Consenting Design Report - Whangarei · Preliminary geotechnical site investigations have been ... The project cost estimate is expected to be ... 274 Whau Valley Road Consenting

Whau Valley WTP AEE

Beca // 18 February 2016

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Appendix E

Consenting Design Report

Report

Whau Valley New Water Treatment Plant - 274 Whau Valley Road Consenting Design Report

Prepared for Whangarei District Council

Prepared by CH2M Beca Ltd

15 February 2016


CH2M Beca // 15 February 2016

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Revision History

Revision Nº Prepared By Description Date

A Francesca Nicklin Draft for discussion 01/10/2015

B Francesca Nicklin Issued for review 12/11/2015

C Francesca Nicklin Issued for submission with AEE and NoR 15/02/2015

Document Acceptance

Action Name Signed Date

Prepared by Francesca Nicklin

15/02/2016

Reviewed by Philip La Roche

15/02/2016

Approved by Philip La Roche

15/02/2016

on behalf of CH2M Beca Ltd

© CH2M Beca 2015 (unless CH2M Beca has expressly agreed otherwise with the Client in writing).

This report has been prepared by CH2M Beca on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which CH2M Beca has not given its prior written consent, is at that person's own risk



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Executive Summary

Commencing November 2013 Whangarei District Council (WDC) undertook a review of its existing Whau

Valley Water Treatment Plant (WTP) and compared the cost and benefits of upgrading its existing plant with

the option of building a new plant. It was concluded that a new treatment plant should be pursued rather

than upgrading of the existing, based on the following key considerations:

n Ability to achieve full compliance with Building Code seismic design requirements.

n Increased asset life as a result of the asset renewal.

n Moving away from the constrained current site in an urban area allows arrangements for safe delivery of

bulk chemicals and storage of chlorine gas to be more readily achieved.

n Opportunity to incorporate current best practice process design, providing decreased risk of Drinking

Water Standards for New Zealand non-compliance.

n Cost margin between upgrading and replacement being such that the benefits of replacement are justified

and in the long term interests of Whangarei.

A range of sites were considered, of which three sites for a new WTP were investigated in greater detail.

274 Whau Valley Road was selected as the most appropriate site for a new WTP.

This report presents a concept design for a new WTP at 274 Whau Valley Road in order to inform the Notice

of Requirement and resource consent process.


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Contents

1 Introduction 5

1.1 Background 5

1.2 Purpose 6

2 Alternative Sites Considered 6

3 Design Basis 10

3.1 Capacity 10

3.2 Treated Water Quality Objectives 10

3.3 Raw Water Quality 12

4 Concept Design 15

4.1 Process 15

4.2 Chemical Dosing 20

4.3 Raw Water and Treated Water Conveyance 21

4.4 Waste Management 22

4.5 Services 23

4.6 Hydraulics 24

5 Site Layout 28

5.1 Survey 28

5.2 Flood Hazard Assessment 29

5.3 Geotechnical Investigations 30

5.4 Bulk Earthworks 32

5.5 National Environmental Standard Study 32

5.6 Traffic Impact, Bridges and Roading 32

5.7 Landscape Design 33

5.8 Future Use of Existing WTP Site 33

6 Consenting and Compliance 34

6.1 Summary of Consenting Process 34

6.2 Operational Noise and Vibration 34

6.3 Ecology 35

6.4 Archaeological and NZ Heritage Assessment 35

6.5 Consultation 35

6.6 Landscape and Visual Assessment 36

7 Concept Construction Methodology 37

7.1 Concept Construction Methodology 37

7.2 Estimated Additional Vehicle Movements 37

7.3 Noise and Vibration 37

7.4 Sedimentation and Erosion Controls 37


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Appendices

Appendix A

Process Flow Diagram

Appendix B

Site Layout

Appendix C

Site Survey

Appendix D

Geotechnical Factual Report

Appendix E

Preliminary Geotechnical Interpretive Report

Appendix F

NESS

Appendix G

Archaeological Assessment Report

Appendix H

On-site Dewatering Assessment Memo

Appendix I

Flood Hazard Assessment



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1 Introduction

1.1 Background

Commencing November 2013 Whangarei District Council (WDC) undertook a review of its existing Whau

Valley Water Treatment Plant (WTP) and compared the cost and benefits of upgrading its existing plant with

the option of building a new plant. It was concluded that a new treatment plant should be pursued rather

than upgrading of the existing, based on the following key considerations:

n Ability to achieve full compliance with Building Code seismic design requirements.

n Increased asset life as a result of the asset renewal.

n Moving away from the constrained current site in an urban area allows arrangements for safe delivery of

bulk chemicals and storage of chlorine gas to be more readily achieved.

n Opportunity to incorporate current best practice process design, providing decreased risk of Drinking

Water Standards for New Zealand non-compliance.

n Cost margin between upgrading and replacement being such that the benefits of replacement are justified

and in the long term interests of Whangarei.

Three sites for a new WTP were investigated and 274 Whau Valley Road was selected as the most

appropriate site for a new WTP. Refer to Section 2 for a detailed summary.

1.1.1 Reference Documents

This report makes reference to the documents in Table 1 issued to WDC by CH2M Beca.

Table 1: Reference documents

Reference document Brief summary of content

Whau Valley New Water Treatment Plant Feasibility Site Assessment Report by CH2M Beca

July 2015

Purpose of report was to investigate factors that could have a significant impact on the cost or viability of the construction of a new WTP. Three site were investigated:

n 213 Whau Valley Road

n 274 Whau Valley Road

n Dam Southern Abutment

This report recommended that it would be in WDC’s best long term interests to build a new plant and that 274 Whau Valley Road has the most potential for development.

Whau Valley New Water Treatment Plant Feasibility Report by CH2M Beca Ltd.

November 2014

Purpose of report was to investigate alternative sites for a new WTP. It focussed on the WDC owned 213 Whau Valley Road site. The geotechnical conditions at 213 Whau Valley Road were found to be unfavourable so more detailed investigations of other sites was recommended.

Whau Valley New WTP Feasibility Memo by CH2M Beca

March 2014

This memo looked at the feasibility of a new WTP, including process design, layout at 213 Whau Valley Road and a very rough order of cost.

Whau Valley Water Treatment Plant Upgrade Options Assessment Report by CH2M Beca

February 2014

Purpose of report was to investigate and lay out upgrade options for the existing Whau Valley WTP. The investigation work found that the cost to refurbish the existing structures to bring them up to an appropriate level of current building code meant that the cost of a new plant could be feasible.



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Reference document Brief summary of content

Whau Valley WTP Asset Condition Assessment Report by CH2M Beca

January 2014

Purpose of report was to provide a structural assessment of the existing Whau Valley WTP and establish the extent of remedial work required to extend the life of the plant by 20 to 30 years. The investigations found that extensive remedial work would be required to address serviceability and seismic issues.

1.2 Purpose

The primary objective of this consenting concept design report is to inform the Notice of Requirement

process for 274 Whau Valley Road.

2 Alternative Sites Considered

2.1.1 Upgrade Existing Plant

Originally WDC intended to upgrade the existing Whau Valley WTP to expand the plant’s capacity, enhance

the treatment process to robustly meet the requirements of the Drinking Water Standards of New Zealand

(DWSNZ) and to extend its life by 20 to 30 years.

A number of plant upgrades were recommended, however the overall cost of these upgrades (largely

influenced by the remedial structural works required to bring the existing plant structures up to an appropriate

level of the building code) was at such a level that WDC has decided to bring forward the construction of a

new WTP forward. Refer to Section 2.1.5 for a summary of estimated costs.

The cost of refurbishing the existing Whau Valley WTP is based upon needing to achieve a minimum of 67%

of the current Building Code seismic requirements. Since this was evaluated in 2013, the New Zealand

Government has updated their policy on the required upgrades to existing structures. The outcome of this is

that WDC (being in a low risk area) would now not need to assess the building seismic strength until 2030,

and would have until 2065 to strengthen the building. However, any significant alteration of the building

would trigger the need to upgrade, and hence the upgrading requirements are not significantly changed

since the previous recommendations were completed.

2.1.2 213 Whau Valley Road

This site is close to the base of the dam and is owned by Whangarei District Council.

Initial consultation has been undertaken with neighbours to this site by Whangarei District Council’s planner.

Initial concerns raised were reasonable and should be able to be managed and mitigated.

Although there is sufficient land area owned at this site for the prosed works, it would be preferable to

purchase one of the two neighbouring properties (either 215 or 227 Whau Valley Road) to enable increased

setback distances and landscaping to mitigate the impact of the plant on the community.

Preliminary geotechnical site investigations have been completed at this site. Ground conditions at this site

are poor, with a large depth to rock (greater than the 30 m depth to which drilling was completed); materials

that are expected to give some settlement and layers with the potential for liquefaction under seismic events.

Allowance for ground improvement works adds an estimated $1.6 million to the cost of developing the 213

Whau Valley Road site. The project cost estimate is expected to be adequate to reduce the risks from long

term settlement and liquefaction settlement to acceptable levels.



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2.1.3 274 Whau Valley Road

There is a flat area of a suitable size for a treatment plant in this area. The site is large enough to provide

reasonable setback from the existing residential properties.

Initial consultation has been undertaken with neighbours to this site by Whangarei District Council’s planner.

Initial concerns raised were considered to be reasonable and able to be mitigated through the design

process.

This site has better ground conditions than 213 Whau Valley Road with a shallower depth to rock being

found. It is still expected to require some ground improvement works but of a lesser cost than for 213.

Cost of services (treated water pipeline and sewer in particular) would be lower for this site due to the shorter

distances.

Preliminary geotechnical site investigations have been completed at this site. Ground conditions at this site

are reasonable. Allowance for ground improvement works adds an additional estimated $1.0 million to the

cost of developing the 274 Whau Valley Road site. The project cost estimate is expected to be adequate to

reduce the risks from long term settlement and liquefaction settlement to acceptable levels.

Although close to the flood plain, the plant will be able to be constructed clear of the 1:100 year flood plain.

There is a risk that the site could be inundated under the worst case dam break.

2.1.4 Dam Southern Abutment

The flat area at the south end of the dam embankment has been formed by the excavation of borrow

material for the construction of the dam. At least 10m of overburden has been removed from the majority of

the site, exposing rock for a significant area. Foundation conditions are expected to be good in this area.

Being on a dam complicates building on this site. The auxiliary emergency spillway would need to be

modified to accommodate a treatment plant in this area. Dam safety aspects would also need to be carefully

considered.

The area is currently zoned open public space and has a public amenity value, which would need to be

considered during a consenting process.

Hydraulically this site would be a substantial change, being elevated at least 20m above other sites being

considered. Raw water pumping would be required from the Dam to the treatment plant. There could be the

opportunity to create supply to a higher level zone, including reducing the pumping to Kamo, off setting some

of the additional pumping energy required for operation at this site.

There have not been any specific geotechnical investigations performed at this site.

2.1.5 Estimated Cost

The total estimated cost of the construction of the new Water Treatment Plant is $18.3 million at 213 Whau

Valley Road, $16.3 million at 274 Whau Valley Road and $18.6 million at the Dam Southern Abutment site,

compared to $12.7 million to upgrade the existing plant.

Key exclusions are:

n Council internal and project costs

n Expected land purchase cost for 274 Whau Valley Road is included.



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n No allowance is included for the potential (but not essential) need to purchase neighbouring sites at 213

Whau Valley Road if this site was selected.

n Cost of any easements required.

n Removal and treatment of any contaminated materials should they be encountered on the site.

n Legal transfers, stamp duties, insurance and the like.

n Escalation and FOREX provisions. These estimates are based on present day (July 2015 ) rates and

allowances and no allowance has been for future escalation and changes in exchange rates

n No allowance for import duties or tariffs

n Premium rates for accelerated programme

n Future reservoirs are excluded from this estimate

n Demolition of existing WTP

n Potential proceeds from the sale of surplus land

n GST

The cost estimates are based on concept level information and the accuracy should be considered to be

consistent with this level of design information.

The estimated additional cost of UV/Peroxide is $2.1 million. UV disinfection would not be expected to be

necessary in addition to UV/Peroxide and hence the additional cost of this option over and above the base

estimate presented above is a net $1.5 million.

The waste management strategy is based on clarifier sludge being discharged to sewer, backwash wastes

being settled and recycled and filter to waste being recycled to the process. This minimises the total waste

discharge volume and is the lowest total lifecycle cost option based on estimates completed. An optional

cost for on-site dewatering, should this option be favoured, is approximately $1.4 million.

2.1.5.1 New Plant versus Existing Plant Upgrade

Previous studies have been completed evaluating the costs of upgrading the existing plant versus

construction of a new plant. Comparative estimated costs are as follows:

Table 1 - New WTP versus WTP Upgrade

Option Estimated Cost Key Assumptions

Upgrade Existing WTP $12,740,000 n Based on refurbishment of all existing clarifiers and filters.

n Based on achieving 67% of current Building Code seismic

requirements.

n Includes $1.25 million for recoating of structures – this may not be

necessary if a long extended asset life is not required.

New WTP at 213 Whau Valley Road

$18,300,000 n Excludes optional organics removal.

n Ground conditions costs are based on excavation and replacement of

the upper soil layer and soil stabilisation.

n New treated water pipe from new WTP to reservoir (no new raw

water pipe from Hatea River or Whau Valley Dam)

New WTP at 274 Whau Valley Road

$16,300,000 n Excludes optional organics removal.

n Ground conditions costs are based on excavation and replacement of

the upper soil layer and soil stabilisation.


water pipe from Hatea River or Whau Valley Dam)



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Option Estimated Cost Key Assumptions

New WTP at Dam Southern Abutment

$18,600,000 n Includes raw water pumping

n Assumes no significant ground improvements are required


water pipe from Hatea River)

The above estimates are done on a comparable scope basis in terms of the process options included.

We consider that approximately 30% cost premium for the construction of a new plant is justified by the

combined benefits of the following, and hence we consider the option of a new plant to be in WDC’s best

long term interests.

n Lower Cost of Asset Upgrades and Renewals. This could be expected particularly over the next 20 or

so years. An upgraded plant would still be likely to need further upgrades and renewals over time, with

only components that have reached the end of their useful life being renewed, in comparison to a new

plant, designed to incorporate advances in process design and including all new structures and

equipment.

n Reduced Risk from Seismic Events – A new plant would achieve full compliance with current seismic

design codes, whereas an upgraded existing plant can only be feasibly upgraded to achieve 67% of the

current Building Code, and further there remains a residual risk that components in the existing plant

could remain (particularly where inaccessible and/or where records of construction are unclear) which

could have lower strength and have significant risk of being unserviceable following a seismic event.

The cost of refurbishing the existing Whau Valley WTP is based upon needing to achieve 67% of the

current Building Code seismic requirements. Since this was evaluated in 2013, the New Zealand

Government has updated their policy on the required upgrades to existing structures. The outcome of

this is that WDC (being in a low risk area) would now not need to assess the building seismic strength

until 2030, and would have until 2065 to strengthen the building. However, any significant alteration of

the building would trigger the need to upgrade, and hence the upgrading requirements are not

significantly changed since the previous recommendations were completed.

n Plant Location - Moving out of the urban area to a less constrained site enables arrangements for safe

storage of chlorine gas and delivery of bulk chemicals to be more readily achieved, can be designed for

greater accessibility for maintenance and will have greater flexibility to incorporate future process

changes which could be required.

n Process Performance and Compliance – the risk of non-compliance would be expected to be lower

with a new plant in comparison to an existing plant where compromises in design are required to fit within

the constraints of the existing structures.



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3 Design Basis

3.1 Capacity

Table 1 - Plant Capacity

Parameter Value Unit Basis

Maximum Treated Water Capacity of Existing Plant

16,800 m3/d WDC RFP document

Proposed Upgrade Treated Water Capacity at New Plant

22,600 m3/d 30% increase in capacity (target value)

WDC strategic direction report.

Minimum Treated Water Capacity of New Plant

2,260 m3/d 10% of maximum design flow as requested by

WDC in email dated 11/09/2015.

Idea is that plant needs to be able to run on low flows (ie during drought).

Expected Raw Water capacity at proposed upgrade treated water capacity

23,950 m3/d 5% allowance for flow variability plus 1% allowance

for waste flow stream

Peak treated water flow 1,256 m3/h 33% allowance for peak flow during filter backwash

– allows for drain down of one filter.

Consented take Whau Valley Dam Unlimited CON19990172502

No restriction

Expires 31 May 2034

Consented take Hatea River 9,000 m3/d CON20030739801

Expires 31 May 2018

Current Average Day Demand 9,600

(400 m3/h)

m3/d

Current Peak Day Demand 13,200 (550 m

3/h)

m3/d

Reservoir A volume 4,500 m3

Reservoir B volume 9,000 m3

3.2 Treated Water Quality Objectives

The treated water quality criteria that the plant must be capable of achieving are:

n DWSNZ 2005 (revised 2008) – compliance with requirements of DWSNZ is to be achieved.

n Grading - Maintain current A1 rating.

n Protozoa and Disinfection – A minimum of 4-log protozoa removal is required (Whau Valley Dam

catchment 3-log, Hatea catchment 4-log). This is expected to be achieved by a combination of

coagulation/clarification/filtration plus UV disinfection. As an operational target, the enhanced filtration

requirements of DWSNZ should be achievable, and as such clarification and filtration alone could meet

the 4 log requirement. The proposed approach is to include UV disinfection and operate to the less

onerous filtered water turbidity requirements for compliance, but operationally targeting 0.1 NTU,

providing a robust buffer between operational limits and compliance. Chlorination should be continued to

provide effective viral reduction and residual disinfection.

n Iron and Manganese – Minimising iron and manganese concentrations in the treated water is

required. Recommended operational targets should be less than 0.05 g/m3 iron and less than 0.02 g/m

3

manganese. These are more stringent than DWSNZ requirements, but utility experience has been that

exceeding these concentrations can result in a higher-than-acceptable frequency of dirty water events. At



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these target concentrations accumulation of deposits and dirty water events can still occur, and hence the

target is to minimise iron and manganese levels.

n Taste & Odour – The process is to include the provision (i.e. space allowance and a plan of how it could

be implemented) to cater for an increase in algae in Hatea River and/or Whau Valley Dam causing algae

toxins and/or taste & odour problems if these occur in future.

n Fluoridation – The upgraded plant is also to have provision (i.e. space allowance and a plan of how it

could be implemented) for the possible addition of fluoride dosing to the process.



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3.3 Raw Water Quality

The following table summarises water quality data collected between November 2013 and September 2015, with grab samples taken every few weeks.

A total of 45 samples from both the Hatea River and Whau Valley Dam source have been taken (ie 90 samples in total).

