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DEVELOPMENT OF WATER SUPPLY & SEWERAGE FACILITY IN ATOLLS PROJECT FUVAHMULAH, MALDIVES

Detailed Design Report - Volume 1 of 3

Al-Habshi Consultants, Kuwait In association with Riyan.Pte Ltd 1 / 39

Table of Contents

1.0INTRODUCTION.............................................................................................................................4

2.0DESIGNREQUIREMENTS..............................................................................................................4

3.0OBJECTIVESOFCONSULTANCYSERVICES.................................................................................4

4.0SCOPEOFCONSULTANCYSERVICES..........................................................................................5

5.0BACKGROUNDOFENGINEERINGDESIGNREPORT.................................................................8

6.0DATACOLLECTION,SURVEYSANDINVESTIGATION...............................................................8

6.1DataCollection.............................................................................................................................8

6.2TopographySurvey......................................................................................................................9

6.3BathymetrySurvey....................................................................................................................10

6.4SocioEconomicSurvey..............................................................................................................11

6.5Soilinvestigation........................................................................................................................12

7.0PROJECTCOMPONENTS&DETAILEDDESIGNWORKS..................................................12

7.1seweragesystem.......................................................................................................................12

7.2Sewagetreatmentfacility..........................................................................................................14

7.3SewageTreatmentfacilityalternatives......................................................................................15

7.4WaterSupplySystem.................................................................................................................16

7.5ReverseOsmosisProcess...........................................................................................................17

7.5.1ProcessDescription................................................................................................................19

7.6WaterSupplyDistribution.........................................................................................................20

7.6.1.DesignConsiderations...........................................................................................................20

8.0 DESIGNSTANDARDS..........................................................................................................21




8.1SewerageDesignStandards......................................................................................................21

8.2WaterSupplyDesignStandards................................................................................................23

9.0 DETAILEDDESIGNOFPROJECTCOMPONENTS................................................................23

9.1SewerageNetworkVacuumsystem..........................................................................................24

9.3SewerageNetworkPumpingMains..........................................................................................29

9.4SewageTreatmentPlant...........................................................................................................29

9.5SeaOutfall.................................................................................................................................31

9.6WaterSupplynetwork...............................................................................................................33

9.7ReverseOsmosisPlant...............................................................................................................33

9.8StorageTank..............................................................................................................................34

9.9BrineWaterCollection&DisposalSystem................................................................................35

9.10FeedwaterStoragetank.........................................................................................................35

9.11TubeWell.................................................................................................................................36

9.12OceanIntakeStructure(Optional)..........................................................................................36

9.13Civil/Structural.........................................................................................................................37

9.14Electrical&Instrumentation...................................................................................................39




LIST OF APPENDICES -Volume 2 of 3

Bounded

Appendix -A - Design Calculations of Vacuum Sewage Network

Appendix- B - Design Calculations of STP

Appendix -C - Design of Ocean Outfall

Appendix -D - Hydraulic Calculations of Water Supply Network

Appendix -E - Design Calculations of RO Plant, Storage Tank, Brine Collection & Disposal

Appendix -F - Design Calculations of Tube Well

Appendix -G - Design Calculations of Civil/Structural Works

Appendix -H - Design Calculations of Electrical & Instrumentation

Appendix- I - Vacuum sewer system design guideline.




1 . 0 I N T R O D U C T I O N

The government of Maldives has received a loan from the Islamic Development Bank (IDB) for the development of water supply and sewerage facilities in the islands of Gn. Fuvahmulah and Ha. Utheeemu. Al-Habshi Consultants, Kuwait in association with Riyan, Male was awarded the Consultancy Contract. The consultancy service includes development of concept designs, detailed designs, environmental impact assessments (EIAs), engineering drawings, preparation of tender documents, assisting in tendering process and supervision of the project work in close collaboration and under the guidance of Ministry of Housing, Transport and Environment (MHTE) in the mentioned islands, as detailed below.

2 . 0 D E S I G N R E Q U I R E M E N T S

The design requirement is to ensure project implementation after carrying out technical assessments and identifying a best option for the islands considering the social norms and community acceptance. The following principles are to be considered in designing and constructing of the sewerage facilities. Conventional sewerage system with minimum number of sea-outfalls. Minimize public health and environmental impacts. Energy efficiency. Urban Development and Land Management Plans: and Low-cost treatment options and technologies.

The water supply and sewerage facilities will be designed and constructed in meeting the long-term needs and objectives of the National Development Agenda giving a design horizon of 15-30 years.

3 . 0 O B J E C T I V E S O F C O N S U L T A N C Y S E R V I C E S

(a) Necessary engineering services for the implementation of the project including preparation and execution of surveys and investigation.

(b) Conceptual and Detailed Design (c) Tender Documents (d) Construction planning




(e) Construction supervision (f) Environmental monitoring and management planning (g) Cost estimates (h) Tendering assistance for selection of contractors (i) Social considerations (j) Financial management (k) Capacity building of government agencies and island communities (l) Preparation of operation and maintenance manuals and

4 . 0 S C O P E O F C O N S U L T A N C Y S E R V I C E S a) Phase 1- Designing

The phase-1 of the project includes preparation of concept designs, field investigations and survey's. Environmental Impact Assessments (EIA). Detailed engineering designs and bidding documents. The consultant shall execute detailed design including the following works: Review and analyze existing data, studies, designs, reports and other available

materials pertinent to the sub projects and natural conditions around the project area

Undertake detailed Field surveys where necessary including updated topographic. Bathymetric current, reef and socio-economic surveys and establish benchmarks on the islands.

Determine dry and wet weather flows for each island including water consumption, compute flow and velocity and prepare system and drawings based on the conditions and criteria to be approved by MWSA.

Prepare at least two appropriate sewage collection, treatment and disposal options and develop cost estimates, economic and financial analysis for each option proposed.

Prepare preliminary design Design Reverse Osmosis (RO) desalinated water-supply system for the

islands including intake and reject water systems, piped network, water storage facilities, disinfection and water treatment facilities, and plant houses.

Execute detailed investigations at the sites of boreholes or intake wells for RO water, seaoutfall; brine discharge locations for geo-physical soil, current, reef and water quality investigations.

After approval of preliminary design prepare detailed design including site plans, profiles long sections and drawings




Determination of mitigation measures for negative environmental impacts Develop separate bidding documents, working drawings, b i l l of quantities and

specifications for water supply and sewerage systems for both Utheemu and Fuvahmulah, under the guidance of Ministry of Housing, Transport and Environment (MHTE) and Tender Evaluation Board of Ministry of Finance and Treasury (MoFT).

Ensure that final tender documents are technically sound and feasible and is developed in a harmonized manner to meet the requirements of Ministry of Housing, Transport and Environment (MHTE). Tender Evaluation Board and Islamic Development Bank (IDB).

b) Phase 2- Tendering and Contract award

The Phase 2 of the project includes tendering and contract award works. The proposed work will be carried out under the guidance of Ministry of Housing, Transport and Environment (MHTE) and Tender Evaluation Board of Ministry of Finance and Treasury (MoFT). This phase is expected to be completed within 3 months. The Consultants shall carry out the following works to assist the Implementing Agencies in Tendering. a) Assist in the preparation of the advertisements for inviting prequalification

application and executing of prequalification evaluation (if required) b) Assist in the preparation of the advertisements for inviting bids and

sending of tender documents to interested companies. c) Assist in preparation of pre-bid meeting, preparation of addenda as

required and preparation of replies to questions from bidders to be carried out in consultation with Ministry of Housing, Transport and Environment (MHTE) and under the guidance of Tender Board of Ministry of Finance and Treasury (MoFT).

d) Assist in management of any disputes, clarification and opening of relevant tenders

e) Assist in evaluation of bids and preparation and presentation of evaluation reports, recommending contract award for approval by the Government of Maldives. During evaluation the followings points must be considered carefully.

