Technical requirements for sewerage

 

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  • 1 Objectives

    The sewerage objectives are seen as being achieved when:

    1. the planning, design and construction of new facilities are adequate in servicing new and future developments in accordance with the requirements of the ACT Government;
    2. there is compatibility with the existing facilities, methods of operation, and maintenance techniques; and
    3. the facilities provide public health, environmental, and asset protection consistent with the accepted design and construction requirements set out in this document and with developments in technology as approved from time to time.

    ACTEW Water's sewerage system is to be designed to ensure the efficient and effective transfer of water-borne wastes. It should be able to be adequately operated and maintained to achieve minimum risk of failure through blockage, collapse or equipment failure, to ensure acceptable asset life. It must meet environmental protection requirements consistent with personal, public and asset safety, public health, economic operations and minimum total cost.

    The pipe system may, on occasions, be subject to "surcharge" (where the hydraulic grade line is higher than the pipe obvert) or "overflows" (where sewage overflows out of maintenance holes). These situations may be the result of blockages and/or flows in excess of the design flows. In establishing the layout of the pipe network, designers should take care to ensure that any overflows are likely to cause only minimal nuisance or damage. The sewerage system is provided for "domestic" sewage. Non-domestic discharges will only be accepted if quality and quantity conform to the requirements set by ACTEW Water, as defined in the Trade Waste Acceptance Criteria. Designers of sewers for industrial blocks should seek early advice on these requirements from ACTEW Water.

    1.2 Maintenance aspects

    1.2.1 General

    The sewerage system is to be designed with due regard to the continuing maintenance requirements after the works have been constructed. A system that can be easily and economically maintained is essential.

    Maintenance holes located in readily identifiable locations (e.g. opposite a building line), and not within leased properties, are an aid to rapid clearance of sewer blockages. By far the greatest maintenance problem is tree root penetration of sewers less than DN450. Designers shall pay attention to this problem particularly in areas of high risks where the sewers are shallow or extensive planting of trees is likely to occur. Particular care in selecting pipe materials and jointing methods should be made in these areas. Refer to the document entitled The Invasion of Sanitary Drains by Plant Roots: Prevention and Cure (Reference 10.9).

    1.2.2 Special equipment

    The purchase of special maintenance equipment and plant requires considerable lead times, special approvals and funding. As a consequence, no design incorporating the need for special or unusual equipment should be prepared without the prior written approval of ACTEW Water.

    This requirement also extends to the need to use special techniques or hired equipment. To ensure that maintenance personnel can respond and overcome operational problems consistent with service objectives, it is essential that maintenance of the system is not dependent on non-standard techniques or equipment.

    1.3 Safety, corrosion and odour aspects

    Hydrogen sulphide poses a potential safety threat to sewer workers, can generate a corrosive atmosphere that corrodes sewerage assets, and is responsible for many odour problems. Odour is a particular problem in the ACT due to the regular occurrence of temperature inversions and nondispersive wind velocities. These problems, which increase the risk of sulphide generation, can be overcome with careful attention.

    In this regard it is important to:

    • use adequate grades for slime control;
    • minimise detention periods by avoiding the use of pump stations where possible;
    • design for pump station reliability;
    • ensure adequate ventilation for trunk sewers;
    • avoid any unnecessary turbulence of stale sewage at junctions and changes in grades (drop junctions, vortex drops and particularly where rising mains enter the gravity system).

    1.4 Discharges from stormwater systems to sewers

    Unless approved otherwise, under the specific Trade Waste Agreement, no stormwater discharge will be accepted into sewers.

    1.5 Non-domestic liquid waste disposal to sewer

    Non-domestic liquid waste may NOT be discharged to sewer without prior approval from ACTEW Water. Acceptance criteria and advice on the discharge of non-domestic waste can be obtained from ACTEW Water's Customer Services Branch in Mitchell, telephone number 6242 1111.

  • 2 Location of sewers

    2.1 Sewer locations

    2.1.1 Sewer layout

    1. Sewers located outside leased lands

      The design of a sewer system should take into account the fact that there is a significant increase in the risk of tree root blockages after a period of about 20 years. Further, the access to sewers for maintenance is a major problem in the ACT despite the use of sewerage reserves for this purpose. Therefore minimising the use of sewer alignments and reserves in leased land is an important feature of good sewer design. Where there is public land at the rear or the side of a leased block the sewer should be located within the public land rather than within the leased block.
    2. Diversion of principal carrier sewers around leased lands

      Blockages in the sewer system have the potential to result in sewage overflows into leased properties.

      To minimise problems caused by blockages, wherever practicable, sewers, particularly main carriers, shall be located in public areas rather than within leases.
    3. Other situations

      Where a sewer is to be constructed across open areas it is to be sited to (1) maximise its use for future development, and (2) minimise its impact on possible future use of the site.

      Wherever possible sewers under playing fields are to be sited so that maintenance holes are not located within the playing area.

      To lessen the risk of overflows into houses the design should include (1) careful placement of maintenance holes to limit the number of connections into small near-maximum loaded sewers, and (2) the location of connection ties in accordance with Clause 6.2.2.

    2.1.2 Standard alignments

    The aim of standardised locations for sewers is to limit the construction clashes with other services and permit ready location by maintenance crews.

    1. Roadways

      Sewers are usually located on the high side of road reserves, which permits relatively short connections from adjacent high-side properties.

      The standard locations for sewers are shown on Road Verge Drawings - Drawing Nos. SEP4 - 01 to 06, Chapter 4 (Road Verges) (Reference 10.15). The usual location for sewers is 1.6 metres outside the property boundary.

      Where there is a significant advantage in placing a sewer on an alignment reserved for another service, it may be so placed provided that the relevant authority agrees in writing to release the reservation. A copy of the agreement is to form part of Design Submission 1.

      On curved roadways curved alignments are permitted as per Clause 2.4 and Clause 2.5.

      In selecting pipe alignments it is necessary to carefully consider maintenance hole and maintenance shaft locations. Maintenance hole and shaft location preferences are outlined in Clause 5.1.3 and Clause 5.2 respectively.
    2. Residential land

      When sewers are required between adjacent properties (either for leases back-to-back or side-to-side) they are usually located along the low side of the uphill property. Sewers are usually constructed parallel to, and uphill of stormwater drains. Pipes connected to sewer service ties shall normally not cross stormwater drains.

      Alignments shall be offset at sufficient distances from property boundaries to allow working room for excavation equipment.

      Acceptable offset alignments from property boundaries are in accordance with Table 3-1.

      Table 3-1
      Sewer alignments - leased blocks


      Size (DN) Rear of property (m) Side of property (m)
      DNl00 to DN225 1.2 1.2
      1.8 (if power poles involved)
      DN300 1.8 1.8 (see note 2)

      Notes

      1. For reserve (easement) requirements see Clause 2.2.

      2. DN300 sewers or larger are normally not permitted within leased residential land.
    3. Commercial and industrial land

      These sewers should also be located along the low side of the uphill property as suggested for residential land (see Clause 2.1.2 (ii) above). However, restrictions on land utilisation for these categories of land are generally less acceptable and development is likely to occur right up to the edge of a service reserve. Consequently, larger sewers are located centrally within a reserve to provide working space on either side of a sewer.

      DN450 sewers or larger are normally not permitted within leased commercial or industrial land.

      Acceptable offset alignments from property boundaries are in accordance with Table 3-1. For reserve requirements see Clause 2.2.

    2.2 Service reserves (easements)

    A sewerage reserve should be wide enough to contain the service and shall provide working space for future maintenance activities on each side of the service. For general information on easements refer to Part 1, General Design Standards (Clause 3.2).

    Acceptable sewerage reserve widths will normally be in accordance with Table 3-2.

    Table 3-2
    Sewerage reserve (easement) widths for sewers up to 5m deep

    Sewer size (DN) Block type Minimum width
    of reserve (m) 100 to 225 Residential 2.5 300 Residential 3.5 100 to 225 Commercial and industrial 2.5 300 and 375 Commercial and industrial 3.5

    Notes

    1. See Clause 2.1.2 for standard alignments.
    2. See Clause 2.3 for building restrictions.
    3. The minimum distance from the centre line of a sewer pipe to either edge of the reserve is 1.2m.
    4. In exceptional circumstances common easements for sewers with other hydraulic services may be approved subject to the following conditions (which apply in addition to notes 1, 2 and 3 above):
      • the minimum clearance between pipes shall be the greater of 600mm or the required clearance to satisfy the conditions set in the diagram below;
      • the minimum common easement width is 3.5 meters, but may be wider if the minimum required spacing between pipes is greater than 600mm;
      • in all cases the MH's on the shallower main shall be founded sufficiently deep to prevent loads from being transferred into a nominal trench of the deeper main.
      The design drawings shall nominate the easement width, spacing between services, and if required minimum depth of footings of MH's on the shallower main.

      Controls on common easements for sewers with other hydraulic services

      Controls on common easements for sewers with other hydraulic services

    5. Reserve widths greater than 3.5 metres are to be specially noted and brought to the attention of ACTEW.
    6. For sewers deeper than 5.0 metres or of size DN525 and larger, a proposed easement width shall be submitted to ACTEW for approval.

    2.3 Building restrictions

    For a diagrammatic representation of controls on building set back and depth of footing refer to the diagram below.

    1. Restrictions due to nearby sewer

      The presence of a deep sewer (either within or outside a leased property) may result in a building, on or near the property line (or edge of reserve), needing its foundations deepened so that the building will not impose loads on the sewer.

      The "zone of influence" from building foundations is taken as being within an angle of 45° to the horizontal below the foundation. Foundations are to be deep enough for this zone to remain beneath the sewer pipe. As detailed below, the minimum permissible depth of foundation is to be calculated and the information provided to the Land Development Branch of the ACT Government for inclusion as a building restriction on lease documents.
    2. Building restrictions over or near sewerage reserves (easements)

      The foundations are designed so that the sewer is not affected structurally or with respect to access (Clause 2.3 (i) above);

      At ground level the building is entirely out of the ACTEW reserve and at least 2.0 metres from the actual centre line of the sewer;

      Building eaves and awnings lower than 3.0 metres above the final surface level must not overhang the easement;

      Overhang of the easement is permitted if the easement width is less than 3.0 metres, and a clear height of 3.0 metres exists between the final surface level and the underside of any permanent part of the building. Minimum clear heights over easements wider than 3.0 metres will be determined by ACTEW on a case by case basis;

      In all cases the extent of the overhang is limited. The furthest edge from the building must not be closer than 600mm horizontal distance to the centre line of the sewer.

      Controls on building setback and depth of footing

      Controls on building setback and depth of footing

    2.4 Vertical curves in sewers

    Vertical curves are permitted if substantial cost savings can be achieved through their use. Vertical curves must not be used within horizontal curves.

    The following limitations apply:

    • vertical curves are only permitted on solvent welded DN150 sewers;
    • grade limitations apply as per Table 3-4 and Clause 3.1.3;
    • the vertical curve length shall not be shorter than 20 metres;
    • vertical curves will start and end at structures;
    • the maximum rate of change in grade shall not exceed 0.1% per metre;
    • the rate in change of grade shall be constant along the whole length of the vertical curve.

    The following will be shown on drawings:

    • rate of change in grade (%/m);
    • chainage and grade at start of curve (%);
    • chainage and grade at end of curve (%);
    • to assure vertical curves are set out correctly, design drawings shall show invert levels and chainage at intermediate points with intervals not exceeding 5.0 metres.