Table 2: Raw water quality data summary

Max Min Median Average 5th Percentile

25th Percentile

75th Percentile

95th Percentile

Hatea River

Turbidity (US EPA) NTU 134 1.64 3.63 8.48 1.88 2.81 6.27 18.34

Alkalinity (Total) g/m3 as CACo3

91.7 12.1 56.5 55.3 28.2 42.7 71.0 78.6

Calcium (Total). g/m3 25 4.6 15.85 15.26 8.38 12.3 18.725 21.91

Iron (Dissolved). g/m3 0.418 0.09 0.215 0.22 0.141 0.19 0.242 0.341

Iron (Total). g/m3 1.13 0.274 0.505 0.54 0.363 0.44225 0.56875 0.8925

Magnesium (Total). g/m3 6.3 1.49 4.3 4.3 2.7255 3.5825 5.0525 5.951

Manganese (Dissolved). g/m3 0.039 0.0016 0.0107 0.0122 0.0052 0.0082 0.0125 0.0300

Manganese (Total). g/m3 0.099 0.0075 0.0159 0.0221 0.0086 0.01325 0.02145 0.0578

Organic Carbon (Dissolved).

g/m3 8.7 1.2 2.5 3.0 1.4 2.1 3.5 5.9

pH 8.1 6.8 7.9 7.7 7.12 7.5 8 8.1

Solids (Suspended) g/m3 37 1 2 4.0 1 1.8 3 12.7

Solids (Total Dissolved) g/m3 193 60 130 128.5 95.3 106.5 149.3 170.6

Ultraviolet Transmission (filtered)

%T 89 52 82.6 79.8 59.1 78.8 85.4 86.9

Colour HU 125 0 15 19 0 5 20 50

Whau Valley

Turbidity (US EPA) NTU 131.4 0.85 2.11 8.91 1.04 1.24 4.05 40.02

Alkalinity (Total) g/m3 as CACo3

51.7 13.6 37.9 36.5 17.7 29.0 45.3 49.7

Calcium (Total). g/m3 21 3.9 10.5 10.6 5.13 7.95 13.05 15.19

Iron (Dissolved). g/m3 0.42 0.02 0.175 0.160 0.038 0.080 0.220 0.284

Iron (Total). g/m3 3.5 0.126 0.315 0.514 0.15475 0.25575 0.426 2.2085



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Max Min Median Average 5th Percentile

25th Percentile

75th Percentile

95th Percentile

Magnesium (Total). g/m3 5.3 1.66 2.975 2.955 1.96 2.5 3.373 3.716

Manganese (Dissolved). g/m3 0.58 0.0005 0.0077 0.0227 0.0007 0.0023 0.0131 0.0452

Manganese (Total). g/m3 0.66 0.0099 0.04 0.0626 0.0147 0.024 0.065 0.1278

Organic Carbon (Dissolved).

g/m3 5.85 1.8 2.85 3.15 2 2.48 3.63 5.18

pH 7.8 6.7 7.3 7.3 6.8 7 7.5 7.68

Solids (Suspended) g/m3 150 1 2 8.2 1 1 2.3 20.4

Solids (Total Dissolved) g/m3 174 82 123 120.7 86.5 98.8 140.8 153.9

Ultraviolet Transmission (filtered)

%T 94.4 51.5 83.4 80.9 66.7 79.8 85.4 87.2

Colour HU 250 0 10 20 0 5 15 58



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3.3.1 Disinfection By Product Formation

Disinfection By Product (DBP’s) formation are a parameter which the existing plant operates at close to the

compliance limits on, and hence consideration should be given to the need for a process that would achieve

improved removal, either as part of the proposed plant construction or for implementation within the life of the

new plant.

DBP’s form when natural organic matter reacts with chlorine. The main approach to reducing the formation

of these by-products is minimising the level of organic matter at the point at which chlorine is dosed.

The toxicity of DBP’s is well established, and hence the need to minimise their formation. There is however

also recognition of the public health benefits from the disinfection provided by chlorine, and acceptance that

the negative impacts from reduced disinfection could substantially outweigh the benefits of reduced DBP

formation should the chlorine disinfection be compromised.

Trihalomethanes (THM’s) and haloacetic acids (HAA’s) are the groups of disinfection by-products typically

present in potable water in the highest concentrations. The following table provides the DWSNZ limits, and

World Health Organisation Limits (WHO), who set guidelines based on the currently available scientific

evidence, and upon which our DWSNZ requirements are largely based.

Table 3: DBP Regulatory Limits

Parameter DWSNZ 2005 (Revised 2008) WHO 2011

Trihalomethanes (THM’s)

Chloroform 0.4 mg/l 0.3 mg/l

Bromoform 0.1 mg/l 0.1 mg/l

Dibromochloromethane 0.15 mg/l 0.1 mg/l

Bromodichloromethane 0.06 mg/l 0.06 mg/l

Total THMs Sum of the Ratio of concentration to its respective MAV must not exceed 1

Haloacetic Acids (HAA’s)

Dichloroacetic Acid 0.05 mg/l 0.05 mg/l

Monochloroacetic Acid 0.02 mg/l 0.02 mg/l

Trichloroacetic Acid 0.2 mg/l 0.2 mg/l

Other

Dibromoacetonitrile 0.08 mg/l 0.07

The DWSNZ requirements for THM’s (the first four parameters in the above table) are the same as the

current WHO guidelines, except that chloroform is more stringent in WHO. This is because DWSNZ was

based on an earlier edition of WHO and has not been updated. Both DWSNZ and WHO have the additional

requirement that the sum of the ratio of concentration to its respective MAV for each THM must not exceed

1. This accounts for the additive toxicity of individual THMs. The Total THM requirement is the more onerous

requirement to meet than the individual limits.

For Haloacetic Acids (the last three parameters in the above table) DWSNZ is consistent with the WHO

requirements. For Dibromoacetonitrile the DWSNZ current limit is slightly below the current WHO standard,

and hence is also at risk of being tightened in future revisions of DWSNZ.

Based on the above and our current understanding of the Ministry of Health’s intentions, we would expect the standards are unlikely to change in the short term, however in the medium to longer term, and certainly within the life of the proposed plant, DBP formation is a parameter which tightening standards are possible to likely.



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4 Concept Design

4.1 Process

The proposed water treatment process for the purpose of this report is:

n Raw water take from both Whau Valley Dam and Hatea River

n Retrofit air burst screen washing at the Hatea River Intake

n Inlet flow control (either control valve alone or combined with a pump as a turbine)

n Pre clarification pH correction

n Coagulation

n Flocculation

n Conventional clarification

n Pre-filter chlorine dosing and pH correction

n Media filtration

n Post-filter pH correction

n UV disinfection

n Chlorine dosing

n Treated water storage in Fairway reservoirs

n Overflow storage in dry pond

Future provisions have been allowed for the following processes:

n Enhanced organics removal which may include:

– Second stage of filtration

– UV Peroxide or alternative advanced oxidation process such as ozone

n On site mechanical dewatering

These processes (including future allowances) are shown on the PFD in Appendix A and are included on the

site layout in Appendix B.

4.1.1 Hatea air burst screen washing

The conventional means of backwashing river wedgewire Tee screens of the type installed in the Hatea

River is by an air burst system where compressed air is stored in a receiver and released as a burst into the

screen, dislodging debris and algae.

A new air compressor including receiver would be installed in the Hatea intake pump station. Compressed air

is stored in a receiver, and discharged as a burst either on an operator set frequency and/or low wet well

level. The sudden release of air cleans the wedgewire screen. A pipeline of nominally 100mm diameter

would be required to the intake screen

4.1.2 Inlet flow control

Refer to Section 4.6.2 for a discussion on plant hydraulics and possibility of energy recovery.

4.1.3 Coagulation

Coagulation would be similar to the existing plant, using either aluminium sulphate or polyaluminium chloride.



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4.1.4 Clarification

The two main alternative process options for clarification are:

n Conventional clarification process such as Upflow Sludge Blanket Clarification

n Dissolved Air Flotation (DAF).

4.1.4.1 Conventional Clarification

Upflow clarification would be similar to the process at the existing treatment plant, although the configuration

of the process would be changed to achieve more economic construction costs. Flat bottom structures are

now commonly used rather than the deeper pyramid shaped tankage used at the existing plant.

There are a number of variants possible, both sludge blanket and non-sludge blanket. For the purpose of

this concept study an upflow sludge blanket clarifier has been assumed. This type of process has been

proven to be effective on this source water with the existing plant.

Tube settlers or lamella settlers would likely be incorporated, allowing higher loading rates and reducing the

area of the structures by around a third. Overall the capital cost would be reduced. Tube settlers do

however hinder access and do not typically have a design life matching the civil structures. Lamella settlers

are available in more durable stainless steel construction, for an increased capital cost. For the purpose of

this study the larger size and cost option has been assumed, but this issue will be considered in more detail

in the preliminary design.

4.1.4.2 Dissolved Air Flotation

Dissolved air flotation (DAF) involves mixing a side stream of water supersaturated with air with the

flocculated raw water. The pressure drop causes the air to be released from solution, forming a cloud of

micro air bubbles. These bubbles then attach to the flocculated particles, causing them to rise to the surface.

The process is particularly effective with low density particles, such as the algae dominated Whau Valley

source.

The process is at a higher rate than typical clarification processes and loading rates in the order of four times

higher are possible. DAF is frequently installed as a “DAF over filter” configuration, significantly reducing civil

construction costs. This configuration does not allow chemical dosing between the clarifier and filter, such as

pre filter chlorine or UV/hydrogen peroxide. Hence for this plant it is expected DAF may be used as a

separate unit process.

DAF is a higher energy process than conventional clarification due to the side stream energy requirements.

Overall DAF is expected to be a more compact, slightly lower capital but higher energy cost process. For the

purpose of this concept design we have assumed the conventional clarification option, being more

conservative in terms of the space and capital cost requirements. DAF is however a process suitable for this

source water and could be considered as an alternative at the next design stage.

4.1.4.3 Clarification versus Dissolved Air Flotation Conclusion

For the purpose of this report the larger footprint, higher capital but lower operating cost clarification option

has been assumed. The following table provides the preliminary design basis.



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Table 4: Clarifier Concept Design Basis

Parameter Value Basis

Capacity 1,036m3/h 22,600 m

3/d treated water capacity

plus 5% allowance for waste flows and 5% allowance for flow control

ie. 24,860 raw water capacity

Flocculation Hydraulic Retention Time 5 minutes Typical/conservative for similar applications

Flocculation Volume 86 m3

Design Hydraulic Loading Rate 2.5 m/h Conservative/appropriate for water source.

Total Clarifier Area 414m2

Area 420 m2

Dimensions 2 no 14x15m or similar

Nominal Depth 4.5m Typical

A minimum of two clarifiers would be built to allow for planned maintenance with continuity of supply, and up

to four clarifiers may be constructed depending on the final design. Two clarifiers are shown on the layout in

Appendix B.

4.1.5 Iron and Manganese Removal

Iron and manganese removal is a requirement and the existing pre filter chlorination is an effective means of

achieving this. UV/peroxide dosing could also be considered, and this is discussed under enhanced

organics removal in Section 4.1.8.

4.1.6 Filtration

Membrane filtration could be considered as an alternative to conventional rapid gravity media filtration. A

significant benefit of membrane filtration is the high level and consistent particulate removal achieved.

Through the membrane integrity test (MIT) the membrane can be verified on a daily basis that the membrane

is integral, and the risk of non-compliance with the DWSNZ protozoa removal requirements is lower than with

conventional filtration.

Membrane filtration is not as amenable to achieving other process objectives in addition to particulate

removal. For Whau Valley iron and manganese removal and enhanced organics removal are key process

objectives more readily achieved with a conventional process.

There would be a cost premium on both capital and operating costs for a membrane based process in

comparison to a conventional process, particularly once the other process objectives are considered. Hence

conventional media filtration is recommended for the purpose of this concept study.

The following table outlines the filtration design basis.

Table 5: Filtration Design Basis


Capacity 1,000 m3/h 22,600 m

3/d treated water capacity

plus 1% allowance for waste flows and 5% allowance for flow control



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Design Hydraulic Loading Rate 12 m/h with one in backwash/out of service

Conservative/appropriate for water source.

Number Filters 4 Expected economic optimum and providing appropriate level of operational flexibility

Area 28 m2

Media:

Sand

Anthracite

450mm 0.5-1.0mm

1000mm 1.25 effective Size

Deep Bed Dual Media Configuration

Nominal Filter Shell Depth 4.8m Allows for plenum floor and proposed media depth plus freeboard

Backwash Volume 150 m3 4 bed volumes plus volume above

media

Backwash Tank Capacity 300 m3 Two backwash volumes

4.1.7 Disinfection

4.1.7.1 UV Disinfection

UV disinfection can provide up to 3 log credits for protozoa removal under DWSNZ. The filtration process

alone can meet the required 4 log credits if operated to the more onerous turbidity compliance requirements.

With a new filtration process meeting best industry practices, compliance could be reasonably achieved

without the addition of UV disinfection. However, consistent with the existing plant, UV disinfection has been

included in the process flow and layout. Should the UV peroxide process be adopted (discussed further in

Section 4.1.8), UV disinfection may not be required.

4.1.7.2 Chlorine Disinfection

Gas chlorine is proposed to be used for residual disinfection, as is used at the existing site; refer to Section

4.2 for a discussion on chemical dosing.

The current chlorine contact time in the reservoirs should be confirmed. Chlorine contact time should be

achievable without modifications to the reservoirs, however scale modelling completed by WDC casts some

doubt and a tracer test is recommended to confirm actual chlorine contact time.

At maximum plant flow approximately 10 minutes of contact time can be achieved in the new treated water

pipeline between the new plant and the existing reservoirs.

4.1.8 Enhanced Organics Removal

Currently disinfection product levels from the existing treatment plant, measured in the distribution system

average around 50% of the DWSNZ maximum acceptable value (MAV) and some exceedances of the MAV

have occurred. The process previously proposed for the new site was based on replacing the existing plant,

like for like, to enable a fair comparison of options to be made.

As discussed in Section 3.3.1, there is a risk that standards could tighten, and it is recommended

consideration be given to options to reduce the formation of DBP’s, for implementation either as part of the

initial development or for future implementation.



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A number of approaches are possible to manage disinfection by product formation, including enhanced

treatment to reduce the level of natural organics in the water prior to chlorination, distribution management to

reduce residence time (a review of WDC’s treated water transmission design and operation would need to be

undertaken) and alternatives to free chlorine disinfection. This report is not intended to provide a full review

of options, but does provide an overview of the more likely options to enable WDC to gauge the likely impact

from this enhancement.

Options focus on reduction of natural organics prior to chlorination. The two options considered here are

second stage filtration and UV/Peroxide. Allowances for both are shown on the layout in Appendix B.

4.1.8.1 Two Stage BAC Filtration

Biological filtration relies on biodegradation of organic matter. It will occur in conventional media filtration

with the large surface area available on the media, although with pre-filter chlorine applied as used at Whau

Valley biodegradation will be substantially reduced. Granular Activated Carbon (GAC) media provides an

ideal support medium for biodegradation, and when used as the filter media it is referred to as BAC

(biologically activated carbon). After approximately the first 6 to 18 months the carbon’s adsorption capacity

is exceeded, and the media works as a support media for biological activity.

The nature of the organics found in the previous investigations suggests the organics are of a lower

molecular weight, non-humic nature and based on this index could be expected to be more readily

biodegraded and suited to biological filtration. Trials would be recommended to gauge the removal

achievable.

An additional observation that the rate of dissolved oxygen decay in the raw water reservoir appears high

also supports the notion that this water might respond well to biological filtration, although this is only a

general observation rather than an absolute measure.

Some requirements for BAC filtration are:

n Chlorine Free - Chlorine free backwash and feed water.

n Media –GAC media is preferred as a support medium of biological filtration

n Media Depth – An EBCT (empty bed contact time) of 10 minutes is commonly used as a design criteria,

providing adequate media area and time for biodegradation.

n Combined air water scour backwash – With the increased biological activity and absence of chlorine in

the backwash, a combined air water backwash is recommended. Combined simultaneous air scour with

a low rate water backwash at the same time provides a mechanism called collapse pulsing in the filter

bed which is very effective in agitating and cleaning the full bed depth, as opposed to air scour alone

where the greatest effect is confined to the surface of the media. The use of a combined air water scour

effectively prevents the use of support gravels in the filter bed, and hence typically requires the use of

media-retaining nozzles and hence requires a significant upgrade to the existing filter nozzles and floor

system.

4.1.8.2 Advanced Oxidation

Advanced oxidation processes such as ozone or UV combined with hydrogen peroxide can both directly

oxidise and reduce levels of organic matter that is a precursor to formation of DBP’s and break organic

matter down into lower molecular weight compounds, more readily biodegraded.

Ozone is generated using electrical energy and oxygen (either purchased liquid oxygen or concentrated on

site). As it is unstable it is generated on site to meet demand. It is dosed into the water stream followed by a



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contact tank. Ozone works by both direct oxidation by ozone (O3) and by reaction with the highly reactive

hydroxyl radicals that form as ozone degrades.

UV peroxide works by the UV energy causing the breakdown of the hydrogen peroxide to form highly

reactive hydroxyl radicals which oxidise organic matter. UV doses are 10 to 15 times higher than required

for protozoa disinfection. The residual hydrogen peroxide needs to be neutralised. If UV peroxide is applied

post-filter this will significantly increase the chlorine dose required. If applied pre-filter, the hydrogen

peroxide will be neutralised in the filter and hence is an advantage of pre-filter dosing. Applying UV peroxide

pre-filter does increase the UV dose required, however trial results from other applications recently on

clarified water have shown this increase to be small.

UV peroxide is a process which is gaining increasing attention, whereas ozone has been established for a

longer period. Benefits of UV peroxide are bromate is not formed (a regulated by product which forms when

water with bromide present is ozonated), it is a compact process and is generally accepted as a simpler and

more operationally robust process than ozone.

Costs of UV peroxide and ozone are expected to be competitive, although they can vary with the application.

For the purposes of this report we have selected UV peroxide as the preferred option. Should this be

selected for development we would however recommend a closer analysis of the merits of ozone versus UV

peroxide. The increased biodegradability caused by these oxidation processes can potentially cause

negative impacts of increased biofilm formation in the reticulation system, but conversely if applied prior to a

biological filtration stage can improve the overall removal of organics due to their greater assimilability.

Both ozone and UV/peroxide can achieve the dual purpose of protozoa inactivation and organics reduction.

Current DWSNZ requirements are for a turbidity of less than 1 NTU 95% of the time prior to either UV or

ozone disinfection to obtain protozoa credits, which would not be consistently complied with pre-filter. We

consider it reasonable to expect some protozoa credits to be given for a UV/peroxide process which provides

a UV dose 10 to 15 times higher than that required for 3-log protozoa credits at the lower turbidity and some

log credits may be able to be negotiated with a more lenient turbidity limit.

4.1.8.3 Enhanced Organics Removal Recommendations

UV/peroxide prior to a single stage of filtration is likely to be able to achieve significant reduction in natural

organics and hence formation of disinfection by products and also meet the other treatment objectives. This

would be lower capital cost than two stage filtration, and clearly lower cost than UV peroxide plus two stage

filtration. Trialling would be recommended given there is some uncertainty regarding the process

performance. A containerised trial plant is available in New Zealand which would be trialled at the existing

Whau Valley plant treating a flow stream equivalent to one filter.

