Tailings generally segregate corresponding to location within the impoundment: coarse- to fine-grained sands at the dams, sandy silts in perimeter mixed zones, and silt (slimes) in the decant area. The latter two types comprise the majority of tailings. Tailings at the point of discharge are typically basic (pH > 9.5). Whether tailings turn acid is dependent on the amount of sulfide minerals, oxygen and water reactants present. Depending on the ore body, tailings with 1 to 3% sulfide (as pyrite) may not turn acid due to the neutralization capacity of the tailings. Typically there is limited oxygen ingress into finer grained tailings whereas dam faces are more susceptible to acid generation due to sufficient air flow. Although a number of studies have shown that the addition of organic matter to circumneutral tailings (such as biosolids and green waste) improves textural properties and fertility and allows revegetation. Slighty acid tailings (i.e. pH > 3) with limited additional pyrite have also been neutralized, amended and re-vegetated successfully. However, limited water availability and high erosion rates make direct revegetation of sandy tailings at the dam faces virtually impossible. The addition of nominal (one foot or less) amounts of growth media significantly affects the revegetation of non-acid tailings. Primary root growth occurs in the growth media, but rooting extends at depth into the tailings in order to extract moisture during dry periods. Indeed, high moisture retention in the sandy silts and slimes can result in vigorous growth of deep-rooted trees and shrubs after reclamation. Acid tailings with high acidity (pH < 3) and/or high residual pyrite concentrations need to be capped with cover material. However, even with thick covers where roots do not extend into the tailings, the moisture retained in tailings can be wicked via evapotranspirative demand during very dry periods.