Investigation, Delineation, and Development of RAP for PHC-Related Impacts, Former Niagara Transit Site

XCG was retained by the City of Niagara Falls (the City) in 2017 to further investigate the presence and delineate the extent of petroleum hydrocarbon (PHC) impacts previously identified by others in soil and groundwater at and in the vicinity of a former transit facility, located at 4320 Bridge Street and 4555 Erie Avenue, Niagara Falls, Ontario (subject site or property).


Between   2015 and 2017 a number of investigations and remedial activities were   completed by others, including Phase I and II Environmental Site Assessments   (ESAs), demolition of the former transit facility building, removal of above   ground and underground storage tanks (ASTs and USTs), soil excavation, and   installation of a free product recovery system.


Following a   review of all previously completed reports documenting the site   investigations and remedial activities, the correspondence received by the   Client from the Ministry of the Environment, Conservation and Parks (MECP),   and reviewing historical information for neighbouring properties, in early 2018,   XCG prepared a detailed workplan to further investigate and delineate the extent   of the free product and PHC-related impacts previously identified on the   subject site and within the Park Street right-of-way, bordering the site to   the south. The additional investigation was completed in 2018 and included the following tasks:

  • A video inspection of the accessible on-site storm and sanitary sewers and sewers located within the streets adjacent to the subject site to determine if free product was entering the sewers.

  • Advanced site characterization activities using laser induced fluorescence (LIF) method to further investigate the extent of PHC-related impacts in the overburden and within sewer trenches. The LIF investigation was completed to determine the appropriate borehole/monitoring well locations and sampling intervals.

  • Completion of an overburden and bedrock drilling program to collect confirmatory soil and groundwater samples to determine the extent of the PHC impacts and free product in the overburden and fractured bedrock. Prior to the drilling activities, daylighting was completed to expose underground utilities.


Based on   the field data, site observations and analytical results, XCG identified a localized   area of free product within a portion of the Park Street storm sewer utility trench, located directly adjacent of the south of the subject site. XCG has   proposed additional overburden and bedrock drilling locations to further delineate   the extent of the free product and PHC-related impacts along and   down-gradient of Park Street. XCG also developed a remedial action plan (RAP)   for the removal of the mobile PHC free product present within the Park Street storm sewer trench. In general terms, the RAP is based on the installation of  a large diameter (0.3-metre) product extraction wells within the storm sewer bedding material. The product recovery will be completed using vacuum trucks and/or submersible pumps. 


XCG anticipates that the additional  investigation work and the construction of the product recovery wells will be  completed in the fall of 2020. It is anticipated that the product recovery activities will be completed over the period of  several months.


Based on the size and complexity of   this project, XCG implemented several innovative technologies to better   understand, monitor, and document the investigation and delineation   activities. Utilizing LIF technology allowed XCG to obtain real-time, in-situ   field screening data to determine the presence of residual and non-aqueous   phase organic contaminants (i.e. PHCs) within the vadose and capillary fringe   zones, saturated subsurface soils, and groundwater. Based on the real-time   data, XCG was able to make informed, real time, site-specific decisions   regarding the extent of impacts and the locations of subsequent LIF borehole locations,   sampling intervals and monitoring well locations and screen intervals. Prior   to the drilling program, daylighting was completed using non-destructive vacuum   excavation methods to allow the boreholes to be advanced in close proximity of   the buried utilities/services, in order to determine if the utility trenches   were acting as preferential flow pathways for the migration of contaminants. The   bedrock drilling program was completed using advanced telescopic drilling   methods which involved temporarily installing steel casings grouted directly into   the bedrock to prevent downward migration of PHC-impacted groundwater from   the upper stratigraphic zones.

Furthermore, free product identified at   select monitoring well locations was sampled and submitted to a laboratory for   chemical analyses and chromatographic profile scanning. XCG had the profile   testing completed to determine the specific components of the free product in   order to differentiate between the PHC-related impacts related to the   historic USTs and the naturally occurring PHCs associated with the bituminous   dolostone, which underlie the subject site. In order to develop an accurate   conceptual site model (CSM) of the subject site and surrounding area, a   topographical and total station survey using high-accuracy GPS surveying   equipment was completed. The survey was used to obtain geospatial coordinates   and reference elevations of all monitoring wells, boreholes, manholes and   other infrastructural features to a common geodetic datum to create highly   detailed and accurate site figures and cross-sectional diagrams.

The site characterization activities   described above, allowed for the development of a focused, cost-effective   remedial approach for dealing with the PHC free product.

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