The site layout has allowed for the inclusion of a future second stage of filtration and UV peroxide should this

be required.

4.2 Chemical Dosing

The following chemicals would be required on site. The quantities estimated are concept estimates, based

on providing at least 30 days storage at maximum flow and typical dose rates, with quantities rounded up.



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Table 6: Chemical Requirements

Purpose Chemical Maximum Expected Quantity

Basis

Coagulant Aluminium Sulphate or Poly Aluminium Chloride

30 m3 25 g/m

3 47% w/w Alum

Flocculant Polyelectrolyte 100 kg 0.1 g/m3

pH Correction Caustic Soda 30 m3 15 g/m

3 @ 30%w/w Caustic

Disinfection Chlorine Gas 2 x 920 kg drums Greater than 30 days storage

Diesel Standby generator 200 litres 24 hour nominal running

Fluoride (future allowance) Several chemical options available; we would recommend HFA as can be bulk delivered as liquid

5m3 0.75g/m

3 14% w/w HFA

Facilities include access and turning for B train bulk chemical deliveries within the site boundary and

entrance gate set back from the road so that B train delivery truck can pull completely off the road before

opening the gate.

4.2.1 HSNO

All new chemical areas will need to comply with the hazardous substances and new organisms (HSNO)

regulations. The concept site layout takes into account the separate bunding, chemical delivery bund and

separate chlorine room as required by HSNO and good industry practice.

The chlorine room is proposed to be located near the centre of the site, to provide maximum possible

separation distance from neighbouring properties and will be in excess of the minimum 15m required by the

chlorine standard AS/NZS 2929: 2001.

4.3 Raw Water and Treated Water Conveyance

The 21 inch existing raw water pipeline would be intercepted in Whau Valley Road. The flow would then be

gravity fed to the proposed treatment plant.

The downstream raw water main back to the existing plant would be utilised as a new raw water main to

convey Hatea water to the proposed treatment plant.

A new treated water pipeline (nominally 525mm CLS) would be constructed from the new treatment plant to

the reservoirs at the existing WTP site at Fairway drive.

As an alternative, the existing raw water pipeline could be used for treated water, and a new smaller

diameter main constructed for the Hatea raw water conveyance. This would be a lower cost option. The

option allowed for provides for renewal of the existing main, simplifies commissioning and avoids issues of

cleaning the existing raw water main to a standard suitable for use with treated water. This alternative could

be considered as part of the next design phase.

The following table summarises the pipe lengths and uses.



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Table 7: Pipe Lengths

Pipe Estimated Length (m) Size Comment

Raw water: Dam to WTP 1,600 21 inch Use existing raw water pipeline

Raw water: Hatea to WTP 1,000 21 inch Use existing raw water pipeline

Treated water: WTP to existing reservoirs

900 525 CLS New treated water pipeline

4.3.1 On-site Treated Water Storage

A treated water surge tower is proposed to be constructed on site to provide a hydraulic break between the

filter pumping and treated water pipeline. From here the treated water would flow by gravity to the existing

reservoirs.

Table 8: On-site Treated Water Surge Tower


Storage time 3 minutes Nominal buffer volume

Surge tower volume 50 m3 3 minutes storage at maximum treated water flow (22,600

m3/day)

Surge tower height 9 m 5m static head between plant floor level and treated water reservoirs, estimated 3m in friction losses along treated water pipe plus 1m freeboard.

Refer to Section 4.6 for hydraulic discussion

Surge tower diameter 3 m

No allowance has been made for future treated water reservoirs at the new site. WDC has confirmed that

they are unlikely to require reservoirs at the 274 Whau Valley Road site.

4.4 Waste Management

WDC is to confirm whether discharge of waste is to be directly to sewer or via on site dewatering. Refer to

Appendix H for a memo date 7 September 2015 which compares the costs and benefits of both options. It

recommends that waste is discharged directly to sewer, but that space is allowed in the layout for the future

addition of on-site dewatering; this has been included on the layout in Appendix B.

Discharge of sludge to sewer is assumed (as recommended), with recycle of filter to waste water, and

settlement and recycle of backwash wastewater, minimising volumes discharged to sewer and maximising

the use of the water resource.

The following table summarises the expected discharge flows to sewer. Note these flows would be

significantly less than the existing plant discharge with the proposal to recycle settled backwash waste.

Table 9: Sewer Discharge

Parameter Value Unit Design Basis

Max Plant Capacity 22,600 m3/d

Average Plant Capacity 10,000 m3/d

Total solids per m3 of treated water 13 g/m

3 Allowance for raw water suspended solids

plus coagulant

Percentage solids in clarifier sludge 0.2% 2,000 g/m3 Could design clarifier so that solids were up

to 1% concentration



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Total solids per day with average flow 130,000 g/d

Clarifier and backwash sludge to discharged directly to sewer at average plant flow

65 m3/d

Total solids per day with max flow/average solids 293.8 kg/d

Clarifier and backwash sludge to be discharged directly to sewer at max plant flow

147 m3/d

Peak flow (approximate nominal) 5.1 L/s 3 times estimated peak day/average solids flow

The nearest public sewer is approximately 250m from the 274 Whau Valley site. A gravity waste pipeline

would be constructed from the WTP site to the sewer network outside 264 Whau Valley Road. Here a 150NB

waste pipeline gravitates to an existing sewer pump station south of the one way bridge. The volume of

waste to be discharged to sewer would utilise around 25-50% of the existing 80 NB rising main. Hence

depending on the utilisation of this pump station by the existing catchment, the existing sewer pump station

and rising main may need to be upgraded.

The reliability and risk of failure of the existing sewer pump station will need to be considered in detailed

design. The treatment plant will have an on site generator as a back up to the grid power supply, however

sewer pumps station currently relies on a portable generator for backup. One option to provide for such

events is a sludge / sewer balance tank to mitigate overflow risk at the existing sewer pump station. This

optional tank is shown on the PFD in Appendix A, but is not shown on the site layout as this tank would be

buried and therefore if implemented will not affect the building envelope.

4.5 Services

4.5.1 Power

A preliminary load list has been prepared as below.

Table 10: Preliminary Load List

Item Number Required Rated Motor Size/Power Requirement

Basis

Filtered Water Pumps 4 7.5 kW Capacity with 3 out of 4 filters on line.

Backwash Pump 2 (Duty/standby) 45 kW Based on preliminary filter sizing

Blower 2 (Duty/standby) 30 kW Based on preliminary filter sizing

UV Disinfection 2 (Duty/standby) 8 kW UV disinfection. UV Peroxide power requirements would be higher.

Service Water Pumps 2 (Duty/standby) 2 kW Chlorine eductor water, poly make up and educator water.

Instrument Air 2 (Duty/standby) 3 kW Typical

Misc Process items 5 kW Allowance

Amenities, lighting and small power

5 kW Allowance



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Based on this load list a transformer capacity of up to 200 kVA would be required. Northpower have

confirmed capacity is available in the local network.

4.5.2 Comms

WDC is to confirm available communication networks (broadband, mobile phone reception) at 274 Whau

Valley Road.

4.5.3 Stormwater

The intent is to discharge stormwater to the proposed site pond, which in turn would discharge to the

Waiarohia stream via a new stormwater pipe. The discharge from the pond would be restricted to attenuate

the peak discharge flow. This pond would also receive plant overflows or out of specification water, which

may occur occasionally. This will include during commissioning where the plant would be operated to waste

for a period to prove the water is suitable for putting to supply.

Water discharged to this pond would be treated or partly treated water, and generally of low aquatic toxicity.

Residual chlorine if present would be toxic to aquatic life. Engineering controls will be in place to control the

discharge of chlorinated water such that any chlorinated water discharges would be very short duration, and

would be expected to be <0.2 mg/l at the discharge from the pond. The settled water overflow point will be

designed to be unchlorinated, and controls will be in place such that if the treated water overflowed, chlorine

dosing would be stopped. The volume in this tank is relatively small, and hence the discharge of chlorinated

water to the pond would be of short duration only and substantially diluted by the pond outlet.

4.5.4 Sewer

We proposed to construct a gravity waste pipeline from the WTP site to the sewer network outside 264 Whau

Valley Road. Refer to Section 4.4 for further details.

4.5.5 Service Water

We propose that on-site service water pumps are provided for the process water requirements (poly dosing,

gas chlorine dosing), providing security independent from the reticulation and that water for amenities and

wash down is provided from the local reticulation at the gate, with chlorine contact time provided in the

existing reservoirs.

4.6 Hydraulics

4.6.1 Hydraulic Grade Line

The following table summarises key hydraulic levels.

Table 11: Key Hydraulic Levels


Dam – Spillway level 107.724 m RL One Tree Point Fundamental Datum from survey September 2014, drawing number T294.

Dam depth at inlet valve tower 18 m On drawing 1893 “Proposed Whau Valley Earth Dam – Typical Cross Sections” spillway noted as 449’ and base of inlet valve tower as 390’; therefore depth is 59’ = 18m

Lowest Intake Level 92.15 m RL RL 398’ (Drawing Valve Tower, 95A-22)

Dam – Floor level at inlet valve tower 89.7 m RL One Tree Point Fundamental Datum. Surveyed Spillway



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level minus Dam depth at inlet valve tower

Existing WTP Reservoir TWL 85.17 m RL One Tree Point Fundamental Datum from survey November 2013

New site ground level at 274 Whau Valley Road

79 to 81 m RL Site survey August 2015; refer to Section 5.1 and Appendix C for further details

A preliminary assessment of the main hydraulic grade line from the dam, through the treatment plant and into

the existing Whau Valley WTP reservoirs has been estimated.

Table 12: Key Hydraulic Friction and Fitting Losses


Raw water pipe to 274 Whau Valley Road

4

m H2O Diameter: 525 CLS from WDC’s GIS intramaps

Length: 1600m estimated from WDC’s GIS intramaps

Pipe roughness 0.3 (conservative for raw water pipe)

Assumed fittings: 4 of 45° bends, 3 of 90° bends. Isolation butterfly valve

Rapid Mixing 2 m H2O Allowance for coagulant rapid mixing

Flocculation structure 0.25 m H2O Over and underflow baffle structure

Clarifier floor 0.1 m H2O Pipework sized for minimum loss

Clarifier launders through to filter inlet 0.1 m H2O Pipework sized for minimum loss

Filtration 3 m H2O Allowance for maximum media loss and hydraulic losses

UV disinfection 0.15 m H2O Standard low pressure reactor capable of 3 log removal at peak flow ~550m

3/h

Treated water pipe from existing reservoir to 274 Whau Valley Road

3 m H2O Diameter: 525 CLS assumed same as raw water pipeline

Length:1000 m estimated from WDC’s GIS intramaps

Pipe roughness 0.3 (conservative for treated water pipe).

Table 13: Hydraulic Grade Line

Position HGL Basis

Dam Top Water Level 107.724 Existing – Level from survey October 2014

Dam Lowest Operating Level 92.15 Based on dam construction drawings

Flocculation Inlet Level 84.75 250mm loss to clarifier

Clarifier TWL 84. 8 Floor level RL 80.3 approx. based on survey August 2015 and flood and dam break levels; refer Section 5.2

Filter TWL 84.45

Filter Outlet 81.45 3000mm allowance for losses through filters

WTP Outlet 90.17 HGL to existing reservoir

Reservoir Inlet (existing) 85.17 Existing - Level from survey November 2013

Hence a total pump head of 9m is required for 274 Whau Valley Road (Filter Outlet to WTP Outlet). Note

under typical operating conditions however (ie clean filters, typical flow), the pumping head would be less.

The levels for the new site are based on the following factors:



6519113 // NZ1-11649715-4 0.4 // page 26

n Existing Ground levels.

n Hydraulic Levels – fitting into the hydraulic grade line from the dam to the existing reservoirs, minimising

energy losses.

n Flood levels –Structures at 274 Whau Valley road are proposed to the have floor levels above the 1:100

year flood zone, estimated at between RL 77.4 m – RL 79.6 mfrom the Northland Regional Council’s

flood map and analysis completed (refer to Section 5.2 for further details). Buildings will have a minimum

floor level of 80.3, or at least 400mm above the estimated flood level.

The proposed levels are only nominally at existing natural ground levels (nominally 80.3mRL). Flood levels

limit the ability to reduce the foundation level, which would be desirable from a geotechnical point of view.

Refinement of the flood levels could result in a small adjustment to these levels.

The preferred hydraulic arrangement would be to separate the backwash and treated water surge tanks.

The water would be pumped into the treated water surge tower to match the flow balance/demand. The level

in this tank would be allowed to vary to match the hydraulic grade line. At high demand the level would rise,

and with low demand the level fall. Pumping head will also vary with filter headloss. Hence with this

arrangement energy consumption is minimised.

The backwash tank will need to be refilled following each backwash. Maintaining this as a separate tank will

preserve the required volume for backwashing without compromising the plant hydraulics.

4.6.2 Energy Recovery

With surplus head available under typical operating conditions (ie dam full), potentially energy could be

recovered, reducing plant operating costs. The following is a preliminary assessment of the energy that

could be recovered.

Table 14: Potential Hydro Power Recovery


Maximum Available Head 17m Dam Top Water Level 107.72

Flocculation Inlet RL 84.75

Total friction losses 6m allowed

Average Flow 115 l/s 10,000 m3/d assumed

Power Output 11.5 kW 60% total pump and motor efficiency assumed

Annual Energy Output 70,500 kWH Assumes 70% utilisation

Value $12,100/annum 18c/kWH assumed. Based on use within the plant. Price for energy sold to the network would be lower.

A simple direct on line pump operating as a turbine arrangement would be the lowest capital cost, with a

basic pump costing around $20,000, or around $60,000 installed, plus building space. A normal end suction

centrifugal pump and induction 3 phase motor would be used, and hence the installation utilises readily

available components. A bypass control valve would be required for operating conditions of lower head (ie

dam level dropping) or higher flow.

Addition of a variable speed drive with an active front end would enable the use of the pump under a wider

range of operating conditions (flow and head), and hence significantly increase the utilisation of the available

energy. This technology is not widely used at this low capacity however and hence further investigation

would be required to determine the cost and viability of this addition.



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Some further energy output could be possible by returning excess flow to the stream when the flow was

available, rather than spilling over the spillway.

With a long term outlook and desire to conserve energy the implementation of a turbine could be considered.

Photovoltaic solar energy could also be considered if the council were interested in minimising their energy

use.

Another advantage of installing a turbine instead of a control valve would be a reduction in operating noise; a

pump as a turbine is much quieter than a control valve.



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5 Site Layout

The 274 Whau Valley Road site is a flat area that has adequate space for the WTP with at least a 10m

setback to neighbouring residents.

The site layout is included in Appendix B. This includes the following infrastructure:

n Enclosed inlet flow control building (to house either control valve or pump as turbine)

n Clarifier/flocculation structure

n Dual Media Filter structure

n Chemical dosing and delivery bunds

n Double story plant building with space for

– UV units

– Enclosed machinery room for air compressors and air blowers to reduce noise at site boundary

– Enclosed generator room to reduce noise at site boundary (note that generator is operated very

infrequently)

– MCC room on upper level, above the highest Whau Valley Dam break level (refer Section 5.2).

– An amenity area to reflect the use of this plant as WDC’s water operations base, equivalent to the

existing plant. This includes a suitable lunch room, control room, offices, meeting room spaces,

storage, workshops and toilets/showers. The control room is to be located on the upper level to give

operators a view out over the filters and clarifies, as requested by WDC operators.

n Gas chlorine building

n Ring road for chemical deliveries and site access

n 12 car parking spaces

n An off spec water / storm water retention pond at the low point of the site, with discharge to the stream

Future provisions are allowed for:

n Second stage of filtration option to provide enhanced organics removal

n UV peroxide dosing - option to provide enhanced organics removal

n Fluoride dosing with HFA

5.1 Survey

A full topographical survey of the project area was undertaken by Boundary Hunter Ltd in August 2015. The

extent of the survey included:

n All above ground infrastructure such as power poles and below ground infrastructure where visible such

as manholes or culverts (note culvert crossing under driveway on north east boundary) within the area of

survey and up to the extent of survey required.

n Topographic features to be surveyed to an accuracy of +/-50mm, over a grid sufficient to generate an

accurate triangulated surface over the area of interest suitable for 0.2m contours.

n Watercourses, drains and swamps or springs within the Area of Survey, and for 10m downstream of the

culvert crossing.

n Marker stakes and locations of ground investigation boreholes where visible (approx 8No.),

n Edge of seal of road and existing vehicle crossings nominally 100m each direction from site boundary.

n Outline detail of the one-lane bridge structure including adjacent pipe bridge,

n Levels and detail to establish overland flow paths.

n Connection to two existing benchmarks at corner of Fairway Drive and Whau Valley Road.

n Accurate boundary data to +/-0.1m or better and current occupation.



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n Survey is to be delivered in terms of Mount Eden 2000, using origin of Coordinates: SS 264 SO 48581

(LINZ Geodetic Code C2NM), and vertical datum One Tree Point 1964.

n All significant (>5m height) trees within survey scope

n Top water level of the Fairway Drive reservoirs

Refer to Appendix C for the survey output. This survey data has been included in the site layout in Appendix

B.

Data from previous site surveys in November 2013 and October 2014 (Dam spillway level, top water level of

Fairway Drive reservoirs) has also been used.

5.2 Flood Hazard Assessment

5.2.1 Flood

The 274 Whau Valley Road is close to the 1:100 flood level, and although shown as clear of the flood plain

on Figure 1, the area is relatively low lying and caution will need to be taken in the development of the site to

avoid flooding risks. The red lines show the approximate site boundary, the yellow square shows the

approximate location of the WTP building and structures, the dark blue in the 1 in 10 year flood mapping and

the light blue is the 1 in 100 year flood mapping.

Figure 1: Northland Regional Council Flood Mapping

The proposed development and any associated bunding will be located away from the flood plain resulting in

minimal change to upstream or downstream flood levels due to the construction of the new water treatment



6519113 // NZ1-11649715-4 0.4 // page 30

plant. The expected flood level across the site is likely to range between RL 77.4 m – RL 79.6 m (refer to

Appendix I for further details . The proposed finished floor level for the water treatment plant is RL 80.3 m,

therefore a minimum freeboard of 0.4 m is provided. A normally dry pond with a flow restricted outlet will be

included in the site development which will buffer stormwater flows from the site such that the risk of

downstream flooding is not increased by this development. Opportunity may also be taken in the

landscaping of the unused and buffer spaces around the site to further reduce the risk of downstream

flooding. During next stage of design, we recommend that an ecologist is consulted for suggested pond

planting.

5.2.2 Whau Valley Dam Break

In the event of a dam break, the worst case peak flood level could inundate the site to a depth of

approximately 5m in the worst case scenario as reported in Whau Valley Dam - Dam Break Flood Hazard Assessment by Opus in September 2010:

n “Sunny day” (non-flood conditions) failures are expected to result in peak levels between 76.5mRL (ie

well below proposed) structure floor levels and 82.7mRL (2.5m above proposed floor level 80.3mRL).

n “Rainy day” (induced by extreme flood) failures are expected to result in peak levels between 79.3mRL

(1m below nominal floor level of 80.3mR) and 85.3mRL (5m above proposed floor level 80.3mRL).

