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5-Waters Volume 2 - Water Supplies
7 Dunsandel Water Supply
7.1 Scheme Summary
Estimated Population Served |
511
|
Scheme Coverage
(1 Jan 2021)
|
Full Charges |
172
|
Half Charges |
0
|
>1 Charges |
4
|
System Components
|
Bores/Intakes (No.) |
1 |
Treatment/Disinfection |
UV |
Reservoirs (No.) |
1 |
Pump Stations (No.) |
1 |
Piped (m) |
9,762 |
History | Original scheme installation date | 1986
|
Value ($)
| Replacement Cost | $1,906,696
|
Depreciated Replacement Cost | $1,201,694
|
Financial
| Operator cost (scheduled and reactive maintenance) per connection
| $319.06/connection
|
Demand (m3) (1 Jan – 31 Dec 2020)
| Average daily | 336
|
Peak daily | 856
|
Minimum daily | 5.9
|
Average daily per connection | 1.78
|
Type of Supply |
| Medium pressure and unrestricted |
Target Pressure & Flow at boundary
| Pressure | >310 kPa |
Flow | >40 L/min |
Sustainability | Well Security | Unsecure |
7.2 Key Issues
The following key issues are associated with the Dunsandel water supply. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.
Table 7‑1 Dunsandel Scheme Issues
Supply is reliant on one source of water
| Investigate an alternative site for a new bore.
|
Catchment management
| To encompass a holistic view of the drinking water supply improved liaison with ECan and study of groundwater quality within the water supply protection zones are being investigated.
|
Backflow risk: the scheme is vulnerable to potential backflow issues associated with commercial and industrial connections.
| There is currently a district wide backflow prevention project underway.
|
7.3 Overview & History
The Dunsandel Water Supply provides untreated groundwater to Dunsandel township and the adjacent 40 lot rural residential subdivision on Irvines Road (Sherwood Estate).
The current scheme was formed by combining the Dunsandel Township (installed 1986) and Sherwood Rural Residential (installed in 1991) schemes in July 1997. This allowed decommissioning of the problematic Dunsandel Well (ECan number L36/0601), and an improved cost/benefit relationship for operating both schemes.
There was also a previous subdivision on the Hororata-Dunsandel Road constructed in 1976 with a communal water scheme that was absorbed and decommissioned with the Dunsandel Township work.
The scheme was designed as a medium pressure, unrestricted metered supply complying with NZ Fire Fighting Code of Practice.
In 2009 the number of water quality transgressions rose significantly, and a combined regional, Selwyn District Council and community approach was taken to investigating the cause and recommending options to make the water safe to drink. An ultraviolet light system was installed and has eliminated bacteria (E.coli) entering the township network.
Figure 7‑2 Scheme Schematic
7.4 System Capacity
Dunsandel has some potential for growth in terms of zoned land availability.
Table 7‑2 Capacity Summary
Consented Take | 25 | 1944 | 291,600
(1) | CRC010891.1 |
Peak Demand - current | 25L/s
(2) | 1,380 (3) | 215,111
(4) |
|
Abstraction capacity | 24.7 | 2134 | - | 1 bore pump |
Treatment capacity | 24.7 | 2134 | - | Assume UV can accommodate bore pump flow rate. Note current UV is non-compliant. And upgrade programmed 2015. |
Distribution pumping
| 35 | 1944 | 291,600 | 2 pumps (duty/assist) from 70m3 storage – can buffer peak flows but not peak days |
(1) inferred value, (2) Jan 2013, (3) 25 Jan 2015 (excluding fire fighting events), (4) Dec 2014- Dec 2015
7.5 Resource Consents
The Dunsandel water supply has a number of resource consents. Table 7‑3 shows the water take permitted by the resource consents for this scheme.
Table 7‑3 Resource Consents
CRC010891.1
| To take and use groundwater | cnr Sh1 & Hororata Dundanel Roads And Cnr Tramway And, IRVINES ROADS DUNSANDEL | 12-Feb-10 | 31-Jan-35 | 22.5 | 1944 |
7.6 Water Quality
The Dunsandel water supply is a non-secure source and is currently sampled twice weekly at the source, treatment plant and weekly in the reticulation.
The following details the E. coli transgressions for the period 2012 to 2020.
Source
There have been 50 incidences of E. coli identified in source water during this period, highlighting the importance of water treatment for this scheme.
Figure 7‑3 E. coli Transgressions - Source
Treatment
There has been one E. coli treatment transgression during this period which occurred in October 2014.
Zone
There has been one E. coli transgressions during this period which occurred in January 2013.
Chemical Analysis
The following is a summary of the raw water chemical analysis carried out at the Dunsandel Water Supply.
Table 7‑4 Dunsandel Water Supply Raw Water Chemical Analysis Summary
Total Lead (g/m3) | 0.01 (Maximum Acceptable Value)
| <0.0001
| <0.00011
| 0.00013
| 0.0002
| < 0.00011 | <0.00011
| <0.00011
| ✓
|
pH (pH units) | 7-8.5 (Guideline Value)
| 7.1
| 7.1
| 7.3
| 7.4 | 7.2 | 7.3
| 7.3
| ✓ |
Total Hardness (g/m3 as CaCO3) | <200 (Guideline Value)
| 63
| 54
| 54
| 67 | 63.2
| 74.3
| 79.7
| ✓
|
Total Calcium (g/m3) | n/v | 16
| 13.7
| 13.9
| 16.8
| 16.64
| 19.71
| 21.02
| ✓ |
Total Iron (g/m3) | <0.2 (Guideline Value)
| <0.02
| <0.021
| <0.021
| <0.021 | < 0.021 | <0.021
| <0.021
| ✓
|
Total Sodium (g/m3) | <200 (Guideline Value)
| 9.4
| 8.8
| 8.6
| 10 | 9.86 | 11.01
| 11.94
| ✓ |
Nitrate - Nitrogen (g/m3) | 11.3 (Maximum Acceptable Value)
| 4.2
| 2.8
| 2.7
| 3.6 | 4.5 | 6.54
| 6.54
| ✓
|
7.7 Scheme Assets
A summary of material and diameter for pipes in Dunsandel is shown by Figure 7‑4 and Figure 7‑5.
