ESIA

SFG1405 v4

ATHI WATER SERVICES BOARD

CONSULTANCY SERVICES FOR A FEASIBILITY STUDY AND DETAILED DESIGN FOR SEWERAGE SYSTEM IN JUJA AND THIKA MUNICIPALITY

(PHASE II)

ENVIRONMENTAL AND SOCIAL IMPACT ASSESSMENT STUDY REPORT FOR THE PROPOSED SEWERAGE SYSTEM IN JUJA AND THIKA SOUTH.

FRAME Consultants Ltd

Consulting Civil, Structural & Geotechnical Engineers

Pension Towers, Loita Street

P.O. Box 58624-00200, Nairobi - Kenya,

Tel: 020 2213744/2251505

Fax: 020 2213990

E-mail: info@frameconsultants.com

Website:www.frameconsultants.com

Athi Water Services Board

Africa Re-Centre 3rd Floor, Hospital Road

P.O Box 45283-00100 Nairobi, Kenya

Tel: 254 020 2724292/3

Fax: 254 020 2724295

Email: info@awsboard.go.ke

Website: www.awsboard.go.ke

AUGUST 2015

AWSB in Partnership with MLHUD Consultancy Services for a Feasibility Study and Detailed Design for Sewerage System in Juja &Thika (Phase II)

FRAME Consultants Ltd 80 ESIA Report

TABLE OF CONTENTSAcronyms and Abbreviations3STUDY AUTHENTICATION4NON TECHNICAL EXECUTIVE SUMMARY51.0 INTRODUCTION131.1 BACKGROUND131.2 THE PROPONENT141.3 PROJECT LOCATION152.0 ANALYSIS OF ALTERNATIVE FOR THE PROPOSED PROJECT172.1 INTRODUCTION172.2 ANALYSIS OF ALTERNATIVE FOR THE TRUNK SEWERS172.3 ALTERNATIVE SITES FOR SEWAGE TREATMENT WORKS202.4 ANALYSIS ALTERNATIVES FOR SEWAGE TREATMENT PROCESSES282.5 THE “NO PROJECT ALTERNATIVE” OPTION302.6 SEWERAGE SCHEME312.7 PROPOSED PROJECT DESCRIPTION312.8 PROJECT ACTIVITIES AND COST383.0 PUBLIC PARTICIPATION AND RESPONSES413.1 INTRODUCTION413.2 CONSULTATION METHODOLOGY413.3 CONSULTATION OUTCOMES424.0 BASELINE INFORMATION464.1 INTRODUCTION464.2 TOPOGRAPHY AND HYDROLOGY464.3 CLIMATE474.4 TEMPERATURES484.4 RAINFALL494.5 EVAPORATION504.6 HUMIDITY504.7 SUNSHINE514.9 SOCIO-ECONOMIC CONDITIONS544.10 DISEASES554.11 EXISTING DOMESTIC WATER SUPPLY INFRASTRUCTURE554.12 EXISTING WASTE-WATER INFRASTRUCTURE574.13 BIODIVERSITY605.0 POLICY, LEGAL AND INSTITUTIONAL FRAMEWORK625.1 ENVIRONMENTAL POLICY FRAMEWORK625.3 WORLD BANK SAFEGUARDS TRIGGERED BY THE PROJECT756.0 POTENTIAL ENVIRONMENTAL IMPACTS AND MITIGATION MEASURES786.1 INTRODUCTION786.2 CONSTRUCTION PHASE ENVIRONMENTAL IMPACTS796.3 POTENTIAL IMPACTS ASSOCIATED WITH OPERATIONS876.4 ENVIRONMENTAL HEALTH AND SAFETY MANAGEMENT956.5 CLOSURE AND DECOMMISSIONING967.0 ENVIRONMENTAL AND SOCIAL MANAGEMENT PLAN997.1 INTRODUCTION997.2 CONSTRUCTION ENVIRONMENTAL, SOCIAL, MANAGEMENT AND MONITORING PLAN998.0 CONCLUSIONS AND RECOMMENDATIONS1228.1 RECOMMENDATIONS1238.3 REFERENCES124APPENDICES:120

List of Appendices

Appendix 1 : Frame Consultants Ltd Practicing License126

Appendix 2: Public Consultation Meetings129

Appendix 3 : List Of Paps176

Appendix 4 : Project Areas Location Map182

List of Tables

Table 1: Design Details of Waste Stabilization Ponds36

Table 2: Temperature Records48

Table 3: Rainfall Records49

ACRONYMS AND ABBREVIATIONS

AWSB Athi Water Services Board

CBSCentral Bureau of Statistics

ESIAEnvironmental Impact Assessment

DNMDDirectorate of Nairobi Metropolitan Development

MLHUD Ministry of Lands, Housing and Urban Development.

MEWNRMinistry of Environment, Water &Natural Resources.

WRMAWater Resources Management Authority

NAMSIP Nairobi Metropolitan Services Improvement Project

NEMA National Environmental Management Authority

RAP Resettlement Action Plan

RUJWASCO Ruiru-Juja Water and Sewerage Company

RFPRequest for proposal

RSPRuiru Sewerage Project

STWSewerage Treatment Works

THIWASCO Thika Water and Sewerage Company

ToRTerms of Reference

WASREBWater Services Regulatory Board

WaSSIPWater and Sanitation Services Improvement Project

WBWorld Bank

STUDY AUTHENTICATION

This ESIA was conducted by:

FRAME Consultants Ltd

Registration No.1711

Pension Towers, Loita Street

P.O. Box 58624, Nairobi-Kenya,

Tel:0202-2213744/2251505

Fax: 0202-2213990

Email: info@frameconsultants.com

Website: www.frameconsultants.com

Signed ………………………………………….Date………………………………

For and on behalf of:

Athi Water Services Board

Signed ………………………………………….Date………………………………

NON TECHNICAL EXECUTIVE SUMMARY

The aim of the proposed project is establishment of feasible and economical sanitation infrastructures and operational structure that adequately address the current, future and ultimate domestic, Industrial and Institutional Sewage demand for Juja Town & Thika Municipality.

Various alternatives (project site and waste water treatment options) were considered. The Preferred Alternative will entail construction of:

i. Six trunk sewer lines including Mugutha, Theta, Thirirka, Kamuguti, Ndarugu and Komu Trunk sewers.

ii. A sewerage treatment plant in Ruiru next to the upcoming STW located at 01°010’46.6”S, 037°01’23.2”E.

iii. Rehabilitation of Existing Thika STW & Construction of new Treatment works located at 01°005’34.1”S, 037°006’56.0”E.

iv. Installation of Jet waste water treatment plant in Ndarugu at 10 05’ 27.14” S; 370 01’ 15.58 E.

The proposed project will erect STW and trunk sewers in the project area. The proposal is informed by the following reasons.

· High incidences of water borne diseases reported at the local health facilities.

· High population growth as the trend shows. This should be matched by a commensurate expansion of waste water disposal infrastructure.

· Ground water pollution due to reliance on pit latrines needs to be checked. Ground water could supplement water supply in the area. As such a sewerage treatment would go a long way in safeguarding its quality.

· It is the right of the residents to have access to sound waste disposal system.

· The Water Service providers are bound by law to provide the facility.

The EIA was conducted mainly to comply with the existing environmental legislation primarily EMCA (1999), and Environmental (Impact Assessment and Audit) Regulations 2003 among others. Specifically, the study sought to:

· Identify possible impacts of the proposed project on the environment.

· Evaluate alternatives to the proposed project.

· Predict likely changes on the environment as a result of the development.

· Propose mitigation measures for the significant negative impacts of the proposed project on the environment

· Generate baseline data for monitoring and evaluation impact, including mitigation measures during the project cycle

· Highlight environmental issues with a view to guiding policy makers, planners, stakeholders and government agencies to make environmentally and economically sustainable decisions.

The EIA study team used a combination of tools to gather pertinent information for the study.

· Field visits to the proposed project site

· Documents analysis

· Key Informants Interviews

· Photography

· Barazas.

During the study, various positive socio-economic and bio-physical impacts that could result from the proposed project were identified. These include inter alia:

· Reduction of health risks associated with exposure of residents with improperly drained sewage in their surroundings.

· Reduction of water borne diseases resulting from possible microbial pollution of drinking water obtained from contaminated shallow wells, or through suction of contaminated water in water supply pipes through accidental negative pressures in water pipes.

· Improvement in groundwater quality through preventing infiltration of sewerage from porous cesspits.

· Improve living conditions for targeted residents through achieving the above environmental benefits, upgrade their real estate values and contribute in alleviating poverty conditions through work opportunities in construction and operation of the project

· Achieve economic benefit by saving some healthcare expenses, improving people’s productivity and improving water resources management.

· Strengthen community participation in environmental protection through involving community based organizations in project operation and mobilization activities.

· Employment of locals as skilled, semi-skilled and unskilled workers.

· Growth of secondary businesses in the project area.

· Enhanced growth of secondary business in project area.

· Increased revenues for the service providers.

