Managing sewage treatment in the extreme cold in Cambridge Bay, Nunavut, northern Canada K. Johnsona,* a *
Cryofront, Edmonton, Canada cryofront@gmail.com
Abstract The community of Cambridge Bay is the largest community in the western region of the Nunavut Territory, in Northern Canada, and located at 69° 07' N latitude and 105°03' W longitude. It is approximately 300 kms above the Arctic Circle, and it is one of the largest communities in Nunavut, with a 2016 population estimate of 1,620. The community is located in the region of Arctic tundra with continuous permafrost and very limited vegetation. The climate may be characterized by long cold winters and short cool summers. The July mean high temperature is plus 12 degrees Centigrade and the January mean high temperature is minus 29 degrees Centigrade. Sewage is collected from 1000 litre tanks in each of the community houses with sewage pump out trucks, and originally discharged into a series of ponds; the sewage was treated to some degree as it flowed through the ponds and into the ocean. Wastewater collected from the community is classified as "high strength" waste because of the trucked water supply and trucked sewage collection, which limits water use to about 120 litres per capita per day. This type of sewage treatment system is common for communities in northern Canada. The ponds are often improved to increase containment with earth berms and flow control structures, however the poor performance of the pond system in Cambridge Bay was a source of concern for both the community and the regulatory organizations. In response, a project was initiated to improve the sewage treatment system. A planning study was completed to identify alternate locations for a new “engineered” lagoon system. A series of potential lagoon sites were identified in consideration of proximity to the community, road access, capital and operation and maintenance costs; and general site development. The community ultimately decided to complete engineered improvements to the existing pond system. The improvements to the existing pond system were based upon developing an engineered 2 cell sewage lagoon system. The system operates as a facultative treatment process, with a primary cell, a retention cell, and a controlled discharge from the retention cell during the summer months – see Figure 1. In support of advancing the redevelopment of the existing pond system, a topographical survey, and a geotechnical investigation were completed. The geotechnical investigation provided information on the soil conditions of the site, and also information on the soil materials around the community that would be used for construction. The primary cell was constructed on the northwest side of the retention pond, where the sewage pump out trucks discharge. The primary cell pre-treats the sewage to remove much of the suspended solids before the sewage enters the retention cell. The
sludge settled in primary cell will be removed every 10 to 15 years and placed in a sludge drying bed. The lagoon is annually decanted from the retention cell using a mobile diesel engine driven self-priming pump. The lagoon system has a capacity of 120,000 cubic metres per year, which will provide enough capacity until the community reaches a population of approximately 2500 people. An engineered wetland was also constructed to further treat the discharge from the annual discharge from the retention cell. The process of a seasonal discharge from a lagoon to a wetlands has been demonstrated to provide significant effluent quality improvements in the Canadian Arctic. The effluent quality discharged into the ocean by the community of Cambridge Bay is generally less than 30 mg/L for Biological Oxygen Demand (5 day), less than 60 mg/L for total suspended solids, and less than 4000 for faecal coliforms. The improvements to the existing lagoon system were planned and executed over several years in order to provide the community with funding and manpower flexibility for the project. The construction cost of the improvements was approximately 3 million dollars (CDN).
Figure 1. Cambridge Bay sewage lagoon system including primary cell, retention cell, pumped discharge, and sewage wetland before discharge into the ocean. Keywords: Wastewater treatment, northern Canada, lagoon system, wetland system
References Johnson, K.R., Yu, M., Sidhu, N. (2007), Engineered Improvements to Sewage Treatment System in Cambridge Bay, Nunavut. Canadian Society for Civil Engineering Annual Conference. Kadlec, R.H., Johnson, K.R., McCracken, C. (2008), Cambridge Bay, Nunavut, Wetland Planning Study. Journal of the Northern Territories Water and Waste Association. Johnson, K.R. (2018), Process Options for a Sewage Lagoon in Sub Arctic Canada. Canadian Society for Civil Engineering Annual Conference.