Design of Partially Combined Sewerage System

7/24/2019 Design of Partially Combined Sewerage System

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PROJECT DESCRIPTION

IDEA OF FUTURE VISION PROJECT

The Future Vision housing scheme project is for providing an economical & perfect residential area for

the people especially of the middle class society with the basic requirements.

The required sewerage system is to be designed to facilitate the people.

GENERAL DESCRIPTION:The Future vision housing society is a complete residential neighborhood in all respects. The scheme

comprises of:

An English-medium school.

Two hundred & Eighty one (281) houses divided into different blocks(A To M).

Three(3) flats & Apartments each.

a well equipped dispensary, with cooperative staff.

Parks.

Graveyard.

These facilities provide ease to the residents All the basic necessities including electricity, gas,

telephone and water are available. The scheme also has its own waste water treatment plant.. Being

adjacent to the Jhelum road, the housing scheme is very easily accessible by road, lying at just 15

minutes drive from Jhelum city.

GEOGRAPHICAL LOCATION:

The Future Vision Society is situated on the west bank of the Upper Chenab canal, 10 km along the

Jhelum road

HOUSING PLAN:

The Future Vision Housing project Housing Plan is divided into: Independent Housing Plots

Apartments(3)

Flats (3)

The independent plots in the society have been divided into 13 housing blocks which are

named: A to M for distinction.

The detail of no. of each housing units is given below

CHAPTER 1


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RELATED THEORY

SEWERAGE:It is the liquid waste or waste water produced as a result of water use.

SEWER:Sewer is a pipe or conduit, generally closed, and flow takes place under gravity.

SOURCES OF WASTE WATER:Sources of waste water or sewage are commonly encountered are:

Domestic Wastewater

It is the waste water from houses, office, other buildings, hotels and institutions.

Industrial Wastewater

It is the liquid waste from industrial process.

Storm water

It includes surface runoff generated by rainfall and the street wash.

COMPONENTS OF WASTE WATER ENGINEERING:

1) Collection system (network of sewer pipes)

2) Disposal work (sewage pumping stations, outfalls)

3) Treatment works (for rendering waste water treatment)

TYPES OF SEWERS: Sanitary sewer

It carries sanitary sewage i.e. waste water from municipality including domestic and industrial

waste water.

Storm sewer

It carries storm sewage including surface runoff and street wash.

Combined sewer

It carries domestic, industrial and storm sewage.

House sewer

It is the sewer conveying sewage from plumbing system of a building to common or municipal

sewer.

Lateral sewer

This sewer carries discharge from house sewer.

Sub main sewer

Chapter 2


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This sewer carries discharge from two or more laterals.

Main / Trunk sewer

It receives discharge from two or more sub mains.

Outfall sewerIt receives discharge from all collecting system and conveys it to the point of final disposal.

TYPES OF SEWER SYSTEMS:

Separate system

In this system storm water is carried separately from domestic and industrial waste water.

Combined systemIn this system sewers carry both sanitary and storm water.

Partially combined system

If some portion of storm or surface runoff is allowed to be along with sanitary sewage, the system is

known as partially combined system.

The sewerage system of the Future Vision scheme has been designed according to partially combined

system, being the most economical option in a developing country such as Pakistan.

DESIGN PERIOD FOR SEWER SYSTEMS:1) Design of Sewer system

Period of design is indefinite, as the system is designed to care for the maximum development of

the area.

2) Design of Sewage pumping station

Design period is usually 10 years.

3) Design of sewage treatment plant

Design period is usually 15-20 years.

STRENGHT OF RCC PIPES:Three edge bearing test is used to measure the strength of R.C.C pipes. Load is applied on the pipe to

produce 0.25mm crack. The test defines the load that can be safely supported by the sewer.

