Section 7

Wastewater

Tauranga City Council

Code Of Practice For Development Tauranga City Council SECTION SEVEN Wastewater

Print Date May 2007 VERSION ONE TCC Ref 790837

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Section 7: WASTEWATER 7.1 Scope

7.2 General

7.2.1 Objectives

7.2.2 Referred documents and relevant guidelines

7.2.3 Connection to Existing Sewer Networks/Approved Contractors

7.2.4 Private drainage

7.2.5 Rural and Rural Residential areas

7.3 Reticulation System

7.3.1 Design responsibilities

7.3.1.2 District Plan

7.3.1.3 Catchment Design

7.3.1.4 Topographical Considerations

7.3.1.5 Geotechnical Investigations,Foundation Design And Groundwater

Control

7.3.1.6 Easements

7.3.2 Design of the wastewater reticulation system

7.3.2.1 Prime Considerations

7.3.2.2 Scheme Layout

7.3.2.3 Pipeline Definitions

7.3.2.4 Proposed & Existing Pipes in Private Property

7.3.2.5 Horizontal Curves

7.3.2.6 Vertical Curves

7.3.2.7 Maintenance Structure Location

7.3.2.8 Underground Services

7.3.2.3 Pipe Materials

7.3.3.1 Acceptable Pipe Materials

7.3.3.2 Pipe Fittings

7.3.3.3 Joints

7.3.4 Clearances

7.3.4.1 Clearance From Underground Services

7.3.4.2 Clearance From Structures

7.3.5 Pipeline design

7.3.5.1 Design Flow

7.3.5.2 Hydraulic Design of Pipes

7.3.5.3 Minimum Pipe Sizes

7.3.5.4 Limitation on Pipe Size Reduction

7.3.5.5 Minimum Grades For Self Cleaning

7.3.5.6 Maximum Velocity

7.3.5.7 Minimum Cover

7.3.5.8 Steep Grades

7.3.5.9 Near Horizontal Bores

Code Of Practice For Development Tauranga City Council SECTION SEVEN Wastewater

Print Date May 2007 VERSION ONE TCC Ref 790837

3

7.3.5.10 Venting

7.3.6 Maintenance structures

7.3.6.1 General

7.3.6.2. Location of Manholes

7.3.6.3 Manhole Spacing

7.3.6.4 Manhole Materials

7.3.6.5 Size of Manholes

7.3.6.6 Base Layout

7.3.6.7 Allowable Deflection Through MHs

7.3.6.8 Internal Falls Through MHs

7.3.6.9 Effect of Steep Grades on MHs

7.3.6.10 Floatation

7.3.6.11 Access

7.3.6.12 Covers

7.3.6.13 Areas Subject to Flooding

7.3.6.14 Rodding Eyes (RE)

7.3.7 Laterals/Connections

7.3.7.1 Subdivision of 4 Lots or More

7.3.7.2 Infill Subdivision – Three Lots or Less

7.3.7.3 Multi Unit Properties (Such as Apartment buildings & Body

Corporation Developments)

7.3.8 Property connections

7.3.8.1 General Considerations

7.3.8.2. Requirements of Design

7.3.8.3 Number of Connections

7.3.8.4 Location of Connection

7.3.8.5 Connection Depth

7.3.8.6 Installation of Connections

7.3.9 Building Close Proximity Rules/Alteration of Ground Levels

7.3.9.1 Rising Mains and Trunk Sewers

7.3.9.2 Reticulation Sewers & Laterals/Connections

7.3.9.3 Ancillary Buildings May Be Exempt

(For Reticulation Sewers and Lateral/Connections)

7.3.9.4 Carports/Decks/Sunrooms

(For Reticulation Sewers)

7.3.9.5 Filling over Pipes

7.3.9.6 Cutting Down Over Pipes

7.3.9.7 Retaining Structures

7.3.9.8 Carriageway Trench Reinstatement

7.4 Construction Specifications (See Appendix C)

7.5 Wastewater pump stations and rising mains (See Appendix E)

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7.1 SCOPE

This Code is based on WSA 02 2002 — Sewerage Code

of Australia, and NZS 4404:2004 Land Development

and Subdivision Engineering. This section of the Code

sets out requirements for the design of wastewater

systems up to and including DN 300 (nominal diameter

300mm) or DN 355mm for PE (polyethylene). The

Code covers wastewater services for both new

developments and re-development areas. For pipes

larger than DN 300 refer to WSA 02 and Council for

specific requirements.

7.2 GENERAL

7.2.1 Objectives

The objectives of the design are to ensure that the

wastewater system is functional and complies with the

requirements of the Council’s wastewater systems. In

principle the wastewater system shall provide:

• A single gravity connection for each property;

• A level of service to the Council’s customers in

accordance with Council’s policies;

• Minimal adverse environmental and community

impact;

• Compliance with environmental requirements;

• Compliance with statutory OSH requirements;

• Adequate hydraulic capacity to service the entire

upper full catchment;

• Long service life with minimal maintenance and

least life cycle cost;

• Zero level of pipeline infiltration on

commissioning of pipes;

• Low level of pipeline infiltration/ex-

filtration/inflow over the life of the system;

• Resistance to entry of tree roots;

• Resistance to internal and external corrosion and

chemical degradation;

• Structural strength to resist applied loads;

• “Whole of life” costs that are acceptable to

Council..

