Preliminary and Detailed Engineering Design Study of · PDF fileThe Gambian Agency for the Management Preliminary and Detailed Engineering Design of Public Works (GAMWORKS) Study for

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POVERTY ALLEVIATION AND CAPACITY BUILDING PROJECT (PACABP)

The Gambian Agency for the Management of Public Works (GAMWORKS)

Preliminary and Detailed Engineering Design Study of The Bakoteh

Dump Site

FINAL REPORT

VOLUME 1

Main Report

August 2004

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The Gambian Agency for the Management Preliminary and Detailed Engineering Design of Public Works (GAMWORKS) Study for Bakoteh Dump Site

Charchi Githinji & Partners in association with Cityscape Associates Final Report

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Charchi Githinji & Partners P.O. Box 60424 - 00200 Nairobi Kenya Email: [email protected]

Cityscape Associates 61, Kairaba Avenue, Fajara The Gambia Email: [email protected]



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Preliminary and Detailed Engineering Design Study of The Bakoteh

Dump Site

FINAL REPORT

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION 1

1.1 STUDY BACKGROUND ............................................................................................ 1 1.2 OBJECTIVES OF THE STUDY .................................................................................... 2 1.3 TERMS OF REFERENCE............................................................................................ 2 1.4 STUDY SCHEDULE .................................................................................................. 2

CHAPTER 2 SOLID WASTE MANAGEMENT IN KMC – SITUATION ANALYSIS 3

2.1 INTRODUCTION....................................................................................................... 3 2.2 INSTITUTIONAL FRAMEWORK................................................................................. 3 2.2.1 INTERNATIONAL AGREEMENTS .............................................................................. 3 2.2.2 THE NATIONAL FRAMEWORK FOR SOLID WASTE MANAGEMENT .......................... 4 2.2.3 THE LOCAL GOVERNMENT FRAMEWORK FOR SOLID WASTE MANAGEMENT......... 4 2.2.4 THE CLEANSING SERVICES UNIT............................................................................ 5 2.2.5 LANDFILL MANAGEMENT CAPACITY ..................................................................... 8 2.3 SOLID WASTE GENERATION AND COMPOSITION .................................................... 9 2.4 SOLID WASTE COLLECTION AND TRANSPORTATION ............................................ 10 2.5 SOLID WASTE DISPOSAL ...................................................................................... 14 2.5.1 BAKOTEH DUMP SITE ........................................................................................... 14 2.5.1.1 General ................................................................................................................ 14 2.5.1.2 Environmental and Socio-economic impacts ...................................................... 15

CHAPTER 3 SOLID WASTE MANAGEMENT SYSTEM FOR THE BAKOTEH DUMP SITE 18

3.1 INTRODUCTION..................................................................................................... 18 3.2 SOLID WASTE AMOUNT ....................................................................................... 19 3.3 DUMP SITE TOPOGRAPHY...................................................................................... 21 3.3.1 TOPOGRAPHIC SURVEYS....................................................................................... 21 3.3.2 GEO-TECHNICAL AND HYDRO-GEOLOGICAL CONSIDERATIONS ............................ 22 3.3.3 LANDFILL AREA WITHIN BAKOTEH DUMP SITE.................................................... 22 3.4 SANITARY LANDFILL ............................................................................................ 26 3.4.1 LEVELS OF OPERATION ......................................................................................... 26 3.4.2 METHOD OF LANDFILLING ................................................................................... 29



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3.5 RECOMMENDATIONS ............................................................................................ 31

CHAPTER 4 ENVIRONMENTAL IMPACT ASSESSMENT 32

4.1 GENERAL.............................................................................................................. 32 4.2 OBJECTIVES OF IMPACT ASSESSMENT. ................................................................. 32 4.3 METHOD OF IMPACT ASSESSMENT ....................................................................... 32 4.4 IDENTIFICATION AND DESCRIPTION OF IMPACTS................................................... 33 4.4.1 IMPACT OF LANDFILL LOCATION.......................................................................... 33 4.4.2 IMPACT ON LAND USE.......................................................................................... 34 4.4.3 VISUAL IMPACTS.................................................................................................. 35 4.4.4 IMPACT ON AIR QUALITY ..................................................................................... 36 4.4.5 IMPACT ON FLORA AND FAUNA............................................................................ 37 4.4.6 IMPACTS ON WATER RESOURCES .......................................................................... 37 4.4.7 IMPACT ON HUMAN BEINGS AND THE HUMAN-MADE ENVIRONMENT. ................. 41 4.4.8 COMMUNITY STABILITY....................................................................................... 42 4.4.9 POTENTIAL NEGATIVE IMPACTS............................................................................ 42 4.4.10 IMPACT ASSESSMENT STATEMENT....................................................................... 44

CHAPTER 5 DETAILED DESIGN OF PROPOSED SOLID WASTE MANAGEMENT SYSTEM 47

5.1 INTRODUCTION..................................................................................................... 47 5.2 DESIGN CONSIDERATIONS AND SOLID WASTE MANAGEMENT ............................. 47 COMPONENTS....................................................................................................... 47 5.2.1 GENERAL.............................................................................................................. 47 5.2.2 TYPE OF WASTE.................................................................................................... 47 5.2.3 LANDFILL AREA AND CAPACITY ........................................................................... 47 5.2.4 ACCESS ROADS..................................................................................................... 51 5.2.5 ENCLOSURE DIKE................................................................................................. 51 5.2.6 LEACHATE MANAGEMENT FACILITIES .................................................................. 52 5.2.7 LEACHATE COLLECTION AND TREATMENT STRUCTURES...................................... 52 5.2.8 LANDFILL LINER .................................................................................................. 52 5.2.9 SELECTION OF GAS CONTROL FACILITIES.............................................................. 53 5.2.10 SELECTION OF LANDFILL COVER CONFIGURATION................................................ 53 5.2.11 SURFACE WATER DRAINAGE FACILITIES ............................................................... 55 5.2.12 ENVIRONMENTAL MONITORING FACILITIES .......................................................... 55 5.2.13 AESTHETIC DESIGN CONSIDERATIONS .................................................................. 56 5.2.14 Equipment Requirements .................................................................................... 57 5.3 LANDFILL OPERATION .......................................................................................... 58 5.4 ESTIMATED COST OF PROPOSED LANDFILL COMPONENTS..................................... 59



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CHAPTER 6 LANDFILL CLOSURE AND POST-CLOSURE CARE 62

6.1 INTRODUCTION..................................................................................................... 62 6.2 ROUTINE INSPECTIONS ......................................................................................... 63 6.3 INFRASTRUCTURE MAINTENANCE........................................................................ 63 6.3.1 GRADING AND LANDSCAPING. ............................................................................. 63 6.3.2 DRAINAGE CONTROL SYSTEMS. ........................................................................... 64 6.3.3 GAS MANAGEMENT SYSTEMS. ............................................................................. 64 6.3.4 LEACHATE COLLECTION AND TREATMENT. ......................................................... 64 6.4 ENVIRONMENTAL MONITORING SYSTEMS. .......................................................... 64

CHAPTER 7 OPERATION AND MAINTENANCE MANUAL OF SANITARY LANDFILL 65

7.1 LANDFILL CONTROL FACILITIES .......................................................................... 65 7.1.1 STRUCTURE OF CONTROL FACILITIES.................................................................... 65 7.1.1.1 Management of sanitary landfill system ............................................................. 65 7.1.1.2 Control facilities Components............................................................................. 65 7.1.2 SAFETY MEASURES .............................................................................................. 72 7.2 RELATED FACILITIES............................................................................................ 73 7.3 LANDFILL WORKS................................................................................................ 76 7.3.1 LANDFILL WORKS................................................................................................ 76 7.3.2 LANDFILL METHOD.............................................................................................. 76 7.3.2.1 Landfill Method................................................................................................... 77 7.3.2.2 Cell Construction................................................................................................. 78 7.3.2.3 Order of Landfill ................................................................................................. 78 7.3.2.4 Landfill Equipment ............................................................................................. 80 7.3.2.5 Cover Soil............................................................................................................ 80

ANNEXE 1 LANDFILL LEACHATE EVALUATION 84

ANNEXE 2 SOIL INVESTIGATION RESULTS 92

ANNEXE 3 WORKSHOP REPORT 98



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LIST OF TABLES

Table 2.1 Projected Household Waste Generation for Kanifing Municipality ........ 9 Table 2.2 Composition of Household Wastes by Weight.......................................... 10 Table 2.3 Solid Waste Collection zones and blocks................................................... 11 Table 2.4 Solid Waste Collection Vehicles for Cleansing Services Unit.................. 12 Table 2.5 Skips and Trailers for Solid Waste Collection.......................................... 13 Table 3.1 The Amount of Waste Expected at the Dump Site................................... 20 Table 3.2 Capacity requirements of the disposal Site ............................................... 20 Table 3.3 Area occupied by Bakoteh Dump Site ....................................................... 25 Table 3.4 Nominal volume of zone 3........................................................................... 25 Table 3.5 Volume of cover material on site and waste outside zone 3..................... 25 Table 3.6 Components of a Sanitary Landfill............................................................ 27 Table 3.7 Classification of sanitary level of landfill system...................................... 28 Table 4.1 Water Sampling Results of the Dump site Pond....................................... 38 Table 4.2 Impact pathways and mitigation measures............................................... 46 Table 5.1 Factors considered in the design of the landfill ........................................ 49 Table 5.2 Estimated useful life of landfill................................................................... 51 Table 5.3 Performance Characteristics of Landfill equipment................................ 57 Table 5.4 Factors considered in the operation of the landfill................................... 58 Table 5.5 Estimated cost of proposed Landfill components..................................... 59 Table 5.5 Estimated cost of proposed Landfill components (continued) ................ 60 Table 6.1 Typical elements of a landfill postclosure plan......................................... 62 Table 6.2 Closed landfill inspection items, frequency of inspection, and potential

problems to be observed ............................................................................. 63 Table 7.1 Check of sanitary landfill system ............................................................... 65 Table 7.2 Classification of control facilities ............................................................... 66 Table 7.3 Typical Input Information.......................................................................... 67 Table 7.4 Typical Information for Management of Sanitary Landfill .................... 68 Table 7.5 Typical Monitoring Scheme (Leachate) .................................................... 69 Table 7.6 Proposed Monitoring Scheme .................................................................... 70 Table 7.7 Monitoring Scheme of Gas ......................................................................... 70 Table 7.8 Landfill Works............................................................................................. 76 Table 7.9 Performance Characteristics of Landfill equipment................................ 80 Table A Landfill Leachate Evaluation ..................................................................... 85 Table B Rainfall Data ................................................................................................ 90 Table C Evaporation Data......................................................................................... 91 Table D Summary of soil investigation laboratory test results.............................. 93



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LIST OF FIGURESFigure 2.1 Cleansing unit organisation chart .............................................................. 6 Figure 2.2 KMC organisation chart ............................................................................. 7 Figure 3.1 Bakoteh Dump Site zoning........................................................................ 21 Figure 3.2 Landfill Method ......................................................................................... 29 Figure 3.3 Landfill Process by Cell Method .............................................................. 30 Figure 5.1 Landfill Liner System Design ................................................................... 53 Figure 5.2 Gas Exhaust Equipment............................................................................ 54 Figure 5.3 Typical cover system.................................................................................. 55 Figure 5.4 Monitoring Well ......................................................................................... 56 Figure 7.1 Monitoring Well ......................................................................................... 71 Figure 7.2 Typical Notice Boards................................................................................ 75 Figure 7.3 Area Method............................................................................................... 77 Figure 7.4 Cell Method ................................................................................................ 78 Figure 7.6 Spreading/Compaction Method................................................................ 79 Figure 7.7 Pushing up and compacting the waste simultaneously.......................... 79



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ABBREVIATIONS AND ACRONYMS

KMC Kanifing Municipal Council KMA Kanifing Municipal Area NEA National Environment Agency GDP Gross Domestic Product GBA Greater Banjul Area NEMA National Environment Management Act GEAP Gambia Environmental Action Plan GSWMSR Gambia Solid Waste Management Strategy Report EDPR Environmental Discharge Permit Regulation DOH Director of Health PHA Public Health Act PHD Public Health Department NAWEC National Water and Electricity Company BOD Biochemical Oxygen Demand COD Chemical Oxygen Demand CBOs Community Based organizations LGA Local Government Act SWM Solid Waste Management TDA Tourism Development Area FC Faecal Coliform TC Total Coliform GMD Gambian Dalasi BDSWMS – 2002 Bakoteh Dumpsite Solid Waste Management Study MDD Maximum Dry Density

Exchange Rate: 1 USD = 30 GMD



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CHAPTER 1 INTRODUCTION

1.1 Study Background Banjul and Kanifing Municipality and part of Western Division together referred to as the Greater Banjul Area, and Brikama Municipality, form the largest urban population representing over 40% of the total population of The Gambia. According to 2001 population projection based on 1993 population census, Banjul, the capital of The Gambia has an estimated population of 40,056 (2004), while Kanifing Municipality with a population of 456,560 (2004) has the highest urban population followed by Brikama with an estimated population of 295,696 (2004). Solid Waste for the City of Banjul is disposed at the Mile 2 dump site while that of the Kanifing and Brikama municipalities is disposed at Bakoteh and Tambana dump sites respectively. The Government of The Gambia (GOTG) initiated, in 2001, a Solid Waste Management Study for The Greater Banjul Area and Brikama whose terms of reference included development of waste management system and a comprehensive study on waste management for the Greater Banjul Area and Brikama. This study identified a new landfill site in Tambana. In 2002, a feasibility study, Support for the Bakoteh Dump Site Waste Management Study, was carried out for the effective management of Bakoteh Dump Site, as an interim short-term measure while the new landfill at Tambana was being developed. The study was completed in October 2002. The study, while disqualifying the site as a landfill site, identified a storage capacity in dump site for a period of 3-5 years. The Bakoteh Dump Site, on the site of an old quarry is surrounded by human settlement and occupies an area of about 17.8 hectares. The Bakoteh dump site is the only official dump site serving the Kanifing Municipality, most populated municipality in The Gambia with an estimated population growth rate1 of 6% per annum (2001). The generation of Solid Waste is estimated to be 219 tons/day (2002). In spite of the above initiatives, the condition at the Bakoteh dump site continues to create hygienic, environmental, as well as aesthetic problems in and around the dump site.

1 Provisional results from 2003 Census indicate a lower growth rate of 3.52%.



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1.2 Objectives of the Study The objective of this study is to prepare preliminary and detailed engineering design of an effective and environmentally safe waste Management system for the Bakoteh Dump Site for a period of 3-5 years while the new landfill site at Tambana and the waste management system for the greater Banjul area is developed. The objective also includes the preparation for the ultimate closure of the Bakoteh Dump Site.

1.3 Terms of Reference This study is based on the feasibility study and the framework developed for the effective waste management of the Bakoteh Dump Site Waste Management Study (BDSWMS) by the international consultant Jackson M. Nzainga of October 2002. In order to meet the objectives of the study, the Terms of Reference cover the following:-

• Carry out the preliminary and detailed engineering design studies, including preparation of bidding documents, and the ultimate closure of the Bakoteh Dump Site in 3-5 years.

• Specifically the study will: - • Identify and locate important features of the dump site and locate proposed

facilities through topographic survey. • Identify and prepare comprehensive action plan on safe operations of the landfill

site, including closure and post-closure procedures of the existing landfill site. • Determine by Geo-technical surveys the potential for excavation within the

landfill and the landfill’s potential to provide cover material. • Determine and mitigate (negative) environmental impacts of the existing and

proposed solid waste management system.

1.4 Study Schedule The contract for Consultants’ services was signed on 23rd February 2004 and the total duration of the study is six months. Four kinds of reports are to be prepared and submitted; i.e. Inception report, Interim report, Draft final report and Final report.



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CHAPTER 2 SOLID WASTE MANAGEMENT IN KMC –SITUATION ANALYSIS

2.1 Introduction The efficiency and effectiveness of the collection, transportation, disposal of solid waste in an environmentally sound manner depends on the efficacy of the institutional arrangements, management structures and resources available for waste management. Waste managers are increasingly challenged to come up with integrated waste management plans which deal with waste generated in a holistic manner. In formulating successful and workable plans, procedures and policies, basic information covering the quantity of solid waste generated and the population covered by the collection services is essential. The availability of reliable data on solid waste generation, composition etc is important for the first stage of planning and designing Solid Waste Management (SWM) facilities. The generation of solid waste varies significantly from one household to another within an area and within a municipality. The volume and composition of waste generated by a household further differs even within a household on different days of a week and months of a year. Thus, it is difficult to assess the per capita generation rate of solid waste. On the other hand calculating the accurate generation rate is very important for planning and designing of an effective solid waste collection and disposal system. The three principal urban areas in The Gambia are Banjul City, Kanifing Municipality and Brikama. Presently the solid waste from these areas are disposed of in Mile 2, Bakoteh and Tambana Dump Sites respectively. The local councils in each of these municipalities is responsible for solid waste management in their jurisdiction. The focus of this Study is the Bakoteh Dump Site, which is the official waste disposal facility within Kanifing Municipality. The waste management strategy and engineering design options available for the Bakoteh Dump Site depend on the conditions and characteristics of the site, the volume and composition of waste generated, transported and disposed at the Site. The institutional arrangements for Solid Waste Management at the National and local level are important in these considerations.

2.2 Institutional Framework

2.2.1 International Agreements The Gambia is party to a number of international agreements covering the environment which are meant to promote international cooperation in environmental protection. However for the purpose of this study, reference is made to the following:



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� The Basel Convention for the control of trans-boundary movements and disposal of hazardous waste adopted in 1989 and ratified in 1997 provided obligations to its parties to ensure that waste that is hazardous to people and the environment are managed and disposed of in an environmentally sound manner.

� The United Nations Framework Convention on Climate Change which is designed to

regulate greenhouse gas concentration in the atmosphere in order to avoid the occurrence of climate change to the extent that would impede or compromise initiative in food production.

2.2.2 The National Framework for Solid Waste Management The Banjul Declaration of 1977 is the first policy initiative regarding the management of the environment at the National level and highlighted government’s awareness that action should be taken to prevent further environmental degradation. Later, in 1982 an Environment Unit was created within the Ministry of Natural Resources & Environment, which was followed by the enactment of the National Environmental Management Act (NEMA) in 1987. The Act created the National Environment Management Council (NEMC) but was repealed and replaced by the NEMA 1994 which created the National Environment Agency (NEA). The NEMC and NEA together with the Department of State for Health Services (DOH) are the three most important institutions concerned with the enactment of environment legislation, formulation and implementation of policy, the setting national standards, monitoring compliance with environmental regulations. The functions of each of these institutions in relation to solid waste management have been dealt with in previous studies2.

