in the lysimeter. Then, everyday, the lysimeter was irrigated and drainage water was collected. After running the experiment for one week, Vogeler et al. (2001) wanted to know how many pore volumes had passed through the lysimeter. One pore volume was calculated as follows. The shape of the lysimeter was that of a large cylinder, 1.30 m long with a diameter of 0.85 m. The volume of the lysimeter was:

Let qs = saturated water content = 0.40 m3/m3. This value was known from previous measurements.

One pore volume = volume x 0s = 0.737 m3 x 0.40 m3/m3 = 0.295 m3.

0.295 m3 x (1 x 106 cm3)/(1 m3) = 295,000 cm3 = 295 liters.

After 7 days of drainage, 70 liters had been collected. Thus, (70 L)/(295 L) = 0.24 or about 1/4 pore volume.

To get one pore volume, Vogeler et al. (2001) needed to collect drainage water for one month. The experiment was run for two months to get two pore volumes.

Another example of calculating pore volumes is given by Singh and Kanwar (1991). They did a column study and calculated the value of one pore volume for each column by multiplying total porosity by the total volume of the soil column. Soil porosity for each column was estimated by using bulk density and particle density (Equation 7.2). Note that in either case [the experiment by Vogeler et al. (2001) or the experiment by Singh and Kanwar (1991)], the whole pore volume is used to calculate pore volume. Vogeler et al. (2001) used the saturated water content (all pores filled with water); Singh and Kanwar used the total porosity.

In the theoretical development of pore volume (Section III), the water-filled porosity, a, is used to calculate a pore volume. In practice, we do not know which pores have air and which pores have water, and hence, which pores are carrying the solute. So in our calculations in this section (above), the water-filled porosity becomes the porosity or the saturated water content. However, we note that the level of saturation affects the shape of the breakthrough curve. We see this by comparing Fig. 12.7, the breakthrough curve for a saturated soil, with Fig. 12.8, the breakthrough curve for an unsaturated soil. As one pore volume is attained, the slope in Fig. 12.7 is steeper than in Fig. 12.8.

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### Responses

• veli-matti
How to find pore volume?
1 year ago
• alfredo
What is the formular for pore volume?
1 year ago
How to calculate pore volume?
1 year ago
• JOEL
How to compute pore volume?
12 months ago
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How many liters is 6 pore volumes?
11 months ago
• Ted
How to calculate the volume of pores?
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How to calculate specific pore volume?
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How to calculate specfific pore volume?
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How to calculate pore volumes?
5 months ago
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How to find volume of pore space?
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How to calculate the pore volume with surface area?
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How to calculate porosity using volumes?
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18 days ago