7.2.2 Referenced documents and relevant guidelines

Wastewater designs shall incorporate all the special

requirements of Council and shall be in accordance

with the most appropriate Standards, Codes and

Guidelines including those set out below:

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AS/NZS 1260:1999 PVC pipes and fittings for drain,

waste and vent applications

NZS 7643:1979 Code of Practice for the installation

of unplasticised PVC pipe systems NZS 7649:1988 Unplasticised PVC sewer and drain

pipe and fittings

AS/NZS 1462-6:1998 Methods of test for plastic pipes and fittings

AS/NZS 4130:2001 Polyethylene pipes for pressure

applications

AS/2033:1980 Installation of polyethylene pipe

systems

AS 2200:1998 Design charts for water supply and

sewerage

AS/NZS 3500:1996 National plumbing and drainage part

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7.2.3 Connection to Existing Sewer

Networks/Approved Contractors

Connection of new sewer mains to the existing sewer

network shall be undertaken in accordance with the

requirements of S2.8 of this Code.

Connection of private drains, infill subdivisions or

developments not the subject of a development plan

approval to an existing sewer network shall be

undertaken by a Registered Drainlayer. The connection

shall be inspected by Council staff prior to backfilling of

the connection occurs.

7.2.4 Private Drainage

All wastewater pipes installed between a building and

the connection point to Council’s sewers mains are

private assets. The Building Act requires that a consent

be obtained for their installation or alteration and that

this work must only be carried out by a registered

drainlayer. A second consent must be obtained before

they may be connected to the sewer main and this

connection may only be carried out by a contractor who

has been awarded a Category F licence by Council.

Consent must also be obtained from Council before

these drains may be connected to the sewer main.

This connection may only be carried out by a contractor

who has been awarded a Category E or F licence by

Council.

6 TCC Ref: 790837

7.2.5 Rural and Rural Residential areas

Connection to Council’s wastewater system will not be

provided to Rural or Rural Residential allotments.

Council has no provision for Rural and Rural Residential

areas to be incorporated into Council’s wastewater

system.

7.3 RETICULATION SYSTEM

All wastewater reticulation systems shall be designed for

an asset life of at least 100 years. Some components

such as valves may require earlier renovation or

replacement. Refer to WSA 02 for the classification of

life expectancy for various components.

7.3.1 Design Responsibilities

7.3.1.2 District Plan

Council maintains a District Plan which sets out

information to be used in the design of new

subdivisions. See Clause 15.1.1 Wastewater Disposal

and Table 15.1 Engineering Performance Criteria.

Where the development area is not included in the

District Plan, the designer shall determine this

information by investigation using this Code of Practice

and recognized engineering principles.

7.3.1.3 Catchment Design

Pipes within any project area shall be designed to be

consistent with the optimum design for the entire upper

catchment area and any future extension of the system

shall be accommodated. This may affect the pipe

location, diameter, depth and maintenance structure

location and layout. Designers shall particularly assess

the depth of the proposed works, adopting the best

design practice to ensure a system with lowest life cycle

cost.

Pipes shall be designed with sufficient depth and

capacity to cater for all existing and potential

development of the catchment. Where future extension

of the pipe is possible, it may be necessary to carry out

preliminary designs for large areas of subdivided and

un-subdivided land. This design shall use safety factors

agreed with Council and include future subdivisions to

determine the necessary depth and diameter for an

extension.

7 TCC Ref: 790837

Where pipes are to be extended in the future, the ends of

pipes if possible shall extend past the far boundary of

the development by a distance equivalent to the depth to

invert and to terminate in a manhole or rodding eye.

This ensures that a future extension of the pipe does not

require unnecessary excavation within lots or

streetscapes already developed.

7.3.1.4 Topographical considerations

In steep terrain the location of pipes is governed by

topography. Gravity pipelines operating against natural

fall create a need for deep installations which can be

very expensive. The pipe layout shall conform to natural

fall as far as possible

7.3.1.5 Geotechnical Investigations, Foundation Design

and Groundwater Control

The designer shall take into account any geotechnical

requirements determined under Section 2 of this Code of

Practice.

The designer shall consider whether special precautions

are necessary against difficult geological and foundation

conditions.

If the predicted foundation conditions and/or the

predicted groundwater conditions (present or likely to

occur) do not call for special design details or

construction practices, then the designer shall state this

on the design drawings. However, if foundation

treatments are necessary, and/or groundwater conditions

affect either the design or construction of the wastewater

system, then the designer shall indicate the following on

the design drawings:

• The extent and all design details of any special foundation treatments required for the pipes and

other structures;

• The extent and all design details of any special methods necessary to control groundwater flow

along the pipe embedment and/or trench backfill

material e.g. bulkheads;

• All sections of the wastewater system where the constructor will need to pay particular attention

to controlling groundwater prior to excavation to

prevent heave or loss of density in the trench

floor material (e.g. “boiling” sand);

• Areas subject to subsidence;

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• Other geotechnical considerations, e.g. “Zone of

Influence” near structures. (See Drawing

WW15)

7.3.1.6 Easements

Easements are required:

• In favour of Council for all rising mains and trunk sewers installed in private property. The

easement shall be a minimum width of 3m,

located centrally about the pipe. The depth and

size of the pipeline may determine the need for

easements of greater width. These easements

shall be agreed at the time of development plan

approval.

