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5-Waters-Volume-3-Wastewater
15 Springston Wastewater Scheme
15.1 Scheme Summary
Estimated Population Served
| 560
|
Scheme Coverage (1 Jan 2021)
| Full Charges | 177
|
| Half Charges | 14
|
| >1 Charges | 2
|
System Components
| Piped (m) | 9109.86
|
| Manholes (No.) | 45
|
| Pump Stations (No.) | 1
|
| Treatment | N/A (to Pines WWTP) |
| Disposal | N/A (to Pines WWTP) |
| History | Original scheme installation date | 1998 |
Value ($)
| Replacement Cost | $5,013,825
|
| Depreciated Replacement Cost | $3,953,324
|
Financial
| Operator cost (scheduled and reactive maintenance) per connection
| $145.26/connection
|
Demand
(1 Jan - 31 Dec 2020)
| Annually (m3) | 34,911
|
| Average daily (m3) | 95.6
|
| Peak daily (m3) | 2,259.6
|
| Minimum daily (m3) | 54.3
|
| Infiltration | Yes |
| Sustainability | Ultimate discharge point | To Pines WWTP |
15.2 Key Issues
The following key issues are associated with the Springston Wastewater Scheme. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.
Table 15‑1 Springston Scheme Issues
| The pump station equipment has a high degree of sophistication with macerators and high head pumps. | Review pump setup at time of renewal. One pump has been replaced with a submersible pump as a trial. |
| Significant infiltration and inflow is experienced during wet weather | Target renewals to address infiltration and investigate sources of infiltration |
15.3 Overview & History
A sewer reticulation system was installed into Springston Township in 1998, following agreement with Christchurch City permitting 24 hour pumping of raw sewage at a maximum flow rate of 6L/s to Christchurch City.
The reticulated sewer discharges to a single pump station on Leeston/Springston Road. Wastewater is pumped via a 100 mm diameter rising main to Springs and Ellesmere Junction road corner where it joins into the 250 mm diameter rising main from the Lincoln WWTP to Christchurch.
In early 2002 a developer (Aylesford Management Ltd) requested if the spare allocation could be used for a development on Blakes and Shands Roads, Prebbleton. Council agreed and accepted that a maximum of 246 connections could be sustained, provided that short and long term infiltration of groundwater is minimised.
In April 2006, Aylesford Management obtained the necessary approvals to develop their land, and hence take up 59 of Springston's sewer connections.
Subsequent to development of the Springston wastewater scheme a portion (equivalent to 59 connections) of the permitted discharge capacity was allocated to a residential development (Aylesford Management Ltd) at Blakes and Shands Roads, Prebbleton, as the Prebbleton scheme capacity is fully allocated.
From December 2012 Springston township wastewater treatment and disposal was undertaken at the Rolleston Pines as part of the Eastern Selwyn Sewerage Scheme.
The 2010/2011 earthquakes had a minor impact on the scheme's below ground infrastructure. Several deep lateral connections separated but were repaired. Based on visual assessment (CCTV and qualified staff) no other damage to the below ground infrastructure or resulting effects e.g. blockages have been detected. There may however be long term but intangible impact on maintenance and renewals programmes.
Figure 15‑2 Scheme Schematic
Figure 15‑3 Pump Station Failure Map
15.4 System Capacity
The current Springston sewage flows are consistent with the design flows for the current number of connected properties.
Figure 15‑4 Wet Weather Flow Capacity Map
15.5 Resource Consents
Springston township is part of the ESSS scheme. Therefore, all wastewater is pumped to the Pines Treatment Plant located in Rolleston. The resource consents required for this treatment plant are in the ESSS section of this plan.
15.6 Scheme Assets
A summary of the assets within this scheme is outlined in this section.
15.6.1 Reticulation Overview
A summary of material and diameter for pipes is shown in Figure 15‑5 and Figure 15‑6.
Figure 15‑5 Pipe Material - Springston
Figure 15‑6 Pipe Diameter - Springston
15.6.2 Treatment and Disposal
Further reference to the treatment and disposal of Springfield wastewater is described in Section 5.0.
15.6.3 Pump Stations
There is only one pump station within the Springston network. This pump stations collects all the sewage and pumps it into the ESSS network, shown in Table 15‑2.
Pump stations where the standby / assist pump is predicted to start have been highlighted in
yellow and
red for those that experience a peak wet weather response.
