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5-Waters-Volume-3-Wastewater
9 Leeston Wastewater Scheme
9.1 Scheme Summary
Estimated Population Served
| 2,857
|
Scheme Coverage
(1 Jan 2021)
| Full Charges | 874
|
| Half Charges | 87 |
| >1 Charges | 15 |
System Components
| Piped (m) | 27,880
|
| Manholes (No.) | 229
|
| Pump Stations (No.) | 5
|
| Treatment | N/A (to Ellesmere STP) |
| Disposal | N/A (to Ellesmere STP) |
| History | Original scheme installation date | 1975 |
Value ($)
| Replacement Cost | $15,310,917
P&E equipment is counted within the Ellesmere Sewerage Scheme
|
| Depreciated Replacement Cost | $9,274,074
P&E equipment is counted within the Ellesmere Sewerage Scheme
|
| Financial | Operator cost (scheduled and reactive maintenance) per connection
| $101.22/connection
|
Demand
(1 Jan - 31 Dec 2020)
| Annually (m3) | 154,468
|
| Average daily (m3) | 423
|
| Peak daily (m3) | 1,372
|
| Minimum daily (m3) | 3.6
|
| Infiltration | Yes
|
| Sustainability | Ultimate discharge point | Land and surface water based treatment. Ultimately discharged to Te Waihora/Lake Ellesmere. |
9.2 Key Issues
The following key issues are associated with the Leeston Wastewater Scheme. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.
Table 9‑1 Leeston Scheme Issues
| Significant infiltration and inflow is experienced during wet weather | Target renewals to address infiltration and investigate sources of infiltration |
| Capacity to meet growth demands | Construct capital upgrades to meet growth demands |
9.3 Overview & History
Leeston Township is located in an area lower than the surrounding land and soakage is very poor. Ground water levels vary from 1.5m in summer to 0.3m below ground level in winter. In 1975 reticulation and an oxidation pond were installed to replace a “night cart" service for the township and sullage that went to local waterways (Tramway Reserve Drain) from side channels.
In 1993 both pump stations were substantially upgraded along with installation of an aeration pond to increase treatment capacity. In 2003 further extension of the treatment system occurred with additional ponds and the upgrading of the wastewater disposal system.
Figure 9‑2 Scheme Schematic
Figure 9-3 Leeston Master Plan
Figure 9‑4 Pump Station Failure Map
9.4 System Capacity
Flows from Leeston, Doyleston and Southbridge schemes are treated at the Leeston Wastewater Treatment Plant. The Doyleston, Leeston and Southbridge schemes are operating within the maximum design limits occasionally reaching the design flow maximum for the current population.
Master planning work for the network has been completed (Figure 9‑3).
Section 9.6.2 provides pump station capacity information.
Figure 9‑5 Wet Weather Flow Capacity Map
9.5 Resource Consents
Leeston township is part of the Ellesmere scheme. Therefore, all wastewater is pumped to the Ellesmere Treatment Plant located in Leeston. The resource consents required for this treatment plant are in the Ellesmere section of this plan.
9.6 Scheme Assets
A summary of the assets within this scheme is outlined in this section.
9.6.1 Reticulation Overview
A summary of material and diameter for pipes is shown in Figure 9‑6 and Figure 9‑7.
Figure 9‑6 Pipe Material - Leeston
Figure 9‑7 Pipe Diameter - Leeston
9.6.2 Pump Stations
There are five pump station within the Leeston Scheme, these pump to Leeston WWTP. Details are tabled below in Table 9‑2.
Table 9‑2 Pump Stations
| Leeston (S) Cunningham St | 1800 Ø | 2.5 | 6 | 2 | Flygt NP3153 13.5 kW | 40 | 37.5 | 0.4 | 0.6 |
| Leeston (S) Lambie St | 900 Ø | 0.6 | 4 | 2 | Flygt NP3085 2.4 kW | 7.5 | 7.5 | 0.4 | 1.1 |
| Leeston (S) Clausen Avenue | 1500 Ø | 1.8 | 5 | 2 | Flygt NP3085 2.4 kW | 8 | 8 | 0.006 | 0.02 |
| Leeston (S) Station St | 2100 Ø | 3.5 | 3.5 | 2 | Flygt NP3127 437 5.9 kW Flygt NP3153 MT433 9 kW | 36 | 32.4 | 1.6 | 4.1 |
| Leeston (S) Lake Rd | 1800 Ø | 4.2 | 3.5 | 2 | Flygt NP3127 437 5.9 kW Flygt NP3153 HT456 9 kW | N/A | 20.4 | 2.3 | 6.1 |
Table 9‑3 Pump Station Storage Time Analysis
Leeston (S)
Cunningham St | Leeston | 111 | 123 | 19.760 | 614709 |
Leeston (S)
Lambie St | Leeston | 40 | 45.6 | 20.409 | 608870 |
Leeston (S)
Clausen Avenue | Leeston | - | - | - | - |
Leeston (S)
Station St | Leeston | 9.55 | 12 | 18.240 | 24393 |
Leeston (S)
Lake Rd | Leeston | 4.6 | 6 | 17.798 | xxxx002045 |
HLA = High Level Alarm. The table assumes the pump station fails at 8:30am with peak flow occurring at 9am.