2.2.3 The Local Government Framework for Solid Waste Management The Kanifing Municipal Council (KMC) was part of the Brikama District Council until 1963 when the Government established the Kanifing Urban District Council (KUDC). In 1990 the KUDC was upgraded to a municipality by the KMC Act 1990. This Act was repealed in April 2002 and replaced by the Local Government Act 2002 (LGA 2002), which establishes and regulates a decentralised local Government system and specifies the functions, powers and duties of established local authorities. The Council is the supreme policy making body of the municipality regarding the duties assigned by the Local Government Act 2002. The KMC has 690 personnel placing it amongst the largest employers within the Municipality. The Cleansing Services Unit with 280 personnel makes for over one-third of the personnel and is responsible for carrying out the Council’s programmes and policies regarding waste management in the Municipality.

2Support for the Bakoteh Dump site Waste Management Study (BDSWMS – 2002)



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While the LGA does not deal with Solid Waste Management specifically, it confers the following responsibilities to the Council:

o Management, protection and conservation of the environment, which includes addressing public concerns on environmental issues and promotion of sanitation practices.

o Establishment, acquisition, erection, maintenance, promotion, with the participation of the citizens, sanitary services for the removal and disposal of night soil, rubbish, carcasses of dead animals and all kinds of refuse and effluent.

o Prohibition, restriction, regulation or licensing the burning of rubbish or the depositing on any street, public place or unoccupied land any refuse, rubbish derelict vehicles, or any other material and to provide for the removal and disposal thereof.

The Act empowers the Council to make By-laws, which may define an offence and prescribe penalties on any of the above. The Local Government Act provides for setting standards and guidelines in liaison with NEA at the national level. The Council, under the LGA has the authority to enter, examine any land or premises within its jurisdiction, for the purpose of carrying out any inspection, inquiry under the act or by-laws of the Council. The Act also confers to the Council authority to arrest without warrant any person it reasonably believes has committed an offence against the provisions of the Act or any order, by law or regulation made under it. Thus KMC has the powers to prevent illegal dumping of solid waste within the municipality.

2.2.4 The Cleansing Services Unit

The functions of the Cleansing Services Unit are to collect, transport and safely dispose of solid waste within the municipality. The Cleansing Services Unit consists of two sections:

• Operations section responsible for collection, transportation and disposal of solid waste.

• Mechanical services section responsible for the maintenance and repair of vehicles and machinery.

The Gambian Agency for the Management Preliminary and Detailed Engineering Designof Public Works (GAMWORKS) Study for Bakoteh Dump Site

Charchi Githinji & Partnersin association withCityscape Associates Final Report

6

Manager1

Assistant Manager1

Principal Supervisor1

Mech Superintendent1

Chief Mechanic1

Mechanic1

Snr Electrician1

Electrician1

Apprentice Mechanic8

Snr Tyre Man1

Tyre Man2

Senior Supervisor1

Field Supervisor28

Head Labourer19

Chief Driver1

Labourers171

Drivers29

Office Cleaners12

Figure 2.1 Cleansing unit organisation chart



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Mayor

Deputy Mayor

Chief Executive Officer

Director of Admin

Adminstration Social Services

Municipal Police Unit Rent Unit Dept of Planning Claensing Services Unit Dept of Finance

AccountingRates Collection

MarketManagement

Refuse CollectionDisposal, Domestic,

Industrial wsate, maintenance of Soakaways

InfrastructureDev Managemnt, Open Spaces, ParksConductPhysical, Social, Economic,

Surveys,Collect Data for municipal, divisions

Prepare local Plans,Diagrams, IInspection, housing control

Fixing Rent, Inspection of PropertiesRegistration, Mediation Court

Execution

Protection of Council PropertiesEnforcement of KMC

RegulationsControl of Stray

AnimalsPrsecute

Mayor

Deputy Mayor

Chief Executive Officer

Director of Admin

Adminstration Social Services

Municipal Police Unit Rent Unit Dept of Planning Claensing Services Unit Dept of Finance

AccountingRates Collection

MarketManagement

Refuse CollectionDisposal, Domestic,

Industrial wsate, maintenance of Soakaways

InfrastructureDev Managemnt, Open Spaces, ParksConductPhysical, Social, Economic,

Surveys,Collect Data for municipal, divisions

Prepare local Plans,Diagrams, IInspection, housing control

Fixing Rent, Inspection of PropertiesRegistration, Mediation Court

Execution

Protection of Council PropertiesEnforcement of KMC

RegulationsControl of Stray

AnimalsPrsecute

Figure 2.2 KMC organisation chart


Charchi Githinji & Partners in association with Cityscape Associates Final Report 8

The principal supervisor is responsible for planning and co-ordinating the collection, transportation and disposal of waste and also scheduling of vehicles and deployment of cleansing personnel. Three senior supervisors assist the principal supervisor. The senior supervisors are responsible for: -

• Collection, transportation and disposal of refuse. • Co-ordinating field operations including the activities at the dump site.

The senior supervisors are assisted by 28 field supervisors who are responsible for monitoring on site activities, collection, transportation and disposal by the labourers. They supervise 190 labourers. There is a records clerk at the Bakoteh Dump Site tasked with keeping record of vehicle number, arrival times, departure times etc. There are labourers at the site detailed to assist direct vehicles at the disposal site. The mechanical superintendent as head of the Maintenance and Repairs Section of the Unit is responsible for ensuring that the vehicle fleet of the municipality are in a good state of repair and are ready and available for use. The efficiency of collection and disposal of solid waste depends on the availability and reliability of its vehicle fleet. According to officials of the council, there are plans to shift the cleansing services unit to the Department of planning which is currently responsible for conducting physical, social and economic survey, in addition to infrastructure development and maintenance. The recurrent expenditure on Environmental and Sanitary Management by the Municipality in 2003 was 16% of total council expenditure and in year 2004 GMD 5,735 Million was budgeted for cleansing services out of a total estimated expenditures of GMD31,729 Million i.e 18% budget allocation. The council plans to purchase some waste management equipment (trailers, tractors etc) on a yearly basis using any surpluses generated from overall income. This implies that council must pursue an aggressive revenue generating strategy whilst keeping tight control on costs. As part of this strategy council acquired one tractor and 4 trailers in year 2003 and there are plans to purchase 1 tractor and 4 trailers before the end of 2004.

2.2.5 Landfill Management Capacity In the event that a sanitary landfill is created out of the Bakoteh Dump Site the cleansing service officials are of the view that there is adequate manpower which can be redeployed to work exclusively at the landfill without adversely affecting the other functions being carried out by the unit. There are cleansing service personnel who have worked with similar equipment that can be trained to operate landfill equipment, supervise the operations and assure the security of facilities. In fact part of the functions of some of the personnel currently assigned to the Bakoteh Dump Site is to ensure the security of the area and direct waste disposal activities. In addition there are trained public health officers (2) within the unit who may be able to provide the necessary supervisory support at the landfill.



In view of the very low vehicle availability ratio (about 45%) and the very high staff/vehicle ratio within the cleansing unit (about 13 personnel/available vehicle) there is good indication that surplus labour is available within the cleansing services unit which can be redeployed to the proposed landfill without adversely affecting the operations of the cleaning unit. This is particularly true for low level non-clerical functions. However it has been noted that the Cleansing Service Unit is not adequately equipped with suitable machinery that can perform the required services at a sanitary landfill without adversely affecting the current performance of the unit in the area of waste collection and transportation.

2.3 Solid Waste Generation and Composition Previous studies3 have established a waste generation rate of 0.54 kg/person/day for the Kanifing Municipality. This value was used in the BDSWMS – 2002 report to calculate the solid waste generated in Kanifing Municipality. No drastic economic changes have taken place to invalidate this value and hence the same is used for solid waste generation projection. The results of the 2003 population census have not been published and hence this study relies on previous population projections. The projected solid waste generation for Kanifing Municipality is shown in Table 2.1.

Table 2.1 Projected Household Waste Generation for Kanifing Municipality

Year Population Generated Waste (Ton/day)

2001 377,693 204 2002 402,243 219 2003 428,389 236 2004 456,234 254 2005 485,890 273 2006 517,472 294 2007 551,108 316 2008 586,930 340 2009 625,081 366 2010 665,711 393

(Source: Support for the Bakoteh Dump Site Waste Management Study - August 2002)

The composition of household waste by weight for Banjul, Kanifing and Brikama is as shown in Table 2.2.

3 Solid Waste Management Study for the GBA and Brikama – April 2002



Table 2.2 Composition of Household Wastes by Weight Material Banjul % Kanifing % Brikama % Sand 48.88 44.18 46.77 Organic 32.44 35.05 37.46 Paper/Carton 9.19 11.42 8.52 Glass 1.48 2.22 - Wood 2.35 0.18 5.37 Metals 1.40 3.11 1.71 Textile 2.25 2.44 0.17 Rubber - 1.40 - Other 2.01 - - (Source: Solid Waste Management Study for GBA and Brikama - Waste Surveys Report April 2002)

2.4 Solid Waste Collection and Transportation The Cleansing Services Unit of the KMC was set-up in 1984 with assistance from the World Bank Urban Management Development Project (UMDP 1984). The unit is responsible for Solid Waste Management in the municipality i.e. the collection, transportation and disposal. Its administration and maintenance workshops are at the KMC Annexe in Kanifing. The KMC provides a daily refuse collection service. The system of collection is both door to door and station type where Skips and Trailers are placed in strategic locations for communal collection. For ease of management the municipality is divided into six collection Zones, which are further subdivided into Blocks. Refuse collection is divided in two shifts, morning shift (8:00a.m - 3:30 p.m.) and afternoon shift (4:00p.m - 12:00 mid night). However, at the time of the study the afternoon shift was temporarily not operational. For door-to-door collections, the onus is on the households to place their refuse along the route of the collection vehicle (usually contained in sacks and buckets). This is in contrast to areas with communal collection points where the residents take their refuse to the collection point (Skip or Trailer). The criteria for adopting either of the two systems is not strictly defined, but in general is guided by the following: -

a) Population density - door-to-door collection is used in relatively less densely populated middle and mostly high income areas while communal collection points are used in the low-income areas and more densely populated areas and where indiscriminate/illegal dumping of refuse is common.

b) Limitations on transport and equipment. c) Accessibility.

The choice of whether a Skip or Trailer (which has a bigger capacity) is used is dependent on the potential volume of waste to be dumped at the particular site.



Table 2.3 Solid Waste Collection zones and blocks Day of Week

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

Collection zone

Serrekunda Kanifing Tallinding Bakau Dippa Kunda

Bundung

Collection

Blocks

Serekunda East

Serrekunda West

Serrekunda Central

New Jeshwang Ibo Town Churcills Town Tallinding Sicap

Kanifing East

Kanifing North

Kanifing West

Old Jeshwang Latrikunda East Latrikunda West

Tallinding East

Tallinding West

Latrikunda Sabiji

Fajikunda

Abuko Extension

Bakau

Cape Point

Fajara East

Fajara west Golf Course

Dippa Kunda East

Dippa Kunda West Dippa kunda central Badarla Section of Bundung East

Bundung

andO

therareas

Setsetalandcom

munity

participation

Source: Adapted and updated from:Support for the Bakoteh Dump Site Waste Management Study, 2002

• Collection and Transportation Equipment Tables 2.4 and 2.5 present an update, from previous studies4, of the collection and transportation equipment available at the municipality and it indicates that only 45% of the vehicle fleet used in the collection and transportation of waste were road worthy at the time of the study. Under these circumstances the choice of using a trailer or skip is guided by availability, volume of refuse generated and the existence of door to door services. Despite the efforts of the KMC and other operators, Solid Waste Management in the Kanifing Municipality is inadequate as visually evidenced by the existence of uncollected refuse at various locations within the municipality and by the state of the Bakoteh Dump Site.

4 Support for the Bakoteh Dump Site Waste Management Study, 2002



Table 2.4 Solid Waste Collection Vehicles for Cleansing Services Unit

No Vehicle No

Truck Description

Capacity Age On the Road

Off the Road

Remarks

1 GG2091 Compactor 15 tons 10 years X 2 KMC13 Pegaso 10 tons 7 years X 3 KMC14 Pegaso 10 tons 7 years X 4 KMC33 Leyland 10 tons 3 years X 5 KMC45 Leyland 5 tons 3 years X Being rehabilitated 6 KMC34 Tractor 5 tons 3 years X 7 KMC35 Tractor 5 tons 3 years X 8 KMC36 Tractor 5 tons 3 years X 9 KMC23 Tractor 5 tons 5 years X 10 KMC15 Tractor 5 tons 7 years X 11 GG2035 Tractor 5 tons 10 years X 12 KMC53 Tractor 5 tons 18 months X 13 KMC54 Tractor 5 tons 18 months X14 GG1901 Bedford 5 tons 11 years X 15 GG1905 Bedford 5 tons 11 years X 16 GG1903 Bedford 5 tons 11 years X 17 GG1930 Bedford 5 tons 11 years X 18 GG1931 Bedford 5 tons 11 years X 19 GG1904 Bedford 15 tons 11 years X 20 KMC55 Compactor 15 tons 15 months X 21 KMC56 Compactor 15 tons 15 months X22 KMC43 Roto Press 15 tons 19 months X 23 KMC11 Roto Press 2 tons 19 months X 24 KMC28 Jolly 3 tons 16 months X 25 GG1469 Nissan Capstan 3 tons 2 years X 26 GG1471 Nissan Capstan 1800litres 14 months X 27 KMC7 Cesspool Emptier 1200litres 15 months X 28 KMC30 Scania Emptier 1000litres 2 years X 29 GG1262 Scania Emptier 2 tons 2 years X 30 KMC46 Skip Trucks 2 tons 2 years X 31 KMC47 Skips Trucks 2 tons 2 years X 32 KMC48 Skip Trucks 2 tons 2 years X Being overhauled 33 KMC49 Skip Trucks 2 tons 2 years X 34 KMC50 Skip Trucks 2 tons 2 years X 35 KMC51 Skip Trucks 2 tons 2 years X 36 KMC52 Skip Trucks 2 tons 2 years X 37 P396 Massy Fergusson

Shovel Loader 11 years X Prone to breakdowns

38 KMC59 Compactor 15 tons 1 year X 39 KMC60 Compactor 15 tons 1year X 40 KMC61 Tipper Truck 10 tons 1 year X Total KMC62 International 7 tons 1year 18 22

Source: Kanifing Municipal Council, Cleansing Services Unit



Table 2.5 Skips and Trailers for Solid Waste Collection

Zone Block Location Skips (Qty)

Trailers (Qty)

Bakau Bakau Bakau Market Saul Samba Dump Neneh Wally Dump Malang Fatty Dump Bakau New Town Market

21111

Bakau Cape Point Cape Point 1 Serrekunda Serrekunda Market Market

Car Park Sandika Market Football Field London Corner Westfield London Corner

1

11111

1Kanifing Kanifing Layout

GTTI Jimpex Road SDA New Jeshwang Old Jeshway Market Methodist academy Old Jeshwang Gardens New Jeshwang

112

11

111

Talinding/Latrikunda Sabiji

Tallinding East Faji Kunda Market Abuko Highway

11

Dippa Kunda/ Latrikunda

Abuko Extension Latrikunda Sabiji Tallinding West Tallinding

Tallinding Police Post Tallinding Market Tallinding Sicap Buffer Zone Latrikunda Sabiji Market Ibo Town Market Border (Ebo Town/Tallinding) Tabokoto Market

1

12

1

11removed temp 1

Dippakunda Latrikunda

Manjai Kunda Bridge Manjai highway Latrikunda Market Kotu Silo Bridge

11

11

Bundung Bundung Charles Jaw School Borehole Market Borehole Footbridge Bundung Bantaba

1

11

1Kotu Gamtel Exchange

Manjai Lodge 1

1Bakotek Bakoteh Annexe

Mosque Layout Tipper Garage

1 111

Total 27 20 Source: Kanifing Municipal Council, Cleansing Services Unit



2.5 Solid Waste Disposal 2.5.1 Bakoteh Dump site 2.5.1.1 General One of the aims of solid waste disposal is to remove solid waste from the urban community immediately and to reduce its volume, making it stable and hygienic. In choosing the process of proper treatment and disposal, not only the geographical area should be considered, but also the financial situation and the level of technology within the organisation responsible for solid waste management. In Kanifing Municipal Area, there is at present only one official landfill site, The Bakoteh Dump Site, located at Bakoteh suburb, some 15 km from Banjul, the capital city of The Gambia. Bakoteh is in the western side of Serrekunda, a town with a catchment of approximately 6 km, under the administration of Kanifing Municipal Council. The main approach to Bakoteh Dump Site is along the Kotu-Manjai Kunda road, off the Serekunda-Sukuta highway and the Senegambia highway. The Dump site is opposite the SOS children’s settlement. The Bakoteh Dump Site is on the site of an old quarry and occupies an area of about 17.8 hectares. The site is not fenced nor is there a clearly defined boundary and can be accessed on foot from all directions. It undulates with mounds and troughs of garbage and because of the uncontrolled nature of dumping at the site, there is an unsightly stretch of garbage across the dump site along the 400 metres or so bordering the SOS highway. The haulage distance to the site is 8 km at most, which contributes to non- economical waste haulage. However, with the steady increase of population and hence demand for land, the dump site is now at the centre of human settlement. Open burning is prevalent and burning and smouldering garbage is a regular feature on the site. Garbage is dumped along the edge of the site and within 6m of the carriageway and a pungent smell engulfs the site and its environs. Management operations at the dump site are minimal. The few KMC personnel stationed at the site try to direct vehicles to “suitable” tipping areas without much success. Waste pickers scour the site for materials of economic or personal value and the returns from the sale of these materials go to the waste pickers. There is no compaction of waste or application of cover material. Indeed there is no equipment on site and the dumping of waste is haphazard. There are dwelling shacks within the site and these are also used as storage areas for scavenged materials.



15

2.5.1.2 Environmental and Socio-economic impacts Delays in waste collection of solid wastes for a long time generates a smelly black liquid called leachate which is considered a high polluter when it reaches water courses due to its high concentration in BOD, COD and chemicals. Burning of waste contributes to air pollution. Indiscriminate dumping of solid waste has a high negative impact on environmental quality. Uncollected garbage also has potential effect on the public health as it allows the reproduction of vectors of diseases such as cockroaches, rats, flies and mosquitoes. On the other hand open dumping as practiced at the Bakoteh dump site poses a risk from a sanitary point of view in that it can affect directly the operators of the site, scavengers and residents living around the site. Such sites normally constitute breeding grounds for different organisms that are carriers of diseases such as malaria, typhoid, dysentery etc. Previous studies5 report grave environmental conditions in and around the dump site. No mitigating measures have been taken and hence the situation continues to deteriorate. The various environmental and socio-economic impacts are as follows:-

• Water in the ponds within the dump site is heavily polluted with Faecal Coliforms (/100ml) >1000, Total Coliforms (/100ml) > 10000, BOD5 mg/l > 4000 and COD mg/l > 6000.

