|Biggest Hurdle:||Due to the age of the building and the construction of the foundation wall, the remedial contractors were unable to safely excavate the residual impacted soil beneath the foundation wall without additional underpinning and support.|
XCG was retained to complete confirmatory soil sampling of the limits of an excavation in the basement of a multi-use commercial and residential building in Toronto, Ontario. Previously, XCG conducted a Phase I Environmental Site Assessment (ESA) in March 2017 and a Phase II ESA in April 2017 at the subject site. The Phase II ESA delineated the known petroleum hydrocarbon (PHC) impacts in the soil below the basement level of the building. The soil impacts were vertically delineated to not extend past 3.05 metres (10 feet) below the surface of the floor and laterally not to exceed 12.5 square metres, with an estimated total volume of PHC-impacted soil of 38 cubic metres. Analytical results from groundwater samples collected at the subject site were below the laboratory reportable detection limits (RDLs) or were detected at concentrations less than the Ministry of Environment and Climate Change (MOECC) standards for residential/parkland/institutional land use for coarse-textured soil in a non-potable groundwater setting [i.e. the MOECC Table 3 site condition standards (SCS)].
Excavation activities were conducted by Accuworx Inc. (Accuworx) in the basement of the subject site beginning October 10, 2017. XCG was on-site periodically to field screen samples from the limits of the excavation (both sidewall and base samples) in order to assist Accuworx in determining the final limits of the excavation. Based on the analytical results, further excavation was conducted as required.
Confirmatory soil samples were collected based on the minimum requirements outlined in Table 3 – Minimum Confirmation Sampling Requirements for Excavation of Ontario Regulation (O. Reg.) 153/04, as amended. Three base and nine sidewall confirmation samples were submitted for laboratory analysis from the excavation to confirm removal of hydrocarbon-impacted soil. Soil samples from within the excavation were submitted for laboratory analysis for benzene, toluene, ethylbenzene, and xylene (BTEX) and PHCs (Fractions F1 through F4).
Based on XCG’s understanding of the site setting and soil conditions, all analytical results were assessed with respect to the generic SCS published by MOECC in the document “Soil, Ground Water and Sediment Standards for Use Under Part XV.1 of the Environmental Protection Act,” dated April 15, 2011 (MOECC SCS). Based on the site location, current and proposed future land use, the MOECC SCS Full Depth Generic Site Condition Standards in a Non-Potable Groundwater Condition (i.e. MOECC Table 3 SCS) were used for comparison purposes.
No elevated soil vapour concentrations were observed in the soil screening samples collected from the sidewalls of the final excavation; however, olfactory evidence of hydrocarbon impacts were observed along the southern wall.
Based on XCG’s field observations and the confirmatory soil sample analytical results, all hydrocarbon-impacted soil related to the historic use of fuel oil at the subject property has been successfully excavated from the subject property and removed off-site for disposal, with the exception of residual impacts located beneath the southern foundation wall of the building. The soil on the subject property in the final excavation meets the applicable MOECC Table 3 SCS, with the exception of the southern wall.
Residual soil impacts remain directly beneath the southern brick foundation wall of the on-site building. Due to the age of the building and the construction of the foundation wall, the remedial contractors were unable to safely excavate the residual impacted soil beneath the foundation wall without additional underpinning and support.
Based on XCG’s observations, the residual impacts remaining on-site are expected to be limited to the shallow fill material, which is underlain by a hard clay. The remaining residual impacts on the subject property are expected to naturally degrade over time. Therefore, it was XCG’s opinion that these residual impacts do not represent a significant environmental liability to the subject property or hinder the current or future use of the subject property for commercial and residential purposes.
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