JOINTS IN SEWER PIPES:There are two types of joints in Concrete (up to 300 mm diameter) and R.C.C pipes (greater than 300

mm diameter)

Bell and Spigot joint (Employed for sewers from 225 mm to 600 mm diameter)

Tongue and groove joint (employed for sizes greater than 600 mm diameter)

SEWER APPURTENANCES:Appurtenances ate those devices, in addition to the pipes and conduits, that all essential for the

operation of the sewer system. They include:


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1. Manhole (provided when drop is less than 0.6m)

2. Drop manholes (provided when drop is more than 0.6m)

3. Inlets

An inlet is an opening into a storm or combined sewer for entrance of storm runoff. It is designed to

permit the passage of water from the street surface into the sewer

a)

Curb inletb) Gutter inlet

c) Catch basins

4. Flush tanks

5. Inverted siphon

6. PUMPING STATIONS:Used to elevate and transport waste water when:

Continuation of gravity flow is no longer feasible

Basements are deep

Any obstacle lies in the path of sewerReceiving stream is higher than the sewer

Sewage is to be delivered to and above ground treatment plant

MAIN COMPONENTS OF SEWAGE PUMPING STATION:Screens

Dry well (for installation of pumps)

Wet well (for receipt of waste water)

Pumps (along with valves, force main, motor, control panel etc)

Design of wet well and pump selection:

In small pumping stations, where pump is sized to meet the peak the peak or maximum flow, the

following considerations are made:

The detention time in the wet well at average flow should preferably be not more than 30

minutes.

The pump must run for at least 2 minutes

Cycle time must not be less than 10 minute.

DESIGN CRITERIA

Complete details are given here regarding all aspects of design of waste water disposal system for this

project.

The Design procedure aims primarily to determine the:

Diameters

Slopes of the pipes to be laid.

CHAPTER 3


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THE SEWER SYSTEM:

For the type of waste water disposal system, three(3 )options were available as shown below:

TYPE OF SEWER SYSTEMS CHARACTERISTICS

Separate systemAll sanitary and storm sewage carried in separate

sewer pipes.

Combined systemAll sanitary and storm sewage carried in same

sewer pipe.

Partially Combined system.

All sanitary sewage carried with a portion of

storm sewage or surface runoff in same sewer

pipe.

SELECTED SEWER SYSTEM: Partially Combined system.

DESIGN SEWAGE FLOW CRITERIA

In general, the design sewage flow for sewer system is calculated using the following equation:

PEAK SANITARY SEWAGE FLOW:

The peak sanitary sewage flow is obtained by application of a peak factor to the average sewage

flow. Relevant equation is as follows:

Peak sanitary sewage flow = Peak factor Average sanitary sewage flow

There are two approaches for determination of peak sewage flow i.e. from WASA specifications or byusing the Herman formula.

USING WASA SPECIFICATIONS:

For the calculation of peak factor for the design purpose, the 1986 specifications provided by the WASA

(Water and Sanitation Agency) have been referred.

AVERAGE SEWAGE FLOW

(m3/day)PEAK FACTOR TO OBTAIN Qmax

2500 4.00

25005000 3.40

500010,000 3.10

10,00025,000 2.70

Design sewage flow = Peak sanitary sewage flow + Storm sewage flow + Infiltration


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In our case, Peak factor for average sewage flow = 4.0

USING HERMAN FORMULA:

An alternative method for determination of peak factor is by using the Herman formula. The formula is

given below

P4

141

Q

QM

AVG

MAX

DESIGN EQUATION:

The Mannings formulais used for design of sewers flowing under gravity.

2

1

3

2

S.R.n

1v

Where v = Velocity of flow (m/sec)

R = Hydraulic mean depth = full)halforfullflowingispipe(when4

D

perimeterWetted

Area

S = Slope of the sewer

n = Mannings coefficient of roughness for pipes (n = 0.013 for RCC pipes)

MINIMUM SELF CLEANSING VELOCITY:

It is the minimum velocity that ensures non settlement of suspended matter in the sewer.For Partially combined sewerage system = 0.7 m/sec

Maximum velocity:Maximum velocity should not be greater than 2.4 m/sec to avoid excessive sewer abrasion and also to

avoid steep slopes.

MINIMUM SEWER SIZE:

The minimum sewer size is taken as 225mm.

MINIMUM COVER:1m is taken as the minimum cover over the sewers to avoid damage from live loads coming on the

sewer.

