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Ecological water and wastewater engineering
DRAFT
Onsite wastewater services: Engineering and EIA Report
For ZROCK Ltd
Site: 437 Cathedral Rd, Cheviot
Date: 16 February 2013
Prepared by
Andrew Dakers
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DOCUMENT CONTROL SHEET
Client ZROCK Ltd Job # 121203GL
Project Title DRAFT: On-site wastewater management services: Port Robinson Camping Ground
Document Title Engineering and EIA Report
Document Ref. 121203GL DR-2
This Document Comprises
Total No. of Pages
List of Tables List of Figures No. of Appendices
25 9 7 0
Rev. Status Author(s) Reviewed By Office of
Origin Issue Date
OR-1 Client Issue
Andrew Dakers Christchurch 13 December 2012
DR-2 Client Issue
Andrew Dakers Christchurch 16 February 2013
63 Bowenvale Avenue, Christchurch, New Zealand Ph (64) (3) 942 7954 Mobile: (64) 021 533386 Email: [email protected] Website: www.ecoeng.co.nz
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Contents 1 Acronyms .................................................................................................................................................. 5
2 Background ............................................................................................................................................... 5
3 Site details ................................................................................................................................................. 5
4 Site Assessment ........................................................................................................................................ 6
4.1 Soils .................................................................................................................................................... 7
5 Wastewater loads ..................................................................................................................................... 9
6 Proposed OWMS ..................................................................................................................................... 10
6.1 Design details. .................................................................................................................................. 11
6.1.1 Septic tank ................................................................................................................................. 11
6.1.2 Grease trap ............................................................................................................................... 11
6.1.3 Horizontal Subsurface flow wetland (HSFW) ............................................................................ 11
6.1.4 Flout and flout chamber ........................................................................................................... 12
6.1.5 Soakage/storage bed ................................................................................................................ 12
6.1.6 The effect of incident rainfall on the wetland .......................................................................... 13
6.2 System components. ........................................................................................................................ 13
Figure 3. Schematic layout .............................................................................................................................. 15
Figure 4. HSFW Cross-Section ......................................................................................................................... 16
Figure 5. Recommend location of main features ........................................................................................... 17
Figure 6. Cross-section of the soakage/storage bed ...................................................................................... 19
7 Consentability ......................................................................................................................................... 19
7.1 Canterbury Regional Council Regional Rules ................................................................................... 19
7.2 Building Act 2004 and regulations ................................................................................................... 22
8 Operation and Management .................................................................................................................. 22
9 Risk assessment, assessment of environmental effects, risk mitigation ................................................ 23
Consultation .................................................................................................................................................... 23
9.1 Effects on groundwater and coastline ............................................................................................. 23
Figure 7. Discharge point in relation to coastal zone, groundwater flow direction and provide property .. 24
9.2 Surface ponding ............................................................................................................................... 24
9.3 Cultural impacts ............................................................................................................................... 24
10 PRODUCER STATEMENT – DESIGN ......................................................................................................... 26
Figures
Figure 1. Site location ....................................................................................................................................... 6
Figure 2. Site location ....................................................................................................................................... 7
Figure 3. Schematic layout .............................................................................................................................. 15
