Dilla Landfill Site Environmental Impact Assessment Report
FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
SOUTHERN NATIONS, NATIONALTIES AND PEOPLES REGIONAL STATE
Dilla City Administration
Urban Local Government Development Project
(IDA CREDIT No.: 4994-ET)
Landfill Site Environmental Impact Assessment Report
October 2010
|Zenas Engineering PLC |
|Tel. +251-11-416 03 35 |e-mail: yyemane@ethionet.et |P. O. Box: 1444 |
|+251-11-416 03 37 | |Addis Ababa, Ethiopia |
EXECUTIVE SUMMARY 4
1 Project Description 7
1.1 General Setting 7
1.2 Meteorological Settings 8
1.3 Site Setting 9
1.4 Ecological Context (Biodiversity) 12
1.5 Infrastructure Status 13
2 POLICIES, LEGISLATIVE AND INSTITUTUINAL FRAMEWORK 15
2.1 Policy Framework 15
2.2 Institutional Framework 15
2.3 Legislative Framework 15
2.4 World Bank Safeguard Policies 18
3. Alternative Analysis 18
3.1. Geology 18
3.2. Structural Geology 19
3.3. Unstable area 21
3.4. Seismicity and Liquefaction Potential 21
3.5. Engineering Geology 23
3.6. HYDROLOGY 25
3.6.1. SURFACE Water 25
3.6.2. GROUNDWATER 25
4. POTENTIAL Environmental & Social Impacts and Their Mitigation measures 28
4.1. Introduction 28
4.2. Community Consultation 29
4.3. Impacts on Air Quality 29
4.4. Impacts on Soils and Terrain 31
4.5. Impacts on Surface Water 31
4.6. Impacts on Ground Water 32
4.7. Impacts on Vegetation and Wildlife 34
4.8. Impacts on Current and Proposed Land use 34
4.8.1. Traffic 35
4.9.2. Nuisances 35
4.9. Impacts on Archaeological Resources 36
4.10. Impact on Safety and Health 36
4.11. Impact on income of the people generating their income from quarry 37
5. ENVIRONMENTAL MANAGEMENT PLAN 37
6. Conclusion and recommendation 42
Annexes 43
ANNEX I - REFERENCES 43
ANNEX II- CHECK LIST USED FOR IMPACT ASSESSMENT 44
Tables
Table 1. Summary of Main Mitigation Measures 5
Table 2: Grain size analysis of soil identified for liner material 24
Table 3 : Summary of coefficient of permeability, MDD and OMC of liner material 24
Table 4.Summary of Environmental and social management Plan (ESMF) 40
Figures
Figure 1 Location and Contour Map of Dilla 7
Figure 2. Satellite Image of Dilla 8
Figure 3 . Monthly Average Rainfall at Dilla 9
Figure. 4. Average monthly temperatures at Dilla 9
Figure 5 .Site plan of Sanitary land fill of Dilla 10
Figure 6 .proposed landfill site 10
Figure 7 .proposed landfill site 11
Figure 8 .proposed landfill site 11
Figure 9 .Majage river gorge adjacent to the landfill site 12
Figure 10. Birds observed at the site (Horn bill) 13
Figure 11.Existing Dump site 14
Figure 12: Photo of the Landfill Site Figure 13 Fault Trending E-W and N -S 20
Figure 14 : Area susceptible to land slide and wedge failure in area previously selected of landfill 20
Figure 15: E—W Trending Fault and Arial photoof the selected landfill site 22
Figure 16 : Water Content verse MMD curve of soil sample TP3 24
Figure 17: Water Content verse MMD curve of soil sample TP1 25
EXECUTIVE SUMMARY
This Environmental Impact Assessment (EIA) has been prepared to address the potential environmental impacts that could arise from the construction and operation of Dilla sanitary landfill facility. The intended facility will be located at outskirt of Dilla town, planned to serve the inhabitants of Dilla, for about 10 years.
The purpose of the project is to alleviate the impacts of the existing dumpsite and uncontrolled solid waste disposal into the environment. Proper design/selection, construction, and management of the solid waste landfill (and upgrading of solid waste collection networks) would mitigate such negative impacts. The main sections of the EIA include overview of the legal and institutional frameworks, description of the project and the environment, impacts assessment, identification of mitigation measures, and presentation of an environmental management plan (EMP).
