Salinization of soil over saline-sodic overburden from the oil sands

Salinization of soil over saline-sodic overburden
from the oil sands in Alberta
Sophie Kessler1, S. Lee Barbour2, Ken C. J. van Rees3, and Bonnie S. Dobchuk1
1
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
O’Kane Consultants Inc., 2312 Arlington Ave., Saskatoon, Saskatchewan, Canada S7J 3L3
(e-mail:[email protected]); 2College of Engineering, University of Saskatchewan, 57 Campus
Dr., Saskatoon, Saskatchewan, Canada S7N 5A9; and 3College of Agriculture and Bioresources,
University of Saskatchewan, 51 Campus Dr., Saskatoon, Saskatchewan, Canada S7N 5A8.
Received 28 January 2010, accepted 20 August 2010.
Kessler, S., Barbour, S. L., van Rees, K. C. J. and Dobchuk, B. S. 2010. Salinization of soil over saline-sodic overburden
from the oil sands in Alberta. Can. J. Soil Sci. 90: 637647. Saline-sodic mine overburden (also referred to as spoil) removed
to access the oil sands in the Athabasca region of Alberta is used as backfill in open pits and is also placed in large upland
structures. These deposits are reclaimed with a soil cover to support re-vegetation. The chemistry within reconstructed soil
profiles over saline-sodic overburden was investigated to determine the nature and spatial distribution of salts in the soils.
Four reclamation treatments were compared: three layered covers (35, 50 and 100 cm thick) and one non-layered cover
(100 cm thick). Salts have accumulated in the cover soils 15 to 20 cm above the overburden, raising the electrical
conductivity in the lower part of the soil to between 4.5 and 6.0 dS m 1, which is beyond the acceptable value for
vegetation growth. Salt redistribution was not related to slope position and the pattern of salt ingress suggests that
diffusion has been the main mechanism driving salt migration into the soils during the initial 4-yr period following
placement. Cover thickness did not affect the extent of salt migration, but the overall quality of the thinner covers (35 and
50 cm) for vegetation growth was compromised by the increased salinity levels.
Key words: Saline/sodic overburden, landform salinity, soil cover salinity, salt migration, salt diffusion,
oil sands reclamation
Kessler, S., Barbour, S. L., van Rees, K. C. J. et Dobchuk, B. S. 2010. Salinisation des sols sur les morts-terrains salins-sodés
des sables bitumineux de l’Alberta. Can. J. Soil Sci. 90: 637647. Les morts-terrains salins-sodés retirer des mines de
l’Athabasca, en Alberta, pour accéder aux sables bitumineux sont employés comme remblais dans des dépotoirs à ciel
ouvert et de vastes ouvrages sur les plateaux. On restaure ces dépôts en les recouvrant de sol sur lequel la végétation pourra
pousser. Les auteurs ont étudié la chimie des profils de sol rebâtis sur les morts-terrains salins-sodés afin de déterminer la
nature et la répartition du sel dans le sol. Ils ont comparé quatre traitements de restauration: une couverture faite de
couches multiples (de 35, de 50 ou de 100 cm d’épaisseur) et une couverture d’une seule couche (de 100 cm d’épaisseur). Le
sel s’accumule dans le sol de couverture, soit 15 à 20 cm au-dessus des morts-terrains, si bien que la conductivité électrique
dans la partie inférieure du profil s’établit entre 4,5 et 6,0 dS m 1, ce qui dépasse le seuil acceptable pour la croissance de la
végétation. La redistribution du sel ne dépend pas de la pente et sa pénétration laisse croire que la diffusion est le principal
mécanisme expliquant sa migration dans le sol au cours des quatre premières années suivant les travaux. L’épaisseur de la
couverture n’affecte pas le degré de migration du sel, mais la plus forte concentration de sel dans les couvertures moins
épaisses (35 et 50 cm) empêche la croissance des plantes.
Mots clés: Morts-terrains salins-sodés, salinité du relief, salinité de la couverture de sol, migration du sel, diffusion du sel,
restauration des sables bitumineux
Oil sands mining operates under the condition that
reclaimed landscapes will have a land capability equivalent to, or better than, that which existed prior to
disturbance. Current reclamation practices involve the
capping of mine spoil with reclamation material, selectively salvaged from the original landscape, with the
characteristics required to support self-sustaining vegetation covers (Sandoval and Gould 1978).
The overburden removed to access the oil-bearing
formation at the Syncrude Canada Ltd. (SCL) Mildred
Lake Operation belongs geologically to the Clearwater
formation, which is of marine origin (Stott and Aitken
1993). The overburden is used as backfill in the open pits
Can. J. Soil Sci. (2010) 90: 637647 doi:10.4141/CJSS10019
and is also placed in large upland structures. Approximately one-third of the final reclaimed landscape at SCL
Mildred Lake operation will be underlain by such
material (Marty Yarmuch, SCL Research and Development, personal communication 2010).
Geochemical characterization (Wall 2005) has shown
that these shales are pyritic and can undergo oxidation
when exposed to atmospheric conditions, as occurs
during mining. The chemical reactions associated with
Abbreviations: SCL, Syncrude Canada Ltd.; EC, electrical
conductivity; TDS, total dissolved solids; SAR, sodium
adsorption ratio
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