    2.5 Horizontal curves in sewers

    Horizontally curved sewers may be utilised where there are significant advantages in their use. Ad hoc curving of sewers to avoid an obstacle such as a power pole, gas main etc. is not permitted.

    Curves in sewers between successive maintenance holes are to be in one direction only (i.e. no reverse curves and combinations of vertical and horizontal curves). In constructing a curved sewer the angles at each joint shall be uniform (i.e. within an accuracy of ±0.25°).

    Preference should be given to solvent welded pipe materials on curved alignments.

    Curve radii are limited in order to minimise obstructions in the pipe bore or failure of jointing, and to avoid other significant maintenance problems. Minimum curve radii are shown in Table 3-3.

    Table 3-3
    Minimum radii

    Pipe material and DN Maximum pipe length (m) Method of jointing Minimum radii (m) VC DN100-300
    (Spigot - socket) 0.6 Rubber ring 30 VC DN100-300
    (Spigot - socket) 1.2 Rubber ring 45 VC DN100-300
    (Spigot - spigot) + polypropylene sleeve coupler 1.6 Twin rubber ring 60 PVC DN100 and DN150 - Solvent welded 50 PVC DN225 3.0 Solvent welded 100

     

    1. Alignment

      Curved sewers should be located so that they follow easily identifiable surface features such as property lines, curb lines, fence lines and building setbacks.
    2. Contributing properties

      The load contributing upstream of a curved sewer shall be at least 10 EP or 3 residential dwellings.
    3. Minimum grades

      It is considered that curved sewers will marginally increase operation and maintenance requirements compared with sewers on straight alignments. Further, accuracy in constructing curved sewers is more difficult to achieve.

      To allow for these factors steeper sewer grades are required.

    Table 3-4
    Minimum grades For curved sewers

    Sewer size (DN) Minimum grade permitted (%) DN150 (refer to Clause 2.5 (ii)) 1.50 DN225 1.25 DN300 1.00

    2.6 Clearance to other services

    Minimum clearances have been established to reduce the likelihood of damage to sewers or other services, and to protect personnel during construction or maintenance work.

    Under no circumstances are:

    • sewers to be cranked to avoid other services or obstacles;
    • sewers permitted to be set longitudinally above or below other underground services in the same trench.

    Clearance provided to other services should be maximised. The design should be based on the actual location of those services, where proving of service depths during the design phase is recommended. Where a sewer crosses another service, the design drawings shall direct the contractor to prove the location of the service by hand excavation.

    Acceptable minimum clearances are as follows:

    1. Parallel services

      The minimum clear horizontal distance permitted between the sewer and another service is 600mm.
    2. Subsurface structures

      Horizontal clearance to structures such as valve pits, stormwater sumps, maintenance holes, hydrants etc. shall be 150mm.
    3. Crossing srvices
      • Stormwater drains: The normal minimum vertical clearance when crossing stormwater drains is 150mm.
      • Water mains: The normal minimum vertical clearance when crossing water mains is 150mm.
      • Telstra: When crossing major and residential Telstra services the minimum vertical clearance shall be 150mm. Increased clearance may be required when crossing coaxial cables.
      • Gas: The minimum vertical clearance to low and medium pressure gas mains shall be 150mm. For high pressure mains the minimum clearance shall be 300mm.
      • Electrical cables: When crossing low voltage cables the minimum vertical clearance shall be 150mm. The minimum clearance to high voltage cables is 300mm.

    2.7 Sewer crossings of roads, creeks and playing fields

    • Roadway crossings - The sewers are to be designed for highway loadings.
    • Creek crossings - These sections are particularly vulnerable to damage by scouring action during flood flows. Depth allowance should be made for scour together with adequate protection measures. If the pipe cover is less than 1.0 metre, concrete encasing of the pipe with rock gabions lining the creek bed will be required.

      Creeks are often lined with disturbed sediments. Prior to pipe laying, unstable material under the creek must be removed to sound ground and replaced with single size crushed rock aggregate. Refer to Standard Drawing No. WSS 056.
    • Playing fields - see Clause 5.1.17.

  • 3 Hydraulic design

    3.1 General hydraulic aspects

    It is required that ACTEW Water's sewerage system be designed using methods and data that ensure compatibility of all system elements. The design of the sewerage system shall be based on the following flows:

    • Peak wet weather flow (PWWF): used to determine the minimum sewer pipe size;
    • Most probable peak dry weather flow (Qdmp): used to ensure that the proposed pipe grade is sufficient for self-cleansing and sulphide-slime control.

    These flows are based upon the contributing "equivalent population" (EP), and, in the case of the PWWF, a further component based on contributing net sewered area (NSA).

    3.1.1 Flow estimation

    1. Equivalent population

      Design EP's for standard, low, and medium density residential housing developments, and for some commercial, industrial and institutional areas, can be obtained from Table 3-5. The residential population for each district and division of the ACT, present and future, can be obtained from the Urban Economics Branch of the Chief Minister's Department. Design EP's for land use types not included in Table 3-5 can be obtained from the document titled Design of Separate Sewerage Systems (Reference 10.2). However, the applicability of these EP's to Canberra should be checked with ACTEW.

      Table 3-5
      Design equivalent populations


      Land use EP Unit
      Residential:
      - Low density (1)
      - Medium density
      - High density (2)
      3.6
      2.5
      2.0
      per dwelling unit,
      per dwelling unit,
      per dwelling unit
      Commercial facilities:
      - Shops and offices
      - Public visitor buildings or sport spectator facilities
      - Restaurants and clubs
      - Tourist or hospital accommodation
      0.3
      0.05

      0.1
      0.5
      per employee,
      per short stay visitor,

      per seat,
      per bed.
      Industrial:
      - Dry trades
      - Wet trades
      0.3
      *
      per employee,
      assess on a case by case basis
      Institutional:
      - Schools and educational facilities
      0.2
      per student or staff


      Notes

      1. Less than 15 dwellings per hectare.
      2. More than 80 dwellings per hectare.

    2. Design flow rates

      Table 3-6
      Definition of terms - input parameters


      Input parameters Abbreviated Unit Used to calculate
      Total equivalent population, Table 3-5 TEP EP ADWF, Qdmp ,PDWF
      Equivalent population from residential catchment REP EP TEP
      Equivalent population from commercial or industrial catchment CEP or IEP EP TEP
      Net sewered area NSA ha PII
      Residential net sewered area (1) RNSA ha NSA
      Industrial net sewered area(1) INSA ha NSA
      Commercial net sewered area(1) CNSA ha NSA


      Notes

      1. Sewered areas exclude arterial roads, major floodways, and parkland.

      Table 3-7
      Definition of terms - flow components


      Flow component Abbrev Unit Used to calculate
      Daily per capita sewage contribution PCC L/EP/Day ADWFs
      Average dry weather flow from gravity source only ADWFG L/s Sewage age, degree of septicity, PDWFs
      Average dry weather flow including pumped flows ADWFT L/s Sewage age, degree of septicity, PDWFs
      Peak dry weather flows (as per ADWFs) PDWFG
      PDWFT      		 L/s
      L/s      		 PWWF, PDWFT Qdmp
      Total pumped flow TPF L/s PDWF, PWWF, cleansing flows
      Most probable peak dry weather flow Qdmp L/s Sewer cleansing grades, sewer slime stripping grades
      Capacity Qf L/s Maximum pipe capacity
      Peak infiltration and inflow PII L/s PWWF
      Peak wet weather flow PWWF L/s Pipe capacity, pump capacity


    3. Flow algorithms
      1. Residential areas
        • PCC = 300 L/EP/day
        • ADWFG = TEP x PCC / 86 400
          = TEP/288
        • ADWFT = ADWFG + 1/3 TPF
        • PDWFG = 5.83 ADWFG /TEP0.1
        • PDWFT = PDWFG + 2/3 TPF
        • PII = 1.43 NSA0.81
        • PWWF = PII + PDWFG + TPF
        • Qdmp = 0.75 PDWFT

          To assist in the calculation of design flows, values of PDWFG and PII can be obtained from Appendix 3-1 and Appendix 3-2 respectively.
      2. Industrial or commercial areas

        Guidance for the estimation of Equivalent Populations (EP"s) for various types of land uses is given in Table 3-5 and the document entitled Design of Separate Sewerage Systems (Reference 10.2). The EP's estimated from these sources shall be used to estimate the ADWF and PDWF from non-residential areas using the same formulae as given in the above section for residential areas.

        For non-residential areas however, the area used to estimate the PII shall be adjusted using the factored method to reflect reduced infiltration/inflow from the greater impervious area, and to reflect fewer service connections typically encountered in non-residential areas:
        • PII = 0.944 (INSA + CNSA) 0.81
      3. Mixed landuse catchment

        The following method of flow estimation shall be used for catchments containing areas of different types of land use. In such cases the peak flows from different areas are nonsynchronous, e.g. the peak morning flow from residential areas precedes the peak flow from commercial areas. For mixed development, the critical design flow may coincide with the peak flow originating from any of the various land use types, depending on the relative multitudes of the contributing EP"s. The TEP is taken as the greater of the following formulae:
        • TEP = REP + 0.67 IEP or
        • TEP = 0.36 REP + IEP
          Use whichever value of "TEP" is higher.
        • ADWFG = TEP/288
        • ADWFT = ADWFG + 1/3 TPF
        • PDWFG = 5.83 ADWFG / TEP0.1
        • PDWFT = PDWFG + 2/3 TPF
        • PII = 1.43 [RNSA + 0.6(INSA + CNSA)]0.81
        • PWWF = PDWFG + PII + TPF
        • Qdmp = 0.75 PDWFT
        For EP's from industrial or commercial areas refer to Table 3-5.

        For land use other than residential, commercial and industrial, ACTEW should be consulted for advice.

        Qdmp can also be derived from Figure 3.3 or Appendix 3-3.

    3.1.2 Pipe capacity

    Surcharge shall be defined as the flow depth exceeding the pipe obvert.

    The principles outlined below reflect the design assumption that the probability of surcharge shall not exceed 1 in 10 years ARI.

    The capacity of the sewer pipe (Qf) shall normally be equal to, or exceed, the PWWF. Pipe capacities can be determined using either the Manning or Colebrook-White equations, with the roughness factors being obtained from Table 3-8. To simplify calculations, pipe capacities can be obtained from Appendix 3-4 or AS 2200 (Appendix 3-4 is based on guideline pipe diameters). Where an actual internal diameter is used for calculations, it shall be taken as the average internal diameter for the representative pipe length including joints. Surcharging of sewers at flows up to PWWF is not normally permitted, and the designer may be required to demonstrate to ACTEW that head losses through maintenance holes when added to pipe friction effects do not result in surcharging.

    Table 3-8
    Pipe roughness factors

    Sewer

    Manning "n"

    Colebrook white "k"

    Gravity mains:
    < DN600,
    - VC or Concrete
    - PVC, PE, GRP

    0.012
    0.011

    1.0mm
    0.6mm

    >= DN600,
    - Concrete, PE, GRP

    0.013 - 0.015*

    1.5 - 3.0mm

    Rising mains:

    0.011

    0.6mm


    * In the case of sewers >= DN600, ACTEW should be consulted for appropriate roughness values.

    Where the above factors conflict with AS 2200, Table 3-8 takes precedence.

    3.1.3 Grades for sewers

    In designing sewer systems it is critical to provide self-cleansing and, in most situations, sulphideslime control grades. This is to minimise operations and maintenance problems.

