The ProblemAs 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. The assessment identified the following:
- Petroleum hydrocarbon contamination in soil ranging from 10 to 17 metres below ground surface (mbgs).
- Depth to groundwater has an average depth of 18 m bgs.
The Implemented SolutionA drive-point network, consisting of 36 injection wells, was installed in 2015 (Figure 1). The BioLodestone, a proprietary amendment solution, was delivered to the contaminated area for 1 month in 2015 and 3-4 months for 2016, 2017, 2018, 2019, 2020.
The ResultsIn late 2020, five solar-powered Soil Sense units were installed at the site including 1 background location, 2 on the plume fringe and 2 within the plume. The strategy for placement of the Soil Sense was to capture areas of high and low benzene concentrations. Soil Sense units make use of concentration gradient methodology with the sensor packs being installed above the LNAPL plume at depths of 3, 5 and 6 m bgs. The Soil Sense, a proprietary technology, uses three solid state sensor packs installed at different depths to measure:
- Hydrocarbon vapours;
- Carbon dioxide; and
Site-wide EstimatesInitial estimates indicated an average site-wide NSZD rate of 0.13 grams per square metre per day (g/m2/d) (Figure 1) with an approximate mass reduction of 15 kilograms per year (kg/yr). The highest NSZD rates were situated within the plume source (location 3).
Comparison to Traditional NSZD MethodsA comparison to traditional NSZD methods (Closed Chamber and E-Flux traps) suggested the Soil Sense units were within the NSZD range (Figure 2). The closed chamber results, while showing lower rates, tend to correlate with the plume areas and our Soil Sense units. Further, the E-Flux results at location 5 correlate to a high degree with the high end of the range for our Soil Sense units. The flux trap at location 3 had a non-detect. This result is anomalous and could have resulted for several reasons but highlights the importance of real time data so that in the event a Soil Sense unit fails it’s identified right away and can be fixed immediately.
Figure 1. Natural Source Zone Depletion Rates highlighting the variation over a 5-month period.
Figure 2. A Comparison of Traditional Natural Source Zone Depletion Rates including Soil Sense (green, formerly EMS-Quantifier), Closed Chamber (purple). E-Flux CO2 traps were installed at the same locations as the Soil Sense.