Forebay and oil-grit separator

Binnie provided municipal engineering services and designed the relocation of the pond inlet, an EFO10 oil-grit separator, and a treatment forebay for the District of Squamish. The total cost of these civil construction works in Downtown Squamish amounted to $1 million.

The construction involved relocating the pond inlet to make room for the building. Due to space constraints, the EFO10 had to be constructed entirely within the existing pond footprint. The pond had to be dewatered partially, and shoring and dewatering were required for the EFO10 excavation.

At the same time, a forebay and oil-grit separator were installed for stormwater treatment. These measures significantly improved the pond’s water quality and allowed operations staff more effective maintenance and oil spill response.

The EFO10 oil-grit separator is amongst the largest and most technologically advanced available in Canada. The forebay berm design was innovative by using soft-armoring cellular confinement technology instead of rip-rap. This environmentally friendly solution enabled the berm and weir to be vegetated while having the required protection against erosion. For more accurate forecasting of maintenance frequency for the OGS and forebay, the expected OGS sediment capture was based on new guidelines from ETV, which uses a particle size distribution that is more representative of typical urban runoff.

On top of this, Binnie staff made recommendations for the forebay size and dimensions, the chosen OGS product based on space constraints/requirements for internal emergency stormwater by-pass, maintenance access/frequency, and re-alignment of storm sewers for cost optimization.

As of today, the water quality in the pond has improved significantly. It is apparent that it is working after a rainfall because even though the water in the forebay is sediment-laden (causing it to appear brown), the main body of the pond is clear. The odour from the pond has also been reduced considerably.  Oil spills are now captured in the EFO10, which can be easily maintained with a vacuum truck, whereas in the past, an emergency response from operations was required.