• Offensive odour from the dump site is prevalent and permeated the environment

during the Study period. Residents and gardeners on the dump site also indicated that offensive odour was one of the environmental nuisances they suffer as a result of the nature and location of the dump site.

• The Bakoteh landfill was a quarry, which was converted into an open garbage

dump. The extensive excavations as a result of stone mining left craters within the site, destroying most of the natural flora that might have been present. The craters serve as collection points for rainwater, garbage and its associated run–off with potential to percolate into the water table.

• Parts of the landfill are green with vegetation during the rainy season as a result of

the gardening activities carried out mainly by women. The fertile grounds in parts of the site already ‘leveled’ are attractive for market gardening, although such gardeners are said to be constrained by broken bottles, non-degradable plastic bags and stones.

• Stray dogs and birds were seen searching for food on the site whilst the study was

in progress.

5 Support For The Bakoteh Dump Site Waste Management Study-2002



16

• According to the 1993 population census. There are 5931 inhabitants of whom 48% are female living in the surrounding settlements of Bakoteh, Dippa Kunda and Manjai Kunda.

• Data on the age structure of the households in the area surrounding the dump site

showed that the mean age is 21 years and the modal age lies between 15 and 19 years.

• Unemployment among heads of household is approximately 23 % while 52% are

self employed. Formal employment is only 21 %. • There are a number of houses located on the perimeter of the dump site and some

of them are not fenced or are only partly fenced. The average distance from the dump site of the households interviewed is 68.56 meters.

• On average there are 15 people per compound. Each family has an average of 5

children and 11 dependants.

• According to the survey conducted, respondents identified malaria (88%) as the diseases from which they suffer most frequently. Respiratory infections (27%), cold (4%).

• Approximately 75% of the compounds located on the perimeters of the dump site

have at least a pit latrine in the compound. Flush toilets are mainly found at the Bakoteh Housing estate and the adjacent institutions. Consequently, with the very shallow water table there is potential risk of ground water pollution from the sewage in the pit latrines.

• The risk of pollution is even higher when it is noted that over 40% of compounds

have open wells and over 90 % of these wells are located in the areas with pit latrines.

• Although 58% of households reported that they have only open wells or no source

of water supply, there was reported interdependence between households regarding water supply especially drinking water.

• Some households with wells, which they deem not fit for consumption, result to

using a neighbour’s well, a public standpipe or a neighbour’s household pipe for drinking purposes. Up to 67% of households living mainly in Manjai kunda, use either their own, a neighbour’s or the community well to bath and wash dishes and clothes and a slightly lower percentage use the wells for cooking purposes.

• Many households either bury or burn their garbage in their compounds or dump it

at the adjacent dump site. The Kanifing Municipal Council does not operate any meaningful garbage collection services covering the areas in the immediate



17

surroundings of the dump site. Invariably such garbage is placed on the fringes of the landfill thus aggravating the negative visual and aesthetic impact of the site.

• The pollution factor identified by households as most bothersome is the odour

generated by decaying garbage especially during the rainy season. Nearly 99% of residents indicated that they suffered inconvenience due to the bad odour emanating from the dump site and equally high number (71%) of residents identify bad odour from the landfill as the primary source of nuisance. The stench and other nuisances are worst during the rainy period as the area becomes infested with flies and other crawling insects and birds can be seen hovering and scavenging for food from the decomposing litter.

• Smoke from the burning debris at times covers large areas of the adjacent houses

and portions of the adjoining road causing potential traffic hazards to motorists and pedestrians. Although residents indicated that smoke emissions are frequent, it is notable that such burning is more frequent during the dry season.

• Debris from the site is blown into residences and neighbouring institutions

especially during the dry season. Residents indicate that the strength of the odour, dust particles in the air and smoke emissions depend on the strength and direction of the wind.

• Water samples collected from the shallow wells at twelve family compounds

located around the dump site, at approximately 10, 50 and 100 meters from the periphery of the dump site showed a high level of Faecal and Total Coliforms. 58% of the samples had Faecal Coliforms counts > 100, 93% had Total Coliforms counts >100 per 100 ml. The high coliforms counts in the wells is attributed to: - proximity of the wells to the dump site; poor sanitary condition around the wells; contaminated vessels for drawing water; rubbish entering the wells directly and seepage water from the surface. There was no correlation between the levels of chemical and/or bacteriological contamination with distance from the dump site.

• There were gardeners (growing and harvesting a wide variety of vegetables and

crops e.g. “Kerengkereng”, Okra, Bitter tomatoes, and Rice, for consumption and sale.) and scavengers, interested mainly in Aluminium and metal parts followed by glass bottles, electric wires and plastic bottles. The items collected are primarily for sale mainly at the market but also to the agents operating around the landfill and within Manjai Settlement. However items not sold will be used by the scavengers themselves and or given away. The mean income of scavengers is D300 per month or an annual income of D3,600 per year. The reported average income from gardening is D772 per season.



18

CHAPTER 3 SOLID WASTE MANAGEMENT SYSTEM FOR THE BAKOTEH DUMP SITE

3.1 Introduction Many industrialized countries now face enormous ecological (and economical) problems, because in the past nobody cared about the dangers of solid waste. The consequence: “the throw-away societies” have contaminated large areas by uncontrolled dumping of waste. They now have to pay for their carelessness by expending billions of dollars year by year. For any country, independently from its state of development, it should be a “must” nowadays to avoid these mistakes of the industrialized countries, and to start as soon as possible with a “waste policy” which keeps their environment as clean and healthy as possible. The most effective ways of reducing the dangers of waste are:-

• To avoid waste wherever it is possible. • To establish effective recycling and re-use systems.

Systems have to be developed and people have to understand the nature of their waste. They have to be convinced that a participation in such a system is a public responsibility and duty. The principles and applications for waste reduction (i.e. waste prevention and waste utilisation) have been presented in earlier study reports6.

Nevertheless, after all the measures of waste prevention and utilisation are carried out there still will be amounts of waste that will require final disposal. A well known and a possible method of waste treatment, reducing the amount of materials which finally will have to be disposed of to a minimum is incineration. But for most developing countries and especially for countries with a tropical climate waste incinerators may be inappropriate because of the composition of the waste (high humidity and low calorific value), the high costs and the technical difficulties of operation (problems of insufficient filter technology, air pollution). However, incineration could be an appropriate method for pathogenic hospital wastes. The actual consequence of the above-mentioned situation will be that in most of these countries the method of final waste disposal normally has to be by landfill.

6 Gambia Solid Waste Management Strategy report, Support For The Bakoteh Dump Site Waste Management Study- 2002, The Solid Waste Management Study for The Greater Banjul Area and Brikama-2001



19

But as it can be seen in most industrialized as well as in many developing countries, uncontrolled open dumping of waste has produced and is still producing great hazards for the environment. Landfills are a vital component of any well-designed solid waste management system. They are the ultimate repository of municipalities solid waste after all other municipal solid waste management options have been exercised and most times are the only option available after the municipal solid waste is collected. Landfills range in type from uncontrolled open dumps to secure sanitary landfills. Generally there are three landfill categories:- • Open dumps • Controlled dumps • Sanitary landfills A number of general characteristics distinguish a sanitary landfill from an open dump, but these characteristics vary from region to region, from nation to nation, and even from site to site. An operated dump may inspect and record incoming waste and include limited compaction by bulldozer and compactor. Engineered landfills embody further attempts to minimize environmental impacts. Sanitary landfills incorporate a full set of measures to control gas and collect and treat leachate, apply a daily soil cover on waste, and implement plans for closure and aftercare long after waste has ceased coming to the site. These three types of landfills are points on a continuum, with facilities in most developing economies often falling somewhere between open dumps and controlled dumps. Open dumps have the lowest initial capital investment and operating cost of the three types of landfills but cause environmental pollution and can potentially affect the health of local residents. Additionally, many open dumps start off as controlled dumps and degrade due to lack of management and other resources. In these cases, the resources expended on a controlled dump have resulted only in an open dump. 3.2 Solid Waste Amount According to the BDSWMS- 2002 report the average amount of solid waste carried by collection vehicles to the Bakoteh Dump Site was 143 tons per day. The report showed that 92 tons were carried daily by KMC while the remaining 36 % i.e. 51 tons of waste was collected by other collectors. Out of the 219 tons/day of solid waste generated (2002) at KMC, The 143 tons/day to the Bakoteh dump site represented 65% collection ratio. However based on the 92 tons per day by KMC, the collection by KMC was only 42%.



20

From the present collection capacity of KMC and the general observation of the state of solid waste management within Kanifing, there is no indication of increased collection efficiency. With the 65% collection ratio, the amount of waste projected to be received at the dump site up to 2007 is as shown in Table 3.1. Table 3.1 The Amount of Waste Expected at the Dump Site

Generated Waste Waste to be disposed (100%)

Waste to be disposed (65%)

Year

(Ton/day) (Ton/day) (Ton/day)

2004 254 254 165 2005 273 273 177 2006 294 294 191 2007 316 316 205

Adapted from: Support For The Bakoteh Dump Site Waste Management Study- 2002

From the above figures and assuming a unit weight of waste of 1.0, the capacity requirements of the disposal site for both 65% and 100% collection efficiency is shown in columns 4 and 5 respectively in Table 3.2.

Table 3.2 Capacity requirements of the disposal Site Year (1) Landfill

Waste (2) Landfill Waste

(3) Landfill Waste

(4) Total Waste

(5) Total Waste

Amount Amount Amount Amount Amount (t/d) (m3/d) (m3/year) (m3) (m3)

Col (1)/1.0 Col (2) x 365 (100%) (65%)

20047 254 254 92,710 46,355 30,131

2005 273 273 99,645 146,000 94,900

2006 294 294 107,310 253,310 164,652

2007 316 316 115,340 368,650 239,623 Adapted from: Support For The Bakoteh Dump Site Waste Management Study-2002

7 Waste amount values are for the remaining six months of 2004 (i.e. 50%)



21

3.3 Dump site topography

3.3.1 Topographic Surveys The objective of the survey was to establish survey control points, define the extent and boundaries of the Bakoteh dump site, fix beacons at the perimeter of the site and produce contoured map to facilitate identification of landfill area and calculation of volume of dumped solid waste and landfill capacity. The topographic survey was carried in line with the zoning in Figure 3.1, identified in the BDSWMS report.

(Source: Support for the Bakoteh Dump Site Waste Management Study - August 2002)

Figure 3.1 Bakoteh Dump Site zoning

Permanent boundary beacons were constructed at all the turning points of the site, at positions indicated to the survey team by KMC as being the boundary line of the Dump Site. Beacons were constructed and inscribed with reference numbers at the turning points of the boundary of the site. The beacons were constructed of concrete and a centrally positioned 16mm diameter iron rod with a centring mark. These reference points will be used for setting out during the construction phase. The location of the survey control points and other features are shown in Volume 2 Drawings.



22

3.3.2 Geo-technical and Hydro-geological considerations The following observations are made from the geological investigations conducted during the BDSWMS and trial pits dug during this study:-

• The surface geology of the site can be described as a poorly consolidated fine grained silty clay layer with very little sand content, embedded with few laterite pebbles, which could be a derived product of the underlying laterite zone. Organic matter is present in the material due to the vegetation cover.

• The surficial material deposit has an approximate thickness of 3.5 metres. It lies

conformably on an underlying laterite zone. Hard ferruginous quartz sandstone occurs at the base of this stratum in the form of large aggregates or boulders approximately 45 – 50cm thick. It overlies a sandy clay layer, which becomes less sandy and more plastic downwards.

• The water level in the pond located in the eastern end of the dump site (zone 1)

represents the water table. The water table is at an average depth of 1.4m in the area around the ponds. The water table at other areas of zone 1 is 2.1 m on average as evidenced by the two trial pits. The water table in zone 3 is at an average depth of 3.3 m.

• There is no water flowing from the adjacent areas into the dump site. The drainage in the surrounding areas follows the roads leading parallel to the dump site from West to East into the Kotu stream and these do not lead to the dump site. These roads are drained at various points and therefore flooding as a result of runoff from the surrounding area is unlikely. The hydrologic conductivity of the area is from West to East towards the Kotu waterway.

• The results of the soil investigations are presented in Annexe 2

3.3.3 Landfill Area within Bakoteh Dump Site Previous studies8 have disqualified Bakoteh Dump Site as a landfill site. The site failed the landfill selection criteria on account of the following:

• Depth to ground water table is less than 10m • Proximity to surface water is less than 1 km • There are visible visual impacts • Down wind impacts are within 1.6 km

8 The Solid Waste Management Study for The Greater Banjul Area and Brikama-2001



23

• Population proximity is within 1.6 km

The prevailing conditions for the Bakoteh dump site are grave compared to the above international guidelines.

• Depth to ground water table in Zone 1 is 1.4 – 2.1 m while in zone 3 is about 3.0 m.

• Residential houses, institutions and a hospital surround the dump site and some

house are within 5m of the active dumping area. The above two factors form strong exclusion criteria and hence the Bakoteh dump site cannot be considered as a landfill site. The preferred and recommended option is to close the dump site immediately and try to mitigate the negative environmental impacts already caused.

A new landfill site has been identified9 in Tambana but construction work has not commenced. The existing dump site has to be used for some time before the new landfill site is developed. The second option therefore would be to allow controlled disposal of waste until the required level of land reclamation is reached while mitigating existing and new environmental negative impacts. The identification of a landfill area within the existing dump site is therefore a stopgap measure and inevitably the standards will not match those attainable at a new site. Indeed compromises must be made but at the same time be well understood. Landfilling solid waste at the Bakoteh dump site has already caused negative impacts as outlined in Section 2.4.1.2, hence identification of landfill area at the dump site is aimed at reducing the negative impacts. Identification of the landfill area within Bakoteh considers the following factors:

• Environmental conservation • Construction cost • Landfill capacity

The three zones (Figure 3.1) identified in the BDSWMS 2002 report are; an active dumping area in the middle (zone 3), a reclaimed area (zone 2) to the west and adjacent to the road, and a disused quarry with a cluster of trees, and a pond area with tall grass to the East (zone 1). Though the demarcation of the zones is clearly identifiable, the dumping activities described in the BDSWMS report have changed significantly. It is worth noting that the

9 Solid Waste Management Study for GBA and Brikama



24

BDSWMS was conducted during the wet season when gardening was widespread at the dump site and burning of waste was minimal as opposed to now when gardening is virtually non-existent and the whole dump site is characterised by smouldering waste. The current status of the zones is as follows: - Zone 1

The semi-motor-able track previously connecting the Serrekunda main road to Manjai Kunda is no longer in use as garbage has extended from both sides blocking any access to the dump site. Whilst there was no dumping in this zone before, there is now dumping of waste from the Serrekunda side threatening to cover the ponds within the zone. The presence of water in the ponds (in the dry season) validates conclusions in the BDSWMS report of high water table. The trial pits dug in this zone indicate water table is within 2 m. Residential houses are within 5 m of the edge of the zone. Presence of vegetation and water ponds in the zone makes it suitable for reclamation. This zone is therefore not considered suitable for further waste disposal due to the potential of direct ground water pollution and its proximity to human settlement. Most of the side slopes in this zone are unstable. Zone 2

The BDSWMS reported this zone to be already filled with solid waste, levelled and being used for gardening by the local residents. Currently no gardening is going on and the whole zone is covered with smouldering garbage rising above the existing ground level. Zone 3

The dumping of waste in the periphery has blocked access to this zone thus leaving the status earlier reported unchanged. This zone forms the middle of the dump site, is part of the disused quarry and forms the larger part of the dump site area. There have been attempts by KMC to use this area as the disposal area but due to poor access and lack of site management most of the accesses are blocked by solid waste leaving the waste scattered at the periphery of the zone. Within the zone are mounds of unexcavated soil material. The topographical survey carried out identified the following: -

• The volume of waste dumped outside zone 3 that would require proper landfilling. • The area of each of the zones.

• The nominal (gross)10 volume of zone 3. • The volume of potental cover material available in zone 3 and elsewhere within

the dumpsite.

10 This capacity is not equal to volume of solid waste that can be placed which is calculated in Chapter 5.



25

In estimating the nominal landfill volume of zone 3 the following assumptions, consistent with landfill design guidelines, were made: -

• A base slope of 0.5% and 0.7% (towards zone 1) fixed on an established elevation 9.987 m (from trial pit results) in the centre of zone 3.

• A final layer slope of 1% and 2% (from zone 2 towards zone 1) fixed on an

established natural ground level 17.068 m in zone 2.

The results of the topographical survey are shown in Tables 3.3 – 3.5.

Table 3.3 Area occupied by Bakoteh Dump Site

Table 3.4 Nominal volume of zone 3

Nominal volume of zone 3

(m3)0.7%/2% (base /final

cover slope) 126,300

0.5%/2% (base /final cover slope)

138,652


289,485


289,828

Table 3.5 Volume of cover material on site and waste outside zone 3

Estimated volume of waste outside zone 3

(m3)

Volume of potential cover material on site

(m3)105,000 39,029

Zone surface area (Hectares)

Zone Area 1 3.79072 7.70113 6.8623

Road 0.2007 Total area 18.5548



26

3.4 Sanitary landfill 3.4.1 Levels of operation A landfill performs two functions: treatment function by which waste is decomposed and stabilised through natural process, and storage function (storing waste). In the broader context, the functions of a sanitary landfill may be listed as follows:

• Storage of waste in hygienic condition

• Environment pollution control

• Facilitate stabilisation of waste To facilitate the above functions fully, the facilities shown in Table 3.6 are necessary. Monitoring of the volume of generated solid waste amount, waste composition, leachate quality, underground water quality of surrounding area of landfill site should be properly carried out. Daily cover soil is necessary to prevent generation of foul odour, scattering and flies. Training the landfill operators is important for proper landfill operation.



27

Table 3.6 Components of a Sanitary Landfill Component Function Access road a. Connect the site with the existing public road

b. Constructed as an essential component of the landfill site

Enclosure Dike a. Prevent dispersion of solid waste b. Prevent influx of rain water from outside c. Limit the range of dumping area d. Placed along the boundary of the site

Divider Dike a. Placed on the boundary of the partition to separate hospital waste from general solid waste

Landfill Area a. Retain sufficient volume of waste to be landfilled

b. The place were waste is placed c. Installed with on-site road, underdrain for

leachate and gas exhaust equipment according to the progress of the landfill operation

Liner Facility a. Prevent or reduce contamination of surface and ground water by leachate.

Rainwater drainage a. Consists of collection facility and discharge facility

Onsite Road a. Connect the landfill area with the access road Monitoring Facility a. Consists of wells

b. Monitor ground water for checking fugitive leachate.