25,00050,000 2.50

50,000100,000 2.30

100,000250,000 2.15

250,000500,000 2.08

> 500,000 2.00


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SPACING OF MANHOLES

sewer size spacing

225mm to 375mm 100m450mm to 750mm 120m

greater than 750mm 150m

HYDRAULIC STATEMENT & DETAILED DESIGN

This chapter deals with the detailed design of future vis ion housing society.

This chapter includes the following:

Design of partially combined sewer system (hydraulic statement)

Design of sewage pumping station (only wet well)

PREPARATION OF HYDRAULIC STATEMENT

Hydraulic statement is : Tabular form or a sheet

Contains information regarding diameters of pipes used, slopes to be maintained, invert levels

etc.

REQUIRED DATA FOR THE PREPARATION OF HYDRAULIC STATEMENT

POPULATION:

The calculation of population was based on the following data:

No of Plots = 281

No of Apartments = 3

No of Flats (2 storey) = 3

Persons /plot=ten(10)

Total population = (281 x 10) + (3 x 600) + (3 x 400)

= 5810 persons.

PER CAPITA WATER CONSUMPTION:

CHAPTER 4


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The per capita water consumption is calculated in liters per capita per day (lpcd) using the following

relation

PER CAPITA WATER CONSUMPTION = 350 + R

Where, R = Registration number of the student = 142

Hence, the per capita water consumption came out to be 492 lpcd.

TOTAL AVERAGE DAILY WATER CONSUMPTION:

The relation used for the determination of total average daily consumption of water is as follows:

Total average daily water consumption = Pd Per capita water consumption

AVERAGE DAILY SEWAGE FLOW

80% of average daily water consumption

DESIGN SEWAGE FLOW CRITERIA:

In general, the design sewage flow for sewer system is calculated using the following equation:

This design sewage flow value is calculated for each sewer line, by determining each of the

three parameters given in the equation above. The detail of determination of these parametersfollows:

Design sewage flow = Peak sanitary sewage flow + Storm sewage flow + Infiltration

PEAK SANITARY SEWAGE FLOW:

The peak sanitary sewage flow is obtained by application of a peak factor to the average sewage

flow. Relevant equation is as follows:

Peak sanitary sewage flow = Peak factor Average sanitary sewage flow

Using WASA Specifications,

Peak factor= 4 for our case.

INFILTRATION:

Infiltration refers to the wastewater that enters sewers through poor joints, cracked pipes, walls and

manhole covers.

Infiltration rate = 10 % of average sanitary sewage flow


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DESIGN FLOW:

IT is given by the following expression:

Design sewage flow = 2 Peak sanitary sewage flow + Infiltration

ORDesign sewage flow=8.1*Q(avg.)

LONGITUDINAL PROFILE OF LONGEST SEWER LINE

It is always recommended to draw a longitudinal profile of sewer line because:

Helps in executing the work of water disposal system

Guides the contractor to execute the work easily & efficiently.

Longitudinal profile is a section along the length showing invert levels, reduced levels, details ofmanholes, diameter of sewer pipe lines, slope of sewer pipe lines, length of sewer pipe line etc.

SEWER INVERT LEVELS:The lowest inside level at any cross section of a sewer pipe is known as the Invert Level at that cross

section.

IMPORTANCE OF INVERT LEVELS:

minimum self cleansing velocity are achieved through calculations of invert levels of sewers atvarious manholes.

Formula for calculation of invert level:

U/S Invert level = NGSL/Road level Depth of sewer Thickness of sewer Diameter of sewer

D/S Invert level = U/S Invert level (Sewer slope

Length of sewer)


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IMPORTANT CONSIDERATIONS IN INVERT LEVEL CALCULATION:

When sewers of equal diameter discharge in a manhole and a pipe of same diameter receives

the total discharge, then the lowest D/S Invert Level among the discharging sewers has been

taken as U/S Invert Level of the receiving sewer.

When the diameter of receiving sewer is greater than that of lowest discharging sewer thefollowing rules are observed in the laying of sewer pipes:

a) The sewer crowns are kept at the same level.

b) U/S IL of receiving sewer is dropped by the difference in diameter of the two sewers.