The Opus report notes that the probability of the Whau Valley Dam actually failing in either sunny or rainy

day mode is extremely low. However, possible mitigation to minimise the return to service should this event

occur will be considered during detailed design and is likely to include locating the MCC room above the

highest probable dam break flood level, ie on the upper floor of the amenities building at 85.3mRL.

5.3 Geotechnical Investigations

A geotechnical investigation has been completed at the 274 Whau Valley Road site. The Geotechnical

Factual Report is contained in Appendix D and Preliminary Geotechnical Interpretive Report in Appendix E.

A soft to firm layer of silt and clay was recorded in all the investigation points between approximately 3 and

9.5m deep. In borehole BH1 a floating basalt boulder was encountered at 8 m depth within the silt-clay

deposit which may make piling difficult. Basalt rock was found at depth around 17 m in this borehole.

Settlement analysis has estimated total static load settlements of up to 210mm could occur without ground

improvement and shallow foundations. In addition under a seismic event settlements of 90 to 140mm could

occur. These total settlements and the potential for differential settlement is such that shallow foundations

are not considered appropriate and some form of ground improvement is required.

Options considered for ground improvement at 274 Whau Valley Road are discussed below.

5.3.1 Preloading

Preloading of the site prior to construction could be designed to consolidate the underlying materials and

remove most of the total expected post construction static settlement. The extent of this would depend on the

extent and duration of the preloading works. Improved drainage, such as the installation of vertical wick

drains, into the compressible silt and clay layer would assist with the dissipation of pore pressure and

increase the rate of consolidation settlement (i.e. reduce the preload time). Approximately 3 to 3.5m of

material would be needed to preload the site.

Our initial settlement analysis shows that the majority of the settlement occurs within the first 2.5 years at the

western end of the site and potentially 6 months at the eastern end of the site. A better understanding of the



6519113 // NZ1-11649715-4 0.4 // page 31

permeability and organic content within the silt and clay layer, and the other geological units, would provide a

more accurate indication of the consolidation timeframes. Low permeability and organic rich materials usually

take a longer period of time to consolidate, and this could affect the suitability of preloading. Preloading will

not prevent or reduce the estimated level of liquefaction settlement occurring at depth.

Some of the preload material could be left as additional fill to elevate the site out of the flood hazard zone,

although building structures upon remaining preload material would defeat the purpose of preloading, and

hence the benefit of the additional fill would only be outside of the building foot print.

5.3.2 Dynamic Deep Compaction

This method involves mechanically inducing settlement by dropping a heavy weight onto the ground surface

from a crane. Improvements in geotechnical properties to depths of about 10m are possible. This method is

a faster way of achieving pre-construction consolidation, but is relatively expensive compared with pre-

loading, and is highly disruptive and potentially damaging to neighboring residences. Due to the nature of the

ground and proximity to residential dwellings, this is unlikely to be a viable option.

5.3.3 Soil Stabilization

The bearing properties of soft silts and clays can be improved by mixing cement into the soil. The method

involves using a specialized rig to rotary drill to desired depths (at this site up to 9m) then inject cement grout

(or other chemical additive) as the equipment is retracted. The result is a chemically stabilized column

usually 300 to 800mm diameter. It would not mitigate any liquefaction induced settlement that may occur at

depth, but would limit differential settlement at the surface by providing a ‘rafting’ effect and liquefaction at

depth is likely to be low.

5.3.4 Partial Compensated Foundation

Excavating and embedding structures into the underlying soils can reduce the overall static loads affecting

the soil. Every meter of soil removed from the surface will reduce the overall static loading by approximately

16 - 17kPa. Reduced static loading will reduce the total settlement that could potentially occur at this site.

The scope to lower foundation levels on this site is limited by the flooding issue at this site. There would also

be issues with the increased depth of associated services and decreased constructability (particularly when

below the groundwater level) would need to weighed against reduction in total settlement.

5.3.5 Excavation and replacement of the upper soil

Differential settlement could be partially mitigated by excavating the upper firm-stiff clayey silt layer (Layer 1),

and recompacting this as fill to develop a raft foundation. A raft foundation would reduce the potential for

differential settlement to occur at the surface during static or seismic settlement, thereby reducing the

potential for structural damage. Reinforcement of this fill layer with geogrids can also help mitigate against

differential settlement. Total settlement would need to be mitigated by other means. The practical extent of

this option will be controlled by the groundwater level, as excavation and compaction are difficult below

groundwater.

5.3.6 Recommendation

Our recommended ground improvement option would be to undertake soil stabilisation (cement columns), in

combination with the excavation and recompaction of the upper soil layer (Layer 1) and piling of heavily

loaded structures. These methods would significantly reduce the estimated consolidation settlement that

could occur in the soft silt and clay layer (Layer 2). Liquefaction would still be expected to occur at depth



6519113 // NZ1-11649715-7 0.7 // page 32

under the design earthquake of the structure, however differential settlements will be mitigated by the

‘stabilised’ soils, and the re-compacted soil at the surface (Layer 1) providing a rafting effect.

5.4 Bulk Earthworks

Bulk earthworks will be required for the construction of the proposed works. The current concept design will

require earthworks comprising an approximate total cut of 4,200m3 and an approximate total fill of 4,700m

3.

The bulk earthworks estimates for the key components of the proposed works requiring earthworks are

estimated below. In summary, a net total of approximately 1,500m3 is estimated to need to be disposed of

off-site, assuming that approximately 1,600m3 imported material is used as fill under the structures and for

the ring road.

Table 15: Bulk earthworks

Area Cut (m3) Fill (m

3) Balance (m

3)

Low level landscaping earth bunds (1)

0 900 900

Water treatment plant structures(2)

2400 2400 (4) Up to -1,000 m

(3)(4)

Dry pond (3) 600 100 -500

Relocate existing drain 700 700 0

Roading 500 600 (5)

-500

(1) 400m length of landscaping bunding, average 6m wide and 0.75m high

(2) Assumes excavation and recompaction of the upper soil layer, assumed 1.5 deep

(3) Average 1m deep

(4) Up to 1,000 m3 of this fill material may be imported fill

(5) Approximately 600 m3 imported fill would be used

5.5 National Environmental Standard Study

WDC has undertaken a search of records for 274 Whau Valley Road to determine the indication of current or

previous activities in the area that are included on the current Hazardous Activities and Industries List (HAIL)

and no such activities were found. The report is contained in Appendix F.

5.6 Traffic Impact, Bridges and Roading

5.6.1 Traffic Impact

A preliminary assessment of increased vehicle movements associated with the operation of the WTP is

estimated to be:

n Up to 8 operators and supervisors arriving and departing several times a day as they would be using the

new WTP as a home base.

n Monthly chemical deliveries for four chemicals – could be expected to receive one delivery a week.

n Service staff such as electricians, fitters, sale reps arriving several time per month

n Other WDC staff visits on a weekly basis

n Irregular and infrequent visits from groups such as schools

Refer to Section 7 for estimated construction related traffic.



6519113 // NZ1-11649715-7 0.7 // page 33

5.6.2 Single Lane Bridge

Preliminary neighbourhood consultation (refer Section 6.5.1) identified concerns with the safety of the one

way bridge at 254 Whau Valley Road.

WDC’s roading engineers have advised that this bridge is up for replacement within the next 20 years and

may be as early as 2024. However, it is unlikely that this bridge could be upgraded to two lanes with funding

from council/NZTA as most of WDC’s 520 bridges are single lane. For funding from council/NZTA, this

project would need to demonstrate that it is a strategic high volume route with significant safety issues if left

as a single lane bridge.

This bridge is currently unable to support overweight loads. A similar sized WTP is currently being

constructed using an 80 tonne crane, which has a 57 tonne body. This is overweight and the bridge would

need to be rated to HNHO. It could be possible to work within the lower capacity of the existing bridge, but

this would constrain the construction methodology.

The construction of a pedestrian bridge on the southern side of the existing bridge has been proposed, in

order to provide safe pedestrian access. The bridge is proposed to be independent of the existing bridge

structure and on the southern side, avoiding the existing raw water pipe. The bridge would span the river

and hence no structures in the river bed are required.

5.7 Landscape Design

A 10m set back from the site boundary has been proposed and is shown on the site layout. We would expect

that this set back would include the boundary fence, either within the setback, or at the edge. The setback

would also include low level earth bunding.

5.8 Future Use of Existing WTP Site

WDC has advised that the existing site on the corner of Fairway Drive does not have a historical

classification and can be decommissioned and demolished post successful commissioning and stable

operation of a new plant. The existing reservoirs are expected to remain in service for some time yet.



6519113 // NZ1-11649715-4 0.4 // page 34

6 Consenting and Compliance

6.1 Summary of Consenting Process

We understand that WDC wish to undertaken the following consenting process for the Project:

n Designate the site via a Notice of Requirement (NoR); and

n Apply for the required regional consents in conjunction with the NoR (bundle the applications),

The above applications shall be submitted to WDC and Northland Regional Council as one comprehensive

application to be processed by Council’s on a fully notified basis.

A number of technical assessment reports shall be prepared to support the application and include:

n Noise Assessment;

n Landscape and Visual Assessment; and

n Ecological Assessment.

A summary of the matters to be considered in the technical assessments is outlined below.

6.2 Operational Noise and Vibration

We would expect that the compressors and backwash blowers to have the highest noise output. Mitigation

such as housing in a machinery room with good sound insulating properties, along with specification of noise

mitigation as part of the compressor and blower packages (ie inlet/outlet silencers and acoustic enclosures)

could be implemented and the project cost estimate has appropriate allowances for this. Measures such as

these would be expected to be adequate to limit noise to levels complying with district plan requirements and

would mitigate impact on the surrounding neighbours.

Should on site sludge dewatering be implemented, centrifuges are likely to be the preferred process

technology for dewatering. Centrifuges have significant noise output which would need to be managed.

Management of noise through sound proofing of buildings and acoustic attenuation of ventilation systems is

feasible, however this is more onerous than other plant equipment given the need to also maintain

reasonable ventilation to maintain a suitable environment within the building.

Standby power generation would output greater noise than the District Plan requirements without significant

acoustic attenuation. Given testing is completed during working hours, use during the more noise sensitive

night period would be rare and leniency is commonly allowed for this use. We would suggest the planning

applications make allowance for more lenient noise levels for emergency generator operation. Mitigation in

the form of both acoustically enclosing the generator set plus housing in a building with substantial

construction (ie concrete/masonry walls and insulated ceiling) can be achieved at reasonable cost and will

substantially reduce the noise output, but would not be expected to achieve full compliance with District Plan

requirements.

The head from the Whau Valley Dam will often need to be broken before entering the flocculation and

clarifiers. As discussed in Section 4.1.2, this could be done using either a control valve or a pump as a

turbine. Of the two options, a control valve is noisier. We propose that either option is enclosed in building

with good sound insulating properties, especially as the location of this building is best located near the

boundary line.

Specialist acoustic engineering advice would be necessary at the detailed design stage to enable

compliance with the district plan requirements to be met.



6519113 // NZ1-11649715-4 0.4 // page 35

Refer to Section 7 for construction related noise and vibration.

6.3 Ecology

The site appears not to contain significant indigenous vegetation or terrestrial habitat features within the

potential footprint of development. Ecological considerations will focus on the aquatic environment. The site

contains an unnamed tributary to the Waiarohia Stream. This very small tributary appears to be pastoral and

infilled and is likely to be highly degraded in terms of instream value, if any. It is unlikely to host aquatic life

and appears not to lead to any upstream aquatic habitat. The Waiarohia stream itself joins the Whangarei

Harbour several kilometres to the southwest. The stream is pastoral on its southern and western sides and

largely urbanised on its northern and eastern sides. It is known to hold a wide range of native fish and

probably also invertebrate species. There is unrestricted access for most native fish species to move

between the mid reaches of the stream and the harbour. However the Whau Valley dam in the upper

reaches of the catchment truncates connection to otherwise potentially valuable habitat and also modifies

the hydrological regime in the stream.

The Ecological Assessment will focus on the influence of the project on the unnamed tributary to the extent

that consequential downstream effects on the Waiarohia Stream might occur. Effects areas include

watercourse crossing, sediment generation during the works period and operational discharges that might

occur or be required periodically from the plant. Effects are anticipated to be minor. There are no ecological

or water quality constraints that would need to be factored into the design.

6.4 Archaeological and NZ Heritage Assessment

WDC has commissioned an archaeological assessment of 274 Whau Valley Road; refer to Appendix G for

the full report.

The report found that there are no obvious archaeological features at 274 Whau Valley Road and thus no

archaeological impediment to developing the WTP on the property. However, the level and well-watered site

would have been suitable for Maori horticulture and related archaeological features may be present below

the ground surface. These may be accidentally encountered during the development of the WTP, therefore

the report recommends that WDC apply for an archaeological authority under Section 44 of the Heritage

New Zealand Pouhere Taonga Act 2014, with associated recommendations for consultation with tangata

whenua, development of archaeological management plan and that the preliminary earthworks are

monitored by an archaeologist. This will be undertaken separate to the NoR / regional consenting process,

and prior to works commencing on the site.

6.5 Consultation

6.5.1 Neighbourhood

WDC has already commenced consultation with surrounding landowners and will continue discussions as

the Project progresses. If the technical assessments identify that there are any adverse effects on

surrounding properties then it will be important to discuss these with any affected landowners and confirm

appropriate mitigation to address these effects.

Concerns raised to date include:

n Visual impact of the treatment plant from the road;

n Impacts on property values;

n Impacts on the look and feel of the rural area;



6519113 // NZ1-11649715-4 0.4 // page 36

n Visual impact of the treatment plant from owners properties;

n Concern that other sites have not been properly considered;

n Concerns about the sufficiency of the landscaping to screen the plant; and

n Safety of the one way bridge and lack of footpath with increased traffic movements

6.5.2 Iwi / Mana Whenua

WDC has undertaken consultation to date. Mana Whenua would like to remain informed.

6.6 Landscape and Visual Assessment

An assessment of landscape and rural character effects, to look at the landscape and character changes

that can be expected will be provided. A landscape integration framework concept will accompany this. It will

be a reasonably schematic and loose diagram to demonstrate what a proposed WTP might look like without

locking down the design in too much detail.

Visualisations can be provided in order to give an indication of the size and bulk of the WTP. These could be

useful for consultation purposes and to accompany the Concept Design Report as a part of the AEE.



6519113 // NZ1-11649715-4 0.4 // page 37

7 Concept Construction Methodology

7.1 Concept Construction Methodology

The new WTP is expected to be constructed in a typical fashion; earthworks, followed by foundation

construction, structural work, and mechanical and electrical fit out.

We expect that the work would be carried out during working hours 7:00 to 19:00 Monday to Friday and 7:30

to 18:00 Saturday.

7.2 Estimated Additional Vehicle Movements

At the construction peak we expect that there will be in the order of 15 vehicles on site, with other vehicles

making deliveries. On site workers could peak at up to 30.

7.3 Noise and Vibration

Assessment of the existing noise levels are currently being undertaken. While testing and analysis is yet to

be completed, initial indications are that the existing noise environment is very quiet therefore there is likely

to be a strong expectation of acoustic amenity. Because of this high level of expectation, it is considered that

a high level of design should be pursued.

7.4 Sedimentation and Erosion Controls

Erosion and Sediment Control generated by construction activities will be managed in accordance with

Auckland Council’s TP90 standard.



6519113 // NZ1-11649715-4 0.4 // page 38

Appendix A

Process Flow Diagram

Whau Dam

Hatea Intake

Caustic Alum Poly

Flocculation Clarifiers

Caustic

Chlorine

4 Filters

Backwash WasteTank

Filter to Waste Recycle

BackwashClarifier

Poly

Caustic

Chlorine

Sewer

Recycle toRaw Water

Poly

Centrifuge

PolySludge

Thickener

Centrate

To Landfill

FutureFilters

UV

To FairwayDrive Reservoirs

Treated Surge Tower

FUTURE DEWATERINGOPTION

HydrogenPeroxide

UV

Backwash Tank300m3

FUTURE UV PEROXIDEOPTION

FUTURE FILTER OPTION

Future Fluoride

Sludge / SewerBalance Tank

OPTIONAL

No. AppdRevision By Chk Date

Drawing Originator:

DO NOT SCALE

* Refer to Revision 1 for Original Signature

Scale (A1)

Scale (A3)Reduced

Dwg Check

Dsg Verifier

Drawn

Original DesignConstruction*

Date

Approved For Client: Project:

IF IN DOUBT ASK.

Title:

Drawing No.

Discipline

Docu

ment

No.

Rev.

Drawing Plotted: 11 Nov 2015 10:15 a.m.

6519

113-

G-01

1.DW

Gw

ww

.ch2

mbe

ca.c

omw

ww

.ch2

mbe

ca.c

om

www.ch2mbeca.comB FEASABILITY STUDY SJB FTN PLR 17.10.14

6519113-G-011 DNEW PLANT PROCESS FLOW DIAGRAM GENERALWHANGAREI DISTRICT COUNCIL WHAU VALLEY WTPNTS

P. LAROCHE

A OPTIONS ASSESMENT SJB FTN PLR 13.03.14

C ISSUED FOR CONSENTING BSE FTN PLR 25.09.15

NOT FOR CONSTRUCTION

PRELIMINARY

D CONCEPT DESIGN BSE FTN PLR 10.11.15



6519113 // NZ1-11649715-4 0.4 // page 39

Appendix B

Site Layout

No. AppdRevision By Chk Date

Drawing Originator:

DO NOT SCALE

* Refer to Revision 1 for Original Signature

Scale (A1)

Scale (A3)Reduced

Dwg Check

Dsg Verifier

Drawn

Original DesignConstruction*

Date

Approved For Client: Project:

IF IN DOUBT ASK.

Title:

Drawing No.

Discipline

Docu

ment

No.

Rev.

Drawing Plotted: 30 Oct 2015 3:49 p.m.