Figure 4. HSFW Cross-Section ......................................................................................................................... 16
Figure 5. Recommend location of main features ........................................................................................... 17
Figure 6. Cross-section of the soakage/storage bed ...................................................................................... 19
Figure 7. Discharge point in relation to coastal zone, groundwater flow direction and provide property .. 24
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Tables
Table 1. Project: On-site wastewater management services: Port Robinson Camping Ground . .................... 5
Table 2. Description of affected ecosystem ..................................................................................................... 6
Table 3. Soil profiles ......................................................................................................................................... 8
Table 4 Analysis of soils .................................................................................................................................... 8
Table 5. Permitted Activity Conditions. NRRP, WQL9 ................................................................................... 20
Table 6 Permitted Activity Conditions. Proposed LWRP, Rule 5.9. ................................................................ 21
Table 7. Building Act 2004 Requirements ...................................................................................................... 22
Table 8. Actual and Potential Effects: Check list ............................................................................................. 23
Table 9. Assessment of cultural impacts. ....................................................................................................... 25
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1 Acronyms amsl: Above mean sea level AS/NZS Australia and New Zealand Standards DLR: Design loading rate defined by AS/NZS1547:2012 Table L1. HSFW: Horizontal subsurface flow wetland LAS: Land application system LASE: LAS envelope LWRP: Land and Water Regional Plan N/A: Not applicable NRRP: Natural Resources Regional Plan OWMS: On-site wastewater management service p.e. Population equivalent. Design occupancy for the dwelling.\ SPn: Soil pit number “n”. ST: Septic tank (as defined in AS/NZS1547:2012 STSA: Septic tank suitability area (Rule 5.9, LWRP) TN Total nitrogen TP58: ARC Environment. 2004. On-site wastewater disposal from households and
institutions. Auckland Regional Council. Technical Report 58. VN: Visitor night
2 Background This report presents the engineering details for the preferred wastewater servicing option for a proposed camping ground facility, 437 Cathedral Rd, Cheviot This is a green fields development. There is no reticulated wastewater service to this site. Under Canterbury Regional Council Rule WQL9, NRRP, and Rule 5.9 pLWRP, ecoEng has assessed this site as a restricted discretionary activity, requiring a resource consent to discharge. Refer to Section 7.
3 Site details Table 1. Project: On-site wastewater management services: Port Robinson Camping Ground .
Job Number 121203GL
Client identity and contact details.
Gordon Lidgard, ZROCK Ltd. Phone: 03 3198994######## [email protected]
Agent N/A
Special Circumstances. Green fields development. No mains power to the site. Only power supply is a low voltage DC supply.
Site location (address). 437 Cathedral Rd , RD3, Cheviot See Figure 1.
Legal description. Lot 1 DP 324200
Area of land parcel 8.5 ha
District Council. Hurunui
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Regional Council. Cantebury
Grid Reference/GPS . WSG84: S42 53.261 E173 18.452
Elevation 10 to 16m amsl
Number of camping sites 30. Refer to Section 5
Wastewater loads. Refer to Section 5
Figure 1. Site location
4 Site Assessment A site assessment by ecoEng was carried out on the December 2012. The key site features are summarized in Table 2. Table 2. Description of affected ecosystem
Issue Description
Site within the STSA? This site is in an unmapped area with respect to the STSA designated by pLWRP 5.9.
Silent files No silent files on this site
Ngai Tahu settlement area None
Topography South east facing linear planar slope at about 4%
Soil description Refer to Section 3.1
Groundwater (gw) direction No data available. Likely south east to the coast.
Aquifer type No data available.
Depth to gw No local data available. The site is more than 10m above mean sea level and it is only 100m to the high tide line. There is no evidence of groundwater emerging between the property and
Site location
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the coastline. It is very likely groundwater depth will be more than 6 m below ground level.
Water supply to property Cheviot Rural Water Supply
Neigbouring water supplies Unknown
Groundwater quality No data
Community supply No community supply within 1km
Groundwater wells No wells with 1km of this site
Springs No wells with 100 km of this site
Surface water bodies and quality
There is a farm drain in the neighbour’s property on the NE boundary. Refer to Figure 2.
Flood risk No flood risk
Figure 2. Site location
4.1 Soils
ecoEng carried out a detailed soils assessment on the site on the 5 December 2012. Two soil pits (SP1 and SP2, Figure 2) were dug to assess the soil profiles to a depth of up to 1400mm .
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Details of the soils assessment follow. The Soil Bureau soil maps (Bulletin 27 1968) classify the soils in the area as Medina (26b) , a medium silt loam. Table 3. Soil profiles
Soil Pit 1 - SP1.
Total pit depth 1400
Sample(s) taken at: Two samples at 650 mm and 1300mm
Depth (mm) Description
0 – 150 Topsoil. Moderate structure. No aggregates.
150– 850 No aggregates. Loam/silt. No mottling. Moderate structure.
850 – 1000 Small stone grit. Structureless. No mottling.