- Ensure that the bids are technically sound and feasible and that the proposals are technically capable of fulfilling their responsibilities.




- Ensure the tenders are financially sound and feasible including the cost are equivalent to local market prices.

- Ensure the tender schedules are sound and feasible including the Consideration that the contractor is capable of fulfilling the responsibilities

outlined in the contract in the allocated time. f) Assist implementing agency in contract negotiations with successful

bidders. g) Assist in preparation of contract documents, contract development, signing

and awarding.

c) Phase 3-Construction supervision and monitoring

The phase 3 of the project includes monitoring and supervision of construction work to be earned out during project implementation. Expected duration of this phase is 18 months for Fuvahmulah a) Setting-out of the work b) Preparation of construction drawings and documents c) Review and approval of Contractor's drawings and documents d) Quantity and quality control e) Monitoring and control of the Work schedule f) Settling of disputes or differences g) Monitoring defects liability period

d) Environmental Study and Monitoring

The Consultants shall carry out environmental study and monitoring including the following to mitigate the negative environment impacts. a) Preparation of environmental screening form for each sub-project to be

submitted to Environmental Protection Agency b) Scoping of Environmental Impact Assessment (EIA) study if required c) Execution of Environmental Impact Assessment (EIA) and preparation of the

reports according to the requirements. d) Facilitation of timely response and approval from Environmental Protection

Agency e) Environmental monitoring during construction works.




5 . 0 B A C K G R O U N D O F E N G I N E E R I N G D E S I G N R E P O R T

The revised concept design after incorporation of all Comments of the Client (MHTE) were submitted on 16/8/09 subsequent to the submission made on 16/12/08 and the various discussions and further meeting held on 8/7/09 in MHTE. MHTE approvals to the concept design and instruction to proceed with detailed design considering Vacuum system sewerage network (in place of conventional system) was issued to Consultant on 15/12/09 based on which this submittal is being made now. This Final Detailed Design Report submission is in compliance with those MHTE comments, the Detailed Design Report is submitted in three volumes, details as below. 1. Volume 1 of 3 Detailed Design Report 2. Volume 2 of 3 Appendices (Detailed Design Calculations) 3. Volume 3 of 3 Appendices (Detailed Design Drawings)

The Detailed Design Report contains the design calculations of all project components which are demonstrated in the following chapters of this report. The Appendices cover the design details in depth. The Detailed Design Drawings are prepared on the basis of detailed design and supporting calculations on standard and international scale and in line with the MHTE design criteria document for sewerage and water supply system. Due to urgency and pressing demand of MHTE and the tender documents of Water Supply and Sewerage System Fuvahmulah Island are also being prepared and shall be submitted with the detailed design documents. The Tender Documents include for the Bills of Quantities in Re-measured Contract format, Technical specification of all project components, contract conditions and bidding procedures.

6 . 0 D A T A C O L L E C T I O N , S U R V E Y S A N D I N V E S T I G A T I O N

6 . 1 D A T A C O L L E C T I O N

The preliminary task was to complete the data collection which comprised of identification of all pertinent informations which may be necessary for the execution of our performance. Since we were involved in the Bankable Document Preparation




for the same project, Al-Habshi Consultants were in possession of the particular datas and the various codes/standards based on which our activities were performed, the actual reference to the particular datas collected are referred below in the forthcoming chapters.

6 . 2 T O P O G R A P H Y S U R V E Y

The Topographic Survey covered the topographical conditions of the whole land area of the project islands above shoreline to give the basic understanding on the topographical considerations for the preliminary design and detailed design for sewer networks. Position, distance, dimension, ground floor level of all the existing facilities, septic tanks and boundary walls was clearly marked in the survey drawing. Scale of these surveys was 1:500

The objective of Topographic survey was to establish Horizontal and Vertical control network and do a asbuilt survey of the area including existing Plot Corners and Block Corners of land parcels, Infrastructure facility features such as electricity posts, cable TV distribution boxes and Spot Heights of the ground specially along the roads. Then to prepare a Topographical plan of the whole land area of the island depicting all existing details of the area. First Horizontal and vertical control network (3D control network) was established. The detail survey was completed using this 3D control network and the topographical maps were prepared. The 3D control network was established using GPS, Total Station and a digital level. The markers used for this were made as the semipermanent markers. The markers established at Fuvahmulah were referred as the control points. First considering the whole island, the control points were established. For the control points, 12inch iron rods were inserted to the ground and 4inch concrete layer was laid for the protection of the iron rod. Two main control points (Base 1 and Base 2) were established closer to the island office. These two main points were observed using TRIMBLE GeoXH GPS receivers. Static observation method was used and the duration of the GPS observation was 2hours. These observed data were processed to obtain the bearing of the points in relation to each other. The distance between the two points was also measured using a Total Station and while maintaining the GPS coordinates for the main control point 1 (Base 1), the distance from main point 1 (Base 1) to main point 2 (Base 2) was plotted along the bearing of Base 2 from Base 1. The adjusted coordinate of Main point 2 (Base 2) obtained by plotting the distance measured using the Total Station was used as the plot coordinates of Main point 2 (Base 2). Finally the coordinates of the Main control points were converted to UTM coordinate system.




The vertical datum used in these surveys was the Mean Sea Level (MSL) derived from tide readings of HDh Hanimaadhoo tide data. A digital Level was used to carryout the level traverse along the traverse points. The level transect of the control points were started by reading a back sight reading to the Main control point 1(Base 1) and using back sight fore sight method was used to complete the traverse back to the first back sight point

Detail Survey was started using the established 3D Control points. Same Total Station instrument was used for the detail surveys. First instrument was set up at a control point (at first main control point as it is mid point of the island). Then coordinates Main control point 1 (Base 1) were input to the instrument. Next to orient the instrument the instruments telescope was pointed towards the Main control point 2 (Base 2) where the target was set up and the target point coordinates were entered. Again target was established at back sight point (here at last traverse point) and observed that for checking the orientation. Here vertical height difference method was used to check the vertical accuracy of the observation.

All the observations were stored in the internal memory of the Total Station as well as they were entered in the field book manually. All the stored data were downloaded using the Tcom software. First using the row data file a Microsoft Excel file was created. After creating the corrected coordinate file of detail survey, through the Tcom software . Dxf" files were developed to use to plot the digital CAD plan.

Four permanent benchmarks were established on the islands. Bench mark at Fuvahmulah is located near harbor and near either side of Rasgfannu and Maaneru road (main road across the island). The Northing and Easting for these benchmarks were given in UTM and their vertical heights are referred to MSL. The horizontal coordinate system used for the topographic surveys was UTM for the horizontal coordinates. The spheroid for this projection is WGS 84. The vertical datum used for these surveys was Mean Sea Level (MSL). The mapping scale for these surveys was 1:500. The heights of the features measured in these surveys were plotted as spot heights on the map

6 . 3 B A T H Y M E T R Y S U R V E Y

A large part of the bathymetric survey was carried out as acoustic depth (z) measurements together with GPS position (x, y) fixings. Acoustic depth measurement systems measure the elapsed time that an acoustic pulse takes to




travel from a generating transducer to the waterway bottom and back. In areas where the water depths were too shallow (over the reef flat) for the survey boat to safe navigation, the Total Station together with a fixed height prism pole was used to measure the sea bottom levels. At Fuvahmulah due to the swell condition lagoon depth and near reef crust depths were not taken. The lagoon depths at the proposed STP outfall area is shallow, just below MSL, while the reef crust area is almost at MSL. The reef area is observed to be of spur and groove formation with sharp drop off from the crust area to depths of 3m, and from this point onwards a shallow flat is observed to depths up to -10m, from this point onwards the reef slope is observed to have a gradual slope down to depths exceeding -100m. Due to the high energy nature of the area it may be required to have armored sheathing for the out fall pipe at reef crust and the flat area, since rocks may move at the spur and groove area and cause damage. It has to be noted that moving north of the proposed location, reef slope is gradual, possibly making it slightly easy for laying the pipe.