• In favour of a property owner whose private drain passes through another property. These

easements shall have a minimum width of 1.5m

centrally located over the pipe.

• Where a main through a property is not parallel or close to a boundary, the easement shall be a

minimum of 3m wide, centrally located over the

pipe.

Easements for reticulation mains under 225mm dia. ID

through private property are generally not required.

7.3.2 Design of the Wastewater Reticulation System

7.3.2.1 Prime Considerations

Pipes shall be designed to:

• Have adequate capacity, grades and diameters;

• Have adequate grade for self-cleaning;

• Be deep enough to provide gravity service to all

lots;

• Comply with minimum depth requirements to

ensure mechanical protection and safety from

excavation;

• Avoid all underground services, whilst

maintaining all the necessary clearances;

• Allow for various drops and losses through

manholes.

• Be laid at sufficient depth to avoid interference

with land drains and gardening activities within

private property.

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7.3.2.2 Scheme Layout

Pipes should be positioned as follows:

• Within the street according to the locally

applicable utilities allocation code. A location

clear of carriageways is preferred;

• Within public land with the permission of

Council;

• Within drainage reserves outside the 1 in 100

year flood area;

• Within private property:- parallel to and located

between 1m and 1.5m from the front, rear and/or

side boundaries.

7.3.2.3 Pipeline Definitions

• Trunk mains - A gravity pipeline with an internal

diameter of 225mm or larger.

• Reticulation main – A gravity pipeline with an

internal diameter of 150mm which terminates

upstream at a manhole.

• Lateral/Connection – A 150mm or 100mm dia

pipeline branch which has no terminal manhole

structure. It may however terminate in a rodding

eye. Lateral/Connection pipes connect a

property’s private drainage to a public main, and

are Council assets.

• Connection Point – The location in a sewer

system where a property’s private drainage

system connects to the public system.

Generally if the pipe connecting the

property to the main is a single straight

length of pipe, it is defined as a connection pipe. If this pipe serves more than one

property then it is known as a lateral and

the upstream pipes serving each allotment

are the connections.

Apart from the junction into the sewer

main a lateral must not include any change

of horizontal direction.

7.3.2.4 Proposed and Existing Pipes in Private

Property

Where pipes are designed to traverse any vacant or

occupied private property, the design shall as far as

practicable allow for possible future building

development.

The design shall allow access for all equipment required

for construction and future maintenance.

Where pipes are designed to traverse properties

containing existing structures e.g. retaining walls,

buildings and swimming pools, the current and future

stability of the structure shall be considered. Pipes

adjacent to existing buildings and structures shall be

located clear of the “Zone of Influence”

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(See Drawing WW15). If this is not possible,

protection of the pipe and associated structures shall

be specified for evaluation and approval by Council.

7.3.2.5 Horizontal Curves

Horizontal curved pipes shall only be used where

approved by Council. Design standards for curved pipes

can be found in WSA 02.

7.3.2.6 Vertical Curves

Vertical curves may be specified where circumstances

provide a significant saving or where maintenance

structures would be unsuitable or inconvenient. The

curvature limitations for vertical curves can be found in

WSA 02.

7.3.2.7 Maintenance Structure Location

Maintenance structures include:

• Manholes (MH).

• Rodding eyes (RE).

7.3.2.8 Underground Services

The location of underground services affecting the

proposed pipe alignment shall be determined. Where

pipes will cross other services, the depth of those

services shall be investigated, and exposed where

necessary. Services upstream of the project area may

affect the design. A future extension of the pipe that will

cross existing and proposed upstream services may

determine the level for the current project infrastructure.

7.3.3 Pipe Materials

7.3.3.1 Acceptable Pipe Materials

Sanitary gravity reticulation systems constructed of the

following materials will be accepted:

• PVC to be manufactured in accordance with AS/NZS

1260 as grade SN16 for up to 5m depth.

Specific design for depths greater than 5m.

• Pipe type to be plain wall construction conforming to

AS/NZS 2566.

• Ductile Iron pipe to AS 2280 (concrete lined with loose

sleeve protection)

• Concrete pipe and other materials (e.g. Hobas GRP to AS

3571) may be approved by Group Manager: City

Services.

11 TCC Ref: 790837

• In general only uPVC shall be used for gravity reticulation

and service connections.

• DN 175mm is not be used in Council’s wasterwater reticulation network.

• PE 100 SDR17 may be used for steeper gradients where specifically approved by Council.

7.3.3.2 Pipe Fittings

• All fittings and service connections shall be factory fabricated of compatible materials to the proposed system

chosen and comply with the relevant Standards. PVC fittings

and service connections DN 100mm and DN 150mm

injection moulded fittings to conform to AS/NZS 1260.

DN225mm and larger factory fabricated PVC fittings to be

made of same grade materials as specified for the pipeline.

• Where the reticulation system is of uPVC the main line connection to each manhole structure is to be with a standard

uPVC proprietary connector (See Drawing WW02). The

requirements for drop connectors are detailed in Drawings

WW03 and WW04.