1000 – 1400 Silty clay. Very stony at 1400mm. Structureless. No mottling.
SP2 soil pit exhibited a very similar profile to SP1
Photo 1 of SP1
Photo 2 of SP2
Table 4 Analysis of soils
Assessment parameter
Sample 1 Sample 2
Sample location Sample taken for SP1 at depth 600-700 mm
Sample taken for SP1 at depth 600-700 mm
Bolus strength Weak Weak
Colour – Munsell chart.
Olive brown 2.5y 4/4. Light olive brown 2.5y 5/4.
Grittiness Fine gritty Fine gritty
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Sponginess Moderate Moderate
Stickiness Nil. Nil.
Stain Clay stain Clay stain
Thread test/plasticity No thread. Low plastic No thread. Low plastic
Ribbon length (mm) 20, 25, 20 40, 40, 30
Feel (smooth, silky) Nil Nil
Shearing resistance Moderate Moderate
Slaking Slake 3, high slaking Slake 3, high slaking
Dispersivity Nil Nil
Texture description Fine sandy loam Fine sandy loam
Category (Table E1, 1547)
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Key findings For the purposes of design of the land application area, the soil is classified as a Category 3, moderately drained (Refer AS/NZS 1547 2012, Table E1).
5 Wastewater loads The actual wastewater volumes for camping grounds depend on facilities provided and can vary from 50 to 130L/day per overnight visitor, (TP58, Ch 6). At this site the basic facilities will include:
1 toilet block – separate male and female facilities with water efficient flush toilets, hand basins and shower units (with low water use shower heads, see http://www.nrl.co.nz/showerheads.aspx ) and no urinal;
1 laundry with wash tub only and no washing machine;
1 kitchen with sinks The volumes of grey and blackwater per p.e. are based on TP58 recommendations and have taken into consideration the installation of water saving technologies, as noted earlier. The proposed system provides for the following wastewater loading scenarios:
Total annual visitor nights (VN) of 7300. (Used to determine sludge accumulation rate).
Full occupancy camping; 30 camping sites at 3.5 campers/site
Four 2 day large events/yr where a large event is 2 days with a maximum of 250 VN/day or 500VN/event.
Scenario 1 Annual VN 7300 Average VN/day (AVNd) 20 Sludge accumulation 80 L/AVNd/yr
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Total annual sludge accumulation 1600 L/yr Pump out frequency, every 3 years Total sludge storage required 4800 L
Scenario 2 Full occupancy camping No. of camp sites 30
Max occupancy/site 3.5 Maxi number of visitor nights 105 Blackwater daily volume/p.e 30 L/day Greywater daily volume/p.e. 60 L/day Design daily blackwater volume 3150 L/day Design daily greywater volume 6300 L/day Total daily peak volume to soakage trenches 9450 L/day
Scenario 3. One-off large event Maximum campers 250
Duration 2 Maxi number of visitor nights/event 500 Blackwater daily volume/p.e 30 L/day Greywater daily volume/p.e. 60 L/day Peak daily blackwater volume 7500 L/day Peak 2-day greywater volume 15000 L/day Design average daily greywater volume to wetland 6600 L/day Total daily peak volume (2 day duration) to soakage trenches 22500 L/day
Loadings used for design
The septic tanks have been design for a capacity for a peak load of 7500L/day and 7300 VN/yr (the latter to calculate annual sludge accumulation rate).
The wetland has been designed for greywater load of 15,000L/day for 2 days followed by 3 days of no more than 800L/day loading. This corresponds to a peak daily average load of an average of about 6600L/day. The design hydraulic retention time of 4.5 days has been adopted for the design of a HSFW to treat greywater.
The soakage/storage bed has been designed for a soakage rate of 4320L/day and a storage capacity of 32326L.
