Report on the ³Extension of Sewerage System to Everyone who Needs it´ ProjectKenji SAKAIConstruction Technology Research Department, Public Works Research InstituteMinamihara 1-6, Tsukuba city, Japan, 305-8516, ksakai@pwri.go.jp
Abstract: To extend sewerage service to a large population under the tight budgetarycondition, the government of Japan started a project to encourage the application of newand ambitious ideas to the works of sewerage system. This paper, after the brief
introduction on the state of wastewater management in Japan, describes the project
including results of efforts made for cost reduction, and some cost reduction ideas preparedby PWRI.
Keywords: Sewerage system, Unconnected population, Construction cost, Cost reduction
1. Background and Purpose of the Project
The ratio of the population connected to sewerage system in Japan is 68% at theend of March in 2005, because of the intensive efforts done by the national government,local governments and related organizations. Wastewater management through seweragesystem has contributed to the improvement of not only everyday life but also water quality
in rivers and seacoasts.
Sewerage system has been constructed mainly in bigger cities and in many local
cities having social needs of such a system. Therefore there exists a difference in connection
ratio to sewerage system among municipalities; the difference has become a kind of social
problem now. There are 24.7 million people left in Japan who are supposed to be covered bysewerage system, but cannot use it at present.
The expenditure on sewerage system construction is expected to be more efficient,because the budgetary conditions of both national government and local governments arequite tight. The national government has started a project to promote sewerage systemconstruction with less cost and less time. In the project, the procedures and the technicalstandards for planning, design and construction of sewerage system are to be revised fromthe viewpoint of cost reduction and time saving.
2. Outline of unconnected population
Figure-1 shows the state of unconnected population. In this paper, ´unconnected
populationµ means the number of people who live in the areas that should be covered bysewerage system but still not due to the delay in construction. The term ´sewerage
populationµ is used for the population that is equal to the sum of unconnected populationand the population that is already covered by sewerage system. In Figure-1, eachmunicipality is classified into seven classes according to the total population size.
- 327 -㪊㪇㪪㫌㫄㩷㫆㪽㩷㫋㪿㪼㩷㪧㫆㫇㫌㫃㪸㫋㫀㫆㫅㩷㫆㪽㩷㪼㪸㪺㪿㩷㪺㫃㪸㫊㫊㩷㩷㩿㫀㫅㩷㫄㫀㫃㫃㫀㫆㫅㪀The ratio of unconnected
population to total population is
19% in Japan, and 77% of theunconnected population belongs to
the classes of 30 to 500 thousand.
Sewerage population in Japan is
88% of the total population. The
ratio of unconnected population to
sewerage population (uncoveredratio) is 22% in average in Japan.
Figure-2 shows the relationshipbetween population of each㪉㪌㪉㪇㪈㪌㪈㪇㪦㫋㪿㪼㫉㫊㪬㫅㪺㫆㫅㫅㪼㪺㫋㪼㪻㪚㫆㫅㫅㪼㪺㫋㪼㪻㪌㪇㪓㪓㪇㪇㪇㪇㪇㪇㪇㪇㪇㪈 㪇 㪇㪄㪉 㪇㪄 㪊 㪇㪄㪌 㪇㪄 㪎 㪄㪈㪇 㪄㪉 㪇 㪄㪊 㪇 㪄㪌㪇 㪇㪇 㪇㪇㪇㪌 㪎 㪇 㪇㪇 㪇㪇 㪇㪇 㪇 㪄㪈 㪈㪊
㪉㪈
㪊 㪌㪇㪈
㪉

㪧㫆㫇㫌㫃㪸㫋㫀㫆㫅㩷㫆㪽㩷㫄㫌㫅㫀㪺㫀㫇㪸㫃㫀㫋㫀㪼㫊㩷㩷㩿㫀㫅㩷㫋㪿㫆㫌㫊㪸㫅㪻㪀㪬㫅㪺㫆㫍㪼㫉㪼㪻㩷㫉㪸㫋㫀㫆㩷㫆㪽㩷㫄㫌㫅㫀㪺㫀㫇㪸㫃㫀㫋㫐䋨䋦䋩municipality and uncovered ratio.
The figure does not include themunicipalities that have nosewerage population, i.e., no planof sewerage system. The biggest
municipality that shows 100% of
uncovered ratio has a populationof 80 thousand. The uncovered
ratio is low in the municipalities
whose population is less than 3thousand or more than 300thousand.
From the data mentioned
above, we can assume that theunconnected population in Japanis mainly in the municipalities
whose population is 30 to 500 thousand.