Currently, municipal solid waste generated within the Dilla town is inappropriately disposed off either in open dumpsite or directly in the environment. The situation is exposing the public to associated negative health impacts and is leading to the deterioration of natural ecosystem in the area. Dilla is also considered as commercial and touristic area, and therefore impacts on the natural and aesthetic value have significant negative implications.
The proper waste collection, treatment and disposal of the municipal solid waste in the area is of utmost importance to avoid such impacts, and will be addressed by the construction of the sanitary landfill, along with other solid waste management measures, to serve the town. The facility will be designed to serve a total design population of 140,000 people.
The main objectives of the Environmental Impact Assessment (EIA) study of this Project are as follows:
• To describe the environmental and socio-economic baseline conditions of the project environment;
• To assess the potential positive and negative effects of the proposed project;
• To recommend appropriate mitigation measures that enables to avoid or minimize any undesirable effects resulting from construction, operation and closure of the proposed project.
The study is intended to ensure that the environmental and social effects of the proposed project activities are adequately and appropriately considered before decisions are taken for their implementation. The output of the environmental impact analysis will therefore, provide decision-makers with adequate information on environmental and social effects of the proposed project.
Potential adverse environmental impacts induced by the construction and operation of the proposed solid waste landfill facility include: (a) Generation of landfill gas and odors from decomposing process. (b) Erosion of soil during construction and operation phases. (c) Contaminations of surface and ground water. (d) Noise, pest, dust and other disturbances. (e) Occupational and public health hazards, and finally, (f) loss of income from displacement of quarry operation. The analysis of these impacts showed that they can be easily mitigated for. Table below includes mitigation measures to reduce further the likelihood and magnitude of such impacts.
Table 1. Summary of Main Mitigation Measures
|Impact |Mitigation Measures |
|Generation of landfill gas and odors from decomposing process|proper ventilation |
| |applying coverage for waste on daily and regular basis |
|Erosion of soil |reduce water flow over bare soil |
| |reduce velocity of water by using effective contouring to reduce slope |
| |grades, ditch blocks to reduce runoff velocities and prompt and |
| |effective re-vegetation of bare ground whenever possible, which |
| |stabilizes the soil and helps to reduce run-off water velocities |
| |appropriate measures including provision of berms and silt traps during|
| |construction |
|Contaminations of surface and ground water |all water from the waste should be kept in an appropriate leachate pond|
| |use appropriate liners- either natural or synthetic to contain leachate|
|Noise, pest, dust and other disturbances |establish buffer zone |
| |daily proper cover of waste |
| |use dust suppressor |
| |proper maintenance of machineries, vehicles, and use of low noise |
| |equipments |
|Occupational and public health hazards |provision and use of proper personal protective equipment |
| |regular medical check-up and provision of appropriate sanitary |
| |facilities |
|Loss of income from quarry operation |provide replacement land/quarry site |
In addition to the unavoidable impacts listed above, there will be several major benefits associated with the proposed projects that are summarized below:
- Long-term environmentally sound solid waste disposal, ensuring capacity for the disposal of wastes consistent with solid waste management proclamation.
- Employ a significant local labor force at the landfill site, for waste collection and transporters, and during construction.
- Enable to safeguard and improve the ecological character of the natural environment from further deterioration and damages.
In order to ensure the proper operation of the Landfill Facility, a management system must be implemented. This management scheme shall assure regular monitoring of the Landfill site and its compliance to regulations and standards, and process performance. Proper staff training and organized record keeping will also take place. Compliance monitoring will take place biannually. However, this frequency of monitoring should not be reduced after the facility has been operational for several years.
According to management and monitoring indicators are identified and discussed in detail, including in a matrix form to help as a checklist for control of major parameters. Costs required during operation phase of the project will be part of the day to day administrative and operational cost that the project is also estimated 375,000 Eth. Birr. The budget will be allocated for training and awareness creation of personnel on the principles of Integrated Solid Waste Management and salary for permanent and temporary staff.