SEWAGE PUMPING STATION:A sewage pumping station is needed to elevate or transport sewage to a higher receiving point in the

sewerage system.

Such a need can arise when:

Continuation of gravity flow is no longer feasibleBuildings in vicinity have deep basements

An obstacle is present in the path of sewer

Receiving stream is higher than the sewer

Sewage is to be delivered to an above ground treatment plan.

PUMPING CAPACITY & DESIGN SEWAGE FLOW:The sewage pump is design according to the maximum design sewage flow of the total population, and

for the current case:

Maximum design sewage flow = 18966.528 m3/day = 13.1712 m3/min

So, required pumping capacity = 13.1712 m3/min

AVERAGE SEWAGE FLOW:

The average sewage flow rate is used along with the minimum rate of sewage flow to calculate the

corresponding cycle time for the pumping station:

Average sewage flow = 2341.538 m3

/day = 1.626 m3

/min

MINIMUM SEWAGE FLOW:

Minimum sewage flow = 50 % of ave rage sewage flow

Minimum sewage flow= 0.5 x 2341.538 m3/day = 1170.769 m3/day = 0.813m3/min

CYCLE TIME:

The cycle time for a sewage pumping station is the time elapsed between 2 successive startups of the

motor pump.


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Cycle time = Time to empty the wet well + Time to fill the wet well

FORMULAfor calculating cycle time

QQV

PVt

VOLUME OF WET WELL:

Volume of wet well corresponding to a certain cycle time is given by the following formula:

4

P.tV min

The wet well should have a volume such that the cycle time is always greater than the minimum cycle

time recommended for a motor pump.

DESIGN CALCULATIONS DESIGN CALCULATIONS DESIGN CALCULATIONS DESIGN CALCULATIONS

(PUMPING STATION)

Given data:

Maximum design sewage flow = Qmax = 9147.26 m3/day

=6.35 m3/min

Average sewage flow = Qavg= 2286.82 m3/day

=1.58 m3/min

Minimum sewage flow = Qmin= 0.5 * 1.58 m

3

/day=0.794 m3/min

Recommended cycle time for pump = 10 minutes

SOLUTION:

Effective volume of wet well = 3min m87.154

106..35

4

tP.

CHECK FOR RUNNING TIME:

t= min2>2.84min794.035.6

87.15

QP

V

min

( OK)

DESIGN

CALCULATIONS


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CHECK FOR DETENTION TIME:

=

Qavg=

.

.= . < 30 min (ok)

So, Volume of wet well = 15.87 m3

Assuming Depth = 2.0 m

Surface Area = 7.935m

Diameter = 3.18 m

DRAWINGS

This chapter deals with the major drawings required for the implementation of the project.

The following drawings are included in this chapter:

1. Longitudinal profile of sewer

2. Manhole

3. Sewage pumping station

4. Sewer joints

LONGITUDINAL PROFILE OF THE SEWER Longitudinal profile of the sewer is:

The graphical representation of Hydraulic Statement.

In our design of future vision housing society I have drawn the longest sewer profile.

The functions of manholes are:

MANHOLES

Cleaning, inspection of sewer pipe Maintenances of sewer

House connections

DIAMETER SELECTED = 3.18 meters

CHAPTER 5


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LOCATION OF MANHOLES

Manholes should be located where ever there is:

Change in sewer direction

Change in slope Change in diameter

A typical figure of manhole is shown in the below figure.

DROP MANHOLES

When lateral or sub main join in a deeper sewer, excavation is saved by keeping the upper

sewer at a reasonable grade and making the vertical drop at the manhole.

Drop manhole is constructed when the drop is more than 0.6m.

A typical figure of drop manhole is shown in the figure.


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SEWAGE PUMPING STATION:

A sewage pumping station is needed :

To elevate or transport sewage to a higher receiving point in the sewerage system.

Such a need can arise when:

Continuation of gravity flow is no longer feasible

Buildings in vicinity have deep basements

An obstacle is present in the path of sewer

Receiving stream is higher than the sewer

Sewage is to be delivered to an above ground treatment plant

The schematic diagram of the pumping station is given below.