6 . 4 S O C I O - E C O N O M I C S U R V E Y

A detailed Socio-economic Survey was conducted with an aim to (a) develop a socio-economic profile of the island based on survey data, census data, and existing information, (b) undertake community consultations with different community groups including youth, women, fishermen, traders, NGO's development committees , Island Council and others and gather their views and incorporate them in project development, (c) ensure community involvement and community participation in the project design, construction and operation and maintenance, (d) provide necessary information that will help to formulate a proper operation and maintenance mechanism and finance the overall project O & M in the long run, (e) identify the willingness to pay and other economic concerns and help to address them in the design and implementation of the project, (f) assist in the evaluation of the costs and benefits of the different options feasible to the project site conditions.

It was observed that the issue of the household connections for both the water and sewerage raised by the people of Fuvahmulah needs to be addressed through community dialogue before implementation of the project. Community sensitization activities are to be undertaken prior to the commencement of work, if the Government sticks on to community taps. The water and sewerage projects proposed to be implemented will strengthen the overall socio- economic status of the islanders. Universally, appropriate and standardized systems of water and sewerage will enhance the social status of the people, particularly that of women. Tourism




prospects will be an added economic component for the future development in the island. Socio-politically, the implementation of the water and sewerage projects will diffuse the pent up emotions of the community.

6 . 5 S O I L I N V E S T I G A T I O N

We analyzed a formally drilled borehole data carried out by Geo Engineering Pvt Ltd, Maldives for MWSC in 2006. According to the data given for well BH-7, the transmisivity co-efficient by using software developed by Prof. Gerrit Van Tonder of the Institute for Groundwater Studies, University of the Free State is shown in given format and the data extracted from DEVELOPMENT BY PUMP RECORD SHEET 1-2 conducted for BH 07 on 03.08.2006 has taken for analyzed. In the Gerrit Van Tonder format software average Q sustain (sustainable yield) is shown as 1.39 l/S with standard deviation 1.22. Transmissivity estimates from derivatives 99.33 m3 /day. This Transmissivity value is rather high value but can accept due to high porous calcareous sand. According to the Gerrit Van Tonder format software there is no value given in the format. The reason to be the data entered it from the informal pumping test. Simple laboratory test done for deeply excavated samples gives the storativity as 0.410 m3.

7 . 0 P R O J E C T C O M P O N E N T S & D E T A I L E D D E S I G N W O R K S

7 . 1 S E W E R A G E S Y S T E M

Various different sewerage system were analyzed during the concept stage of the project and a techno-financial analysis was carried out to actually establish the technically most feasible and financially viable sewerage system i.e. Vacuum Sewerage System for Fuvahmullah Island considering long term efficiency of this system which comprises of sewers network, Two Vacuum Station and a sewage treatment plant. The Vacuum sewer system design is mainly based on (1) EPA Alternative Wastewater Collection Systems Chapter 3 and (2) Guideline of Developer volume ii (from Malaysia Water Association) design criteria. A copy of both guidelines is attached in this report Appendix- I The sewage is collected from each household by means of an inspection chamber and Vacuum chamber at suitable intervals, and allowed to flow to vacuum stations for onward pumping to the treatment plant. The sewage from 6 to 10 houses is




connected to a vacuum chamber by a gravity network. The Vacuum chambers are connected to main Sewer lines with vacuum pressure. These main sewer lines are further connected to two zonal Vacuum stations, which should be capable to create sufficient vacuum pressure in all main sewers laid all over the Island. The vacuum station is designed for each Island sewer zone to receive the flow of the sewage from each House connections, for further pumping to the sewage treatment plant, which will reduce the BOD and SS levels substantially in line with the EPA regulations and standards for domestic wastewater disposal. The resultant effluent will be pumped back to deep sea through sea outfall. The sludge which is resulted from the sewage treatment also will be pumped back to sea on a monthly basis which is no more septic.

UPVC PN-06 pipes of minimum 110, and 160 mm outer diameter are used for the household connection to vacuum chambers with a slope of 1:100, whereas the main sewer which is interconnecting vacuum valve chambers and vacuum stations, is 110, 125, 160, 200, and 250 mm diameter PVC Schedule 40, SDR 21 solvent welded pipe, to meet the future population and laid in a saw tooth profile with a slope ranges from 0.2 % to 2%. (1) For 100-125 mm diameter pipe: 80 % pipe diameter or 0.2 % gradient. (2) For 150-250 mm diameter pipe: 40 % pipe diameter or 0.2 % gradient. The design of vacuum sewage profile is based on attached EPA alternative sewage design criteria (Appendix-I) table 3-2, 3-3, 3-4, and lift height is based on table 3.1. The minimum suction pressure at each vacuum interface unit will be 5 ft and the frictional losses in the vacuum pipe will not go beyond 2 feet. The losses on account of static lift will not go beyond 11 feet. The upper velocity limits are even more in the vacuum sewers which exclusively depend upon the value of vacuum in the vacuum sewage network. The velocity may up to range 4.6 5.5 m/sec depends on value of volume in line and vacuum pipe diameter, thereby providing a non-clogging and trouble free drainage system. The piping is properly sized to handle the recommended maximum permissible flow from all house drains and vacuum chambers connections. Minimum cover over sewer are regulated to 900mm as instructed by MHTE through their comments on Concept Design and all gravity and vacuum sewer pipes are bedded with sand. Each household is provided with an Inspection Chambers, 600mm diameter HDPE chambers installed in individual households for the tenant to carry out house connections. For every 6 to 10 number of houses one vacuum valve pit is provided.




Two Vacuum Stations are provided in Fuvahmullah at convenient and suitable locations to develop sufficient vacuum pressure in each sewer zone. The total available head loss for vacuum station should be between 18 to 23 feet. The Outfall discharge pipe should be made of 250 mm HDPE pipe, which is laid on a trench over the reef and ocean by using concrete ballast blocks located at an appropriate distance. The Ocean Outfall effluent mixing Design Criteria is taken as a minimum port exit velocity of 4m/sec, initial dilution as 1:100 and Bacterial reduction to be 1000 MPN/100 ml.

7 . 2 S E W A G E T R E A T M E N T F A C I L I T Y

Considering the low ground water table profiles of the Maldivian islands and other environment constraints, we considered the following 4 type of sewage treatment technologies. A. Oxidation Process based on Activated Sludge with Extended Aeration B. Rotating Biological Reactor (RBC): C. Submerged Aerobic Filter (SAF) D. Sequencing Batch Reactor (SBR) Technical comparison, advantages and disadvantages of sewage treatment process were detailed out in the conceptual design, resulting in finally recommending the Oxidation Ditch Process based on Activated Sludge with Extended Aeration System for Fuvahmulah Island. The selection of a particular process for sewage treatment is affected by diurnal and seasonal flow variations, sewerage strength (variability of wastewater constituents) infiltration / inflow, ambient temperature and its induced septicity, degree of treatment required, magnitude and direction of wind etc.

The extended aeration process holds wastewater in closed endless loop channel to aerate for 18 hours or more and the organic wastes are removed under aerobic conditions. Air is supplied by mechanical rotor through rotating action. The wastewater is screened to remove large suspended or floating solids before entering the aeration chamber, where it is mixed, and oxygen is added. The solids settle out and are returned to the aeration channel to mix with incoming wastewater. The clarified wastewater flows to a collection channel before being diverted to the disinfection system. The sludge is periodically removed from the units. In Aeration tank (extended aeration), suspended microbial growth is maintained for the biological oxidation of organics. Surface or Diffused aeration system is provided to meet the




oxygen requirement of micro organisms and to keep the liquor in completely mixed regime.

7 . 3 S E W A G E T R E A T M E N T F A C I L I T Y A L T E R N A T I V E S

The following types of sewage treatment facilities were analyzed and studied.

