Air Filled Porosity

In partially saturated media, the diffusion coefficient also is a function of the volumetric water content, 9. Calvet (1984) showed that the variation in soil water content influences the apparent diffusion coefficient for organic contaminants in two ways by changing the ratio of gas diffusion of volatilizable pollutants to liquid diffusion, because the air-filled porosity is affected, and by modifying pollutant... 

Groffman P. M. and Tiedje J. M. (1991) Relationships between denitrification, CO2 production and air-filled porosity in soils of different texture and drainage. Soil Biol. Biochem. 23, 299-302. 

Air-filled porosity of the soil at a given soil water content is obtained by subtracting the water content value from its total pore space. 

Subtract the value of volumetric water content finm the value of total porosity to get the value of air-filled porosity... 

Relation between volume wetness (0), air filled porosity (fa) and degree of saturation... 

The oxygen status of a soil is governed by the percent of soil pores filled with water, or air-filled porosity. Air-hlled porosity is dehned as the bulk volume of soil that is filled wifh air at any given time or under a given condition (such as specified moisture content), and can be described as follows ... 

FIGURE 6.4 Relationship between air-filled porosity of soil and the volume of anaerobic sites. 

Redox potential that measures electron activity in soils is used as an indicator of soil aeration status in upland environments. Changes in Eh values are small if sufficient oxygen is present in the soil pores. Aerated soils have characteristic Eh values in the range of +300 to +500 mV and air-filled porosity of 0-60% (Figure 6.5). The low concentration of redox couples in aerated soils reduces... 

FIGURE 6.5 Relationship between air-filled porosity and redox potential of soil. 

Discuss the factors influencing oxygen exchange in flooded or waterlogged soil. Explain the importance of water-filled porosity as compared to air-filled porosity on oxygen exchange. 

Strength, porosity and ease of compaction,and ultimately affects the rate of biodegradation. Air-filled porosity and permeability relationships are different for different substrates and mix of these substrates, as each substrate and mix will have a different distribution of particle sizes and shapes, and these mixtures can be compacted to various wet and dry bulk densities. " ... 

Terra-Vac, Inc., developed the In-Situ Vacuum Extraction process, which removes volatile organic constituents (VOCs) from the unsaturated zone of soils through extraction wells. The extracted gases and water proceed to a vapor-liquid separator and an emission control system. The process has been employed at over 60 sites. Four case studies, including three Superfund sites, have been documented. The process represents a viable technology to fully remediate sites contaminated with volatile organics. Considerations for use include contaminent volatility, site-specific cleanup level, and soil properties. The process works well with most soil types. The air-filled porosity of a soil is an important criterion to indicate whether vacuum extraction will work. Soils with low permeability but with... 

Many empirical equations describing the relationship between the effective diffusion coefficient and the air-filled porosity of homogeneous soils have been developed of the form... 

Sallam, A., W. A. Jury, and J. Letey. 1984. Measurement of gas diffusion under relatively low air-filled porosity. Soil Science Society of America Journal 48 3-6. 

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