Sampling will be performed by certified laboratories; however, in house sampling will take place to ensure process performance. It is the responsibility of the Municipality and the Landfill facility management to ensure the development of a database that includes a systematic tabulation of process indicators, performed computations, maintenance schedules and logbook, and process control and performance monitoring outcomes. Such a historical database benefits both the plant operator and design engineers in order to predict any adjustments needed to be performed ahead of time. In addition, in accordance with the requirements of the regulatory authority, the Landfill facility management should submit a periodic compliance monitoring report to the assigned authorities.
Project Description
1 General Setting
Dilla is a town in the Southern Nation Nationals and Peoples Regional State and it is the administrative capital of the Gedeo zone. The town lies in the eastern escarpment of the Ethiopian Rift Valley with fertile green mountains and is also known for the excellent coffee grown in its vicinity. The town is located approximately 360 km south of Addis Ababa and 90km from Awassa town, the capital for the Regional State. The town is characterized by gentle slope from east to west, with the 1600 m above sea level in the east dropping to 1,400 m above sea level in the west. Geographically the town is located at 6o 20' – 6024'’N latitude and 38017'-38020’’E longitude. The town covers 1123.47 hectares of land.
The main highway that connects Ethiopia to its' southern neighbor, Kenya crosses the town. Apart from this highway, there is good road network in the town to connect different parts of the town. There are two rivers; namely Legedarra at the North and Chichiu at the South which are flowing east and west down to Lake Abaya.
The project area is located on the outskirt of the town of Dilla, on the northwestern part of the town. The site is accessible in order to allow machinery to reach the site and perform the excavation and building works during the construction phases and at operation phases too. The presence of a good road network system is also very important for the collection of waste from all kebeles of the town. The total project area is 2 hectar.
[pic]
Figure 1 Location and Contour Map of Dilla
[pic]
Figure 2. Satellite Image of Dilla
3 Meteorological Settings
Precipitation
The climate of Dilla in general is influenced by the topographic features of the country. The annual average precipitation observed in Dilla is about 1253 mm.
Figure 3 depicts monthly rainfall distribution from data collected at a station in Dilla.
The following observations can be made:
• Precipitation patterns show that two distinctive rainy seasons with picks in April and September.
• A marked decrease in precipitation levels is noticed between December and February
• Based on the above observations, about 84 percent of precipitation is distributed between March and October.
[pic]
Figure 3 . Monthly Average Rainfall at Dilla
Temperatures
The mean annual temperature at Dilla is 20° C. The warmest months are February to April, when mean daily maximums temperatures can rise above 30 ºC.
Temperature variations between day and night are in general ranging between 10 and 18oC.
[pic]
Figure. 4. Average monthly temperatures at Dilla
4 Site Setting
As mentioned above, the site is located at the northwestern outskirts of the town, far-away from most of the populated area. The area surrounding the site is area designated for industrial zone. The site is located around 1km from Dombosco Catholic School, 2km from Walleme village which is part of the Dilla town and adjacent to Dombosco School and 2.6km from Dilla University. The proposed site is surrounded to the north by Majage River (gorge) which is completely covered by forest, to the south and south-waste by industrial zone, to the west by farm land adjacent to the industry zone and to the east by trees and Dombosco fence.
[pic]
Figure 5 .Site plan of Sanitary land fill of Dilla
There is active quarry site at the northern side and an abandoned quarry site little bit to the north and central part. The slope of the landfill site is fairly inclined towards the Majage River.
[pic]
Figure 6 .proposed landfill site
[pic]
Figure 7 .proposed landfill site
Figure 8 .Proposed landfill site
[pic]
Figure 9 .Majage river gorge adjacent to the landfill site
5 Ecological Context (Biodiversity)
Ecologically, the proposed location is not in an area of special concern, such as areas designated as having national or international importance (e.g. cultural heritages, wetlands, biosphere reserve, wildlife refuge, or protected areas). The project will neither lead to the extinction of endangered and endemic species, nor the degradation of critical ecosystems, and habitats.
The project area is situated in the industrial zone. Since the site has been cleared before, no major trees or plants are observed. The proposed landfill site is covered by grass and some bushes at the western and southern side, to the north and northwest side it is covered by grass and some parts are exposed soils, and eastern side is covered by bushes and some trees (include eucalyptus trees).
There are several species of birds on the site as observed on 17/04/10 morning (Dinbit, Tiku Amora, and many others, see photo).