㪝㫀㪾㫌㫉㪼㪄㪈㩷㪪㫋㪸㫋㪼㩷㫆㪽㩷㪬㫅㪺㫆㫅㫅㪼㪺㫋㪼㪻㩷㫇㫆㫇㫌㫃㪸㫋㫀㫆㫅㪈㪇㪇㪐㪇㪏㪇㪎㪇
㪍㪇㪌㪇㪋㪇㪊㪇
㪉㪇
㪈㪇㪇
㪈㪇㪇

㪈㪇㪇㪇

㪈㪇㪇㪇㪇

㪈㪇㪇㪇㪇㪇

㪈㪇㪇㪇㪇㪇㪇

㪧㫆㫇㫌㫃㪸㫋㫀㫆㫅㩷㫆㪽㩷㫄㫌㫅㫀㪺㫀㫇㪸㫃㫀㫋㫐㪈㪇㪇㪇㪇㪇㪇㪇

㪝㫀㪾㫌㫉㪼㪄㪉㩷㩷㪧㫆㫇㫌㫃㪸㫋㫀㫆㫅㩷㩽㩷㫌㫅㪺㫆㫍㪼㫉㪼㪻㩷㫉㪸㫋㫀㫆㩷㫆㪽㩷㫄㫌㫅㫀㪺㫀㫇㪸㫃㫀㫋㫐

3. Efforts toward cost reduction and their results up to now
The government of Japan started the organized program toward cost reduction of
public works in January 1997. In the field of sewerage system construction, national
government published the documents to encourage the efforts toward cost reduction in
1997, and announced action programs in 2001 and 2005.
Among the results up to now, a good example is the revision of the standard for
installation of sewer pipe under public roads. The revision in 1999 allowed sewer pipe to beburied more shallowly than before: Pipes with a diameter of 300 mm or less should becovered at least 60 cm of filling under the surface of roadway and 50 cm under sideway,
while 100 cm was required before the revision.
- 328 -To evaluate the effect of the efforts toward cost reduction, an installation works ofsewer pipe in K city was taken as an example. The outline of the works is shown in Table-1.
   Table-1 Outline of Installation works of sewer pipe
Items

ContentDiameter

200 mmLength200 m (not straight)

Construction method

Open cut

Gradient of road23 to 72 ̟

Number of connections

20 houses

Related works

Repair of road is included
Temporary displacement of other pipes is excluded

The change in price and wage and the revised design parameters affected the cost.
The cost of the works was estimated under three sets of conditions as listed in Table-2.
Cases-1 and -2 used the same design parameters as the city actually used then, while inCase-3 some parameters were changed to achieve cost reduction.
Table-2 Design parameters for Cost comparison and the results
Design parameters 㧒 Cost

Case-1Case-2Case-3

Year of Price list

19962006

2006

Minimum depth of pipe

120 cm120 cm

70 cm

Type of pipe

VU pipe

Plastic rib-pipe

Plastic rib-pipe

Filling material around pipe

Sand (around pipe)+Sand (under pipe) +Sand (under pipe) +Improved excavated soil

Improved excavated soil

Improved excavated soil

Width of trench

110 cm110 cm85 cm

Width of road base repair

170 cm110 cm85 cm

Retaining wall

Installed

Installed

Not installed

Type of manhole

Type-1 in 7 sites

Type-1 in 7 sites

Type-1

in 1 site

Small type in 5 sites
Curved pipe in 1 site
Depth of inlet to sewer

80 cm

80 cm

60 cm

Total Cost

32.6 million yen

19.5 million yen

12.7 million yen

Cost per pipe length

163,000 yen/m97,400 yen/m63,400 yen/mRelative value of cost

1006039The conditions in detail and the results of calculation are listed in Table-2. From theresults of Cases-1 and -2, the cost in 2006 is estimated to be 60% of the cost in 1996. The
revision on road repair and filling material contributed most to the cost reduction. Iffurther changes were made as indicated in Case-3, the cost would be reduced to 39% of thecost in 1996.