Net Fence and Gate a. Placed along the boundary of the site b. Separate the site from the outside c. Prevent intruding outsiders

Administrative Facility a. Consists of control office, rest house, truck scale, car washing pool, garage parking lot

b. Occupation by the necessary operation staff c. Limit the landfill activity within the site

Leachate Collection and Drain a. Collect rainwater (leachate) through the solid waste pile

b. Supply air to into the solid waste layer to facilitate aerobic decomposition which shorten the time required to stabilize the solid waste

Retention pond a. Adjust the flow rate of collected leachate to keep the necessary retention time in treatment facility

Leachate treatment facility a. Consists of Anaerobic pond, Facultative pond and Maturation pond

b. Treat leachate by biological process and discharge

Gas Exhaust Equipment a. Made of porous material to facilitate the penetration of gaseous substances

b. Installed vertically through the solid waste layer and cover soil and connected with the underdrain

c. Discharges gaseous substance generated in the solid waste layer

d. Supply air into the solid waste layer to facilitate aerobic decomposition



28

The level of operation of a sanitary landfill system can be classified into four levels each of which achieves a different sanitary level and hence different environmental impacts control. The four levels are shown in Table 3.7.

Table 3.7 Classification of sanitary level of landfill system Level Category Achievement Level 1 Controlled Tipping • Establishment of access to site.

• Establishment of site boundary. • Introduction of inspection, control and

operational records of incoming waste. • Introduction of amenities for the staff such as

sanitary facilities and locker room. • Environmental protection measures are not

established. Level 2 Cover soil • Application of daily cover to disposed of

waste. • Establishment of drainage system to divert

storm water from surrounding areas and hence reduce leachate production.

• Establishment of site boundary to distinguish the disposal site and control scavenging.

• Efficient control of landfill operations. • Reduced impacts from landfill operations.

Level 3 Control of Leachate effluent

• Establishment of leachate control by the installation of effluent collection, storage and monitoring facilities.

• Installation of gas removal facilities. Level 4 Leachate treatment

System. • Establishment of treatment by the installation

of waste stabilization system etc. • Establishment of seepage control.

The sanitary level achieved depends on the suitability of the site, the level of investment and management of the landfill. Competent, safe operation is what distinguishes a landfill facility from a dumpsite. Indeed careful operation can make up for some deficiencies in siting or design. Conversely, careless site management can turn even the best designed facility into an environmental disaster. The current open dumping practice at Bakoteh is below level 1 of the above classification.



29

3.4.2 Method of Landfilling The area identified for the landfill (zone 3) was a quarry area and hence the topography is suitable for Cell Method operation and uphill method for bedding and compaction. This method is illustrated in Figures 3.2 and 3.3.

Figure 3.2 Landfill Method



30

Figure 3.3 Landfill Process by Cell Method



31

3.5 Recommendations The existing landfill system is an open dump site with very ineffective controls resulting to the existing unhygienic scenario. The landfill method to be used should mitigate the existing negative impacts while considering environmental conservation, construction costs, landfill capacity and future land use. The design of the major facilities therefore should consider the following concepts: - • Prevent dispersion of solid wastes. • Prevent or reduce contamination of public water and underground water by

leachate. Treat leachate produced. • Separate hazardous waste from general solid waste.

• Utilize excavated soil.

• Reduce the leachate by diverting surface runoff.

The recommended approach requires progressively instituting control measures to attain controlled landfill operations with proper recording of delivered waste, limiting access into the landfill, organized tipping operations, daily waste cover and monitoring the environmental effects of waste disposal.



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CHAPTER 4 ENVIRONMENTAL IMPACT ASSESSMENT

4.1 General The objective of final disposal of solid waste is to ensure that it is stabilized and rendered hygienic to prevent secondary pollution. This objective is defeated by the current disposal method adopted which may cause environmental pollution and can potentially affect the health of the local residents living near the disposal site and the community. The Bakoteh dump site has a symbiotic relationship with the surrounding community as it affects and is affected by their actions and activities. Any intervention on the Bakoteh dump site is likely to generate some environmental impacts and it is therefore necessary that society is not left worse off by the actions taken to remedy the situation. Consequently an assessment was made of the impact of the current conditions of the dump site on the environment, the impact of the recommended intervention and potential impacts of the construction activities during the implementation phase of the project. In addition the potential impact of the pre and post closure stages of the proposed landfill are assessed. The purpose of this assessment is to mitigate any adverse impacts identified and provide an Environmental Monitoring Plan. 4.2 Objectives of Impact Assessment. The following are the main objectives of the Environmental Impact Assessment undertaken as part of this study:

i. To ensure that environmental considerations are explicitly addressed and incorporated into the development of the recommended interventions for the dump site.

ii. To anticipate and avoid, minimize or offset the adverse significant biophysical, social and relevant effects of the developments proposed.

iii. To protect the productivity and capacity of natural systems within the dump site and the ecological processes that maintain their functions and

iv. To promote development that is sustainable and optimize resource use and management opportunities.

4.3 Method of Impact Assessment The Environment Impact Assessment (EIA) of the proposed intervention was conducted based on the EIA Guidelines, 1999 of the National Environment Agency.



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The EIA of this study must be seen as a continuation of some of the areas already covered in the preceding chapters where some of the requirements of the guidelines regarding the nature, physical characteristics and purpose of the proposed project have been dealt with.

In this study, every stage of the intervention is identified and the impact of the recommended action on the socio-economic and environmental situation both on and offsite the proposed landfill is assessed. For every intervention recommended by the study, the transmission media is noted, the impact on the environment is evaluated, the exposure route and primary receptors of the impact are identified and significance of the impact evaluated on an ordinal scale. These considerations together with the results of the assessment are presented in Table 4.2.

4.4 Identification and description of impacts

4.4.1 Impact of Landfill Location A site investigation11 on the location of Bakoteh Dump Site found that it does not fulfil the standards required for locating a landfill. Despite the failure of the landfill to meet both local and international siting criteria it is not feasible to close the site as should have been the case because a suitable alternative site is yet to be developed. Tambana near Brikama has been identified as a possible landfill site for the waste collected in the Greater Banjul Area and Brikama. As a result Bakoteh will continue to be used as an area for dumping waste in the near future whilst arrangements are being made for an alternative site. The decision to continue with the disposal of waste at the Bakoteh landfill has the negative impact of contravening established national and international environmental standards. This situation is not desirable since The Gambia is party to a number of international conventions and agreements and the continued use of Bakoteh as a dump site does not reflect well on the countries commitment to environmental protection. This negative impact of the dumpsite on the country’s environmental image will continue during the construction phase and will improve during the operation phase. It is expected that the impact will cease at the closure and post closure phases of the project. Consequently, there is need to minimize the period that the site will be used as an active dumping area and the proposed intervention of relocating the existing waste will effectively reduce the lifespan of the landfill Given the volume of waste on the site and the available capacity, a good percentage of the available waste capacity will be filled at the commencement of the project by

11 Solid Waste Management Study of Greater Banjul Area & Brikama, 2002



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removing waste inappropriately dumped and placing it in the identified landfill area (zone 3). This will be one of the mitigating measures that should be undertaken in the early part of the construction phase. It is anticipated that an alternative landfill area will be prepared in the intervening period and waste disposal at Bakoteh will cease within the shortest possible time.

4.4.2 Impact on Land Use The proposed interventions will change the topography of the area from an undulating field with mounds and deep craters to a smooth landscape green with vegetation. The intension is to reduce soil erosion due to rain action on exposed and unstable surfaces, land slipping due to poor embankment grading by compaction and reclamation of the identified land area. It is further proposed that a chain link fence be constructed around the dump site and a single access be provided for vehicles and pedestrians as indicated on the site layout. It is further proposed that active waste disposal be localized in Zone 3. When completed, these interventions will improve the aesthetic quality of the area and reduce the negative impact that the location of the open dump currently has on property values in the surrounding areas. Moreover, the site will be fully prepared for alternative land use which will not contravene international and national regulations covering the environment. This is because of the following reasons:

� The construction of a chain link fence, vegetative hedges and the restriction of access to a single gate near the proposed administrative building will form an integral part of the site management control system and prevent uncontrolled, indiscriminate and illegal dumping of waste around the periphery of the site.

� The fence will prevent uncontrolled access to children and intruders, stray dogs

and domestic animals feeding on waste which may be hazardous to themselves and human beings. Human contact with waste disposed will be reduced whilst a short route is provided for pedestrians wishing to access Manjia Kunda from Bakoteh without using the detour around the site.

� Open burning of waste will be prevented, the aesthetic quality of the area improved and the garbage disposed will be shielded from public view

� It will then be possible to prevent gardening at the site and eliminate the danger of

contaminated vegetables and edible shrubs from the site entering the food chain and posing a risk to human health. Vegetable gardening takes place during the rainy season and vegetable farmers have indicated that they will willingly resort to other alternative sources of income once the site is no longer available for gardening.



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� On the other hand, registered scavengers will be given access to the site in an organized manner through the gate and their activities subjected to supervision at an area designated for sorting waste and a shed reserved for processing re-usable and recyclable items. The supervision of scavengers will ensure that hazardous waste and non-usable waste is not permitted to re-enter the community.

� By constructing a physical boundary around the area it will be possible to prevent

human settlement and encroachment to the site and minimize potential problems regarding title and ownership of the area in future.

These positive impacts will be felt at start of the operations phase of the land fill and will continue to be realized after closure of the site to active dumping. In fact the fence will serve as an effective enforcement of the post closure programme. During the construction of the fence, administrative building and other facilities, beach sand will have to be extracted from one of the areas authorized for commercial sand mining. Special attention should be paid to prevent using sand which is obtained from illegal sand mining in coastal or beach areas which have already benefited from the Coastal Protection Program or which are not available for that purpose. The beach sand, construction material and equipment can be easily stored within zone 1 where a construction depot can be easily located when it has been reclaimed and levelled. This will mean that there shall not be any displacement of property resulting from the construction activities.

4.4.3 Visual Impacts The dump site is located in an area which is densely populated and is visible to residents, passers-by and motorists. It is on the highway leading to the Tourism Development Area and forms and unsightly spectacle of strewn garbage as a result of indiscriminate and uncontrolled dumping of waste. Bakoteh Dump site has a negative visible impact on residents and tourists visiting The Gambia. It is proposed that during the operation phase, unsightly garbage at the periphery of the landfill be place within the activity disposal area, the waste be compacted and covered and a fence and vegetative hedge be planted around the site. These interventions will reduce the risk of litter especially synthetic garbage bags being blown towards the fence, roads and residences and therefore provide a more positive visual impact of the site. The environmentally friendly vegetative hedges will be visually pleasant and once the vegetation has blossomed the landfill will cease giving the country a poor health and environmental image. In addition, the planting of some vegetation in zone 3 which is presently excavated and undulated will further improve the positive visual impacts of the site.



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These positive impacts will be felt during the operations, closure and post closure phases of the landfill. Another source of negative visual impacts is the smoke from burning debris which at times covers parts of the residential areas and the main road linking Serrekunda to the Tourism Development Area significantly reducing the visibility of motorists and pedestrian. The interventions proposed will ensure that no fires are deliberately started at the landfill and in the event of accidental fires action will be quickly taken by landfill staff to put out such fires. After closure of the site, the placement of exhaust vents will reduce the risks of fire outbreaks. This will prevent smoke emanating from the dump site and hence reduce the risk of road accidents arising from poor road visibility.

4.4.4 Impact on Air Quality At present easy and uncontrolled access makes the Bakoteh Dump Site amenable to uncontrolled dumping and indiscriminate burning of waste. The waste is not covered nor is it compacted leaving the stench of decaying garbage in the atmosphere around the site. Due to its proximity to residential areas, residents and passers-by are affected by down wind impact of smoke from burning debris and stench of decomposing waste. In an earlier survey12 residents indicated that the stench from decaying garbage was the most bothersome problem emanating from the presence of the site within their vicinity and respiratory infections were identified as the second most common disease affecting residents. Under the existing conditions open burning of unsorted waste is common during the dry season and during summer the stench of decomposing garbage fills the surrounding atmosphere. Birds, cattle and wild dogs can be seen hovering around the site in search of food.

The problem of indiscriminate open burning of waste will be minimized by daily covering of waste that is disposed of at the landfill as recommended by the study. The impact of poor odour will continue to be felt during the construction phase and is expected to subside during the operations phase. This is because during the operations phase, the covering of waste may not be immediate and in between the period that the waste is disposed and covered bad odour may be felt by workers, near-by residents and passers-by. When the site is being closed and after closure it is expected that the poor odour emanating from the site will cease completely.

12 Jackson Nzainga et al, Support for the Bakoteh Dump Site Waste Management Study, 2002



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The construction of the proposed enclosure dyke and access road, excavation and shifting the waste into zone 3 and building an administrative block will generate dust in the air which will impact negatively on the quality of air within the area. Inhaling contaminated air can be inconvenient and lead to respiratory infections on humans and animals. Watering construction areas will mitigate wind blown dust from the construction activities being inhaled by landfill workers, pedestrians and neighbouring residents. In this regard the mitigation measures highlighted in Table 4.2 are very important.

4.4.5 Impact on Flora and Fauna At present, although green vegetation can be seen in parts of the dump site during the rainy season and some trees are located in the ‘reclaimed” parts of the site, most of the vegetation is destroyed during the dry season as a result of indiscriminate dumping of waste. The trees are in danger of being uprooted because of the erosion of the surrounding soil. The natural pond (in Zone 1) harbouring some wild life like frogs and tadpoles is heavily polluted due to its proximity to the active dumping area. The fauna of the area will be enhanced by planting vegetative hedges and the area within the landfill that is reclaimed will be used to create flora for a park. Also the area used for gardening during the summer months will instead be used for the regeneration of flora to improve the natural vegetation within the landfill and enhance its aesthetic quality. Backfilling, compaction and preparation of the landfill will minimize the extensive soil erosion at the site. The provision of soil cover will discourage the hovering of birds, dogs and other rodents in search of food, which might be contaminated and harmful to them. The treatment of the natural pond, the prevention of water bodies developing in some other areas of the landfill will eliminate potential breeding grounds for mosquitoes and other crawling insects which can spread diseases. These impacts will be felt primarily during the operation phase of the landfill into the closure and post closure phases. However during the construction phase care should be taken to prevent destroying flora and fauna by the use of heavy equipment for excavation and compacting.

4.4.6 Impacts on water resources • Impact on Surface Water The Kanifing Municipality has no major surface water bodies running across the municipality. However, to the south of the dump site adjacent to the Bakoteh Filling



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Station runs the Kotu Stream which derives its sources from Nema Kunku and opens up into the Atlantic Ocean. Run off from the dump site with contaminants dissolved or suspended in the water enter Kotu stream with the potential to negatively impact on people coming into contact with the stream. The construction of drainage facilities will channel run-off rain water into a designated treatment facility to decontaminate and render the polluted water safe for other purposes. The natural pond is found to be heavily polluted and the results of the survey conducted by Nzainga et al, 2002 is reproduced below. Table 4.1 Water Sampling Results of the Dump site Pond

Parameters Unit Max Limit Measured AmountChemical Oxygen Demand (COD) mg/l 10 6000 Biochemical Oxygen Demand (BOD) mg/l 5 4000 Total Coliform per 100 ml 1-10 1000 Faecal Coliform per 100 ml 0 1000

Source: The Gambia Environmental Quality monitoring and Enforcement, May 1997 & Support for the Bakoteh Dump site Waste Management Study, 2002.

The above table indicates that the results of the analysis of water from the natural pond compares unfavourably with the pollution standards set in The Gambia Environmental Quality monitoring and Enforcement Report, 1997.

The water is not suitable for human consumption and therefore any use or contact with people can be potentially harmful and not desirable. Voluntary human contact with the pond was noted and intruders use it for washing clothes that are then left to dry on the grounds of the site. The chances that such persons will be contaminated through dermal absorption are quite high and the consequent potential impact on their health is apparent. Within the context of the intervention designed for a sanitary landfill, the pond will be treated to render it safe. In addition the restriction of garbage disposal activity to the identified active landfill area, the laying of liners, the construction of drains to direct run-off to the water treatment facility will prevent further contamination of the natural pond and encourage the development of wild life. • Impact on Groundwater

o Quality It is generally known that leachate generated within the landfill is emitted to soil and water and the quantity generated depends on the net precipitation, the type and frequency of landfill cover that is applied etc. Leachate typically contains concentration of organic carbons, ammonia, chloride, potassium and hydrogen carbonate. Once released into the



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soil, contaminants can enter the ground water and or surface water where it can affect human health. The groundwater table at the bottom of the quarry is less than 2 meters in some places and an all season natural pond is found in zone 1. About 40% of the compounds surrounding the dump site have open wells which are reportedly used for bathing, washing clothes and dishes. There is high level of Faecal and Total Coliform contamination from some wells located in the surroundings of the site which are attributable to closeness of the wells to the dump site, unhygienic conditions around the well, contaminated buckets and waste entering the wells. The high level of bacteriological contamination means that the water should not be used even for washing utensils or bathing.13

Although no direct link could be established between the quality of ground water and the distance between the ground water source and the dump site, there is very high indication that the presence of the waste disposal facility impacts on the quality of water found in some of the wells within the vicinity. The proposal to use liners or clay material on the landfill before tipping, spreading, compaction and applying daily cover will minimize contamination of the groundwater arising from leaching by compression and percolation. In the event clay is used, it may have to be extracted from one of the clay mining sites within the western division. There are mining sites at Mandina ba which is 37 Kilometres from Bakoteh, Kuloro and Faraba Bantantag which are 34 and 45 Kilometres from the sites respectively. However, there may be negative impacts on the ecology of the clay mining areas identified that must be adequately mitigated in the event the option to use clay as cover material is adopted. The preparation and construction of a buffer between the active landfill area and the existing wells is expected to reduce the pollution of the groundwater through dispersion and dilution of potential contaminants. Moreover, the construction of rainwater collection and the leachate treatment facilities using biological processes and discharge will reduce the impact of laechate on the groundwater. The retention pond will regulate the flow of collected leachate and maintain the necessary time in the treatment facility. Monitoring wells will check for the impact of fugitive leachate on the groundwater and serve as an indicator of the effectiveness of interventions in controlling groundwater contamination. This will ensure that additional preventive or corrective measures are taken during all the phases of the proposed intervention.