Potential negative ecological and socio-economic impacts identified during the study and practical mitigation measures include:

POTENTIAL IMPACT

MITIGATION MEASURES

1. Air pollution

· A regular vehicle maintenance and repair program.

· Ensure that all vehicles involved in the transport of construction material and staff, and machinery involved in the construction is properly maintained and serviced.

· Machines must not be left idling for unnecessary periods of time; this will save fuel and reduce emissions.

· Use of dust control methods, such as covers, water suppression.

· Ensure that all material (sand and aggregate) stockpiled on the site to be used in construction activities are regularly sprayed to reduce the effects of wind whipping.

· Ensure that all trucks carrying aggregate and sand are covered during delivery to the site.

2. Water pollution

· Provide workers at the development site with chemical toilets during this phase of the development. A reasonable ratio would be fifteen (15) workers per toilet.

· Store all raw materials away from the vicinity of water bodies located on the property to avoid contamination in these areas.

· General refuse generated during these phases of the development must be stockpiled in one central area of the development site, away from existing water bodies and collected, transported and disposed of appropriately at the designated disposal site.

· Waste water Management

3. Soil erosion and contamination

· Only remove vegetation from areas for the STW/sewers construction ;

· Install appropriate drainage systems to direct water away from slopes;

· Designate a main access route for heavy machinery;

· Avoid site Preparation in period when wind velocities are highest.

· Areas storing hazardous substances such as diesel must be properly contained in a bunded area.

· In the event of an oil spill the contaminated soil must be removed and disposed off.

· Develop a spill management plan (with appropriate budget).

4. Solid wastes

· Use an integrated wastes management system.

· Agreement with suppliers to accept the return of unused materials.

· Agreement with and license details of companies to be used for the off-site transport of wastes

· The Contractor shall set up a solid waste control and removal system.

· Bins shall be emptied on a daily basis.

· Waste and litter shall be disposed of into scavenger – and weather proof bins.

· Agreement with the County government and for timely removal of solid waste.

5. Flora and fauna (biodiversity loss)

· Only clear vegetation that is absolutely necessary for the construction activities;

· Avoid the use of Invasive Alien Species in the landscaping activities

· Determine access roads which are to be used by machinery used in the construction and site clearance phase of the development to avoid the unnecessary trampling of vegetation that will be maintained within the development area.

· Ensure that ‘green belts’ which have been proposed for the STW are large as possible as small patches may not be able to support viable populations of some species and these small patches tend to more susceptible to edge effect

6. Disturbance of traffic and difficulty of access

· Provide diversion routes where possible.

· Give a construction itinerary in advance so that the potentially affected population can use alternative routes and start early to get to their destinations on time.

· Erect warning signs of ongoing works.

· Expedite construction works so as to reduce the times where roads are blocked.

· Access of residents should be facilitated by installing appropriate temporary bridges over the pipeline trenches.

· Suitable warning signs should be placed at near locations and should be visible at night.

· A guard should be available 24 hours to help people access across pipeline trenches.

7. Damage of underground infrastructure

· Get maps of the underground infrastructure from the relevant institutions.

· Sensitise workers carrying out excavations so that they exercise caution to minimize chances of underground infrastructure damage.

· Work closely with the responsible institutions such as Kenya Power, THIWASCO, RUJWASCO and Telkoms so that incase of damage, the services are restored within the shortest time.

· Reroute sensitive infrastructure where possible.

8. Structural stability

· The geotechnical report should include suitable measures for confining vibrations within project sites.

· These recommendations identified in the geotechnical report (such as secant piling or sheet piling or establish cut-off walls) should be implemented by the contractor and supervised by EHS Advisor.

· Blasting should not be done near houses or power lines.

9. Occupational accidents

· Ensuring that the drivers and machine operators hired to work on the site are qualified.

· Workers on site must be provided with appropriate PPE.

· Appropriate signs must be erected on the site to warn workers and visitors.

· Machines should be properly maintained.

· A first aid kit should be provided and a trained first aider should always be on site.

· Fire extinguishers should be provided.

· No worker should be allowed on site while under the influence of alcohol.

· Inspection of workers to ensure they are using the PPE at all times when necessary.

· Provide a fully stocked First Aid box on the site

10. Sanitation at contractor’s camp

· Toilet facilities supplied by the contractor for the workers shall occur at a minimum ratio of 1 toilet per 30 workers (preferred 1:15).

· Sanitation facilities shall be located within 100m from any point of work, but not closer than 50 m to any water body.

· All temporary/portable toilets shall be secured to the ground to prevent them toppling due to wind or any other cause.

· The contractor shall ensure that the entrances to toilets are adequately screened from public view.

· The contractor shall ensure that no spillage occurs when the toilets are cleaned or emptied and that the contents are removed from site to an approved disposal site.

11. Social conflicts

· Immediate action undertaken as soon as possible and within 24 hours of receipt of a complaint

· Investigations completed within seven days of receipt of complaint.

· All corrective actions implemented by due date

· All incidents or complaints about either environmental or social issues will be managed in accordance to the existing procedure in line with the legal framework.

· All incidents and complaints will be recorded in the contractors incident reporting system

· Maximize hiring of unskilled and skilled workers from the project affected communities.

12. Spread of HIV and AIDS

· Sensitize the migrant workers and local population on dangers of risky sexual behaviour.

· Have VCT services on site and encourage workers to undergo the same.

· Uptake of VCT by project workers and the host community.

· Provision of condoms to the workers.

· Maximize hiring of unskilled and skilled workers from the project affected communities.

13. Displacement of people

· Avoid displacement as much as possible.

· Prompt and fair compensation of all the PAPs before beginning of works on the site

· Pre and post resettlement counselling’s support : including timely information sharing and grievance redress.

· Financial education for the recipients of compensation funds including women in the HHs.

· Identification and full resettlement assistance for vulnerable PAPs.

14. Water and soil pollution from leaks and sewage overflow and leaks

· Awareness raising among community members not to dumpsolids that can cause blockage leading to bursts and spills.

· Ensure sufficient hydraulic capacity to accommodate peak flows and adequate slope in gravity mains to prevent build-up of solids and hydrogen sulphide generation;

· Design manhole covers to withstand anticipated loads and ensure that the covers can be readily replaced if broken to minimize entry of garbage and silt into the system;

· Development of an inventory of system components, with information including age, construction materials, drainage areas served, elevations, etc

· Regular cleaning of grit chambers and sewer lines to remove grease, grit, and other debris that may lead to sewer backups. Cleaning should be conducted more frequently for problem areas. Cleaning activities may require removal of tree roots and other identified obstructions

· Monitoring of sewer flow to identify potential inflows and outflows

· Conduct repairs prioritized based on the nature and severity of the problem.

· Immediate clearing of blockage or repair is warranted where an overflow is currently occurring or for urgent problems that may cause an imminent overflow.

· Citizens sensitization of the importance of monitoring and operational costs related to the sewer lines to promote security of the infrastructure and timely attention to need of repairs.

15. Accidents and injuries in STW

· Install railing around all process tanks and pits. Require use of a life line and personal flotation device (PFD) when workers are inside the railing, and ensure rescue buoys and throw bags are readily available;

· Use PFDs when working near waterways;

· Implement a confined spaces entry program that is consistent with applicable national requirements and internationally accepted standards.

· Valves to process tanks should be locked to prevent accidental flooding during maintenance;

· Maintain work areas to minimize slipping and tripping hazards;

· Use proper techniques for trenching and shoring;

16. Exposure to hazardous chemicals

· Implement a training program for operators who work with chlorine and ammonia regarding safe handling practices and emergency response procedures;

· Provide appropriate personal protective equipment and training on its proper use and maintenance.

· Prepare escape plans from areas where there might be a chlorine or ammonia emission;

· Install safety showers and eye wash stations near the chlorine and ammonia equipment and other areas where hazardous chemicals are stored or used;

· Communicate escape plans on the regular basis to the relevant stakeholders

· Continuously monitor air quality in work areas for hazardous conditions (e.g. explosive atmosphere, oxygen deficiency);

· Prohibit eating, smoking, and drinking except in designated areas;

· Rotate personnel among the various treatment plant operations to reduce inhalation of air-stripped chemicals, aerosols, and other potentially hazardous materials.

17. Liquid effluents

· Design, construct, operate, and maintain wastewater treatment facilities and achieve effluent water quality consistent with applicable national requirements or internationally accepted standards and consistent with effluent water quality goals based on the assimilative capacity and the most sensitive end use of the receiving water;

· Consider discharge of treated wastewater to natural or constructed wetlands, which can buffer the impact from discharge on the aquatic environment, unless the wetland itself would be degraded by the discharge;

· Treat greywater, if collected separately from sewage, to remove organic pollutants and reduce the levels of suspended solids, pathogenic organisms and other problematic substances to acceptable levels based on applicable national and local regulations.

· Based on an assessment of risks to human health and the environment, consider re-use of treated effluent, especially in areas with limited raw water supplies.

· Monitoring the effluent quality through sampling and laboratory analysis.