- 329 -4. Construction Cost of Sewerage System
To promote the project, construction cost of sewerage system was studied. The
average cost can be obtained from the total expenditure and the number of new customers.
From the data of the period from 1998 to 2002, the average construction cost per customer
in Japan is calculated to be 980,000 yen. .
The construction cost per customer can be calculated from the data of themunicipalities that are almost completing construction of sewerage system. Using thenational statistics of 2003, 18 municipalities which satisfy the following conditions wereselected for the study.
Condition-A: Ratio of the population covered by sewerage system to total population
is equal to or more than 80%.
Condition-B: Construction works started after 1990.

㪚㫆㫅㫊㫋㫉㫌㪺㫋㫀㫆㫅㩷㪺㫆㫊㫋㩷㫇㪼㫉㩷㪺㫌㫊㫋㫆㫄㪼㫉㪊㩿㪈㪇 㩷㫐㪼㫅㪆㪺㫌㫊㫋㫆㫄㪼㫉㪀

Condition-C: Both sewers and treatment plants are owned by one municipality.
Condition-D: No investment to rain water control.
Selected 18 municipalities are all located in non-urbanized area, and their population was1,881 to 17,806 in 2003.
The relationship between㪊㪇㪇㪇
sewer pipe length per㪉㪌㪇㪇
customer and construction
cost per customer of both㪉㪇㪇㪇
sewersandsewerage㪈㪌㪇㪇system in 18 municipalities
is shown in Figure-3. Linear㪈㪇㪇㪇㪚㫆㫊㫋㩷㪽㫆㫉㩷㫊㪼㫎㪼㫉㪸㪾㪼㫊㫐㫊㫋㪼㫄
relation can be obtained for㪚㫆㫊㫋㩷㪽㫆㫉㩷㫊㪼㫎㪼㫉㫊㪌㪇㪇
both. In the case of 10 m percustomer, the construction
㪇㪇
㪌㪈㪇
㪈㪌
㪉㪇
㪉㪌
cost per customer is 1.5㪪㪼㫎㪼㫉㩷㫇㫀㫇㪼㩷㫃㪼㫅㪾㫋㪿㩷㫇㪼㫉㩷㪺㫌㫊㫋㫆㫄㪼㫉㩷㩿㫄㪆㪺㫌㫊㫋㫆㫄㪼㫉㪀million yen for seweragesystem, and 1 million yen㪝㫀㪾㫌㫉㪼㪄㪊㩷㩷㪪㪼㫎㪼㫉㩷㫇㫀㫇㪼㩷㫃㪼㫅㪾㫋㪿㩷㪸㫅㪻㩷㪚㫆㫅㫊㫋㫉㫌㪺㫋㫀㫆㫅㩷㪺㫆㫊㫋for sewers. The construction
cost of sewers per unit length in the studied 18 municipalities is 100 thousand yen permeter on average.
5. Cost to be balanced with customers¶ charge
One of the important points for setting the target of construction cost is to balance
investment with income. A trial calculation to balance capital investment with customers·
charge was done using the data of the municipalities practicing good seweragemanagement. The conditions of calculation and the results are listed in Tables-3 and -4
respectively. The construction cost per customer that is balanced with customers· charge
under the conditions of Table-3 is 766 thousand yen in the case that interest rate is 3%.
- 330 -Table-3 Conditions of Calculation
Items

Conditions

Customers· charge

200 yen/m3-wastewater

Maintenance cost

80 yen/m3-wastewater

Water consumption

0.25 m3/d/customer

Coverage by charge

Maintenance cost + half of Capital cost

Ratio of bond

50%, 60%, 70% of Total Investment

Interest rate

2, 3, 4%

Table-4 Calculated cost ( in 103 yen/customer)
Interest rate

Ratio of bond
50%

60%

70%

2%

858

715

613

3%

766

638

547

4%

688

573

491

6. Promotion of the project
To promote the project, in September 2006 all the municipalities were asked to makeproposals that contribute to the cost reduction in sewerage works of each municipality for
unconnected people, and to try them in actual works. Municipalities can propose any ideas.
The national government will choose both the acceptable ideas and the municipalities thatwill try them in actual works. After being constructed, these ideas will be evaluated byrelated municipalities, the national government and PWRI from the viewpoint of both cost
reduction and the applicability to other municipalities.
Our institute prepared a list of ideas for reference that is shown in Table-5. The listed
ideas were mainly taken from the answers to the questionnaire survey conducted in 2003.
Table-5 List of ideas for reference prepared by PWRI
Ideas