9.6.3 Rising Mains
Table 9-4 Rising Mains
| Cunningham to WWTP | PVCU | PN12 | 180 | |
| Lake Road to WWTP | PVCU/PE80 | PN12/PN8 | 135 | Assumed pressure rating on DN150 rising main |
| Clausen Avenue | PVCU | PN12 | 102 | |
| Lambie St | PVCU | PN9 | 81 | |
9.7 Operational Management
The wastewater schemes are operated and maintained under the maintenance contract as follows:
- Contract 1241: Water Services Contract. Contract is with SICON who undertakes investigations, conditions inspections, proactive and reactive maintenance and minor asset renewals.
Wastewater sampling is completed under an agreement with Food and Health Ltd as required.
9.8 Photos of Main Assets
Photo 1 - Station Street Pump Station
| 
Photo 2 – Lake Road Pump Station
|
9.9 Risk Assessment
A risk assessment has been undertaken for the Leeston scheme. The key output from the risk assessment is the identification of any extreme and high risks which need to be mitigated. In order to mitigate these risks they have been included and budgeted for in the projects within this LTP. There were no risks identified for this scheme.
9.10 Asset Valuation Details
The total replacement value of assets within the Leeston Scheme is $15,310,917 as detailed in Table 9‑5 below. This excludes P&E equipment, which is counted within the Ellesmere WWTP scheme valuation.
Table 9‑5 Replacement Value, Leeston
Wastewater Reticulation
| Chamber | $1,451
|
| Lateral | $2,822,190
|
| Manhole | $1,509,938
|
| Pipe | $10,925,344
|
| Valve | $51,993
|
9.11 Renewals
The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme are shown by Figure 9‑8 below.
Figure 9‑8 Leeston Wastewater Renewal Profile
9.12 Critical Assets
The criticality model for Leeston has been updated for the 2021 AcMP. The methodology of the criticality model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the criticality has been calculated for the reticulation assets. Table 9‑6 and Figure 9‑9 below shows the calculated criticality for all of the assets within this scheme that have a recorded known length.
Table 9‑6 Length of Assets per Criticality Level
5
| Low | 15,988
|
4
| Medium-Low | 7,669
|
3
| Medium | 2,647
|
2
| Medium-High | 859
|
1
| High | 952
|
9.13 Asset Condition
The asset condition model was run for Leeston in 2021. The methodology of the model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the model has been calculated for the reticulation assets (particularly pipes). Figure 9-10 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.
Table 9‑7 provides a description of the condition rating used within the condition model.
Table 9‑7 Asset Condition Grading
| 1.0 | Excellent |
| 2.0 | Good |
| 3.0 | Moderate |
| 4.0 | Poor |
| 5.0+ | Fail |
9.14 Funding Program
The 10 year budgets for Leeston and the Ellesmere Sewerage Scheme are shown by Table 9‑8. Budgets are split into expenditure, renewals, projects and capital projects. Expenditure and renewals have been reported on a district-wide basis in Volume 1.
All figures are ($) not adjusted for CPI “inflation". They are calculated on historical data, and population growth where relevant.
Table 9‑8 Leeston Budget Summary
| 2021/2022 | -
| $100,000
|
| 2022/2023 | -
| -
|
| 2023/2024 | -
| -
|
| 2024/2025 | -
| -
|
| 2025/2026 | -
| -
|
| 2026/2027 | -
| -
|
2027/2028
| -
| -
|
2028/2029
| -
| -
|
2029/2030
| -
| -
|
2030/2031
| -
| -
|
Total
| -
| $100,000
|
An explanation of the categories within the budgets are as follows below:
- Expenditure consists of operation and maintenance costs;
- Renewals are replacement of assets which are nearing or exceeded their useful life;
- Projects are investigations, decisions and planning activities which exclude capital works; and
- Capital projects are activities involving physical works.
Table 9‑9 Key Projects
| Capital Projects | -
| Refurbishment of pump station (Lambie Street pump station)
| $100,000
| -
| -
| -
| TBC
|
* LoS refers to Level of Service; G refers to Growth
The list of district wide projects can be found in 5Waters Activity Management Plan: Volume 1.
Discussion on Projects
Projects have been determined based on their:
- Relevance to the scheme
- Requirement to be completed under legislation
- Ability to bring the scheme up to or maintain the Level of Service required under council's Asset Management Policy.
Many projects are
jointly funded by more than one scheme and activity. Each scheme pays a pro-rata share only, equivalent to the number of connections.
Discussion on Capital and Projects
Where relevant, Capital (Levels of Service) and Capital (Growth) projects have been included in the scheme financial details.
Levels of Service Projects and growth splits have been provided to ensure the costs of population driven works are clear.
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