Assessment of a Reclamation Cover System for Phosphogypsum Stacks in Central Alberta, Canada

Abstract

Phosphogypsum (PG), a byproduct of the phosphate fertilizer industry, was produced and stockpiled at the Agrium Fort Saskatchewan facility from 1965 to 1991. Upon decommissioning, the outer slopes of the PG stacks were reclaimed by applying 15 cm of topsoil and planting a non-native seed mix. Physical, chemical, and hydrologic evaluations of the cover system confirmed that plants were successfully growing in various soil capping depths and were often rooting more than 200 mm into the PG. Percolation past the substrate into PG during a typical storm event was low (< 10 mm), and runoff from the stacks was negligible. Runoff quality met most guidelines, but some parameters, including fluoride, were up to 18 times higher than provincial or federal guidelines for soil and water quality. However, the cover system, when applied appropriately, does meet basic reclamation objectives. The exceedances are found in areas where the cover system has been compromised by erosion or mixing or in areas where the cover system has not been fully applied, such as roads or the inner basin. In areas where the cover system has been applied successfully, basic reclamation requirements are met.

Phosphogypsum Capping Depth Affects Revegetation and Hydrology in Western Canada

“…Precipitation amount and antecedent precipitation index did not appear to influence water content below the soil/PG interface. Hallin (2009) and Hallin et al (2010) also found that high‐magnitude events resulted in small ΔW in PG (0.3–1.9 mm) on sites with cover material between 20 and 27 cm.…”

“…Richardson et al (1995) studied Florida PG stacks and found numerous grass species established on PG with pH >4 or with amendments such as limestone, sand tailings, overburden, or composted municipal solid waste. Hallin (2009) and Hallin et al (2010) found that water movement through a 20-to 27-cm-thick soil cap into PG was low during rainfall events of varying magnitudes. In Florida, Fuleihan et al (2005) found that leached PG side slopes with dolomitic limestone disked into the upper 15 cm followed by sodding yielded runoff water of suitable quality for discharge into surface water bodies.…”

“…Hallin (2009) and Hallin et al (2010) found that water movement through a 20‐ to 27‐cm‐thick soil cap into PG was low during rainfall events of varying magnitudes. In Florida, Fuleihan et al (2005) found that leached PG side slopes with dolomitic limestone disked into the upper 15 cm followed by sodding yielded runoff water of suitable quality for discharge into surface water bodies.…”

“…Thorne (1990) found adding soil or lime to PG tailings in a greenhouse addressed many revegetation limitations. In Fort Saskatchewan, Alberta, a 15‐yr‐old cover on a PG stack provided an effective barrier between PG and the environment (Hallin, 2009; Hallin et al, 2010). Caps met Canadian and Alberta guidelines with small fluorine exceedances.…”

Soil science at the University of Alberta: a century of service to science and society

“…Other areas of reclamation built on initial research and included soil physical properties (Naeth et al 1991;Naeth 1995, 1996). Phosphogypsum stack reclamation research showed the importance of cover soils for revegetation, and to minimize leaching and percolation through the stack (Hallin et al 2010;Jackson et al 2011;Turner 2012;Abou Rizk 2015;Robinson 2018). Limestone quarry reclamation was enhanced with soil capping, amendment with pulp mill biosolids and manure, and with erosion control materials (Cohen-Fernandez et al 2013;Cohen-Fernández and Naeth 2013).…”