13 Jackson Nzainga et al. Support for the Bakoteh Dumpsite Waste Management Study, 2002



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However, there may be negative impacts on the ecology of the clay mining areas during the construction and operations of the landfill that must be adequately mitigated in the event the option to use clay as cover material is adopted. The preparation and construction of a buffer between the active landfill area and the existing wells is expected to reduce the pollution of the groundwater through dispersion and dilution of potential contaminants after the construction phase. Moreover, the construction of rainwater collection and the leachate treatment facilities using biological processes and discharge will reduce the impact of laechate on the groundwater. The retention pond will regulate the flow of collected leachate and maintain the necessary time in the treatment facility. Monitoring wells will check for the impact of fugitive leachate on the groundwater and serve as an indicator of the effectiveness of interventions in controlling groundwater contamination. This will ensure that additional preventive or corrective measures are taken during all the operations, closure and post closure phases of the proposed intervention.

o Quantity - supply On the other hand, water will be needed in large quantities during the construction implementation and post closure phases of the project. Large amounts of ground water resources will be required to compact the area, water the vegetation and flowers, service the utility facilities provided for the landfill workers. This will place an additional strain on an already strenuous situation regarding availability of pipe borne clean water within the municipality. The extensive use of pipe borne water for gardening purposes may reduce the water pressure to the surrounding community during the peak demand times. In the event the community is deprived of pipe borne water at crucial times they may resort to using polluted well water for domestic purposes. This potential impact is particularly important since it can continue indefinitely into the post closure phase of the project and become a persistent community problem with no immediate sustainable solution in sight. In this regard alternative water sources should be envisaged to mitigate the impact on the available water resources of the municipality or the community surrounding the site. One possible alternative intervention is to sink a borehole within zone 2 to avail the site of constant water supply primarily for irrigating the flora envisaged for the area. This mitigating measure highlighted in Table 4.2 will reduce the impact of the construction and operating activity on the availability of clean water to the community. It will minimize the potential post closure impact of the project



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However, the initial capital cost of this alternative may be prohibitive within the budget provided for the proposed intervention. Moreover, there is no guarantee that the water from such a borehole will be safe for utility purposes.

4.4.7 Impact on Human Beings and the Human-made Environment. At present the site is a breeding ground for mosquitoes, rodents, rats and other types of wild life and domestic animals like cattle, goats, sheep, chicken can be seen feeding on the food found at the site. In addition to the risks posed by food grown at the site these activities raise the possibility of contaminated foodstuff entering the human food chain. The interventions identified will prevent gardening and domestic animals feeding on the site and minimize the impact on public health as soon as all construction work is completed and land operations commences. These positive impacts will be felt at the closure and post closure stages assuming that all the measures recommend are fully adopted. The proposed intervention will impact positively on the health and safety of the community within the vicinity of the dump site and those who will be working in the area once the operation of the land fill commences. It is expected that after closure the mitigation measures recommended in Table 4.2 will be adopted to prevent any post closure negative health impacts. The fencing of the site and provision of cover on a daily basis will all go towards improving community health once construction is completed and operations are undertaken. . It is anticipated that the potential for surface and groundwater pollution will be reduced, and the population of flies and other crawling insects within the surroundings of the site will also reduce. In the event these developments are realized there will be a positive impacts on the risks and incidence of rashes, dysentery and diarrhoea. When waste is burnt, harmful chemicals such as Carbon Monoxide (CO) Carbon Dioxide (CO2), Nitrogen Oxide (NO) and Sulfur Oxides (SOx) are produced and these chemicals are toxic to people, animals and plants. The chemicals may react to form ozone, which contributes to smog, haze and reduced visibility. In addition pollutants released from open burning of waste are transported through the air and deposited on the land or water bodies. In case of Bakoteh Dumpsite the relevant water body is the Kotu Stream. Some of these pollutants like dioxins and furans persist for long period and may bio-accumulate. These Persistent Organic Pollutants are associated with cancers, reproductive failures, immune system weaknesses among people and wild life. By preventing open burning of waste, the proposed intervention will minimize the impacts of this activity on the health of landfill employees, surrounding residents and pedestrians. This positive impact will felt once landfill operations commence and will continue into the post closure phase of the project.



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At present, scavengers and gardeners carrying out informal activities on the site are not provided with any protective clothing and they are exposed to being injured by contaminated broken bottles, metal parts, batteries etc. The establishment of the administration facilities where scavengers can be monitored and the provision of utility services within the site and protective clothing for the workers will impact positively on the health and safety of the workers whilst the landfill is in operation. The construction and operation of the landfill will create some local employment and contribute towards poverty alleviation. However during the construction phase, noise will be generated by the activities of bulldozers and trucks working on the landfill. It is expected that these activities will generate some dust during the construction and operations phase of the landfill. There may be mud and clay strewn on the roads as trucks enter and leave the landfill bringing heaps of gravel and clay for compaction. In the event mud is strewn on the roads, it will constitute an inconvenience to pedestrian and make the roads corrugated and inconvenient to drive upon with negative implication for road safety.

4.4.8 Community Stability Previous studies14 have indicated that the mean age of residents around the Bakoteh Dump Site is 21 years and the modal age lies between 15 and 19 years. There is very high incidence of malaria and respiratory diseases which can be attributed to the proximity of the dumpsite to the residential areas. The prevalence of these diseases is a threat to the stability of the community and it is anticipated that the proposed interventions will reduce the incidence of these diseases and improve the life expectancy and the quality of life of the residents. These developments should impact positively on the stability of the community once the operations of the landfill commence and should continue well into the post closure phase of the project. However, there is no risk of human displacement during any of the stages of the Intervention therefore no need to prepare alternative settlement plans for this project.

4.4.9 Potential negative impacts • Landfill Gas Emissions The main components of landfill gas are methane and carbon dioxide, which are emitted through the top and or sides of the landfill and then dispersed in the atmosphere. Methane and carbon dioxide are green house gasses with negative impacts on the climate.

14 Nzainga et al. Support for the Bakoteh Dump Site Waste Management Study, 2002.



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Methane is highly flammable and its presence in large quantities can lead to unwanted fires within the landfill. Where landfill gas is flared low levels of pollutants such as dioxins, which bio-accumulate and can cause wide ranging health effects are formed during the combustion process. Consequently the placements of exhaust vents for the gases will reduce the risk of fire outbreaks on the site during the operations and after the closure of the landfill as an active disposal site. • Disruption of the Flora and Fauna Construction activities on the scale envisaged to transform Bakoteh Dump site into a controlled landfill is potentially disruptive to surrounding flora and fauna and action should be taken to minimize these impacts on all life forms and their habitats. It is however noted that zone 1 will be turned to a forest by levelling the existing ground and planting Eucalyptus trees. The loss in the life forms in the ponds is insignificant.

• Impact on Agricultural Production The intervention prohibits agricultural and food gardening activity on the Dump site and should impact negatively on the availability of some of the crops grown there. However, this shall only be the case in the event gardeners are unable to find alternative sites for their activities.

In addition, the extraction of clay from any of the identified sites within Western Division on the scale required by the proposed intervention during the operations phase may leave deep craters in these areas which can serve as breeding grounds for vector carrying insects if surface water from adjoining rice fields is permitted to escape into the pits created by clay mining. Moreover, there is good chance that the surrounding life forms and wildlife may be disrupted by such an activity. This disruption if not mitigated may be prolonged and lasting. In order to minimise this potential negative impact water retention dykes should be constructed around the areas of excavation to prevent surface water spilling into the crater. Moreover, the area should be properly restored preferably using cost efficient measures and proven techniques already in place. Commercial clay miners are known to plant bamboo trees in the pits as a restoration measure which may not be adequate for the craters that will be left after the large scale excavation that is anticipated by the proposed intervention. As a result, the damage to flora and fauna of the area, the cost of ensuring proper restoration of the site may be prohibitive.



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• Liquid Emissions and Discharge The trucks and bulldozers that will be used in the construction of the landfill will invariably be diesel powered with the potential to spill fuel and oil on the ground surface which may seep into the water table during construction and landfill operations. Moreover, exhaust fumes will be emitted which will impact unfavourably on the surrounding air quality further compounding the problem of poor odour at landfill during these stages. Attention should be paid to the technical and operational soundness of the vehicles and bulldozers that will be used within the landfill to prevent on-site breakdowns of machinery. Recovery of vehicles that breakdown on the site will be expensive and can be potentially disruptive to the progress of the works, the land area and life forms. • Traffic Delays and Disruption The landfill is located in an area with relatively dense traffic during the morning and afternoon peak hours. The trucks and Bulldozers that will be plying this road during the construction phase will constitute additional traffic, reduced vehicle movement; increase congestion along this road. There is potential for dust, debris and mud to litter the roads during the transportation of gravel, clay and soil cover to the landfill causing inconvenience to motorists and pedestrians and the community living along the road. It is required that vehicle drivers be sensitized regarding maintenance and repair of vehicles and equipment and the potential negative environmental impacts of failing to do so effectively on time.

4.4.10 Impact Assessment Statement Having assessed the current impact of the site on the environment, the impacts during construction, operations, closure of the landfill, it is clear that on balance the intervention envisaged will have a positive impact on the overall environment. The advantages that accrue to the landscaping of the site, planting trees in zone 1 and grass in zone 2 and eventually in zone 3, protecting the groundwater from being contaminated by compaction of the landfill base, placing clay material or membrane liners before disposing of the waste, covering the disposed garbage to reduce bad odour and completely stopping open burning of waste far outweighs the minimal negative impacts that are envisaged. Plans have been developed to mitigate these negative impacts arising from any of the stages already indicated and Table 4.2 gives the basic outline of the anticipated environmental impact pathways and the recommended mitigation measures.



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The realization of these positive impacts will depend of the efficiency and effectiveness of the construction of the landfill as designed, the extent to which the mitigation measures highlighted are enforced during operations, closure and the post closure phase and the implementation of the environmental management and monitoring plan. In Table 4.2, the source of landfill contaminant is identified, the media affected, the places and routes for potential exposure are noted, the phase of occurrence highlighted, the primary receptors indicated, the potential significance of the impact rated and mitigation measures prescribed. The table is a summary of the environmental impact pathways identified.



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Table 4.2 Impact pathways and mitigation measuresContaminantRelease

AffectedMedia

ExposurePoint

ExposureRoute

PrimaryReceptors

ImpactStages

Significanceof Impacts

Mitigation Measures

DirectContact

Soil Onsite IngestionDermal AdsorptionPhysical Hazards

TrespassersSite UsersSite workersDomestic AnimalsArea residents

PSHigh Provide soil cover and protective membrane

Wind Air Dust OnsiteOffsite

Inhalation Residents & AreaWorkers

PS,CP,

High Provide daily cover of garbage

Erosion &Run offof soluteand suspension

Surface waterSediments

OffsiteOnsite

IngestionBio-concentrationDermal Absorption

TrespasserPond usersAquatic wildlifeSite workers

PS,CS

High Construct and maintain drains

Leaching by:CompressionPercolation

Ground Water,ResidentialWells

OnsiteOffsite

IngestionDermal absorption

Pond usersSite workers & usersAquatic wildlifeDomestic animals, residents

PS,CP

High Provide drains, membrane linersProvide pipe borne water for the surrounding community.Maintain the ring drains outside the landfill &enclosure dike.

Landfill Gas Vadose zone OffsiteOnsite

InhalationExplosion

ResidentsSite workers

O CLPC

Low Provide exhaust vents

Open burning Smoke in Air Onsiteoffsite

InhalationPhysical Hazards

ResidentPedestriansSite workers

PS High Prevent onsite firesProvide exhaust vents for the landfill area

Offensive odour Air Onsiteoffsite Inhalation

ResidentsSite workersPedestrians

PS CS HighDaily soil covering of disposed garbage

Dust Exhaust FumesFrom vehiclesand Equipment

Air OffsiteOnsite Inhalation

PedestriansCommunitySite workersArea Residents

CS Low Water access roads and work sitesConduct proper vehicle maintenanceControl vehicle speed

Trucks and equipmentEmitting noise Air

OffsiteOnsite Hearing

ResidentsSite workersPedestrians

CS Low Proper vehicle maintenanceNo Operations at night

Harmful Insects OffsiteOnsite

Dermal Contact ResidentsSite workers

PS High Daily soil cover of disposed garbage

Site Location Land values Offsite Area property owners PS,CS,OP

High Construction and proper maintenance of sanitary landfillClosure in shortest possible time

Vehicle discharge Soil & groundWater

OnsiteOffsite

Seepage Area resident, Site users CS, OP Low Proper maintenance of vehicles

Vehicle movement Road Traffic Offsite Traffic Motorists CS, OP Low Retain road worthy vehiclesLegend: Present Situation (PS) Construction Phase (CP) Operation Phase (O) Closure Phase (CL) Post Closure (PC)

The Gambian Agency for the Management Preliminary and Detailed Engineering of Public Works (GAMWORKS) Design Study for Bakoteh Dump Site

Charchi Githinji & Partners in association with CityScape Associates Final Report 47

CHAPTER 5 DETAILED DESIGN OF PROPOSED SOLID WASTE MANAGEMENT SYSTEM

5.1 Introduction The design considers the following: layout of landfill site, types of wastes that must be handled, estimation of landfill capacity, selection of leachate control facilities, selection of landfill gas control facilities, layout of surface drainage facilities, aesthetic design considerations, monitoring facilities, landfill equipment and development of an operations plan. Sanitary landfill system requires a large amount of capital investment. Taking into consideration that plans are underway to construct a new landfill at Tambana and the short life of the identified landfill area , it may not be prudent to adopt a sanitary landfill system at Bakoteh. It is also important to consider achieving a balanced urban infrastructure improvement and aspects of urban environmental preservation.

5.2 Design considerations and Solid Waste Management Components

5.2.1 General The layout of the landfill site accommodates the following facilities: access roads; administrative office, scavengers shed, sorting out area, disposal sites for special wastes; landfill area and areas for stockpiling cover material; drainage facilities; location of landfill gas management facilities; location of leachate treatment facilities, location of monitoring wells; and plantings. The design considerations of the landfill are presented herebelow. 5.2.2 Type of waste The landfill will mainly receive municipal solid waste. From previous studies, hazardous waste disposed at the site includes hospital waste and used dry and wet batteries. Two chambers for each of the waste already exist in the dump site but are almost full. Accessibility to the chambers and lack of site management has limited their use. Two new chambers each 10 m x 3 m x3 m deep, based on the size of the existing chambers, are proposed. Hospital waste and batteries will be disposed in the special waste chambers. 5.2.3 Landfill area and capacity Zone 3 with an area of 6.8623 hectares has been recommended as the landfill area as it offers the maximum area.



The nominal volume of the landfill site was determined in Chapter 3. The following calculations consider the impact of the compactibility of the solid waste and the impact of daily cover.



Table 5.1 Factors considered in the design of the landfill Factor Proposed

Access All-weather access roads to landfill site; temporary roads to unloading areas.

Landfill area Maximum available area considering acceptable base and final cover slope.

Landfilling method Cell method of landfilling.

Surface drainage Storm water drains to divert surface water runoff at the periphery of the landfill area.

Intermediate cover material Maximise use of onsite soil materials; additional cover material from borrow areas to be identified.

Final cover Minimum final cover slope of 2% recommended 5%. The allowable minimum slope is to safeguard ponding and hence increased risk of precipitation to percolate through the landfill cover resulting to possible leachate. Multi-layer design to be considered.

Landfill liner Multi-layer design incorporating the use of a geo-membrane to be considered. Constraints in the use of geo-membranes due to cost and availability of construction technology envisaged. Minimum base slope 0.5%, desirable 2%. Piped bottom type leachate collection system at 0.5%. slope. Pipe perforation, diameter and spacing of pipes to be determined.

Cell design and construction Each day’s wastes to form one cell; cover at end of day with 150mm of earth. Cell width, lift height, slope of working faces to be determined.

Groundwater protection Perimeter drains to be provided.

Landfill gas management Landfill gas management plan to be considered.

Leachate collection Determine maximum leachate flow rates and size leachate collection pipe and/ or trenches; size leachate pumping facilities; select collection pipe materials to withstand static pressures corresponding to the maximum height of the landfill.

Leachate treatment Based on expected quantities of leachate appropriate treatment process will be considered.

Environmental requirements Groundwater monitoring facilities to be provided.; locate ambient air monitoring stations.

Equipment requirements Number and type of equipment to be determined.

Fire prevention Water to be provided onsite.

Enclosure Dike Prevent dispersion of solid waste Prevent influx of rain water from outside Limit the range of dumping area Placed along the boundary of the site

Divider Dike Placed on the boundary of the partition to separate hospital waste from general solid waste Special waste Chambers to be considered.



• Determination of waste to cover soil ratio

o Data Waste deposited per day = 254 tons Lift height = 3 m Cell width = 5 m Number of lifts = 2 Slope of working face =3:1 Average specific weight of compacted waste = 1000 kg/m3

Daily soil cover = 150 mm o Determination of the daily volume of waste deposited

Volume = 254 m3

o Determination of the length of each daily cell

Length, L = 254/(3 x 5) = 17 m

o Determination of cell surface areas Top of cell = 17 x 5 = 85 m2

Face of cell = 17 x [32 + (3 x 3)2]1/2 = 161 m2

Side of the cell = ½(5 +14) x 3 = 28.5 m2

o Determination of volume for daily cover

Volume = 0.15 x (85 +161 + 28.5) = 41.2 m3

o Determination of ratio of waste to cover soil RW:C = 254/41.2 = 6.2 (use 6:1 soil to cover ratio)

Volume of landfill available for waste = 6/7 x 289485 (0.7% base slope, 1% final cover slope - Section 3.3.3) = 248130 m3

Estimated waste on site to be landfilled = 105000 m3 (Section 3.3.3) Estimated landfill capacity = 143130 m3

The estimated useful life of the landfill (based on Section 3.3.3 and the assumptions above) is shown in Table 5.2:



Table 5.2 Estimated useful life of landfill

Landfill base and final cover slopes

Nominal volume ofzone 3

m3

Net volume zone 3

m3

Volume of zone 3less 105,000 m3

m3

Useful life15

of landfill (100% collection) months

Useful life of landfill (65% collection) months

0.7%/2% (base /final cover slope) 126,300 108,257 3,257 0 0




A final cover slope of 2% gives only 1 – 2 months of landfill useful life. Considering the hot climate in the Gambia, ponding is not a serious concern and hence a 1% slope is acceptable. A 0.7% base slope and a 1% final cover slope have been adopted for this design. These afford 18 to 26 month of useful life of the landfill site. 5.2.4 Access roads The planned access road will provide the shortest access to the existing road. A standard gravel road of 6m width, with drainage facilities and 10 ton bearing capacity is proposed The trucks require access to the tipping area, which is at the working cell. Three onsite roads are proposed. The onsite roads are of lower standard than the access road since they are temporary. The on site roads will be necessary for the Cell Method Operations and will be constructed as landfilling progresses. The level of the access road has been designed to be the finished level of the landfill at closure at the proposed 1% slope. The embanked section of the access road provides part of the capacity of the landfill and also facilitates diversion of storm water from the periphery of the landfill. It is expected that the void between the embanked access road and the built up area will be filled with inert waste material and hence will create a buffer zone. 5.2.5 Enclosure Dike The landfill area will be separated from Zone 1 by an enclosure dike. The enclosure dike will prevent dispersion of solid waste, prevent influx of rain water from outside and limit the range of dumping area. The enclosure dike, which is an earth embankment will also, together with Zone 1, mitigate the negative impacts of proximity to the built-up area. As noted in Section 3.3.3, the semi-motor-able track previously connecting the Serrekunda main road to Manjai Kunda is no longer in use as garbage has extended from both sides blocking any access to the dump site. It is noted that Bakoteh Primary School and Manjai-Kunda settlement from where the school draws most of the pupils are located

15 From end June 2004



at the opposite sides of the dump site. This has necessitated children to crisscross through the open dump site. A gravel road is proposed at the enclosure dike to facilitate this human traffic. Just as for the access road, the level of the enclosure dike/road has been designed to be the finished level of the landfill at closure at the proposed 1% slope. The embanked section of the enclosure dike/road provides part of the capacity of the landfill and also facilitates diversion of storm water from the periphery of the landfill.