    Minimum pipe grades shall be in accordance with the following criteria:

    1. Minimum grades - general

      Where physically and economically practicable, all gravity sewers shall be designed with grades exceeding the sulphide-slime control grade (Sss). For sewers less than DN300, where large cost penalties are involved in achieving Sss, some relaxation of requirements may be permitted. Cases where Sss can not be achieved should be referred with supporting data to ACTEW for a decision. For DN300 and larger sewers this requirement will be stringently applied. All sewers shall be laid on grades exceeding the self-cleansing grade (Ssc).

      Relevant design submittals shall show the proposed grades, minimum slime control grades and any septicity control measures considered to be necessary. These measures may include limitations on pipe materials, special internal coatings or linings, forced ventilation, flushing flows etc. Normally unprotected concrete will not be permitted in systems where grades are less than those required for slime control.

      The designs shall give consideration to load build up within the catchment. Where it is unlikely that self-cleansing flows will be achieved within 2 years of the first connections to the system, or slime control grades within 5 years, the designer shall develop proposals for self-cleansing and slime control and refer these to ACTEW for approval.

      The minimum grades for self-cleansing and sulphide-slime control in sewers larger than DN150 can be derived as follows:
      • Ssc = 0.0135/Rp
      • Sss = 0.0338/Rp

        where:

        Ssc = minimum grade for self-cleansing (%)
        Sss = minimum grade for sulphide slime control (%)
        Rp = hydraulic radius at Qdmp (m)

        The absolute minimum grade (Smin) for sewers of DN225 or larger shall be obtained from the following equation:
      • Smin = 80/ID

        where:

        Smin = absolute minimum sewer grade (%)
        ID = pipe internal diameter (mm)

        Appendix 3-5 may be used to assist in determining the required minimum grades. Note that the Qf shall be used to calculate the minimum grades, not the PWWF.
    2. Minimum grades for DN150 pipes

      Minimum permissible grades of the uppermost reaches of sewers are dependent on the number of connections at the upstream end of the reticulation line and are given in Table 3-9 below.

      Table 3-9
      Minimum grades for DN150 pipes


      Ultimate number of residential properties draining to sewer Minimum grade (%)
      1 house l.25
      2 houses 1.2
      7 houses 1.1
      12 houses l.0
      18 houses 0.9
      28 houses 0.8
      35 houses or thereafter 0.7


      These are the absolute minimum grades that shall be used. In general, it is not considered good practice to use a minimum grade on a short intermediate section of sewer when the upstream and downstream sections are laid at steeper grades.
    3. Maximum grades for sewers

      Restrictions are placed on the maximum grades of sewers to limit internal erosion of pipe material, and/or pipe movement (due to trench flows causing loss of bedding).

      The maximum pipe grade for sewers larger than DN150 is 15%. Where grades steeper than 15% are planned the circumstances are to be referred to ACTEW prior to Design Submission 1.

      To limit the scouring effect arising from water flow within the pipe bedding material, and also to anchor the pipe, special bedding, scour stops or trench stops may be required in accordance with Standard Drawing Nos. WSS 056 and WSS 012. To enable easy location, scour and trench stops shall be placed at intervals of equal length with spacing not exceeding that which is specified on Standard Drawing No. WSS 012. The actual spacing and number of stops shall be nominated on layout drawings.
    4. Grade changes between pipe reaches

      It is essential in the lower reaches of the sewerage system, where sewage may have low dissolved oxygen levels, that turbulence leading to the release of hydrogen sulphide from solution be avoided. In these areas, conditions such as a rapid change from steep to flat pipe slope, which favours the formation of a hydraulic jump at dry weather flows, must be avoided.

      For sewers larger than DN375 the potential for hydraulic jump formation must be checked wherever, at full development, a change occurs at Qdmp (refer Clause 3.1.1 (iii)) from a Froude number greater than 1.5 to less than 1.0 between adjacent sewer reaches. Designs shall be arranged so as to avoid formation of a jump at Qdmp, possibly by the introduction of a "neutralising length" of intermediate grade and a suitable length between the steep upstream and flat downstream sections. In relevant cases, calculations shall be submitted with Design Submission 2 justifying the neutralising slope and length adopted.

    3.2 Minimum diameters

    • Service tie for one residential block: DN100;
    • Sewer mains: DN150;
    • For sewers up to DN600: the downstream sewer shall not be smaller than the upstream sewer.

    3.3 Dead-end pipelines

    Sewers should normally terminate with a maintenance hole located 2.0 metres uphill of the low point of the most upstream property. A "dead-end" shall be defined as the section of sewer upstream of the last maintenance hole. Prior to using a "dead end" pipeline, all reasonable measures should be taken to achieve termination of a sewer with a maintenance hole by readjustment of maintenance hole locations, and/or slightly increased maintenance hole spacing. However, a "dead end" may be utilised if its use results in significant cost saving without creating undue additional maintenance problems.

    "Dead end" pipelines shall terminate with a rodding point as per Standard Drawing No. WSS 061.

    Acceptable "dead end" pipelines will have:

    • a diameter not less than DN100 where serving a single property;
    • a diameter not less than DN150 where serving two or more properties;
    • a maximum length of 20 metres from the nearest downstream maintenance hole;
    • no curved alignment (vertical or horizontal).

    3.4 Sewer main junctions

    Within a sewerage system it is mandatory that all sewer main junctions occur within maintenance holes (refer Clause 5.1.13). However, DN100 sewer tie connections can be connected by means of maintenance holes or sloped junctions. For connection of service ties see Clause 6.2.5.

  • 4 Structural design

    4.1 Sewer pipe materials and construction methods

    4.1.1 Types of pipe

    Sewers shall be constructed from materials proven to be structurally sound and durable, and shall have satisfactory jointing systems. The use of two or more types of pipe material on a single run of pipe between adjacent maintenance holes is not acceptable.

    Materials approved for use in ACTEW Water sewers are:

    • Vitrified Clay - VC
    • Reinforced Concrete - RC, see notes 1, 2 and 3
    • Ductile Iron - DICL, see notes 1, 2
    • Polyvinyl Chloride - PVC (Equivalent to class SEH, solid wall or approved structured wall), see note l
    • Glass Reinforced Plastics - GRP, see note 4 (Polyester Based)
    • Polyethylene - PE, see note 4
    • Acrylonitrile Butadiene Styrene - ABS, see note 4

    Notes

    1. Not to be used within, nor up to 1 km downstream of industrial areas or hospitals.
    2. Concrete shall be made with Type "SR" sulphate resisting cement with a tri-calcium aluminate content not greater than 5%, or Type "LH" low heat cement. Concrete pipes intended for other than trunk sewers shall be manufactured with a minimum 10mm sacrificial layer on the inside of the pipe. Thickness of sacrificial layers in sewers larger than DN375 shall be as shown in Table 3-10. The sacrificial layer thickness shall be the thickness required over and above that required for minimum cover to reinforcement and structural integrity.

      TABLE 3-10
      Sacrificial Layer Thickness - Sewers Larger than DN375


      DN Thickness of sacrificial layer (measured on radius )
      450
      20mm
      525
      25mm
      600
      30mm
      675
      40mm
      >= 750
      50mm
    3. Concrete pipes are not acceptable for DN150 and DN225 sewers.
    4. Subject to special conditions and only with written approval of ACTEW.

    Proposals for the use of other materials will be considered if supported by adequate technical and performance data.

    Where the pipe material is known it shall be shown on the drawings. Where the pipe material is not known prior to submission for detailed design acceptance, the drawings are to contain notes ensuring that the above requirements are satisfied.

    4.1.2 Class of pipes

    • Sewerage pipes must be of adequate strength to meet overburden and traffic loads. Loads are to include loads created from likely construction and maintenance activities;
    • VC pipes shall be Class 4 or stronger;
    • Class 2 (X), 3 (Y) and 4 (Z) reinforced concrete pipes manufactured in accordance with the latest version of AS 4058 are acceptable if used in accordance with the requirements of AS 3725;
    • PVC pipes shall be of grade Sewer Extra Heavy (SEH) or of equivalent SN grade in accordance with AS/NZS 1260;
    • Classes for Ductile Iron, Glass Reinforced Plastics, Polyethylene, or ABS pipes shall be approved by ACTEW prior to use.

    Notes

    1. Where load limits apply the locations shall be clearly designated on drawings.
    2. During the construction phase specific load provision shall be made for heavy construction equipment where required.
    3. No more than one type of pipe material will be used between successive maintenance holes or sewer maintenance shafts.

    4.1.3 Pipe jointing

    The sewer pipes are to be capable of excluding groundwater, resisting root intrusion, and withstanding pressure loading, both internal and external. Sewer systems must also have some flexibility, either through controlled deflection at joints (rigid materials) or pipe bending (flexible materials).

    Acceptable pipe jointing systems are:

    1. VC pipes with rubber ring jointing comprising:
      • Spigot - Socket system;
      • Spigot - Spigot system utilising approved Socket-Socket coupler.
    2. Reinforced Concrete Pipes, Spigot-Socket, with rubber ring jointing.
    3. PVC pipes:
      • DN100: solvent welded;
      • DN150: rubber ring jointed or solvent welded; *
      • Larger than DN150: rubber ring jointed. *

    * All PVC pipes laid on horizontal or vertical curvatures shall be solvent welded if <DN300.

    4.2 Depth of sewer and cover

    1. Minimum depth for sewers outside of leased blocks

      The minimum cover, measured from the top of the pipe to the final surface level shall be the greater of:

      • The depth needed to provide 600mm of clear cover;
      • The depth needed to serve the whole of the adjacent block (see Clause 6.2.1);
      • In road verges, the depth needed to provide 750mm of clear cover;
      • Under minor sealed roads, the required cover is 900mm;
      • Under unsealed roads, proposed future roads or sealed arterials, cover is 1.2 metres.
    2. Minimum Depth Within Leased Blocks

      The minimum sewer depth shall be the greater of:

      • the depth needed to provide 600mm of cover;
      • the depth needed to serve the whole of the block;
      • the depth prescribed by upstream sewers.
      Where the whole block cannot be serviced, advice must be provided to ACTEW and the Land Development Group of the ACT Government to assure relevant constraints are noted as a building restriction on lease documents.
    3. Maximum Depth

      Sewer mains are to be designed for a maximum depth to invert of 5.0 metres. In special cases (e.g. to avoid a pump station or for a short length of line through a ridge) specific approval may be sought from ACTEW to exceed this limit.

    4.3 Pipe bedding and backfill

    Bedding and backfill of pipes shall be in accordance with Standard Drawing No. WSS 056, the Basic Specification (Reference 10.12), and any relevant Australian Standard. Bedding shall provide continuous support for joins and shall be well compacted and not disturbed by groundwater or other conditions.

    The materials used for bedding shall be durable stone or washed sand, and shall have low permeability and high stability when saturated. Bedding shall be free of organic matter.

    For sewers on steep grades the bedding requirements are set out in Clause 3.1.3 (iii).

    4.4 Pipes at interfaces with rigid structures

    Where pipes are connected to rigid structures or are embedded in concrete it is necessary to provide flexibility so that any differential settlement does not result in pipe damage.

    An acceptable design will incorporate:

    • at maintenance hole inverts, a flexible joint at the maintenance hole wall with a second in close proximity achieved through the use of a short pipe length (300mm to 600mm);
    • for concrete encasement, flexible joints in close proximity to the face of the encasement achieved through the use of a short pipe length (300mm to 600mm).