18. Sludge disposal

· Select appropriate sludge treatment technologies

· Develop and Implement faecal sludge management plan

· Land application or other beneficial re-use of wastewater treatment plant residuals should be considered but only based on an assessment of risks to human health and the environment.

· Processing, disposal and re-use of wastewater treatment plant residuals should be consistent with applicable National requirements or, in their absence, Internationally accepted guidance and standards.

19. Offensive odours

· Provide adequate buffer area, such as trees, or fences, between processing areas and potential receptors;

· Cover emission points (e.g., aeration basins, clarifiers, sludge thickeners, tanks, and channels), and vent emissions to control systems (e.g., compost beds, bio-filters, chemical scrubbers, etc.) as needed to reduce odours and otherwise meet applicable national requirements and internationally accepted guidelines;

· Where necessary, consider alternate aeration technologies or process configurations to reduce volatilization.

· Proper operations and maintenance of the STW.

· Monitoring daily to ensure pH is optimum for proper functioning.

· Fill the facultative ponds with fresh water before commissioning.

20. Health risks related to irrigation with treated sewage

· Consider use of drip irrigation of treated wastewater, which minimizes worker exposure and the amount of water needed.

· Control vectors and intermediate hosts of disease-causing micro-organisms.

· Treat wastewater and sludge used for land application in a manner consistent with WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater and applicable national requirements;

· Stop irrigation with treated wastewater two weeks prior to harvesting;

· Limit irrigation with treated wastewater to crops that are cooked before eating;

· Restrict public access to hydraulic structures carrying wastewater and to fields irrigated with treated wastewater.

21. Wildlife and scavenger birds attractions to the STW.

· Proper fencing of the Plant to keep off wildlife is recommended

· Maintaining high standards of hygiene at the site throughout the operation phase of the facility

· Constant consultations with KWS in event that wildlife is spotted in the area.

· The inlet works should be enclosed in a building to avoid exposure to birds

· Daily Burying of the wastes in appropriate solid Waste disposal section covering with soil, this reduces the tonnage of wastes on site and exposing the wastes to scavenging birds

22. Risks of sewers clogging

· Sensitisation of users to avoid disposing solids in the sewers.

· Constant monitoring of sewer lines.

· Flushing the system to unblock the lines.

1.0 INTRODUCTION1.1 BACKGROUND

There is a growing concern in Kenya and at global level that many forms of development activities are causing damage to the environment. Development activities have the potential to damage the natural resources upon which the economies are based. A major national challenge today is how to attain sustainable development. It is now accepted that development projects must be economically viable, socially acceptable and environmentally sound. To balance economic goals and ecological imperatives, certain tools have been developed over time. Environmental and Social Impact Assessment (ESIA) is such one tool.

Environmental impact assessment is management tool for the protection of the environment from the negative effects of development activities. With roots in the EPA Act of 1969 in the United States, ESIA application has spread worldwide. Although different political jurisdictions have their own legal and administrative requirements in ESIA application, there are accepted cardinal principles which inform the ESIA process no matter the jurisdiction.

In Kenya, ESIA can be considered a relatively young entrant in environmental management. It became compulsory after the enactment of Environmental Management and Coordination Act, 1999 (EMCA). According to, EMCA, 1999 and its subsequent Environmental (Impact and Audit) Regulations, 2003, it is mandatory to get environmental clearance for certain development projects. Among these projects are; rivers and water resources development and waste disposal projects including:

i. Storage projects, barrages and piers;

ii. Rivers diversions and water transfers between catchments; flood control schemes;

iii. Drilling for the purpose of utilizing ground water resources including geothermal energy.

iv. Sites for hazardous waste disposal;

v. Sewage disposal works;

vi. Works involving major atmospheric emissions;

vii. Works emitting offensive odours;

viii. Sites for solid waste disposal.

(EMCA, 1999, Second Schedule; Part IV.)

The proposed sewerage project thus falls under projects which must undergo an environmental impact assessment before implementation.

1.2 THE PROPONENT

Athi Water Services Board (AWSB) is one of the eight Water Services Boards under the Ministry of Environment, Water and Natural Resources created to bring about efficiency, economy and sustainability in the provision of water and sewerage services in Kenya. AWSB is created under Section 51 of the Water Act 2002. AWSB is currently serving a population of over 4.5 million people.

The Board ensures the provision of quality and affordable water and sewerage services in its area of jurisdiction through its twelve (12 No.) appointed Water Services Providers (WSPs) namely:

· Nairobi Water and Sewerage Company

· Thika Water and Sanitation Company

· Limuru Water and Sewerage Company

· Ruiru-Juja Water and Sanitation Company

· Runda Water Ltd

· Kikuyu Water Company

· Karuri Water and Sanitation Company

· Gatundu Water and Sewerage Company

· Githunguri Water and Sewerage Company

· Gatanga Community Water Scheme

· Kiambu Water and Sanitation Company

· Karimenu Community Water and Sanitation Company

The Proponent is a product of the reforms initiated in the Water Sector after enactment of Water Act 2002 to provide for the enabling legal and institutional framework for more effective management, conservation, use and control of water resources. The National Water Policy has four broad objectives: -

· To preserve, conserve and protect available water resources and allocate them in a sustainable rational and economic way,

· To supply water of good quality and in sufficient quantities to meet the various water needs,

· To establish an efficient and effective institutional framework to achieve a systematic development and management of the water sector, and

· To develop a sound and sustainable financing mechanism for effective water resources management.

1.3 PROJECT LOCATIONThe proposed project straddles between Juja and Thika towns.Juja town is located in Thika West District in Kiambu County, 10 km South-East of Thika Town and 12km North-West of Ruiru, latitudes -1.1833 and Longitude 37.1167 about 30km North of Nairobi. It is the administrative centre for Jomo Kenyatta University of Agriculture and Technology (JKUAT).

The project area can be accessed through the A2 (Nairobi – Thika) dual highway or the Nairobi – Nanyuki railway line. The northern boundary of Juja is the Komu River, whilst the southern boundary is the Theta- Thiririka Rivers. The eastern boundary is the Nairobi-Athi Rivers.

The Thika Municipality is situated in Thika West District, Kiambu County, approximately 45 km North-East of Nairobi. It stretches approximately 24km in an east-west direction and tapers from a width of about 2.5km on western side to 5.0km on the Eastern edge. The total area of the municipality is 93km2. The main Nairobi/Nyeri road, which runs in a north-south direction, dissects the Municipality just to the west of the commercial and administrative centre of the town.

The northern and southern boundaries of Thika Municipality are well demarcated by rivers which flow in an easterly direction. The Karimenu-Chania-Thika Rivers form the northern boundary while the Komu Rivers forms the Southern boundary.

The STW will be located on public land. This includes Gatongo’ra in Ruiru next to Phase I and next to the existing Thika STW. In this case then there will be no compensation. Trunk sewers will run along road and riparian reserves to minimise displacement. Where this cannot be avoided or the reserves have been encroached, compensation as per the law will be made.

Project location maps are attached as Appendix 4

Location of Project Area

2.0 ANALYSIS OF ALTERNATIVE FOR THE PROPOSED PROJECT 2.1 INTRODUCTION

The project area is at different stages of development and it is therefore prudent to stage the development of the sewerage systems to follow suit. Provision of a sewerage system will require the construction of a reticulation system to serve areas that are either already developed or are in the process of development.

2.2 ANALYSIS OF ALTERNATIVE FOR THE TRUNK SEWERS

The natural drainage system has been used as a basis of design of the trunk sewer system. The trunk sewers have been located at the lower drainage boundaries as much as permissible so as to maximize sewage collection from feeder lines. Some trunk sewers drain into treatment works whilst some drain to other larger trunk sewers.

The sewer routes as were identified during the detailed survey by the consultant together with a representative of the county government have been adopted in the design. Proposed sewers have been routed on rivers riparian, road reserves and utility way-leaves as much as possible. Main sewers have been provided for areas currently served with piped water and those with the potential of being served with piped water soon, as identified.

The following trunk sewers have been identified in the project area using the natural drainage patterns;

i.Mugutha River Trunk Sewer: This sewer follows the Mugutha River and will drain parts of Mugutha and Theta sub-locations in Ruiru. This sewer will empty in to the Theta River Trunk Sewer.

ii.Theta River Trunk Sewer: This follows the Theta River and is proposed to drain parts of Theta sub-location in Ruiru and Milimani sub-location in Juja as well as flows conveyed by the Mugutha River Trunk Sewer. This sewer will empty into the Thiririka River Trunk Sewer.

Figure 1 Mugutha, Thiririka and Interceptor Trunk sewers

iii.Thiririka River Trunk Sewer: This will follow the Thiririka River and will serve Milimani and Kalimoni sub-location. It will empty to the Interceptor Trunk Sewer and eventually to the Treatment plant.

iv.Kamuguti River Trunk Sewer: This sewer will follow the Kamuguti stream and empty into the Komu River Trunk Sewer. The sewer will serve Witeithie sub- location.

vii.Komu River Trunk Sewer: This will follow the Komu River draining the Karimenu (Ngoingwa), Komu, Weteithie, Kianjau and Komo sub-locations of Thika. It will eventually empty into the Treatment Plant at Thika.