5.2.6 Leachate management facilities The principal leachate management facilities required in the design of a landfill include the landfill liner and leachate collection system and the leachate treatment facilities. The type of landfill liner used depends on the local geology and hydrogeology. The current trend is towards the use of composite liners including a geomembrane and clay layer. In extremely arid areas where no possibility exists of contaminating the groundwater, it may be possible to develop a landfill without a liner. Nevertheless, the use of a liner system is a critical factor in siting landfills. To determine the size of the leachate collection and treatment facilities requires the quantity of leachate to be evaluated. The evaluation of leachate is presented in Table A in Annexe 1. From the rainfall and evaporation data available, the calculations indicate that no leachate will be formed. The results of the calculation support the previous opinion in the Gambia Solid Waste Management Strategy report, that no leachate will be expected to form during the dry season (8-9 months annually) and during the wet season, a large amount of water can be expected to be absorbed by the waste before this becomes saturated and free leachate flows into the groundwater. 5.2.7 Leachate collection and treatment structures The most common alternatives that have been used to manage leachate collected from landfills include, leachate recycling, leachate evaporation, treatment followed by disposal, and discharge to municipal wastewater collection systems. For the Bakoteh landfill a combination of anaerobic leachate treatment and leachate evaporation is ideal due to the low cost and favourable climate. A system of collection of leachate, treatment and evaporation consisting of perforated laterals, treatment in a 45m3 septic tank before discharge into a 90m3 open lined pond was proposed in the draft final report of this study. However with the calculations indicating no possibility of leachate formation and clients budgetary constraints, leachate collection and treatment structures have been omitted in the final report.. 5.2.8 Landfill Liner The current practice is to install impermeable barriers within landfills. Land fillers are now commonly used to limit or eliminate the movement of leachate and landfill gases. Clay is favoured for its ability to adsorb and retain many of the chemical constituents in the leachate and gas.



A multi-layer design composite barrier shown in Figure 5.1 was presented in the Draft Final Report of this study.

Figure 5.1 Landfill Liner System DesignIt is noted that a landfill liner is a requirement even when calculations indicate no leachate formation as it not only allays public fears of groundwater contamination but also guarantees safety under any eventuality.

The landfill sealant proposed for Bakoteh dumpsite is compaction of the sub-grade to 100% MDD and a 300 mm-compacted clay layer.

5.2.9 Selection of gas control facilities The uncontrolled release of landfill gas, especially methane, contributes to the greenhouse effect. Landfill gas can migrate laterally and potentially can cause explosions or kill vegetation and trees and hence, most new landfills are equipped with gas collection and treatment facilities. The movement of landfill gases is controlled to reduce atmospheric emission, to minimize the release of odorous emissions and to minimise subsurface gas migration. Control systems can be either passive or active. In passive gas control systems, the pressure of the gas that is generated within the landfill serves as the driving force for the movement of the gas. A simple gas venting system shown in Figure 5.2 has been proposed for the Bakoteh Dump site. 5.2.10 Selection of landfill cover configuration The primary purposes of the final landfill cover are (1) to minimize the infiltration of water from rainfall after the landfill has been completed, (2) to limit the uncontrolled release of landfill gases, (3) to suppress the proliferation of vectors, (4) to limit the



potential for fires, (5) to provide a suitable surface for the revegetation of the site, and (6) to serve as the central element in the reclamation of the site. To meet these purposes the

Figure 5.2 Gas Exhaust Equipmentlandfill cover (1) must be able to withstand climatic extremes (e.g., hot/cold, wet/dry cycles); (2) must be able to resist water and wind erosion (3) must have stability against slumping, cracking and slope failure, and downslope slippage or creep; (4) must resist the effects of differential landfill settlement caused by the release of landfill gas and the compression of the waste and the foundation soil; (5) must resist failure due to landfilling operations such as surcharge loads due to stockpiling and the travel of collection vehicles across completed portions of the landfill; (6) must resist deformations caused by earthquakes; (7) must withstand alterations to cover materials caused by constituents in the landfill gas; and (8) must resist the disruptions caused by plants, burrowing animals, worms, and insects. The general features of a landfill cover, some typical types of landfill cover designs, and the long-term performance requirements for landfill covers are considered below.

A landfill cover, is made up of a series of layers, each of which has a specific function. The subbase soil layer is used to contour the surface of the landfill and to serve as a subbase for the barrier layer. In some cover designs, a gas collection layer is placed below the soil layer to transport landfill gas to gas management facilities. The barrier layer is used to restrict the movement of liquids into the landfill and the release of landfill gas through the cover. The drainage layer is used to transport rainwater and snowmelt that percolates through the cover material away from the barrier layer and to reduce the water pressure on the barrier layer. The protective layer is used to protect the drainage and barrier layers. The surface is used to contour the surface of the landfill and to support the plants that will be used in the long-term closure design of the landfill.



As a consequence, the use of one or more geomembranes is recommended over the use of clay as barrier layer in landfill covers. Geosynthetic clay liners have also been used for the barrier layer. The use of a geomembrane liner as a barrier layer is favoured to limit the entry of surface water and to control the release of landfill gases. The specific cover configuration is depended on the location of the landfill and the climatology conditions. To allow for re-grading, it is desirable to allow for the use of deep layer of soil. To ensure the rapid removal of rainfall from the completed landfill and to avoid the formation of puddles, the final cover should have a minimum slope of 1-2%. A composite multi-layer landfill configuration was presented in the Draft Final Report of this study and is shown in Figure 5.3. As no leachate is anticipated and due to budgetary constraints, a 300 mm clay final cover layer and 500 mm top soil is proposed.

Figure 5.3 Typical cover system

5.2.11 Surface water drainage facilities An important step in the design of a landfill is to develop an overall drainage plan for the area that shows the location of storm drains, culverts, ditches, and subsurface drains as the filling operation proceeds. Perimeter drains will be provided in zone 3 to divert any storm water ingression into the landfill. A combination of Invert Block Drains and Earth drains is proposed. In selecting the drains consideration has been given to the final landscape land use. The alignment of the drains and typical cross sections are presented in Volume 2 (Drawings) of this report. 5.2.12 Environmental monitoring facilities



Monitoring facilities are required at landfills for gases and liquids in the vadose zone, for groundwater quality both upstream and downstream of the landfill site, and for air quality at the boundary of the landfill. No special gas monitoring faculties are proposed for the site. Organoleptic detection is recommended. No appreciable amount of gas is expected to be formed due to the small size of the landfill and the dry nature of the waste. Any gas formed will be vented off with the equipment proposed in section 5.2.8. Three ground water monitoring wells of the nature shown in Figure 5.3 are proposed. The recommended sampling periods and parameters to be investigated are presented in Chapter 7. The proposed locations of the monitoring facilities are presented in Volume 2 (Drawings) of this report.

Figure 5.4 Monitoring Well5.2.13 Aesthetic design considerations

Aesthetic design considerations relate to minimizing the impact of the landfilling operation on nearby residents as well as the public that may be passing by the landfill. • Screening of the daily landfilling operations from nearby roads and residents with

plantings is recommended. • Wind blown paper, plastics, and other debris can be a problem at some landfills. The

most common solution is to use portable screens near the operating face of the landfill. However the Bakoteh landfill is relatively small. The proposed net perimeter



fence and regular litter removal is the recommended solution. To avoid problems with vectors any material lodged on the fence must be removed daily. Dust will be controlled by spraying water on the approach and internal access roads.

• Flies and mosquitoes will be controlled by the placement of daily cover and by the

elimination of standing water. Rats and other burrowing animals will be controlled by the use of daily cover.

5.2.14 Equipment Requirements The type, size, and amount of equipment required is a function of the size of the landfill and the method of operation. The types of equipment that have been used at sanitary landfills include crawler tractors, compactors, draglines, and motor-graders. Of these, crawler tractors are most commonly used. Properly equipped tractors can be used to perform all the necessary operations at a sanitary landfill, including spreading, compacting, covering, trenching and even hauling cover materials. Some generalized information on the performance of landfill equipment is summarized in Table 5.3.

Table 5.3 Performance Characteristics of Landfill equipment

Solid Waste Cover material Equipment Spreading Compacting Excavating Spreading Compacting Hauling

Crawler tractor Wheeled compactor Scraper

EENA

GENA

EPG

EF-G E

GENA

NA NA E

Rating key: E, Excellent; G, good; F, fair; NA, not applicable.

From the projected collection rate of 165 ton/day (2004) and using the unit weight of waste of 0.3 ton/m3, the equipment requirements are as follows: Waste quantity : 143 ton/day (550 m3/day) Bulldozer Capacity (15t class) : 50 m3/hour (500 m3/day - 10hr day) Required number of Bulldozers : 1 From the projected waste generation, the amount of waste will vary from 254 ton/day (2004) to about 300 ton/day (2006). Assuming 100% collection and disposal, the equipment requirement will be as follows: Waste quantity : 254 ~ 300 ton/day (846 ~ 1000 m3/day) Bulldozer Capacity (15t class) : 50 m3/hour (500 m3/day) Required number of Bulldozers : 2 The recommended equipment is therefore 1-2, 15-ton bulldozers and one water truck. The proposed Tambana landfill site however requires16 a 20-ton bulldozer. Due to the relative short life of the Bakoteh landfill it is recommended that the 20-ton be procured and be transferred to Tambana site after Bakoteh landfill is closed.

16 Solid Waste Management Study for the Greater Banjul Area and Brikama – May 2004



5.3 Landfill operation The development of a workable operating schedule, a filling plan for the placement of solid wastes, landfill operating records and billing information, a load inspection plan for special wastes, and site safety and security plans are important elements of a landfill operation plan. Other factors that must be considered in the operation of a landfill are presented in Table 5.4 Table 5.4 Factors considered in the operation of the landfill. Factor Proposed Days and hours of operation Seven-day week as is current practice.

Night hours to be discontinued since lighting is not provided.

Communication Potable radio communication between active landfill site and site manager’s office. Base radio at KMC cleansing unit.

Employee facilities Administrative office with bathroom and toilet facilities and drinking water.

Litter control Initially daily picking of litter and later as required.

Operational records Trucks, waste type and volume (to be converted to tonnage) of waste to be recorded.

Salvage Scavenger sheds. Processing of scavenged goods at scavengers sheds.

Scale No scale. Ocular/volume measurements. Security Locked gate and fencing; lighting of gate,

guardhouse and administrative block.

Spread and compaction Spread and compact waste in layers less than 600 mm thick to achieve optimum compaction.

Unloading area

17 m.

To determine the quantities of waste that are disposed, an entrance scale and gatehouse are normally required. The gatehouse would be used by personnel who are responsible for weighing the incoming and outgoing trucks. Though a scale will be incorporated in the design, due to the short lifespan of this site it may be uneconomical to install. Volume measurements of the trucks and use of the dry density of the waste will facilitate estimation of tonnage of waste received. Load inspection at the guardhouse will also detect special wastes, which will be disposed at the special waste chambers.



In order to safeguard the health and safety of landfill workers attention must be given to the types of protective clothing and boots, air-filtering head gear, and puncture proof gloves supplied to the workers. The site will have restricted access, will be fenced and posted, with no trespassing and other warning signs to safeguard public safety. Litter and waste bins (trailers) will be appropriately located, to minimize public contact with the working operations of the landfill. The proposed landfill operation structures are presented in Volume 2 (Drawings) of this report. 5.4 Estimated cost of proposed Landfill components The full range of the proposed landfill components and their specifications are presented in the bidding documents accompanying this report. Table 5.5 gives a summary of the major components.

Table 5.5 Estimated cost of proposed Landfill components

ESTIMATED COST OF PROPOSED FACILITIES

D E S C R I P T I O N UNIT QUANTITY RATE AMOUNT Item No. Dalasis

1 Clearance of all waste already littered in the dumpsite m³ 120000

2 Roadworks and Drainage Item Sum

4 Supply and install VHF radios - ONE Base radio and TWOportable radios including all requisite licenses Item Sum

5 Supply landfill Bulldozer Item Sum

6 Supply Skips No 7

7 Administration Block Item Sum

8 Guard House Item Sum

9 Fence

10 Scavengers Shed Item Sum


Charchi Githinji & Partners in association with

Cityscape Associates Final Report 60

Table 5.5 Estimated cost of proposed Landfill components (continued)

ESTIMATED COST OF PROPOSED FACILITIES

D E S C R I P T I O N UNIT QUANTITY RATE AMOUNT Item No. Dalasis

11 Equipment Shed Item Sum

12 Landfill Area

a General excavation for cover material and to prepare landfill base in all areas of landfill m³ 100000

b Spread, grade and compact insitu subgrade material at the

base of the landfill area (zone 3) a to100% MDD m2 68623

c Spread, grade and compact zone 2 formation level to100%

MDD m2 77011

d Spread and grade zone 1 without compaction as directed by m2 37907

e Imported fill in normal or soft material for landfill base clay liner (zone 3) m³ 23000

f Imported fill in normal or soft material for final clay cover (zone 2) m³ 25000

g Site stockpiled fill in soft material for top soil in Zone 1 and 2 m³ 60000

h Landfilling of solid waste includingprovision of all plant and materials m³ 175261.5

I Grassing in Zone 2 m2 77000

j Tree planting in zone 1 m2 37907

k Gas Venting No 11

l Ground Water Monitoring boreholes No 3

m Special Waste Chambers as per specifications m3 60

Total




The above proposed basic components are estimated to cost about Seventy Million Dalasis. It is noted however that most of the components are designed considering closure of the landfill site. Needless to say that even if the dumpsite was not to be used for a day more, reclamation of the land due to the dumping operations for a long period would require a big proportion of the estimated costs. Once the landfill area is full, the final level and landscape would allow the dumpsite area, zone 2 and zone 3 to be used as a park, a recreational area, a nature preserve, a botanic garden or just open space.




CHAPTER 6 LANDFILL CLOSURE AND POST-CLOSURE

CARE

6.1 Introduction Landfill closure and post-closure care are the terms used to describe what is to happen to a completed landfill in the future. Some possible uses for the closed landfill would be a park, a recreational area, a nature preserve or a botanic garden. Whatever the final use, the ideal situation is to ensure that the closed site is maintained into perpetuity. The facilities at a closed landfill must be maintained over the period of time that the landfill is producing products of decomposition. Because the waste placed in landfills will decompose at different rates, there can be extreme variations in the period of time that maintenance will be required at a closed landfill. The practice is that maintenance period is 20 to 30 years. At the time of site closure, or other time as specified by local regulations, a postclosure maintenance plan will be developed. Long-term postclosure care involves a series of continuing activities, beginning at the closed landfill with monitoring of environmental

controls. Typical elements of a postclosure plan are identified in Table 6.1.

Table 6.1 Typical elements of a landfill postclosure plan

Post closure land use Designation and adoption Routine inspection schedule See Table 6.2 Infrastructure maintenance Preparation of a description of the programs

for final cover, vegetative cover, final grading, drainage systems, gas monitoring and control systems, and groundwater monitoring system

Environmental monitoring systems Setting of specific tasks and schedules System operation Description of systems to be operated,

frequency of operation, and responsible agency

Reporting Identification of reports required, timing, and format

Facility changes Preparation of as-built descriptions of current monitoring, collection, and treatment systems

Emergency response plan Preparation and submittal




6.2 Routine Inspections Routine inspections are conducted to characterize the condition of landfill closure facilities. Personnel from the solid waste management agency may be responsible for conducting the inspection, although a closed landfill may be used and the land area managed by a different department of the community. The responsible agency and its duties in regard to inspections will be identified and set forth in the postclosure maintenance plan. A listing of items to be inspected, the suggested frequency of inspection, and typical problems that might be observed is presented in Table 6.2.

Table 6.2 Closed landfill inspection items, frequency of inspection, and potential problems to be observed

6.3 Infrastructure Maintenance The infrastructure of landfills includes grading and landscape features, drainage control systems, gas management systems and leachate control systems. This infrastructure must be maintained systematically through a planned schedule of preventive maintenance to protect the integrity of the landfill cover and prevent contamination of the air, water, and soil environment adjacent to the landfill.

6.3.1 Grading and Landscaping.

Inspection item Frequency of inspection Potential problems to be observed

Final cover Once per year, and after each substantial rainfall

Erosion to expose the synthetic liner; landslides

Vegetative cover Four times per year Dead plants Final grades Twice per year Standing ponds of water Surface drainage Four times per year, and after

each substantial rainfall Debris in drains; broken drain pipes

Gas monitoring Continuous as required by the postclosure maintenance and management plan

equipment inoperable; high gas readings in monitoring probes; broken gas well pipes

Groundwater monitoring As required by equipment and the postclosure maintenance and management plan

Damaged wells; inoperable sampling

Leachate management As required by the postclosure maintenance and management plan

blockage in leachate collection pipes




Closed landfills will have significant settlement, which will affect land surfaces and the plants used for landscaping. The site manager must have the equipement and funds necessary to maintain the required grades and plants. Each closed landfill will have a specific set of equipment and funding requirements based on the size and slope of the land area to be maintained and the type of vegetation.

6.3.2 Drainage Control Systems. Drainage control at closed landfills includes both run-on and runoff of surface waters. The drainage control systems to be maintained will be the facilities identified and installed as a part of the landfill closure plan. Drainage facilities at closed landfills are subject to long-term settlement, which causes concerns for the preservation of gravity flow systems that discharge to offsite conveyance facilities. Maintenance of drainage control systems must be coordinated with maintenance of land surfaces and revegetation of landscape plants.

6.3.3 Gas Management Systems. Gas management will be required at closed landfills as long as landfill gas is produced. Gas management systems are installed as a landfill is operated before closure. The gas extraction wells and gas collection pipes installed in the wastes or in the final cover over the wastes is a high-frequency maintenance item because of settlement of the wastes. Waste settlement will dislocate pipes and wells, and a significant disclosure will cause the pipe and well casings to break.

