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.