CYCLE TIME:

The cycle time for a sewage pumping station is the time elapsed between 2 successive startups of the

motor pump.

Cycle time is given by the following formula:

QQ

V

P

Vt

VOLUME OF WET WELL:

4

P.tV min

SEWER JOINTS:

There are two types of joints in Concrete (up to 300 mm diameter) and R.C.C pipes (greater than 300

mm diameter)

Bell and Spigot joint (Employed for sewers from 225 mm to 600 mm diameter)

Tongue and groove joint (employed for sizes greater than 600 mm diameter)

The figure of bell and spigot joint and tongue and groove joints is given below.


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BILL OF QUANTITY (BOQ) & BEDDING

(a) FOR EXCAVATION

Sr

No. Sewers Diameter Excavation(meters) Quuantity Rate Amount(RS)

Description (mm) L(m) W(m) H(m) m3 Rs/C Rupees Millions

1 M1 - M2 225 106 0.638 1.321 89.27 123 10979.79 0.011

2 M2M8 225 37 0.638 1.296 30.57 123 3760.04 0.004

3 M7M8 225 106 0.638 1.321 89.27 123 10979.79 0.011

4 M8M10 225 37 0.638 1.346 31.75 123 3905.10 0.004

5 M9M10 225 106 0.638 1.071 72.37 123 8901.86 0.009

6 M10M11 310 37 0.765 1.598 45.23 123 5563.46 0.006

7 M13M12 225 89 0.638 1.288 73.08 123 8988.58 0.009

8 M12M11 310 23 0.765 1.324 23.30 123 2865.38 0.003

9 M11- M16 380 39 0.870 1.852 62.84 123 7729.12 0.008

10 M3 - M16 225 110 0.638 1.304 91.44 123 11247.49 0.01111 M16- M17 460 34 0.990 1.925 64.80 123 7969.85 0.008

12 M4- M17 225 108 0.638 1.275 87.78 123 10797.40 0.011

13 M17- M18 460 48 0.990 1.736 82.49 123 10146.85 0.010

CHAPTER 6


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14 M5- M18 225 110 0.638 1.229 86.18 123 10600.59 0.011

15 M18M19 530 55 1.095 1.625 97.87 123 12037.47 0.012

16 M6M19 310 112 0.765 1.495 128.09 123 15755.27 0.016

17 M19M20 610 42 1.215 1.61 82.16 123 10105.47 0.010

18 M20M23 610 43 1.215 1.154 60.29 123 7415.76 0.007

19 M14M15 225 45 0.638 1.004 28.80 123 3542.68 0.00420 M15M21 225 163 0.638 0.754 78.35 123 9637.05 0.010

21 M24M23 225 150 0.638 1.206 115.32 123 14184.82 0.014

22 M23M21 310 46 0.765 0.988 34.77 123 4276.43 0.004

23 M21- M22 310 15 0.765 0.671 7.70 123 947.07 0.001

24 M22D.S 690 17 1.335 0.859 19.50 123 2397.89 0.002

194735.19 0.195

,

(B)FOR SEWER MATERIAL

Sr. No. Description Quantity Unit Rate(RS/m) Amount(RS)

1 225mm Sewer 1167 Meters886.1 1034078.7

2 310mm Sewer 236 Meters1354.95 319768.2

3 380mm Sewer 39 Meters1669.2 65098.8

4 460mm Sewer 2 Meters

2104.3 4208.6

5 530mm Sewer 82 Meters 2573.65 211039.3

6 610mm Sewer 85 Meters 2992.35 254349.75

7 690mm Sewer 17 Meters 3575.55 60784.35

1949327.7

TOTAL COST OF EXCAVATION=0.195 MILLIONS

Total cost forsewerage=1.94 Millions


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BEDDING PROVIDED

Prov

Dia

(m)

H(m) B(m) C H/B

Load(kg/m

Load

(Lbs/ft/ft

3 edge

bearing

Standardvalue(lb/ft/ft

3 edge

bearing

valuefor prov

dia.