    Where PVC pipes are used, the section through a maintenance hole wall shall be either epoxy primed and coated with coarse sand, or an approved manufacturer's maintenance hole entry-fitting is to be used. The external interface between the pipe and the maintenance hole wall should be sealed with a 12mm fillet of bitumastic sealant.

    4.5 Ventilation

    Sewers are subject to corrosion induced by biochemical processes related to the formation and release of hydrogen sulphide gas.

    There are three basic controls in the management of the release of hydrogen sulphide gas:

    1. delay the production of the gas for as long as possible;
    2. properly manage its release from the sewage once its production becomes inevitable;
    3. remove the gas from the sewerage system in a manner that minimises impact.

    The production of gas is minimal in fresh, aerobic sewage. Therefore, at upper parts of each catchment or sub-catchment, this condition should be maintained for as long as possible. Flows can be turbulent and sewers vented through house vents. Boundary traps and special vents will generally not be required.

    The need to manage release of hydrogen sulphide gas usually relates to sewage age. Typically this occurs when the size of the sewer pipe is greater than DN300 and as soon as "stale" pumped sewage is discharged into the system. Each particular catchment will have its own characteristics that require investigation and judgement to determine where this condition commences.

    Corrosion is coupled to the release of hydrogen sulphide gas which occurs in parallel with moisture uptake from the sewage. Release is controlled primarily by ensuring that surface turbulence is minimal under most flow conditions. Moisture uptake from the sewage surface depends on:

    • the surface area of sewage;
    • the relevant velocity between the sewage surface and sewer air;
    • the temperature of the sewage;
    • the relative humidity of the sewer air;
    • the presence of surface modifying substances such as grease, oil, surfactants; and
    • the degree of surface turbulence.

    The management of sewer air must be based on the consideration of alternatives of natural ventilation and forced ventilation. Both involve provision of inducts, educt vent stacks, and curtains, in various combinations, to control the airflow in separate sections of the sewer. A forced ventilation option utilises fans to provide a greater level of control of airflow.

    Once the release of hydrogen sulphide gas occurs, it is essential that it be managed to minimise damage to the sewerage system. This again is done by controlling the sewer air volumes and velocities. A balance between the needs for control of moisture uptake from the sewage surface, and extraction of gas from the sewerage system must be made.

    Each catchment has its own characteristics that affect sewer ventilation. This includes topography, microclimate, land uses generating the sewage, and land uses affected by the ventilation works. It is essential that sewerage system designs, for catchments which require collector or trunk sewers and sewage pump stations, be assessed for corrosion control by an engineer experienced in this field.

    In particular, the need for sewer ventilation must be carefully assessed for sewers larger than DN450, and for sewers conveying pumped sewage. For works of these types, proposals for sewer ventilation shall be submitted to ACTEW for consideration and approval. Ventilation works shall generally be designed in accordance with the latest edition of the document entitled Hydrogen Sulphide Control Manual - Septicity, Corrosion and Odour Control in Sewerage Systems (Reference 10.13), and any specific requirements of ACTEW for that location.

    Large sewers and pump stations are a high cost asset where protective measures are very cost effective in terms of life cycle costs.

    4.6 Alternative pipelaying methods

    ACTEW may at times approve the use of alternative pipelaying technology such as thrust boring, directional boring, or pipe bursting. Where such methods are envisaged to be used ACTEW should be consulted for appropriate standards and specifications.

  • 5 Structures and fittings

    5.1 Maintenance holes

    5.1.1 General

    Maintenance holes are provided so that access to a sewerage system, for investigations, clearance of blockages and maintenance purposes, can be obtained.

    They are necessary at locations:

    • where there is a high risk of blockage (e.g. changes in direction, changes in grade, changes in size of pipe and changes in level);
    • where junction structures are required to combine flows (e.g. with other sewers and with service ties DN150 and larger);
    • at shallow points in the system (to form an emergency overflow relief path in times of acute hydraulic overload or blockage of the pipe system); and
    • at regular intervals, for access.

    Maintenance holes should be of a size and shape that provides reasonable access for personnel and equipment to flow channels, with a minimal likelihood of problems.

    5.1.2 Materials and construction methods

    Maintenance holes should be constructed so that they are structurally sound and do not permit ingress of water through the walls or joints. Maintenance holes should be resistant to erosion and corrosion.

    The following construction methods have been approved:

    • In-situ concrete — the most common method of construction. The concrete is to have adequate cement content and be well compacted and cured.The shape of the maintenance holes can be either standard circular or of special shapes and sizes suitable for larger pipes and junctions. Special approval from ACTEW will be required for the use of non-circular shaped maintenance holes for sewers less than DN450.
    • Pre-cast concrete — maintenance holes utilising pre-cast concrete units have significantly more joints and therefore special care is required to ensure the joints do not form entry paths for tree roots and/or infiltration.Pre-cast maintenance holes shall be in accordance with Standard Drawing Nos. WSS 057 and WSS 058. Make-up neck rings are to be selected so that the neck length does not exceed 200mm.Pre-cast concrete maintenance holes shall be limited to a depth of 6.0 metres.
    • Other materials — where other materials such as Polyethylene (PE) or Glass Reinforced Plastics (GRP) are considered viable, written approval for their use in designs shall be sought from ACTEW.Where cast in-situ or pre-cast concrete maintenance holes are used, concrete shall be made with Type "SR" sulphate resisting cement having a tri-calcium aluminate content not exceeding 5%, or Type "LH" low heat cement to AS 3972.Standard maintenance holes will be provided with a step-iron access. Mild steel step-irons will be hot dip galvanised or be coated with an approved anti-corrosion agent.

    5.1.3 Location

    Access to maintenance holes may be required at any time of day or night, consequently they should be located where maintenance staff with machinery can obtain direct access at all times. Preference should be given to locating maintenance holes in public land rather than in leased properties. Unnecessary maintenance holes are to be avoided.

    In roadway services maintenance holes should be located in positions where a measure of safety for maintenance staff is provided. Maintenance holes located in pavements are also likely to be covered over by re-sheeting of pavements during road maintenance. In conclusion, it is preferable not to locate maintenance holes in road pavements. Maintenance holes must not be located in pavements at road intersections and roundabouts.

    Maintenance holes in road pavements shall have covers located in the middle of the slowest lane of traffic.

    The preferred location of maintenance holes in roads is:

    • within roadside verges;
    • in footpaths; within median strips;
    • in the centre of the slowest lane;
    • maintenance holes must not be located in pavements at road intersections or roundabouts.

    Where practicable, maintenance holes or shafts should not be located within driveways or on cycleways. Maintenance holes also provide overflow points for sewage. Consequently, they should be located so that any overflow will be contained within acceptable flow paths such as road reserves or other public land.

    5.1.4 Maximum spacing on straight sewers

    General access is maintained on long sewers by providing intermediate maintenance holes. Maximum maintenance hole spacing is dependent on whether entry into the pipeline is possible. For pipelines of less than DN600 the maximum spacing is dependent on the type of equipment available to maintenance crews.

    Acceptable maximum maintenance hole spacings are presented in Table 3-11.

    Table 3-11
    Maximum maintenance hole spacing — straight sewers

    Pipe size (DN) 

    Maximum maintenance hole spacing (m)

    150 to 450 

     100

    525 to 900 

     150

    1050 to 1650 

     300

    1800 and larger

     500

    5.1.5 Spacing on curves

    It is considered that curved alignments will require more maintenance than straight alignments. Visual inspection from maintenance hole to maintenance hole is generally not possible. As a consequence closer maintenance hole spacing is required on these alignments.

    Acceptable maintenance hole spacing on curved sewers shall be in accordance with Table 3-12. Maintenance holes shall be located on tangent points where the curve does not form a true tangent to the preceding or following straight.

    Table 3-12
    Maximum maintenance hole spacing — curved sewers

    Pipe size (DN) 

    Maximum maintenance hole spacing (m)

    150 to 450 

     80

    525 to 900 

     100

    1050 to 1650 

     300

    1800 and larger

     500

    Notes

    1. The combination of a single straight length and a single curve is acceptable. For purposes of maximum lengths between maintenance holes Table 3-12 shall apply.

    5.1.6 Fall through maintenance holes

    The fall through a maintenance hole is defined as the difference between the invert levels of the inlet and outlet pipes, measured at the inside face of the maintenance hole wall. Invert levels shall in all cases be at the inside face of the maintenance hole wall. Acceptable falls through maintenance holes are:

    • For DN150 sewers:

      a) For maintenance hole deflections less than 90º:
      - 30mm minimum;
      - 100mm maximum.

      b) For maintenance hole deflections 90º or greater:
      - 80mm minimum;
      - 100mm maximum.
    • For DN225 or DN300 sewers:
      - 30mm minimum;
      - 100mm maximum.
    • For sewers DN375 and larger:
      - Sufficient to maintain smooth laminar flow.

    Irrespective of the above requirements, the grade shall not be reduced through the maintenance hole.

    5.1.7 DN1050 Maintenance hole: Standard Drawing No. WSS 052

    DN1050 maintenance holes shall be in accordance with Standard Drawing No. WSS 052. DN1050 maintenance holes shall be used when:

    • the outlet sewer diameter is DN450 or less; and
    • the maintenance hole depth is less than or equal to 6.0 metres.

    A minimum neck height of 100mm and a maximum neck height of 200mm is also required for ease of access. Where maintenance holes are to be located in roadways the neck height shall be 200mm to allow for possible future level adjustment. A permanent system for descending into the maintenance hole is to be provided. This will normally consist of step irons located over the outlet pipe. The internal diameter of a DN1050 maintenance hole may not, in some instances, comply with channel radius requirements (Clause 5.1.11 (ii)), in which case either a DN1200 maintenance hole (Clause 5.1.8) or a special maintenance hole (Clause 5.1.9) will be required.

    5.1.8 DN1200 Maintenance hole: Standard Drawing No. WSS 053

    DN1200 maintenance holes shall be in accordance with Standard Drawing No. WSS 053. DN1200 maintenance holes shall be used when either: the sewer size is in the range DN525 to DN675; or the sewer depth is in the range 6.0m — 8.0m; or where a larger structure is required to accommodate working space requirements as per Clause 5.1.11 (iii). in situations where a special maintenance structure (Clause 5.1.9) is not warranted. Sewer maintenance holes for these situations need to be larger in diameter, compared to the DN1050 maintenance hole, to provide better access and more working room for specialised equipment. DN1200 maintenance holes shall have a minimum wall thickness as shown in Table 3-13.

    Table 3-13
    Minimum wall thickness — DN1200 maintenance holes

    Depth range (mm)

    Minimum wall thickness (mm) 

    0 to 6.0 

     150

    6.0 to 8.0 

     225

    5.1.9 Special maintenance holes

    Where the outlet pipe diameter is greater than 675mm, the depth is greater than 8.0 metres, or channel radius requirements (Clause 5.1.11 (ii)) cannot be accommodated by either the DN1050 or DN1200 maintenance holes, then either a large diameter maintenance hole or a special chambered maintenance hole shall be used.

    • Large diameter maintenance holes: DN1500 to DN1800Large diameter maintenance holes shall generally be DN1500 to DN1800 unless prior approval has been given to use other sizes.The configuration of large diameter maintenance holes shall be based on the ladder or step-irons being placed above the benching rather than over the outlet pipe (refer Clause 5.1.11 (iii) for details).