Yellow Pumps are can convey the peak flow without backing up the system
Red Pumps are unable to convey the peak flow causing the system to back up
Table 15‑2 Pump Station Overview
| Springston (S) Leeston Rd Ps | 2200Ø | 2 | Mono CEO72 progressive cavity | 7.8 | 7.8 | 1.2 | 2.9 | 11.1 |
Table 15‑3 Pump Station Storage Time Analysis
| Springston (S) Leeston Rd Ps | Two surface mounted mono pumps with munches (mechanical screens before pumping) | 10.6 | 12.3 | 550770 |
15.6.4 Rising Mains
Table 15‑4 Rising Main Overview
| Springston (S) Leeston Rd Ps | Springston | 4,093 | 35.2 | 1.2 | 6.7 | 0.0 | 6.7 | 395 | 75 - 280 - 370 |
Although not currently used, the agreement between Selwyn District Council and Christchurch City Council, allows for untreated wastewater from Springston to be pumped 24 hours a day at a maximum flow rate of 6 L/s into the Christchurch System. The maximum volume of discharge is 75,000m3 in each financial year.
15.7 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.
15.8 Photos of Main Assets
Photo 1 - Springston Pump Station
15.9 Risk Assessment
A risk assessment has been undertaken for the Springston 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. Table 15‑5 details the risk priority rating, Table 15‑6 outlines the risks for this scheme.
Table 15‑5 Risk Priority Rating
| > 50 | Extreme | Awareness of the event to be reported to Council. Urgent action to eliminate / mitigate / manage the risk. Document risk and action in the AMP. |
| 35-50 | Very High | Risk to be eliminated / mitigated / managed through normal business planning processes with responsibility assigned. |
| 14-35 | High | Manage risk using routine procedures. |
| 3.5-14 | Moderate | Monitor the risk. |
| < 3.5 | Low | Awareness of the event to be reported to Council. Immediate action required to eliminate / mitigate / manage the risk. Document risk and action in the AMP. |
Table 15‑6 Risks - Springston
| Pump selection does not take advantage of new technology and changes to the pressure main alignment. | Renewal project: take 2 monopumps out and replace with submersible pumps | 2014 | 27 | 27 | 6 |
The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.
15.10 Asset Valuation Details
The total replacement value of assets within the Springston Scheme is $5,013,825 as detailed in Table 15‑7 below.
Table 15‑7 Replacement Value, Springston
Plant and Equipment
| $207,963
|
Wastewater Reticulation
| Chamber | $260,437
|
| Lateral | $692,181
|
| Manhole | $331,035
|
| Pipe | $3,498,899
|
| Valve | $23,310
|
15.11 Renewals
The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme are shown by Figure 15‑7 below.
Figure 15‑7 Springston Wastewater Renewal Profile
15.12 Critical Assets
The criticality model for Springston has been updated for the 2021 AcMP. The methodology of the criticality model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the criticality has been calculated for the reticulation assets. Table 15‑8 and Figure 15‑8 below shows the calculated criticality for all of the assets within this scheme that have a recorded known length.
Table 15‑8 Length of Assets per Criticality Level
5
| Low | 7,252
|
4
| Medium-Low | 1,188
|
3
| Medium | 236
|
2
| Medium-High | 287
|
1
| High | 180
|
15.13 Asset Condition
The asset condition model was run for Springston in 2021. The methodology of the model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the model has been calculated for the reticulation assets (particularly pipes). Figure 15‑9 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.
Table 15‑9 provides a description of the condition rating used within the condition model.
Table 15-9 Asset Condition Grading
| 1.0 | Excellent |
| 2.0 | Good |
| 3.0 | Moderate |
| 4.0 | Poor |
| 5.0+ | Fail |
15.14 Funding Program
The 10 year budgets for Springston are shown by Table 15‑10. Budgets are split into expenditure, renewals, projects and capital projects. Expenditure and renewals have been reported on a district-wide basis in Volume 1. All figures are ($) not adjusted for CPI “inflation". They are calculated on historical data, and population growth where relevant.
Table 15‑10 Springston Budget Summary
| 2021/2022 | -
| -
|
| 2022/2023 | -
| -
|
| 2023/2024 | -
| -
|
| 2024/2025 | -
| -
|
| 2025/2026 | -
| -
|
| 2026/2027 | -
| $675,000
|
2027/2028
| -
| -
|
2028/2029
| -
| -
|
2029/2030
| -
| -
|
2030/2031
| -
| -
|
| Total | -
| $675,000
|
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 15‑11 Key Projects
Capital Projects
| -
| New pipeline direct to Selwyn Road PS
| - | -
| -
| $675,000
| 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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