<< 5-Waters Volume 2 - Water Supplies

<< Dalethorpe Water Supply

6 Darfield Water Supply

6.1 Scheme Summary

Description		Quantity
Estimated Population Served		3,846
Scheme Coverage (1 Jan 2021)	Full Charges	1,026	Includes 260 restricted connections Rural A 173 connections (629 Units) Rural B 87 connections (211 Units)
	Half Charges	0
	>1 Charges	302
System Components	Bores/Intakes (No.)	2
	Treatment/Disinfection	UV treatment installation underway Chlorination to follow
	Reservoirs (No.)	2
	Pump Stations (No.)	2
	Piped (m)	163,130
History	Original scheme installation date	1971
Value ($)	Replacement Cost	$22,277,512.91
Value ($)	Depreciated Replacement Cost	$13,226,768.38
Financial	Operator cost (scheduled and reactive maintenance) per connection	$111.44/connection
Demand (m³) (1 Jan – 31 Dec 2020)	Average daily	1,893
	Peak daily	4,746
	Minimum daily	36
	Average daily per connection	1.43
Type of Supply		High pressure with restricted and unrestricted
Target Pressure & Flow at boundary	Pressure	>200 kPa (150 kPa restricted)
Target Pressure & Flow at boundary	Flow	>20 L/min (±maric restricted)
Sustainability	Well Security	Secure

6.2 Key Issues

The following key issues are associated with the Darfield water supply. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.

Table 6‑1 Darfield Scheme Issues

What's the Problem	What we plan to do
The water system is subject to high leakage.	Council continue to monitor flows during periods of low flow to quantify estimated losses and consider options to address leakage as deep well water is costly to deliver.
Decision to facilitate growth through provision of further water supply capacity needs to consider the associated wastewater disposal issues.	In considering growth the focus remains on providing sufficient water, however this needs to also account for wastewater management as additional loading to ground may reduce downstream water quality overtime.
Catchment management	Council are investigating groundwater quality within the water supply protection zones, and working with ECan on this matter
Pressure zoning will be required within Darfield's reticulation network as the town expands	Council are developing a Target Pressure Plan and Network Management Strategy
The water supply is becoming more vulnerable to contamination from backflow, because there are industrial, commercial and irrigation sites in Darfield	Council are underway with a district-wide backflow prevention project. In Darfield, 296 rural connections which only contain brass restrictors and air gaps are in the process of being fitted with manifold backflow devices.
The scheme has no ability to chlorinate if required in an emergency	Council are planning for upgrades to the Darfield water supply to allow on-demand chlorination, if there is an emergency or transgression/contamination event.

6.3 Overview & History

A piped water supply was installed for the township in 1971 to replace a system of water races within the township from which property owners pumped directly for their domestic use.

In about 1969 an investigation well was drilled in the Darfield Domain to a depth of 103.5m which in those days was the maximum drilling depth. No water was found and an intake was then installed on the Waimakariri River (No. 1 well). A further intake was installed in 1977 (No. 2 well) and was extended in 1988 with the installation of a 20m long gallery. The supply was further upgraded in 1995/96 with the installation of a new well (No. 3), rising main and booster pump at the reservoir.

The scheme boundary was extended in 1988 to include the then Rural A Zone surrounding the Darfield Township on a restricted supply. The supply was further expanded in 1999 to cover the Rural B area with a restricted supply.

To ascertain if the use of ground water was viable an exploratory well was drilled in 1999 to a depth of 200m adjacent to Horndon Street (eastern end). The well had a capacity of 11 litres/sec. Following public consultation in 2004 it was agreed to continue using the Waimakariri River as the supply source.

Manifolds were installed to replace existing toby valves for the township from 1995 to 2000 and metering of all unrestricted connections began in July 2002.

Prior to November 2011 the Darfield Water Supply provided chlorinated surface water to both the Darfield Township (unrestricted supply) and two restricted supply zones in the rural area surrounding the township. Up to 3.5 m³/day may be used in the Rural A zone and up to 2 m³/day plus stock use is permitted in the Rural B zone. Water was pumped from wells adjacent to the Waimakariri River to the Kimberly Road reservoir from where it was conveyed to Darfield via a gravity main. During peak demands a booster pump located at the reservoir operated to maintain a pressure of 35 psi within the township.