      The appropriate diameter of the structure can be determined by sketching out the angles and junction flow requirements.Large diameter maintenance holes will require a reinforced concrete flat-top cover, and access shall be through a short neck section. Class D, sealed (gastight) solid-top metal access covers shall be provided.Large diameter maintenance structures will incorporate the above features and shall be shown in detail on the design drawings for ACTEW approval.
    • Special chambered maintenance structuresThe configuration of special chambered maintenance structures shall be based on the ladder or step-irons being placed above the benching rather than over the outlet pipe (refer to Clause 5.1.11 (iii) for details).The appropriate inside dimensions of the maintenance hole can be determined by sketching out the angles and junction flow requirements.

      The minimum structure length shall be 1.5 metres. For sewers DN675 or larger the structure shall be provided with handgrips above the PDWF to facilitate safe access into the benching channel.Special chambered maintenance structures will require a reinforced concrete flat-top cover, and access shall be through a short neck section. Class D, sealed (gastight) solid top metal access covers shall be provided.Special chambered maintenance holes will incorporate the above features and shall be shown in detail on the design drawings for ACTEW approval.

    5.1.10 Ladders and landings for deep maintenance holes or structures

    For maintenance holes deeper than 6.0 metres, ladders and intermediate landings shall be required. The minimum headroom to the underside of all landings shall be sufficient to permit maintenance personnel to stand erect under the landing. Generally, the minimum acceptable headroom will be 2.1 metres. The level of the top face of each landing shall be shown on the detailed design drawings. Ladders and landings shall be stainless steel as shown on Standard Drawing No. WSS 002. Alternative corrosion resistant materials will be considered provided details are submitted to ACTEW for written approval.

    5.1.11 Benching

    • Depth of benching

      To minimise stranding, hydrogen sulphide generation, and hydraulic losses through the maintenance hole, a channel is to be formed within the maintenance hole base to provide a smooth flow transition.For sewers up to and including DN375, the bench shall be up to the obvert level of the inlet pipe. The maximum depth of benching in these small diameter sewers shall be 400mm.For DN450 sewers, the bench shall be to a minimum depth of 400mm. For sewers larger than DN450 the trench shall be at the mid height of the highest incoming pipe + 100mm, or to a depth of 400mm, whichever is greater. Where benching depth exceeds 600mm and space allows, a step-down shall be provided in the benching.

      The step shall:

      - be 225mm x 225mm in plan;
      - self-drain into the sewer at 2%;
      - be at least 400mm above the invert;
      - be located on the inside of the curve, near the hand-holds.

    For pre-cast concrete maintenance holes, the bench shall be 100mm above the incoming pipe to allow for an effective seal against infiltration.

    • Radius of benching

      Changes in direction at a maintenance hole or special chamber shall be accommodated entirely within the structure. This shall be achieved by a curved channel of uniform radius.A desirable minimum internal benching radius is 2.5 times the nominal diameter (DN). Benching curves on Standard Drawing No. WSS 062 have been selected to minimise hydraulic losses and to allow access by CCTV equipment. Parameters for intermediate angles can be interpolated from these drawings.(refer also Standard DrawingNos. WSS 052 and WSS 053).
    • Minimum working space

      A minimum clearance of 375mm benching space, both in front of or next to the step-iron or ladder access, and 225mm on the opposite side of the channel, is required to provide adequate working space. This will generally require offsetting the centre of the structure to the sewer pipes. For offsets on commonly found configurations refer to Standard Drawing No. WSS 062. For non-standard configurations, details of the offset layout shall be submitted in Design Submission 2 (as per Clause 5.1.12).

    5.1.12 Offset of maintenance hole centreline

    To accommodate a change of direction at maintenance holes, to meet benching and maintenance space requirements, it is required that maintenance holes be "offset" . The key criteria to be accommodated are outlined in Clause 5.1.11. Maintenance hole offset requirements for standard pipe configurations in DN1050 and DN1200 maintenance holes are shown on Standard Drawing No. WSS 062. Details of the offset layout shall be submitted in Design Submission 2.

    For non-standard configurations this will include a 1:20 scale plan of each maintenance hole showing:

    • internal diameter;
    • channel benching and invert centre lines;
    • offsets necessary to position the maintenance hole in relation to the pipeline intersection point;
    • step-irons or ladders;
    • external drops; platforms (if any), and clearance beneath and above the platform.

    5.1.13 Junction maintenance holes

    Maintenance holes are to be constructed where sewers, or property ties of DN150 or larger, form a junction with a main sewer. The maintenance hole junctions are to be designed to provide a smooth flow transition from the branch sewer, and to maintain a free air path through the maintenance hole for all flows less than the PDWF. The designer shall ensure that deep flows up to the PWWF in the major line do not result in surcharging of the branch line.

    Inlet and outlet pipes must be set at levels relative to each other such that flows do not stagnate in any of the connected pipes. Channel benching on all branch sewers shall be graded to ensure smooth flow transition from inlets to outlet. These requirements should be achieved using Table 3-14 and Table 3-15. When utilising Table 3-14, note must be taken of data in Table 3-15 which takes precedence for minimum falls across maintenance holes.

    Table 3-14
    Branch-to-main sewer connections

    Main sewer table 3-14

    Notes

    1. OL = pipes connected obvert level to obvert level.
    2. CL = pipes connected centreline to centreline.

    Where both sewers are larger than DN300, the design of junction angles shall incorporate sound hydraulic principles to limit turbulence and hydrogen sulphide emissions. A suggested method of "balanced lateral momentum" is given in The Control of Sulphides in Sewerage Systems (Reference 10.3). ACTEW may request to review these calculations and sketch layouts during Design Submission 2.

    Table 3-15
    Difference between branch and main sewer invert levels at maintenance holes

    Main sewer table 3-15

    (1) Both sewers with similar hydraulic loads. (2) Branch sewer collecting 5 or less residential dwellings.

    Notes

    1. The minimum fall in Table 3-15 shall be defined as the difference between the branch inlet invert level and the maintenance hole outlet invert level, measured at the inside face of the maintenance hole.

    5.1.14 Vertical drops

    • Drop pipe configurations

      Generally, drops are used to connect shallow branches to deep mains or to avoid other underground services. Major changes in level are achieved by using a vertical drop pipe integrated with the maintenance hole structure (normally external to the main chamber). The requirements for the design of the drop are:

      - the pipe shall not be liable to blockage at either the top or the base;
      - easy to maintain (ie. clearing of any blockage);
      - ability to convey flows without splashing or undue turbulence; and
      - not to be intrusive on the working space in the maintenance hole.

    Vertical drops are usually achieved through the use of a DN1050 or DN1200 (Standard Drawing Nos. WSS 052 and WSS 053) maintenance hole with external vertical drop.

    The limitations on the arrangement are:

    • the drop pipe is restricted to a maximum size of DN375 (refer also (b) below);
    • the invert level of the inlet pipe shall be at least 675mm below the bottom of the tapered cone.

    Sewers should be graded out to avoid drops not in accordance with the above. See Standard Drawing Nos. WSS 052 and WSS 053 for drop details.

    • DN100 to DN375 incoming high level sewer
      Drop pipes are to be as shown on Standard Drawing Nos. WSS 052 and WSS 053. The minimum fall between the invert level at the base of the drop and the outlet pipe shall be 50mm.
    • DN450 and larger incoming high level sewers
      Drops for sewers larger than DN375 shall be designed as special structures, such as vortex drops, to ensure satisfactory dissipation of energy.

    Pipe support to branch lines

    • The inlet pipes for maintenance holes with vertical drops are laid over a section of backfill. Consequently, they have a tendency to fracture when settlement of the backfill occurs. To limit this problem special attention shall be given to ensure adequate compaction under the inlet pipe. In addition the pipes are to be designed to allow for some settlement.The first section of the inlet pipe upstream of the maintenance hole shall be constructed from DICL, with two 600mm lengths of standard pipe added immediately thereafter. The ductile iron pipe shall be long enough to span the backfill section.

    5.1.15 Standard covers

    Sewer maintenance holes are to have standard size reinforced concrete seating rings and lids. This is so that they can be readily identified, opened using currently available maintenance lifting gear, and be readily replaced from existing stock while ensuring compatibility between lid and ring.

    Only Class B (AS 4198) concrete covers and matching surrounds are to be used. These covers are to meet dimensions nominated in Standard Drawing No. WSS 058. Class B covers and surrounds shall be used in all applications other than those itemised under Clause 5.1.16.

    For seating ring and surround fixing requirements in standard cover applications refer to Standard Drawing No. WSS 053.  

    5.1.16 Metal access covers

    The covers of sewer maintenance holes which are subject to:

    • internal surcharge loading;
    • or are within 100 metres of the receiving point of pumped flows;
    • or are subject to external vehicle loads;
    • or are installed in areas lower than the expected 100 Year ARI flood level;
    • or are installed in poorly ventilated areas;
    • or are installed on sewers greater than DN300;
    • or are installed in areas which are mowed using tractor mowers;
    • or are installed in areas likely to experience ponding due to lack of drainage;

    shall be Class B, C or D in accordance with AS 3996.

    These covers and surrounds shall be specified as SEALED (watertight and gastight) solid top, and be used as follows:

    • Maintenance holes in pavements:
      - Road carriageways (Class D);
      - Public car parks or residential driveways (Class D);
      - Driveways in industrial areas (Class D generally, but higher may be required in some circumstances, e.g. airports etc.);
      - Paved pedestrian city areas (Class C);
    • Maintenance holes on sewers larger than DN300, or deeper than 6.0 metres, or those which receive pumped flows (Class B minimum, Class D when subject to traffic loading);
    • Maintenance holes may require bolt-down locking to resist internal surcharges, in this case stainless steel bolts are to be used to secure the cover to the seating ring. The seating ring is to be structurally secured to the maintenance hole chamber. This is required for:
      - Maintenance holes at the bottom of steep (supercritical flow) sections (Class B minimum, Class D if trafficable);
      - Maintenance holes with cover levels below the 100 Year ARI flood level (Class D).
    • Areas which are mowed using tractor mowers (Class C minimum, if area is likely to serve as car parking Class D).

    Cast-iron covers shall be "GATIC" , or of an "approved equivalent" type, so that they can be readily interchanged from existing or new stock if damaged. For seating ring and surround fixing requirements in metal access cover applications refer to Standard Drawing No. WSS 053.  

    5.1.17 Maintenance hole cover levels

    Maintenance hole cover levels shall be designed to ensure that the cover can be easily located by maintenance personnel while not creating a hazard. It is preferred that maintenance hole covers be located above the 100 Year ARI flood level. No cover shall be lower than the 2 Year ARI flood level. Covers can be located between the 2 Year and 100 Year ARI levels provided:

    • The maintenance hole cover and surround are bolted down to withstand internal surcharge pressure and external water drag (refer to Type 5 fixing detail on Standard Drawing No. WSS 053).
    • Dry vehicular access is available up to the maintenance hole for all flood events smaller than 2 Year ARI.

    Covers and surrounds must be graded to:

    • maintain surface tolerances suitable in maintaining driving comfort;
    • minimise transfer of horizontal dynamic wheel loads to the maintenance hole;
    • prevent pedestrian trip and slip hazards;
    • maintain ease of location.

    Maintenance holes located beneath finished surfaces are generally not permitted. In situations where sewers cross playing fields or golf fairways the designer should discuss the alignment issues with ACTEW during Design Submission 1. Steeply sloping covers are unsatisfactory for maintenance reasons. Where finished surfaces have slopes greater than 1 in 8 the cover, and an adjacent area sufficient to lay the removed cover, shall be no steeper than 1 in 8.

