Pilot Dredging Project

	Project Background
	Project Purpose
	Pilot Project
	Environmental Assessment
	Public Consultation

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Then and Now

View maps and photographs of Burnaby Lake and see how both human and natural encroachment have impacted the lake over the years.

The Pilot Project

In the late 1990's, a pilot project was conducted to determine if it was feasible to dredge the lake. This successful project was the framework for the current project. Learn more ...

Pilot Dredging Study - Summary

A pilot scale dredging of Burnaby Lake was conducted in the summer of 1999 to determine the technical feasibility of dredging the lake. The dredging and sediment processing methodologies and technologies used successfully demonstrated that the project was achievable. 

The pilot scale dredging of Burnaby Lake conducted from August 21 to September 11, 1999 removed approximately 2,500 cubic metres of sediment.  The objectives of the pilot program were to:

• Demonstrate the technical feasibility of dredging the various types of sediments and vegetation present in Burnaby Lake under typical access conditions;
• Demonstrate the technical feasibility of dewatering dredged lake sediment to produce a dry, truckable product;
• Identify any measurable environmental impacts to Burnaby Lake caused by the dredging operations and any procedures to mitigate them;
• Demonstrate the technical feasibility of meeting regulatory agency water quality requirements for the discharge of process water back to Burnaby Lake;
• Characterize the chemical composition of the dewatered sediment in the context of identifying potential end use or disposal alternatives; and
• Evaluate the potential costs of a future full-scale dredging program.

Overall, the study successfully demonstrated that dredging and sediment dewatering are technically feasible and that the dredging program can be conducted without adverse environmental impacts to Burnaby Lake or its tributary streams.  The following paragraphs summarize the significant findings of the pilot study.

The pilot study used a hydraulic suction dredge outfitted with a specially designed cutter head. The study demonstrated that the dredge easily removed lakebed sediment from shallow areas overgrown with lily pads and from upland areas containing dense patches of cattails and/or purple loosestrife.  The dredging encountered some difficulties due to low water levels and patches of refuse on the lake bottom, but these difficulties did not affect the overall feasibility of the dredging program.  Rather, the study demonstrated the technical feasibility of the dredging operation.

Similarly, the pilot study demonstrated the technical feasibility of dewatering the dredgeate using centrifuges.  The dredgeate initially contained about 3% solids.  Centrifugation removed 99% of the solids from the dredgeate and increased the solids concentration of the processed sediment to 20%-40% (average 27%).  The resulting material consistently was firm enough to be handled easily and loaded into open trucks for transport. The processing technology thus was able to provide the desired dewatered sediment characteristics.

Monitoring during the pilot dredging operation showed no significant impacts to the water quality of Burnaby Lake.  Significant increases in TSS and turbidity generally were limited to the area inside the silt curtain that isolated the work area from the main body of Burnaby Lake.  The monitoring showed that dredging did not increase the concentrations of metals, sulphide or phosphorus in the water column.  There was some evidence of a release of ammonia from the sediment, but this phenomenon was confined to the area within the silt curtain, and the ammonia level never exceeded provincial water quality criteria for protection of aquatic life.  Dissolved oxygen within the silt curtain became very low during dredging, but this apparently was the result of drawing low oxygen water from the adjacent water lily zone rather than an effect of dredging.  Thus, the study showed that dredging created few adverse effects on water quality, and that the effects that did occur could be mitigated effectively.

The pilot study included a water treatment system to improve the centrate (“process water”) quality such that it would meet regulatory agency requirements for discharge to Still Creek/Burnaby Lake.  The Department of Fisheries and Oceans (DFO) stipulated that the total suspended sediment (TSS) concentration in the discharge could not be more than 25 mg/L above the background TSS concentration in Burnaby Lake and that the turbidity in the discharge could not exceed 5 NTU above background. 

Composite samples of the dewatered sediments were analyzed for metals, polycyclic aromatic hydrocarbons (PAH), extractable petroleum hydrocarbons, and chlorinated organics.  Due to elevated zinc, PAHs and the heavy fraction of extractable petroleum hydrocarbons (HEPH), some dewatered sediment samples did not meet the Contaminated Sites Regulation (CSR) standards for residential land use.  In addition, the zinc concentrations in four samples did not meet the CSR standard for Residential, Commercial and Industrial land use.  These results suggest that there will be some limitations on the disposal options for dredgeate from the full-scale program, and sediment sampling will be required.

Pilot Dredging Study - Complete Report

For further details about the pilot project, view or download the complete Pilot Dredging Report.