Figure 2Komo and Kamuguti Trunk

Provision of a sewerage system will require the construction of a reticulation system to serve areas that are either already developed or are in the process of development.

The secondary sewers have been proposed as collectors for the laterals and are planned such that they discharge the flows at appropriate points to the proposed trunk sewers.

Tertiary sewers have been located on the residential/estates road network so as to facilitate ease of property connection.

2.3 ALTERNATIVE SITES FOR SEWAGE TREATMENT WORKS

An initial consideration in the selection of a site for sewage treatment is whether treatment should be carried out at one central location or whether a number of different sites would be more appropriate. Factors affecting this consideration include;

· Pattern and rate of development

· Shape and size of the catchment area

· Topography of the area

· Availability of suitable sites

· Cost effectiveness of options

Several alternative locations and subsequent sewerage network layouts were identified, considered and are discussed below;

2.3.1Alternative 1 - Centralised System

Option A - Nanga Site

This entail draining all the sewage generated in the project area to a site in Nanga. The Nanga site (01002’41.2”S, 037011’09.8”E) is located adjacent to the confluence of the Thika and the Kabuku rivers close to the Nanga Estate.

The advantages of this site are that the land is owned by the government and is currently not used. Also, the entire project area can be served by a single treatment works.

The main disadvantages of this option is very long trunk sewer system with very deep excavations in rock will be required for gravity flow of sewage to be achieved. Having a single treatment works for the entire project area will require merging of resources from the two (2No.) water service providers, which may complicate revenue collection and cost sharing.

Option B - Munyu Site

This option entails gravitating all the sewage generated in the project area to a site in Munyu. The Munyu site is located on the eastern edge of the project area along the Athi River about four (4) kilometres east of the existing waste stabilisation ponds for Thika Town.

The advantage with this option is that the whole of the project area will be served by a single treatment works. However, sewage generated from the Northern parts of Thika (drained by the Thika River) will continue to be pumped to this site, or an independent treatment works be provided at Nanga.

Other disadvantages of this option are;

· A very long trunk sewer will be required to reach this site from Ruiru and Juja areas,

· The land is owned by private individuals hence repossessing is required,

· Merging of resources from the two (2) water service providers for management of the unified treatment works may complicate their operations.

· The soils are black cotton clays overlying rock at a shallow depth and are therefore not ideal for the construction of ponds due to the large rock excavation that would be required.

· Tana & Athi river development authority (TARDA) have proposed to build a dam downstream of the confluence of Athi & Ndarugu Rivers. This may result in land proposed for the STW being submerged by backwater from the dam. This may then lead to a considerable length of the effluent channel being constructed to ensure that the effluent from the ponds is discharged into Athi River downstream of the dam.

· A very long trunk sewer will be required to reach this site from Ruiru and Juja areas,

2.3.2Alternative 2: De-centralized System

Juja Farm Site and Munyu Site

This will entail splitting the sewage flows in to two (2No.) catchments as follows;

· Juja Farm Site: This is located just after the confluence of the Thiririka and Ruiru rivers. This site had been identified during the Nairobi Masterplan for Sewer, Sanitation and Drainage as an appropriate site for Ruiru Phase II Sewage Treatment Works. The site can serve the lower regions of Ruiru Municipality not covered under Phase I, Mugutha river drainage area, Theta drainage areas and the Thiririka Drainage area. The area proposed is at Coordinates S01°11’04.2’’, E037°05’28.1’’

· Munyu Site: This will remain similar to Alternative No. 1 Option B but will handle sewage flows only from the Kurakuta, Ndarugu, Kamuguti and Komu drainage areas.

The advantages of this option are;

· The sites are further downstream of current urban settlements hence will be able to serve even beyond the ultimate design period,

· Each of the two (2) water service providers in the project area will manage sewage generated in their respective service areas.

The disadvantage of this option is that both the sites are privately owned and will require to be purchased. Plots at Juja Farm have already been sub-divided and hence the acquisition process may be problematic. Other Disadvantages are:-

· The site topography at Juja Farm may not be conducive for a waste water treatment plant receiving flows by gravity. Preliminary investigations have revealed the most viable location for an STW is located approximately 1490m above sea level. This location was also proposed by the Nairobi Master Plan team. Ruiru STW is at 1478m and 1480m at Thiririka & Theta confluence, making it improbable for future flows to flow by gravity. A pumping station will therefore be required. There is an alternative site right next to the proposed location at coordinates S01°11’09’’, E037°06’19.6’’ but this site is too small for a waste water treatment plant treating ultimate flows (area available is about 5ha).

· Munyu site are as outlined in alternative 1 option B.

2.3.3Preferred Alternative

A decentralized system is most preferred based on the following reasons:-

· Shorter Trunk Lines. Trunk lines for sewerage flows for Ruiru & Juja will be shorter.

· The two sewerage systems will be maintained separately by the two Water Service Providers, making it easier to maintain.

· Nanga site as a centralized system will not be adequate to treat ultimate flows for Ruiru, Juja, Thika South & Thika North.

· Extremely deep excavations will be avoided.

As with any other sewerage system, this alternative will be implemented in two phases; immediate (Phase I) and future (Phase II). Various options based on smaller STW locations for immediate implementation were identified;

OPTION A - Kalimoni Site, Ndarugu Site and existing Thika STW

This option entails construction of three new STWs and the rehabilitation of the existing Thika STW.

· Kalimoni Site: This site is located at Kalimoni just after the confluence of Theta and Thiririka Rivers. The site can accommodate sewage generated in the Mugutha, Theta and Thiririka drainage areas. This site is located on coordinates 01009’09.4”S, 037002’16.4”E.

· Ndarugu Site: This site is located along the Ndarugu River about 5km downstream of Thika Highway. Its located on coordinates 01007’15.0”S, 037004’25.3”E.

· Rehabilitation/Expansion of Existing Thika STW. This entails considering flows from Thika South area and draining them into the existing Thika STW site. The Thika STW is an existing waste stabilisation ponds system preceded by an inlet works located at the edge of Komu River. The system comprises six separate rows of ponds, each with two primary facultative ponds operating in parallel followed by one secondary facultative pond. Two (2No.) tertiary ponds are provided, each one taking the flow from three rows of primary and secondary ponds. The system total design capacity is 6,100m3/d. This site is located on coordinates 01005’34.1”S, 037006’56.0”E.

The advantages with this option are;

· All the trunk sewers will be comparatively shorter;

· There will be no need to acquire new STW’s land for Thika South as the existing STW will be rehabilitated and expanded.

Disadvantages are:

· The sites are not located at the end of the drainage basins, hence sewage generated in some areas will not be covered by gravity flow;

· Kalimoni & Ndarugu sites are close to existing urban settlements and sub-divided plots, this means that settlements will overtake the site and move downstream necessitating pumping of sewage generated in downstream areas or construction of another treatment plant further downstream;

· Land acquisition will be required for Kalimoni and Ndarugu sites.

OPTION B – Ruiru S.T.W Site, Ndarugu Site, and existing Thika STW Site

This option entails construction of two new STWs and the rehabilitation of the existing Thika STW.

· Ruiru STW Site: This site is located along the Ruiru River in Gatong’ora area. A STW comprising of a Waste Stabilisation Ponds system is currently under construction in this site for the Ruiru Sewerage Project (Phase IA).For this option, it’s proposed that a STW be built in the remaining space in the site. This site is located on coordinates 01010’46.6”S, 037001’23.2”E.

· Ndarugu Site: This site is located along the Ndarugu River about 5km downstream of the Thika Super Highway. Its located at coordinates 01007’15.0”S, 037004’25.3”E.

· Rehabilitation of Existing Thika STW & Construction of new Treatment works. This entails considering flows from Thika South area and draining them into the existing Thika STW site. The Thika STW is an existing waste stabilisation ponds system preceded by an inlet works located at the edge of Komu River. The existing system with a design capacity of 6100m³day comprises six separate rows of ponds, each with two primary facultative ponds operating in parallel followed by one secondary facultative pond. Two (2No.) tertiary ponds are provided, each one taking the flow from three rows of primary and secondary ponds. A new system is proposed to be built adjacent to the existing works on land currently owned by THIWASCO. This site is located on coordinates 01005’34.1”S, 037006’56.0”E.

The advantages with this option are;

· All the trunk sewers will be relatively shorter;

· There will be no need to acquire land for Thika South as the existing STW sites will be adequate. Land is also available at the existing Ruiru STWs for Juja scheme although not yet acquired.

· The area between Ruiru & Thika South will be adequately served by the Sewerage system.

Disadvantages are:

· The sites are not located at the end of the drainage basins, hence sewage generated in some areas will not be covered by gravity flow;

· The proposed sites are close to existing urban settlements and sub-divided plots, this means that settlements will overtake the sites and move downstream necessitating pumping of sewage generated in downstream areas or construction of other treatment plants further downstream;

· Land acquisition costs may be prohibitively expensive.