6519

113-

G-01

2.DW

G

6519113-G-012 A

AMENITIES BUILDINGPLAN GENERALWHANGAREI DISTRICT COUNCIL WHAU VALLEY WTPAS SHOWN

AS SHOWN

P. LA ROCHE .10.15C. HILLENAAR .10.15

A ISSUED FOR APPROVAL CPH FTN PLR 30.10.15

FOR APPROVAL

NOT FOR CONSTRUCTION



6519113 // NZ1-11649715-4 0.4 // page 40

Appendix C

Site Survey

OIS IV DP157587

80.18

SSMH

77.75

SSMH

77.55

TELECOM

power pole

TELECOM

power pole

power pole

power pole

BOUNDARY PEG

78.13

powerpole

totara

totara

BOUNDARY PEG

78.52

totara

STAKE

BOREHOLE

STAKE

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BOREHOLE

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TROUGH

RL 79.88

(base)

totara

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fo

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tio

n

swampy

ground

swampy ground

swampy

ground

o

p

e

n

flo

w

in

g

stre

a

m

o

p

e

n

flo

w

in

g

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a

m

Sewerage pump station

footbridge

8

0

°4

0

'2

0

"

(1

8

6

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5

)

5

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5

3

4

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0

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7

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5

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3

1

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9

2

8

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2

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0

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2

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4

0

'

256.77

(318.57)

7

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6

6

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1

1

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0

"

7

8

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0

2

1

0

8

°

4

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0

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(

7

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278

149

161

248

250

252

254

258

260

276

159

264

266

276A

274

175

Lot 1

DP 348519

Lot 5

DP 340586

4.8550

Lot 1

DP 405632

Lot 2

DP 348519

Lot 2

DP 340586

Lot 1

DP 340586

Lot 2

DP 195500

Lot 2

DP 207775

Lot 1

DP 207775

Lot 1

DP 41275

Lot 2

DP 41275

Lot 3

DP 41275

Lot 3

DP 199102

Lot 1

DP 38871

Lot 2

DP 51603

Lot 9

DP 157457

culvert

f

e

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78.45

power poles

power pole

seale

d fo

rmatio

n

BK BM

REV.

SURVEY

24/08/15

BY DATE

Hz. 1:500 @ A1

Existing Contour Survey

Proposed Whau Valley Water Treatment Plant

Email. [email protected]

Ph. 09 435 5387

Prepared By:

LTDBOUNDARY

09 435 5382

HUNTER

SCALE:

TITLE:

4662

JOB:

CAD FILE REVISION

1

SHEET

1000\4662\4662.dwg

purpose other than originally intended, without the permission of Boundary Hunter Ltd.

This drawing shall not be reproduced or copied in whole or in part,or used for any

CHECKED B Smith 26/08/15

DRAWN

BK 25/08/15

REV.

NOTES:

- Contours are at 0.2m intervals.

- Levels are in terms of LINZ One Tree Point Datum SS264 SO48581 (C2NM) R.L.88.75.

- All underground and above services may not be surveyed or shown on this plan.

Please consult Service Providers before carrying out any excavation or construction.

- Boundary Hunter Ltd accepts no responsibility for services omitted by this survey.

COUNCIL

DISTRICT

WHANGAREI

Prepared for:

Meters

0

15

30

AutoCAD SHX Text

Fax



6519113 // NZ1-11649715-4 0.4 // page 41

Appendix D

Geotechnical Factual Report

Report

Whau Valley WTP Upgrade Addendum Geotechnical Factual Report - 274 Whau Valley Road



26 June 2015

Conten

1 Introd1.1 O

1.2 S

2 Previ

3 Curre3.1 M

3.2 C

4 Appl

5 Refer

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rences

ndices

ix A

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ix B

ne Borehole

ix C

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Scope of Inve

n and Descri

estigation

Investigareholes

ration Tests (

Statemen

Logs and Co

Test Logs

Whau

estigations

ption

ns

ations

(CPT)

nt

ore Photogra

Valley WTP Upgr

aphs

rade Addendum GGeotechnical Factuual Report - 274 W

CH2M B6519113 // NZ

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ying ground cnterpretive Rpment of this

tion associatWhau Valley W

reports for th

WTP Upgraber 2014. WTP Upgraber 2014.

escription

oad accordinalley Road. T

west orientedn at the baseed east, wesed creek flowhe Whau Vall

as an elevatio

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igations

CH2M Becaarei District C

Valley WTP Upgr

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d CH2M Bec

gations

Road for fea is the seconconditions at

Report which s site.

ted with the gWTP Upgradhe previous s

ade – Geotec

ade – Geotec

n

ng to WDC InThe centre o

d valley with e of the vallest approximaws down this ley.

on of approx

s

a. 2014. WhaCouncil, Octo

rade Addendum G

arei District CWhangarei.

ca Ltd.

asibility of cond site to be t two boreholwill assist th

ground invesde Addendumsites are:

chnical Factu

chnical Interp

ntramaps proof this site is a

drainage towey. 274 Whauately 200m w

valley and jo

ximately 80m

au Valley WTober 2014.

Geotechnical Factu

6

Council (WDC

nstructing a investigatedle locations. e geotechnic

stigation. Thism Geotechni

ual Report, R

pretive Repor

operty GIS syapproximate

wards the noru Valley Roa

wide and 550moins the Waia

m, but is surro

TP Upgrade –

ual Report - 274 W

CH2M B6519113 // NZ1-1089

C) to underta

new water tr. The purposThis informacal issues an

s report is tocal Interpret

Report prepar

rt, Report pre

ystem. It is sely 1717378E

rth east. Whad is otherwism long near arohia stream

ounded by hi

– Geotechnic

Whau Valley Road

Beca // 26 June 201599613-1 0.1 // page 1

ake

reatment se of this ation will be nd

o be read in ive Report –

red for

epared for

situated E 6048677N.

au Valley se known as the mouth

m which

lls of up to

cal Factual

d

5 1

3 Cu

Field investlocations arBeca EnginBeca Engin

A list of stan

Table 1 - Sum

Field Proced

Soil and Roc

Standard Pen

3.1 Ma

Machine bosummary of

Table 2 - Sum

BH No.

BH1

BH2

Notes: All su In-situ testin

Standarduncorrec

Machine bobeen loggedbeing transf

The core sadesiccation

Upon comp

urrent F

igations comre presented eering Geoloeering Geolo

ndards used

mmary of Stan

dure

ck logging

netration Test

achine Bo

oreholes weref all machine

mmary of Bore

Location

Western sfield

Eastern sfield

rvey coordina

ng, undertake

d Penetrationcted N-value

orehole logs ad, they were ferred to the

amples will band degrada

pletion, both b

Field In

mmenced on in Figure 1 A

ogist. Unlessogist.

during the fi

ndards used in

ting

oreholes

e drilled by Pe boreholes u

eholes Drilled

E

side of 1

ide of 1

tes given in N

en during dri

n Tests (SPTs are recorde

and core phowrapped in Beca Auckla

e stored for aation of the c

boreholes we

Whau

vestiga

8 June 2015Appendix A. s otherwise s

eld investiga

n this Investiga

Pro-Drill (Aucundertaken is

Easting

1717352

1717407

ZTM

illing of the m

Ts) were typied on the bo

otographs arplastic to redand office at

a period of score samples

ere backfilled

Valley WTP Upgr

ations

5 and were c The machistated, all so

ations are sh

ation

Stan

In geSocie

ASTM

ck) Ltd usings given Table

North

6048

6048

machine bore

ically carriedorehole logs.

re presented duce moistur21 Pitt Stree

six months fos will occur th

d with gravel

rade Addendum G

ompleted byne boreholes

oil and rock lo

own in Table

dard Used

eneral accordaety Guidelines

M D 1586 Rev

an AMS Soe 2.

hing

660

666

eholes comp

out at nomin

in Appendixre loss and pet, Auckland

ollowing delivhrough time

, sand and b

Geotechnical Factu

6

y 15 June 201s were superogging has b

e 1, below:

ance with News (NZGS, 2005

v A, 2008

nic 150hz Ro

R.L. grou(m)

80.5

79.5

rised:

nal 1.5m cen

x B. After theplaced in labefor storage.

very of this refollowing sto

bentonite.

ual Report - 274 W

CH2M B6519113 // NZ1-1089

15. The invervised full-tim

been underta

w Zealand Geo5).

oto-Sonic Dr

und Tota

19.0

11.1

ntres and the

e core samplelled core bo

eport. Someorage.

Whau Valley Road

Beca // 26 June 201599613-1 0.1 // page 2

estigation me by a aken by a

otechnical

rilling Rig. A

al Depth (m)

0

5

e

es had oxes before

e natural

d

5 2

3.2 Co

Static Conemeasure cobelow. TestAppendix C

Table 3 - Sum

CPT No.

CPT1

CPT2

CPT3

CPT4

CPT5

Notes: All su

4 Ap

This report use for the pby any persown risk.

This is a faclocations anlocations arour observaunderlying c

No interpretthe applicabindependen

one Penet

e Penetrationone resistanct records for

C.

mmary of CPT

Loca

See

See

See

See

See

rvey coordina

pplicab

has been prepurpose for w

son contrary

ctual report ond no inferenre made. Fuation of the sconditions.

tation of the bility of this rent investigatio

tration Te

n Tests (CPTce, sleeve friccone resista

T Locations

ation

Figure 1.

Figure 1.

Figure 1.

Figure 1.

Figure 1.

tes given in N

ility Sta

epared by Bewhich it is intto the above

of field investnces about thrthermore loamples reco

investigationreport for the ons to satisfy

Whau

ests (CPT

T’s) were conction and wance, sleeve f

Easting

1717347

1717390

1717393

1717415

1717411

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atemen

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e, to which Be

tigations. Thehe nature andgs are provid

overed in the

n results has proposed de

y your needs

Valley WTP Upgr

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nducted by Pater pressurefriction, frictio

N

6

6

6

6

6

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pecific instruccordance wieca has not

e field investd continuity oded presentifieldwork an

been made evelopment ds.

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ro-Drill (Aucke. CPT test loon ratio, and

Northing

6048684

6048671

6048650

6048651

6048677

uctions of ourth the agreedgiven its prio

tigations havof ground coing descriptiond may not b

in this repordescribed he

Geotechnical Factu

6

k) Ltd using aocations are pore pressu

R.L. g

80

79

79

79

79

r Client. It is d scope of wor written con

ve been undeonditions awaon of the soile truly repres

t. Should yoerein, it is ess

ual Report - 274 W

CH2M B6519113 // NZ1-1089

a model 662summarised

ure are includ

ground (m)

solely for ouwork. Any usensent, is at th

ertaken at disay from the inls and geologsentative of

ou be in any sential that y

Whau Valley Road

Beca // 26 June 201599613-1 0.1 // page 3

22 CPT rig tod in Table 3 ded in

Total Depth (m)

9.6

7.9

12.7

13.8

7.6

ur Client’s e or reliance hat person's

screte nvestigation gy based on the actual

doubt as to you carry out

d

5 3

o

t

5 Re

ASTM. 201Sampling of

CH2M BecaWhangarei

CH2M BecaWhangarei

NZ Geotechdescription

NZ Standar

eferenc

1. D 1586 REf Soils. ASTM

a. 2014. WhaDistrict Coun

a. 2014. WhaDistrict Coun

hnical Societof soil and ro

rd 4402. 1986

ces

EV A StandaM Internation

au Valley WTncil, October

au Valley WTncil, October

ty. 2005. Fielock for engin

6. Methods o

Whau

ard Test Methnal, West Co

TP Upgrade r 2014.

TP Upgrade r 2014.

ld Descriptioneering purpo

of Testing So

Valley WTP Upgr

hod for Stannshohocken

– Geotechni

– Geotechni

on for Soil anoses. Decem

oils for Civil E

rade Addendum G

dard Penetra, PA, 2011.

ical Factual R

ical Interpreti

d Rock - Guimber 2005.

Engineering

Geotechnical Factu

6

ation Test (S

Report, Repo

ive Report, R

ideline for th

Purposes.

ual Report - 274 W

CH2M B6519113 // NZ1-1089

SPT) and Spl

ort prepared

Report prepa

he field classi

Whau Valley Road

Beca // 26 June 201599613-1 0.1 // page 4

lit-Barrel

for

ared for

ification and

d

5 4

Appendix A

Figures

Whau Valley WTP Upgrade - 274 Whau Valley Road, Proposed Layout with Investigation Locations

6519113 Figure 1

Appendix B

Machine Borehole Logs and Core Photographs

CH2M Beca// 17 February 2014 // Page 1 3200000 // NZ1-1439856-CH2M BOREHOLE LOG KEY SHEET (0).doc

Log Key Sheet

CLASSIFICATION Based on USBR Unified Soil Classification System WATER

Water level on date shown METHOD (shows drilling method) OB open barrel Wash wash boring TT triple tube UT thin walled undisturbed tube SPT standard penetration test – open nose sampler SN standard penetration test – solid nose sampler MA machine auger PS piston sample PCT percussion – top drive PCB percussion – bottom drive Conc concentrics Sonic sonic SAMPLES Dx Disturbed sample, number x Bx Bulk sample, number x Ux(d) Undisturbed sample, number x, tube diameter d in mm Wx Water sample, number x MOISTURE D Dry, looks and feels dry M Moist, no free water on hand when remoulding W Wet, free water on hand when remoulding S Saturated, soil below water table

SOIL AND ROCK DESCRIPTIONS Soil and Rock Descriptions are generally as described in the NZ Geotechnical Society “Field Description of Soil and Rock – Guideline for the Field Classification and Description of Soil and Rock for Engineering Purposes”, dated December 2005. Vane Shear Strength measurements in accordance with the NZ Geotechnical Society “Guideline for hand held shear vane test” dated August 2001. INSITU TESTS SV = 40/10 Insitu shear strength and remoulded shear

strength respectively, as measured by Pilcon Shear Vane

= 50/12 Vane shear strength and remoulded vane shear strength respectively, corrected to BS1377

UTP = Unable To Penetrate with Shear Vane N = 15 SPT uncorrected blow count for 300mm

penetration Laboratory Test(s) carried out: AL Atterberg limits UU Unconsolidated undrained triaxial PSD Particle size CU Consolidated undrained triaxial CONS Consolidation COMP Compaction UCS Unconfined compression WEATHERING CW Completely weathered HW Highly weathered MW Moderately weathered SW Slightly weathered UW Unweathered

CONSISTENCY Cohesive Soils Undrained Shear Strength (kPa) Non-cohesive Soils SPT – Uncorrected Very soft <12 Very loose 0 to 4 Soft 12 to 25 Loose 4 to 10 Firm 25 to 50 Medium dense 10 to 30 Stiff 50 to 100 Dense 30 to 50 Very stiff 100 to 200 Very dense >50 Hard >200 GRAPHIC LOG (1 or a combination of the following)

Organic material

Mudstone

Gravel

Silt

Sandstone

Limestone

Clay

Siltstone

Shells

Sand

Volcanic Rock

No Core

ORGANIC SOILS Von Post Degree of Hummification H1 Completely unconverted and mud-free peat, when pressed gives clear water and plant structure is visible. H2 Practically unconverted and mud-free peat, when pressed gives almost clear water and plant structure is visible. H3 Very slightly decomposed or very slightly muddy peat, when pressed gives marked muddy water, no peat substance passes through the fingers and plant

structure is less visible. H4 Slightly decomposed or slightly muddy peat, when pressed gives marked muddy water and plant structure is less visible. H5 Moderately decomposed or very muddy peat with growth structure evident but slightly obliterated. H6 Moderately decomposed or very muddy peat with indistinct growth structure. H7 Fairly well decomposed or very muddy peat but the growth structure can just be seen. H8 Well decomposed or very muddy peat with very indistinct growth structure. H9 Practically decomposed or mud-like peat in which almost no growth structure is evident. H10 Completely decomposed or mud peat where no growth structure can be seen, entire substance passes through the fingers when pressed.

xxxxxxxxxxxxxxxx

xxxxxx

c c c c

. . . . .

. . . . .

. . . . .

v v vv v v

x xx x

9/06

/201

5

Son

icS

PT

Son

icS

onic

SP

TS

onic

SP

TS

onic

SP

TS

onic

SP

TS

onic

Very soft clayey SILT with trace organics; dark brown; moist, high plasticity. Organics:rootlets[Topsoil]

Firm silty CLAY; orange brown; moist, high plasticity.Mottled grey.

Soft; light grey.

No recovery. Rods dropped under own weight.

Very soft silty CLAY; grey; wet, high plasticity.

Soft organic SILT; dark greyish brown; moist, low plasticity. Organics: fibrous (Peat:H6)

Very soft clayey SILT minor organics; greyish brown; moist, highly plastic.

Soft organic SILT; dark greyish brown; moist, low plasticity. Organics: fibrous (Peat:H6) thinly interbedded with very soft clayey SILT minor organics; greyish brown; moist,highly plastic.

40mm lens Organics: amorphous

Soft clayey SILT with trace organics; brownish grey; moist, high plasticity.

20mm lens of brown, amorphous organicsGrey speckled black

Loose GRAVEL; black; moist, non plastic. Gravel: vesicular basalt

Dense BOULDERS; black; moist, non plastic. Boulder: up to 300mm, strong, slightlyweathered, vesicular basalt.

Very soft silty CLAY; dark grey speckled black; moist, high plasticity.

Dense BOULDERS; black; moist, non plastic. Boulders: <500mm, strong slightlyweathered; black; vesicular basalt.

To

pso

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ary

Allu

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121222

N=7

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N=0

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N=0

000009

N=9

215526

N=18

100

%50

%10

0 %

0 %

100

%10

0 %

100

%10

0 %

100

%10

0 %

10 %

100

%

MWP9/6/158/6/15

EQUIPMENT:DRILL METHOD:DRILL FLUID:

DRILLED BY:

LOGGED BY:SHEAR VANE No:

FOR EXPLANATION OF SYMBOLS AND ABBREVIATIONS SEE KEY SHEETA4 Scale 1:50

DIAMETER/INCLINATION:

DATE FINISHED:DATE STARTED:

AMS Sonic 150hz Roto-SonicPro-Drill (Auck) Ltd

DA

ILY

WA

TE

R L

EV

EL

DRILLING

-/ 90°

SC/Sonic/SPTWater

ME

TH

OD

GR

AP

HIC

LO

G

SOIL / ROCK DESCRIPTION

DE

PT

H (

m)

1

2

3

4

5

6

7

8

9

IN-SITU TESTS

GE

OLO

GIC

AL

UN

IT

R L

(m

)

80

79

78

77

76

75

74

73

72

71

SA

MP

LES

SPT'N'C

OR

E R

EC

OV

ER

Y

RQ

D

CA

SIN

G

FLU

ID L

OS

S

SV (kPa)

COMMENTS:SC = Solid Cone SPT

BE

CA

LIB

1.0

7.1.

GLB

Log

BE

CA

MA

CH

INE

BO

RE

HO

LE 2

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HA

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4-12

-16

COORDINATE ORIGIN: MAPACCURACY: 5

N 6,048,660 mE 1,717,352 m

BH1

SHEET 1 of 2

JOB NUMBER:PROJECT: Whau Valley WTP Upgrade

CLIENT:SITE LOCATION: 274 Whau Valley Road

6519113

CIRCUIT: NZTM West side of fieldCOORDINATES:

Whangarei District Council

R L: 80.5 mDATUM: MSL

MACHINE BOREHOLE LOG

BOREHOLE No:

BOREHOLE LOCATION:

Son

icS

PT

Son

icS

PT

Son

icS

CS

onic

SC

Son

icS

CS

onic

Son

icS

C

Medium dense fine to coarse GRAVEL, some silt, trace cobbles; dark grey; saturated,non plastic. Gravel: vesicular basalt.

Medium dense fine to coarse GRAVEL with minor silt; dark grey; saturated, non plastic.Gravel: vesicular basalt.