• In potentially unstable ground or where special protection is required, the sewer pipelines should be specifically

designed, using structural design as specified in either

AS/NZS 2566 “Buried Flexible Pipelines – Structural

Design”.

7.3.3.3 Joints

• All joints on pipes and fittings shall be factory made

flexible type.

• Under no circumstances will mortar joints be permitted.

• Gibault joints shall be “denso” wrapped and sealed with

approved outer wrapping.

• Pipe to manhole joints shall be of proprietary type and

shall incorporate a “pipe short” for each joint (see Drawing

WW02).

7.3.4 Clearances

7.3.4.1 Clearance FromUnderground Services

For normal trenching and trenchless technology

installation, clearance from other service utility assets

shall not be less than the minimum vertical and

horizontal clearances shown in Table 7.1. Written

.

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agreement on reduced clearances and clearances for

shared trenching shall be obtained from Council.

Table 7.1

Clearances between wastewater pipes and other

underground services

Utility (Existing

service)

Minimum

horizontal

clearance (mm)

Minimum

vertical

clearance (1)

(mm)

Gas mains 300(²) 150

Telecommunication

conduits & cables

300(²) 150

Electricity conduits

and cables 500(²) 225

Stormwater/Waste

water 300(²) 150

Water mains 1000/600 (³) 500

NOTE:

(¹) Vertical clearances apply when wastewater pipes

cross one another, except in the case of water mains

when a vertical separation shall always be

maintained, even when the wastewater pipe and

water main are parallel. The wastewater pipe should

always be located below the water main to minimize

the possibility of backflow contamination in the

event of a main break.

(²) Clearances can be further reduced to 150mm for

distances up to 2m when passing installations such

as poles, pits and small structures, providing the

structure is not destabilized in the process.

(³) When the wastewater pipe is at the minimum

vertical clearance below the water main (500mm)

maintain a minimum horizontal clearance of

1000mm. This minimum horizontal clearance can be

progressively reduced to 600mm as the vertical

clearance increases to 750mm.

7.3.4.2 Clearance From Structures

Pipes adjacent to existing buildings and structures shall

be located clear of the “Zone of Influence” (Drawing

WW15) of the building foundations. If this is not

possible, a specific design shall be undertaken to cover

the following:

13 TCC Ref: 790837

• Protection of the pipeline;

• Long term maintenance access for the pipeline;

and

• Protection of the existing structure or building

shall be specified by the designer for evaluation

and acceptance by Council.

7.3.5 Pipeline Design

7.3.5.1 Design Flow

The design flow comprises domestic wastewater,

industrial wastewater, infiltration and direct ingress of

stormwater.

Pipe size shall be based on the need to transport the

design flow without surcharging.

The design flow shall be calculated by the method

nominated by Council. In the absence of this

information from Council the following design

parameters are recommended:

(a) Residential Flows

i. Average dry weather flow of 210 litres per day per person

ii. Dry weather diurnal peak flow of 2.5

iii. Dilution/infiltration factor of 2 for wet weather

iv. Number of people per dwelling: 2.7

In practical terms, in a catchment not exceeding 250 dwelling units, and where no pumping

station is involved, DN 150 pipes laid within the

limits of table 7.5 will be adequate without

specific hydraulic design

For small contributing catchments, peak flows can be

significantly higher but, due to the requirement for a

minimum pipe size of DN150, such flows will not

govern the design.

(b) Industrial / Commercial Flows

i. Where flows from a particular industry or commercial development are known they

should be used as the basis of design. Where

there is no specific flow information available

and Council has no design guide, Table 7.2 is

recommended as a design basis. These flows

include both sanitary wastewater and trade

wastes and include peaking factors.

ii. Notwithstanding the above, provision for trade waste must be agreed by Council and shall be

subject to the provisions of the Council Trade

Waste Bylaw.

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iii. Pre-treatment of trade waste may be a condition of any Trade Waste Agreement.

Table 7.2 Industrial/commercial flows (Peak Wet Weather

flows)

Industry type Design flow

(Water usage) (Litre/second/hectare)

Light 0.4

Medium 0.7

Heavy 1.3

7.3.5.2 Hydraulic Design of Pipelines

The hydraulic design of wastewater pipes should be

based on either the Colebrook-White formula or the

Manning formula.

The coefficients to be applied to the various materials

are shown in Table 7.3.

Table 7.3 Coefficients for gravity lines

Material Colebrook-White

coefficient

Manning roughness coefficient

K(mm) (n)

UPVC 0.6 0.011

PE 0.6 0.011

GRP 0.6 0.011

Cement lining 1.5 0.012

PE or epoxy lining 0.6 0.011

7.3.5.3 Minimum Pipe Sizes

Irrespective of other requirements, the minimum sizes of

property connection and reticulation pipes shall be not

less than those shown in Table 7.4.

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Table 7.4 Minimum pipe sizes for wastewater

reticulation and connections to property

Pipe Minimum size DN

Lateral servicing 1 or 2 dwelling units 100

Lateral servicing more than 2 dwelling units

150

Lateral servicing commercial and industrial lots

150

Reticulation servicing residential lots 150

NOTE: For infill subdivisions, particularly where

upgrading of existing DN 100 connections in sound

condition and at reasonable grades would be impractical,

up to four dwelling units may be connected subject to

the Council approval.

