We focused our results on PHC F1-BTEX in the soil and F2 in groundwater as these fractions had concentrations above the applicable Tier 2 criteria. PHC F2 and F3 in soil also exceeded guidelines pre-remediation treatment (2015) however, we do not have comparable data (processed similarly) for both time periods. Of note, two boreholes drilled in 2020 had PHC F2 concentrations above soil guidelines.
Between 2015 and 2020, mean saturated soil F1-BTEX concentrations decreased by 94% (613.6 to 33.8 ppm) (Figure 2). Due to the large variance and small sample size, the decrease in soil F1-BTEX was not significant (P = 0.091). While the mean F1-BTEX concentrations give an overall site-level assessment of contamination and highlight the reduction of high concentrations, soil volume and mass estimates (below) better portray the spatial extent of contamination and areas above guidelines pre- and post-remediation treatment.
Soil volume and mass estimates
After 3 years of our remediation system running, we reduced the estimated volume and mass of F1-BTEX (CCME Tier 2 guidelines, F1-BTEX concentrations > 210 ppm) in soil by 88.7% (Figure 4). Specifically, we reduced soil F1-BTEX volume in soil from 762.2 m3 to 85.8 m3 and estimated mass of F1-BTEX from 571.7 kg to 64.3 kg (Table 1).
In 2020 all groundwater monitoring wells had dissolved F2 concentrations below Tier 2 applicable criteria (Figure 1). Mean dissolved F2 concentrations in groundwater (2.8 to 0.4 ppm) remained unchanged (P > 0.05) though were below SEQG in 2020.