Medium dense sandy fine to coarse GRAVEL with trace cobbles, trace silt; darkreddish brown; wet, non plastic. Gravel: vesicular basalt.

Minor cobbles

Trace cobbles

Minor silt

Very dense BOULDERS, some silt, trace gravel, trace sand; dark grey speckled white,moist, non plastic. Boulders: <600mm, slightly weathered, vesicular basalt.

Very dense sandy GRAVEL trace cobble, trace silt; dark reddish brown; wet; nonplastic. Gravel: vesicular basalt.

Very dense BOULDERS; dark greyish brown speckled white: moist, non plastic.Boulders: <500mm, slightly weathered, vesicular basalt.

Very dense gravelly COBBLES with some sand, trace silt; dark reddish brown; wet;non plastic. Cobbles: <200mm, strong vesicular basalt.

Very strong to extremely strong, UW, dark grey speckled white vesicular BASALT,homogeneous. Defects: moderately widely spaced, gently-steeply inclined, rough,undulating, clean.

Defects: closely spaced

Defects: moderately widely spaced

No recovery

END OF LOG @ 19.01 m

Ker

iker

i Vo

lcan

ic G

rou

p

15229345

N=21

20 for40mm

Bouncing5 for0mm

N=50+

20 for25mm

Bouncing5 for0mm

N=50+

225 for50mm

Bouncing5 for0mm

N=50+

25 for50mm

Bouncing5 for0mm

N=50+

50 for10mm

Bouncing5 for0mm

N=50+

100

%45

%10

0 %

22 %

100

%0

%10

0 %

0 %

100

%0

%10

0 %

40 %

MWP9/6/158/6/15


DRILLED BY:






DA

ILY

WA

TE

R L

EV

EL

DRILLING

-/ 90°

SC/Sonic/SPTWater

ME

TH

OD

GR

AP

HIC

LO

G


DE

PT

H (

m)

11

12

13

14

15

16

17

18

19

IN-SITU TESTS

GE

OLO

GIC

AL

UN

IT

R L

(m

)

70

69

68

67

66

65

64

63

62

61

SA

MP

LES

SPT'N'C

OR

E R

EC

OV

ER

Y

RQ

D

CA

SIN

G

FLU

ID L

OS

S

SV (kPa)

COMMENTS:SC = Solid Cone SPT

BE

CA

LIB

1.0

7.1.

GLB

Log

BE

CA

MA

CH

INE

BO

RE

HO

LE 2

74 W

HA

U V

ALL

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RO

AD

LO

GS

.GP

J <

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201

4-12

-16


N 6,048,660 mE 1,717,352 m

BH1

SHEET 2 of 2



6519113

CIRCUIT: NZTM West side of fieldCOORDINATES:




BOREHOLE No:

BOREHOLE LOCATION:

274 Whau Valley Road

BH1

Job number: 6519113 Machine Borehole Photos

BOX: 1 DEPTH: 0.0 to 2.55m



BH1





BH1


BOX: 5 DEPTH: 11.15 to 13.75m

BOX: 6 DEPTH: 13.75 to 15.7m


BH1



BOX: 8 DEPTH: 18.3 to 19.01m

9/06

/201

5

Son

icS

PT

Son

icS

PT

Son

icS

PT

Son

icS

PT

Son

icS

PT

Son

icS

PT

Son

ic

Soft organic clayey SILT; dark brown; wet, high plasticity. Organics: Rootlets[Topsoil]

Stiff silty CLAY, trace organics; orange brown; moist, high plasticity.

No organics

Orange brown mottled grey

Firm clayey SILT, minor fine to medium gravel; grey mottled orange brown; moist; highplasticity. Gravel: subrounded to subangular, greywacke.

Medium dense SILT, minor fine to coarse sand, trace to no clay, trace gravel; greybrown mottled dark grey; moist, non plastic to low plasticity.

Very soft silty ORGANICS with some clay; grey brown/black; moist, high plasticity.Organics: fibrous. (Peat: H7)

Very soft clayey SILT, trace organics: grey brown speckled black; moist, high plasticity.Organics: fibrous.

Very soft organic clayey SILT; grey brown/black; moist, high plasticity. Organics:fibrous. (Peat: H7)

Very soft clayey SILT, trace organics: grey brown speckled black; moist, high plasticity.Organics: amorphous.

Loose fine to coarse SAND, minor silt; black; wet, non plastic. (Angular basalt)

Trace gravel: vesicular basalt

To

pso

ilQ

uat

ern

ary

Allu

viu

m

101122

N=6

445666

N=23

211111

N=4

000001

N=1

000000

N=0

211101

N=3

100

%10

0 %

100

%50

%10

0 %

28 %

100

%10

0 %

100

%10

0 %

100

%10

0 %

100

%

MWP9/6/159/6/15


DRILLED BY:






DA

ILY

WA

TE

R L

EV

EL

DRILLING

-/ 90°

Sonic/SPTWater

ME

TH

OD

GR

AP

HIC

LO

G


DE

PT

H (

m)

1

2

3

4

5

6

7

8

9

IN-SITU TESTS

GE

OLO

GIC

AL

UN

IT

R L

(m

)

79

78

77

76

75

74

73

72

71

70

SA

MP

LES

SPT'N'C

OR

E R

EC

OV

ER

Y

RQ

D

CA

SIN

G

FLU

ID L

OS

S

SV (kPa)

COMMENTS:

BE

CA

LIB

1.0

7.1.

GLB

Log

BE

CA

MA

CH

INE

BO

RE

HO

LE 2

74 W

HA

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ALL

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RO

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eca

1.07

201

4-12

-16


N 6,048,666 mE 1,717,407 m

BH2

SHEET 1 of 2



6519113

CIRCUIT: NZTM East side of fieldCOORDINATES:




BOREHOLE No:

BOREHOLE LOCATION:

Son

icS

PT

Medium dense fine to medium GRAVEL, minor sand, trace silt; black; wet, non plastic.Gravel: vesicular basalt.

Reddish brown

END OF LOG @ 11.15 m

Ker

iker

i Vo

lcan

ic G

rou

p

322336

N=14

100

%10

0 %

MWP9/6/159/6/15


DRILLED BY:






DA

ILY

WA

TE

R L

EV

EL

DRILLING

-/ 90°

Sonic/SPTWater

ME

TH

OD

GR

AP

HIC

LO

G


DE

PT

H (

m)

11

12

13

14

15

16

17

18

19

IN-SITU TESTS

GE

OLO

GIC

AL

UN

IT

R L

(m

)

69

68

67

66

65

64

63

62

61

60

SA

MP

LES

SPT'N'C

OR

E R

EC

OV

ER

Y

RQ

D

CA

SIN

G

FLU

ID L

OS

S

SV (kPa)

COMMENTS:

BE

CA

LIB

1.0

7.1.

GLB

Log

BE

CA

MA

CH

INE

BO

RE

HO

LE 2

74 W

HA

U V

ALL

EY

RO

AD

LO

GS

.GP

J <

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ile>

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7/06

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5 15

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8.3

0.00

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l Lab

and

In S

itu T

ool -

DG

D |

Lib:

Bec

a 1.

07 2

014-

12-1

6 P

rj: B

eca

1.07

201

4-12

-16


N 6,048,666 mE 1,717,407 m

BH2

SHEET 2 of 2



6519113

CIRCUIT: NZTM East side of fieldCOORDINATES:




BOREHOLE No:

BOREHOLE LOCATION:


BH2





BH2





BH2



Appendix C

Cone Penetration Test Logs

0 2 4 6 8 10 12 14 16 18 20

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

qc [MPa]

fs [MPa]

0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Depth [m]

-0.1 0 0.1 0.2 0.3 0.4 0.5

0 1 2 3 4 5 6 7 8 9 10

u2 [MPa]

Rf [%]

Test no:

CPT1Project ID:

274WhauValleyRdClient:

BECAProject:

274WhauValleyRd

WL - Collapsed and Dry at 1.5m

Position:

X: 0 m, Y: 0 mLocation:

WhangareiGround level:

0.000Date:

15/06/2015Scale:

1 : 83Page:

1/1Fig:

File: 274WhauValleyRd_CPT1.GEF

U2

Sleeve area [cm2]: 150

Tip area [cm2]: 10

Cone No: S10CFIIP.S14547

Classification by

Robertson 1986

Clay (3)

Sensitive fine grained (1)

Silty sand to sandy silt (7)

Sandy silt to clayey silt (6)

0 2 4 6 8 10 12 14 16 18 20

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

qc [MPa]

fs [MPa]

0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Depth [m]

1.8

-0.1 0 0.1 0.2 0.3 0.4 0.5

0 1 2 3 4 5 6 7 8 9 10

u2 [MPa]

Rf [%]

Test no:

CPT2Project ID:


BECAProject:

274WhauValleyRd

WL - 1.8m

Position:



0.000Date:

15/06/2015Scale:

1 : 83Page:

1/1Fig:


U2


Tip area [cm2]: 10


Classification by

Robertson 1986


Clay (3)

0 2 4 6 8 10 12 14 16 18 20

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

qc [MPa]

fs [MPa]

0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Depth [m]

2.6

-0.1 0 0.1 0.2 0.3 0.4 0.5

0 1 2 3 4 5 6 7 8 9 10

u2 [MPa]

Rf [%]

Test no:

CPT3Project ID:


BECAProject:

274WhauValleyRd

WL - 2.6m

Position:



0.000Date:

15/06/2015Scale:

1 : 83Page:

1/1Fig:


U2


Tip area [cm2]: 10


Classification by

Robertson 1986

Clay (3)


0 2 4 6 8 10 12 14 16 18 20

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

qc [MPa]

fs [MPa]

0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Depth [m]

1.1

-0.1 0 0.1 0.2 0.3 0.4 0.5

0 1 2 3 4 5 6 7 8 9 10

u2 [MPa]

Rf [%]

Test no:

CPT4Project ID:


BECAProject:

274WhauValleyRd

WL - 1.1m

Position:



0.000Date:

15/06/2015Scale:

1 : 83Page:

1/1Fig:


U2


Tip area [cm2]: 10


Classification by

Robertson 1986

Clay (3)

Sand to silty sand (8)


Clay (3)




0 2 4 6 8 10 12 14 16 18 20

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

qc [MPa]

fs [MPa]

0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Depth [m]

1.1

-0.1 0 0.1 0.2 0.3 0.4 0.5

0 1 2 3 4 5 6 7 8 9 10

u2 [MPa]

Rf [%]

Test no:

CPT5Project ID:


BECAProject:

274WhauValleyRd

WL - 1.1m

Position:



0.000Date:

15/06/2015Scale:

1 : 83Page:

1/1Fig:


U2


Tip area [cm2]: 10


Classification by

Robertson 1986

Clay (3)


Clay (3)




6519113 // NZ1-11649715-4 0.4 // page 42

Appendix E

Preliminary Geotechnical Interpretive Report

Report

Whau Valley WTP Upgrade Addendum Geotechnical Interpretative Report - 274 Whau Valley Road



3 July 2015


CH2M Beca // 3 July 2015

6519113 // NZ1-10914614-12 0.12 // i

Revision History

Revision Nº Prepared By Description Date

1 Jacqui Coleman Draft for internal review July 2015

2 Jacqui Coleman Final for issue July 3rd

2015

3

4

5

Document Acceptance

Action Name Signed Date

Prepared by Jacqui Coleman

Reviewed by James Burr

Approved by Philip La Roche

on behalf of CH2M Beca Ltd

© CH2M Beca 2015 (unless CH2M Beca has expressly agreed otherwise with the Client in writing).

This report has been prepared by CH2M Beca on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk.



6519113 // NZ1-10914614-12 0.12 // ii

Executive Summary

CH2M Beca Ltd has been commissioned by Whangarei District Council to undertake a feasibility stage

geotechnical assessment of two vacant sites for development for a new water treatment plant. The new

water treatment plant would comprise a series of large concrete structures, including reservoir tanks, clarifier

tanks and associated buildings.

This is the second site to be investigated for suitability for the proposed development. 274 Whau Valley

Road is otherwise known as site B in the appraisal and lies in a side valley oriented west-east that is

approximately 200m wide and 550m long near the mouth of the Whau Valley and lies within the 1:100 year

flood hazard zone.

A geotechnical investigation was undertaken in June 2015. This comprised two machine boreholes drilled to

19 m and 11 m respectively, and five Cone Penetration Tests (CPT’s) whose maximum depth was 13.9 m

depth.

The geotechnical investigations recorded shallow groundwater and Tauranga Group swamp and alluvial

deposits of variable strength and composition overlying Kerikeri Volcanic Group sands, gravels and basalt

rock at depth. A soft to firm layer of silt and clay was recorded in all the investigation points between

approximately 3 and 9.5m deep. In all the investigation points, the silt and clay layer was underlain by sands

and gravels of the Kerikeri Volcanic Group. In borehole BH1 a floating basalt boulder was encountered at 8

m depth within the silt-clay deposit which may make piling difficult. Basalt rock was found at depth around 17

m in this borehole.

A settlement analysis was undertaken using inferred parameters from the site investigations and relevant

laboratory parameters from the previous site investigated at 213 Whau Valley Road in 2014. We simulated a

30m circular pad foundation loading 50kPa onto the surface of the site. Our analysis estimated total

settlements in the order of 20 to 600 mm at the centre of the structure, and 20 to 300mm at the edge of the

structure. Most of this settlement was occurring in the silt and clay layer from approximately 3 to 9.5m depth.

This layer thins towards the southeast and the estimated settlement reduces as well.

A liquefaction analysis was undertaken for this site. The site was deemed likely to be a Class D – ‘deep soil’

site, and the design peak ground accelerations were quantified as 0.26g for Ultimate Limit State and 0.15g

for Serviceability Limit State. Simulating these seismic accelerations on our ground model showed that the

site will be prone to liquefaction induced settlement. Settlements calculated were in the order of 10 to 90 mm

for the Serviceability Limit State analysis and 10 to 140 mm for the Ultimate Limit State Analysis. Most of this

liquefaction settlement was occurring in the silty sand layers (Layer 2a) from approximately 0.5 m to 6.2 m

depth. This layer thickens towards the south-eastern end of the site.

The key geotechnical consideration for developing this site is mitigation of the static and seismic settlements.

Deep foundations would need to be founded into the basalt gravels and boulders below 9 m depth and may

be economically feasible subject to further investigations. Shallow foundations may also be possible in

combination with ground improvement. Options for this include preloading, dynamic compaction, soil

stabilisation, partially compensated foundation, and excavation and replacement of the upper soil. These

options will limit the potential total and differential settlements, but not eliminate them. A combination of these

methods is likely to be the most effective.

Our recommended ground improvement option would be to undertake soil stabilisation (cement columns), in

combination with the excavation and recompaction of the upper soil layer (Layer 1) and piling of heavily

loaded structures. These methods would significantly reduce the estimated consolidation settlement that



6519113 // NZ1-10914614-12 0.12 // iii

could occur in the soft silt and clay layer (Layer 2). Liquefaction may still occur at depth below the basalt, but

differential settlements will be mitigated by the overlying basalt and stabilised/recompacted soils providing a

rafting effect.

Further ground investigation data would be required to develop these options further.



6519113 // NZ1-10914614-12 0.12 // i

Contents

1 Introduction 1

1.1 Proposed Development 1

2 Site Location and Description 1

3 Geotechnical Investigations 2

3.1 Recent Investigations 2

3.2 Previous Investigations 2

4 Geology and Ground Profile 3

4.1 Regional Geology 3

4.2 Faulting 3

4.3 Ground Profile 4

4.4 Groundwater 5

5 Geotechnical Assessment 5

5.1 Slope Stability 5

5.2 Settlement 5

5.3 Seismicity 6

6 Potential Foundation Options 9

6.1 Shallow Foundations 9

6.2 Deep Foundations 10

6.3 General Considerations 10

7 Recommendations 11

8 Applicability 11

9 References 12

Appendices

Appendix A

Figures



6519113 // NZ1-10914614-12 0.12 // page 1

1 Introduction

Whangarei District Council (WDC) is undertaking a feasibility study for upgrading the Whangarei Water

Treatment Plant (WTP). WDC have identified two potential sites that they wish to investigate further for

suitability. This site at 274 Whau Valley Road is the second site to be investigated. CH2M Beca Ltd has

been commissioned by WDC to undertake a feasibility stage geotechnical assessment of this site.

This Addendum Geotechnical Interpretive Report has been prepared to inform WDC of the geotechnical

issues and constraints to the proposed development. We have provided concept foundation and ground

treatment options to mitigate some of the geotechnical issues present at this site, and provide

recommendations for progression of this scheme. This information is aimed at assisting WDC with making

an informed decision on the suitability of this site for the development of a new water treatment plant.

This report is to be read in conjunction with CH2M Beca, 2015 (Whau Valley WTP Upgrade – 274 Whau Valley Road Addendum Geotechnical Factual Report), report prepared for Whangarei District Council.

Associated reports for the previous site are:

n CH2M Beca. 2014. Whau Valley WTP Upgrade – Geotechnical Factual Report, Report prepared for

Whangarei District Council, October 2014.

n CH2M Beca. 2014. Whau Valley WTP Upgrade – Geotechnical Interpretive Report, Report prepared for

Whangarei District Council, October 2014.

This report is the property of our client, WDC and CH2M Beca Ltd.

1.1 Proposed Development

The new water treatment plant will comprise a series of large concrete structures, including two reservoir

tanks, clarifier tanks and associated buildings. Other associated structures include chemical storage, filter

tanks and clarifiers, along with utilities and access roads.

The Preliminary ‘New Plant Site Layout’ plan (Appendix B) indicates the 4000m3 capacity tanks are likely to

be the largest structures proposed at this site. To represent these structures, a 30m diameter circular pad

with 50kPa surcharge was used for the analysis.

2 Site Location and Description

The site is titled 274 Whau Valley Road according to WDC Intramaps property GIS system. It is situated

approximately 1.4km along Whau Valley Road. The centre of this site is approximately 1717378E 6048677N.

Whau Valley is a northeast, southwest oriented valley with drainage towards the northeast. Whau Valley

Road is aligned northeast-southwest along the centre of the valley. 274 Whau Valley Road is otherwise

known as site B and lies in a side valley oriented west-east, and is approximately 200m wide and 550m long

near the mouth of the Whau Valley. The site is some 60m south of a small unnamed creek that flows to the

east and joins the Waiarohia stream which originates from the dam at the head of the Whau Valley.

The site is predominantly flat and has an elevation of approximately RL 80 m, the site is approximately 4.86

hectares in area.



6519113 // NZ1-10914614-12 0.12 // page 2

3 Geotechnical Investigations

3.1 Recent Investigations

A ground investigation comprising two machine boreholes and five cone penetration tests (CPTs) was

recently undertaken at the site. The works commenced on 8 June 2015 and were completed 15 June 2015.