· Proposed location for Ndarugu STW is on private land. There was an attempt by the consultant to get ownership details from the provincial administration, which unfortunately was unsuccessful. We foresee difficulties in acquiring the mentioned Land and assistance from project stakeholders, especially the County government, will be required.

OPTION C – Ruiru Site, and existing Thika STW

This option entails construction of two new STWs at the existing sites at Ruiru & Thika treatment works. It entails also the rehabilitation of the existing Thika STW.

· Ruiru STW Site: This site is located along the Ruiru River in Gatong’ora area. A STW comprising of a Waste Stabilisation Ponds system is currently under construction in this site for the Ruiru Sewerage Project (Phase IA). For this option, it’s proposed that a STW be built in the remaining space in the site. This site is located on coordinates 01010’46.6”S, 037001’23.2”E.

· Rehabilitation of Existing Thika STW & Construction of new Treatment works. This entails considering flows from Thika South area and draining them into the existing Thika STW site. The Thika STW is an existing waste stabilisation ponds system preceded by an inlet works located at the edge of Komu River. The existing system with a design capacity of 6100m³day comprises six separate rows of ponds, each with two primary facultative ponds operating in parallel followed by one secondary facultative pond. Two (2No.) tertiary ponds are provided, each one taking the flow from three rows of primary and secondary ponds. A new system is proposed to be built adjacent to the existing works on land currently owned by THIWASCO. This site is located on coordinates 01005’34.1”S, 037006’56.0”E.

The advantages with this option are;

· All the trunk sewers will be shorter;

· There will be no need to acquire new STW’s land for Thika South as the existing STW will be rehabilitated and expanded.

· Acquisition of Land at Ruiru for Phase II will be easier as Land has already been identified and set aside for the Works.

· This option will be easier and faster to implement due its lower cost (approx. cost estimates of 2.9B) and land availability.

Disadvantages are:

· The sites are not located at the end of the drainage basins, hence sewage generated in some areas will not be covered by gravity flow;

· Ruiru is close to existing urban settlements and sub-divided plots, this means that settlements will overtake the site and move downstream necessitating pumping of sewage generated in downstream areas or construction of another treatment plant further downstream;

· Land costs at Ruiru may be expensive.

OPTION D – Ruiru Site, Ndarugu Pumping Station and existing Thika STW

This option entails construction of two new STWs that comprises of waste stabilization ponds for Thika South and Juja at Ruiru. Ndarugu drainage basin will consist of a Jet waste water treatment plant due to the little waste water generated from the basin. Works will also involve rehabilitation & reconstruction of the existing Thika STW.

2.3.4Preferred Sewerage Treatment Site

The Consultant recommends Option D for immediate implementation. (Year 2015). This is due to the following reasons;

· Land is available at the existing Thika Treatment works and hence no costs associated with Land acquisition;

· Land is available at the existing Ruiru treatment works site

· There is need to serve all persons living near the Thika Super highway. The proposed railway stations at Ruiru & Juja to be implemented under the Nairobi Metro transit system will also be adequately covered under this option.

· The Jet Wastewater treatment facility has a smaller ecological foot print.

A decentralized system is most preferred based on the following reasons:-

· Shorter Trunk Lines. Trunk lines for sewerage flows for Ruiru & Juja will be shorter.

· The two sewerage systems will be maintained separately by the two Water Service Providers, making it easier to maintain.

· Nanga site as a centralized system will not be adequate to treat ultimate flows for Ruiru, Juja, Thika South & Thika North.

· Extremely deep excavations will be avoided.

Figure 3: Existing Thika STW and site for new WSPs

Figure 4 Ruiru Phase I and Site for Phase II WSPs

2.4 ALTERNATIVES FOR SEWAGE TREATMENT PROCESSESSo as to establish a method of treatment that can achieve the required effluent standards in the most economical and technically appropriate way for this project area, the following table summarises the operating characteristics, advantages and disadvantages of common alternative sewage treatment processes.

Treatment process

Brief description

Advantages

Disadvantages

1. Waste stabilisation ponds

· Are open flow through lagoons

· Generally the most suitable method of wastewater treatment in hot climates

· Generally sub-divided into anaerobic ponds, facultative ponds and maturation ponds

· No power

requirements

· Very low O&M

requirements

· No mechanical installations

· Very simple method of treatment

· High land

requirement

· Odour nuisance, particularly from the anaerobic ponds

· Sensitive to temperature variations

2. Constructed

wetlands

· Are an artificial wetland

created for sewage treatment

· Used in conjunction with waste stabilisation systems for refining the quality of effluent

· Have substantial

capacity for wastewater treatment

· High land

requirement

· Requires relatively flat or gentle slopes

· Requires specific aquatic plants

· Appropriate for small institutions

3. Aerated lagoons

· A more intensive system of treatment resulting in greater removal of organics per unit volume of treated wastewater than in WSPs.

· Oxygen is supplied to wastewater by aerators floating or fixed in the lagoons.

· Detention time less than in stabilization ponds

· Less land requirement as compared to WSP

· High O&M

requirements

4. Oxidation

ditches

· An extended aeration

plant best suited to small communities.

· The aeration tank is in the form of a long continuous channel, oval in plan and with rotor suspended over the channel for aeration, mixed liquor propulsion and prevention of suspended particles from settling out.

· Relatively low land

requirement and suitable where land is at a premium price.

· High O&M

requirements

· Not effective in removing Faecal Coli Form.

5. Percolating/Trickling filters

· Sewage is evenly distributed on the surface and effluent collected through under drains that also help in aeration.

· The units are preceded by settling tanks to collect the settle able organic solids delivered from the filters.

· Durability in all

weather conditions and in the presence of corrosive effluents

· Does not upset for variation of hydraulic or organic loading

· Limitation in

volumetric loading

· Significant loss of head

· Nuisance due to flies

· Medium O&M cost

6. Activated sludge process

· Involves aeration of settled sewage mixed with return sludge within an aeration tank during which time the micro-organisms in the sewage multiply through assimilation of the organics in the influent wastewater.

· Biomass generated is normally collected in settlement tanks.

· Any degree of

treatment is possible

· Final effluent is clear and odourless

· Low land requirement

· Freedom from odour nuisance

· Freedom from nuisance due to flies

· Recommended for treatment of sewage from large communities (not small works)

· Sensitive to organic

loading particularly for industrial wastes which result in bulking of sludge

· High O&M

requirements

· High skilled management

· Sensitive to shock loading

· Produces large quantity of sludge whose disposal is a problem

A waste stabilisation ponds (WSP) system is recommended for sewage treatment due to its low operation and maintenance, and effectiveness in the local climate. From experience, the capital cost of buying land required for WSPs by far outweighs the operational and maintenance cost of the other alternatives. Together with the recommended WSP system, a comprehensive inlet works is recommended. The inlet works should comprise screens, grit removal and flow measuring mechanism as well as an emergency by-pass.

The trunk sewers will be made of concrete pipes which are resistant to corrosion. Thus leaks and consequent ground water pollution will be averted. In case of road and river crossing, steel pipes encased with bitumen will be used. The WSPs will be made of concrete and lined with an appropriate material to prevent leakage.

2.5 THE “NO PROJECT ALTERNATIVE” OPTION

This “alternative” implies maintenance of the status quo. That is, the proposed project is put on hold and mechanisms currently being used for disposal of sewage be maintained. This would have far reaching negative implications on the environment in its totality including among others:

· Loss of economic benefits from the construction and operation of the proposed project.

· Continued pollution of ground due to reliance on pit latrines.

· Pollution of surface waters by raw sewage being washed into these bodies.

· Population will continue to be affected by water borne and other diseases associated with exposure to raw sewage.

· Access to proper sanitation is a human right. If this option is adopted, the population will be denied this right.

This being the case then, “No Project Alternative” is discarded in favour of the Preferred Alternative which will lead to realisation of the project objectives which are for the good of the greatest majority.

2.6 PROPOSED SEWERAGE SCHEME

The Consultant recommends Alternative No. 1 as the most cost effective to construct, maintain and operate, as well as the most technically viable sewerage system for the project area for implementation (Year 2015). This recommended option consists of works to be implemented before the initial design horizon, 2015, and comprise of the following;

a) Construction of the trunk sewers along the Mugutha, Theta, Thiririka, Kamuguti and Komu rivers as well as interceptor sewer to the Ruiru S.T.W site. The trunk sewers are to be constructed for the ultimate sewage flows but will only cover the lengths from the treatment works inlet works to the areas already settled.

b) Extension of Ruiru S.T.W under construction and Existing Thika S.T.W. It is recommended that the waste stabilization ponds system be designed to handle initial sewage flow in their respective drainage basins.

2.7 PROPOSED PROJECT DESCRIPTION

The detailed hydraulic analysis has indicated that the proposed sewer reticulation network would require sewers of 300 mm diameter. The trunk sewer will however range between DN300mm diameters to 750mm.