A. Sewage treatment facility with secondary treatment and effluent disposed to sea. Customarily, the sewage of household used to be disposed direct to the sea which has made alarm on the environmental conditions around the shore. The authorities have prohibited such disposal and the consultant proposes to have secondary treatment before disposing the effluent to deep sea, the process steps are tabulated below.

Standards for effluent are as shown below.

EFFLUENT STANDARD

Parameter Value

Total Suspended Solids (TSS) 150 mg/l

Bio-chemical oxygen demand (BOD) 40 mg/l

Fecal Chloroforms 100 org/ 100 ml

Oil & Grease 5 mg/l

Residual chlorine 0.1 mg/l

Nitrates as N 15 mg/l

Free and saline Ammonia as N 10 mg/l

Phosphate as P 10 mg/l

Chemical Oxygen Demand 40 mg/l

Process stage Purpose Preliminary Treatment Screening and grit removal flow measurement

Secondary Treatment by

Bio-Remediation

Oxygenations by means of Aerations followed by

clarification-separations of effluent and sludge.

Sludge Treatment/Removal Sludge dewatering /digestions/ disposal




B. Sewage treatment facility with tertiary treatment and effluent used for irrigation

purpose. Level of Treatment: Tertiary treatment is provided to secondary treated sewage for re-use applications. Dualmedia granular filtration and subsequent disinfection is used as the tertiary level of treatment when TSE is intended to be used for irrigation of landscaping/agriculture where vegetables/crops not eaten raw are cultivated. Highly Advanced level of Treatment using Reverse Osmosis (R.O) is considered when TSE can be used for agriculture of vegetables/fruits eaten raw. The required Effluent standards would be as follows.

Sl No. Parameter Symbol Standard

1 Biochemical Oxygen Demand BOD5 10mg/l 2 Total Suspended Solids TSS 10mg/l

3 Ammonia cal Nitrogen NH3 1mg/l C. Sewage treatment facility with tertiary treatment and effluent used for fresh

groundwater lens recharge. Long-term, large-scale pumping without subsequent replacement of groundwater can result in fissures and land subsidence. The most serious problem is the permanent loss of an aquifers storage capacity. When considering Fuvahmulah Island in the drought especially in the month of March extraction of water from pure water lens is serially damage to the pure water lens. Artificial recharging can be applied in rainy season as well a in the drought. In rainy season rain water can be injected to the ground by construction of injection well at nearby areas of Sault water extraction wells. In the drought treated waste water can inject to the ground through injecting wells. Tertiary treated waste water can be recharged to the ground subject to strict quality control of the same, should there be any compromise on the quality, and the recharged water may result in adverse effect on the overall ground water. A provision of the tertiary treatment and necessary ground water recharge will be allocated in the Bills of Quantities as provisional items.

7 . 4 W A T E R S U P P L Y S Y S T E M

Various water supply alternatives were studied thoroughly during the concept design stage which included the surface source, Exploring ground water potentials, Rain Water Harvesting and Desalination. The process of RO system has many merits like less energy dependence, less maintenance, easy operation, few personnel, lower




thermal brine impact, advanced membrane technology, etc. Moreover, RO plants are widely and effectively used in many countries in such situations. Besides, RO plant is available locally in different capacities. And hence, could be adopted conveniently for the present and further expansion as per the growing requirements. Considering all these factors, especially on the social acceptability, RO plants for the design capacities are recommended for the islands of Fuvahmulah. As a standby it is suggested to maintain the RSW and wells catering for the washing and other purposes. Extraction of Sea water could be either by drilling a bore hole of 40-50m in the ground or direct extraction from the ocean. Groundwater extraction is through drilling a tubewell into the rock strata. The temperature of water extracted by this method is lower than that of water extracted from sea; this will affect the quality of treatment. Because of this low temperature a better quality drinking water could be produced compared to direct extraction from ocean. Other advantages include free from fecal contamination, better maintainability of the water extraction system and less likely to be damaged due to storms.

In the direct extraction system, a 200 mm pipe is laid though reef up to Deep Ocean and sea water is sucked by a pump through a strainer attached at the end of the pipe line, and pumped towards the RO plant. Further to a detailed techno - economic analysis, the bore hole sea water extraction is preferred in Fuvahmulah Island. Four number test bore wells are to be drilled and converted to two tube wells are proposed to extract deep groundwater which will feed water to 2 Nos R.O. Plants. If this option is not workable, the sea water pumping option is designed as optional item.

The water supply pipeline network is designed to cover the whole of the islands including houses and institutional building according to land use plan. However, the current execution works will be limited to community taps without household connections. At present, adequate provision is made to install stand posts fitted with taps depending on the number of houses within each block to facilitate convenient collection of safe drinking water.

7 . 5 R E V E R S E O S M O S I S P R O C E S S

The feed water for the operation of RO is from the tube well. After the primary treatment, water is subjected to RO treatment. Once, fresh water is separated, the water left behind called Brine needs to be disposed. Brine is highly dense and also




polluted. In RO, feed water is pumped at high pressure through permeable membranes, separating salts from the water. The feed water is pretreated to remove particles that would clog the membranes. The quality of the water produced depends on the pressure, the concentration of salts in the feed water, and the salt permeation constant of the membranes. Product water quality can be improved by adding a second pass of membranes, whereby product water from the first pass is fed to the second pass.

Quality of desalinated water from RO will be as follows.

Feed Water to RO Plant Product from RO Plant

Ca 448.00 0.60

Mg 1330.00 1.78

Na 11400.00 89.15

K 383.00 3.88

NH4 0.00 0.00

Sr 0.10 0.00

Ba 5.80 0.01

Fe 0.00 0.00

Mn 0.00 0.00

CO3 0.50 0.00

HCO3 132.00 1.88

SO4 2940.00 3.50

CI 20600.00 143.60

NO3 0.00 0.00

Fe 0.00 0.00

SiO2 1.00 1.01

CO2 2.66 2.63

Sum of lons 37240.40 244.41

TDS 37173.23 243.45

Ph 7.50 6.50

(asCaCO3) 6595.82 8.83




Feed Water to RO Plant Product from RO Plant

Hardness

7 . 5 . 1 P R O C E S S D E S C R I P T I O N

1. Ultra-Filtration as Reverse Osmosis Pre-filter System.

The UF Feed Pump will draw the sea water from a Sea water Storage Tank which sea water of Total Dissolve Solid < 38,000ppm is passed through the bag filter (100 micron) as the first line of protection to remove all large and abrasive debris prior to channeled to the UF system.

The UF system with the filtration pore size of 0.1 micron, which is very effectively removing the microorganisms and suspended from the sea water.

The permeate is then passed through the Ultra-Filtration (UF) unit operating in a dead-end mode and stored in the UF Back Flush Tank and UF Permeate Tank (supply by others). The unit comprises of a number of UF S860 Ultra-Filtration membrane with preset timer for automatic back flushing. The water for the back flushing is drawn from the UF Back Flush Tank. The UF S860 membrane has pore size of less then 0.1 micron and is capable of producing permeate with high degree of cleanliness suitable as Reverse Osmosis (RO) feed water. Thus, the RO unit will be able to maintain high flux and quality of permeate water with minimum maintenance and worries on the clogging or fouling.

The UF Back Flushing water is discharge back to the sea. 2. Reverse Osmosis (RO) System for Sea Water Desalination Process.

The RO process operates in a cross flow mode with 40% recovery where high pressure pump drawn the water from UF Permeate Tank and feeding toward RO unit. The UF permeate is first passed through a guard filter follow by treating with anti-scalant and neutralization with Sodium Meta-Bisulphate. The guard filter is just another precaution to protect the RO unit in the event of any contamination from the UF Permeate Tank.The dosing of sodium Meta bisulphate is also able to serve as disinfection.

The RO Permeate with Total Dissolve Solid < 500ppm is then channeled to the RO Permeate Tank. The Reject water with Total Dissolve Solid > 60,000ppm is diverted to the Energy Recovery / Pressure Exchange Unit to recover most of the waste energy prior to discharge back to sea.