The scheme was designed as a high pressure, unrestricted and restricted supply to meet New Zealand Fire Service Firefighting Water Supplies Code of Practice. A second bulk conveyance main was installed along Kimberly Road in 2007. This PE main increased capacity and allows for main future decommissioning of the AC.

Several other deep bores were drilled in an effort to identify a high-yielding secure groundwater source that could be used without treatment, as an alternative to upgrading treatment of the existing Waimakariri source. This was generally unsuccessful until a high yielding deep groundwater bore source was obtained north-west of the town (SH73 bore) and brought into service in 2011. The Waimakariri River source was retained as a backup source. During November 2011 the wells adjacent to the Waimakariri River were mothballed as Council connected a new deep bore to the Darfield Water Supply. This first deep bore was purchased in 2009 from Stanwood Holdings (Jim Brooker), becoming the primary source for Darfield. The water from this bore is estimated to be 265 years old (limiting concerns of nitrate intrusion), with a flow of 85 L/s. A second bore located on Tramway Road was developed but proved to be of no yield.

A second successful deep bore source was constructed in 2013 and commissioned in 2014, along with a 1000 m³ reservoir and associated pump station at the SH73 site. This allowed full disconnection of the shallow Waimakariri River bore sources and associated treatment plant. The Kimberley Road reservoir has been retained.

A contamination incident occurred in 2012 when the Waimakariri River source was brought back into service after the SH73 bore pump had failed. E. coli was detected in the water supply and illness was reported in the community. It was found that the chlorine supply had been exhausted so the water was not receiving disinfection treatment. A wide range of other contributing factors were identified in a subsequent review.

Currently the Darfield Water Supply Scheme is a high pressure restricted-unrestricted supply. Development of the water supply to the Darfield community has been progressive over time to accommodate population growth and business development.

The Darfield Water Supply Scheme is currently comprised of 2 No. bores, 2 No. reservoirs and 2 No. pump stations feeding the Darfield network.

Figure 6-1
DARFIELD Water - Scheme map
Open larger map: 'Water Scheme'

Figure 6‑2 Scheme Schematic

6.4 System Capacity

Darfield is expected to experience growth in population and new connections over the next 30 years. This will result in an increase in water demand for Darfield. The predicted increase in demand (in accordance with the latest house projections) until 2051 is shown in Figure 6-3. This forecast includes a new commercial development with an assumed demand of 26.4 L/s (0.7 L/s per ha).

Hydraulic models have been used to plan future water infrastructure for Darfield, as part of a master planning exercise. The master planning provides an assessment of the sizing and timing of new infrastructure for new water sources (wells) and pipelines to service growth. Part of the master planning requires a water balance to be developed to forecast growth, using historical peak demand per household. The water balance forecasts the peak instantaneous flow per year versus the water resources available to determine the staging of new wells. The well staging assumes that one well is redundant for each water supply, to take into consideration maintenance of wells, planning/timing of new wells and security of supply i.e. to maintain average/peak demand. The master planning exercise has identified that two new wells be required in Darfield, in year 2027/28 and 2042/43 respectively (Table 6-3).

Two reservoirs (the Kimberley reservoir, 450m³, and the SH73 reservoir, 1000m³) play a vital role in meeting peak hour demand and providing security of supply in the event of loss to the SH73 well and pumps. There is little redundancy for Darfield, because the flow is constrained by the pumping capacity. The Council may consider an additional well in future to increase the resilience of this scheme, in addition to the wells required to meet growth.

V3 Darfield - Water Balance Assessment.PNG
Figure 6‑3 Darfield Water Demand

Table 6‑2 Water Source Current Capacity

Sites Available	Well	Capacity (L/s)	Comments
State Highway 73	1	63	Maximum available flow 83 L/s from surface pumps
State Highway 73	2	71	Maximum available flow 83 L/s from surface pumps

Table 6‑3 Water Source Future Capacity Required

New Site ID	Indicative Location	Planning Year	Yield (L/s)
Darf1	Creyke Road	2027/2028 (2021/22 Drilling)	45
Darf2	Creyke Road	2042/2043	45

Darfield - Master Plan.png

Figure 6‑4 Darfield Master Plan

6.5 Resource Consents

The Darfield water supply has a number of resource consents. Table 6‑4 shows the water take permitted by the resource consents for this scheme.

