Phosphogypsum (PG) is an acidic byproduct of the phosphate fertilizer industry, consisting primarily of gypsum (CaSO4.2H2O). It is typically stockpiled in waste repositories that can cover several hundred hectares in area and be over 30 meters high. Currently there are no regulations regarding closure and reclamation procedures for PG stacks in Alberta; each site is dealt with on an individual basis. One common reclamation objective for each site is to prevent water from percolating through the drained stack, as water collecting within PG can lead to dissolution of gypsum and surface instabilities such as sinkholes.

A research project was recently initiated on an inactive PG stack near Fort Saskatchewan, Alberta to determine if the establishment of a vegetation cover with a minimal amount of soil is adequate to prevent the infiltration of water into the gypsum stack in a semi-arid environment. Research is currently underway to assess the amount of infiltration at various positions on the PG stacks in association with different vegetation types. The quality and quantity of runoff is also being assessed.

Preliminary results suggest that water infiltration is greater than runoff at most sites on the stacks, and data from TDR probes is used to describe small scale moisture profiles. Moisture profiles are compared with topsoil depths to identify relationships between depth of water percolation and depth of cover material. These relationships could be useful for establishing common reclamation practices for other PG stacks in similar climate conditions.