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:
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
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:
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.
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
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)
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.
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:
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.