Table 6‑4 Resource Consents

Consent	Description	Location	Date Issued	Expiry Date	Bore	Consented Max Instantaneous Flow (L/s)	Consented Max Daily Volume (m³/day)
CRC960148.1	To take groundwater.	Old West Coast Road, DARFIELD	29-Sep-09	29-Sep-30	L35/0534	30	2,592 or 7,344 when combined with consents CRC991423 and CRC143985
CRC143985	To take and use groundwater for the purposes of community supply.	Bangor Road, DARFIELD	28-Mar-14	16-Nov-45	L35/0980 BX22/0006	83 (combined rate)	6,000 or 7,344 when combined with consents CRC991423 and CRC960148
CRC991423	To take and use water for public supply - Waimakariri river flow	Waimakariri River Bed, BLEAK HOUSE ROAD	9-Sep-04	8-Sep-39	Waimakariri River shallow bores L35/0176 and L35/0245 and L35/0534	85 (combined rate) Depending on river flows	5,460 (combined) Depending on river flows; Cannot be exercised concurrently with consent CRC960148
CRC991604	To divert water for the water supply wells at Bleak House Road	Waimakariri River Bed, BLEAK HOUSE ROAD	9-Sep-04	8-Sep-39	N/A Diversion of water from Waimakariri River Bed to water supply wells	Combined with CRC991423	Combined with CRC991423

6.6 Water Quality

The Darfield water supply is currently deemed to be a secure source. Sampling is conducted monthly within the treatment plant and weekly within the reticulation. Darfield also has a back-up supply (from the Waimakariri River) which is only tested if used - the results below only reflect testing from the SH73 deep bores.

The following details E. coli transgressions for the sample periods 2012 to 2020. There has been no E. coli identified in sampling at both of the SH73 bores.

Treatment

There have been no E. coli treatment transgressions during this period.

Zone

There have been two E. coli zone transgressions during this period. These occurred in August 2012 and December 2013.

Chemical Analysis

The following is a summary of the raw water chemical analysis carried out at the Darfield Water Supply. As both wells source water from the same aquifer, only one well is sampled.

Table 6‑5 Raw Water Chemical Analysis Darfield Water Supply

Parameter	Standards	Plant 2015	Plant 2017	Plant 2018	Plant 2019	Status
Total Lead (g/m3)	0.01 (Maximum Acceptable Value)	0.00132	0.000373	0.000209	0.000172	✓
pH (pH units)	7-8.5 (Guideline Value)	7.8	7.7	7.6	7.7	✓
Total Hardness (g/m3 as CaCO₃)	<200 (Guideline Value)	62	54.5	57.2	56.0	✓
Total Calcium (g/m3)	n/v	21	18.64	19.66	19.17	✓
Total Iron (g/m3)	<0.2 (Guideline Value)	<0.021	< 0.021	<0.021	<0.021	✓
Total Sodium (g/m3)	<200 (Guideline Value)	9.8	9.56	10.08	9.67	✓
Nitrate - Nitrogen (g/m3)	11.3 (Maximum Acceptable Value)	5.8	4.99	5.30	5.02	✓

6.7 Scheme Assets

A summary of material and diameter for pipes in Darfield is shown below by Figure 6‑5 and Figure 6‑6.

Figure 6‑5 Pipe Material – Darfield

Figure 6‑6 Pipe Diameter – Darfield

6.8 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.

6.9 Photos of Main Assets

Photo 1: SH73 Bore No 1	Photo 2: SH73 Bore No 2, Reservoir
Photo 3: SH73 Booster Pump Shed and Reservoir	Photo 4: Kimberley Road Reservoir

6.10 Risk Assessment

A risk assessment has been undertaken for the Darfield 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 6‑6 outlines the risk priority rating, Table 6‑7 outlines the risks and the list of key projects is found in Table 6‑12.