[pic]
[pic]
Figure 10. Birds observed at the site (Horn bill)
6 Infrastructure Status
Infrastructure within the town is well noted to road network, telephone, electricity, and water supply. An adequate municipal solid waste management system in the town does not exist. The Dilla municipality is responsible for the collection and disposal of solid waste to the open dump. The percentage of the waste collected and disposed at the dumping site is about 34%. The remaining are openly dumped and burnt along roadways, ditches and in the environment.
[pic]
Figure 11.Existing Dump site
POLICIES, LEGISLATIVE AND INSTITUTUINAL FRAMEWORK
1 Policy Framework
Environmental Policy of Ethiopia
The Environmental Policy of Ethiopia (EPE) was issued in April 1997. The overall policy goal is to improve and enhance the health and quality of life of all Ethiopians and promote sustainable social and economic development through sound management and use of natural, human-made and cultural resources and their environment as a whole, so as to meet the needs of the present generation without compromising the ability of future generations to meet their own needs.
The policy seeks to ensure the empowerment and participation of the people and their organizations at all levels in environmental management activities, raise public awareness and promote understanding of the essential linkage between environment and development. In addition to its guiding principles, the policy addresses sectoral and cross sectoral environmental issues.
Environmental Impact Assessment (EIA) policies are included in the cross sectoral environmental policies. The EIA policy emphasizes the early recognition of environmental issues in project planning at all levels of administration.
The policy establishes the Federal Environmental Protection authority (FEPA) to harmonize Sectoral Development Plans and implement environmental management programs for the country.
2 Institutional Framework
Environnemental Protection Organs Proclamation 295/2002
The proclamation is aimed to assign responsibilities of the environmental management activities to separate organizations on the one hand, and environmental protection, regulations and monitoring on the other, in order to ensure sustainable use of environmental resources, thereby avoiding possible conflicts of interest and duplication of efforts. It is also intended to establish a system that fosters coordinated but differentiated responsibilities among environmental protection offices at a federal and regional level.
At the federal level the Environmental Protection Authority is in charge of policies, directives and standards and of enforcing the laws and policies including EIAs and environmental monitoring, for all projects or activities that falls under the control of the Federal Government.
Each of the main federal institutions active in the construction of infrastructure, or economic development is required by law to have its own environmental unit.
According to the Environmental Protection Organs Proclamation, the regional states are required to create their own regional environmental agencies. These institutions are to deal, among others, with EIAs for regionally managed infrastructures or development activities.
3 Legislative Framework
The Constitution
The Constitution of Ethiopia, which was adopted in August 1995, requires current and future legislation and the conduct of the Government to conform to a bill of rights. The concept of sustainable development and environment rights are entrenched in the rights of people in Ethiopia through articles 43 and 44, which states among others the right to development and right to live in clean and healthy environment.
Without prejudice to the right to private property, the government may expropriate private property for public purposes subject to payment in advance of compensation commensurate to the value of the property (Article 40(8)
Article 43 (2) dealing with the rights to development states that nationals have the right to participate in national development and, in particular, to be consulted with respect to policies and projects affecting their community.
Regarding compensation, Article 44(2) of the Constitution states that all persons who have been displaced, or whose livelihood has been adversely affected as a result of State programmes have the right to commensurate monetary or alternative means of compensation including relocation with adequate State assistance .The government shall pay fair compensation for property found on the land but the amount of compensation shall not take into account the value of land.
The Federal Government is responsible for enacting laws for utilization and conservation of land and other natural resources and historical sites.
Article 92 of the Constitution states that the design and implementation of any program and development projects shall not damage or destroy the environment, and people have the right to be fully consulted and express their views in planning and implementation of environmental policies and project.
Environmental Pollution Control Proclamation 300/2002
The proclamation on pollution control was issued in December 2002.It was issued mainly based on the principle that each citizen has the right to have a healthy environment, as well as the obligation to protect the environment of the country from pollution.
