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5-Waters-Volume-3-Wastewater
2 Castle Hill Wastewater Scheme
2.1 Scheme Summary
Estimated Population Served
| 415
|
Scheme Coverage (1 Jan 2021)
| Full Charges | 134
|
| Half Charges | 119
|
| >1 Charges | 0
|
System Components
| Piped (m) | 8,720
|
| Manholes (No.) | 99
|
| Pump Stations (No.) | 0
|
| Treatment | 1 x treatment plant
|
Disposal
| Pond system with land irrigation
|
| History | Original scheme installation date | 1982 |
Value ($)
| Replacement Cost | $4,998,794
|
| Depreciated Replacement Cost | $2,549,933
|
Financial
| Operator cost (scheduled and reactive maintenance) per connection
| $76.02/connection
|
Demand
(1 Jan - 31 Dec 2020)
| Annually (m3) | 20,403
|
| Average daily (m3) | 55.9
|
| Peak daily (m3) | 253.4
|
| Minimum daily (m3) | -
|
| Infiltration | Infiltration / inflow is an issue for this scheme
|
| Sustainability | Ultimate discharge point | Land Irrigation
|
2.2 Key Issues
The following key issues are associated with the Castle Hill Wastewater Scheme. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.
Table 2‑1 Castle Hill Scheme Issues
High peak flows in wastewater system
| Investigate source of infiltration / inflow. |
| Potential pond seepage | The pond is currently being lined due to be completed 2021
|
2.3 Overview & History
This scheme is entirely gravity reticulated, taking advantage of the steep natural gradient. Effluent is treated in a single stage oxidation pond and disposed of through land irrigation. The irrigation area is used on average once every two years as the levels in the pond are low due to evaporation and suspected seepage.
The first water right to discharge sewage effluent onto the land was issued in 1979 and it was in the name of Castle Hill development. This right was transferred to the Malvern County Council in June 1986. The current permit is CRC991052
There are few permanent residents in the village which has been developed in stages since the early 1980s. Most properties are used as seasonal holiday homes with a number available for holiday rental. There are currently no business activities in the village. Further development is planned with a café and fuel station.
The remote location and harsh alpine environment present challenges for operation and maintenance of a wastewater scheme. The village can be isolated following heavy snowfall and storm events that periodically close State Highway 73.
The community is located within the alpine fault line, and is expected to incur significant damage to its water infrastructure should a significant rupture occur.
Figure 2‑2 Scheme Schematic
2.4 System Capacity
Recent development at Castle Hill means that the wastewater scheme is now near capacity.
2.5 Resource Consents
The Castle Hill wastewater scheme has a number of resource consents. Table 2‑2 shows the discharge permitted by the resource consents for this scheme.
Table 2‑2 Resource Consents
CRC991052
| To discharge contaminants to land | Castle Hill Village, CASTLE HILL | 27-Jan-10
| 26-Jan-35 | 785
|
This consent has a condition that wastewater shall only be discharged during the months of September, October, November, December, January, February, March and April.
Council are currently underway with an application for a winter discharge consent and land use consent for the Castle Hill WWTP.
2.6 Scheme Assets
A summary of the assets within this scheme is outlined in this section.
2.6.1 Reticulation Overview
A summary of material and diameter for pipes is shown in Figure 2‑3 and Figure 2‑4.
Figure 2‑3 Pipe Material – Castle Hill
Figure 2‑4 Pipe Diameter – Castle Hill
2.6.2 Treatment and Disposal
Treatment and disposal consist of a 10,600m3 oxidation pond and land irrigation through 4.25ha of border dykes with pop up outlets for flow control. The pond was designed by Steven Fitzmaurice and Partners in 1982. There are issues associated with the Castle Hill treatment systems structural integrity. These were greatly improved in the early 1990's by the addition of Bentonite.
