The scenic Town of Banff is a unique community nestled within Banff National Park in Alberta. Over the years the town has worked diligently to reduce the environmental impact created by its residents, businesses and the town’s up to five million annual visitors.
The town has been composting its biosolids with woodchip amendment since 2003; more recently, food waste has been co-composted with biosolids.
In-vessel composting is undertaken at the wastewater treatment plant (WWTP); uncured compost has been cured and used for remediation purposes at an old landfill in the park. This site is now considered rehabilitated, but remains in use as an interim site for excess compost curing and for storage.
The town sought to identify and justify suitable locations for both the curing and end use of the composted product, and to establish appropriate protocols/mitigations for both activities. With a limited town land base, sites in the wider park had to be considered (with the agreement of Parks Canada, of course).
A study was undertaken to help find a new curing location and to identify options for compost curing and finished biosolids compost utilization. While composted biosolids have been identified as an organic material for ecological restoration in Canada’s protected areas (Parks Canada and the Canadian Parks Council, 2008), concerns were raised locally about the potential impacts of chemical constituents that may be present in the biosolids and possibly the biosolids compost. The study included a Risk Assessment to help identify, assess and manage any risks to public health/safety and ecological integrity from the curing and end-use of biosolids composts. The study has some further implications regarding the use of biosolids compost: if it’s acceptable for use in a beautiful national park where requirements are very stringent, it can (in theory) be used almost anywhere.
The project was undertaken by 2cg Inc. and Golder Associates. It was jointly funded by the town along with Parks Canada and, given the province’s interest in the findings, Alberta Environment.
The analysis of biosolids compost using conventional laboratory testing and ecotoxicity testing (i. e., receptor exposure toxicology) resulted in a Risk Assessment and ultimately allowed the development of a Risk Characterization. The RA tested the requirements of the CCME Compost Quality Guidelines and other environmental requirements, and included possible risk parameters not currently captured in these environmental requirements. A risk management strategy was developed to guide how compost would be cured and utilized.
The biosolids compost produced at the Banff WWTP can be categorized as a natural organic material. This compost meets CCME Category B compost requirements and, except for marginally higher Se (Selenium) in some samples, meets all CCME Category A compost requirements.
The metal concentrations in Banff’s biosolids are relatively low. This is not unexpected as the town’s industry is generally limited to tourism, making its quality of biosolids quite high. Table 1 depicts selected metal concentrations undertaken by Environment Canada in a comprehensive study of wastewater sludge (Environment Canada, 2007) and compares them to concentrations from samples collected for this study. The concentrations measured for this study are relatively low and echo historical data.
Ecotoxicity testing revealed that some endocrine disrupting chemicals (EDC) were detected in both biosolids compost and the undisturbed soil. This was not unexpected as all fecal matter could be expected to have some concentration of these chemicals. Based on limited analysis there is some indication that these chemicals are decomposed during the composting process. The literature suggests that composting can have a positive impact on decomposing these chemicals. Furthermore, the literature suggests these chemicals break down quickly in soil.
The Risk Assessment and Risk Characterization exercise showed that:
• The leachate of uncured compost is acutely toxic to fish;
• There is the presence of EDC in some compost and undisturbed soil elutriate; and • The use of undiluted compost has a negative
impact on plant emergence and plant growth. There were a number of Risk Management recommendations for a new curing site that emanated from the results of the Risk Assessment including:
• The curing area should be set-back from surface water;
• Although the risk does not appear great, the curing area should be kept away from recreational areas to avoid exposure to compost or leachate by the general public; and
• Although the risk does not appear great, the curing area should not be readily accessible (e. g., fenced) to terrestrial receptors to avoid
exposure to compost or leachate. None of these outcomes was unexpected and essentially reaffirm current knowledge and well established best practices to mitigate these risks.
Curing site selection
It was determined that about 0.4 ha (one acre) of space was required to manage curing, screening and finished product storage.
A number of previously disturbed sites (gravel pits, etc.) were examined in the Banff area and in the park that could be used to cure compost. This included examination of space at the WWTP, a site outside of town used to dispose of clean fill, as well as some other sites. The goal was to find a curing site that afforded proper curing but at the same time was close to areas where the compost could be used.
Ultimately an isolated, previously disturbed site on the outside of town was selected for curing. This site featured old lined sewage lagoons.
The reasons for this selection included:
• Option to contain leachate generated during curing process;
• Option to fence the curing area;
• Close proximity to WWTP; and
• Odour contained well away from visitors and residents. This site is currently in the design phase; it’s expected that an impermeable curing pad will be constructed in early 2010.
It was recommended that two main compost products be produced: a Landscaping Grade and a Reclamation/Remediation Grade, with about half of annual compost production dedicated to each use.
Banff produces high quality compost from its biosolids. This high quality production is expected to continue with the addition of food wastes. The risks to curing and utilizing this compost were assessed and the means to mitigate these risks have been identified and discussed. A strategy to cure and utilize this compost has been developed.
Banff and Parks Canada should be able to build on the success of their shared responsibility in composting and utilizing biosolids compost, to continue to contribute positively to maintaining and improving the ecological integrity of the national park.
Paul van der Werf is president of 2cg Inc. in London, Ontario. Contact Paul at www.2cg.ca;
Chad Townsend is Environmental Coordinator, Planning & Development with the Town of Banff, Alberta. Contact Chad at firstname.lastname@example.org
“Banff produces high quality compost from its biosolids. This high quality production is expected to continue with the addition of food wastes.”
“Ultimately An Isolated, Previously isturbed Site On The utside Of Town Was elected For Curing. his Site Featured Old ined Sewage Lagoons.”
Report Fate and Significance of Contaminants in Wastewater Sludge Generated at Municipal and Other Publicly owned Wastewater Treatment Facilities (Environment Canada, 2007)
Principles and Guidelines for Ecological Restoration in Canada’s Protected Natural Areas (Parks Canada and t
he Canadian Parks Council, 2008)