Summary of Feasibility study on Mitubiri Landfill CAPACITY BUILDING WORKSHOP PROGRAM 22/02/2018 NAIROBI METROPOLITAN SERVICES IMPROVEMENT PROJECT (NaMSIP) Consultancy services for preparation of feasibility studies, plans, final designs and bidding documents for integrated solid waste management & investment within the Nairobi Metropolitan Region
Project Presentation Project Objective Identify the best location for a new landfill in the Nairobi Metropolitan Region (NMR), prepare its detailed design and all the tender documents for its construction and operation. Project Phase Landfill Site Identification Feasibility Study Detailed Engineering Design Services Environmental Review 2
Waste management context
Majors issues identified from actual dump sites Proximity to urban areas: most of the sites are now surrounded houses; some are in the middle of the town. This proximity causes two problems. First, the population is directly exposed to odors, noise, water and air pollution, visual impacts, etc. Second, dumpsites being surrounded by habitations, it leaves no room for extension. Closeness to surface water: some of the dumpsites actually in operation are very close to rivers. The leachate from the waste is a direct source of contamination to rivers, under the form of leachate or of waste. Poor management: some dumpsites have ‘managers’ (county employees) that can monitor the amount of waste disposed and check that the waste is disposed on the right place; but in most of the sites visited are not controlled whatsoever. Limits: some dumpsites are fenced, but in most cases there is no clear boundary between the dumpsite, and the land nearby. This issue leads to site uncontrolled extension: the waste is disposed all around instead of in one designated place increasing land consumption and contamination. ISWM - NMR - 29/04/2015 4
Improving waste treatment Modern sanitary landfills need to be developed, to insure a proper waste treatment without environmental impacts ISWM - NMR - 29/04/2015 5
Integration of the waste treatment Need for incorporate waste treatment in urban planning development plans : It is an essential service for the population like wastewater treatment Need to take into account the future growth of the population : The more people, the more waste : the growth in the waste production needs to be evaluated in order to design proper treatment capacities Need to take into account the urbanization : Location of waste treatment facilities must be carefully selected, and take into account the development of the cities ISWM - NMR - 29/04/2015 6
Landfill Site Selection
Methodology for Site Identification Objectives Select the most suitable site(s) in terms of technical, economic, environmental and social criteria Methodology GIS-based spatial multi-criteria analysis GIS Model A widely used tool for landfill site selection Imaging and analysis of spatial data (buffer zones, overlay, etc.) Criteria selection Based on World Bank’s guidelines and the Consultant’s experience 8
GIS-based Spatial Multi-Criteria Analysis • Negative mapping • Exclusion of areas that are not suitable for landfill development Phase 1 e.g., airports, surface water bodies and protected areas… Positive mapping Evaluation of the suitability of non-excluded areas using criteria which are rated and weighted by order of importance. Phase 2 e.g., road accessibility, land use and slope… • Identification of potential sites • Identification of the best potential sites in collaboration with each county. During this process, land Phase 3 availability and current land use of the sites will be verified. • Evaluation of candidate sites • Final review of candidate sites for which counties have confirmed availability using secondary criteria such as visibility from residential neighbourhoods and availability of borrow material for Phase 4 construction. 9
Feasibility study
Site overview 11 TITRE DE LA PRÉSENTATION / SOUS-TITRE / DATE
Location The site is located in Murang’a County, in the Maragwa Constituency 12