The investigation locations have been located using NZTopo 50 1:50,000 topographic map following

completion of the fieldwork in terms of NZTM 2000 and are presented on Figures 1 and 2 (Appendix A). A

summary of the boreholes is shown in Table 3.1 and a summary of CPTs is shown in Table 3.2 below:

Table 3.1 Summary of Boreholes

BH No. Location Easting Northing R.L. (m) Total Depth (m)

BH1 Western side of paddock

1717352 6048660 80.5 19.0

BH2 Eastern side of paddock

1717407 6048666 79.5 11.15

Notes: All coordinates given in NZTM

Table 3.2 Summary of CPTs

CPT No. Location Easting Northing R.L. (m) Total Depth (m)

CPT1

See Figure 1. 1717347 6048684 80 9.6

CPT2

See Figure 1. 1717390 6048671 79.5 7.9

CPT3

See Figure 1. 1717393 6048650 79.5 12.7

CPT4

See Figure 1. 1717415 6048651 79.5 13.8

CPT5

See Figure 1. 1717411 6048677 79.5 7.6

Notes: All coordinates given in NZTM

3.2 Previous Investigations

Previous investigations carried out in the wider Whau Valley area including those previously undertaken at

the Whau Valley Dam are summarised within the CH2M Beca. 2014. Whau Valley WTP Upgrade – Geotechnical Factual Report.



6519113 // NZ1-10914614-12 0.12 // page 3

4 Geology and Ground Profile

4.1 Regional Geology

The published 1:25 000 geological map, Geology of the Whangarei Urban Area (White and Perrin, 2009)

indicates that the site lies within a down faulted half graben type feature where the hills to the northwest and

southeast comprise hard greywacke (Waipapa Terrane) that accumulated several hundred million of years

ago (Permian-Jurassic). The site itself is underlain by Tauranga Group Quaternary aged (less than 1.8

Million years old) alluvial and swamp deposits comprising unconsolidated sand, mud and gravel, commonly

interbedded with thin peat beds and sporadic input from the nearby Puhipuhi – Whangarei Volcanic Field.

The mapped geology of the site is presented in Figure 4.1 below.

At the mouth of Whau Valley (approx. 1km southeast of the site) is an unnamed basalt vent that occurs along

the North-South aligned Kamo Fault and is considered to have last erupted in the order of 300,000 years ago

(White and Perrin, 2009). The Whau Valley is said to have been blocked by the volcanic activity associated

with the basalt vent and subsequently filled with swamp and alluvial deposits originating from up the Whau

Valley.

4.2 Faulting

The Kamo Fault located approximately 1 km east of the site is not recorded as ‘active’ in the GNS active

faults database. The Northland region is generally considered to have low earthquake risk and no active

faults are known to exist in the Whangarei Geological Map area (Edbrooke, 2009).

W=Waipapa Terrane

greywacke

kl=Kerikeri Volcanic

Group Basalt

274 Whau Valley

Road

fa=Tauranga Group

Basalt vent



6519113 // NZ1-10914614-12 0.12 // page 4

Figure 4.1: Geology map of the Whau Valley (White and Perrin, 2009)

4.3 Ground Profile

Recent Investigations conducted by CH2M Beca Ltd have enabled us to create the following ground profile

for 274 Whau Valley Road as shown in the Table 4.1 below and are presented in Figures 3 and 4, Appendix

A.

Table 4.1: Soil Profile for 274 Whau Valley Road

Layer Geological

Unit

Description Depth

to top

(m)

Thickness

(m)

SPT N

blows/300

mm

qc

(MPa)

1

Ta

ura

ng

a G

roup

Firm to stiff silty CLAY 0 2-3.5 6-7 1

*2a Medium dense SILT/silty SAND/ clayey SILT

with minor gravel.

0.8-3 0-4.5 4-23 4-12

Typ= 4

2 Soft clayey SILT with peat beds with isolated

basalt boulders

5-5.5 2-6.5 0-1 Typ= 0 0.3-0.9

Typ=

0.6

3a*

Ke

rike

ri V

olc

an

ic

Gro

up

Loose silty Sand 7.8-9 0-6.5 3 2-4

Typ=3

3 Medium dense to very dense basalt

BOULDERS and GRAVELS

9.5-9.8 7.5 18 - 50+

Typ=50+

15-30

4 Very strong UW vesicular BASALT 16.8 2m+ 50+ -

n *Soil layers 2a and 3a were not encountered within borehole BH1 and CPT1.

n Typ=typical values

The properties of Soil layer 2 are interpreted to be similar to the properties of Soil Layer 2 in the CH2M Beca

2014 reports and therefore similar engineering parameters have been used for this layer in the following

sections. The assessed engineering parameters used in the following sections are presented in Table 4.2.

Table 4.2 – Estimated geotechnical parameters for analysis

Layer Description Bulk density (kN/m

3)

Mv (m2/MN) Cv (m

2/yr) Elastic modulus

(MPa) Su (kPa)

1 Firm to stiff silty CLAY 17 0.2 1.5 60

2a Medium dense SILT/silty SAND/ clayey SILT with minor gravel.

17 - - 20

2 Soft clayey SILT with peat beds with isolated basalt boulders

16 0.9 9.5 - 25



6519113 // NZ1-10914614-12 0.12 // page 5

Layer Description Bulk density (kN/m

3)

Mv (m2/MN) Cv (m

2/yr) Elastic modulus

(MPa) Su (kPa)

3a Loose silty SAND 17 - - 20

3 Medium dense to very dense basalt BOULDERS and GRAVELS

18.5 - - 135 -

4 Very strong UW vesicular BASALT

17 n/a n/a n/a

4.4 Groundwater

Ground water was measured within the CPT’s and the machine boreholes straight after drilling. The water

table measured within the CPT’s varied between 1.1 and 2.6 m depth. The boreholes indicated water levels

between 4.5 and 7 m depth, these values are likely to be influenced by the drilling and are therefore not

considered further. A water level of 0.5 m below the ground surface was used for the liquefaction

assessment.

5 Geotechnical Assessment

The key geotechnical considerations for the site are discussed in the following sections:

5.1 Slope Stability

The site occupies a flat area at the centre of the valley. The adjacent side slopes of the valley are moderately

steep and large scale historical landslide features have been identified. The site is considered to be at

sufficient distance from the toe of the adjacent slopes to be at minor risk from landslip debris under normal

conditions. Slope stability therefore has not been considered further.

5.2 Settlement

5.2.1 Settlement Analysis

A settlement analysis was undertaken using the Roc-Science computer programme Settle3D using the soil

profile and estimated material parameters shown in Table 5.1. With limited geotechnical data a number of

assumptions were made. These include:

n Simulated loading from a 30m diameter, circular section water reservoir, applying 50kPa to the ground

surface was used for the analysis.

n The ground profile was assumed to be normally consolidated.

n Immediate settlements are based on the Es (elastic modulus) values.

n Linear consolidation was assumed using the strain based on Mv data based on laboratory testing

undertaken in the CH2M Beca 2014 report.

n Time dependant consolidation was analysed using a Cv value based on laboratory testing undertaken in

the CH2M Beca 2014 report.

n Secondary consolidation was excluded from the analysis.

n The groundwater table was located at approximately 0.5 m below the current ground surface.

n Assumed two way drainage of the silt and clay layer (drainage through top and base).



6519113 // NZ1-10914614-12 0.12 // page 6

The estimated settlements due to static loading are shown in Table 6.2 below.

Table 6.2 - Estimated static settlement

Analysis Settlement Values BH1 profile Settlement Values BH2 profile

Centre of

structure

Edge of

structure

Centre of

structure

Edge of

structure

Total Settlement 150-600 mm 90-300 mm 45-180 mm 20-80 mm

Consolidation

Settlement

150-600 mm 90-300 mm 40-160 mm 15-70 mm

Immediate Settlement < 5 mm < 5 mm < 25 mm < 5 mm

The analysis showed:

n The large range in estimated settlements is to account for the natural variability in the soils and the limited

data. It is estimated that settlements will be greater in the northwestern end of the site, in the area of

borehole BH1.

n Greater than 80% of the total settlement was consolidation settlement from within the silt and clay layer

(layer 2).

n The ground profile in the eastern part of the site (borehole BH2) indicated a thinner layer of compressible

materials at depth than the area investigated around borehole BH1. It is noted that based on the current

layout most of the infrastructure is in this area.

n A time analysis showed that it would take approximately 2.5 years to undergo 90% of the total settlement

in the area of borehole BH1, and 6 months in the area of borehole BH2.

While only this nominally sized tank has been analysed, it is reasonable to expect that any large or heavily

loaded foundations will result in significant settlements due to the layer of compressible soils underlying the

site. Only small lightly loaded shallow footings are likely to result in settlements within normal tolerances

(25mm).

5.3 Seismicity

5.3.1 Site Subsoil Classification

The seismic design criteria have been assessed for this site using the NZ Standard 1170.5(2004). Based on

the profile, the recommended site subsoil class for this site is ‘Class D – deep soil’. The maximum depth of

the investigations at the site was 19 m. Basalt rock was encountered in the western part of the site but its

depth below the ground surface was observed to highly variable, it is of unknown thickness and is potentially

underlain by more Tauranga Group sediments. Subsoil class C was deemed not appropriate because this

basalt unit does not constitute sound rock/bedrock in terms of NZS1170.5.

The parameters for determining the design peak ground acceleration at ‘Ultimate Limit State’ and

‘Serviceability Limit State’ conditions (NZS1170.0), and the resultant peak ground acceleration values (PGA)

are summarised in Table 5.1. Serviceability Limit State is defined as ‘the structure maintains operational

continuity after the SLS2 earthquake’. Ultimate limit state is defined as ‘states associated with collapse, or

with similar forms of structural failure’ (NZS1170.5).



6519113 // NZ1-10914614-12 0.12 // page 7

Table 5.1 - Seismic Design Parameters

Parameter Ultimate Limit State Serviceability Limit State

Design working life 50 years 50 years

Importance Level 4 4

Spectral shape factor 1.12 (class D site) 1.12 (class D site)

Hazard factor 0.13 0.13

Near fault factor 1 1

Return period factor 1.8 (1 in 2500 year event) 1.0 (1 in 500 year event)

Design PGA (g) 0.26 0.15

These Peak Ground Acceleration values have been used to assess liquefaction and cyclic softening of the

soil layers present at site.

5.3.2 Liquefaction

Liquefaction occurs when loose, saturated cohesionless soils lose strength under earthquake or other

applied cyclic loading. The loose soil will tend to compact or densify under this loading. When the soils are

saturated, the relatively incompressible pore water around the soil particles does not allow this densification

to occur in the short-term. This causes the pore water pressure to increase significantly and for the effective

stress within the affected soil to correspondingly decrease. Liquefaction occurs where these effective

stresses approach or equal zero, and the soil loses most of its shear strength. This condition will persist until

excess pore water pressures dissipate. Effects may continue after the earthquake shaking has stopped.

The effects of liquefaction can include localised lateral and downslope movements during an earthquake

where the static plus earthquake loads exceed the available strength of the liquefied soil profile. More

substantial lateral movements and widespread failures can occur where the strength loss is sufficiently

greater and the soil profile can no longer sustain static loads alone.

In addition to liquefaction and densification, cyclic strain softening could also affect fine-grained soils on-site

during earthquakes. Cyclic strain softening is the onset of strength loss resulting in significant strains in

saturated silts and clays during earthquakes. The cyclic strain softening causes the shear strength of the soil

to reduce under successive cyclic action. Although softening does not contribute to the settlement, it would

affect the stability of deep foundations, if proposed.

5.3.3 Liquefaction Assessment

Our investigation indicates that some conditions at this site will make it prone to liquefaction during an

earthquake. The high groundwater level, and the relatively low density and granular nature of the underlying

soils of the site are the main contributors to the liquefaction susceptibility.

Idriss and Boulanger (2008) indicate that the soils that are most likely to liquefy are alluvial, fluvial, marine

and deltaic soils that are recently deposited. Therefore at this site only the surficial deposits are considered

to have liquefaction potential and the volcanic deposits such as Layer 3a are considered unlikely to liquefy.

A summary of the susceptibility, based on the generalised ground model presented in Section 4, is provided

in Table 5.2 below.



6519113 // NZ1-10914614-12 0.12 // page 8

5.2 - Summary of liquefaction susceptibility of site materials

Soil Layer

Description Assessed liquefaction susceptibility

Comments

1 Stiff silty CLAY Non liquefiable. High clay content. Cohesive.

2a Medium dense SAND/silty SAND/clayey SILT

Liquefaction likely in sandy beds Variable clay content, but low relative density and saturated.

2 Soft silty CLAY Non liquefiable. Generally high clay content. Cohesive.

3a Loose silty SAND and Sand

Unlikely to liquefy due to age and volcanic source

Variable clay content, but low relative density and saturated.

3 Medium dense to very dense BOULDERS and GRAVELS

Non liquefiable.

4 Basalt rock Non liquefiable.

We have undertaken a liquefaction analysis to quantify the estimated amount of liquefaction induced

settlement under ‘ultimate limit state’ and ‘serviceability limit state’ PGA’s. This uses the descriptions, insitu

strength tests and observations recorded from each borehole. The analysis has been based on the methods

in the NCEER Workshop (1997), Tokimatsu and Seed (1987a & b), Olsen and Stark (2003), Boulanger and

Idriss (2006, 2007) and Zhang et al (2007).

The resultant settlement values are presented in Table 5.3:

Table 5.3 - Liquefaction Analysis Results

Analysis Settlement Extent

Serviceability Limit State 10 - 90 mm

Ultimate Limit State 10 – 140 mm

Our analysis indicates:

n The large range in estimated settlements is due to the variable ground profile encountered in the

investigations across the site. It is estimated that liquefaction induced settlements will be greater in the

southeastern end of the site, in the area of borehole BH2.

n The liquefaction induced settlement occurs only within sandy horizons of soil Layer 2a from approximately

0.5 to 6.2 m depth. This unit is thickest in the south-eastern part of the site (refer Figures 3 and 4).

It should be noted that the “rafting” effect of the overlying Layer 1 will reduce the potential for differential

settlements to manifest at the surface across the site. Note that this analysis is for a ‘free field’ scenario, and

the effect of surcharge loading from structures is not taken into account.



6519113 // NZ1-10914614-12 0.12 // page 9

6 Potential Foundation Options

6.1 Shallow Foundations

The use of shallow foundations would require some form of ground improvement due to the strong possibility

of high static and seismic induced settlements. The ground improvement may comprise preloading of the site

prior to construction, removal of the upper soils and embedment of the structure, or potentially more

substantial measures such as soil stabilization. To be more effective, a combination of these measures may

also be adopted.

Ground improvement measures would be expected to reduce, but not eliminate, the total and differential

settlements that could occur at this site.

6.1.1 Preloading

Preloading of the site prior to construction could be designed to consolidate the underlying materials and

remove most of the total expected post construction static settlement. The extent of this would depend on the

extent and duration of the preloading works. Improved drainage, such as the installation of vertical wick

drains, into the compressible silt and clay layer would assist with the dissipation of pore pressure and

increase the rate of consolidation settlement (i.e. reduce the preload time).

Our initial settlement analysis shows that the majority of the settlement occurs within the first 2.5 years at the

western end of the site and potentially 6 months at the eastern end of the site. A better understanding of the

permeability and organic content within the silt and clay layer, and the other geological units, would provide a

more accurate indication of the consolidation timeframes. Low permeability and organic rich materials usually

take a longer period of time to consolidate, and this could affect the suitability of preloading. Preloading will

not prevent or reduce the estimated level of liquefaction settlement occurring at depth.

Some of the preload material could be left as additional fill to elevate the site out of the flood hazard zone.

6.1.2 Dynamic Deep Compaction

This method involves mechanically inducing settlement by dropping a heavy weight onto the ground surface

from a crane. Improvements in geotechnical properties to depths of about 10m are possible. This method is

a faster way of achieving pre-construction consolidation, but is relatively expensive compared with pre-

loading, and is highly disruptive and potentially damaging to neighboring residences. Due to the nature of the

ground and proximity to residential dwellings, this is unlikely to be a viable option.

6.1.3 Soil Stabilization

The bearing properties of soft silts and clays can be improved by mixing cement into the soil. The method

involves using a specialized rig to rotary drill to desired depths (at this site up to 9m) then inject cement grout

(or other chemical additive) as the equipment is retracted. The result is a chemically stabilized column

usually 300 to 600mm diameter. It would not mitigate any liquefaction induced settlement that may occur at

depth below the basalt, but would limit differential settlement at the surface by providing a ‘rafting’ effect.

6.1.4 Partial Compensated Foundation

Excavating and embedding structures into the underlying soils can reduce the overall static loads affecting

the soil. Every meter of soil removed from the surface will reduce the overall static loading by approximately

16 - 17kPa. Reduced static loading will reduce the total settlement that could potentially occur at this site.



6519113 // NZ1-10914614-12 0.12 // page 10

The scheme designers may need to investigate the viability of embedding some structures below ground to

help mitigate differential settlement. The increased depth of associated services and decreased

constructability (particularly when below the groundwater level) would need to weighed against reduction in

total settlement.

6.1.5 Excavation and replacement of the upper soil

Differential settlement could be partially mitigated by excavating the upper firm-stiff clayey silt layer (Layer 1),

and recompacting this as fill to develop a raft foundation. A raft foundation would reduce the potential for

differential settlement to occur at the surface during static or seismic settlement, thereby reducing the

potential for structural damage. Reinforcement of this fill layer with geogrids can also help mitigate against

differential settlement. Total settlement would need to be mitigated by other means. The practical extent of

this option will be controlled by the groundwater level, as excavation and compaction are difficult below

groundwater. For this option to be considered further we recommend further shallow investigations be

carried out with samples collected for laboratory testing of Soil Layer 1 for compaction parameters.

6.2 Deep Foundations

Piles could be used to support the structures and avoid the risks from both total and differential settlements.

Piles could potentially be founded into the medium dense to dense basalt gravel beds (Soil layers 3 and 3a),

at some 9 m depth assuming the soil layers are of adequate thickness and at a consistent depth across the

site. The CPT’s, CPT3 and CPT4 suggest that the more competent material is deeper in the ground profile

towards the southeast. The floating basalt boulders up to 600 mm observed within borehole BH1, could be

problematic for driven piles, so predrilling may be required or potentially bored piles may be more suitable at

this site. Further deeper investigations would be required to confirm the depth and thickness of the

competent layer and to determine appropriate piling parameters.

6.3 General Considerations

Further considerations for earthworks include the following:

n The topsoil is in the order of 200 to 300 mm thick at this site and will require removal prior to any

earthworks.

n A CBR for the subgrade, based on the CPT results, is estimated to be about 3-4.

n Any preloading of the site and the construction of an engineered fill platform to keep the site above the

flood hazard zone, will need use imported fill from local quarry sources. These local fill sources will need

to be investigated.

n Soil Layer 1 may be suitable for reused if the Partial Compensation Foundation option is used to develop

this site. Further shallow investigations and laboratory testing will need to be carried out to confirm

compaction parameters.



