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5-Waters-Volume-3-Wastewater
1 Arthurs Pass Wastewater Scheme
1.1 Scheme Summary
Estimated Population Served
| 29
|
Scheme Coverage
(1 Jan 2021)
| Full Charges
| 9
|
| Half Charges | 1
|
| >1 Charges | 0
|
System Components
| Piped (m) | 430
|
| Manholes (No.) | 7
|
| Pump Stations (No.) | 0
|
| Treatment | Primary and Secondary Septic Tank
|
| Disposal | Sand beds
|
| History | Original scheme installation date | 1999
|
Value ($)
| Replacement Cost | $304,471
|
| Depreciated Replacement Cost | $193,875
|
Financial
| Operator cost (scheduled and reactive maintenance) per connection
| $6,023.64/connection
|
Demand
(1 Jan - 31 Dec 2020)
| Annually (m3) | 5,310
|
| Average daily (m3) | 14.5 |
| Peak daily (m3) | 2,561
|
| Minimum daily (m3) | 0.0
|
| Infiltration | - |
| Sustainability | Ultimate discharge point | Discharge to ground within a national park |
1.2 Key Issues
The following key issues are associated with the Arthurs Pass Wastewater Scheme. A list of district wide issues are located in 5Waters Activity Management Plan: Volume 1.
Table 1‑1 Arthurs Pass Scheme Issues
| Cost of scheme operation and maintenance | Council will review options to reduce operation and maintenance costs and optimise renewals. In September 2015, the facility was inspected. It was found that the Rough Creek STP appears to be performing well, and is consistent with the expectations outlined in the design of the system.
|
1.3 Overview & History
The sewer network serves the southern side of Sunshine Terrace (originally known as Rough Creek Subdivision). The sewage gravitates to a large septic tank and sand soakage disposal area. The majority of properties in the village have on-site septic tanks.
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 event occur.
Figure 1‑2 Scheme Schematic
1.4 System Capacity
In general the Arthurs Pass scheme is underutilised as the occupancy rate within the houses that the scheme serves is low. There are peak periods but these too are well within the consented limits. During freezing conditions people tend to run their taps resulting in peak flows, but these are isolated cases. Refer to Section 1.6.3 for the design capacity of the system.
There is not expected to be significant growth in the area serviced by this scheme and scheme expansion is not expected to be required over the planning horizon of this AcMP.
1.5 Resource Consents
The Arthurs Pass wastewater scheme has a number of resource consents. Table 1‑2 shows the discharge permitted by the resource consents under Selwyn District Councils name in Arthurs Pass.
Table 1‑2 Resource Consents
CRC073351
| To discharge contaminants to land | Sunshine Terrace Road, ARTHURS PASS | 5-Nov-07 | 30-Oct-27
| 23
|
1.6 Scheme Assets
A summary of the assets within this scheme is outlined in this section.
1.6.1 Reticulation Overview
A summary of material and diameter for pipes is shown in Figure 1‑3 and Figure 1‑4.
Figure 1‑3 Pipe Material – Arthurs Pass
Figure 1‑4 Pipe Diameter – Arthurs Pass
1.6.2 Treatment and Disposal
Treatment and disposal consists of primary and secondary septic tanks which enables settlement of solids. Partially treated effluent is then discharged to a sand soakage bed. There are no known issues with the Arthur's Pass treatment and disposal facilities. Details are tabled below.
Table 1‑3 Treatment and Disposal
| Primary Septic Tank | 23.6m3 elliptical tank with dia. 3.8 x 3.1 and height 2.9m | 1999 |
Secondary septic tank
| 15.9m3 elliptical concrete tank dia. 3.8 x 3.1 and height 1.9m, with two Zabel filters | 1999
|
| Pump chamber in secondary chamber | Two submersible pumps (1 duty and 1 standby) | 1999 |
Sand Soakage bed
| 23m x 10m x 800mm deep, also contains 3 plate lysimeters for monitoring purposes | 1999
|
1.6.3 Design
The design data for the Arthur's Pass system is tabled below.
Table 1‑4 Design Data
Full time
| 22 | 250 | 5.5 |
13.9
|
| Lodge | 78 | 120 | 9.36 |
| Holiday house | 42 | 180 | 7.56 |
| Combined | 142 | |
22.42 |
Currently the treatment plant and consent capacity is underutilised.
1.6.4 Pump Stations
There are no pump stations within the Arthur's Pass reticulation. There is a pump chamber and two pumps at the secondary septic tank pumping partially treated effluent to the sand soakage bed.
1.7 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.
1.8 Photos of Main Assets
Photo 1 - Pump Station
1.9 Risk Assessment
A risk assessment has been undertaken for the Arthurs Pass 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 1‑5 details the risk priority rating and Table 1‑6 outlines the risks.
Table 1‑5 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 1‑6 Risks – Arthurs Pass
| Non-consented activities | Renewal of consents | 2014 | 27 | 27 | 6 |
| Sewerage system becomes uneconomic | Review operating costs and report on value engineering opportunities | 2014 | 12 | 12 | 6 |
The list of district wide risks can be found in 5Waters Activity Management Plan: Volume 1.
1.10 Asset Valuation Details
The total replacement value of assets within the Arthurs Pass Scheme is $304,471 as detailed in Table 1‑7 below. The majority of value is made up of plant and equipment.
Table 1‑7 Replacement Value, Arthurs Pass
Plant and Equipment
| $216,106
|
Wastewater Reticulation
| Lateral | $33,706
|
| Manhole | $16,797
|
| Pipe | $37,862
|
1.11 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 1‑5 below.
Figure 1‑5 Arthurs Pass Wastewater Renewal Profile
1.12 Critical Assets
The criticality model for Arthurs Pass 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 1‑8 and Figure 1‑6 below show the calculated criticality for all of the assets within this scheme that have a recorded known length.
Table 1‑8 Length of Assets per Criticality Level
5
| Low | 104 |
4
| Medium-Low | 176 |
3
| Medium | 0 |
2
| Medium-High | 0 |
1
| High | 0 |
1.13 Asset Condition
The asset condition model was run for Arthurs Pass 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 1‑7 below shows the level of asset condition for all of the assets within this scheme that have a recorded known condition.
Table 1‑9 provides a description of the condition rating used within the condition model.
Table 1‑9 Asset Condition Grading
| 1.0 | Excellent |
| 2.0 | Good |
| 3.0 | Moderate |
| 4.0 | Poor |
| 5.0+ | Fail |
1.14 Funding Program
There are no projects specific to Arthurs Pass in the 10 year budgets.
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5-Waters-Volume-3-Wastewater