Load

factor

Bedding

suggested

0.2251.321

0.64 1.66 2.07 1237.65 2722.84 1500 1107.3

2.46 concrete

cradle

0.2251.296

0.64 1.64 2.03 1219.08 2681.99 1500 1107.3

2.42 concrete

cradle

0.2251.321

0.64 1.66 2.07 1237.65 2722.84 1500 1107.3

2.46 concrete

cradle

0.2251.346

0.64 1.69 2.11 1256.06 2763.33 1500 1107.32.50 concrete

cradle

0.2251.071

0.64 1.40 1.68 1044.56 2298.04 1500 1107.3

2.08 concrete

cradle

0.311.598

0.77 1.67 2.09 1793.56 3945.83 1500 1525.6

2.59 concrete

cradle

0.2251.288

0.64 1.63 2.02 1213.11 2668.84 1500 1107.3

2.41 concrete

cradle

0.311.324

0.77 1.44 1.73 1541.50 3391.29 1500 1525.6

2.22 concrete

cradle

0.381.852

0.87 1.70 2.13 2354.40 5179.68 1500 1870.1

2.77 concrete

cradle

0.2251.304

0.64 1.65 2.05 1225.04 2695.10 1500 1107.3

2.43 concrete

cradle

0.461.925

0.99 1.58 1.94 2837.49 6242.49 1500 2263.8

2.76 concrete

cradle

0.2251.275

0.64 1.62 2.00 1203.36 2647.40 1500 1107.3

2.39 concrete

cradle

0.461.736

0.99 1.45 1.75 2609.50 5740.90 1500 2263.8

2.54 concrete

cradle

0.2251.229

0.64 1.57 1.93 1168.53 2570.76 1500 1107.3

2.32 concrete

cradle

0.531.625

1.1 1.27 1.48 2778.13 6111.89 1500 2608.32.34 concrete

cradle

0.311.495

0.77 1.59 1.95 1701.13 3742.48 1500 1525.6

2.45 concrete

cradle

0.611.61

1.22 1.15 1.33 3105.20 6831.43 1500 3002.0

2.28 concrete

cradle

0.61 1.154 1.22 0.86 0.95 2315.54 5094.18 1500 3002.0 1.70 Brick Ballast

0.2251.004

0.64 1.33 1.57 989.92 2177.83 1500 1107.3

1.97 Crushed

Stone

0.225 0.754 0.64 1.04 1.18 774.51 1703.92 1500 1107.3 1.54 Brick Ballast

0.225 1.206 0.64 1.55 1.89 1150.90 2531.97 1500 1107.3 2.29 concretecradle

0.31 0.988 0.77 1.12 1.29 1204.02 2648.84 1500 1525.6 1.74 Brick Ballast

0.31 0.671 0.77 0.80 0.88 854.30 1879.45 1500 1525.6 1.23 Brick Ballast

0.69 0.859 1.34 0.60 0.64 1956.82 4305.01 1500 3395.7 1.27 Brick Ballast


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RECOMMENDATIONS & COMMENTS

I have Carried out the design of this waste water disposal system for the Future Vision housing

scheme with great zeal and the design is complete & will work for the betterment of the people.

Design report is prepared considering all possible features.

Manhole are provided where they were required.

Standard diameters of the pipes have been selected.

Pipes with sufficient length have been provided.

Prper joints have been suggested based on the diameter provided for the pipes.

Required cost for laying the pipes has also been calculated.

The bedding is selected on the basic of required load factor.

Rats for the sewer pipes & excavation were picked from the finance department website.

(http://punjab.gov.pk/aug-jan-2013)

I have also suggested the type of bedding based on the considerations given by WASA LAhORE.

For the effective utilization of the system cleaning and inspection be conducted after a proper

time duration.

I have not provided the flush tank as they were not required.

Proper maintenances should be provided when required.

Proper maintenances of pumps are also required at regular interval.

In the end,I will conclude that this complete design of partially combined sewer improved my

knowledge the design of this system done by me will work very efficiently.

.

CHAPTER 7

MUHAMMAD USMAN 2009-CIVIL-142

SECTION C
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Design of Partially Combined Sewerage System

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