Chlorine could be added at the RO Permeate for further disinfection prior to supply to the consumer.

Cleaning-in-place (CIP) for RO is used to provide chemical cleaning periodically to eliminate the clogging issue.

Detailed RO process flow diagram is attached in Appendix- E

7 . 6 W A T E R S U P P L Y D I S T R I B U T I O N

The two options considered were Water supply network with above ground storage tank with a 15 -20 m height water tower and Water supply system with pressurized pumped loop system. On the storage tank option, treated water from RO plant will be stored in an above ground tank designed for 6 hours of average day demand and further it is pumped to a 10-15 m height water tank tower which is designed for 4 hours storage of average day demand. The ground tank will be GRP and the tower tank shall be constructed by Reinforced Concrete. On the pumped loop system, Triplex or Duplex pumps with pressure regulator are used to maintain the head throughout the piping network. The pump will start and stop according to the pressure reduction in the water supply piping network caused by water usage. The storage tank option was selected for further detailed design works.

7 . 6 . 1 . D E S I G N C O N S I D E R A T I O N S

Water demand estimates

Per capita water consumption for drinking and culinary application has been estimated at 30 litres/ person/ day, considering a population of 16206 people. Peak daily demand is taken as 2.5 times of average daily water demand.

Network sizing

The pipe sizing is done considering the peak flow rate expected in the network. It has also considered the future requirement to provide house connection to the residents. The maximum velocity in the pipe network is set to below 1.5 meters/ second. The maximum flow is expected only on the feeding line from the elevated tank to the pipe network. The network analysis is done with EPANET software is attached in Appendix- D Water supply hydraulic calculation. For the purpose of the calculation, the total flow of 29.3 L/s is assumed to deliver through 30 outlets, each with a discharge flow of 0.975 L/s. The outlets are strategically located considering the density of population. The density of outlets in the water network will be high where the population density is high and vice versa. The distribution of the valve outlet and the flow parameters derived from the calculation thus provides a realistic water flow




distribution through the network. The maximum velocity on the feeding line is 1.66 meters/ second.

Inference

A minimum pressure of 9.69 meter pressure is available at the hydraulically most remote flowing node (node 92). Maximum flow velocity of 1.66 meters/ second is developed on LINK 1, which is the main supply header from the overhead tank at the calculated peak flow of 29.25 L/s.

8 . 0 D E S I G N S T A N D A R D S

8 . 1 S E W E R A G E D E S I G N S T A N D A R D S

The plots within the Fuvahmulah Island shall be provided with a comprehensive Vacuum based system for sanitary pipe work. All plots have individual inspection chamber and is connected to the foul water system network. The whole island is divided as 2 zones; each zone has its own vacuum station. Pressure lines from each vacuum zone are connected to the sewage treatment plant.

Sanitary Water Drainage Design Data.

GEOGRAPHICAL INFORMATION

Area 420.00 Hec MOAD

Length 4500m MOAD

Width 1200m MOAD

Distance from Male 493.67 km MOAD

Longitude 73o 25' 40' E MOAD

Latitude 00o 17'53" N MOAD

PROJECTED POPULATION

POPULATION CURRENT 10506 MOAD

GROWTH RATIO 1.3% MOAD

PROJECTED POPULATION IN 30 YEARS 14604 MOAD

ADD FOR MIGRATION (15%) 2191 MOAD

TOTAL PROJECTED POPULATION IN 30

YEARS

16206




TOTAL NO. OF HOUSEHOLDS/ BUILDING 2639 MOAD

AVERAGE NO OF PERSON/ HOUSEHOLD 6 MOAD

Flow calculation is based on MWSA design criteria for sewage network 2007.

EPA Alternative Wastewater collection system, Chapter-3 (Attached as Appendix-I)

Guideline of developer volume II (From Malaysia water association) (Attached as

Appendix-I)

Min Pipe Cover - 900 mm as per MHTE Sewerage

design criteria

Discharge load and hydraulic calculations - BS EN 12056

Amount of sewage is calculated based on the total population. From the above design data projected population for 30 years = 16206 According latest received land use plan from MOH total number Of plots including existing, under construction and future plots, = 2639 Therefore average no of person per house = 16206/2639 = 6.1 6 According to MWSA design criteria 2007 Average daily water usage/ Person = 180 lpd. For design of sewage system consider 70 - 80 % of water usage / person/day. Total waste water generated / person/ day is 180* 0.80 = 144 Other Standards used for the design works are as listed below

Sanitation Guidelines from MWSA 2003 General guidelines for domestic waste water disposal from MWSA 2006 EPA Alternative Wastewater collection system, Chapter-3 (Attached as Appendix-I) Guideline of developer volume II (From Malaysia water association) (Attached as

Appendix-I) General EIA Guidelines from MWSA 2004 Five years Activity Plan of MWSA (2006-2010) May 2006 Water & Sanitation policy statement from MEEW July 2005 Design Criteria for sewerage system from MEEW Jan 2007




International Water Supply & Sewerage Design Criteria Wastewater disposal guidelines, MWSA

8 . 2 W A T E R S U P P L Y D E S I G N S T A N D A R D S

Water supply pipe line network is divided in 02 zones. The piping network consists of 100mm, and 80 mm size HDPE pipes according to ASTM standard. The main water supply network loop would be of 100mm and sub lines are of 80 mm diameter pipes. The total network is designed such as it should be able to deliver constant flow, with minimum head of 5m at the farthest point at all times. Valve chambers are provided at each junction of main line and sub lines, for providing servicing and maintenance easiness. The network is designed such as it should be easily accessible from each individual housing and institutional plots, so that, future authority can make the individual connection comfortably, according to future water demand. The system is developed for Fuvahmulah Island is designed in accordance with international standards and the following regulations.

Sanitation Guidelines from MWSA - 2003 General guidelines for domestic waste water disposal from MWSA 2006 General EIA Guidelines from MWSA -2004 Five years Activity Plan of MWSA (2006-2010) May 2006 Water & Sanitation policy statement from MEEW July 2005 Design Criteria for sewerage system from MEEW Jan 2007 International Water Supply & Sewerage Design Criteria

The current British Standard Specifications and Codes of Practice apply to all construction works and materials. For design calculations 30 Liter per day per person is considered which is for the drinking and cooking purposes.

9 . 0 D E T A I L E D D E S I G N O F P R O J E C T C O M P O N E N T S

The detailed design calculations are attached to the following Appendices A, an abstract of the calculations with the methodology is narrated below.




9 . 1 S E W E R A G E N E T W O R K - V A C U U M S Y S T E M

UPVC pipes of minimum 110 and 160 mm size are used for the household 600mm HDPE inspection chamber and further connection to Vacuum collection chambers (VC), whereas the main Vacuum sewer is made of 110, 125, 160, 200, and 250 mm PVC Schedule 40, SDR 21 solvent welded pipe, to meet the future population and laid in a saw tooth profile with a slope ranges from 0.2 % to 2%. (1) For 100-125 mm diameter pipe: 80 % pipe diameter or 0.2 % gradient. (2) For 150-250 mm diameter pipe: 40 % pipe diameter or 0.2 % gradient. The design of vacuum sewage profile is based on attached EPA alternative sewage design criteria (Appendix-I) table 3-2, 3-3, 3-4, and lift height is based on table 3.1. The minimum suction pressure at each vacuum interface unit will be 5 ft and the frictional losses in the vacuum pipe will not go beyond 2 feet. The losses on account of static lift will not go beyond 11 feet. The upper velocity limits are even more in the vacuum sewers which exclusively depend upon the value of vacuum in the vacuum sewage network. The velocity may up to range 4.6 5.5 m/sec depends on value of volume in line and vacuum pipe diameter, thereby providing a non-clogging and trouble free drainage system. Two Vacuum Stations are provided in Fuvahmullah at convenient and suitable locations to develop sufficient vacuum pressure in each sewer zone. The total available head loss for vacuum station should be between 18 to 23 feet.