Table 6‑6 Risk Priority Rating

Risk Score	Level of Risk	Risk Response
> 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 6‑7 Risks – Darfield

Risk	Action/Project	Year Identified	2014 Risk Rating	2017 Risk Rating	Residual Risk Rating
Failure of single pipe connection from source to township	Review options to include redundancy within the reticulated network with focus on linkages between the reservoir site and township.	2014	40	40	20
Failure of the main pipe from the reservoir would drain the Kimberly Rd reservoir	Install a 300mm non-return valve as a backflow provision at SH73 on or near the Haldon Street corner	2014	40	40	40
Lack of capacity for the growth in Darfield	Install additional bores for capacity in the future	2014	45	45	20
Lack of capacity for the growth in Darfield	Investigate the pump operations, to allow both wells to run at the same time, need power cable upgrade	2014	45	45	20
No reservoir turnover/usage at Kimberly road	Review Reservoir turnover and upgrade controls including auto flushing as required	2014	20	3.5	3.5
Unmarked critical water infrastructure could be damaged by others causing system failure	Install marker posts	2014	40	20	20
Electrical failure due to lightning or network spikes	Install surge diverters	2014	20	7	7
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	45	0.6	0.6
Non-compliance with the DWSNZ	DWSNZ - Age Testing	2014	20	0.7	0.7
Non-compliance with the DWSNZ	DWSNZ - Bore-head security	2014	20	20	20
Non-consented activities	Renewal of consents	2014	27	27	6
pump failure long lead time for pump	Spare pump	2017		6	2.1

The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.

6.11 Asset Valuation Details

The total replacement value of assets within the Darfield water scheme is $22,277,512.91 with further details in Table 6‑8 below.

Table 6‑8 Replacement Value, Darfield

Asset Class 1	Asset Class 2	Sum of Replacement Value
Plant and Equipment		$3,599,100
Water Reticulation	Hydrant	$464,134
	Lateral	$625,949
	Pipe	$15,901,984
	Supply Point	$1,227,391
	Valve	$458,955

6.12 Renewals

The renewal profile has been taken from the 2019 5 Waters Valuation. A graph showing the renewals for this scheme is shown in Figure 6‑7 below. The majority of renewals occur in 2020/2021.

Figure 6‑7 Darfield Water Renewal Profile

6.13 Critical Assets

The criticality model for Darfield 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 6‑9 and Figure 6‑8 below shows the calculated criticality for all of the assets within this scheme that have a recorded known length.

Table 6‑9 Length of Assets per Criticality Level

Criticality Bands		Length (m)
5	Low	105,718
4	Medium-Low	28,862
3	Medium	13,694
2	Medium-High	14,625
1	High	3,709

Figure 6-8
DARFIELD Water - Criticality map
Open larger map: 'Water Criticality'

6.14 Asset Condition

The asset condition model was run for Darfield 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 6‑9 below shows the level of asset condition for these assets within this scheme that have a recorded known condition.

Figure 6-9
DARFIELD Water - Condition map
Open larger map: 'Water Condition'

Table 6‑10 provides a description of the condition rating used within the condition model.

Table 6‑10 Asset Condition Grading

Condition Rating	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 6‑10 shows the known historic pipe failures within this scheme.

Figure 6-10
DARFIELD Water - Pipe Faults map
Open larger map: 'Water Pipe Faults'

6.15 Funding Program

The 10 year budgets for Darfield are shown by Table 6‑11. 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 6‑11 Darfield Budget Summary

Years	Projects	Capital Projects
2021/2022	$25,000	$1,008,510
2022/2023	-	$686,150
2023/2024	-	$387,930
2024/2025	-	-
2025/2026	-	-
2026/2027	-	-
2027/2028	-	-
2028/2029	-	-
2029/2030	-	-
2030/2031	-	-
Total	$25,000	$2,082,590

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.

There are a number of major projects for Darfield water scheme in the LTP budget.

Table 6‑12 Key Projects

Account Label	GL	Description	Year 1($)	Year 2($)	Year 3($)	Years 4 to 10	Funding Split *
Capital Projects	401590001	Darfield Water Supply Upgrades	$1,008,510	$336,150	$187,930	-	100% Growth
Capital Projects	TBC	Connect bottom end of Sheffield reticulation to Darfield scheme to improve turnover of Kimberley reservoir	-	-	$200,000	-	100% LoS
Capital Projects	TBC	Additional small reservoir at Kimberley Road to allow maintenance; pressure sensors; pipe upgrades	-	$100,000	-	-	100% LoS
Capital Projects	TBC	RPZ backflow devices between urban and rural parts of reticulation	-	$250,000	-	-	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.