Thunder Bay Regional Health Sciences Centre

Parking Lot B Expansion and Storm Water Management System Design and Construction

Background and Scope

The existing Thunder Bay Regional Health Sciences Centre (TBRHSC) site consists of eight parking lot facilities, three internal roads and two main buildings within the 24.2-hectare parcel of land. The project consisted of design and construction of a new 300-stall parking lot and access road, modifications to the existing storm water management system, and the associated permits and approvals. True Grit Engineering  (TGE) was responsible for completing surveys, geotechnical engineering, storm water management design, an Environmental Compliance Approval (ECA) application, and lot grading design in accordance with Ontario Ministry of the Environment and Climate Change (MOECC) requirements and the City of Thunder Bay Site Control Agreements.

Project Challenges

The design of the project was challenged due to various factors such as environmental constraints, poor sub-grade materials (wet bog), drainage, storm water management plan, landscaping, safe conditions for the users, and reduction of long-term maintenance costs. For example, an existing cold water bog surrounded by current ECA-approved storm water infrastructure would require special considerations and process to achieve the desired integration.

Engineering Solutions

TGE designed an innovative, low impact storm water management facility in accordance with MOECC design criteria and utilized quality and quantity controls to effectively reduce the impacts of the proposed development. The first control was a landscape strip located in the middle of the parking lot facility. The strip increases the pervious area, introduces tree shade and a minimal amount of attenuation. Storm water runoff overflow from these strips conveys via sheet flow to curb inlets and the main treatment system. A bio-retention facility, located along the south perimeter of the parking lot, provides quantity controls for 2-, 10- and 100-year storm events. Quality controls for the proposed development are provided via a submersed infiltration trench beneath the bio-retention facility.

In addition, the proposed pavement structure requires complete removal of deleterious materials such as muskeg and peat to depths ranging from 1.5 to 2.5 m. The sub-base of the parking lot structure is a deep drainage layer of Granular B Type II material overlain by non-woven geotextile and a layer of Granular B Type I material that promotes infiltration of storm water runoff and groundwater free flow. The road and parking lot were constructed of Granular A material and surfaced with HL4 asphalt pavement.