Fabricated soil mixes to be used to cover Vancouver Landfill
Overall case specific learning outcome: characterize the soil quality of fabricated (manufactured) soil used as topsoil in the final cover system of the phase 1 closure area of Vancouver Landfill in Delta, BC, with an emphasis on soil chemical properties.
With the help of a series of guiding questions and the interaction with instructors, you will accomplish the following tasks:
- Interpret the results of the past soil testing of four soil mixes.
- Describe your learning in written format (as individual students) and orally (as a working team).
Vancouver Landfill, that currently occupies 225 ha, has been in operation since 1966. To date none of the areas of the landfill has been permanently closed. In 2000, a detailed Design and Operations Plan was prepared for the landfill and it includes phase development strategy for progressive closure. An area of the landfill selected for the initial closure consists of 40 ha located in the western part of landfill. This area does not receive any additional garbage (it was in operation from 1966 to 1982), but will be re-contoured with wood waste and demolition material. The Closure Plan for the western 40 ha of Vancouver Landfill was prepared in 2004 by the Speriling Hansen Associates in cooperation with several other consulting companies.
Another area of the landfill is proposed for closure in 2007. This area of the landfill is known as “Phase 1” and consists of the most eastern section, approximately 20 ha in size. The final system for the closure on both these areas have not been identified, but the recommended final cover system will utilize a geomembrane barrier layer and system comprised of: top soil, sub soil, gravel drainage layer, geomembrane, and possibly a secondary clay liner. The focus of this case study will be on creation of fabricated soil mixtures that will be used as topsoil in the final cover system of the phase 1 closure area of Vancouver Landfill.
Elaborate on main types of fabricated soil mixtures proposed for use in the Landfill Closure Plan
- Review the background information on the Vancouver landfill from the final report “Closure Plan for the Western 40 ha at the Vancouver Landfill” prepared by the Speriling Hansen Associates in cooperation with Golder Associates, Sylvis Environmental, Sharp and Diamond, and Golf Design Services. [Please focus on the following chapters: Summary, 1, 2, 9, and 15]
- Share individual learning with group members (ongoing for weeks 1-4).
- Discuss climate, parent material, topography, and vegetation of the area where the Vancouver Landfill is located
- What are the layers of the final cover material?
- Final report “Closure Plan for the Western 40 ha at the Vancouver Landfill” prepared by the Speriling Hansen Associates in cooperation with Golder Associates, Sylvis Environmental, Sharp and Diamond, and Golf Design Services [Chapters: Summary, 1, 2, 9, and 15]
- Krzic, M. and M.P. Curran. 2005. Forest soils and tree nutrition. pp. 358-393. In S.B. Watts and L. Tolland (eds.) Forestry handbook for British Columbia, 5th edition. University of British Columbia, Vancouver.
Soil cover of the Vancouver landfill will be designed to support the plant growth. In doing so it will need to serve the following three main roles: (i) to provide nutrients for optimum plant growth, (ii) to store and supply water to plants, and (iii) to provide structural media capable to support the growth of established plants. Consequently, the landfill cover must allow for an appropriate balance between structural components, water, and air. Without sufficient soil depth and the appropriate soil physical, chemical, and biological properties the plant community will not be sustainable, and will require continuous maintenance through repeated seeding and nutrient additions.
Fabricated soil mixes needed for closure of Vancouver Landfill will be created on-site. Three basic feedstock materials are usually incorporated into a fabricated soil mix:
- Mineral sources (e.g., sand, soil from construction excavations, or fines from a sedimentation pond) provide structure and allow adequate aeration and drainage,
- Carbon source (e.g., alder shavings, composted fir bark, fir sawdust, fir/pine woodchips and sawdust, deinking plant sludge) provides organic matter, which mediates retention and supply of nutrients and water, and
- Biosolids source provides N, P, and other nutrients and organic matter. The use of a particular biosolids depends on its treatment and characteristics. To achieve Class A or B biosolids category under the BC Organic Matter Recycling Regulation (OMRR), biosolids treatment must include recognized pathogen and vector attraction reduction processes, and the concentration of pathogens and trace elements in the biosolids must be below limits. Pathogen reduction is achieved by thermophilic anaerobic digestion at temperature greater than 50°C (as required for Class A biosolids pathogen reduction of the OMRR). Anaerobic digestion should reduce the mass of volatile solids to allow biosolids to achieve vector attraction reduction.
The feedstock materials are identified based upon quantities available, temporal patterns of availability, logistics in access and transportation, quality (composition and aesthetics), consistency of quality and supply, and cost. Consistently high quality feedstocks are preferred for a fabricated soil. Fluctuations in feedstock quality can cause the fabricated soil to not meet the OMRR or market requirements.