6 Proposed OWMS Full details and specifications of the proposed OWMS are presented in the ecoEng Installation Report 17 February 2013. It has been agreed (with the property owner) to separate grey and blackwater. Black water is to be advanced primary treated with a multi chamber (enlarged) septic tank system fitted with a commercial filter(s). The greywater to be treated using a horizontal subsurface flow wetland (HSFW). The kitchen wastewater would first pass through a grease trap before being discharge to the HSFW. Secondary effluent from the wetland is to be dose loaded (using flout) to a soakage/storage bed. The septic effluent would drain, via the same flout chamber, to the same soakage/storage bed.
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The soakage and storage bed provides three key functions:
Final soakage to ground of treated grey and blackwater;
Storage of treated wastewater during high peak flow events;
Emergency pump out and cartage off-site should excessive loading pump out and cartage off-site should excessive loading be experienced.
The soakage/storage bed is to be fitted with a visual water level indicator. The purpose of this is to indicate to the camping ground manager when the storage is approaching near full.
6.1 Design details.
6.1.1 Septic tank
A dual chamber conservatively design septic tank system is proposed. For a design daily flow of 7500L/day (Scenario 3), annual VN of 7300 and sludge pump out frequency of 3 years, the minimum recommended septic tank capacity is 7300+4800 = 12,100L. (Ref: Crites and Tchabanoglous, 19981) The proposal is to install two 10,000L septic tanks with the final tank to be fitted with commercial septic tank filters with a flow capacity of 7500L/day. An example of a suitable filter would be Zabel A100-12 Series. The increased septic tank capacity with a high quality septic filter will ensure advanced primary treatment. The residence time for peak events will be greater than 2 days and for a full camping ground will be nearly 5 days. Normal accepted residence time for septic tank design is 1 day. (Ref: Crites and Tchabanoglous, 1998)
6.1.2 Grease trap
A commercial grease trap is recommended to receive kitchen sink wastewater. The recommended capacity is at least 2000L. (Example of a suitable grease trap would be the Hynds GT3000). This is based on:
Recommended volume 1 to 3 times average daily wastewater volume from kitchen sink (Ref: Crites and Tchobanoglous1 (p326) and TP58 (7.2.6)).
Calculation of kitchen wastewater volume is based on 15L/camping group/day. (typically a camping group will wash once per day however to be conservative it is assumed 2 washes per camping group/day. For 30 sites at full capacity this is corresponds to 2 x 30 x 15 = 900L/day.
In the case of the large 250 person 2 day event, it has been assumed an average of 5 person/group therefore 50 x 2 x 15 = 1500L/day.
A grease trap capacity of 2000L would seem appropriate.
6.1.3 Horizontal Subsurface flow wetland (HSFW)
The design criteria for the HSFW are for greywater are:
Average daily flow 6600L/day;
1 Crites, R and G Tchobanoglous. 1998. Small and decentralised wastewater management. McGraw Hill.
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Hydraulic retention time 4.5 days;
Inlet to be humus and geofabric filter (to mitigate build-up of organics at the wetland inlet);
Graded sand zone at outlet for physical filtering;
Extended freeboard (200mm) for emergency storage.
As noted above the wetland has been designed for greywater load of 15,000L/day for 2 days followed by 3 days of no more than 800L/day loading. This corresponds to a peak daily average load of an average of about 6600L/day. For the full camping occupancy scenario (Scenario 2) the maximum daily greywater volume is only 3150L/day. This corresponds to a hydraulic retention time of over 9 days.
6.1.4 Flout and flout chamber
Treated effluent from the septic tank and the HSFW drain to the flout chamber. The recommended dose volume from the flout chamber to the soakage bed is at least 500L. The dose is to be released into one of the centre 250mm PVC pipes within the bed.
6.1.5 Soakage/storage bed
The design loading rate (DLR) of the soakage/storage bed is based on the following criteria and considerations:
DLR is to be based on Table L1, AS/NZS1547:2012;
Soil category 3 structureless soil. (Note a structureless soil offers no additional impediment to water permeability).
The effluent quality from the wetland will be secondary and is the greater volume. The effluent quality from the septic tank is advanced primary, and is the lesser volume. Table L1 recommends DLR 15 mm/day to 50 mm/day, for well or moderately structured Cat 3 soils depending on effluent quality.
The loading to the soakage trench is seasonal; offering rest periods of either no loading or very low loading.