The Proclamation contains provisions for the control of pollution, management of municipal waste, and management of hazardous waste, chemical and radioactive substances. It also encompasses provision for the formulation of practicable environmental standards by the Federal Environmental Protection Authority (FEPA), in consultation with the relevant agencies. Furthermore it empowers the Federal Environmental Protection Authority or the Regional Environmental Authority to assign environmental inspectors with the duties and responsibilities of controlling environmental pollution
Environmental Impact Assessment Proclamation 299/2002 and Guidelines
The main objective of this Proclamation is to make the EIA mandatory for specified categories of activities undertaken either by the public or private sectors. Among others, the Proclamation defines the scope of the environmental impact assessment by outlining the contents of EIAs, and determining the duties of the project proponent. The general provision of the Proclamation includes the followings among others:
• Implementation of any project that requires an EIA is subject to an environmental clearance or authorization from the EPA or Regional Environmental Agency (REA).
• The EPA or the relevant REA, depending on the magnitude of anticipated impacts, may waive the requirement for an EIA.
• Approval of an Environmental Impact Study Report (EISR) or the granting of authorization by the EPA or the REA does not exonerate the proponent from liability for damage.
To put into effect this Proclamation, the EPA issued an EIA Guideline Document, which provides details of the EIA process and its requirements. The document provides background to environmental impact assessment and environmental management in Ethiopia. The Document is used as a reference material to ensure effective environmental assessment and management practice in Ethiopia for all parties who are engaged in the process. The document details the required procedures for conducting an EIA. In addition, the document specifies tools that may be considered when engaged in the EIA process. Reference is made to the legislation and policies with which potential investors and developers must comply in specific development sectors.
According to this guideline projects are categorized into three schedules:
Schedule 1: Projects which may have adverse and significant environmental impacts thus requiring a full Environmental Impact Assessment
Schedule 2: Projects whose type, scale or other relevant characteristics have potential to cause some significant environmental impacts but are not likely to warrant a full EIA study
Schedule 3: Projects which would have no impact and do not require an EIA
However, projects situated in an environmentally sensitive areas such as land prone to erosion; desertification; areas of historic or archaeological interest; important landscape; religiously important area, etc. will fall under category 1 irrespective of the nature of the project.
According to this guideline all project proponents and executing bodies (agencies) in the country should operate in close cooperation with the EPA to ensure that proper mitigating measures are designed and implemented, especially for projects with an adverse effect on the environment. This in effect means that an Environmental Impact Statement (EIS) should be prepared by project proponents and be examined, commented and approved by the EPA.
Solid Waste Management Proclamation 513/2007
Municipalities play a central role in solid waste management activities in Ethiopia. Traditionally, solid waste collection and disposal has been the responsibility of the urban administrations. The recent Solid Waste Management Proclamations 513/2007 urges urban administrations to establish a solid waste treatment facility. Article 14 of this proclamation states that urban administrations shall ensure that:
• Solid waste disposal sites are constructed in conformity with the relevant federal environmental standard and are properly used.
• Any new solid waste disposal site being constructed or an existing site undergoing any modification has had an EIA according to the relevant law.
4 World Bank Safeguard Policies
Legal and Administrative Framework WB Operational Manual OP 4.01 is designed to ensure that Bank-Financed Projects are environmentally sound and sustainable, and that decision-making is approved through appropriate analysis of actions and of their likely environmental impacts.
This policy is triggered if a project is likely to have potential adverse environmental risks and impacts in its area of influence. OP 4.01 requires an Environmental Assessment (EA) to be carried out for any project proposed for bank financing.
It outlines an environmental and social screening process which will enable qualified project personnel to screen sub-projects for potential negative environmental and social impacts and to identify, implement and monitor appropriate mitigation measures. OP.4. 01 requires these reports to take into account natural environment (air, water and land), human health and safety and social aspects (involuntary resettlement, indigenous peoples, and cultural property).
3. Alternative Analysis
Two potential sites ( Site -1, Waleme and Site -2: Chichu ,) were visited and assessment for their suitability as a sanitary landfill was evaluated.
During the inception phase of the project, Dilla City Administration made the Waleme site, which it selected for development of the sanitary landfill, known to the Consultant. Subsequently, the consultant, while searching for alternative sites, commenced assessing suitability of the site for the desired purpose based on the developed criteria. Consultant’s attempt to choose the final sanitary landfill site from number of nominee sites was impaired due to location of the competent sites out side the territory of Dilla City Administration and even that of Gedeo Zone.
Hence, sites left for final choice were the Waleme site, located in the north western part of the city, and Chichu site in the south eastern part of the city. Therefore, the latter site was abandoned because of its proximity to boreholes supplying water to the city and the Waleme site which was originally proposed by the city administration was selected.
