Once the LNAPL is in contact with the capillary fringe, when it reaches and exceeds the entry pressure (inversely related to the pore throat radius), it can displace water and penetrate the water table; otherwise, it starts spreading laterally [4-6].
According to the Pancake Model, once LNAPL reaches the water table, due to its immiscibility in water, it remains suspended on the capillary fringe above the water table as a buoyant pool with uniform, constant, and complete saturation [4, 6, 32, 33] (although sometimes a saturation lower than 1 is assumed ).
We estimated the height of the capillary fringe (CF) in the soil using a 90-cm long, clear plastic cylinder (4.8-cm inside diameter) filled with dry soil in the same manner as pots.
RESULTS--Four independent trials indicated the height of the capillary fringe in the pots of soil likely reached the surface of the soil in the treatments [D.sub.W] = S but not in the treatments [D.sub.W] = L.
The capillary fringe (CF), the zone immediately above the water table, is nearly saturated even though it is considered to be part of the vadose (unsaturated) zone.
Solute transport in the capillary fringe and shallow groundwater: Field evaluation.
- The capillary fringe
of the watertable must be close enough to the surface of the playa such that evaporation will cause water to discharge to the surface.
However, salt build-up in the capillary fringe
means that the salinity of the groundwater needs to be relatively low (<5 dS/m), or uptake rate from the watertable low, unless leaching takes place.
The two most common classes are a) NAPLs composed of fuel hydrocarbons that are lighter (LNAPLs) than water and, thus, more easily detected, because they tend to remain within the unsaturated zone or capillary fringe
areas of an aquifer; and b) organic solvent or dense NAPLs (DNAPLs) that tend to migrate deep into formations, becoming entrapped in irregular finger-like structures or pooled on low permeability strata.
Tree whips were placed immediately above the capillary fringe
of the water table (at six to nine ft below ground surface) with 0.5 to one exposed above ground.
Extending above the water table is a wet zone created by capillary rise called the capillary fringe
. The height of the fringe varies from about six inches in sand to about eighteen inches in fine-textured soil.
In periods when salt accumulates in the root zone between the capillary fringe
and the soil surface, the tree drops its leaf water potential, a mechanism which increases its ability to extract water from the soil.