Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6b. In Situ Remediation of Petroleum Hydrocarbons

Formatted Title:

Steam Enhanced NAPL Recovery at a Former Manufacturing Site in Canada: Challenges and Solutions

Background/Objectives:

An historical contaminant source zone of light non-aqueous phase liquid (LNAPL) was identified at a former manufacturing facility in central Canada. LNAPL apparent thicknesses of up to 1.5 m had been noted in monitoring wells. The LNAPL was distributed within the upper 5 meters (m) of an aquifer with moderate permeability (10^-4 centimeters per second) and the high viscosity product was comprised of BTEX, PAHs, and chlorinated solvents. An options appraisal was performed to evaluate remedial options, and when compared to both excavation and a traditional pump and treat approach, thermal treatment was identified as the most viable technology. This choice was due primarily to the short timeframe of implementation, high treatment certainty, and avoidance of building demolition.

Approach/Activities:

LNAPL samples were heated at laboratory scale to measure the effect of temperature on viscosity. 45 °C was identified as a target temperature required to reduce the viscosity at ambient temperature from 5,400 centipoise (Cp) to less than 1,000 cP. Based upon this and selection of steam enhanced extraction (SEE) as the heating methodology, a thermal model was completed that estimated heating time to be between 12 and 16 weeks, assuming 550 kg/hr total well field steam input.

Results/Lessons Learned:

Several challenges were encountered during the implementation of the thermal remediation at the Site, including:

The presence of legacy, above-grade infrastructure limited drill rig access, and uniform well geometries could not be achieved. Based on these constraints, PetraSim was used to optimize well placement and confirm that target temperatures were attainable.
Achieved steam injection rates were less than design due to the subsurface permeability, which was lower than that often seen at SEE sites. Following system initiation, average flow rates increased from 175 to 350 kg/hr as the formation was heated.
The project was implemented during the COVID-19 pandemic, restricting the project team’s mobility and ability to source global vendors. In-country vendors with limited SEE experience were used, resulting in design and implementation challenges. ERM worked closely with them to facilitate safe and effective remediation.
Field scale steam propagation and permeability test were not completed. This led to some equipment operational challenges that had to be resolved by unplanned strategy modifications during the heating stage.
High resolution site characterization was not performed, and the known extent of LNAPL was inferred based on sparse data. Further delineation of the Site may have led to the plume being heated in its entirety.
Equipment challenges: Delays from permitting led to an operations period six months later than scheduled, and the implications of this on treatment system design required a different chiller to be provided. Furthermore, limited boiler availability resulted in an oversized boiler being procured and therefore an upsized gas line had to be installed to satisfy supply requirements.

The steam system operated for 13 weeks, achieving an average subsurface temperature of 65°C at which point the boiler was de-energized. Mass recovery from the site was calculated to be approximately 6,500 kg. Subsequent well monitoring has confirmed minimal residual LNAPL volume remains.

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Blake Svendsen