    Acceptable finished cover levels shall be:

    • paved areas — flush with finished surface; footpaths and bicycle tracks — flush with finished surface;
    • plantations already established and grassed — 25mm above surface (see note 1);
    • elsewhere — 75mm above surface to allow for topsoil and grassing (see note 1).

    Notes

    1. To remove trip hazards and to reduce horizontal forces on the cover, fill should be placed and compacted around the raised surround and graded down to the natural surface at a slope of 1 in 10.

    5.1.18 Surface clearance to covers

    To maintain accessibility a minimum horizontal clearance of 1.0 metre from the edge of the cover in any direction must be assured. No major tree planting or structures are permitted in this zone (refer also to Clause 2.3).

    5.1.19 Maintenance holes receiving pumped flows

    Maintenance holes receiving pumped flows via a rising main are frequently subjected to hydrogen sulphide corrosion and therefore require special consideration.

    For receiving maintenance holes less than 6.0 metres deep the receiving structure shall be designed to minimise turbulence, and shall be located adjacent to the receiving gravity main (refer Standard Drawing No. WSS 055). The short gravity pipe between the receiving maintenance hole and the gravity main shall be designed to (1) minimise turbulence within the gravity pipe, and (2) prevent gravity flows entering the rising main. This section of the sewerage system shall be of a material not subject to hydrogen sulphide corrosion (refer to Clause 7.2).

    Ventilation should also be incorporated into receiving maintenance holes and the first maintenance hole immediately downstream. Receiving maintenance holes are to be internally coated with approved epoxy.

    5.2 Sewer maintenance shafts

    Maintenance shafts permit maintenance and monitoring equipment to be inserted into the mains but do not allow maintenance personnel access. These maintenance shafts are typically of size DN225, are vertical, and are enlarged at the base to cater for long objects entering the sewer. The top of the shaft has a rubber ring sealed cap. A conventional cover is placed on top to protect the shaft from surface loads. Maintenance shafts offer four key benefits:

    • they are substantially cheaper than maintenance holes;
    • they reduce the safety risks associated with conventional maintenance holes;
    • they involve less excavation impact;
    • they are more resistant to groundwater infiltration.

    Maintenance shafts can be used in lieu of maintenance holes within the following constraints:

    • only ACTEW approved shaft products will be installed as per Standard Drawing No. WSS 061;
    • shafts shall only be used on DN150 and DN225 mains;
    • the maximum spacing between conventional maintenance holes shall not exceed 160 metres, the distance between a maintenance shaft and the nearest maintenance hole shall not exceed 80 metres;
    • maintenance shafts shall not be used at sewer main branch junctions but may be used to accept property connections;
    • maintenance shafts shall not receive pumped flows;
    • the maximum sewer deflection shall be limited to 55°, this represents the sum of the deflection through the shaft and one or two external bends. The maximum deflection through the shaft chamber must not exceed 45°;
    • the maintenance shaft cap shall not be bolted or screwed down of relief should the sewer surcharge. The cap must always be above the 100 Year ARI flood level; a maximum of two bends can be used outside the shaft chamber, one at the inlet and one at the outlet. The bends and shaft must deflect in the same direction;
    • the fall of the maintenance shaft is fixed at between 2% and 3%, and the access shaft must always be installed vertically. To eliminate undue turbulence in the shaft chamber, and to assure join deflections are not exceeded, maintenance shafts shall not be used if the grade of the upstream or downstream sewer exceeds 5%; pipe connection to the shaft shall be made using rubber ring connectors or where material allows by means of solvent welding. If reducers are required they shall be eccentric tapered reducers.

    5.3 Other special structures

    The design of other sewerage structures such as siphons, vortex drops etc. are not covered in this document and shall be referred to ACTEW for detail requirements.

  • 6 Service connections

    6.1 Lease drainage

    The sewerage system shall be designed so that waterborne wastes can be efficiently removed from each lease. The design should allow for probable site earth works consistent with the nature of likely site development, for example the creation of large level areas for industrial or commercial buildings.

    Increasing the depth of sewers external to leases at extra public cost in order to permit gravity drainage of basement fixtures within specific leases is not normally permitted. Basements will be required to be serviced by sullage pumps to prevent risk of backflow and flooding from external mains.

    For design of service ties see Clause 6.2.

    An acceptable design shall provide service connection ties to suit the individual needs.

    6.2 Service ties (house connections)

    A sewerage service tie is to be provided for each leased block (see Clause 6.1).

    6.2.1 Depth of tie

    A service tie is required to serve the entire leased block. However, where building restrictions do not permit part of the block to be developed (e.g. setback distances from the front building line), then depths may make allowance for this limitation.

    In calculating the depth requirements, the designer should be familiar with the various requirements for grade, depth and special structures provided for in the Water and Sewerage Regulations 2001 (Reference 10.1) and AS/NZS 3500.

    Allowance should be made for any possible earthworks that may occur during the development of the site (e.g. providing driveways and/or a level area for buildings). For industrial blocks, where considerable earthworks are normal practice, this allowance is particularly important.

    An acceptable design will have the following minimum depths of tie:

    • for residential blocks: calculated on the basis of a minimum cover of 600mm and a maximum possible length of house drain at a grade of 1 in 60;
    • for industrial and commercial blocks: calculated on the basis that the whole of the building zone is excavated to the lowest level of the building zone, and with minimum cover, lengths and grade as above. Where the effect of providing the excavation requirement involves substantial lowering of the sewer (e.g. greater than 1 metre for more than 500 metres downstream), the matter shall be referred to ACTEW for resolution;
    • 750mm of cover if located in road reserves, or 600mm of cover if located within blocks.

    The maximum permissible depth of a sewer tie is 2.5 metres.

    6.2.2 Location

    A service tie connecting to a sewer outside the leased block should generally be at right angles to the sewer. Where a service is to a maintenance hole or "dead-end" , the service shall be at an angle between 90° and 180° from the downstream sewer to ensure a smooth flow of entry into the main line.

    Service ties shall be located clear of driveways and retaining walls unless specifically approved by ACTEW.

    Where the sewer is located outside the leased block, the tie shall terminate just inside the property line.

    Where possible, the tie should generally be located on the sewer at 1.0 metre from the lowest corner of the property. However, it is permissible to locate the tie at a position other than the lowest corner of a residential block provided that.

    • no more than fourteen (14) residential dwellings, and
    • no non-residential leases,

    are serviced upstream of that block. In such circumstances, particular attention must be paid to the requirements of Clause 6.2.1 regarding the maximum permissible depth of a sewer tie, and also to the requirements of Clauses 4.2 and 6.2.1 relating to the servicing of an entire lease.

    The upstream end of any "dead end" sewer shall extend to at least 1.0 metre past the block boundary to accommodate a service tie (for "dead ends" refer to Clause 3.3).

    Where practical, a service tie should discharge directly into a maintenance hole in lieu of a separate branch connection to a sewer.

    Service tie locations shall be as per Standard Drawing No. WSS 054. The tape shall be nominally 75mm wide and coloured "cream" to AS 2700 in accordance with AS 2648.

    No more than three (3) consecutive service ties on a reticulation main are permitted to cross a roadway unless specifically approved by ACTEW.

    6.2.3 Size of tie

    Sewer service ties are normally DN100 rubber ring jointed or solvent welded pipes. For multiple dwellings a single tie is to be provided per property. In certain circumstances a larger connection might be required for a large or special site e.g. commercial and industrial sites. In such cases the tie should be sized to cater for the hydraulic requirements in accordance with the Water and Sewerage Regulations 2001 (Reference 10.1) and AS/NZS 3500. If the service tie is DN150 or larger it shall be connected to a sewer maintenance hole.

    6.2.4 Grade

    The service tie shall have a minimum grade of 2.0%, generally a maximum grade of 100%, and terminate in a sealed pipe socket.

    For ties to deep sewers, 45° jump-ups or buried vertical risers may be used (refer to Standard Drawing No. WSS 054).

    6.2.5 Connection of DN100 Service Ties

    Service tie connections into sewers of DN150 to DN300 may be by the means of a 60° rubber ring jointed slope junction, a 30° bend, and a length of pipe (refer to Standard Drawing No. WSS 054 for details). The pipe length is to be sufficient to extend to at least the property boundary, and to a maximum of 600mm within the property. The end of the service is to be sealed.

    Service tie connections into DN375 to DN600 sewers are to be directly into maintenance holes. Where additional maintenance holes are required to comply with this arrangement, or the sewer is deep, a parallel, shallower "pick-up" sewer may be advantageous.

    6.2.6 Buried Vertical Riser (BVR)

    On deep sewers that are near boundaries it may be necessary to use a BVR. These are to be noted on drawings and constructed as per Standard Drawing No. WSS 054.

    It is absolutely critical that BVR's are installed on a compacted trench base with suitable concrete support.

  • 7 Design criteria for small pump stations and rising mains

    7.1 Small pump stations

    7.1.1 General considerations

    ACTEW has a preference for gravity sewerage systems because of the ease of operation and the minimisation of hydrogen sulphide corrosion of the sewers. For systems that will be owned and operated by ACTEW, sewage pumping should only be adopted where shown on ACTEW's Sewerage Strategy Plans, or after discussion and agreement with ACTEW regarding the economics of pumping versus other alternatives.

    The design of pump stations is heavily influenced by the locality. There is no single set of standards that can apply to all locations. Standard Drawing No. WSS 055 has been prepared to provide basic guidelines in the design of each station. It is recommended that the agent consult ACTEW at the earliest possible time to quantify site specific issues relating to proposed sewer pump stations.

    Sewage pumping may be appropriate:

    • where sewerage facilities are required to serve developments that cannot drain to existing or proposed gravity systems;
    • to prevent excessive depth of sewer lines in flat terrain (not generally the case in Canberra);
    • to provide surcharge relief on overload sewerage systems by transfer to a different catchment;
    • to lift sewage into a sewage treatment plant.

    The following general requirements are for small neighbourhood pump stations intended to be owned and operated by ACTEW, and which handle PWWF's up to about 50 litres per second. The more detailed aspects of station design should be discussed with ACTEW at an appropriate stage during design.

    For stations larger than 50 litres per second, design requirements will normally be specified in an ACTEW brief tailored to the individual project.

    Where a proposed pump station is associated with a single specific lease, and the station and rising main are to remain the responsibility of the lessee, ACTEW's main concern will be to ensure that the design and operation of the station and rising main are such as to prevent hazardous conditions, corrosion, or odour problems within the receiving ACTEW system.

    7.1.2 Station catchment and siting

    The station location and duty shall be based on the service areas shown on ACTEW's Sewerage Strategy Plans using flow estimating procedures as set out in Clause 3.1.1.

    The siting and depth shall be chosen to command the service areas by gravity while allowing adequate incoming grades. In determining station depth, it is important that the constraints governing wet well depth be clearly identified, and excessive depth be avoided. Measures such as concrete encasement of gravity sewers under roadways and floodways to reduce depth of cover, and in appropriate cases relaxation of "slime control" criteria for critical sewers (refer Clause 3.1.3 (i)), should be used.

    Station siting shall provide optimum integration of the station with adjacent land uses, landscaping, all weather access, hardstand areas for maintenance vehicles, and satisfactory overflow arrangements. Minimum turning radii around the station and access tracks shall be suitable for an 8.8 metre service vehicle as per Austroads Standards Australia — AS HB72. The vehicle must be able to be reversed or driven to enable parking (with the rear or side of the vehicle next to the well). Access track grades steeper than 2% shall be cement stabilised, and tracks steeper than 5% must be sealed. In areas where the station is at the end of a dead-end access, the hardstand must allow for the truck to be turned around within the pavement area.