All Sewage Vacuum network is designed for a projected population of 30 years. Design flow is calculated based on the following methodology. a) Considered daily waste water generated should be equal to 144 Lit/Day/Person

which is 80% of total water consumption/person/day i.e. 180 Lit/day/person (MWSA Design Criteria). Remaining 20% is considered as losses by evaporation and transportation.

b) All gray water and black water from each house, Institutions and Industries are connected to the sewage network.

c) Design flow is obtained by adding Peak Dry Whether flow, and Institutional flow. d) Peak Dry weather flow is obtained by multiplying peak factor to average dry weather

flow. e) Average Dry whether flow is obtained by multiplying 30 years projected population to

waste water generated per person per day (144 LPD). f) Design Flow Calculation




Wastewater flow rate per day (average flow) = 2,700.00 m/day = 112.50 m/hr

Peak flow factor is vary from place to place depending on variables design consideration such as premises type, water consumption per person per day, daily peak hour, seasonal activity and population size. The most important criteria to be incorporated in this design are knowledge relating to local conditions which may affect directly to the sewerage system daily operation. Therefore, the flows estimation used for the vacuum sewerage system in this project based on the Code of Practice for the Design and Installation of Sewerage Systems.

Peak flow factor (assumption) = 3.8 Design wastewater flow rate (peak flow) = 427.50 m/hr = 7.13 m/min Number of vacuum station = 2nos Design wastewater flow rate (peak flow) per vacuum station = 213.75 m/hr

= 3.56 m/min g) Vacuum Sewage system Design.

Vacuum Sewer Reticulation The vacuum sewer network is designed based on the peak flows of the propose development and the individual pipe size selection which depends on:- ( a ) The capacity of wastewater to be collected and conveyed by the sewer reticulation. ( b ) The distance of the vacuum sewer pipeline. The selection of the vacuum sewer pipe sizes shall be based on the table below (From Guideline of developer vol.2 (Malaysia water association attached in Appendix-I) :

Vacuum Sewer Maximum Flow Maximum Nominal Diameter Transported Pipe Length

(mm) (Liters/Sec) (m) 110 2.0 600 125 5.0 1000 160 10.0 1500 200 16.0 No limit 250 30.0 No limit

If the lengths recommended for the pipe size are exceeded prior to flow limit being reached, then the next size of sewer is chosen irrespective of the flow being transported. The minimum and maximum pipe sizes recommended for the Network System's collecting and conveyance mains shall be 100mm and 250mm respectively. However, the "crossover" pipe work connecting a collection chamber to the vacuum network mains




shall be typically 90mm nominal diameter. A saw-tooth profile enables sewers to be placed at shallow depths along its length, and can be designed to ensure that sewage seals the pipe at low points within the network. A lift within a saw-tooth profile shall consist of two 45 degree elbows and a straight piece of pipe. Ideally the minimum distance between two adjacent lifts should not be less than 3 meters so as to avoid possible sewage backflows within the sewer system. Generally the vertical drop between lifts shall be the larger of: - For 100-125mm diameter: 80% pipe diameter or 0.2% gradient - For 150-250mm diameter: 40% pipe diameter or 0.2% gradient In general vacuum sewers are sloped at minimum gradient of 0.2 percent towards the Vacuum station.

h) Typical Vacuum Valve chamber design. The vacuum valves we propose to the Fuvahmulah project are single valve collection chamber. The valve can be serving up to 40 liters per cycles. Base on the Fuvahmulah design, 90 % of valve chambers are connected by a group of 10 houses then Total flow towards each pit = 10x6x144 liter/day

= 8,640liter/day or 6 liter/min. Total peak flow per minute = 6 liter/min x 5 (peak flow factor)

= 30 liter/min. Therefore, Maximum interface valve operate per minute = 30 liter/min Divide38 liter/cycle =0.75 time/min. The sump heights of 76 cm and 135 cm both 45 cm in diameter at the bottom and 90 cm in diameter at the top will be used depending upon the above flow requirement. For any increased flow based on future site condition same sump pit size with depth up to 1 meter is recommended. One 7.5 cm (3 inch) diameter opening, with an elastomeric seal, is pre-cut should be installed to accept the vacuum sewer line. The pit bottom should be 6 mm thick at the edges and 8 mm thick in the center. Valve bottom should be provided with holes pre- cut for 7.5 cm suction line, 10 cm cleanout/sensor line and the sump securing bolts.




Cast Iron covers and frames generally 45 kg and 40 kg weight should be used for covering the valve chamber. The deepest section for fiberglass material valve pit shall be 2.4 meter, therefore any for any section of valve pit deeper than 2.4 meter should be of Reinforced cement concrete and the maximum depth of reinforced cement concrete section should be 3 meter, however, the special care is required to select the depth of Valve Pit depth, since the amount of lift available is going to be 1.5 meter (5 feet). A typical Buffers Tank is designed and attached in the design drawing to take care of larger flows for attenuation coming from institutions like schools, hospitals and offices. (Refer to Fig. 3-14. EPA Alternative Wastewater Design criteria Chapter 3) for flow capacity more than 2 L/s.

i) Vacuum Station Equipment Design.

a. Vacuum Pump Design.

The vacuum pumps are operate on a duty and standby/assist mode. The vacuum pumps will operate through electrical control panel which base on signal from pressure switches fixed on the collection tank. The vacuum pumps and collection tanks are sized to evacuate the collection piping to its operating level is not greater than 3 minutes, nor less than 1 minute. The vacuum pump capacity required (m3/min), Qvp = A x Qmax where, Qvp = The vacuum pump capacity required (m3/min)

Qmax = Design flow rate (peak flow) A = Factor in vacuum pump sizing

Factor in vacuum pump sizing, A = (Air liquid ratio x Atmosphere pressure) / Absolute pressure b. Discharges pump Design.

The discharge pump capacity required (m3/min), Qdp = 1.1 x Qmax where, Qvp = The vacuum pump capacity required (m3/min)

Qmax = Design flow rate (Peak flow) A = Factor in discharge pump sizing

c. Pump discharge head calculation.




Total head of the discharge pump, HT = Ha - Pc/9.8 + hs + hd Where, HT = Total heads (m)

Ha = Actual static heads (m) Pc = Max degree of vacuum collection tank (kPa) hs = Head loss of suction pipe (m) hd = Head loss of delivery pipe (m)

d. Vacuum collection tank design. Design Criteria

The vacuum collection tank size is selected base on four important factors as follow:- (a) The volume allowed for wastewater collected and vacuum pressure storage is

enough. (b) The tank structure is a safe to sustain a negative pressure of -80kPa. (c) The tank is made by an anti-corrosion material, or have a corroded spare thickness

and anti-corroded coating. (d) The consideration of sludge or rubbish removal without affected to the vacuum sewer

operation. At the project, the storage volume of the tank is calculated based on the volume of sewage collected as the dry weather flow (average flow) enters the collection tank over a period of 10 minutes (also to comply MS1228:1991 minimum 6 cycles/hour for pump operation)

Design Capacity

The operational capacity (VO) for wastewater vacuum collection tank is calculated using the formula below.

Vacuum collection tank design capacity, Vct = 3 x Vo

At design waste water flow, Qin(max) > or = 1/2 Qout

Vo = T x Qout / 4 where, Vct = Collection tank design capacity (m3)

Vo = Operational capacity (m3) T = Discharge pump operate interval (minute) = 10.00 min

e. Bio filter Design

Bio Filter is sized by using the following formula




Vm = Q x EBCT 60 s/min

where, Vm = Media volume (ft3) Q = Airflow rate (ft3/min) EBCT = Empty Bed Contact Time (s), 15 seconds

Detailed design Calculation of Vacuum Sewage system is attached in Appendix A

9 . 3 S E W E R A G E N E T W O R K - P U M P I N G M A I N S

a) Design of pumping main from each vacuum station is designed based on 30 years projected population design flow.

b) Flow velocity should be between 0.6 to 3.5 m/sec c) Diameters of pumping main HDPE pipe shall be of 300 mm and 250mm dia, to

reduce the frictional loss and increase the pump stability. d) All pipe bends and supports shall be supported with thrust blocks. e) Pipe junctions will be provided with valve chambers.