Based on the above criteria and consideration, ecoEng recommends a DLR of 30mm/day. This is considered conservative for this site. The soakage area recommended is 18m x 8m = 64m2 . At 30mm/day this corresponds to a daily soakage rate of 4320L/day. The storage capacity of the bed is 32,326L. The following is an analysis of the two loading scenarios; Scenarios 2 and 3 (Refer to Section 5).
Scenario 2
No of occupied campsites 30 No. of campers/site 3.5 Maximum occupancy VN/day 105 Total volume to soakage 9450 L/day
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Daily volume in excess of daily soakage 5130 L/day Max no. of full occupation days before overflow 6.3 days Time to empty full soakage bed 7.5 days
The key outcomes of the above Scenario 2 analysis are:
The soakage/storage bed will reach maximum capacity after 6 days of full camping ground occupancy.
If the storage bed is not pumped out it will take at least 7 to 8 days for the stored volume to soak away.
Scenario 3
Event occupancy 250 campers Duration of event 2 days Total VN per event 500 Total grey and blackwater volume to soakage/event 36360 L Total soakage during event 8640 L Post event storage requirement 27720 L Storage remaining post event 4606 L Zero discharge period, post event for total soakage 6.5 days
The key outcomes of the above Scenario 3 analysis are:
The storage capacity within the soakage bed is more than sufficient (spare 4606L)
If the storage is not to be pumped out it will take about 6-7 zero load days for the storage to empty by soakage to ground.
Note: The maximum number of large events proposed is 4 / year.
6.1.6 The effect of incident rainfall on the wetland
Rainfall into the wetland will add to the volume of water to be discharged from the wetland. The 24hr 1:10yr rainfall event for this site is about 115mm ( HIRDS data, NIWA Depth duration rainfall data). This corresponds to an input volume to the wetland of 19,000L, just over half the storage capacity (32,326L) of the bed. While occupancy of the camping ground is likely to be low or zero during wet weather, there are several management strategies to deal with such an event. These include:
Raising the adjustable outlet of the wetland to provide additional storage within the wetland. The wetland has been designed to offer about 31,000L of buffer storage within the freeboard zone. This can then be strategically released to the soakage bed.
Pump out the storage bed.
Allow for low to zero camping ground occupancy post large rainfall events. Note: The soakage/storage bed is mounded to shed incident rainfall.
6.2 System components.
As noted above, full details and specifications of the proposed OWMS are presented in the ecoEng Installation Report 17 February 2013.
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The key system components are illustrated is follows:
Figure 3 is a schematic flow diagram of the proposed system. Figure 4 shows wetland details. Figure 5 is a possible layout within the site of key features. This layout allows gravity flow to all
components. Figures 5 and 6 illustrate the details of the soakage bed.
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Figure 3. Schematic layout
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Figure 4. HSFW Cross-Section
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Figure 5. Recommend location of main features
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Figure 6. Cross-section of the soakage/storage bed
7 Consentability
7.1 Canterbury Regional Council Regional Rules
The consentability of for this site has been assessed by ecoEng Ltd in terms of Natural Resources Regional Plan, Environment Canterbury June 2011, Rule WQL9, Discharge contaminants into land from an on-site wastewater system, and the proposed Land and Water Regional Plan (LWRP), rule 5.9. Conditions not met include:
Plan Rule Description
NRRP WQL9 (Table 5)
1 Daily discharge > 2000L 9a Groundwater depth less than 6m?
11 a Set back from boundary less than 5 m. 12a 2AQ sand is not proposed for the soakage bed.
LWRP (Table 7) 1 Weekly discharge >14,000L 2 Located in an un-mapped STSA area
It is ecoEng’s assessment that this proposal is therefore a discretionary activity. ecoEng is satisfied that all building code requirements can be met. Refer to Table 8.
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Table 5. Permitted Activity Conditions. NRRP, WQL9
Condition Criteria Comments
1 &2 The wastewater is domestic wastewater and the maximum daily discharge will not exceed 2000L.