    Security fencing shall enclose the key components. Appropriate warning signs shall be visible.

    Designers should be aware that the noise of mechanical equipment may cause irritation to adjacent residents. Keep stations well away from adjacent residential development and/or provide appropriate soundproofing. Covers and vents that are prone to flooding or are required for station access during floods shall be above the 100 year ARI flood level of any adjacent waterway or pond. Siting should attempt to minimise pump station, gravity and rising main costs, and ensure economic and timely availability of power supply, telephone and town water connections necessary for commissioning and operation.

    7.1.3 Design objectives

    The overall objectives for sewage pump station design are as follows:

    • safe working conditions for operations and maintenance personnel;
    • ease of accessibility and operation;
    • long term reliability;
    • minimum capital, and operating and maintenance costs of the station, gravity mains and rising mains;
    • unobtrusive location;
    • energy efficiency.

    With the exception of temporary facilities intended to be superseded within a few years, station components shall be designed for the following design lives:

    • Civil works — 100 years;
    • Electrical and mechanical equipment — 15 to 25 years.

    Works shall make appropriate provision for initial and foreseeable future design loadings. The economics of staging, temporary cut-off walls or curtailments, initial use of reduced impeller sizes, or planned upgrading of the pump capacity should be considered.

    For ease of maintenance, and in minimising stores inventories, equipment should be of standard types. The equipment should be interchangeable with, or preferably identical to equipment incorporated into existing ACTEW stations. Designs incorporating new or unusual equipment require the prior approval of ACTEW.

    7.1.4 Station arrangement and services

    For stations up to 50 L/s capacity, unless there are good reasons to the contrary and prior written agreement from ACTEW is obtained, a single wet well configuration with submersible centrifugal pumps should be adopted. Valves and meters shall be housed in isolated chambers at shallower levels.

    These stations should be oriented such that the incoming line is perpendicular to the axis of the pumps. The valve chamber shall be integral with the wet well, and located on the side opposite the incoming sewer for cast in-situ construction. For pre-cast wet wells, the valve pit is located adjacent to the wet well. Switch and control gear shall be located such that access to the wet well or valve pit does not interfere with the operation of the station.

    Water supply shall be provided for washdown purposes and shall terminate in a 25mm quick coupler connection. To prevent cross-contamination of the town supply, an approved backflow preventer shall be fitted in accordance with the Water and Sewerage Regulations 2001 (Reference 10.1) and AS/NZS 3500. A telephone connection is required for telemetry of remote alarms.

    Power supply, switching, control, and telemetry equipment should be located in a vandal-proof, above ground, painted metal kiosk.

    Permanently installed lifting equipment is not required for individual loads less than 500kg. For heavier loads, permanent lifting facilities (such as gantries or booms) shall be provided.

    Adequately drained hardstand areas shall be provided, and shall be of a size sufficient for two service vehicles. Access covers to wet well and valve pit(s) shall be arranged either to prevent vehicle access, or designed for vehicle loadings.

    Excessive flows, blockages, and operational failure of the pump may occur, dictating the need to provide an overflow for incoming sewage. The overflow pipe can be located in the collection maintenance hole, with the invert level located above the obvert level of the incoming sewer pipe. Suitable means of disposal of the flow from the overflow pipe is generally site specific, and shall be discussed with ACTEW and the Environment ACT at an early stage in the design. In general, overflows shall not be permitted to enter leases, and should be collected by the stormwater drainage network as soon as practicable. The overflow pipe outlet shall be arranged to prevent stormwater from entering the sewer system up to the 100 Year ARI flood level of any adjacent watercourse or waterbody.

    In general all components of the station which require manual handling shall be designed to conform with the ACT Standard and Code of Practice on Material Handling (Reference 10.14).

    7.1.5 Station capacity and pumping units

    Pump configurations should be:

    • two fixed speed pumps each sized for PWWF; or
    • three pumps each sized for 50% of PWWF; or
    • two variable speed pumps each capable of PWWF.

    Pumps and motors shall be sized to handle the full range of flows and delivery heads expected to be encountered (including wet well levels varying between minimum operating and "flood" levels). Flood levels shall be calculated as the maximum level in the wet well to which incoming sewage can surcharge (including due to flooding of any adjacent watercourse). Units shall be selected for optimum efficiency under the most commonly expected average flow conditions. Motors shall be non-overloading for free discharge. Details on the preferred pumps should be obtained from ACTEW prior to the start of the final design.

    Impellers shall be of the "non-clog" type capable of passing DN75.

    Each pump shall be provided with a re-circulation flush valve, which mixes the sludge that accumulates at the base of the pumps. Details on the preferred flush valves should be obtained from ACTEW prior to the start of the final design.

    7.1.6 Station inlet

    Pump stations shall be provided with a single inlet pipe. Sewage from additional pipes may enter the station via the collection maintenance hole located adjacent to the station.

    Provision for isolating the station from incoming gravity flows is required to permit maintenance or other works to be undertaken. This is usually achieved via a penstock (or knife-gate valve) located on the end of the inlet pipe within the station. The penstock shall be operable from the surface via an extension spindle manufactured from a non-corrosive material (preferably stainless steel 316L).

    7.1.7 Wet well

    All structures to be designed to accommodate appropriate structural loads as outlined in AS 3735 and AS 1170. The station will be provided with appropriate brackets to enable erection of safety equipment over the well. Details are to be obtained from ACTEW prior to design taking place.

    The volume of the wet well is a function of the incoming sewage flow rates and the pump capacity. Where feasible, the wet well volume between switching levels shall be sufficient to limit pump starts, under any conditions, to 12 per hour.

    The active volume of the wet well may be determined from the following formula:

    • WV = (900 x Qp)/S

    where:

    WV = wet well volume (L)

    Qp = pump capacity (L/s)

    S = number of starts per hour

    Switching levels shall be as follows:

    1. Bottom water level (BWL)

      The BWL is to be set as low as possible (to minimise dead storage), while still maintaining sufficient submergence to provide adequate suction head at the pump inlet, and to prevent any vortex actions. For small pumps the BWL may be set approximately one quarter of the way up the motor housing. For larger pumps the manufacturer will need to be consulted.
    2. Top water level (TWL)

      The TWL is defined by the volume between this level and the BWL (required to limit pump starts to the maximum permitted number per hour). The duty pumps are switched on at this level.
    3. Maximum top water level (MTWL)

      The MTWL is set 150mm below the invert level of the incoming sewer pipe. The standby pumps are switched on at this level.

    The shape of the wet well shall incorporate the following features:

    • benching of the base of the wet well (to direct flow to the pump suction);
    • adequate (but not excessive) clearance between the pump inlet and the base of the wet well (to enable removal of solids and to provide efficient pump operation);
    • reduction in the plan area of the wet well below the minimum water level needed for pump operation (to optimise pump efficiency);
    • sufficient area to install machinery to the tolerances required by the pump manufacturer (to enable the operation of level regulators and permit access via ladders);
    • access to the wet wells of pump stations is required for cleaning, removal of obstructions and maintenance or replacement of pumps and level regulators. Consideration shall be given to maintenance access to the bottom of the wet well. Means of access shall include movable ladder extensions with suitable brackets for extensions as required (refer to Standard Drawing No. WSS 023), and ladders permanently fixed within the wet well. Where ladders are used, these shall be manufactured from a non-corrosive material, preferably stainless steel 316L. The maximum length of any ladder is to be 6.0 metres, with landings required at 6.0 metre intervals for deeper wells. A vertical clearance of 2.1 metres shall be provided beneath each landing.

    Openings shall be provided in the concrete roofs of pump stations (designed to facilitate the installation and removal of pumps). The covers fitted to a pump station shall be sealed (gastight) metal covers, Class B (Class D if trafficable). Elsewhere covers shall be made from aluminium.

    Plate covers shall be hinged, and a post (or similar) provided to rest the opened covers. Covers shall be light enough to be lifted by one person. The top of the structure shall have no projections that constitute a trip hazard. All locks and hinges shall be recessed.

    The wet well will be provided with an automatic well washing system. The wash cycle is to parallel each pump cycle. Details on the preferred well washing systems should be obtained from ACTEW prior to design taking place.

    The well shall be painted with grease repelling epoxy.

    7.1.8 Pipework

    Pipework shall be designed to suit the pumping units and to comply with the following:

    • reflux valves shall be provided on the discharge side of each pump;
    • isolating valves shall be provided on suction lines (on the discharge side of each pump downstream of the reflux valve), on any cross connections, to permit operation of any one pump independently of other(s) removed for maintenance, and on the rising main(s) immediately downstream of the junctions of discharge lines from the individual pumps;
    • dismantling joints shall be provided to permit piecework within the station to be removed consistently with normal maintenance requirements;
    • pipework shall be sized to give a minimum velocity of 1.0 metre per second. Maximum velocities shall be arranged to prevent undue abrasion of pipe linings or excessive headloss;
    • a drainage line shall be provided allowing sewage within the rising main to be emptied into the pump station (to facilitate maintenance on the rising main).

    7.1.9 Mechanical equipment

    All parts shall be accessible for maintenance and replacement. Allowance shall be made in the design of equipment for wear and tear, including that due to pumping of abrasive solids. Provision shall be made for any necessary adjustments.

    7.1.10 Electrical equipment

    All pump stations are to be equipped with the following:

    • electricity supply meter: records the energy consumption of the total pump station;
    • power supply unit: this distributes power to all the control and starter units, with power generally being 3 phase 415 volts. The features of the unit are the main switch, voltmeter, phase failure relay LED, and circuit breakers;
    • common auto control unit: this unit houses all the control equipment for the automatic operation of the station. Components within this unit include the duty selector switch, top water level override button, maximum top water level override button, and the flood level indicating light;
    • motor starter units: these units control each pump and house all of the motor protection equipment and alarm lights. The components include the control selector switch, thermal overload indicating light, thermistor LED, seal failure light, seal failure reset button, ammeter, hours run meter, and the number of starts meter;
    • an hours run meter and ammeter for each pump;
    • telemetering unit;
    • programmable logic controller (PLC) to ACTEW specification;
    • auxiliary board: includes a twin 10 ampere general purpose outlet and a light switch to turn on the internal fluorescent tube.

    The programming of the PLC's will be carried out by ACTEW at the developers expense prior to the handover, the developer needing to make the necessary arrangements with ACTEW for this to occur.

    7.1.11 Flow metering

    Flow metering requirements shall be obtained from ACTEW prior to commencing design.

    7.1.12 Protection and alarms

    Protection and alarm requirements shall be obtained and verified by ACTEW prior to commencing design. At most locations ACTEW will request that a security system be installed.

    In environmentally sensitive locations the Environment ACT may require that emergency storage and or backup generators be provided adjacent to the pump station.

    If storage or generators are considered necessary, the degree of protection required will be determined by the locality of the station and the nature of the receiving water body. Some guidelines on integration of storage tanks to pump stations is provided on Standard Drawing No. WSS 055. Storage structures introduce maintenance constraints, ACTEW should be consulted during the planning and design to assure that the technology implemented complies with ACTEW's operating and maintenance capability.

    7.1.13 Ventilation

    For small wet well pump stations with submersible pumps, natural ventilation of the wet well using ash-down vents is generally adequate, however, such ventilation may not be appropriate for sites where public access is likely. In such localities tall mechanised vents will need to be constructed to ensure gasses are adequately dispersed. In very sensitive areas such as public parks, and sites in close proximity to residential leases, odour scrubbing may need to be considered.