7.3.5.4 Limitation on Pipe Size Reduction

In no circumstances shall the pipe size be reduced on

any downstream section.

7.3.5.5 Minimum Grades for Self-Cleaning

Self-cleaning of grit and debris shall be achieved by

providing minimum grades, as specified in Tables 7.5

and 7.6.

In practical terms, in a catchment not

exceeding 250 dwelling units, and where no pumping station is involved, DN 150

pipes laid within the limits of table 7.5

will be adequate without specific

hydraulic design.

Table 7.5 Minimum grades for wastewater mains

Pipe size

DN

Minimum grade

(%)

150

225

300

0.55

0.33

0.25

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Table 7.6 Minimum grades for lateral connections

and permanent upstream ends

Situation Minimum grade

(%)

DN 100 lateral pipes

DN 150 lateral pipes

1.65

1.20

1 .00

7.3.5.6 Maximum Velocity

The preferred maximum velocity for peak wet weather

flow is 3.0 m/s. Where a steep grade that will cause a

velocity greater than 3.0 m/s is unavoidable see WSA 02

for precautions and design procedures.

7.3.5.7 Minimum Cover

• In Private Property: The minimum cover for

unreinforced pipes shall be 600mm. Where due

to topography this cover cannot be provided,

approved protection shall be provided to the

pipeline or a ductile iron pipe used. Where the

reticulation lines are located in the front yard of

lots, the invert level shall be deep enough so as

not to interfere with any future driveway

construction.

• Under Carriageways or in the Road Reserve:

Pipes shall be specifically designed to support an

8.2 tonne axle design loading. Manufacturers’

certification shall be required for all pipes

installed under carriageways with less than

750mm cover.

7.3.5.8 Steep Grades

Bulkheads and trench stop configuration shall be

detailed on the design drawings and shall be in

accordance with the drawing WW18. Spacing of

bulkheads shall be in accordance with Table 7.7.

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Table 7.7 Bulkhead Spacing

Grade

%

Requirement Spacing (S)

(m)

15 – 35 Concrete bulkhead S = 100/Grade (%)

>35 Special design Refer to Council

NOTE: On flat grades where scour is a problem, sand bags

are often used to stabilize the trench backfill.

Where the natural transfer of water from the trench into

the surrounding ground will not provide sufficient

drainage, trench drainage shall be provided to divert the

water.

7.3.5.9 Near Horizontal Bores

Near horizontal boreholes may be used to facilitate the

economic installation of pipes, usually in difficult areas

such as under railway lines, highways, to avoid

environmentally sensitive areas, and where excavation

may pose a high risk to adjacent building or structures.

For design guidelines and tolerances refer to Appendix C

Stormwater and Wastewater Construction Specifications..

7.3.5.10 Venting

In urban developments, pipes will normally be

adequately ventilated within the private property

drainage via the terminal vent stacks. However there are

some situations where additional vent stacks will be

needed such as:

• At pumping stations

• At manholes where pumping station rising mains

discharge to a gravity pipe.

In such situations vent stacks shall be installed as per the

requirements of WSA 02 and WSA 04.

7.3.6 Maintenance Structures

7.3.6.1 General

This section describes the requirements for structures

which permit access to the wastewater system for

maintenance. Theses are categorized as:

• Manholes (MH);

• Rodding eyes (RE);

The selection of a suitable location for maintenance

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structures may influence the pipe alignment. Generally,

a minimum clearance of 1000mm should be provided

around maintenance structures clear of the opening to

facilitate maintenance and rescue. Council may

determine other specific requirements subject to the

individual site characteristics.

Maintenance structures shall be located: -

• Where long term, safe access is available; (if

possible / practicable)

• Clear of floodways, stormwater detention areas,

stormwater secondary flow paths and inter-tidal

regions

7.3.6.2 Location of Manholes

The design shall include manholes at the following

locations:

• Intersection of pipes except for junctions

between mains and laterals;

• Changes of pipe size;

• Changes of pipe direction, except where

horizontal curves are used;

• Changes of pipe grade, except where vertical

curves are used;

• Combined changes of pipe direction and grade,

except where compound curves are used.

• Changes of pipe invert level;

• Changes of pipe material, except for

repair/maintenance locations;

• Permanent or temporary ends of a pipe

• Discharge of a pressure main into a gravity pipe

7.3.6.3 Manhole Spacing

For reticulation pipes, the maximum distance between any

two consecutive manholes shall be 120m.

7.3.6.4 Manhole Materials

Standard MHs shall be manufactured in pre-cast

reinforced concrete. However, if aggressive groundwater

or other special conditions exist, alternative materials

may be more appropriate as MHs.

For alternative materials check with the manufacturer on

their suitability for the purpose intended. Approval by

the Council would be required.

19 TCC Ref: 790837

Trunk mains require specific manhole design.

7.3.6.5 Size of manholes

The standard internal diameter of circular MHs is

1050mm and preferred nominal internal diameters are

1050mm, 1200mm and 1500mm. When considering the

appropriate MH diameter, consideration shall be given

by the designer to the base layout to ensure hydraulic

efficiency and adequate working space in the chamber.