3.1. Geology
In order to evaluate the landfill site’s suitability and capability to diminish possibility of contamination, getting hold of detail understanding of the local geological setting of the sites was essential. With this regard, details of the geological structure, characteristics of the solid strata, and composition and distribution of the subsoil were examined. The factors of interest in the solid strata included type of rock, state of weathering, extent and distribution of structural features (such as faults, joints and bedding planes), and the permeability of strata. For subsoils, it was necessary to know the composition, the lateral and vertical continuity of the strata, the permeability, and resistance to erosion.
Dilla area is made up of trachyte flows, minor basalts, tuffs and ignimbritees. The rocks around the town are mainly trachyte flows with minor basalt. The tuffs and the ignimbrite lay on the top of trachytic flows and mainly exposed to the west and south-west of Dilla. These rocks form layered sections that tilted towards the north-west and west. The trachyte is medium grained with irregular open joints forming big blocks of trachyte. Weathering in the trachyte has normally taken place along these joint fractures. The basalts are found in few localities intercalated within the trachyte flow. The tuffs and ignimbrites are mainly exposed to the west and south-west of Dilla.
In area close, Geology of the landfill site can be characterized by different layers of basalt, ignimbrite, and trachyte overlie by alluvial soil. The degree of weathering decrease to ward south east and the opening of fractures and joints increase in the same direction.
3.2. Structural Geology
Referring to the geological structures, Dilla is situated in the Eastern Fault Belt of the southern part of Main Ethiopian Rift (MER). Rift faulting and a number of extension fault zones are common around the area particularly downstream of the landfill site. The faults have N-S and E-W trend, however, some minor fault systems trend in the direction of NW-SE.
In locating areas suitable for landfill, it is difficult to avoid area close to geological ‘faults’. Even though the majority of faults increase the permeability of the bedrock in the fault zone it would normally not be appropriate to rule out or downgrade a site because of the presence of faults. Equally the absence of faults should not be taken as an absolute assurance that a site is geologically suitable.
Therefore, following assessment of the structure of the Waleme area, selection of particular development site was selected. The consultant made sure that this site is not in direct contact with faults. Should be avoided in situations where investigations show that the fault zone is excessively permeable. It is recommended that there should be no general prohibition of landfill sitting on areas with geological faults.
Figure 12: Photo of the Landfill Site Figure 13 Fault Trending E-W and N -S
Downstream of the Landfill Site.
1
3.3. Unstable area
Unstable area which is susceptible to natural or human-induced events capable of impairing the integrity of the landfill structural components should be avoided. These include poor foundation conditions, areas susceptible to mass movements (landslide and subsidence), and highly erodible material.
Topographical data were used in the assessment of the likelihood of slope failure, failure over unstable ground and in the interpretation of the topographical expressions of the geology and hydrogeology. All the factors mentioned have been checked for the current landfill site. The previously selected site was located at close distance (about 20m) to area susceptible to land slide.
Hence, to ensure structural stability of the proposed landfill during the operation phase, the site was shifted during the site investigation
3.4. Seismicity and Liquefaction Potential
Because Dilla is located in an earthquake prone area, assessing resistance to the dynamic forces which can be applied during earthquake was incorporated in the landfill design investigation.
In the geotechnical evaluation the soil behaviour was examined with respect to earthquake intensity. This evaluation of the soil characteristics necessitated finding out the soil strength as well as the magnitude or intensity of the earthquake in terms of peak acceleration. Other soil characteristics, including degree of compaction, sorting, and degree of saturation, was also considered because of their potential influence on site conditions. For example, compaction of deposits of loose granular soils found as upper layer in the Waleme site through the ground vibrations an earthquake induces is possible. Ultimate result of such volume reductions could would be large uniform or differential settlements of the ground surface.
Figure 15: E—W Trending Fault and Arial photoof the selected landfill site
Very steep slopes of weak, fractured and brittle rocks were found in the eastern part of previously selected site; unsaturated loess are vulnerable to transient shocks caused by tensional faulting. Similar effects are possible in sensitive cohesive soils when natural moisture exceeds the soil's liquid limit. Dry cohesionless material on a slope at an angle of repose will respond to seismic shock by shallow sloughing and slight flattening of the slope.
