Theme: 01. Remediation Technology Innovations

Topic Area: 01d. Combined Remedies and Treatment Train Technologies

Formatted Title:

LNAPL Remediation in Bedrock: Combining MPE and Injection of a Carbon-Based Remedial Amendment

Background/Objectives:

Until recently, light, non-aqueous phase liquid (LNAPL) remediation in fractured bedrock was very challenging with a low probability of success. Variable fracture networks and contaminant back diffusion from the rock matrix combined with a lack of appropriate (i.e., effective and persistent) remediation technologies, frustrated consultants, contractors, and stakeholders alike. However, with each passing year, new remedial techniques and strategies are developed. The purpose of this talk is to present a case study showcasing a treatment train approach employing an ‘old’ remediation technology followed by the use of a ‘new’ in situ remediation technology to successfully remediate a complex LNAPL bedrock site.

Approach/Activities:

A desirable waterfront property in eastern Ontario containing deteriorating infrastructure was in desperate need of revitalization. The site had a history of heavy industry that resulted in LNAPL contamination, which posed environmental and public health risks. To remediate the site, a combination of two proven remedial technologies were employed: multi-phase extraction (MPE) and in situ injections using an innovative, activated carbon-based remedial amendment. The MPE system was utilized to remove mobile LNAPL to the point where diminishing returns were reached. In situ injections using new drilling approaches to facilitate surgical amendment delivery within the fractured bedrock were then used to deliver the AC-based remedial amendment to rapidly treat the residual LNAPL mass.

Results/Lessons Learned:

Over a 12-month period throughout 2021 the MPE system operated on 12 wells at the site and removed fuel oil to the point where the cumulative LNAPL thickness on the wells was reduced from 11.5 ft to less than 4 inches and the plume area had been reduced by approximately 75%. At this point diminishing returns had been reached, and the remediation program transitioned to in situ treatment using a combination of carbon adsorption and enhanced anaerobic biodegradation. A novel injection technique was utilized to emplace the remedial amendment across the overburden/weathered bedrock interface. Within 2 months of the remedial injection no LNAPL was measurable in two of the three remaining wells, with a decreasing trend in LNAPL thickness recorded in the third well.

The combined approach proved to be highly effective, resulting in a significant reduction in LNAPL to levels that could facilitate a risk assessment for future redevelopment of the site. The use of these two technologies in combination allowed for a more comprehensive approach to remediation. The successful remediation of this site demonstrates the effectiveness of combining remedial technologies to achieve optimal outcomes at sites even with high contaminant levels and challenging geology.

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Bruce Tunnicliffe

Biography