Theme: 04. Addressing Challenging Site Conditions

Topic Area: 4a. Adaptive Site Management: Lessons Learned for Site Characterization and Remedy Implementation

Formatted Title:

International Excavation Activities to Remediate Soils

Background/Objectives:

Background/Objectives. A project was undertaken by a former site owner to remediate soil and groundwater at a former petrochemical storage and handling facility located in Quebec, Canada to levels below the applicable provincial criteria limit for commercial and/or industrial site usage. The facility had historic releases of toluene, motor oil and mineral oil; contaminants of concern (COCs) to be remediated included BTEX, PAHs, VOCs, metals, monocyclic aromatic hydrocarbons, and petroleum hydrocarbons (C10-C50). Historically, an internal UST/AST farm was located inside the building and contained in a sunken area of the warehouse. An additional historical UST was located outside the building. The objective of the excavation activities was to remediate impacted soils inside the building (former office area, UST area and warehouse area) and outside the building to acquire the equivalent of a No Further Action from the Quebec Ministry of the Environment and the Fight Against Climate Change (MELCC). The No Further Action nomenclature did not coincide with what the MELCC was willing to supply, and a compromise had to be negotiated with the MELCC and the property Owner.

Approach/Activities:

Approach/Activities. The approach to excavation activities was directed toward mitigating and addressing multiple challenges. The activities included:

Working with the owner of the property (not the client) to develop the remedial plan and resolve any issues that came up for the course of the project;
Acquiring structural engineering support to evaluate and provide (as needed) structural support to the building and also hydro poles within the excavation areas;
Removing and updating the high voltage electric panel;
Removing and replacing concrete inside and outside the building;
Removing and replacing ~100 feet of a railway line and spur that services the building;
Removing and sampling impacted soils to bedrock (approximately 10 feet bgs);
Pressure washing the bedrock and collecting and treating the wash fluid and groundwater accumulations in the excavation;
Excavating additional contamination found along a water line (unanticipated pathway of migration) inside the building into the office area;
Rebuilding the office area;
Rebuilding the warehouse floors, various access ramps and stairs removed for the decontamination work; and,
Resurfacing areas with seed, asphalt or concrete, including considerations for drainage and erosion.

After excavation activities, monitoring wells were replaced in the formerly impacted areas to evaluate groundwater impacts. Following the remediation, groundwater is not impacted and site closure is anticipated in late 2023.

Results/Lessons Learned:

Results/Lessons Learned. Three critical lessons were learned during completion of the work:

Several site investigations were completed to delineate in preparation for excavation activities. As health and safety protocols would not allow borings within 5-10 feet of known utilities, borings were completed near the water line inside the building but not directly adjacent to the water line. During excavation activities, it was discovered that significant impacts had traveled from the internal UST farm along the water line (that acted as a preferential pathway) to under the office area. Therefore, utility corridors, if they abut or intersect impacted areas, should be fully investigated prior to excavation (to the extent practicable).
When ~100 feet of railway was removed prior to excavation activities, the property owner indicated that only half the length removed needed to be replaced. Upon further research, it was discovered that the property owner had an agreement with the railroad that does not allow for any alterations to the facility rail set up without prior railroad approval. In addition, it was discovered that the new rail areas will need to be inspected by the railroad entity prior to use. Fully investigate all relevant documents prior to starting work, with particular attention when the client is not the owner of the property.
There will always be challenges to completing international work and adjusting to the local laws and regulations. For example, Canada limits the times of the year that work can be done that affects roadways (soil disposal/heavy equipment) and when is a stop work period (contractor’s holiday) for two weeks in August, where no field work is completed. In addition, this work was completed where French is the official language. Working with a local company that fully understands the local laws, regulations and language is a necessity.

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Tony Hawke