Detailed Calculations are attached in Appendix A

9 . 4 S E W A G E T R E A T M E N T P L A N T

Oxidation Ditch Process based on Activated Sludge with Extended Aeration System is selected as sewage treatment process for Fuvahmulah Island. The selection of a particular process for sewage treatment is affected by diurnal and seasonal flow variations, sewerage strength (variability of wastewater constituents) infiltration / inflow, ambient temperature and its induced septicity, degree of treatment required, magnitude and direction of wind etc.

The extended aeration process holds wastewater in closed endless loop channel to aerate for 18 hours or more and the organic wastes are removed under aerobic conditions. Air is supplied by mechanical rotor through rotating action. The wastewater is screened to remove large suspended or floating solids before entering the aeration chamber, where it is mixed, and oxygen is added. The solids settle out and are returned to the aeration channel to mix with incoming wastewater. The clarified wastewater flows to a collection channel before being diverted to the disinfection system. The sludge is periodically removed from the units. In Aeration tank (extended aeration), suspended microbial growth is maintained for the biological oxidation of organics. Surface or




Diffused aeration system is provided to meet the oxygen requirement of micro organisms and to keep the liquor in completely mixed regime. The site selection for the outfall location was based on the locations identified for the sewage treatment plant (STP). The location for STP was initially identified in consultation with island community especially with that of the officials in the Island office. The island office been the responsible agency indicated the potential areas for the STP based on the housing plots, the need for future housing plots and other essential infrastructure. The final approval for the STP site was based on the consultation with Ministry of Housing and Urban Development (currently under Ministry of Housing, Transport and Environment) to ensure that the sewerage network and related infrastructure is appropriately included in the future development plan for the island. Amount of sewage going to sewage treatment plant is calculated based on the total population. From the above design data projected population for 30 years = 16206 According latest received land use plan from MOH total number of plots including existing, under construction and future plots, = 2639 Therefore average no of person per house = 16206/2639 = 6.1 According to MWSA design criteria 2007 Average daily water usage/ Person = 180 lpd. For design of sewage system the international practice is taking 70 - 80 % of water usage / person/day. Then total waste water generated / person/ day is 180* 0.80 = 144

STPFLOWCALCULATIONFuvahmulah

Present 11000 144 1,584,000 158,400 79,200 1,822 After15years 13352 144 1,922,635 192,264 96,132 2,211 After30years 16206 144 2,333,665 233,367 116,683 2,684

Averageflow/Person/DayinLitter

AverageflowtowardsSTPinLittre/day

Assumed10%ofaverageflowasInstitutionalflow

Assumed5%ofaveragedailyflowasotherflows

TotalFlowtowardsSTPinM3/Day

Description Population




Based on above calculation a treatment plant facility should be provided for a capacity of 30 years, (ie 2700 m3 Average daily flow) design period and equipments are designed for 15 years projected population.

Detailed Calculations are attached in Appendix B

9 . 5 S E A O U T F A L L

The Outfall discharge pipe should be made of 250 mm HDPE pipe, which is laid on a trench over the reef and ocean by using concrete ballast blocks located at an appropriate distance. The Ocean Outfall effluent mixing Design Criteria is taken as a minimum port exit velocity of 4m/sec, initial dilution as 1:100 and Bacterial reduction to be 1000 MPN/100 ml.

The shoreline consists of a narrow (5 to 15m) berm of coral sand mixed with rubble and then a wide, partially sub-tidal shelf of coral rock, with sandy lagoon inter mixed, with relatively suitable surface (superficial) that appear suitable for direct laying of a pipeline. Current speeds on the shelf at the time, as observed at the shoreline only, were very low and would not affect the construction method The island of Fuvahmullah with several openings, therefore oceanic currents influence and tidal fluctuations and its influence to the atoll basin is relatively good with high mixing potential and short residential time of atoll lagoonal waters. Proposed site for STP was inspected in October 2008 and March 2009 and a site at the south-eastern end of the island has been selected from the two sites short listed It is likely that the outfall alignment would take it SE beneath the land and foreshore to a -15 m MSL, following a depth contour over a length of about 240m. Current measurements were undertaken using a drogue system and a GPS, leading to currents in the order of 0.5to 0.7m/s in a coast parallel direction (southeast to northwest along the reef margin). This current speed enhances initial dilution and keeps the plume away from the coast (follow the reef margin). Tide range on that day (also annual) was relatively small (approximately 1 m) and this current was most likely caused by the tidal currents and wind speed at the time of the recording winds (up to 10 knots estimated, as measured by hand-held anemometer). Ocean currents are variable in the Maldives influenced by tidal (whole water body) and wind (surface) driven movement of water body. Due to the small amplitude of tide currently speeds within the atoll are relatively small. However, currently of 0.7 m/s or above has been recorded, which are considered strong, in the narrow passes in the atoll rims of Maldives. It is estimated that currents of 0.2m/s will




facilitate adequate mixing of the effluents. Although the island is within the atoll basin, relatively wide channels on all sides of atoll peripheral reefs provide a setting for appropriate mixing of the effluents especially with that of secondary level treatment as proposed.

Seabed inspection showed that the bed is essentially coral rock with well consolidated coral formations including encrusting and massive coral formations, more true beyond the surf zone. Near-shore seabed substrate is dominated by sand intermitted with coral and rocky out crops. Some seabed preparation will be required to ensure that the pipeline and installation collar weights are laid on the seabed without being twisted so that the collar weights are in even contact with the seabed.

Initial Dilution The Initial Dilution can be calculated by using the following equation: S = ubz/Q Where S Initial Dilution u Ocean Current Speed m/s 0.7 m/sec b Effective Diffuser Length m 0.4 m z Effective Mixing Depth m 15 m Q Wastewater Discharge Rate 0.05 m3/s Diffuser Port Dimensions Discharge Pipe Diameter 200 mm Pumping velocity 1.6 m/s Discharge 0.05 m3/s Assume that opening in discharge pipe is 40% of the pipe area Effective area of discharge port (3.14*0.25*0.20*0.20*0.4) 0.01256 m2 Hence Diffuser Exit Velocity (0.0316/0.007065) 4 m/s Initial Dilution For Sea Outfall Sea Current Velocity 0.7 m/s Therefore Initial Dilution (S)= ubz/Q (0.7*0.40*15/0.05) 84 Say 84 Since the Initial Dilution is less than 100, so increase the depth of Diffuser and then calculate until it become more than 100




Detailed Calculations and Plume modeling software outputs are attached in Ocean Outfall Design Appendix C

9 . 6 W A T E R S U P P L Y N E T W O R K

The pipeline network is designed to cover the whole of the islands including houses and institutional building according to land use plan. However, the current execution works will be limited to community taps without household connections. At present, adequate provision is made to install stand posts fitted with taps depending on the number of houses within each block to facilitate convenient collection of water. a) All networks are designed for a flow of 30 years projected population. b) The minimum size of the distribution network is maintained as 80mm and the

required terminal pressure at all the supply points will not be less than 5 meters, as per International Water supply and sewerage criteria.

c) All water supply network lines are designed for a peak hour flow considering 2.5 times of average flow.

d) Institutional flow assumed as 10 % of average daily flow. e) Currently 30 outlet points are taken for software simulation in total Island network. f) Detailed Design calculations are done by using EPANET hydraulic network design

software. g) Assumed all 30 outlet points are operating at a time in most remote area from

reservoir, and each outlet point can deliver a flow of 0.975 liter/second. h) The Earth cover over pipe is taken as 0.9m in vehicular traffic lanes and for non

vehicular lanes cover is provided as 0.6m i) All lines having earth cover equal to or less than 0.6 m because of topographic

problem shall be having the concrete encasement. Water supply detailed network calculation using EPANET software is attached in Appendix D

9 . 7 R E V E R S E O S M O S I S P L A N T

Further to a detailed techno - economic analysis, the bore hole sea water extraction is preferred in Fuvahmulah Island. Four number test bore wells are to be drilled and converted to two tube wells are proposed to extract deep groundwater which will feed water to 2 Nos R.O. Plants. If this option is not workable, the sea water pumping option is designed as optional item.