    Stations or tanks deeper than 6.0 metres, or those that exceed a total internal volume of 50m3, will be fitted with a DN375 PVC pipe attached to the wall of the station. This pipe will extend from beneath the cover slab surface of the station to 200mm above the MTWL. A DN400 metal cover will be constructed directly above the DN375 conduit, a second DN600 metal cover being provided on the opposite side of the station. This system will be used in conjunction with a portable fan to force out gasses that may have accumulated at the base of the structure (prior to entry).

    7.1.14 Public safety and security

    The pump station and surrounds are to be designed to avoid hazard to the public and to resist vandalism. This would include consideration of:

    • gently sloping banks around the station;
    • concealed electrical cables;
    • high standard of locking doors etc;
    • fencing of the station site, if appropriate;
    • provision of intruder alarms on cabinets or buildings;
    • use of anti-graffiti paint for above ground components.

    7.1.15 Operation and maintenance manuals

    Draft operation and maintenance manuals for the pump station are required to be produced and presented by the developer to ACTEW at least three weeks prior to the handover date. ACTEW will examine these draft manuals and comment on their suitability within two weeks. The draft manuals are to include (but not be limited to) final wiring diagrams, a final ladder diagram, and final PLC software (on floppy disk). Final manuals are to be presented at handover.

    7.2 Rising mains

    Rising mains are to be designed to minimise septicity of sewage while in traverse, and to ensure ease of operation and maintenance of the main.

    To minimise septicity, sizing shall be determined by minimum velocity requirements that will limit both slime growth and the detention time of the sewage in the pipe. In general, rising main velocities between l and 3 meters per second are acceptable.

    To minimise potential operations and maintenance problems the smallest possible diameter pipe shall be used, with a minimum size of DN80 for carrying raw sewage and DN50 for carrying septic tank effluent. Rising mains shall be graded so as to be continuously rising. In the terminal (discharge) region the vertical alignment of the pipe should be designed to minimise the length of a partly full pipe between pumping cycles (refer to Clause 5.1.19). If such grading is not practical, automatic air valves and manually operated scour valves may be required. In such cases, proposals should be discussed with ACTEW at an early stage in the design.

    Corrosion and rupture resistant pipe materials shall be used for the rising main. Rising mains shall be located outside leased land to protect lessees from the effects of possible pipe rupture.

    The rising main, up to the discharge maintenance hole, is considered an integral part of the pump station. It is therefore required to be handed over at the same time as the pump station.

    Issues relating to high septicity, due to long retention periods during early stages of development, shall be resolved using hydrogen sulphide control principles as set out in the document entitled Hydrogen Sulphide Control Manual — Septicity, Corrosion and Odour Control in Sewerage Systems (Reference 10.13).

    Refer to Standard Drawing No. WSS 055 for a typical rising main connection to gravity sewer.

  • 8 Standards covering sewerage practice

    Work carried out and testing performed under this clause shall comply with the requirements of the SAA Codes and Standards listed below, to the extent that these are relevant and cannot be overridden by ACTEW's Standards. Any queries are to be referred to the Manager, Water and Sewerage Assets.

    SAA Standards must include current amendments at the time of use.

    8.1

    Materials — DICL pipes fittings

    AS 1646

    Elastometric Seals for Waterworks Purposes (1992)

    AS 2280

    Ductile Iron Pressure Pipes and Fittings (1995)

    8.2

    Materials — PVC pipes

    AS/NZS 1260

    PVC Pipes and Fittings for Drain, Waste and Vent Applications (1996)

    AS/NZS 1477

    PVC Pipes and Fittings for Pressure Applications (1996)

    AS/NZS 4441(Int)

    Oriented PVC (OPVC) Pipes for Pressure Applications (1996)

    8.3

    Materials — PE pipes

    AS/NZS 4130

    Polyethylene (PE) Pipes, Pressure Applications (1997)

    8.4

    Materials — VC pipes

    AS 1741

    Vitrified Clay Pipes and Fittings with Flexible Joints — Sewer Quality (1991)

    8.5

    Materials — Steel pipes and specials

    AS 1646

    Elastometric Seals for Waterworks Purposes (1992)

    AS 1830

    Iron Castings — Grey Cast Iron (1986)

    AS 3996

    Metal Access Covers, Road Grates and Frames (1992)

    AS 4087

    Metallic Flanges for Waterworks Purposes (1996)

    8.6

    Materials — Concrete pipes and specials

    AS 4058

    Precast Concrete Pipes (Pressure and Non-pressure) (1992)

    AS 4198

    Precast Concrete Access Chambers for Sewerage Applications (1994)

    8.7

    Materials — Pipes (specials)

    AS 3518

    Part 1 (AS 3518.1) — Acrylonitrile Butadiene Styrene (ABS) Pipes and Fittings for Pressure Applications — Pipes (1988)

    AS 3571

    Glass Filament Reinforced Thermosetting Plastics Pipes (GRP) — Polyester Based — Water Supply, Sewerage and Drainage Applications (1989)

    8.8

    Pipelaying and general construction

    AS 1170

    Minimum Design Loads on Structures, Part 1 (AS 1170.1) — Dead and Live Loads and Load Combinations (1989), Part 2 (AS 1170.2) — Wind Loads (1989), Part 3 (AS 1170.3) — Snow Loads (1990), Part 4 (AS 1170.4) — Earthquake Loads (1993)

    AS 1289

    Methods of Testing Soils for Engineering Purposes, Part 0 (AS 1289.0) to Part 7.1.3 (AS 1289.7.1.3) inclusive (various editions)

    AS 1657

    Fixed Platforms, Walkways, Stairways and Ladders — Design, Construction and Installations (1992)

    AS 2032

    Code of Practice for Installation of UPVC Pipe Systems (1977)

    AS 2200

    Design Charts for Water Supply and Sewerage (1978)

    AS/NZS 2566

    Plastics Pipelaying Design (1982) (superseded by AS/NZS 2566.1 — 1998 but is still made available)

    AS 2648

    Part 1 (AS 2648.1) Underground Marking Tape — Non-Detectable Tape (1995)

    AS 2700

    Colour Standards for General Purposes (1996)

    AS/NZS 3500

    National Plumbing and Drainage Code (Part 0 to Part 4.2 inclusive)

    AS 3571

    Glass Filament Reinforced Thermosetting Plastics Pipes (GRP) — Polyester Based — Water Supply, Sewerage and Drainage Applications (1989)

    AS 3600

    Concrete Structures (1994)

    AS 3725

    Loads on Buried Concrete Pipes (1989)

    AS 3735

    Concrete Structures for Retaining Liquids (1991)

    AS 3855

    Suitability of Plumbing and Water Distribution Systems Products for Contact with Potable Water (1994)

    AS 3972

    Portland and Blended Cements (1997)

    AS 4060

    Loads on Buried Vitrified Clay Pipes (1992)

    AS HB72

    Design Vehicles and Turning Path Templates (1995)

  • 9 Standard drawings

    Road verge drawings — drawing Nos. SEP4 — 01 to 06, chapter 4 (road verges) (Reference 10.15)

    WSS 001 — Design Symbols and Notation

    WSS 002 — Access Ladder and Staggered Step Iron Details

    WSS 052 — DN1050 Cast In-situ Maintenance Hole

    WSS 053 — DN1200 — 1500 Cast In-situ Maintenance Holes

    WSS 054 — Typical House Connections (Service Ties)

    WSS 055 — Typical Minor Neighbourhood Sewage Pump Station and Rising Main

    WSS 056 — Standard Bedding Details for Sewer Mains DN100 — DN300

    WSS 057 — Precast Concrete Maintenance Hole Components

    WSS 058 — Class B Concrete Maintenance Hole Cover and Surround

    WSS 061 — Sewer Maintenance Shaft (SMS) and Rodding Points Typical Arrangement

    WSS 062 — Standard Offsets for Simple Maintenance Hole Configurations

  • 10 References

     

    10.1 Water and Sewerage Regulations 2001 (ACT) and the Water and Sewerage Act 2000 (ACT) (having replaced the Canberra Sewerage and Water Supply Regulations 1999).

    10.2 Metropolitan Water Sewerage and Drainage Board, Sydney (1979), "Design of Separate Sewerage Systems" .

    10.3 Thistlethwayte, D.K.B. (Ed.) (1972), "The Control of Sulphides in Sewerage Systems" , Butterworths, Sydney.

    10.4 Boston Society of Civil Engineering (1942), "Minimum Velocities for Sewers" , Journal, Post Soc C E, Vol 29 No 4, October.

    10.5 Public Works Department, NSW (1984), "Manual of Practice — Sewer Design" , Sydney.

    10.6 Public Works Department, NSW (1986), "Manual of Practice — Sewage Pump Station Design" , Sydney.

    10.7 Melbourne and Metropolitan Board of Works (1970), "Colombo Plan Lectures — Sewerage Design" , Melbourne.

    10.8 Commonwealth Department of Works (1972), "Notes for Guidance in the Design of Hydraulic Services" .

    10.9 CSIRO: Engineering and Building Section (1984), "The Invasion of Sanitary Drains by Plant Roots: Prevention and Cure" , Technical Record 503, Sydney.

    10.10 Commonwealth Department of Works (1973), "Review of Sewer Standards" , ACT Region Internal Report.

    10.11 Committee on Uniformity of Plumbing and Drainage Regulations in New South Wales (1987), "New South Wales Code of Practice — House Drainage" .

    10.12 Totalcare document, ACT Public Works "Basic Specification — Roads, Hydraulic Services and Landscape" , Edition No 1 (July 1991) as amended (including in particular Corrigendum No 1 to Volume 1, 11 December 1992) plus the associated "Users Guide for the Basic Specification" .

    10.13 Major Urban Water Authorities of Australia: Technological Standing Committee on Hydrogen Sulphide Corrosion in Sewerage Works (MMBW-1990), "Hydrogen Sulphide Control Manual — Septicity, Corrosion and Odour Control in Sewerage Systems" .

    10.14 "ACT Standard and Code of Practice on Manual Handling" , Second Edition 1993.

    10.15 Roads and Transport Section, ACT Department of Urban Services, "Standard Engineering Practice — Roads and Bridges" , Draft No 5, 5 November 1995.

  • 11 List of appendices

    Appendix 3-1 — Peak dry weather flow (PDWF)

    Appendix 3-2 — Peak infiltration / inflow (PII)

    Appendix 3-3 — Most probable peak dry weather flow (Qdmp)

    Appendix 3-4A: Pipe capacities — DN150

    Appendix 3-4B: Pipe capacities — DN225

    Appendix 3-4C: Pipe capacities — DN300

    Appendix 3-4D: Pipe capacities — DN375

    Appendix 3-4E: Pipe capacities — DN450

    Appendix 3-4F: Pipe capacities — DN525

    Appendix 3-4G: Pipe capacities — DN600

    Appendix 3-4H: Pipe capacities — DN675

    Appendix 3-4I: Pipe capacities — DN750

    Appendix 3-4J: Pipe capacities — DN825

    Appendix 3-5 — Minimum grades and proportional hydraulic data

  • 12 List of figures

    Figure 3.1 — Peak dry weather flow (PDWF)

    Figure 3.2 — Peak infiltration / inflow (PII)

    Figure 3.3 — Most probable peak dry weather flow (Qdmp)