Figure 7‑4 Pipe Material – Dunsandel
Figure 7‑5
Pipe Diameter – Dunsandel
7.8 Operational Management
The water supply is operated and maintained under two maintenance contracts as follows:
- Contract 1241: Water Services Contract. Contract is with SICON who undertakes investigations, conditions inspections, proactive and reactive maintenance and minor asset renewals; and
- Contract 1202: Parks and Reserves Contract. Contract is with SICON who undertakes the maintenance of land scape features related to water services e.g. mowing, gardens etc.
Water quality sampling is completed under an agreement with Food and Health Ltd as required.
7.9 Photos of Main Assets
Photo 1: Site Layout
7.10 Risk Assessment
A risk assessment has been undertaken for the Dunsandel 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 7‑5 outlines the risk priority rating, Table 7‑6 outlines the risks and the list of key projects is found in Table 7‑10. The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.
Table 7‑5 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 7‑6 Risks – Dunsandel
Lack of water storage | Demolish the concrete tank and replace with 33m3 tanks (min 4) | 2014 | 27 | 27 | 12 |
Often power outages (especially when wind storms occur) | Install a generator on this scheme | 2014 | 12 | 2.1 | 2.1 |
Only one source of supply - risk of loss | Investigate suitable location for second bore | 2014 | 6 | 6 | 6 |
Electrical failure due to lightning or network spikes | Install surge diverters | 2014 | 10 | 3.5 | 3.5 |
Failure to meet NES water meter standards | NES Water Meter Compliance | 2014 | 20 | 6 | 6 |
Inability to collect income from non-metered properties | Install property water meters | 2014 | 27 | 0.6 | 0.6 |
Non-compliance with the DWSNZ
| DWSNZ - Age Testing | 2014 | 10 | 0.7 | 0.7
|
Non-consented activities
|
Renewal of consents
| 2014
| 27
| 27
| 6
|
Inadequate treatment under all conditions |
Install filtration | 2017
|
| 40
| 7
|
7.11 Asset Valuation Details
The total replacement value of assets within the Dunsandel water scheme is $1,906,636 with further details in Table 7‑7 below.
Table 7‑7 Replacement Value, Dunsandel
Plant and Equipment
| $596,693
|
Water Reticulation
| Hydrant
| $59,003
|
---|
Lateral | $39,417
|
Pipe
| $1,040,827
|
Supply Point | $136,576
|
Valve | $30,256
|
7.12 Renewals
The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme are shown by Figure 7‑6 below. The majority of renewals occur in 2022/2023.
Figure 7‑6 Dunsandel Water Renewal Profile
7.13 Critical Assets
The criticality model for Dunsandel has been updated for the 2021 AcMP. The methodology of the criticality model can be found in 5Waters Activity Management Plan: Volume 1 and it provides details of how the criticality has been calculated for the reticulation assets. Table 7‑8 and Figure 7‑7 below shows the calculated criticality for all of the assets within this scheme that have a recorded known length.
Table 7‑8 Length of Assets per Criticality Level
5
| Low | 2,559
|
4
| Medium-Low | 3,039
|
3
| Medium | 2,127
|
2
| Medium-High | 1,088
|
1
| High | 0 |
7.14 Asset Condition
The asset condition model was run for Dunsandel in 2021. The methodology of the model can be found in 5Waters Activity Management Plan: Volume 1 which provides details of how the model has been calculated for the pipe reticulation assets. Figure 7‑8 below shows the level of asset condition for these assets within this scheme that have a recorded known condition.
Table 7‑9 provides a description of the condition rating used within the condition model.
Table 7‑9 Asset Condition Grading
1.0 | Excellent |
2.0 | Good |
3.0 | Moderate |
4.0 | Poor |
5.0+ | Fail |
The number of pipe faults is also measured through the asset management system. Figure 7‑9 shows the known historic pipe failures within this scheme.
7.15 Funding Program
The 10 year budgets are shown by Table 3‑12. Budgets are split into expenditure, renewals, projects and capital projects. Expenditure and renewals have been reported on a district-wide basis in Volume 1.
All figures are ($) not adjusted for CPI “inflation". They are calculated on historical data, and population growth where relevant.
Table 7-10 Budget Summary
2021/2022 | $31,000
| $15,000
|
2022/2023
| -
| $590,000
|
2023/2024 | -
| $400,000
|
2024/2025 | -
| -
|
2025/2026 | -
| -
|
2026/2027 | -
| -
|
2027/2028 | -
| -
|
2028/2029
| -
| -
|
2029/2030
| -
| -
|
2031/2032
| -
| $600,000
|
Total | $31,000
| $1,605,000
|
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 7-11 Key Projects
Capital Projects
| -
| WTP Upgrade
| -
| $560,000
| $400,000
| -
| TBC
|
Capital Projects
| -
| Second WTP/source/reservoir
| -
| -
| -
| $600,000
| TBC
|
Capital Projects
| -
| Valves each side of SH
| -
| $30,000
| -
| -
| 100% LoS
|
Capital Projects
| -
| Pressure sensors
| $15,000
|
| | | 100% LoS
|
* Where LoS refers to Level of Service and 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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5-Waters Volume 2 - Water Supplies