Where the effective working space is reduced by internal

drop pipes, a larger diameter may be required. Where

there are several inlets, the designer may require

guidance as to the best layout of the chamber

7.3.6.6 Base Layout

• An area shall be provided in the base of each MH

that provides a safe place to stand for

maintenance purposes.

• The area will be close to flat with a cross fall

(2H:1V) into the MH pipe system for drainage

purposes.

• Channels shall have a minimum inside radius of

300mm.

7.3.6.7 Allowable Deflection Through MHs

A maximum allowable deflection through a MH

shall comply with Table 7.8.

Table 7.8 Maximum allowable deflections through MHs

Pipe size

DN

Maximum deflection

Degrees (º)

150 to 300

150 to 300

Up to 120º for internal fall

along MH channel

Up to 150º when using an

internal or external drop

structure

7.3.6.8 Internal Falls Through MHs

a) Reticulation pipes

• The minimum internal fall through a reticulation channel in a MH shall comply with Table 7.9.

• The maximum benched fall through a MH is to be 600mm.

• Where the outlet diameter at a MH is greater than the inlet diameter, the minimum fall through the

20 TCC Ref: 790837

MH shall be not less than the difference in

diameter of two pipes, in which case the pipes

shall be aligned soffit to soffit.

• On pipes where the maximum internal fall of 600mm across the base of the MH is not

achievable due to a large difference between the

levels of incoming and outgoing pipes then

internal or external drops shall be provided. (see

Drawings WW03-04)

Table 7.9 Minimum internal fall through MH joining

sewer main pipes of same diameter

Deflection angle at MH

Degrees (°)

Minimum internal fall

(mm)

0 to 30

>30 to 60

>60 to120

30

50

80

b) Lateral/Connections to Manhole

• The invert of a lateral/connection must connect to

the MH at a level no lower than the average of

the soffit levels of the main inlet and outlet pipes.

• Maximum angle of deflection of

lateral/connection into the manhole main channel

shall be 90 degrees.

7.3.6.9 Effect of Steep Grades on MHs

Where a pipe of grade >7 % drains to a MH, the

following precautions shall be taken:

• No change of grade is permitted at inlet to a MH;

• Steep grades are to be continuous through the

MH at the same grade;

• Depth of MH is to exceed 1.5m to invert for DN

150 and DN 225 pipes;

• Depth of MH is to exceed 2.0m deep for DN 300

pipes;

• Change of direction at the MH is not to exceed

45 degrees;

• No drop junctions or verticals are to be

incorporated in the MH;

• Inside radius of channel inside the MH is to be

greater than 6 times the pipe diameter; and

• Benching is to be taken 150mm above the top of

the inlet pipe.

21 TCC Ref: 790837

• To avoid excessively deep channels within MHs,

steep grades (>7 %) shall be “graded-out” at the

design phase where practicable. The design of

pipelines on gradients over 7% must be agreed

with Council.

• Benching of channels must ensure that the final

platform is parallel with the main channel so that

maintenance workers are able to stand

comfortably on a flat surface. The benching shall

be sloped towards the channel.

7.3.6.10 Flotation

In areas of high water table, all MHs shall be designed

to provide a factor of safety against flotation of 1.25.

7.3.6.11 Access

MH steps shall comply with Drawing WW05

7.3.6.12 Covers

MH covers with a minimum clear opening of 500 mm in

diameter, shall be used.

• “Non-rock” covers must be used on all State

Highway and Level 2 roads. (roads with greater

than 10,000 vehicles per day).

• “Heavy Duty” covers must be used in the road

reserve, carriageway, commercial and industrial

properties and all public areas.

• “Standard” covers may only be used on

residential properties.

• All covers must be painted with white road

marking paint.

7.3.6.13 Areas Subject to Flooding

Watertight type bolt-down metal access covers:

• In systems where the possibility of surcharge

exists; and

• Along creeks subject to flooding above the level

of the cover, in tidal areas, or in any location

where surface waters could inundate the top of a

MH.

The top of MHs in areas subject to flooding shall be a

minimum of 300 mm above the 1% AEP flood level.

7.3.6.14 Rodding Eyes (RE)

• An RE is required to be constructed at the ends of

some lateral pipes that are installed between a

22 TCC Ref: 790837

property connection point and the Council sewer

main network. (See Clause 7.3.7.1)

• uPVC bends up to 45 degrees are acceptable.

• A manhole frame and cover shall be installed

over the entry point where the RE is to be located

in areas other than permanent hardstand areas.

• The cover type shall be as required by Clause

7.3.6.12.

• A fire hydrant base and RE cover may only be

installed in permanent hardstand areas.

• Typical details of RE structures are shown on

Drawings WW08 and WW09

7.3.7 Laterals/Connections

The general levels and locations of all wastewater pipes

shall conform with Council’s overall plan for

reticulation. Provision must be made for connection into

the existing reticulation system. Refer to Section 7.3.5

for pipeline design.

• Where practicable and where connection is to be

within 5m of a manhole the connection shall be

to the manhole.

• Where the main line is within public property

and within 5m of the property boundary a

separate connection shall be provided to each

allotment.

• Connections to trunk mains will generally not be

approved by Council.