The design has recommended for Trunk lines spigot and socket for rigid jointed concrete pipes manufactured to BS 5911 part 1 1985. The pipes will be laid on 150mm thick Class 20 concrete bedding on swampy sections. All the bedding types would be similar or equivalent to Nairobi City types A, B, C, or D depending on the soil type at individual locations.

uPVC Pipes will be used for trunk sewers of DN 300mm dia. GRP pipes are not recommended for use on any section of the works due to the prohibitively high costs.

2.7.1Sewage Collection and Conveyance System

Table below shows a summary of the design details for reticulation and trunk sewers. The sewer pipes have been designed for ultimate sewage design flow.

Sewer

Sewer Pipe Diameter (mm)

Sewer Pipe Length (m)

Sewer Pipe Material

No. of Manholes

Mugutha River Trunk Sewer

450mm

2300m

PCC

40

375mm

1700m

PCC

31

Theta River Trunk Sewer

525mm

6231m

PCC

107

450mm

49m

PCC

1

Thiririka River Trunk Sewer

525mm

5000m

PCC

87

450mm

3860m

PCC

68

Interceptor Trunk Sewer

750mm

4313m

PCC

75

Kamuguti River Trunk Sewer

450mm

2260m

PCC

40

375mm

3740m

PCC

64

Komo River Trunk Sewer

675mm

3240m

PCC

58

600mm

2500m

PCC

41

525mm

1500mm

PCC

29

450mm

2500mm

PCC

42

375mm

960mm

PCC

17

Juja Reticulation Sewers

300mm

21,900m

uPVC

368

Thika South Reticulation Sewers

300mm

14,800m

uPVC

250

2.7.1Sewage Treatment Works

The proposed sewage treatment works for Juja and Thika South are provided at different locations depending on the natural drainage patterns. The designed STW are:-

i. Juja STW at Ruiru T-Works, serving a section of Ruiru and Juja area, is located near Ruiru River,

ii. Thika STW is an existing works located along Komo River. A new system will be designed to cater for Southern parts of Thika Municipality on Land adjacent to the existing treatment works. The existing treatment works will be rehabilitated and expanded.

The sewage treatment works recommended will comprise of the following units:-

a) Inlet works with coarse and fine bar screens,

b) Horizontal flow grit removal channels,

c) Flow measuring Parshall flumes,

d) Waste Stabilization Ponds,

e) Utility Buildings expansion/Rehabilitation, if required, consisting of offices, workshop and Generator Rooms at both sites.

f) Rehabilitation/Expansion of double grade 9 staff house at Thika.

A. Inlet works

The Inlet Works has been designed to consist of coarse and fine screens, grit removal channel, flow measuring Parshall flumes, an over flow chamber and flow splitting chambers. It’s at the inlet works that preliminary treatment of the sewage is achieved.

The coarse and fine bar screens, grit removal channel and Parshall flumes have been provided in two (2No.) sets so as to accommodate ease of operation of the system if a unit is taken out of service either for servicing or during breakdown.

The units provided in the inlet works are described below;

i. Manually Raked Bar Screens: This is the first step in the removal of the coarse solids. Here, the influent wastewater will be passed through coarse bar screens and then fine bar screens. The designed screens have the following dimensions;

a. Coarse Bar Screens: This consist of bars 10mm thick, 50mm deep and placed such that they slope at 600 to the vertical so as to have maximum area and ease of cleaning using a hand held rake. This will have a clear spacing between the bars of 50mm.

b. Fine Bar Screens: This consist of bars 10mm thick, 50mm deep and placed such that they slope at 600 to the vertical so as to have maximum area and ease of cleaning using a hand held rake. This will have a clear spacing between the bars of 25mm.

ii. Grit Removal Channel: This has been designed to effect removal of grits, consisting of sand, gravel, or other heavy solid materials that have subsiding velocities. A horizontal flow, velocity-controlled grit chamber type has been designed.

iii. Flow Measurement Parshall Flumes: This has been incorporated at the main inlet channel. A measuring scale is installed on the upstream side of the flume which will be read every day. However, the actual measurement is to be carried out by use of an electroflo recorder that measures the depth of water on the upstream side of a flume, and records on a pedestal. These instrument records the rate of flow and also the total amount that flows.

iv. Overflow Chamber: An overflow chamber has been incorporated to assist in regulating the quantities of sewage that flows in to the waste stabilization ponds. The overflow chamber incorporates the use of a transverse weir and a stilling chamber. Excess sewage flow will be drained into the overflow/outfall open channel that drains into the nearby rivers.

v. Flow Splitting Chambers: This has been provided to split the flow into the various parallel streams of waste stabilization ponds. The flows have been provided to be controlled by use of sluice gates operated using rotary wheels. An emergency open channel has been provided to bypass the waste stabilization ponds in to the river via the overflow/outfall channel.

The design details of the units of the inlet works for the sewage treatment works sites are presented in the table below;

Design details of the inlet works units for the various S.T.W

Unit

Sewage Treatment Works

Juja (at Ruiru)

Thika South

1.

Coarse Screens,

Cross-sectional Area, m2

No. of units, Nr

No. of bars per unit, Nr

Thickness of bars, mm

Spacing of the bars, mm

0.5

2

16

10

50

2

2.

Fine Screens,

Cross-sectional Area, m2

No. of units, Nr

No. of bars per unit, Nr

Thickness of bars, mm

Spacing of the bars, mm

0.5

2

27

10

25

2

3.

Grit Removal Channel,

No. of Units, Nr

Length of each channel, m

Width of each channel, m

Depth of each channel, m

2

2

4.

Flow Measuring Parshall Flumes, ISO 9826:1992

Number of units, Nr

Upstream step slope

Upstream stilling channel length, m

Throat breadth, m

Downstream opening, 0

2

2

B. Waste stabilization ponds

A Waste Stabilization Ponds system has been provided for the treatment of the sewage. The ponds are designed such that the works are functional even during maintenance period when one system is closed. A series comprising of Anaerobic, Facultative and three (3No) Maturation ponds have been found to be adequate to fully treat the sewage to acceptable levels in each site.

The Table 1 below summarizes the design characteristics of each of the ponds in each of the sewage treatment works sites;

Table 1: Design Details of Waste Stabilization Ponds

Pond

Parallel Ponds (Nr)

Pond Dimensions (m)

Retention Time (days)

Effluent BOD5 (mg/l)

Effluent FC (/100ml)

Net Area

(Ha)

D

T.W.L

EM.L

JUJA (AT RUIRU) SEWAGE TREATMENT WORKS – 10,500m3/d

Anaerobic

2

4.00

72 x 31

77.3 x 35.8

1

263

114

0.55

Facultative

2

1.75

296 x 91

300.6 x 92.5

9

114

29

5.56

1st Maturation

2

1.50

196 x 78

201.0 x 80.4

5

29

21

3.23

2nd Maturation

2

1.50

196 x 78

201.0 x 80.4

5

21

16

3.23

Total

20

12.6

THIKA SEWAGE TREATMENT WORKS EXTENSION WORKS – 6,522m3/d

Anaerobic

3

4.00

46 x 24

50.9 x 29.4

1

267

116

0.45

Facultative

3

1.75

182 x 59

187.3 x 63.8

9

116

29

3.58

1st Maturation

3

1.50

109 x 55

114.5 x 59.7

5

29

22

2.05

2nd Maturation

3

1.50

109 x 55

114.5 x 57.2

5

22

16

1.97

Total

20

8.05

D – Effective depth of the pond

FL.L – Ponds Floor Level

T.W.L – Ponds Top Water Level

EM.L – Ponds Embankment Level

C. Outlet Works

In each of the sites, an outfall sewer line has been provided that drains the effluent treated waste water in to the nearby rivers.

D. Ancillary Works

For effective operation and maintenance of the sewage treatment works, the following ancillary works have been incorporated in the designed system;

i. Double Grade 9 Staff House: Rehabilitation and possible expansion of the Staff houses

ii. Landscaping, Fencing and Gate House: It has been provided that surplus excavated material is used in general site levelling. Also planting of grass within the site has also been provided. A chain link fence has been provided around the site constructed with concrete fence posts. A standard gate with a pedestrian gate has been provided at the entrance and additional access gates provided along the fence. A gate house has also been provided at the main entrance gate. These works have been provided for at both sites, but scaled down for Thika South.

iii. Access Road, onsite roads and storm water drainage works: An access road has been provided from the nearest road to the S.T.W. Onsite road work will consist of drainage. This has been provided at the Ruiru Treatment Works only.

E. Rehabilitation Works for Thika S.T.W

The existing sewage treatment works for Thika are currently working beyond the design capacity. The following works have been proposed to be undertaken as part of the rehabilitation of the existing system at Thika STW;

i. Construction of a new inlet works complete with coarse and fine bar screens, grit channels, flow measuring Parshall flumes and overflow chamber to replace the current broken inlet works;

ii. Conversion of the existing Primary ponds to a Hybrid system comprising of Anaerobic and facultative ponds to increase efficiency. This will translate to an improved capacity of waste water treatment from the current 8000m3/day (currently working over-capacity) to 10,500m3day.

iii. De-slugging all 6No. primary facultative ponds;

iv. Rehabilitation of staff houses.

v. Minor works like bush clearance, reinstatement of drainage system and repair of fence.

