AWARD OF MERIT: Wastewater Treatment Plant Miramichi, New Brunswick

Category: Water Resources

ADI AND GEMTEC

When the amalgamated City of Miramichi in New Brunswick was incorporated in 1995, one of its priorities was to replace deficient wastewater treatment plants that were discharging into the Miramichi River. A study had found the health of the river was suffering, and that the effluent discharges from the plants were well in excess of the provincial standard limits.

The city decided to replace the existing plants in Douglastown and Newcastle by a new treatment plant to service the entire northside area of the community. They retained ADI Limited to design the plant and decided on the Strawberry Marsh area as its location. The plant is now named the Paul J. Hayes, P.Eng. Wastewater Treatment Plant (after the late director of engineering for the city who was killed in a boating accident in July 2000).

The choice of this site was unusual because it incorporates a former garbage dump. Economics helped to drive the decision. The site was acquired without cost, plus there was no other low lying site of required size. It was also close to existing infrastructure. A sanitary solid waste disposal site had been operated there between 1960 and 1980. Afterwards the site was used as a ball field. In 1991 the provincial government expropriated it for construction of the Miramichi River Bridge, and waste material from that project was also stockpiled on the property.

The conversion of the landfill material as a structural fill for such an aerated lagoon is unprecedented in Canada, but shows an innovative and effective way of reclaiming former landfill areas. Prime consultant ADI, Gemtec and the city’s engineering department worked through the design. They had no technical reports to guide them in their approach. One of the most critical aspects is that the north lagoon berm — an 8-metre high structure — is founded on an organic silt foundation. Geotechnical experiments and pilot testing played a pivotal role in its construction.

Environmental approvals

An environmental impact assessment screening document was submitted to the New Brunswick Department of Environment for approval. The proposed site did not have the required area to accomodate the aerated lagoon, so approximately 1.7 hectares of the Miramichi River had to be infilled. Also, the former town of Newcastle dump encompassed part of the site, which added to the complexity of the approvals and construction.

The New Brunswick Department of the Environment laid down some basic requirements regarding opening up the old dump. They required that all the excavated materials were to remain on site, but that wood products, rubber tires and any toxic products had to be disposed of in a sanitary landfill (one is located 50 kilometres away). Berms were to be capped with a high density polyethylene (HDPE) liner to prevent infiltration and subsequent leaching.

The garbage, which was burned when it was originally left, consisted mostly of metals and glass. The metals were separated into (i) a size that could be mixed with sandstone rockfill and compacted in lifts, and (ii) oversize metal parts that were placed in the outer portion of certain sections of the berm and mixed with other waste in such a way than no large voids existed in the mixed fill. The peat and organic soil waste material was mixed with sandstone rockfill to act as a void filler. Constant inspection and plate load tests checked the compressibility of the fill as it was placed.

The seawall along the Miramichi River had to be built up to 8.2 metres and was subject to strict monitoring for settlement and pore water pressures in order to maintain sufficient stability at all stages. The actual settlement of the floor, as recorded during the filling of the reservoir, varied between 37 and 71 mm.

The treatment facility is designed to manage the combined wastewater flow from the north side of Miramichi for 30 years. The wastewater is conveyed by the Newcastle Lift Station into the lagoon, which is a four-cell, incompletely mixed, aerated lagoon equipped with a Biolac aeration system, the first of its type used in New Brunswick. The lagoon has a capacity of 11,800 m3/d, and a surface area of 5 hectares.CCE

Name of project: Paul J. Hayes, P.Eng. Wastewater Treatment Plant

Client: City of Miramichi

Award winning firms: ADI (prime consultant), and Gemtec (geotechnical subconsultant) Fredericton, N.B.

Project team leaders: Hollis Cole, P.Eng., Dave Crandall, P.Eng., Tim Murphy, P.Eng., Dan Scott, P.Eng., Mark McCormick, P.Eng., Bruce Pearson, P.Eng., Kevin McNulty, Darrell DeMerchant, P.Eng., Arvid Landva, P.Eng., Greg Robinson