7.3.7.1 Subdivision of 4 Lots or More

Minimum pipe sizes are 150mm diameter nominal size

for reticulation sewers and 100mm diameter nominal

size for laterals. For the purposes of this clause a

reticulation sewer is any pipeline terminating with a

manhole at its upstream end and a lateral is any public

pipeline connecting from the reticulation sewer to an

individual allotment

23 TCC Ref: 790837

• Lateral with single connection (out of manhole)

Fig.1:

For 100mm dia lateral up to 25m no RE required.

For 100mm dia lateral between 25m and 50m in

length terminate in a RE or where lateral passes

through adjacent property.

Above 50m normal sewerage reticulation standards

apply.

150mm diameter lateral pipe must be used under all

carriageways.

• Lateral with two connections (out of manhole) Fig.

2:

For 100mm dia laterals up to 25m in length

terminate in a RE.

For laterals over 25m and up to 50m use 150mm dia

pipe and terminate with RE.

Above 50m normal sewerage reticulation standards

apply.

150mm diameter lateral pipes must be used under all

carriageways.

• Lateral with greater than 2 connections and a max of

6 connections (out of manhole) Fig. 3:

Use a 150 mm dia pipe up to 50m in length and

terminate in RE.

Above 50m normal sewer reticulation standards

apply.

150mm diameter pipes must be used under all

carriageways.

24 TCC Ref: 790837

• Lateral Out of Main Servicing One Allotment: Fig 4

For 100mm dia pipe up to 25m no RE required.

For 100mm dia pipe between 25m and 50m in length

or where the line passes through an adjoining lot

terminate in RE.

150mm diameter pipes must be used under all

carriageways.

• Lateral Out of Main Servicing 2 Allotments, Fig. 5 and Fig. 5A:

For 100mm diameter up to 25m terminate in RE.

For 25m to 50m in length use 150mm dia pipe and

terminate in RE.

150mm diameter pipes must be used under all

carriageways.

25 TCC Ref: 790837

7.3.7.2 Infill Subdivision - Three Lots or Less

(Excludes Existing Lot)

It is recognized that infill subdivisions require flexibility

in their reticulation layout. However, normal trade

practices and standards are needed to ensure that the

desired service life is achieved.

Reticulation of infill subdivisions shall comply with the

following criteria.

• Infill subdivisions are to be reticulated on a site

by site basis to the approval of Group Manager:

City Services

• Where practicable, drainage reticulation should

be constructed or upgraded in accordance with

this Code. (See 7.3.7.1 above) These drains can

therefore be declared public and provide each

allotment with the same standard of individual

connection as new ‘greenfields’ allotments. (Fig

6.) Where this is considered impractical or

unnecessary, the Consent Holder may make

application to Council to accept the drain as

private within an appropriate easement.

However common private drains are not

encouraged so as to alleviate the friction that

sometimes occurs between neighbours when

shared services are involved. (Fig 7)

• Drainage lines are to be separated at the point of

connection to Council’s reticulation system and

remain separate for each lot unless specific

approval is granted by Council (Fig 6 and 7).

Where the main is within a neighbours property,

the new junction may be installed immediately

within the property being subdivided.

7.3.7.3 Multi-Unit Properties (Such as Apartment

Buildings and Body Corporate

Developments)

• For multiple occupancies (unit title, cross lease

or company lease), service of the whole property

shall be achieved by providing a single point of

connection to the wastewater system. Connection

of the individual units is by joint service pipes

owned and maintained by the body corporate,

tenants in common or the company as the case

may require.

26 TCC Ref: 790837

In this instance the whole of the multiple

occupancy shall be regarded as a single lot. All

drainage within the development boundary would

be private.

• Alternatively, if authorized by Council,

developers may have the option of providing

wastewater facilities to the individual titles or

tenements in new developments by extending the

public line into the lot and providing a separate

lateral/connection to each unit. If so all internal

drainage must be to the normal Code of Practice

standards

• Where the above developments are proposed a

single DN 150 lateral/connection will be required.

Multi-unit developments will generally be required

to upgrade existing laterals if less than DN 150.

• The connection shall include a surface accessible

inspection chamber or manhole immediately inside

the boundary.

7.3.8 Property Connections

A connection is the point of union between a property’s

private drain and the public wastewater network. Private

drainage generally extends through to the property

boundary, at which point Council accepts responsibility

for the downstream pipelines.

7.3.8.1 General Considerations

• The property connection should be designed to

suit the existing situation and any future

development.

Where practicable, pipes shall be designed to

provide a service for the whole of the property

they serve. Where, for physical reasons, it is not

practical to fully service a property, a partial

service may be acceptable to Council provided the

unserviceable area is identified by a building line

restriction or minimum floor level consent notice.

7.3.8.2 Requirements of Design

The design shall specify the requirements for the

property connections including:

• Plan location and lot contours;

• Invert level at property boundary or junction with

the main as applicable.

27 TCC Ref: 790837

7.3.8.3 Number of Connections

It is normal practice to provide one connection per lot.

Provision of additional connections shall be subject to

justification by the developer and approval by Council.