6.3.4 Leachate Collection and Treatment. Closed landfills with installed leachate collection systems must collect, remove and treat leachate as it appears over the post closure period. The leachate management system will operate as long as is necessary to meet the applicable water discharge standards set for the closed landfill. The maintenance of leachate collection and treatment facilities requires systems operators who are skilled in handling changing quantities of wastewater that varies in strength.

6.4 Environmental Monitoring Systems. The environmental monitoring systems to be maintained during the post closure period are the systems designated in the closure plan and approved by the regulatory agency. Although each closed landfill will have specific monitoring requirements, the typical systems to be maintained will include monitors in the vadose zone, water wells and well caps, gas probes, and survey instruments.




CHAPTER 7 Operation and Maintenance Manual of Sanitary Landfill

7.1 Landfill Control Facilities

7.1.1 Structure of control facilities Competent, safe operation is what distinguishes a landfill facility from a dumpsite. Indeed careful operation can make up for some deficiencies in siting or design. Conversely, careless site management can turn even the best designed facility into an environmental disaster. For proper management of a sanitary landfill system, facilities to control operations and monitoring, a site office and access roads, etc must be constructed. The type and number of the control facilities available in any sanitary facility is depended on the level of operation of the landfill. This may range from simple groundwater monitoring to measurement of gas components and landfill settlement. 7.1.1.1 Management of sanitary landfill system This involves the proper control of solid waste quality and quantity, Landfill operations, management of landfill layers, facilities included in the sanitary landfill system as well as other facilities as shown as in Table 7.1

Table 7.1 Check of sanitary landfill system

Management items Remarks Landfill Waste Record quality and quantity of waste Landfill Work Cover material, landfill plan Landfill Layer Leachate and gas generation, ground

settlement etc Facilities Proper maintenance and repair of all

facilities

Sanitary landfill system control

Others Counter measures for fire, disaster etc

7.1.1.2 Control facilities Components Control facilities include the site office to facilitate recording and control of the quality and volume of landfill waste, landfill vehicles used for landfill operations, fuel storage tanks, places for washing vehicles, monitoring facilities, roads for management, and others as shown in Table 7.2




Table 7.2 Classification of control facilities

Main Facilities Incoming vehicles control facility Monitoring facility Site office Access road

Control Facilities

Other (Garage, Fuel Fan, Vehicle washing facility, etc)

• Quality and quantity of waste

o Checking Landfill Waste Landfill waste must be checked for smooth operations as well as to prevent land pollution due to inclusion of harmful substances. Therefore, the type, components, quality, etc of the solid wastes must be carefully checked. Landfill waste not passing through any intermediate treatment facility is usually checked by its outward appearance. It is normally convenient if a platform is built near the weighbridge such that the components on the truck can be inspected. When necessary, the solid waste should be first unloaded and then inspected. A place for inspection is thus necessary.

o Weigh-bridge At the sanitary landfill system, a weighbridge should be constructed at the entrance to the landfill site so as to be able to weigh and record landfill waste. The weighbridge weighs the trucks loaded with the solid waste as they enter the landfill site. There are several weighbridge systems ranging from mechanical systems to digital systems. Factors like, The total number of collection vehicles per day solid waste collection system and maximum number of collection vehicles at peak delivery hours etc have to be considered before deciding on the number of weigh-bridge to be installed.

o Solid Waste Quality Besides checking to see if the solid waste meets the requirements set, the quality of the solid waste must also be investigated. By knowing the quality of the landfill waste, the type of gas generated in the landfill, the leachate quality, the amount of settlement due to compaction of the landfill layer etc can be understood. This is also important data when designing the usage of the completed landfill site as well as for future landfill sites. When samples of the solid waste are to be taken, an inspecting place to take the samples after the landfill waste is dumped should be prepared.




o Analysis of Control Data

The data on the weights and results of the inspection of the garbage should be analysed on a regular basis for each type of solid waste and site filled. Daily, monthly and annual reports are usual. The times of deliveries are on daily reports; the dates of deliveries on monthly reports while the monthly information are included in the annual reports.

o Landfill Records The landfill waste volume, quality, place, time of landfilling, solid waste type, etc are all very important data, which should be recorded. Typical required input and output information is shown in Table 7.3 and Table 7.4.

Table 7.3 Typical Input Information

Items Date Entry Time Departure Time Operator’s Name Driver’s Name Vehicle Registration Number Waste Type Collection Points (Route) Gross Load Unladen Weight Net Load




Table 7.4 Typical Information for Management of Sanitary Landfill

Required Information Number of collection vehicles The total waste brought into the site Classification of waste type and quantity of each type Classification of waste generation in each collection area Waste charge calculation Daily, Monthly and Annual reports for all above.

• Monitoring Facilities The purpose of monitoring facilities is to monitor landfill layers and the environment.

o Monitoring the Landfill Layers Landfill layer monitoring during the course or after a landfill operation checks the changes in the solid waste component and measures the amount of settlement in the landfill layers and the data obtained can be used for designing future leachate treatment plants. The data is also useful in determining the land use of completed landfill site.

o Monitoring Environment The environment is monitored during and after land filling operations so as to measure the environmental impact or to equip the sanitary landfill system so as to prevent pollution. In all the above, the amount of data collected or analysed will determine how well future projects can be planned. It is important therefore, that data on solid waste component, leachate, underground water, gas, bad odours, etc be regularly collected. (a) Leachate and Discharged Water

As part of management and maintenance of a sanitary landfill system, the quality and frequency of the discharged water should also be checked. In case of leachate, this should be done for the water flowing into the leachate treatment facility. The amount of pollutants and harmful substances in the water flowing out of a landfill site should also be measured. The discharged water quality should be monitored in order to prevent pollution of water in the areas where untreated water is discharged. A comprehensive monitoring scheme is shown in Table 7.5.




Table 7.5 Typical Monitoring Scheme (Leachate)

Sampling place Monitoring Parameters Frequency

Leachate reservoir, pond and discharged water

pH, CN, pd, T-Hg, Cd, BOD, COD, SS, MPN, Colour.

1/month

(b) Ground water

The reasons for monitoring of ground water in areas surrounding a sanitary landfill system are two fold:- • To check if the natural or artificial liner system in the site is effective. • In the case where the natural or artificial liner system is not effective, to prevent

and/or mitigate effects of pollutants discharged on the ground water and to the inhabitants in the area.

The monitoring facilities established enable determination of the quality and hence the possible usages of groundwater in the areas around the sanitary landfill system. This concept allows for the determination of the number and location of the monitoring wells. A well should be placed directly below the direction of flow of the subterranean water in the landfill for the purpose of monitoring the amount of seepage before the pollutants in the water are dispersed into the ground water. In addition, a second monitoring well should be built downstream where the dispersion of pollutants has the highest possible and fastest effects. Generally the wells should be more than 100 mm in diameter with a strainer at the water table. The water quality inspection by monitoring wells can be divided into regular and routine inspection. Regular inspection includes inspections on the land use in the neighbouring areas. Routine inspection requires immediate detection of pollutants leakage and therefore, instruments like pH meters or electric conductivity meters, to measure changes in the water quality are usually built at the subterranean water collection and discharge facility or the monitoring well that are directly below the landfill site. On the other hand, regular inspections are for checking seasonal changes in the subterranean water quality. As such, the water quality should be checked at the same time each year at each monitoring well. Figure 7.1 shows some observed results and Table 7.6 shows proposed monitoring scheme of ground water.




Table 7.6 Proposed Monitoring Scheme

Sampling Points Monitoring Parameters Frequency Monitoring Well pH, CN, Pb, T-Hg, Cd,

BOD, COD, SS, MPN, Colour

1/month

(c) Gas When waste with organic substances is buried in a landfill site, monitoring of the gas generated will help to determine the decomposition condition of the landfill waste. Even in a landfill which uses mainly incombustible waste, the landfill waste should also be monitored since the waste may include organic substances Gas venting facilities in the landfill are used for monitoring the gas generated. The monitoring should be more frequent when active generation occurs and thereafter, during stable periods, monitoring frequencies can be reduced. This therefore calls for a flexible monitoring system. Table 7.7 shows the monitoring scheme of gas.

Table 7.7 Monitoring Scheme of Gas

Sampling point Monitoring Parameters Frequency Gas out-let pipe Temperature and humidity original

air, Temperature and volume of gas, component analysis (CH4, CO2, O2)

1/month

(d) Bad Odours The observation points and times for bad odours must be done after giving consideration to the living conditions in the surrounding area as well as weather conditions. Bad odours monitoring is usually done once a day in 3-months at 2 to 3 places on the landfill site boundaries. Observation methods and items include the analysis of 8 parameters such as ammonia, thiorumethane, hydrogen sulphide, methyl sulphide, triethylamine, acute aldehyde, styrene, methyl disulfide and tests on their effect on human senses (comparison of 3 test bags by smell), but the method should be selected after considering the solid waste quality and the local conditions.




Figure 7.1 Monitoring Well




(e) Others

Beside the above, other effects on the environment like noise vibrations, animals, plants and appearance; etc must also be considered when necessary. • Site Office The inspection and weighing of the landfill waste, checking of landfill progress and conditions, securing of cover soil materials, installation of section walls, operation, maintenance and monitoring of leachate treatment facilities at the sanitary landfill systems must be systematically performed so as to protect the environment, promote safety of the plant and improve the cost effectiveness. Typically the site office should include management office, test laboratory and analytical room, worker’s rest room, locker room, showers, a room for boiling water, canteen, toilets, conference room, etc. Ventilation and telecommunication should also be considered. In any case, the type of facility or room required at a site depends on the scale of the landfill site and management policies, the number of employees and managers at the site, etc. The site office should be placed in a convenient position so as to enable easy control of landfill waste and the landfill operation itself. Measures to prevent noise or bad odours must also be taken into consideration. In order to prevent the collection vehicles from carrying dirt onto the public roads, a vehicle washing facility should be installed at the existing roads. Whenever necessary, garages, petrol, station, warehouses, machine, inspection and maintenance facilities, lights, telecommunication facilities, etc. should be installed too.

7.1.2 Safety Measures A landfill site should be fenced off to prevent the general passers by from trespassing, as most parts of the landfill are dangerous. The fencing off is also to prevent other people from illegal dumping their own waste on the landfill. Net fences or barbed wire fences are usually used around the sanitary landfill system while corrugated plates are used to fence off the area from public roads or general housing. Regularly inspection and maintenance is necessary. Since the area to be controlled is wide, the name of the landfill site, operator, addresses, etc. should be clearly indicated on a no trespassing sign. The sanitary landfill system should be also clearly indicated. Inspection and maintenance of landfill site should also be done to prevent scavengers from climbing over the fences and entering the enclosed area. The following dangerous places and their measures should be carefully considered.




Leachate treatment facilities and leachate control pond should be fenced off and the entrance to them is properly locked. • Manholes must have heavy lids. • Gas venting facilities must be fenced off with barbed wire, etc. and a danger sign

placed on the fence. • Landfill equipment must be steered in specified places and when necessary, a buffer

area established. • Depending on the progress of the landfilling, surface drainage should be elaborately

performed since potholes are easily formed and water easily collects. • Lighting during nights is also important for safety and to prevent illegal dumping.

Light bulbs or electrical wiriness must be regularly inspected. Guards must always be stationed during nights and Sundays and holidays when necessary.

7.2 Related Facilities (1) Composition of Related Facilities The related facilities are necessary for the effective management and operation of the landfill site. Depending on the size of the landfill site, land conditions, etc. related facilities should basically include the following: • approach roads or access roads for effective delivery of waste or building materials

into the landfill site, • facilities to prevent littering of waste at the landfill site; • signs with clear indications prohibiting illegal entrance or illegal dumping in the area, • fire prevention and/or fire fighting measures within the landfill site; A portion of these related facilities should be build during landfill operation while the rest can be built even after completion of landfill if they are for control and management of a completed landfill site. (a) Approach Road The approach roads to the landfill site can be divided into two parts: public roads and roads leading from the public roads up to the landfill site.




When a public road is also used as a route for transporting solid waste signs to indicate this dual purpose must also be erected. The junction should also be designed as not to obstruct the free flow of the existing public road. Road construction (route, alignment, width, structure, etc.) must be done with the final land use of the landfill area in mind and in particular, if the approach roads are to become public roads in future. (b) Littering prevention facility/Buffer zone To prevent solid waste from littering or flowing out of the landfill, cover soil should be laid as soon as possible. Sometimes for some reasons like insufficient cover soil, etc. this is not possible. In this case, littering prevention facilities/buffer zones must be installed. Littering prevention fence should be about 3 to 4 times the height of the perimeter fencing. Trees should be planted to act as wind breakers especially where strong winds or seasonal winds are prevalent. In the case of ash which disperses easily, water should be sprayed to prevent dust from rising but care should be taken not to over spray. However, the structure and height of a fence has its limits when preventing solid waste dispersion. Therefore, it would be more effective if the solid waste is divided into dispersible and non-dispersible waste when it is delivered into the landfill. If that is not possible, then the landfill area should be controlled and covered immediately. Fences are constructed for preventing illegal trespassing, littering as well as to camouflage the unsightly site. The fences must be strong against the wind but from the cost effectiveness point of view, a height of less than 3m should be sufficient. In the landfill site where there are a lot of trees, these may also be used as a fence or buffer zone. (c) Notice Boards, Doors/Gates, Etc Notice board must be built to clearly indicate the purpose of the landfill site. The following items must be clearly marked. Figure 7.2 shows a typical design for notice board.




Name: Bakoteh Sanitary Landfill Site Generic Type of Waste Landfill Period From To Supervisor Contact Address

Figure 7.2 Typical Notice Boards

Doors/Gates must be built at all entrances or exits to the landfill site. At the end of a day’s work, they must be closed and locked. (d) Fire Prevention Facilities Fires at the sanitary landfill system usually spread out because of the generation of methane gas. To prevent outbreaks of fire, it is therefore advisable that gases generated must be removed as fast as possible. By releasing the gas into the atmosphere, explosion can be prevented. Fires may start due to gas leakage from within the ground via cracks or holes in a landfill site and glass pieces in the waste may act as tiny lenses to focus the sun’s energy and start fires. It should be noted that if water is poured into the gas venting pipes, very dangerous subterranean explosion might occur. Fire breaks must be build around the landfill areas, water, sand, etc. should be provided. Stockpiles of cover soil must be made available such that when a fire breaks out, the fire can be extinguished by covering it and stopping oxygen from reaching the fire. Dump trucks, dozer shovels etc. should also be used when necessary. Extinguishing of fires at the initial stages is most important. As such daily routine inspection is important. Fire drills must also be regularly arranged.




7.3 Landfill Works

7.3.1 Landfill Works The landfill works means the whole series of works, which include the delivery of solid waste into the landfill site, spreading mixing, final cover soil and all those related temporary measures. A summary of this is shown in Table 7.8 and this includes landfill works, cover soil works, road works as well as constructing the load slopes.

Table 7.8 Landfill Works

Major Work Items Land Filling Land-filling method

Order of land-filling Spreading and compaction

Covering Daily cover Intermediate cover Final cover Selection of cover material Application of cover material Control of cover soil

Landfill Works

Access road Main road Branch road

The solid waste is placed within the landfill site so as not to cause environmental problems in the sanitary landfill system. Stabilization of the landfill layer must also be promoted. At the same time, it would also be important that effective and economic solid waste disposal within a limited landfill space be considered. Natural Conditions such as the surrounding environment, geography of the land fill site, weather, the type and amount of solid waste generated per day, financial and technical aspects, etc. have to be considered before proceeding with the landfill work.

7.3.2 Landfill Method The method and order of landfill must be carefully selected so as to improve stabilization on the landfill, create a physically strong foundation and improve the usability of completed landfill site. At the same time, proper landfill equipment must be used to sufficiently compact the landfill waste. To improve the potential usage of the completed landfill site, separate landfill methods should also be used when necessary. Data on the amount and type of landfill solid waste, their changes with time should also be noted for future reference or for maintenance of the landfill.




7.3.2.1 Landfill Method • Area Method The area method is used when the terrain is used when the terrain of one lift (2-3m) is first constructed to get the support for compaction. The waste is unloaded at the toe of the earth dike and spread and compacted on the slope of the dike in a series of layers that vary in depth from 30 cm to 60 cm. The recommended slope of these layers is 1 to 3. The width of the working face should be as narrow as possible to confine the waste to the smallest possible area but at the same time it should be wide enough to give necessary manoeuvrability to bulldozers. At end of each day’s operation a 15 cm to 30 cm layer of cover soil is placed over that day’s completed fill. This one-day’s completed fill including the cover soil is called a cell. When all the area is covered by one layer of cells it is called a lift. One more lift can be constructed on the top of the preceding lift whenever it does not surpass the final topography set by the design.

Figure 7.3 Area Method




7.3.2.2 Cell Construction • Cell Method This method, shown in Figure 8.5-8 has a cell of solid waste topped with a layer of cover soil and is the most popular method today. The size of each cell is determined by the amount of solid waste used per day. Since each cell is an independent landfill area, each cell acts as a fire-breaker. It also prevents the solid waste from being scattered emission of bad odours and harmful vectors from breeding. The disadvantage is that gas generation and water flow within the landfill will be hindered.

Figure 7.4 Cell Method

7.3.2.3 Order of Landfill • Order of Landfill on Landfill Site The order of landfill can either be from ‘upstream down’ or from ‘downstream up’. In the former method, easy access to the landfill via the already filled-up area is possible. However the rain water absorbed into the inner landfill layers during the early stages of landfill may be difficult to remove resulting in slipping of the landfill layer. This sometimes may result to damage of the liners. On the other hand, the latter method, which is proposed, enjoys these points that are demerits in the former method.




• Spreading and Compaction This is depicted in Figure 7.5 where the solid waste is dumped from the collection vehicles, “Pushed Up” a slope by bulldozer or a loader. The landfill layer should be made as uniform as possible and when necessary, the solid waste can be pushed up a slope when separating and compacting the solid waste. A slope gradient of (about 3:1 about 20 degrees) is normal The spreading and compaction is shown in Figure 7.6 and Figure 7.7.

Figure 7.6 Spreading/Compaction Method

Figure 7.7 Pushing up and compacting the waste simultaneously




7.3.2.4 Landfill Equipment • Selection of Landfill Equipment Landfill equipment is selected after considerations to the land structure, size of landfill, landfill method, soil, and waste in the sanitary landfill system. Landfill machines can be classified according to their functions into the following:

o Equipment to spread and compact a landfill layer of uniform thickness o Excavation, cover soil and spreading equipment. o Other machines required for smooth landfill operations.

Tractor such as crawler tractors and wheel tractors are usually used for the first two operations. The crawler tractor is called a bulldozer or tractor shovel depending on the type of arm attached to the crawler tractor like for instance, buckets or blades. These have different purposes. Some generalized information on the performance of landfill equipment is summarized in Table 7.9.