2.8 PROJECT ACTIVITIES AND COST

Project phase determines the activities in question. Phases of the proposed project are:

a. Pre-construction.

Specific activities in this phase include:

· Confirmation of Trunk Sewer Routes through Surveying.

· Pegging of trunk sewer route.

· Site clearance.

· Securing the site through fencing

· Erection of site office and contractors camp.

· Compensation of and resettlement of PAPs whose land is taken by the proposed project.

· Mapping of underground infrastructure.

· Relocation of underground infrastructure where necessary.

b. Construction phase

· Excavation of the WSP site.

· Excavation of trenches for trunk sewers.

· Laying foundation of the WSPs.

· Masonry works on the WSPs

· Procurement and stockpiling of materials on the site.

· Laying of pipes along the TS.

· Backfilling.

· Blasting.

· Ballast crushing.

GRAND SUMMARY OF THE BILL OF QUANTITIES

Description

Amount (KES)

Preliminaries and General Items

357,400,000.00

Schedule of Day works

17,760,000.00

Sewers

932,994,750.00

Sewage Treatment Works

1,595,890,100.00

Total

2,904,044,850.00

2.9 CONSTRUCTION MATERIALS

The pipe materials have been selected taking into consideration availability, durability and cost. Circular pipes have been adopted in this design. uPVC pipes are recommended for sewers with bore less or equal to 300mm. Precast Concrete pipes have been adopted for the sewers greater than 300mm.lines. Steel pipes are recommended for all river aerial crossings, Class A and B road crossings, rail crossing and deep sewers. Different pipe bedding types have been used depending on the nature of the ground. These have been classified as bedding type A, B, C, and D.

i. Concrete Pipes

Spun Concrete Pipes to relevant Kenyan and British Standards are manufactured locally by a number of Companies. They form the most common choice for Sewer Pipes. Spigot and socket jointed pipes are manufactured in sizes ranging from 100mm to 915mm diameter, and ogee jointed pipes are available in sizes from 100mm to 1525 mm diameter.

Rubber ring, flexibly jointed pipes are manufactured in sizes ranging from 150mm to 975mm diameter and strength classes M and H, or reinforced. Pipes are vertically cast in vibrated moulds and supplied and supplied moulds and supplied with rubber rings. Rigid jointed pipes require jointing with tarred hessian and cement mortar.

ii. uPVC Pipes

Un-plasticised PVC pipes are manufactured in Kenya in metric sizes up to 450mm diameter. A number of firms are involved in production, including Polypipes Ltd and Eslon.

iii. Glass Fıber Reınforced Polyester (GRP)Pıpes & Fıttıngs

Glass fibre reinforced polyester pipes are imported and sizes range between nominal diameters 250mm to 4,000mm. They are lighter, corrosion resistant and are much easier to install when compared to Steel and Concrete pipes. The considerably higher costs associated with importation make them infeasible for long trunk lines and reticulation but will be explored for use in inter-pond connections.

A Comparison of costs for GRP, Steel and Concrete is summarized below:-

GRP

STEEL

Concrete

Weight

Light

Heavy

Heavy

Service Life

70 years

35 years

50 years

Nested Transport

Installation

Easy

Tough

Tough

Maintenance

Minimal

Minimal

Minimal

Corrosion Resistance

Good

Needs additional internal layer

Poor

Availability(Locally)

Not available

Available

Available

Source:-Superlit Pipe industries Inc.

GRP will not be utilized in this project due to its higher cost in comparison to PCC.

iv. Steel Pipes

Steel pipes are manufactured locally. They are generally used in locations where sewers are exposed or in situations such as river crossings. Protection against corrosion is required internally and externally. Bitumen sheathing is normally used, the external sheathing generally being reinforced with glass fibre windings.

3.0 PUBLIC PARTICIPATION AND RESPONSES3.1 INTRODUCTION

Stakeholders are ‘all those people and institutions who have an interest in the successful design, implementation and sustainability of the project. This includes those positively and negatively affected by the project. Stakeholder participation involves processes whereby all those with a stake in the outcome of a project can actively participate in decisions on planning and management. They share information and knowledge, and may contribute to the project, so as to enhance the success of the project and hence ultimately their own interests’. Different types of stakeholders can contribute to the EIA process in different ways and, in most cases; inputs from a broad variety of stakeholders will complement the EIA process. Stakeholder interests exist at different levels. For example, at the local project level, they might include land or water access rights, pollution or market opportunities.

Kenya has entered the era of participatory development in all matters of national life. Participation in this case is not just through elected representatives but also through direct action. The Environmental Management and Coordination Act (EMCA, 1999) and its subsequent Environmental (Impact Assessment and Audit) Regulations, 2003 underscore the need for stakeholder participation in the EIA process. Neighbours of a proposed project have to live with the project if implemented. They have the most to gain if the project impacts are beneficial to them. Conversely, they have the most at stake if the project goes awry. Not just neighbours but for projects whose impacts have a wide geographical spread, distant communities need to be involved. Stakeholder input is thus vital at the earliest stage possible in project development and should continue throughout the project cycle.

3.2 CONSULTATION METHODOLOGY

There is no single ‘public’; instead there are a number of publics some of whom may emerge at any time during the process depending on their particular concerns and the issues involved. Strategies for involvement must be appropriate to the individual, the community or the region potentially being affected. A successful public involvement process must take the characteristics of the potential publics and their changing views of contentious issues into consideration. The public could be:

i. Experienced in public involvement.

ii. Informed or uninformed about the issues.

iii. Hostile or apathetic.

iv. United or divided.

The study made use of the following consultation strategies:

· Public Barazas (Appendices 1-3).

· Stakeholder workshop report .( Appendix XI)

Public consultation was extensively carried out in the entire project area to elicit concerns and compliments from the PAPs. The proposed project spans a fairly large administrative area with a mix of socio-economic characteristics. Consequently, this meant “diverse publics”. Consultation meetings were convened in public areas to enable maximum attendance. These were organised in collaboration with respective are Chiefs and Assistant Chiefs.

That notwithstanding, it is worth noting that consultation is an on-going process throughout the ESIA study. After publication of the report in local dailies and Kenya Gazette, Publics will have another opportunity to comment on the proposed project. Consultation goes on even after license issuance to the implementation phase and audit.

3.3 CONSULTATION OUTCOMES

A wide range of public was consulted on the proposed project. These people gave a candid view of the proposal. The views reflect different interests and positions in the community. They expressed appreciation to the proponent for the proposal.

The following is the summary of issues emerging from consultations:

3.3.1 Positive impacts

i. Employment

This is a key benefit of any project that host communities can gain from a proposed project. They thus expressed the need for the proponent to observe the following with regard to employment.

· Those responsible for project implementation ensure that youth from the area are given priority in recruiting labour force. They were emphatic especially on the recruitment of manual labour.

· While recruiting employees during the operation phase there is need to consider local population skilled in various issues.

ii. Mutual respect

With the new found relationship between the community and proponent, respect was paramount for the success of the proposed project both in the short and long term. They noted that this is a key aspect of sustainable enterprises.

iii. Participation in the life of the community

The proponent has become part and parcel of the local community. There is thus need to fully participate in the life of the local community in improving the lot of the people.

iv. Implementation

Given the immense benefits that the proposed project will produce, the community members urged the proponent to hasten so that the community can start benefitting from it. Those living in towns are especially very keen on the sanitation aspect.

v. Manual labour

As much as is practically possible, machinery should not be used where manual labour can be used to increase employment opportunities for the community.

vi. Remuneration

Contractors should be advised not to underpay local people who will be employed on casual basis.

vii. Peaceful coexistence

Since the Proponent acquired the piece of land, the community bond has continued to become strong. It was observed that this cordial relationship between the proponent and the local community.

viii. Open communication

To avert unnecessary conflicts, there is need for prompt communication to all stakeholders. This could be through the use of the local administration and other such fora. Any information or clarification about stakeholders’ position on project need to be promptly availed to any interested party.

ix. Project acceptance and support

There was support for the proposed project. This was as a result of clear explanation of what is proposed and the way forward in the implementation process. The community understood that the project is feasible in all aspects. In addition, the project will spur growth in the area. The local administration indicated that it and the entire community would support the project as long as it promoted development in the area. The community has no objections for the project since there are similar projects in other parts of the country that have benefitted the residents. In addition, the fact that access to water and decent sanitation is aright enshrined in Constitution of Kenya increases support for the proposal. The community thus embraces the project which will go a long way in making this right a reality.

The community also expressed concerns related to undesirable impacts from the proposal. These varied from location to location and were greatly a function of the socio-economic characteristics of the location.

i. Pollution of surface water

This concern emerged in Kimuchu, Witeithie, Athena and Murera. As of now, there is a large population that has no piped water and relies on streams, wells and rivers in the area.

ii. Displacement

Kimuchu, Witeithie, Athena and Murera again led in this concern. It emerges from the fact that the plots are too small (30feet by 60feet on average). The concern is that laying trunk sewers may displace some of the residents from their plots.

iii. Change of user

In Ngoingwa/Mang’u Investment area, this was the main concern. Currently, the laws allow only single dwellings. With the sewerage system, change of user will be easily granted allowing for construction of flats. Those who have invested in domestic houses felt they will lose privacy as a result.

