In December 1995, an oil spill was discovered along a section of pipeline located near the bank of a major river, less than 1 km upstream of the water supply intake of a southern Alberta community. The spill, which involved light crude oil, was observed at ground surface over an area of approximately 3 000 m2 at the top of the river slope and had also migrated downslope through the subgrade soils and along the groundwater table toward the river.

The initial emergency response activities consisted of removing and disposing of oil-stained vegetation and snow, and the containment and recovery of free oil pooled on ground surface. Subsequent subsurface assessments involved the drilling of test holes and boreholes, and installation of groundwater monitoring/recovery wells. Based on the results of these assessments, a remedial action plan was developed. As part of this plan, some of the impacted soils were excavated and placed in lined treatment cells for bioremediation. The limits of the excavation were based on field screening measurements and on soil clean-up criteria developed through an assessment of the human health risk and ecological impacts.

Investigations conducted at the site also indicated that phase-separated crude oil had migrated further downslope and had accumulated at the water table within the flood plain sediments adjacent to the river. Therefore, remediation systems were installed to recover the oil, recover and treat the impacted groundwater, and prevent further migration of the impacted groundwater and oil toward the river. Impacted groundwater recovered from the flood plain deposits was treated onsite and was then injected back into the flood plain deposits via an infiltration gallery. The performance of the pumping and remediation systems was monitored regularly and water samples were recovered from the treatment system, selected monitoring wells and the river. Based on the results of these analyses, the quality of local groundwater steadily improved and the zone of impacted water was effectively contained.

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