The location for RO plant (freshwater production) was initially identified in consultation with island community especially with that of the officials in the Island office. The island office been the responsible agency indicated the potential areas for the STP based on the housing plots, the need for future housing plots and other essential infrastructure. Consequently this was approved by MHTE. The shoreline consists of a narrow (5 to 15m) berm of coral sand mixed with rubble and then a wide partially sand and coral mixed sea bottom. Pipeline length is about 250m from the proposed pump station (RO plant). The terminal end of the brine (concentrated saline water from the desalination plant) would thus be in the sub-tidal lagoon consisting of sand and coral substrate. The average depth of the lagoon to the terminal end of the brine disposal outlet is 1m MSL. With the sub-tidal nature of the lagoon and diurnal tidal variation experienced in the Maldives it would be fairly accurate to conclude that there would be adequate flushing and dilution of the effluents quickly to the background salinity of seawater (32-36ppt).

RO Plant designed for 15 years period

Calculated Maximum Daily Requirement = 672,000 Lpd

Input Capacity of RO Plant per hour = 133,500 Liter per hour

Input Capacity of One RO Plant = 70,000 Liter per hour

Output Capacity of One RO Plant = 28,000 Liter per hour

Provide 2 No. RO Plant of input Capacity 70,000 Liter per hour

The input capacity of one No R.O. Plant will be 70,000 Liters per hour which will deliver clean water @ 28,000 liters per hours and brine water @ 42,000 liter per hour.

Detailed Calculations are attached in Appendix E

9 . 8 S T O R A G E T A N K

Storage Tanks designed for 30 years period

Total Daily Water Consumption = 534600 Liter

Ground Storage Requirement = 6 hours

Capacity of Ground Storage Tank = 135 m3, GRP Tank

Tower Tank Storage Requirement = 4 hours

Capacity of Tower Storage Tank = 90 m3, RCC Tank




Pumping Machinery for Clear Water = Designed for 15 years

OH tank storage capacity for 30 years = 73425 Liters/day

Transfer pump Capacity for 2 hour pumping = 37 m3/hour

Provide 3 Nos pumps of capacity 13 cubic meter per hour each @ 20 m head, both working based on float sensors. The balance capacity will be provided in future.


9 . 9 B R I N E W A T E R C O L L E C T I O N & D I S P O S A L S Y S T E M

Design Period considered is 30 years for Brine Tank, 15 years for pumping Machinery

Average volume of Brine generated from R.O. Plant = 801900 Liters per day

Provide nominal storage of 4 hours = 133650 Liters per day

Capacity of Brine Storage Tank = 134 M3, RCC Tank

Max day volume of Brine generated from 2 R.O. Plant = 110138 Liters per day

Considering 4 hours working, pump capacity = 28 M3 per hour

Provide 3 Nos pumps of capacity 10 cubic meters per hour each, both will act as duty pumps with no standby. The balance capacity will be provided in future.

Total Maximum daily requirement = 486000 Liter per day

Total maximum Brine production after 30 years = 1166400 Liters per day

Considering 3 hours storage, total flow through brine discharge pipe will be 146 m3/hour Assuming Velocity of 2.5 m/sec, Diameter required for brine outfall pipe line = 0.061 m Selected pipe diameter is 6 " ie 150 mm dia HDPE pipe is selected for Brine out fall.


9 . 1 0 F E E D W A T E R S T O R A G E T A N K .

Feed water requirement after 30 years = 1944000

Liters per day

Provide nominal storage say 3 hours 1/8 th of day demand = 243000 Liters




Therefore select a feed water storage tank capacity of = 240 M3


9 . 1 1 T U B E W E L L

Tube Well designed for 15 years period & 30 years for feed storage tank

Total input water requirement for R.O. Plant = 133,500 Liters per Hour= 37 lit/sec

Safe Yield = 25 Liters per second

Therefore No of Tube Wells required = 2 No

Detailed Calculations are attached in Appendix F

9 . 1 2 O C E A N I N T A K E

S T R U C T U R E ( O P T I O N A L )

Total flow through feed water intake pipe should be 243 Cubic meter per hour

For getting a pumping velocity of 2.5 m/sec the required discharge pipe diameter = 200 mm

Selected pump Capacity =45 M3/hour @ 10 m head.


Dia of Housing Pipe ( Steel) 9 mm thick 30 cm Length of Housing 50 meters Dia of Strainer 25 cm Length of Strainer 20 meters Length of Blind pipe (Steel of 9 mm thick) 12 meters Dia of Blind pipe (Steel of 9 mm thick) 25 cm Dia of Bail Plug 25 cm Length of Bail Plug 2.5 meters Total depth of bore well 84.5 meters Thickness of Pea Gravel 12.7 cm Dia of gravel 63.5 cm

Volume of Pea Gravel 6.5 Cubic meters




9 . 1 3 C I V I L / S T R U C T U R A L

The buildings designed comprises of an Administration building, a R O P unit, a C S T U building, Tube Well Building and an overhead water tank structure along with the vacuum station and STP concrete chambers.

STRUCTURAL DESIGN PARAMETERS: Codes of Practice:

BS8110: Part -1: 1996 Structural Use of Concrete

- Code of Practice for Design and Construction

BS6399 - 1: 1996 Loading of Buildings

Part 1- Code of Practice for Dead and Imposed Loads

BS6399 - 2: 1996 Loading of Buildings

Part 2- Code of Practice for Wind Loads

Uniform Building Code (UBC) - 1997 - Volume 2

BS648 Weights of Building Materials

AISC Structural Steel Design Manual

Material Properties:

Strength of Concrete:

For the structure works, concrete of grade C25 (or 25N/mm2 cube compressive strength) is used for superstructure and C35 (or 35N/mm2 cube compressive strength) for substructure works For sub-structure works, the cement used in the concrete is Sulphate Resistant Cement (SRC).

Compressive strength of concrete (blinding) = 10N/mm2

Compressive strength of concrete (reinforced) = 25N/mm2 (for superstructures)

Compressive strength of concrete (reinforced) = 35N/mm2 (for substructures)

Yield Strength of steel reinforcement = 460N/mm2

Cover to Steel Reinforcement:

Appropriate concrete cover to all reinforcement is to be provided to minimize the risk of corrosion to the steel reinforcement in reinforcement concrete.

Columns/ Beams = 40mm

Slabs/Ribs = 30mm




Foundations = 50mm

Concrete finishes: Concrete finishes are in accordance with architectural requirements.

Concrete Material Properties:

Density = 3000kg/m3

Youngs Modulus = 25000N/mm2 (Short term), 9000N/mm2

(Long term)

Poissons Ratio = 0.2 (allow for creep & shrinkage)

Coefficient of thermal expansion = 9.9 x 10-6 / C

Steel Strength: = 44ksi.

Soil Bearing Capacity: From the bore hole reports, the SBC is considered as 65 KN/m2, the values are to be checked by the Contractor and provisions made in contract accordingly.

CALCULATION OF LOADS:

The structures are modeled in 3dusing STAAD/pro software is a 3D frame. Loads are as follows:

Self weight of structure = taken by STAAD/Pro and SAP 2000

Finishes (SIDL) = 4.0kN/m2

Wall loads = 0.20 x 22 x 3.6 = 15.6kN/m

Wind loads = as per code (taken by STAAD & SAP)

(Refer BS 6399: Part 2 - Loading of buildings code of practice f