EIA Team explained the proposed mitigation measures to their concerns among other potential negative impacts. This allayed fear from the community.

Plate 1: Public engagement in Ngoingwa

Following is a compendium of the consultation meetings held. The output and participants are in respective Appendices.

No

Date

Venue

Location

1

12/1/14

Ngoingwa (Kisiwa Grounds)

Karimenu Location

2

23/2/14

Witeithie

Komo Location

3

8th November, 2013

Senate Hotel, Juja

All Stakeholders

4

26th July 2015

Kimuchu Open Grounds

Komo Location

5

22nd July 2015

Theta Secondary School

Murera Location

6

26th July 2015

Kalimoni Open Grounds

Kalimoni Location

7

2nd August 2015

Ngoingwa Open Grounds

Karimenu Location

8

29th July,2015

Assistant’s Chief Office

Mugutha Location

4.0 BASELINE INFORMATION4.1 INTRODUCTION

Baseline conditions entail the sum-total of all biophysical and socio-economic conditions in the project area. Gathering of baseline data is necessary to meet the following objectives:

· To understand key biological, physical, ecological, social, cultural, economic, and political conditions in areas potentially affected by the proposed project;

· To provide data to predict, explain and substantiate possible impacts;

· To understand the expectations and concerns of a range of stakeholders on the proposed development ;

· To inform the development of mitigation measures; and

· To benchmark future socio-economic changes/ impacts and assess the effectiveness of mitigation measures.

4.2 TOPOGRAPHY AND HYDROLOGY

The topography of the project area is dominated by the Aberdare Mountains to the West. To the East of the town rises the only mountain in the immediate vicinity, OlDoinyo-Sabuk. The Eastern slopes of the Aberdares have been dissected by swift-flowing streams. The project area is situated strategically where most of these rivers merge and flow together to the East of the project area.

Generally, the area covered by the Municipality slopes gently from an altitude of 1560m at the western boundary down to 1440m A.S.L towards the eastern edge. To the West of the A2 Nairobi-Thika road, there are undulating coffee plantations with many large scattered trees. The major part of the undeveloped area to the east of the A2 Nairobi- Thika road is uncultivated plains with scattered trees and shrubs. The land falls steeply to the river valleys with heavy vegetation.

The area has numerous rivers and streams which flow throughout the year. The rivers include Thiririka, Theta, Ndarugu while the streams include Mugutha, Karakuta among others. In some areas these rivers are heavily polluted by municipal wastes. In other cases, they are over-abstracted for irrigation.

Plate 2: Section of Ndarugu River

Plate 3: Confluence of Theta and Thiririka Rivers at Murera

4.3 CLIMATE

The major parameters of the Climate of the study area are controlled by the large-scale pressure systems of the western Indian Ocean and the adjoining continents, and its day-to-day weather is related to the very considerable day-to-day variation in the detail of these pressure systems. In addition, differences in topography lead to a diversity of climates due to the tendency for greater cloudiness and precipitation at higher altitudes and on windward slopes, and lower temperatures with increasing altitude.

In the study area, the year can be sub-divided on the basis of predominant wind direction and general weather characteristics, into four well-marked seasons. These are:

a. North-East Monsoon

This season runs from December to March and is warm, clear and sunny with persistent north-easterly winds and occasional showers.

b. Rainy Season; “Long Rains”

The “Long Rains” usually run from Late March to May bringing warm rainy weather with light winds varying from North-Easterly to South-Easterly by the end of the period.

c. South-East Monsoon.

From June to September the weather is usually cool and overcast with persistent south easterly winds, little rain but drizzle which becomes heavier towards the end of the season.

d. Rainy Season; “Short Rains”

The “Short Rains” usually occupy the month of November when the weather is warm, sunny and showery, with a light wind changing from south-Easterly to north-Easterly during the month.

There are two meteorological stations at Thika that monitor climatic conditions. They are located at the Thika Horticultural Research Station (0º 50’S and 37° 04’E; altitude, 1549m) and Thika Agromet Research Station (1º 01’S and 37° 06’E; altitude, 1477m).

4.4 TEMPERATURES

The mean minimum and maximum temperatures for the period 2011-2013 are as given in

Table 2: Temperature Records

Month

Maximum

Minimum

January

27.8

12.90

February

24.3

13.92

March

24.7

14.28

April

26.9

16.57

May

26.1

15.43

June

24.5

14.10

July

23.7

12.97

August

24.1

12.60

September

26.4

13.44

October

26.5

18.65

November

25.9

18.96

December

26.1

21.39

Mean

25.58

15.43

The annual mean maximum temperature is 25.58°C, while the annual mean minimum temperature is 15.43ºC. The annual average temperature is 20.51°C.

4.4 RAINFALL

Precipitation in the project area is mainly bi-modal. Rainfall data for the period 2011-2013 is as given in Table 2 below. The mean annual rainfall measured during these periods of record collection was 987.43mm. The mean monthly rainfall in the wettest month (April) was 262.5mm. There is usually no rainfall during the months of July, August and September.

There are no recorded incidences of flooding in the project area. This is mainly due to the amounts of rainfall received and the topography which allows rain water to drain.

Table 3: Rainfall Records

Month

Rainfall, mm, 2011 – 2013 (Means)

January

28.04

February

22.94

March

123.18

April

262.50

May

91.47

June

32.51

July

3.37

August

19.57

September

23.07

October

93.00

November

172.00

December

115.80

Total

987.43

4.5 EVAPORATION

The rate of evaporation recorded during the periods 2011-2013 using an evaporation pan Type-A are as shown in Table 2.3 below. The annual mean evaporation is 1,452mm, with a mean monthly maximum of 182mm in March.

Table 4: Evaporation Records

Month

Mean Evaporation, mm

(2011-2013)

January

151

February

170

March

182

April

125

May

100

June

85

July

81

August

79

September

112

October

131

November

110

December

126

Total

1,452

4.6 HUMIDITY

The relative humidity in percentages, measured at 0600 and 1200, for the period 2011-2013 is as given in Table 2.4 below. The average annual values are 78.3% in the morning and 49.6% in the afternoon. There is not a great monthly variation in humidity with the highest reading being around 84.3%.

Table 5: Relative Humidity

Month

Mean Humidity % (2011-2013)

0600 GMT

1200 GMT

January

72.7

37.5

February

61.2

34.5

March

61.0

34.0

April

83.3

55.7

May

82.3

56.3

June

83.7

55.5

July

82.7

52.5

August

84.3

56.0

September

83.7

47.3

October

82.3

52.3

November

83.5

61.0

December

78.5

53.0

Average

78.3

49.6

4.7 SUNSHINE

The number of hours of daily sunshine recorded for the period 2011-2013 is as given in Table 4 below. The annual average daily sunshine is 6.7 hours, with monthly high and low means of 9.0 and 2.9 hours observed in the months of January and August respectively.

Table 6: Sunshine Records

Month

Mean Sunshine, hours

(2011 – 2013)

January

9.0

February

8.8

March

8.0

April

8.3

May

6.7

June

6.0

July

5.0

August

2.9

September

3.7

October

6.4

November

7.6

December

7.7

Mean

6.7

4.8 GEOLOGICAL AND SUB-SOIL CONDITIONS

4.8.1Geology

The eastern half of the project area is formed by rocks of the basement system, while to the west, lavas, pyroclastic and sediments of the tertiary age are exposed. In general, the rocks in the area can be divided into three main age groups:

a) Archean: Basement system.

b) Tertiary: Volcanic and sediments

c) Recent: Soil and alluvial deposits

The Basement System is believed to represent an original sedimentary series of limestones, Shales and sandstones, into which basic magma has been intruded. Intense compression with rising temperatures has resulted in these rocks being transformed into a highly folded metamorphic series.

The volcanic and sediments occur in the western half of the area, forming the plains south of the project area. The volcanic and sediments are probably all of the tertiary age but, as no fossils are available and no age determination have been made, it is not known whether they range into Pliocene.

The term “building stone” is used to describe the series of massively bedded, fine-grained tuffs or clay stones occurring in the area.

Recent deposits in the area include soils and alluvial sand deposits. The soils are normally residual weathering deposits, whose composition is controlled more by the physical conditions of formation than by the type of rock from which they were derived. In general, the well-drained soils are sandy and the badly drained soils black cotton in nature. On the basement system, red lateritic soils are the most common, but in places they give way to more sandy soils and even black cotton soils. The variation of soils on the volcanic rocks is not so great, the principal soils being black and grey clays.

Another important feature of the soils on the plains south of Thika is the development of mound topography. The mounds are usually about 20 to 50m in diameter, and on top of the mounds, the underlying rock, which is usually composed of cemented brecciated material, is exposed or covered by only a few centimetres of