In August, a period of hot weather resulted in extremely dry soil conditions in
ID: 804511 • Letter: I
Question
In August, a period of hot weather resulted in extremely dry soil conditions in the eastern portion of the province. On August 10, water content in the Orthic Dark Gray Luvisols of the area northeast of Two Hills had dropped to 40% of field capacity. On August 12, a PCB spill occurred during replacement of transformers on a power line. A 50 m2 area of soil surface was contaminated. The power company's spill clean-up crew was dispatched with orders to remove the surface soil to a depth of 15 cm and ship it to the Swan Hills Toxic Waste Facility for disposal. But on the evening of August 12, before the clean up commenced, a rainfall of 6 cm occurred and infiltrated the soil. The clean-up crew was worried that the contaminant may have been moved below 15 cm with the infiltrating water, and wondered if they should excavate to a greater depth to ensure removal of all the contaminant.
a. As the company's soil expert, you are called to calculate the excavation depth required to insure removal of possibly contaminated soil water. Express your answer in centimeters of soil to be removed
there is no preferential flow in these soils, and each incremental soil layer remains at field capacity as the wetting front moves downward,
water content at field capacity for this soil is 49%
water content at the wilting point for this soil is 24%
total porosity is 65%
the texture is: sand (19%), silt (30%), clay (51%)
the organic matter content is 3.4%.
Explanation / Answer
Answer:
To avoid the contaminated water, 15 cm depth excavation would be fine as the soil layer have only 65 % total porosity. And texture also having 51 % clay, 30% silt which only give porous medium not permeable to reach the contaminant upto more deeper level.