3 There is to be no discharge of wastewater to surface waters or into groundwater.
4 There is to be no surface ponding or seepage.
5 Property boundary is not be within 30m of a sewage pipeline network and property is less than 4 ha, and distance from wastewater source to the network is less than 60m and network operator will accept the wastewater.
6. Existing system
Specifies conditions that apply where there is an increase in the volume of the discharge or a modification of the system.
N/A
7. Existing system
Specifies conditions that apply should the system be located within a community drinking water supply protection zone (refer to schedule WQL2).
N/A
8a A setback of 20 m is required from a river, lakes, artificial water course or the coastal marine area.
8b Elevation to be less than 1200 m above mean sea level.
8c Land slope to be less than 20°
8d The land is not at risk from a flood event 2% AEP (1 in 50 yrs event) or where water is known to pond for at least 2hrs from a one in five year rainfall event.
8e Setback from a wetland boundary to be 20 m N/A
9a For an unconfined or semi confined aquifer the highest groundwater table is to be 2 m below ground level for subsurface drip irrigation fields, and 6 m for all other land application systems.
?
The actual gw level is unknown but likely to be >6m. Refer to Table 2.
9b For coastal confined aquifers, and for all land application systems, there is to be at least 2 m separation between point of application and Aquifer 1 and any water table overlying Aquifer 1
N/A
10 a Refers to set backs from community drinking water supply sources. Refer to Part A Schedule WQL6.
10 b
Setback from any private bore is to be 50m up gradient and 30m down gradient (Refer to Part B Schedule WQL6), unless the land application system is a drip irrigation field, the lot area is greater than 1 ha or a reticulated water supply provides drinking water to all properties in the area.
11a For land application systems other than subsurface irrigation fields, the set back from a boundary is to be 20 m to the nearest down gradient boundary in the direction of groundwater flow and 5 m to all other boundaries.
11b For subsurface irrigation fields, the set back from all boundaries is to be at least 2 m
N/A
12a For trenches, beds or mounds, 600 mm of 2A (or equivalent ) sand is required and wastewater is to be dose loaded evenly at no more than 50L/ m² per day.
12b For subsurface irrigation fields, pressure compensating drippers are required and hydraulic loading to be in accordance with AS/NZS1547, Table 4.2A4.
N/A
13 For trenches, beds or mounds an equivalent reserve area is required.
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14. The wastewater is to pass through a proprietary effluent filter before being discharged to the land application system.
15 A copy of the design plan is to be submitted to Ecan at least 20 working days prior to the installation of the system.
16 Completion certificate is to be provided to Ecan.
17 The system is to be operated and maintained in accordance with the system’s design specifications.
18a Primary treatment tanks are to have appropriate access and inspection points.
18b Primary treatment tanks are to be inspected at lease every three years.
18 c Primary treatment tanks are to be desludged when the scum and sludge occupies more than two thirds of the volume of tank.
19 a&b Maintenance and servicing records are to be made available to Ecan upon request
20 For wells listed in WQL2, there is to be no discharge within community drinking water supply protection zone.
Table 6 Permitted Activity Conditions. Proposed LWRP, Rule 5.9.
5.7 The discharge of wastewater from a new or upgraded on-site domestic wastewater treatment system onto or into land in circumstances where a contaminant may enter water is a permitted activity, provided the following conditions are met:
1 The discharge volume does not exceed 14 m3 per week;
2 The discharge is within the area marked “Septic tank Suitability – Area A” on
the Planning Maps;
Area un-mapped
3 The discharge is not onto or into land:
a Where there is an available sewerage network;
b That is potentially contaminated;
c Listed as an archaeological site;
d Where the discharge would enter any surface water body;
e Within 20 m of any surface water body or the Coastal Marine Area;
f Within 50 m of a bore used for water abstraction; or
g Within a group or community drinking water supply protection area as set out
in Schedule 1.
4 The treatment and disposal system is designed and installed in accordance with Sections 5 and 6 of New Zealand Standard AS/NZS 1547:2012 – On-site domestic wastewater management; and
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The treatment and disposal system is operated and maintained in accordance
with the system’s design specification for maintenance or, if there is no
design specification for maintenance, Section 6.3 of New Zealand Standard
AS/NZS 1547:2012 – On-site domestic wastewater management.