Table 2‑3 Treatment and Disposal Facilities
| Oxidation Pond | 10,600m3 operating storage | 1982 |
| Land Disposal | 4.25 ha of border dykes with pop up outlets for flow control | 1982 |
2.6.3 Design
Table 2‑4 Design Data
| Population | 1,220 |
260
|
95.16
|
640
|
| Occupancy rate | 30% |
| Design P.E. | 366 |
Castle Hill scheme has the potential to accommodate additional demand. While there is no threat of exceeding the design capacity in the immediate future, growth in the area should be monitored and capacity checked before consents granted.
Peak flows are high for this scheme which should be investigated further.
2.6.4 Pump Stations
There are no pump stations within the Castle Hill sewerage system.
2.7 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.
2.8 Photos of Main Assets
Photo 1 - Pond
|
2.9 Risk Assessment
A risk assessment has been undertaken for the Castle Hill 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 2‑5 details the risks, Table 2‑6 outlines the risks and the list of key projects is found in Table 2‑11.
Table 2‑5 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 2‑6 Risks – Castle Hill
| Plant operation causes breach of consent | Review and document disposal procedure | 2014 | 12 | 10 | 10 |
| Non-consented activities | Renewal of consents | 2014 | 27 | 27 | 6 |
| Pond leaking | Review options e.g. package plant or pond lining | 2017 | | 45 | 2.1 |
| Infiltration overwhelms network | Lift MH lids | 2017 | | 12 | 6 |
The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.
2.10 Asset Valuation Details
The total replacement value of assets within the Castle Hill scheme is $4,998,794 as detailed in Table 2‑7 below.
Table 2‑7 Replacement Value, Castle Hill
Plant and Equipment
| $2,249,671
|
Wastewater Reticulation
| Chamber | $54,346
|
| Lateral | $854,125
|
| Manhole | $483,752
|
| Pipe | $1,342,515
|
| Valve | $14,385
|
2.11 Renewals
The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme are shown by Figure 2‑5 below.
Figure 2‑5 Castle Hill Wastewater Renewal Profile
2.12 Critical Assets
The criticality model for Castle Hill has been updated for the 2021 AcMP. The methodology of the criticality model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the criticality has been calculated for the reticulation assets. Table 2‑8 and Figure 2‑6 below show the calculated criticality for all of the assets within this scheme that have a recorded known length.
Table 2‑8 Length of Assets per Criticality Level
5
| Low | 2,498
|
4
| Medium-Low | 3,115
|
3
| Medium | 0 |
2
| Medium-High | 1,705
|
1
| High | 0 |
2.13 Asset Condition
The asset condition model was run for Castle Hill in 2021. The methodology of the model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the model has been calculated for the reticulation assets (particularly pipes). Figure 2‑7 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.
Table 2‑9 provides a description of the condition rating used within the condition model.
Table 2‑9 Asset Condition Grading
1.0
| Excellent |
| 2.0 | Good |
| 3.0 | Moderate |
| 4.0 | Poor |
| 5.0+ | Fail |
2.14 Funding Program
The 10 year budgets for Castle Hill are shown by Table 2‑10. Budgets are split into expenditure, renewals, projects and capital projects. Expenditure and renewals have been reported on a district-wide basis in Volume 1.
All figures are ($) not adjusted for CPI “inflation". They are calculated on historical data, and population growth where relevant.
Table 2‑10 Castle Hill Budget Summary
| 2021/2022 | -
| $750,000
|
| 2022/2023 | -
| -
|
| 2023/2024 | -
| -
|
| 2024/2025 | -
| -
|
| 2025/2026 | -
| -
|
| 2026/2027 | -
| -
|
2027/2028
| -
| -
|
2028/2029
| -
| -
|
2029/2030
| -
| -
|
2030/2031
| -
| -
|
| Total | - | $750,000 |
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 2‑11 Key Projects
| Capital Projects | -
| Automate irrigation system
| $400,000
| -
| -
| -
| 100% LoS |
| Capital Projects | -
| Purchase land for irrigation
| $350,000
| -
| -
| -
| 100% LoS |
* LoS refers to Level of Service
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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