There are several regulatory regimes that will influence the closure activities. The BC Organic Matter Recycling Regulation (OMRR) regulates the use of biosolids in BC. The landfill fabricated soil will include biosolids, hence the OMRR may be the most applicable regulation. The OMRR identifies what organic matter is eligible for land application under the regulation and currently excludes pulp sludge. Development of fabricated soil mixtures to be used as landfill cover faces considerable challenges, since the fabricated soil cover needs to have adequate soil quality while meeting and regulatory standards. For example, mixtures may contain trace element concentrations higher than allowed under the OMRR, yet be a productive, high quality landfill soil cover.
Formulation of fabricated soil mixtures
Upon identifying feedstock materials that could be potentially included into fabricated soil mixtures for a landfill closure feedstock analysis is carried out by an optimization model that predicts the quality on numerous potential landfill soil mixtures. The model serves as a useful starting point for trace elements and certain nutrient concentration predictions. It is; however, of limited use in predicting the concentration or level of certain soil quality parameters (i.e., pH and C:N ratio) that are significantly influenced by the physical mixing of the feedstock materials. The subsequent phase in the development of fabricated soil mixtures involves assessment of the “mixability” of the feedstock materials and determination of the quality following mixing. Interpretations of advantages and disadvantages of each fabricated soil mixture are based upon quality and regulatory requirements, as well as cost.
Identify soil quality indicators, with emphasis on soil chemical properties, that could be used to assess how well a soil mixture is functioning as a cover for the Vancouver Landfill
- Review the soil data for the four fabricated mixtures (see Excel file)
- Considering the three main roles that fabricated soil mixtures need to fulfill, develop the soil quality framework that would help with soil quality assessment
- What are some general advantages and disadvantages of (i) mineral source, (ii) C source, and (iii) biosolids source components of the fabricated soil mixes?
Keep in mind the requirements of soil quality and regulation. (Note - in real-life, cost assessment is also taken into account, but to simplify your work during this course, it is omitted from the discussion)
- BC Ministry of Environment. 2002. BC Organic Matter Recycling Regulation. Available at http://www.qp.gov.bc.ca/statreg/reg/E/EnvMgmt/18_2002.htm
- Craul, P.J. 1999. Urban Soils: applications and Practices. Wiley, New York, NY. Chapter 4- overview of soil quality and functions and chapter 5- overview of soil specifications [pdf posted on the Connect].
- Kidder, G. 2000. Management of organic wastes in urban areas. pp. 93-118 In R.B. Brown et al. (eds.) Managing Soils in an Urban Environment, Agronomy no. 39. ASA, CSSA, and SSSA. Madison, WI. [pdf posted on the Connect]
- National Biosolids Partnership web site provides information on biosolids and biosolids land uses in a variety of sectors. http://www.biosolids.org/
- Northwest Biosolids Management Association web site contains basic fact sheets and detailed information on biosolids and biosolids use in a number of sectors. http://www.nwbiosolids.org/
Learning objective is to identify soil quality indicators, with emphasis on soil chemical properties, that could be used to assess how well a soil mixture is functioning as a topsoil part of the cover for the Vancouver Landfill.
- Continue with the review the soil data for the four fabricated mixtures (see Excel file)
- Based on the soil quality indicators and regulation considerations, recommend (out of 4 proposed mixes) the most promising fabricated soil mix to be used to cover western 40 ha of the Vancouver Landfill.
- Preparation for group presentations
- How would you evaluate the fabricated soil mixture?
- Do each of the four fabricated soil mixes meet the Organic Matter Recycling Regulations (OMRR) criteria?
- Are any important soil quality indicators missing in the data set?
- BC Ministry of Environment. 2002. BC Organic Matter Recycling Regulation. Available at http://www.qp.gov.bc.ca/statreg/reg/E/EnvMgmt/18_2002.html
- McDougall, R., Van Ham, M.D., and Douglas, M.J. 2002. Best management practices guidelines for the land application of managed organic matter in British Columbia. [focus only on chapters 2, 3, 4, and 8]
Tutorial: Group presentations and synthesis
Each group will present results of their work on case 2 (please remember that your presentation should be max 20 minutes long) and along with the instructors compare and contrast the methods of diagnosis and interpretations of soil chemical quality in the four case studies:
- Soil fertility management at the UBC Farm,
- Forest nutrition management, and
- Soil quality assessment of Riley Park community garden,
- Fabricated soil mixes to be used to cover Vancouver Landfill.
The presentations will be evaluated on the basis of content, structure, and delivery (for specific details of evaluation criteria please refer to the course syllabus). One of the signs of successful presentation is how well the presentation engages other groups into discussion.