Description in present standards

Use of inverted siphon

No use in principle

Setting of sewer gradient at a starting point No description
by velocity of 60 cm/s under half full flow
Raise of upper limit of velocity in sewer

3m/s

Reduction of gradient of house connection

2/100 for a connection of less than 150
customers

Use of curved pipe

Not allowed

Raise ofmanholes

maximum

distance

between 75 m for a pipe diameter under 600 mm

Reduction of diameter of inlet to sewer

20 cm or more

Reduction of HRT of bioreactor

24 hrs for Oxidation ditch- 331 -Inlet 䇭Manhole
Outlet 䇭Manhole
Among the ideas in Table-5,two examples, inverted siphon
and curved pipe are explained
briefly.
Figure-4 is a structuredrawing of inverted siphon thatis utilized to sanitary sewer in T
city. The slope of bothFigure-4 Structure drawing of inverted siphon
descending and rising pipe isusually 1 to 1 (vertical to horizontal)
in Japan. Deposits such as sand or
small stone accumulated in inverted

siphoncanbecleaned
bywater-jetting. By use of inverted
siphon, downstream sewer pipe canbe buried more shallowly, ormanhole type pumping stations canbe avoided.
Figure-5 is a part of sewer
network map of K city. In several
points of change of sewer direction,
curved pipes are utilized instead ofmanholes. The angles of the curved
pipes utilized in Figure-5 are 5.625,
11.25, and 22.5 degrees. These
curved pipes were manufactured in䋺 site of cur䌶ed pipe
factory.
Recently a new type of curved Figure-5 Use of curved pipe in K citypipe was developed; a curved plastic
rib-pipe as shown in Figure-6.
The results of the project will help not only
the extension but also the reorganization ofsewerage system.
Figure-6 Curved Plastic Rib-pi pe- 332 -- 333 -Ｔo extend sewerage system quickly
to everyone who needs it
Reducing both cost and time ofconstruction
By new and ambitious ideas forplanning, design and construction

Purpose of the Project

Public Works Research InstituteKenji SAKAI

project“Extension of Sewerage System
to Everyone who Needs it”

4. Promotion of the project

3. Construction cost of Sewerage System

2. Efforts toward cost reduction up to now

1. State of Wastewater Management

Overview

３．Increasing needs torenewal & rehabilitation of facilities

２．Tight budgetary conditions ofboth national & local governments

１．Existence of 24 million people
who are waiting for sewerage system

Background of the project

05

1015

2025

30

10<-30-5050-

70

70

-1

1000

0-

22000
0-

33000
0-

505000-1000
1000<

Population of municipalities (in thousand)1030

OthersUnconnected
Connected

Distribution of unconnected population

・ Unconnected population: Population to be covered by seweragesystem, but not now

・ Connected population: Population covered by sewerage system

Definition of the terms

Sum of the Population ofeach class (in million)- 334 -

Summary of the state ofUnconnected population

68%

Sewerage System(Connected)
Sewerage System(Unconnected)
On-site system &others

belongs to the municipalities of
10 to 500 thousand in population.

• Ratio: 19% of the total population in Japancannot use sewerage system.
• Distribution:
89% of the unconnected population

19%

13%

State of Wastewater Management in 2004

- 335 -• In 2001 & 2005, Action programs toward
cost reduction of sewerage systemconstruction.

L=200 m, D=200 mm

Plan of sewer pipe installation in K city

Example：・ Installation of sewer pipe by open cut
method・ Diameter 200 mm, Length 200 m
・ Gradient of road 23～72 ‰Method:・ Calculate the cost under the conditions
adopted in 1996 and 2006 by K city,and proposed in 2006 by PWRI

Case study for cost comparison• Minimum depth for small pipe
BeforeAfter
100cm → 60cm under roadway
50cm under sideway

Change of the cost in 10 years• Small pipe (with a diameter of 300 mm or less)can be buried more shallowly than before.

pipe installation under public roads in 1999

:Revision of the standard for

An Example of the results up to now• In 1997, Program toward cost reduction ofpublic works.
Documents to encourage cost reductionof sewerage system construction.