Urban Planning Ownership of the site The land is a private land located in Mitubiri/Wempa/Block 1/6824 under one title deed and it is one block of 121.3 hectares. Initially, the owner of the site agreed to sell 50 acres for the project. However, considering the development around the site, it has been recommended that a buffer zone should be created between the landfill site and this area. The feasibility recommended that the Murang’a County acquire 50 acres for the landfill + 20 acres for the buffer zone. Situation of the site during feasibility study : The area in which the land was found was not subject to any physical development plan The land was covered in eucalyptus vegetation and the surrounding areas were cultivated land. A Land Subdivision Scheme had been issued with a project for housing construction – but it was not approved when the site was selected. The feasibility study recommended that : A buffer zone was established to create a distance between the site and the future development zone. The county government pushed for the physical planning of the Maragua Sub-county to forestall any unwarranted developments and guide all physical developments (including the definition of buffer zones, proposition for sequential development, restriction in the land use on the landfill site after its closure) 13
Fields surveys 14 TITRE DE LA PRÉSENTATION / SOUS-TITRE / DATE
Topographical survey The topographic survey was finalized on October 7 th 2015 TITRE PRÉSENTATION / SOUS TITRE / DATE 15
Tests pits 23 tests pits for soil identification Black cotton soil Red soil Laterites Basaltic tuff Test Pits n°1 : black cotton soil Test Pits n°25 : red soil TITRE PRÉSENTATION / SOUS TITRE / DATE 16
Core holes Regarding the particularity of the soil, it was decided to conduct 12 core holes to have a better understanding of the nature of the soil Results were presented in the forms of geological log and geological cross section TITRE PRÉSENTATION / SOUS TITRE / DATE 17
Geological logs (CS1) CS1 0m Black Coton Soil 0,80m Fracture 1 1m Fracture 1,55m Highly Fracture 1,8m weathered tuff 2 2,20m Fracture 2,5m 2,5m Fracture 3 Fracture 3,7m Weathered tuff 4 4,2m Fracture 5 6m 6 Fresh tuff 6,4m End of drilling 7 TITRE PRÉSENTATION / SOUS TITRE / DATE 18
Location map of geological cross-sections TITRE PRÉSENTATION / SOUS TITRE / DATE 19
Geological Section CS1 – CS3 TITRE PRÉSENTATION / SOUS TITRE / DATE 20
Findings Results confirm that the site may be divided into 3 distinctive parts: In the Northern half of the site, topsoil is composed of black cotton soil. The underlying rock is composed of weathered tuff at different degrees of alteration with highly decomposed tuff at depths ranging from 3.60 m to 7.10 m. At the base of this formation is the fresh tuff, between 6 and 7 meters except in drilling CS2 where fresh tuff is observed at 3.60 m depth. In CS3 and CS4 no fresh tuff was observed even when bedrock is less weathered (end of drilling at 5,80 m and 6,20 m respectively). In the central part of the site, the topsoil is composed of lateritic soil. The underlying rock is composed of fresh tuff with depths ranging from 4,20 m to 4,90 m. At the base of this formation, weathered tuff is found, with highly weathered tuff in boreholes CS08 and CS09. In the South section of the site, topsoil is composed of lateritic soil South-east and red soil in the South West. The underlying rock is composed of slightly to highly weathered tuff with no fresh tuff except between 2,95 m and 3,80 m depth in borehole CS10. TITRE PRÉSENTATION / SOUS TITRE / DATE 21
Drilling of piezometers Boreholes for test wells were drilled up to a depth of 40 m for PZ1 North East of site, 30m depth for PZ2 South-West of site as well as PZ3, West of site. Formations encountered in deep boreholes are in fully consistent with the results of core drillings Water level is measured at around 12 bgl m in PZ1 and 18m in PZ2, corresponding to a shallow superficial aquifer, overlaying the main rock mass. A second water strike occurs between 20 to 25 m deep in PZ1 and PZ2. No water strike has been observed in PZ3 at that depth. The piezometers were equipped to operate as groundwater monitoring wells TITRE PRÉSENTATION / SOUS TITRE / DATE 22
Others tests Permeability tests on site Laboratory tests : Classification Tests on Soils Triaxial Compression Test Shear test Compaction Unconfined Compression Tests on Rock Cores TITRE PRÉSENTATION / SOUS TITRE / DATE 23
Conceptual design Based on the fields surveys and tests realized during the feasibility study, a conceptual design was proposed for the site. 24 TITRE DE LA PRÉSENTATION / SOUS-TITRE / DATE
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