Oil Sands Tailings Capping Study

HBT AGRA Limited
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In the summer of 1990, research plots were designed and constructed on the Syncrude Canada Ltd. (SCL) mine site at Mildred lake to test the effect of thickness and quality of replaced soil over tailings sand on the performance of trees and shrubs. Treatments included three cap thicknesses (70, 50 and 30 cm) of replaced soil salvaged from an area rated as \"fair\" soil suitability for reclamation, as well as one cap (70 cm) of replaced soil salvaged from an area of \"poor\" soil suitability. Following plot construction, seedlings of four species were planted including: jack pine, white spruce, aspen, and dogwood. Baseline soil data were collected and height was measured on a random selection of permanently marked seedlings. Survival and growth data were collected annually from 1991 to 1993. Soil analysis after plot construction indicated good control of cap thickness during soil placement but minimal difference in the quality of replaced soil between plots constructed from the \"fair\" and 'poor\" rated source materials. Seedling survival after three growing seasons ranged from 68 to 96 %. Almost all mortality occurred during the first overwinter period. Spruce had the highest survival and dogwood the lowest. In general seedlings doubled\" doubled in size during the three year period. Survival and were growth unrelated to soil thickness or quality. Naturally invading plants, primarily weedy species varied according to the amount of peat present near the surface of the replaced soil.