Table 7.9 Performance Characteristics of Landfill equipment

Solid Waste Cover material Equipment Spreading Compacting Excavating Spreading Compacting Hauling

Crawler tractor Wheeled compactor Scraper

EENA

GENA

EPG

EF-G E

GENA

NA NA E

Rating key: E, Excellent; G, good; F, fair; NA, not applicable. Besides the above, equipment relevant to the third operation like watering trucks, disinfecting trucks, fire fighting trucks etc. may also be required on large scale landfill sites. 7.3.2.5 Cover Soil • Efficiency and necessity of Cover Soil The cover soil prevents diffusion of bad odour, the littering, flowing out of water and breeding of vectors and other animals. It also prevents fire from spreading. Cover soil also provides a good appearance as it acts as a means of protecting the environment. Further, it also allows easy waste spreading and compaction and prevents rainwater from seeping into the inner layers of the landfill site (thus reducing laechate volume). However, when a large amount of cover soil is used, the capacity of landfill becomes smaller and it also reduces the permeability of the landfill such that the filled-up waste may not decay. The availability of cover material may depend on the location and condition of the landfill site and the financial capability of the operator. If new cover soil material is not




available, the old filled-up waste buried for about 3 to 6 months can be utilized effectively as cover soil. The filled up waste should never be left as it is. It must always be covered with a soil whose thickness depends on the type of waste and cover soil used. Cover soil must be laid in a specified area to prevent gas dispersion, fire and also for movement of collection vehicles, when necessary. A final cover must be laid on the top most layer of the landfill site. In this case, the thickness of the final cover soil depends on the way in which a competed landfill site is used. Cover soil material should be selected depending on its purpose. The cover soil must properly cover the landfill wastes, sufficiently spread and compacted with a proper thickness and gradient in specified places. • Type of cover soil Depending on the purpose, cover soil can be classified into daily, intermediate and final cover soil. • Daily cover soil When the landfill layer has reached the specified thickness or when one day’s portion of the landfill works is complete, a cover is laid to prevent:

Littering of wastes Bad odour Harmful vectors like flies from breeding. • Intermediate cover soil This is laid as the landfill work progresses. Unlike the daily cover soil, this is laid to create the foundation for roads for the collection vehicles or for draining rain water away from those landfill sites which are to be left for considerably long period. • Final cover soil When all the landfill works have finished, this top most final cover soil is laid, bearing in mind that the post closure land use of the completed landfill site, and leachate volume reduction purposes.




• Selection of cover soil In general cover soil is classified into grainy type and clayish type. The consistency or the permeability of the cover soil will then differ according to different types used. In most cases, earth is used, as this is easily available. As far as possible, extremely acidic or alkaline types of soil should be avoided, or those that contain harmful substances, or even anything that deteriorates the leachate quality. Earth that contains substances that are harmful to plants should also be avoided. The different types of soils are listed below:

o Daily cover soil As far as possible, permeable and porous sand types should be used to reader easy compaction of the solid waste, stabilise the landfill layer as well as not hinder waste decomposition. The thickness of the daily cover soil when the solid waste is mainly combustible and large in size is 300 to 500 mm while for crushed waste and ash is 150 to 200 mm. When uncrushed waste is used, it should be about 450 mm thick while crushed waste cover soil should be about 200 mm thick.

o Intermediate cover soil Clayey soil is suitable to prevent gases from dispersing or rainwater seeping but when the cover soil is to be used as a foundation for roads then crusher stones are recommended. When the cover soil is to be exposed for a fairly long time the thickness should be about 500 mm.

o Final cover soil The thickness of the cover soil is determined by the expected final land use, solid waste landfilled, landfill structure used, environmental conservation etc. When impermeable soil such as silt or clay is used, the cover soil should be as thin as possible. When planting grass or low plants and bushes, the final cover soil should be more than 500 mm. When medium height to tall trees are planted the thickness should be more than 1m. Until the time when the landfill site can be used as a completed landfill site, the proper cover thickness should be laid for trees planting. • Cover Soil Works and Maintenance

The cover soil must be uniformly spread and compacted by using the appropriate type of landfill equipment depending on the thickness of the cover soil, the area and quality. In particular, it takes some time before the final cover soil on a slope stabilizes and as such, care must be taken to prevent this final layer from being eroded by rainwater.




One measure is to have a gradient of about 2 to 3%. Cover soil is usually laid with the help of landfill layer, spreading and compaction equipment. But in the case of the final cover soil, graders or rollers used in making roads are suitable. Cover soil maintenance is a part of landfill site maintenance, besides leachate and gas treatment, etc. The surface of the final cover soil may settle, crack and form potholes. This will result in potential increase in leachate volume, gas leakage, erosion of the cover soil, landslides, fires, etc. In particular, when the surface of the landfill site depresses or cracks, rainwater will seep into the inner layer via these areas thus potentially increasing the amount of estimated leachate volume. These areas will also be the points for gas release and for these reasons; the surface of the final cover soil should always be checked and repaired.




ANNEXE 1 Landfill Leachate Evaluation




Table A Landfill Leachate Evaluation

landfill Leachate Production

1. Waste Quantities

a. Waste deposited per day 254 tons

b. Number of operating days 300

c. Waste deposited per year, kg 7.62E+07 kg

2. Waste Characteristics

a. Compacted specific weight of the waste 600 kg/m3

b Initial moisture content of the waste 20%

c. Assume no sludge will be deposited with the waste

3. Landfill Characteristics

I General

a. Lift Height 3 m

b Waste to cover ratio 6:1 by Volume

c Number o Lifts 2

ii Cover Material

a. Soil Specific weight 1800 kg/m3

b Moisture content of the Soil is assumed to be at

field capacity

iii Gas Production

a. Water consumed in the formation of landfill gas 0.16 kg/m3

b Water present as water vapour in the landfill gas 0.016 kg/m3

c Specific weight of landfill gas 1.34 kg/m3

iv Field Capacity

FC=0.6-0.55{W/10000+W]

FC=Fraction of water in the waste based on dry

Weight

W= Overburden weight calculated at the midheight

of the waste in the lift,

4 Rainfall Quantities




a Annual Rainfall that infiltrates the daily cover 787 mm/yr

a Annual Evaporation 772 mm/yr

Net rainfall 14 mm/yr

Calculation

a Determine the weight of cover material and solid

waste in each lift

Weight of Cover Material 1800*3*1/7 771.4 kg

Weight of Solid waste 600*3*6/7 1542.9 kg

Total weight of lift 2314.3 kg

b Dry weight of solid waste 1542.9*0.80 1234.32 kg

c Moisture content in solid waste 1542.9*0.20 308.58 kg

d Weight of effective rainfall entering landfill

Rainfall weight 14 kg

e Total weight of lift 1556.9

2 Prepare a water balance for lift 1 at end of year 1

and determine the quantity of leachate to be

expected from lift 1

a Gas produced 0 m3

Weight of gas produced 0 m3

b Weight of water consumed in the production of 0 kg

landfill gas

Weight of water consumed 0 kg

c Weight of water vapour in the gas 0 kg

Weight of water vapour 0 kg

d Weight of water in the solid waste in lift 1 322.58 kg

weight of water 322.58 kg

e Dry weight of solid waste remaining in lift 1 at the

end of year 1

Dry weight of solid waste 1234.32 Kg

f Average weight on the waste placed in lift 1.

Note: the average weight in lift 1 will occur at the

midpoint of waste in lift 1

Average weight: 0.5X(1234.32+1095.58)+771.4 1936.35 kg

g Field capacity 0.578




h Amount of water that can be held in the solid waste

Water held in solid waste in Lift 1 0.578x1234.32 713.4 kg

I Amount of leachate formed

Leachate formed: Actual water in solid waste-field

capacity of solid waste 324.58-713.4 -388.82 kg

Because the field capacity of the waste is greater

than the actual amount of water present in the

waste, no leachate will form.

j Determine the amount of water remaining in lift 1 at the end of year 1

Water remaining 322.58 kg

k Determine the total weight of lift 1 at the end of year 1

Total weight of lift=dry waste+water remaining+ cover 2328.3 kg

3 Prepare a water balance for lift 1 at end of year 1

and determine the quantity of leachate to be

expected from lift 1

a Gas produced:0.03m3/kg waste converted 37.03 m3

Weight of gas produced: 49.62 kg

b Weight of water consumed in the production of

landfill gas 5.92 kg

c Weight of water vapour in the gas 0.59 kg

d Weight of water in the solid waste in lift 1 at end of

year 2

Wt of water 316.1 kg


end of year 2





Average weight 3853.1 kg





Leachate formed: Actual water in solid waste-field capacity of solid waste -98.3 kg







j Determine the amount of water remaining in lift 1 at the end of year 1

Water remaining 322.58 kg

k Determine the total weight of lift 1 at the end of year 1

Total weight of lift=dry waste+water remaining+ cover 2284.6 kg

4 Prepare a water balance for lift 1, 2 and final lift at

end of year 3 and determine the quantity of leachate

to be expected from lift 1

a Gas produced:0.032m3/kg waste converted 39.50 m3

Weight of gas produced: 52.93 kg

b Weight of water consumed in the production of

landfill gas 6.32 kg

c Weight of water vapor in the gas 0.63 kg

d Weight of water in the solid waste in lift 1 at end of

year 3

Wt of water 256.8 kg


end of year 3





Average weight 6106.7 kg





Leachate formed: Actual water in solid waste-field capacity of solid waste 324.58-713.4 -81.7 kg







Estimate total leachate quantities

Total weight of solid waste placed in a landfill lift 1542.9 kg/m2.yr

that is one meter square and 3m high

Total area occupied by each lift expressed in meter

square is

Total area : (76.2x108 kg/yr)/(1542.9kg/m2.yr) 4.94E+04 m2

Leachate obtained from the entire landfill (4,034,208) m3/year

A negative value indicates water is required to maintain precipitation/evaporation balance.




Table B Rainfall Data

Jan feb Mar april may June July aug sep Oct Nov Dec Annual1977 0.0 0.0 0.0 0.0 0.0 0.0 10.5 222.0 296.0 49.8 0.0 0.0 578.31978 0.0 0.0 0.0 0.0 70.2 337.0 403.0 213.0 66.1 42.9 0.0 1132.21979 24.5 0.0 0.0 0.0 1.3 217.0 261.0 244.0 131.0 0.0 0.0 4.9 883.71980 0.0 0.0 0.0 0.0 0.0 6.4 74.4 225.0 320.0 0.0 0.0 0.0 625.81981 0.0 0.0 0.0 0.0 11.6 41.9 229.0 244.0 103.0 34.9 0.0 0.0 664.41982 0.0 0.0 0.0 0.0 0.0 16.3 312.0 436.0 140.0 40.3 0.0 0.0 944.61983 0.0 0.0 0.0 0.0 0.4 21.1 89.0 236.0 77.5 1.7 0.0 0.0 425.71984 0.0 0.0 0.0 0.0 0.0 173.0 140.0 137.0 213.0 18.0 0.7 0.0 681.71985 0.0 0.0 0.0 0.0 0.0 29.1 205.0 288.0 286.0 21.4 0.0 3.8 833.31986 0.0 0.0 0.0 0.0 0.0 20.6 85.8 297.0 217.0 56.5 0.0 0.0 676.91987 0.0 0.0 0.0 0.0 0.0 60.6 135.0 287.0 279.0 82.1 0.0 0.0 843.71988 0.0 0.0 0.0 0.0 6.6 40.7 364.0 428.0 231.0 55.2 0.0 0.0 1125.51989 0.0 0.0 0.0 0.0 0.0 146.0 113.0 287.0 290.0 61.3 0.0 0.0 897.31990 0.0 0.0 0.0 0.0 0.0 1.2 128.0 353.0 149.0 17.9 0.0 0.0 649.11991 0.0 0.0 0.0 0.0 0.0 0.0 168.0 286.0 404.0 40.2 0.0 0.0 898.21992 0.0 0.0 0.0 0.0 36.7 42.7 247.0 349.0 199.0 33.1 0.0 0.0 907.51993 0.0 0.0 0.0 0.0 0.0 2.6 194.0 183.0 192.0 65.3 0.0 0.0 636.91994 0.0 0.0 0.0 0.0 0.0 0.6 211.0 564.0 381.0 129.0 0.0 0.0 1285.61995 0.0 0.0 0.0 0.0 0.0 0.0 277.0 124.0 0.0 0.0 401.01996 0.0 0.0 0.0 0.0 0.0 0.0 139.0 25.5 0.0 0.0 164.51998 0.0 0.0 0.0 0.0 0.0 3.7 109.0 241.0 216.0 18.1 0.0 0.0 587.81999 0.0 0.0 0.0 0.0 0.0 62.4 105.0 595.0 153.0 97.7 0.0 0.0 1013.12000 0.0 0.0 0.0 0.0 0.0 48.3 349.0 294.0 292.0 92.6 0.0 0.0 1075.92001 0.0 0.0 0.0 0.0 0.0 80.3 348.0 276.0 193.0 52.7 22.3 0.0 972.32002 0.0 0.0 0.0 0.0 0.8 62.3 91.0 480.0 173.0 39.8 0.0 0.0 846.92003 0.0 0.0 0.0 0.0 0.0 110.0 109.0 147.0 264.0 88.5 0.0 0.0 718.5

0.9 0.0 0.0 0.0 2.2 48.3 183.9 312.6 224.2 50.5 2.5 0.3 787.3




Table C Evaporation Data

Jan feb Mar april may June July Aug sep Oct Nov Dec Annual1977 0.0 0.0 0.0 0.0 0.0 13.6 87.7 162.0 242.0 38.3 0.0 0.0 543.61978 0.0 0.0 0.0 0.0 0.0 57.3 262.0 428.0 200.0 127.0 14.4 28.1 1116.81979 12.0 0.0 0.0 0.0 9.2 126.0 282.0 188.0 150.0 68.7 25.2 6.2 867.31980 0.0 0.0 0.0 0.0 0.3 14.0 49.9 204.0 345.0 16.1 0.0 1.6 630.91981 0.0 0.0 0.0 0.0 10.1 29.2 126.0 236.0 39.4 76.3 0.0 0.0 517.01982 0.0 0.0 0.0 0.0 6.1 41.4 290.0 388.0 116.0 54.0 0.0 0.0 895.51983 0.0 0.0 0.0 0.0 0.0 14.5 116.0 116.0 89.2 21.8 0.0 0.0 357.51984 0.0 0.0 0.0 0.0 0.0 99.8 101.0 246.0 69.0 52.1 17.6 0.0 585.51985 0.0 0.0 0.0 0.0 0.0 84.5 277.0 311.0 233.0 23.5 0.0 3.8 932.81986 0.0 0.0 0.0 0.0 0.0 22.9 54.5 286.0 241.0 92.3 0.0 0.0 696.71987 0.0 0.0 0.4 0.0 0.0 68.4 155.0 394.0 218.0 61.9 0.0 0.0 897.71988 0.0 0.0 0.0 0.0 8.0 31.8 232.0 510.0 181.0 68.1 0.0 0.0 1030.91989 0.0 0.0 0.0 0.0 0.0 123.0 192.0 199.0 354.0 30.5 0.0 0.0 898.51990 0.0 0.0 0.0 0.0 0.0 3.7 110.0 382.0 179.0 40.6 0.0 0.0 715.31991 0.0 0.0 0.0 0.0 0.0 0.0 158.0 355.0 128.0 52.7 0.0 0.0 693.71992 0.0 12.1 0.0 0.0 49.1 34.0 184.0 280.0 279.0 38.9 0.0 0.0 877.11993 0.2 0.7 0.0 0.0 0.0 5.3 144.0 261.0 144.0 47.3 0.0 0.0 602.51994 0.0 0.0 0.0 0.0 0.0 15.3 308.0 213.0 267.0 122.0 0.9 0.0 926.21995 0.0 0.0 0.0 0.0 0.0 71.9 279.0 317.0 210.0 118.0 0.0 4.2 1000.11996 0.0 0.0 1.5 0.0 0.0 56.6 227.0 147.0 131.0 28.8 0.0 0.0 591.91997 0.3 0.0 0.0 0.0 0.0 129.0 73.7 297.0 310.0 22.3 0.0 0.0 832.3

0.6 0.6 0.1 0.0 3.9 49.6 176.6 281.9 196.5 57.2 2.8 2.1 771.9




ANNEXE 2 Soil Investigation Results

The Gambian Agency for the Management Preliminary and Detailed Engineeringof Public Works (GAMWORKS) Design Study for Bakoteh Dump Site

Charchi Githinji & Partnersin association with


Table D Summary of soil investigation laboratory test results

GRADATION REMARKSTrial pit Location

DepthSampleNo

MaximumDry DensityKg/m3

OptimumMoisture%

LiquidLimit

Plasticlimit

P/I LinearShrinkage

Insitu.Density

Percentagepassing sieve2.36mm

Percentagepassing sieve No.75 Microns (claycontent)

2 BDS * 1 – – 28 13 15 6 – 84 30

1700mmBDS * 2 – – 32 14 18 7 – 81 29

–

–

3BDS *

2300mm 1 – – 19 Non Plastic – 100 7A uniform medium to fine sand.

2 750mm 2 1981 8.50 25 12 13 6 – 77 21Greyish gravel with bouldersmixed with clayey silty sand.

3 850mm 2 1860 16.40 22 11 11 5 – 77.00 17

From stock on site Fill 1990 11.00 27 15 12 5.4 – 91.00 36 Proposed fill materials.

* BDS (Bakoteh Dump Site)

Permeability Range 10-2 – 10-5 mm S-1 (Trial pit 2 & 1 for sample Nos. 1 & 2)




TRIAL PIT 1 SOIL PROFILE.

150mm Dark Agricultural Soil

650mm Greyish Gravel with boulders mixed with clayey silty sand

600mm Reddish silty sand with pebbles and about 25% silt and clay

710mm (Red silty sand with clay and pebbles

Level of water table

2110m




TRIAL PIT 2: SOIL PROFILE

220mm Dark fibrous organic Soil

1330mm Greyish Gravel with boulders cemented together with sandy clay material.

1650mm Mixture of Red and Grey sandy clay

Water table level at 3200mm

3200m






850mm Greyish Gravel with boulders interspersed with sandy clay with silty.

1080mm Reddish gravel with sandy clay

400mm Sandy clay (low plasticity) with pebbles

Bottom of trial pit

Level of water table

2500m






11050mm Greyish Gravel with silty clay.

1500mm Reddish gravel silty clay

300mm Greyish silty clay with pebbles

water table

3.20m




ANNEXE 3 Workshop Report wb12009 C:\Documents and Settings\WB12009\My Documents\E1152.doc 03/05/2005 10:26:00