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7.2 Building Act 2004 and regulations
Table 7. Building Act 2004 Requirements
Code/clause Requirements Assessment
B1 Structural The proposed structures are to be of such a standard to ensure public safety and protection of property.
For all options there are no significant structural components that would trigger the structural requirements in B1.
B2 Durability To ensure durability of the “building”. The code implies durability of materials.
ecoEng is confident that all component materials for all options will, within reason, meet the durability requirements of B2, and in particular Table 1 requirements for plumbing and piping.
G13 Foul water
This code applies to above-ground non-pressure (gravity flow) sanitary plumbing for buildings having 3 levels or less and includes all pipework for foul water within, or on the building, including any basements.
All conditions and requirements under G13 can be met.
E1 Surface water
(a) Safeguard people from injury or illness, and other property from damage, caused by surface water, and (b) Protect the outfalls of drainage systems
All stormwater is to be diverted away from the installed on-site wastewater system.
8 Operation and Management Refer to ecoEng Installation Report, 17 February 2013, Section 7, for full details.
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9 Risk assessment, assessment of environmental effects, risk mitigation
Environmental impact of this proposal is based on the identification of the key relative risks, specific to this proposal and site. Refer to Table 8 for risk check list Table 8. Actual and Potential Effects: Check list
Effects on gw Nitrate - N
Refer to Section 9.1.1
Cumulative effects Site is very isolated. Less than minor.
Pathogens Refer to Section 9.1
Human and stock health
Main risk would be surface ponding. Refer to Section 9.2
Discharge to surface waters
There is a farm drain in the neighbour’s property on the NE boundary. This is 39m from the proposed land application system. Refer to Figure 2. The risk of discharge to surface water is considered less than minor
Flood hazard. Risk is considered less than minor
Ngai Tahu values The site is not a silent file area, Ngai Tahu settlement area. Refer to Section 9.3.
Amenity values The site is located in an isolated area. The risk to community amenity values is considered less than minor.
Other effects There are no other effects likely at this site.
Additional mitigation N/A
Consultation It was not considered necessary to consult with any neighbours or Iwi.
Consideration of alternatives
The site constraints limit the options for alternative management of the wastewater. The main constraint for this site is lack of mains power supply. The only power supply is a low voltage DC supply. Therefore a low energy demand gravity system is the only option at this site.
9.1 Effects on groundwater and coastline
The primary risks of this proposal are risk to coastal water and surface ponding during peak loading events. As noted in Table 2, there is no local groundwater depth data available. However the LAS site is more than 10m above mean sea level and 100m to the high tide line. The treatment of the blackwater is primary and therefore there is minimal removal of pathogens or nutrients prior to being discharged to the soakage bed. Within the bed there will be minimal attenuation of either pathogens or nutrients. The groundwater will be more than 4 to 5m below the point of discharge. The soils are sandy. Because of the substantial distance of travel (vertically at least 4m and horizontally about 100m) before reaching the coastline, the pathogen removal will be substantial As illustrated in Figure 7, the direction of groundwater flow from the point of discharge will be in an easterly south-easterly direction. There is no private property between the south-eastern boundary of Lot 1 DP 324200 and the coastal reserve area. Therefore the groundwater, if contaminated, cannot affect a neigbouring property owners now or in the future. The risk that may arise is if contaminated groundwater
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was to surface within the coastal zone putting public visitors at risk. ecoEng saw no evidence groundwater surfacing in this zone. Furthermore the land owner of this proposal who has lived in this area for 11 years has never seen any evidence of groundwater surfacing within this coastal zone. The beach is considered too hazardous for swimming, is steep and there are dangerous rips. There is no immediate site for diving or other seafood gathering activities in this area. Figure 7. Discharge point in relation to coastal zone, groundwater flow direction and provide property
Nitrate nitrogen will be more mobile. If nitrate rich seepage does reach the coast the risk will be less than minor due to massive dilution effects. The coastal zone is remote and very unsuitable and unsafe for recreational activities. The risk of pathogens and nutrient contamination is considered to be less than minor.
