Natural Source Zone Depletion (NSZD) refers to microbial and physical processes that reduce hydrocarbon content in the subsurface. Microorganisms degrade hydrocarbons deep in the soil and rapidly deplete available oxygen and other electron acceptors in the soil and groundwater.  At that point, microorganisms begin to ferment hydrocarbons, producing organic acids. These organic acids are used by a group of microorganisms called methanogens, which consume these organic acids and release methane. The methane migrates towards the upper layers of soil, where another group of organisms, called methanotrophs, consume the methane and release carbon dioxide as a product.

An active petroleum hydrocarbon pipeline site had 20,000 m³ of impact and an initial plume area of 8,100 m²  based on an environmental consulting firm’s Phase II Environmental Assessment. An active recovery program over five (5) years had recovered approximately 14% of the released product but was discontinued due to declining extraction efficiencies with high operating costs.

The textbook approach to new or legacy spills is to ensure that you have a vertical and horizontal delineation of the pollutants. This understanding of how deep and wide your pollutant has travelled is essential before you can begin any remediation, restoration, or reclamation process. The rationale for this approach is that we should not begin a remediation process until we have enough information to ensure that it can be successful. Thus, we carefully assess a site, set data quality objectives, and carefully plan out the goal of a remediation program.

In 2003, a third-party contractor conducted a phase II Environmental Site Assessment (“ESA”) due to light non-aqueous phase liquid (LNAPL) observed in one of the Underground Storage Tanks (“USTs”) nest piezometers. Soil and groundwater impacts exceeded the applicable criteria on and off-site (Figure 1). Follow-up groundwater monitoring events recorded concentrations of petroleum hydrocarbons (PHCs) in 2004 and 2005 exceeding guidelines.

As part of the decommissioning process, an initial Phase II Environmental Site Assessment was conducted on a former Bulk Fuel Facility that operated from the early 1960s to 2002.

An Above Storage Tank (“AST”) fuel spill occurred at the site on July 19, 2010, of which 3,581 litres of 10% blended ethanol gasoline leaked into a containment dyke.