Efforts toward Cost Reduction up to now
by the national government

- 336 -

1.2 m

VU

Minimum depth of pipe

Type of pipe

Installed

Type-1Retaining wall

Type of manhole

In 1996

Pipe80 cm

Type-1

Installed110 cm

110 cmIn 2006 + proposal

SandSandIn 2006

Improved excavated soil

60 cm& Curved pipe

Type-1, Small,

Not installed

85 cm

85 cm

Sand

Improved excavated soilRoad base

Asphalt

Sand

Rib-pipe

0.7 m

2006

Case-3

Improved soil Improved soil

Sand

Rib-pipe

1.2 m

2006

Case-2

Revision of road repair
and filling material

80 cm

170 cmDepth of inlet to sewer

110 cmWidth of road base repair

over pipe up to 30 cm

Width of trench

SandSand

under pipe

Filling material

1996

Year

Case-1

Design parameters for cost comparison

Relative value(EUR/m)100(1,087)

Total cost
32.6(million yen)
Cost per unit length(yen/m)
163,000

Case-159.8(649)

97,40019.5

Case-238.9(422)

63,400

12.7

Case-3

Small type in plastic

D= 300mm

Results of cost comparison

Type-1 (ordinary type)

D= 600mm

Type of Manhole

0500

1000

1500

2000

2500

3000

0

1015

Pipe length per customer (m/customer)

520

Cost forsewerage system
Cost for sewers

Sewer pipe length and construction cost

2. Cost in the municipalities that arealmost completing construction(6,500EUR/customer)25

1. Average cost in Japan (1998 to 2002): 980,000 yen/customer(Cost = investment /new customers)

whole sewerage system

Construction cost of

C onstruc tion c ost p e r cu stom e r(1 0 3 y e n /c u stom e r)

- 337 -

Trial calculation was doneusing the data of the municipalities
practicing good sewerage management.

One idea is
to balance construction cost withcustomers’ charge.

Target of construction cost

Conditions for selection
A: Ratio of connected population tototal population is 80% or more
B: Construction works started after 1990
C: Both sewers and treatment plants areowned by one municipality
D: No investment to rain water controlCharacteristics of selected 18 municipalities: Located in non-urbanized area
: Population of 1,881 to 17,806 in 2003

Selection of municipalities- 338 -80 yen/m3-wastewater

200 yen/m3-wastewater

Conditions

・ Construction of sewerage systemusing revised methods

・ Evaluation of the ideas:
Cost and Applicability to other municipalities

・ Selection of the ideas andthe municipalities which will do them・ Proposal from municipalities & private companies

Promotion of the project

0.25m3/d/customer
Maintenance cost +half of Capital cost
Ratio of bond/investment 50, 60, 70%
Interest rate
2, 3, 4%

Customers’ charge
Maintenance cost
Volume of wastewater
Coverage by charge

Items

Conditions of Calculation

638
573

766
688

3%
4%

491

547

613

70%

・Reduction of diameter of inlet to sewer
・Reduction of HRT of Bioreactor

Others・Use of curved pipe
・Use of small manhole
・Raise of maximum distance between manholes

Reduction of manholes

・Use of inverted siphon
・Raise of upper limit of velocity in sewer
・Reduction of gradient of house connection

Ｓｈａｌｌｏｗ installation

List of ideas presented by PWRI

715

60%

85850%

Ratio of bond/investment

2%

Interest rate(thousand yen/customer)

Calculated cost- 339 -I

8 months of operation, 3 houses discharged

Exit pipe from inlet manholeof inverted siphon

Channel1 year of operation, 5 houses discharged

Exit pipe from inlet manhole

L= 8.5 m

Box culvert for rain water
H= 2.37 m

Outlet Manhole

Inlet Manhole

Inlet chamber

Outlet chamber

Improved type of inverted siphon

Conventional type of Inverted siphon
in Japan- 340 -: site ofcurved pipe

Curved Plastic Rib-pipe

Use of curved pipe in K city

Route of steep sewer

Residential area on the hill

Use of steep sewer to connect the area on the hillin Ohtsu city

Curved pipe

Curved pipe in construction site- 341 -Energy absorber for steep sewer（Stilling pond)

Mean gradient = 420 ‰402 m

H= 170 m

170 m

Cross section view of steep sewer in Ohtsu city

H= 7.4 m

Drop shaftof sewerage system.

the extension and the reorganization

The results of the project will help both

Prospects

Stilling pool
Stilling pool

Energy absorbers utilized for steep sewerin Ohtsu city

- 342 -Thank you for your attention