9.2 Surface ponding
The main risk at this site is surface ponding of contaminated wastewater during high load events. Mitigations measures include:
In-built storage within the soakage bed designed to absorb peak loads.
Additional balancing storage in the wetland.
Monitoring of subsurface water level in the soakage bed and scope to pump out and cart off site excess wastewater.
Due to these mitigation measures the risk of surface ponding is considered less than minor.
9.3 Cultural impacts
An assessment of the possible impact of this proposal on matters of importance to Ngai Tahu are identified and addressed Table 9.
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Table 9. Assessment of cultural impacts.
Issue Comments
1 Papatipu Rūnanga Te Runanga o Kaikoura Takahanga Marae P O Box 39, Kaikoura
2 Is the activity within, adjacent to, or likely to affect a Statutory Acknowledgement Area?
No
3 Is the activity within a silent file area? No
4 Iwi management plan special requirements
ecoEng has checked the Iwi Management Plan, Te Rūnanga o Kaikōura and can find no reference to the area within which Lot 1 DP 324200 is located.
5 What matters of importance to Ngāi Tahu are likely to be affected by the activity?
As the site is not located located in Statutory Acknowledgement and Silent file areas (items 2 and 3) it is likely that Ngāi Tahu will be unaffected There will be no discharges to surface or ground waters.
6 What is the best way to avoid, remedy or mitigate effects on Ngāi Tahu values?
N/A
7 How does the activity fit within Part 2 of the RMA?
N/A
8 Is the activity consistent with policies and objectives of iwi and council planning documents?
We believe so.
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10 PRODUCER STATEMENT – DESIGN ISSUED BY: Andrew Dakers, ecoEng Ltd TO: On-site wastewater management services: Port Robinson Camping Ground TO BE SUPPLIED TO: Canterbury Regional Council and Hurunui District Council IN RESPECT OF: AT:
NZ Grid Reference: WSG84: S42 53.261 E173 18.452 Legal Description: Lot 1 DP 324200 District/City Council: Hurunui Regional Council: Canterbury Regional Council. Site Address: 437 Cathedral Rd,Cheviot
ecoEng Ltd has been engaged to provide the technical design details for an on-site wastewater service. The design has been carried out in accordance with AS/NZS 1547:2012. On-site domestic wastewater management For details of site assessment and design, refer to ecoEng Engineering and EIA Report 16 February 2013 and ecoEng Installation Report , 17 February 2013. Other resources used for this design include:
o ARC Environment. 2004. On-site wastewater disposal from households and institutions. Auckland Regional Council. Technical Report 58. Also refer to: On-Site New Zealand special report 05/1
o Tanner, C. C. , Headly, T. R. Dakers, A.J. 2011. Guidelines for the use of horizontal subsurface-flow constructed wetlands in on-site treatment of household wastewaters. Prepared for Gisborne District Council an Envirolink Project, June 2011.
This is an independent design, covered by a current policy of Professional Indemnity Insurance. I BELIEVE ON REASONABLE GROUNDS that this design has been carried out accordance with best practice in engineering design principles and procedures. NOTE: This statement does not approve the installed system.
Disclaimer The Client is to make full disclosure of relevant information on existing and/or proposed activities on the site that will influence estimation of likely daily wastewater quantity (potential number of bedrooms and other wastewater producing activities) and quality (in particular any chemicals in the water supply and/or wastewater stream potentially toxic to biological wastewater processes). This design is based on the site assessment carried out by ecoEng Ltd. Subsequent changes to the site that might affect the topography and soil profiles are to be notified by the client. Failure, by the Client, to provide this information will invalidate this design producer statement. Approval is to be sought from ecoEng Ltd, should variations to the specification and layout in this report/drawing be considered necessary by the installer prior to or at the time of installation. Failure to do so will invalidate the Design Producer Statement and ecoEng Ltd will no longer take responsibility for the design.
Date. 17 February 2013
A.J. Dakers BE(Nat Res), ME.