7.3.8.4 Location of Connection

• The connection shall be located to service the lowest practical building platform on the property

and where possible:

• Be clear of obstructions, e.g. tree, tree roots, paved areas;

• Be easily accessible for future maintenance;

• Be clear of any known future developments, e.g. swimming pools or driveways;

• Be no deeper than 1.5m where practicable

7.3.8.5 Connection Depth

Connection depths shall be set to drain the whole

serviced area recognizing the following factors:

• Surface level at plumbing fixtures of buildings

(existing or proposed);

• Depth to invert of pipe at plumbing fixture or

intermediate points;

• Minimum depth of cover over connection to be

600mm unless protected by hard surface.

• Invert of public main at junction point;

• Allowance for crossing other services (for

clearances see 7.3.4);

• Allowance for minimum gradients of laterals and

private drainage;

• Lateral junctions installed at minimum of 45

degrees (vertical) to main(refer to drawing

WW13);

• Connections deeper than 3.0m must be approved

by Council.

The designed invert level at the connection shall be not

higher than the lowest calculated level consistent with

these factors.

Deep connections shall be brought up to within 1.5m of

finished surface (Drainlayer can then cut connection

down to required level if necessary)

28 TCC Ref: 790837

7.3.8.6 Installation of Connections

• Connection of a private wastewater drain to the

public system can only be carried out by a

Contractor holding a Category E licence and

after drainage consent has been approved by

Council.

• The end of each connection pipe shall be sealed

with a solvent welded cap, painted red, in

greenfield developments or if connection does

not to occur immediately.

• All connection points shall include an

underground inspection fitting the same size as

the lateral connection to the property. Where the

inspection is to a property servicing multiple

residential units then refer to 7.3.7.3 for a surface

accessible inspection chamber.

• Each connection point shall be marked with a 50

x 50mm timber stake which shall extend from

the invert to a minimum of 300mm above

finished ground level. A PVC marker tape

labelled “sewer” shall be attached to the

connection pipe, brought up and tied to the top of

the stake.

7.3.9 Building Close Proximity Rules and Alteration

Of Ground Levels (see drawings WW15 and 16)

7.3.9.1 Rising Mains and Trunk Sewers

• Buildings or structures to be constructed close to a

rising or trunk main shall comply with the

requirements of Drawing WW15. Piles and ground

beams shall be designed by a Chartered Professional

Engineer.

• Minimum horizontal clearance between pipe exterior

and piles/building shall be 1500mm.

• All buildings shall be at least 500mm clear of the

external wall of a manhole.

• No building or concrete slab may be constructed

over a connection point to a sewer main.

7.3.9.2 Reticulation Sewers and

Laterals/Connections

• Buildings or structures to be constructed close to a

public reticulation main or lateral/connection must

comply with the requirements of Drawing WW15.

Piles and ground beams must be designed by a

Chartered Professional Engineer.

29 TCC Ref: 790837

• Minimum horizontal clearance between pipe

centreline and piles/building shall be 1000mm.

• All buildings shall be at least 500mm clear of the

external wall of a manhole.

• No building /concrete slab to be constructed over a

connection point to a sewer main.

7.3.9.3 Ancillary Buildings may be Exempt (for

Reticulation Sewers and

Lateral/Connections)

• No enclosed building or structure shall be sited over

a manhole or closer than 500 mm from the outside

wall of the manhole structure.

• Corner foundations shall be a minimum of 600mm off the pipe centre line.

• Where dispensation has been granted for a building or structure to be built over a reticulation sewer or

lateral/connection, foundations shall be designed by

a Chartered Professional Engineer. Piles and /or

foundations must conform with specifications shown

in Drawing WW15.

• No buildings will be allowed over the sewer main if

there is a connection closer than 1000mm to the

buildings, unless the connection is relocated to the

satisfaction of Council.

7.3.9.4 Carports / Decks / Sunrooms (for

reticulation sewers)

These structures may be sited over reticulation sewer

pipelines provided:

• There is no connection point closer than 1000mm to

the structure.

• No enclosed building or structure shall be sited over

a manhole or closer than 500 mm off the outside

wall of the manhole structure.

• The structure is designed such that it can be

dismantled easily in sections (bolting is the preferred

method of construction);

7.3.9.5 Filling over Pipes

Any ground level raising carried out on a property must not

result in a depth of fill material greater than 3.0 metres over

a sewer pipe invert, within the 45 degree “Zone of

Influence” of the pipe.

30 TCC Ref: 790837

7.3.9.6 Cutting Down Over Pipes

The cover over the top of a public sewer in private property

shall not be reduced to less than 600mm.

7.3.9.7 Retaining Structures

Minimum design constraints for retaining structures/piles

shall be as in WW16

7.3.9.8 Carriageway Trench Re-instatement.

Where pipe servicing in the carriageway is required, the

trench re-instatement works shall follow the minimum

requirements shown in drawing D16 and R32.

Pipe trenches within a carriageway shall be backfilled using

an approved hardfill placed immediately above the pipe

surround and compacted in layers not exceeding 200mm in

depth.

In existing sealed streets, the top section of the trench shall

be backfilled as specified by TNZ M/4. The depth of base

course and type of finishing coat seal shall conform at least

to the standard of the existing road construction, but may

require being greater.

7.4 CONSTRUCTION SPECIFICATION

Construction Specification for both wastewater and

stormwater are provided in Appendix C.

7.5 WASTEWATER PUMPSTATIONS

AND RISING MAINS. Construction Specifications for wastewater pumpstations

and rising mains are contained in Appendix E.