Unlocking Risk Assessment Closures at LNAPL Sites

Light Non-Aqueous Phase Liquids (LNAPLs) remain one of the most persistent and misunderstood challenges in environmental remediation. When it comes to risk assessment (RA)-based closures, the presence of LNAPL can significantly delay or even prevent regulatory acceptance altogether, especially in complex hydrogeologic environments or in jurisdictions with strict rules on petroleum hydrocarbons (PHCs).

Various Methods of Visually Detecting LNAPL in the Subsurface

At this year’s annual Canadian Brownfields Network (CBN) conference, Daniel Brenner of VEI Contracting Inc. shared an overview of how new technologies and implementation strategies are transforming the ability to remediate LNAPL in support of RA-based closure strategies. This newsletter article provides more detail.

The Risk Assessment Challenge with LNAPL

Many Canadian provinces now allow RAs as part of site closure strategies for PHC-impacted sites, but LNAPL introduces significant complications.

For example:

Alberta allows LNAPL to remain in place if it is “non-mobile” and “stable” but requires active remediation where mobility is demonstrated.
British Columbia classifies sites with >2 mm LNAPL thickness or demonstrated mobility as “high risk,” often triggering additional remediation or barrier installation.
Ontario permits RA approaches, but only if LNAPL is removed “to the extent practicable,” including even residual sheens or high-solubility concentrations.
Quebec does not currently allow RAs for PHC-impacted sites involving LNAPL.

These regulatory constraints have prompted practitioners to ask: Can we effectively destroy or immobilize LNAPL in-situ to allow easier RA approvals and reduce long-term risk? The answer is increasingly: Yes.

High-Resolution LNAPL Characterization: LIF Technology

Accurate delineation is the first step toward any effective LNAPL remediation strategy. Laser Induced Fluorescence (LIF) technology offers a powerful, real-time method for detecting, characterizing, and “fingerprinting” LNAPL across both saturated and unsaturated zones.

LIF surveys use ultraviolet laser pulses transmitted through a fiber optic probe. The laser excites PHC compounds, especially PAHs, causing them to fluoresce. This fluorescence is detected and interpreted, providing semi-quantitative data on PHC type, concentration, and depth distribution.

Laser Induced Fluorescence (LIF) for Detecting LNAPL In-Situ

The technique not only identifies mobile and residual LNAPL but also enables cost-effective optimization of remedial strategies—focusing efforts where they matter most.

To learn more about LIF and other High Resolution Site Characterization (HRSC) techniques offered by VEI, visit our HRSC Services page.

Destroying LNAPL In-Situ: Trap & Treat® BOS 200+®

One of the most promising recent advances in in-situ destructive remediation of LNAPL is the use of the Trap & Treat® BOS 200+® technology. We’ve never experienced a product as effective in addressing zones with high PHC concentrations and heavier molecular weight compounds (like diesel and heating oil). BOS 200+® combines:

High-performance activated carbon (AC) for rapid adsorption,
Anaerobic and co-metabolic biodegradation enhancers, and
Bio-regenerative capabilities that maintain AC sorption performance over time.

The coal-based AC in BOS 200+® has a measured saturation limit of up to 58% by weight, far exceeding traditional AC assumptions. Yet, contrary to opinion, AC performance is not limited by its adsorption capacity. The adsorbed PHCs remain bioavailable, allowing microbial activity to degrade and regenerate the AC matrix. As microbial degradation reduces concentrations, AC pore capacity is freed up to adsorb additional PHCs.

Trap and Treat BOS 200 Plus Combines AC Adsorption and Enhanced Biodegradation of LNAPL-

Degradation rates of 0.5 to 1.0 kg PHC/kg AC per year have been observed, making BOS 200+® not only effective—but sustainable over the long term.

You can read more about this technology on our Trap & Treat® page.

Immobilizing LNAPL In-Situ: Block & Adsorb©

For sites where complete degradation is impractical—or where migration prevention is the primary goal (i.e., in the absence of actual risk)—Block & Adsorb© provides an effective alternative. This in-situ immobilization approach, developed by VEI, combines:

Portland Cement (PC) to lower permeability and create a binding matrix, and
Granular or powdered activated carbon (GAC/PAC) to sorb dissolved-phase PHCs.

In field applications, this dual-treatment significantly reduces LNAPL mobility, immobilizes visible sheens, and decreases PHC concentrations in groundwater.

Control vs Test Plots Treated with Block and Adsorb

Control vs Test Plots Treated with Block & Adsorb©

Block & Adsorb© can be implemented through soil mixing or injection into overburden and fractured bedrock zones, even in sensitive or inaccessible areas like beneath building foundations or adjacent to property lines and underground services. The result is a treated zone that remains “soil-like” in character while drastically reducing exposure pathways.

This method is especially attractive since no excavation or waste generation is necessary.

Putting It All Together: A Recent Case Study from Ontario

At a confidential former industrial site in Gananoque, Ontario, the VEI team was tasked with remediating an area impacted by LNAPL and dissolved-phase PHCs—predominantly at the interface between the till overburden and the underlying fractured bedrock.

Site Layout Showing Presence of LNAPL and PHCs in Groundwater

The remediation strategy involved:

Source Removal: Decommissioning of a leaking underground storage tank and excavation of impacted soil.
LNAPL Recovery: A 12-month Multi-Phase Extraction (MPE) system was installed with six LNAPL wells, overland lines, and dual-phase GAC treatment vessels. This removed over 75% of the initial LNAPL mass present in the subsurface.
In-Situ Polishing: A focused injection of 2,200 kg of BOS 200+® was completed using the GeoTAP™ method (for bedrock) and direct-push (for overburden). A total of 15 injection points were advanced at the site in just two days.

Post-injection sampling, eight months later, showed continued LNAPL destruction, no rebound, and marked reductions in dissolved-phase PHCs.

Post-Injection LNAPL Thickness Measurements Over Time

This integrated approach—source removal, aggressive recovery, and smart in-situ polishing—demonstrated how even challenging sites can progress toward RA-based closure.

For more examples of our injection expertise, explore our in-situ remediation portfolio.

Closing Thoughts

LNAPL no longer needs to be a showstopper for risk-based site closures.

With modern tools like LIF characterization, Trap & Treat® BOS 200+®, and Block & Adsorb©, sites impacted by free product can now be remediated more effectively, more sustainably, and more cost-efficiently—helping consultants and developers alike meet regulatory obligations while advancing redevelopment goals.

Whether you’re managing a complex fuel release, navigating evolving regulations, or trying to unlock a difficult site for closure, VEI Contracting can help.

Interested in learning more about facilitating risk-based closures on LNAPL sites? Sign up for the VEI webinar on this topic on October 1, 2025.

Let’s Talk About LNAPL Solutions

Want to know if your LNAPL site is a good candidate for treatment using these technologies?

Contact Daniel Brenner, P.Eng.
VEI Contracting Inc.
danielb@vei.ca
www.vertexenvironmental.ca

Or visit our Contact Us page to speak to one of our remediation specialists today.