Because the material selected for the liners is flexible, unlike rigid concrete the liner will not be susceptible to cracking. Thus, future instability that could possibly considered was only for the leachate collection system, which is a concrete structure. However, for life time of the proposed landfill is short (10 years), and probability of occurrence of earthquake of significant horizontal acceleration in this period is very low, the site is not endangered by seismic effect of natural earthquake. On the other hand, presence of a quarry site adjacently can subject the leachate collection system to dynamic forces as a result of material production using blasting techniques.
Susceptibility of the landfill site for liquefaction potential was assessed during the site investigation. Liquefaction is one of secondary effects that is directly related to earthquake shaking or dynamic vibration resulted from blasting. The typical subsurface soil condition that is susceptible to liquefaction is loose sand and silt, which has been newly deposited or placed, with a shallow groundwater table. The development of high pore water pressures due to the ground shaking and the upward flow of water may turn the sand/silt into a liquefied condition, which has been termed liquefaction. During an earthquake, the propagation of shear waves causes the loose sand to contract, resulting in an increase in pore water pressure. Because the seismic shaking occurs so quickly, the cohesionless soil is subjected to an undrained loading. The increase in pore water pressure causes an upward flow of water to the ground surface, where it emerges in the form of mud spouts or sand boils. This condition can interrupt the overall structural arrangement of the landfill.
In Waleme landfill site the loose sandy and silty soils are intercalated/sandwiched between clayey silt layers, which seems to make liquefaction potential of the site very high due to grain size distribution and low degree of compaction. However, the presence of the groundwater at great depth limits the possibility of occurrences of liquefaction particularly in adjacent the landfill area. Moreover, complete excavation of the overburden loose soil and the highly weathered earth material during construction will found the landfill on a moderately weathered trachyte.
3.5. Engineering Geology
i. General
The geotechnical survey for the selected landfill site was commenced with careful desk study leading to field investigation and laboratory testing. Direct information on the subsoil was obtained from gulley cuts instead of test pits digging. The site investigation work (including sampling and description of soils and rocks) was carried out to the appropriate standard.
ii. Properties of the Foundation Material
Alluvial soils having about 6m thickness overlies weathered trachyte. The thickness of the layer decrease toward the east direction. The section mainly exposed on the side of gulley consists of: 0-1.2m clayey silt, 1.2-3m clayey silty sand, 3-5m clayey silt and 5-6m gravelly material with slight variation in thickness and gradation from place to place. The upper and the lower fine grained layers are moderately to highly plastic. The in situ degree of compaction of the overburden material is relatively low. The upper and lower fine grained layers of soil can be used as liner material and the middle layer as a cover material.
a. Grain Size Analysis
Dry sieve analysis on coarse fraction and hydrometric analysis on fine fraction was made on three different samples of liner material. The test result shows a dominance of clay fraction in each sample. Figure xx shows the grain size distribution graph of the soil samples.
• 53.75 % clay, 45.54 % silt and 0.71% sand for Tp1
• 48.68 % clay, 24.56 % silt and 26.76% sand for Tp2
• 41.55 % clay, 37.15 % silt and 21.30% sand for Tp3
b. Standard Procter Compaction and Permeability
From the standard compaction test conducted on the samples the optimum moisture content (OMC) varies from 22 to 27.55 % and the corresponding maximum dry density is between 1.44 to 1.63 g/cc (Table 4.6). The permeability value of the soil specimen computed from grain size distribution graph. The results showed that the materials are impervious with coefficient of permeability ≤5.26 x 10-7cm/s.
Table 2: Grain size analysis of soil identified for liner material
|Sample |Depth |Percentage |Soil Type |Soil |
|No. | | | |Classification |
| | |Gravel |Sand |Fine | | |
| | | | |Silt |Clay | | |
|Tp1 |0-1.2 |- |0.71 |45.54 |53.75 |Fine grained |Silty clay |
|TP2 |3-5 |- |26.76 |24.56 |48.68 |Fine grained |Silty clay |
|TP3 |0-1.6 |- |21.30 |37.15 |41.55 |Fine grained |Silty clay |
Table 3 : Summary of coefficient of permeability, MDD and OMC of liner material
|S.No. |Coefficient permeability [cm/s] |MDD [g/cc] |OMC [%] |
|1 | ................
................
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