6519113 // NZ1-10914614-12 0.12 // page 11

7 Recommendations

Our analysis of this site has shown heavy structures will be prone to significant total and differential

settlement (both static and seismic). The key geotechnical issue for developing this site is mitigating the

impact or the extent of this settlement.

Based on our ground investigation information, piled foundations are potentially an economically viable

option at this site subject to further investigations to confirm piling parameters, depths of piles and an

appropriate method. There is also a range ground improvement methods that can mitigate this settlement

and allow structures to have shallow foundations. The costs of these options would need to be evaluated for

the viability of this site for the water treatment plant.

The recommended option we believe would be most suitable to the conditions at this site would be

undertaking soil stabilisation (cement columns) down through Soil Layers 2 and 2a, in combination with the

excavation and recompaction of all or part of the upper soil layer (Layer 1). Depending on the depth of soil

stabilisation, this method would significantly reduce the estimated consolidation settlement that could occur

in the soft silt and clay layer (Layer 2). Differential settlements will be mitigated by the ‘stabilised’ soils, and

the re-compacted soil at the surface (Layer 1) providing a rafting effect.

Preloading of this site would reduce the expected static consolidation settlement of Layer 2. This option

could provide an opportunity to further optimise the ground improvement approach and potentially reduce the

costs.

The structural design of the shallow foundations would need to allow for significant total settlement that could

occur during a large earthquake and ensure structural tolerances are adequate.

Further ground investigation data would be required to develop both of these options further. Subject to the

preferred layout of the plant and in particular the heavy or settlement sensitive structures, we recommend

that strong consideration should be given to undertaking the following additional geotechnical testing:

n Seismic CPT’s. These would provide information for accurately determining the seismic classification of

the site.

n Three additional machine boreholes drilled in the southeastern part of the site to confirm if there are more

floating basalt boulders and the depth of the basalt. These boreholes would also assist in confirming

potential pile lengths and confirm the material parameters below the current site investigation data

undertaken in this area.

n Shallow investigations in the form of test pits undertaken across the site to confirm subgrade CBR values

and samples collected for laboratory testing to provide compaction parameters.

n A desktop study of local quarries that would be able to provide suitable fill for the plant platform and for

preloading the site.

8 Applicability

This report has been prepared by CH2M Beca Ltd on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which CH2M Beca has not given its prior written consent, is at that person's own risk.



6519113 // NZ1-10914614-12 0.12 // page 12

Should you be in any doubt as to the applicability of this report and/or its recommendations for the proposed development as described herein, and/or encounter materials on site that differ from those described herein, it is essential that you discuss these issues with the authors before proceeding with any work based on this document.

9 References

Craig, R. F., 2004. Craig’s Soil Mechanics. Seventh Edition. Spon Press.

Damwatch, 2011. Whau valley Geotechnical Investigation Factual Report

Edbrooke, S.W., Brook, F.J., 2009. Geology of the Whangarei Area 1:250,000 Geological Map. IGNS Map 2.

Idriss, I.M and Boulanger R.W., 2008. Soil Liquefaction during Earthquakes. Earthquake Engineering

Research Institute.

NZGS, 2005. Field Description of Soil and Rock. Guideline for the Field Classification and description of soil

and rock for engineering purposes. NZ Geotechnical Society.

NZS1170.5. 2004. Structural Design Actions, Part 5: Earthquake Actions – New Zealand. Standards New

Zealand.

Tonkin & Taylor. 1968. Whau Valley Water Supply Dam, Design Drawings.

WDC ‘Intramaps’ GIS, accessed 17 September 2011. http://gis.wdc.govt.nz/whangarei/

White, P.J., and Perrin, N.D., 2003. Geology of the Whangarei Urban Area. Part Sheets Q06 and Q07 Scale

1:25,000. Institute of Geological and Nuclear Sciences. Geological Map 26.

http://gis.wdc.govt.nz/whangarei/



6519113 // NZ1-10914614-12 0.12 // page 13

AA

Appendix A

Figures

Whau Valley WTP Upgrade - 274 Whau Valley Road, Proposed Layout with Investigation Locations

6519113 Figure 1

Approximate 1:100 yr Flood Level (WDC)

Site Location



6519113 // NZ1-11649715-4 0.4 // page 43

NE

Appendix F

NESS

Private Bag 9023 | Whangarei 0148 | New Zealand T: 09 430 4200 | 0800 WDC INFO | 0800 932 463 | F: 09 438 7632

W: www.wdc.govt.nz | E: [email protected]

Report of the outcome of a “Potentially Contaminated Site” Property search under Section 6 of the Resource Management (National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health) Regulations 2011.

Application No: PCS150046

Name of Applicant: Whangarei District Council - Policy & Monitoring

Postal Address Private Bag 9023, Whangarei 0148

Contact: [email protected]

Date report compiled: 22/06/2015

Property Search Details:

Address: 274 Whau Valley Rd

Legal Description: LOT 2 DP 195500

LOT 5 DP 340586

LOT 1 DP 405632

PID NO: 103096

The search undertaken on Council records for the property and adjacent area has not identified any indication of current or previous activities in the area of the site that are included on the current version of the Hazardous Activities and Industries List (HAIL) issued by the Ministry for the Environment.

The following references to Engineers’ reports from the subdivision files on these lots are noted as they indicate descriptions of the sites’ current and known use.

TRIM NO. Detail

15/56199 RC39600 – Richardson Stevens Engineering Suitability report 13.03.2006

07/28140 RC39600 - Richardson Stevens revised Engineering Suitability report 28.03.2007, and

Ecoprojects Consulting Network Ltd – Assessment of Potential Landscape Effects – 10.04.2007

07/33364 Littoralis 30.04.2007 – review of Ecoprojects report

15/56243 Richardson Stevens Engineering report on Flooding and Stormwater 14.06.2006

DISCLAIMER

This Report has been prepared for the purposes of Section 6 of the Resource Management (National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health)

Regulations 2011 and contains all information known to the Whangarei District Council to be relevant to the

land as described. It is based on a search of Council records only and there may be other information relating to the land which is unknown to Council. The Council has not undertaken any inspection of the land

or any building on it for the purposes of preparing this report.

Caroline Blakeley

Property and Project Assessment Officer

mailto:[email protected]



6519113 // NZ1-11649715-4 0.4 // page 45

Appendix G

Archaeological Assessment Report

Archaeological Assessment of the

Whau Valley Proposed Water Treatment Plant Site

28 July 2015

Prepared for:


Private Bag 9023 Whangarei 0148

Prepared by:

Geometria Limited

3/3 Margaret Street Freemans Bay Auckland 1045

Page 2 - Whangarei District Council Water Treatment Plant

Geometria Ltd

Quality Information

Document: Archaeological Assessment of the Whau Valley Proposed Water Treatment

Plant Site.

Ref: 2015-033

Date: 3 August 2015

Prepared by: Russell Gibb

Revision History

Revision Revision Date Details Authorized

Name

Draft 24 July 2015 Drafted R. Gibb

Minor edits 24 July 2015 Reviewed by J. Carpenter

Client draft 28 July 2015 Distributed R. Gibb

Final 3 August 2015 Minor edits J. Carpenter

© GEOMETRIA Limited 2015

The information contained in this document produced by GEOMETRIA Limited is solely for the use of the Client identified on the cover sheet for the purpose for which it has been prepared and GEOMETRIA Limited undertakes no duty to nor accepts any responsibility to any third party who may rely upon this document.

All rights reserved. No section or element of this document may be removed from this document, reproduced, electronically stored or transmitted in any from without the written permission of GEOMETRIA Limited.

File ref.: 2015_033/WDC/20150727_Whau_Valley_WTP_Final.docx

Whangarei District Council Water Treatment Plant - Page 3

Geometria Ltd

CONTENTS

1.0 Introduction .................................................................................................................................................... 4 1.1 The Heritage New Zealand Pouhere Taonga Act 2014 ................................................................... 4 1.2 The Resource Management Act 1991. ........................................................................................... 4 2.0 Location and Proposed Development ............................................................................................................. 5 3.0 Methodology ................................................................................................................................................... 6 4.0 Background...................................................................................................................................................... 6 4.1 Physical Environment ..................................................................................................................... 6 4.2 Historic Background ....................................................................................................................... 6 5.0 Archaeological and Other Values .................................................................................................................. 20 5.1 Assessment Criteria ...................................................................................................................... 20 6.0 Assessment of Effects .................................................................................................................................... 21 7.0 Discussion ...................................................................................................................................................... 21 8.0 Recommendations and Mitigation ................................................................................................................ 22 9.0 Summary ....................................................................................................................................................... 22 10.0 References ................................................................................................................................................... 23 Appendix A - Site Record Forms ......................................................................................................................... 24 FIGURES

Figure 1: Location map showing 274 Whau Valley Road. ...................................................................... 5 Figure 2: Footprint of the proposed Water Treatment Plant. Source: Whangarei District Council. ..... 6 Figure 3: ML 29 (1865) titles Plan of a piece of land situated at Ketenikau. Source: Quickmap 2015. . 7 Figure 4: Section of S0 1090 (1887) showing the settlement of Peheawere. ...................................... 8 Figure 5: Whauwhau Block, printed upside down. ................................................................................ 9 Figure 6: Plan SO 761 (1869) showing the subdivision of Whau Valley. .............................................10 Figure 7: Rowdy Town at Whau Valley, 1860s (Florence Keen Collection, Whangarei Museum). The

first flats to be built in Whangarei are on the left of the photograph. ................................11 Figure 8; Announcement of the establishment of the Whau Valley tramway (Daily Southern Cross 6

October 1865). .....................................................................................................................12 Figure 9: Looking up the Whau Valley ca. 1900. Subject property right mid-ground with diagonal

crop lines visible on the property (The Camera in Early Northland. Northern Advocate, 9 November 1974)...................................................................................................................13

Figure 10: Whau Valley in 1922 (Ferrar and Harris 1922). ..................................................................13 Figure 11: Archaeological sites in the vicinity of the subject property (Archsite, accessed 15 July

2015).....................................................................................................................................15 Figure 12: Q06/240 as mapped in 1979. .............................................................................................16 Figure 13: Q06/392 the Whau Valley Coal Mine in 1865. ...................................................................16 Figure 14: Overlay of ML441 showing ‘Old native cultivations’ proximate to the subject property (in

blue)......................................................................................................................................17 Figure 15: Section of SO761 showing ‘Old cultivations – Rich fern flat’ over the subject property,

allotment 61 (in blue). ..........................................................................................................17 Figure 16: View looking west over the subject site from Whau Valley Road. .....................................18 Figure 17: Part of ridgeline where archaeological sites Q06/240, 249, 376, and Q06/392 are located. ..............................................................................................................................................18 Figure 18: Looking south over the subject site from the northern ridgeline ......................................19 TABLES Table 1: Archaeological sites proximate to the subject property ........................................................15


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1.0 Introduction G. Sands of the Whangarei District Council (WDC) commissioned Geometria Ltd to undertake an archaeological assessment of the site for a proposed new water treatment plant (WTP) to be located in the Whau Valley. The new plant would replace an existing water treatment plant located on the corner of Whau Valley Road and Fairway Drive. The Whau Valley has a long history of Maori occupation as evidenced by the archaeological sites recorded in the area, as well as a long European history of farming, horticulture and mining dating back to the 1850s.

Under the Heritage New Zealand Pouhere Taonga Act 2014 (HNZPTA 2014; previously the Historic Places Act 1993, HPA 1993), all archaeological sites are protected from any modification, damage or destruction except by the authority of Heritage New Zealand Pouhere Taonga.

This survey and assessment uses archaeological techniques to assess archaeological values and does not seek to locate or identify wahi tapu or other places of cultural or spiritual significance to Maori. Such assessments may only be made by Tangata Whenua, who may be approached independently of this report for advice.

1.1 The Heritage New Zealand Pouhere Taonga Act 2014

Under the HNZPTA all archaeological sites are protected from any modification, damage or destruction. Section 6 of the HNZPTA defines an archaeological site as:

" any place in New Zealand, including any building or structure (or part of a building or structure), that—

(i) was associated with human activity that occurred before 1900 or is the site of the wreck of any vessel where the wreck occurred before 1900; and

(ii) provides or may provide, through investigation by archaeological methods, evidence relating to the history of New Zealand; and

(b) includes a site for which a declaration is made under section 43(1)”

To be protected under the HNZPTA an archaeological site must have physical remains that pre-date 1900 and that can be investigated by scientific archaeological techniques. Sites from 1900 or post-1900 can be declared archaeological under section 43(1) of the Act.

If a development is likely to impact on an archaeological site, an authority to modify or destroy this site can be sought from the local Heritage New Zealand Pouhere Taonga office under section 44 of the Act. Where damage or destruction of archaeological sites is to occur Heritage New Zealand usually requires mitigation. Penalties for modifying a site without an authority include fines of up to $300,000 for destruction of a site.

Most archaeological evidence consists of sub-surface remains and is often not visible on the ground. Indications of an archaeological site are often very subtle and hard to distinguish on the ground surface. Sub-surface excavations on a suspected archaeological site can only take place with an authority issued under Section 56 of the HNZPTA issued by the Heritage New Zealand.

1.2 The Resource Management Act 1991.

Archaeological sites and other historic heritage may also be considered under the Resource Management Act 1991 (RMA). The RMA establishes (under Part 2) in the Act’s purpose (Section 5) the matters of national importance (Section 6), and other matters (Section 7) and all decisions by a


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Council are subject to these provisions. Sections 6e and 6f identify historic heritage (which includes archaeological sites) and Maori heritage as matters of national importance.

Councils have a responsibility to recognise and provide for the relationship of Maori and their culture and traditions with their ancestral lands, water, sites, wahi tapu, and other taonga (Section 6e). Councils also have the statutory responsibility to recognise and provide for the protection of historic heritage from inappropriate subdivision, use and development within the context of sustainable management (Section 6f). Responsibilities for managing adverse effects on heritage arise as part of policy and plan preparation and the resource consent processes.

2.0 Location and Proposed Development The proposed site is located is located at 274 Whau Valley Road and comprises an area of 48550m2 flat, fenced pasture fronting Whau Valley Road (Figures 1). The legal description is Lot 5 DP 340586.

The proposed development comprises a new water treatment plant and associated infrastructure although detailed design work has not yet been undertaken (Figure 2).

Figure 1: Location map showing 274 Whau Valley Road.


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Figure 2: Footprint of the proposed Water Treatment Plant. Source: Whangarei District Council.

3.0 Methodology The methods used to assess the presence and state of archaeological remains on the property included both a desktop review and field survey. The desktop survey involved an investigation of written records relating to the history of the property. These included regional archaeological publications and unpublished reports, New Zealand Archaeological Association Site Record Files (NZAA SRF) downloaded via the ArchSite website (www.archsite.org.nz), local histories, aerial photography, local authority heritage lists, the Heritage New Zealand List, and land plans held by Land Information New Zealand.

The field assessment was undertaken on 20 July by Russell from Geometria and was conducted on foot, examining the surface area of the property. Probing but no test pitting was undertaken.

4.0 Background 4.1 Physical Environment

The floor of the Whau Valley comprises Holocene river deposits consisting of unconsolidated to poorly consolidated mud, sand, gravel and peat deposits of alluvial, colluvial and lacustrine origins. There is a smaller area of Pleistocene undifferentiated swamp deposits on the south eastern side of the valley. The higher ground of the hills and ridges are Waipapa group sandstones and siltstones deriving from the weathered greywacke beneath.

4.2 Historic Background

4.2.1 Maori History In early times Whangarei was the territory of the Ngai Tahuhu iwi who built villages and fortifications on or around strategic points on the harbour and surrounding hills, while the outlying flat areas were cultivated. One significant site in Mairtown was Parihaka Pa with an associated large kainga and communal area known


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as Tawatawhiti. The surrounding land was cultivated over an area that stretched from the current CBD, through the suburbs of Regent and Kensington, to the Whau Valley.

In the mid 1700s Ngai Tahuhu were driven out of the area by the Ngapuhi under Te Pouaharakeke and other related chiefs who secured the land from Whangarei to Waipu and Waihonga to Tangihua. One of these chiefs, Ngaoro ki te uru, was given substantial holdings, which included Kamo, Tamaterau, Parihaka and land further north. His people became known as Ngati Kahu, a hapu of Ngapuhi.

A kainga called Ketenikau was located on the western side of Kamo and was associated with extensive cultivations (Johnson 2002:3). Ketenikau is shown on ML 29, dated 1865, but this name probably represents a boundary marker, rather than the actual site of the Ketenikau kainga (Figure 3). This plan also shows the area in cultivation at the time. Another kainga called ‘Peheawere’ is shown on S0 1090 (1887) as a ‘Native Settlement’ to the east side of the junction between the Mangakino and Waitaua Streams (Figure 4).

Figure 3: ML 29 (1865) titles Plan of a piece of land situated at Ketenikau. Source: Quickmap 2015.


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Figure 4: Section of S0 1090 (1887) showing the settlement of Peheawere.

4.2.2 European History The following account is largely provided by Between Two Mountains by Florence Keene, p24, 136-138, and Whangarei: The founding years by Nancy Preece Pickmere, p 56 and 101. This is supplemented with reference to articles in the Northern Advocate. Deed information is provided by H. H. Turton (1877).

In February 1857 the first land sales in the Whangarei north area occurred, with the Kaurihohore Block to the east of Whau Valley. In February 1858, a block of land called Kamo, consisting of 296 acres, was purchased and Whau Whau that same month, followed by Ruatangata in 1861 and Te Tupua Apotu and Hikurangi in 1862.

The Whau Whau Block, which included Whau Valley, was sold on the 23 February 1858 (Figure 5). It was sold by Whare Te Puia, Wiremu Pohe, Manihera Iwitahi, and Hone Poukoura with the sale witnessed by settler John Fifield and Pita Hunia Tetau. The vendors received 100 pounds that day from John Grant Johnson the Government Land Commissioner

The deed states:

“This Deed…is a full and final sale conveyance and surrender by us the Chiefs and People of the Tribe The Parawhau whose names are hereunto subscribed And Witness that on behalf of ourselves our relatives and descendants we have by signing this Deed under the shining sun of this day parted with and for ever transferred unto Victoria Queen of England Her Heirs the Kings and Queens who may succeed Her and Her and Their Assigns for ever in consideration of the sum of One Hundred Pounds (£100.0.0) to us paid by John Grant Johnson on behalf of Queen Victoria…all that piece of our Land situated at Whangarei and named Te Whau Whau the boundaries whereof are set forth at the foot of this Deed and a plan of which Land is annexed thereto with its trees, minerals, waters, rivers, lakes, streams, and all appertaining to the said Land or beneath the surface of the


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said Land and all our right title claim and interest whatsoever thereon To Hold to Queen Victoria Her Heirs and Assigns as a lasting possession absolutely for ever and ever.”

The boundaries appended to the deed state the block comprised the land:

“commencing at Pongatahi thence along the surveyed line to the edge of the lake –thence it ascends the range and descends to the stream Waituia thence it ascends and goes to Paikapakapa thence to Whakatoetoe, where it turns till it joins the boundary of Carruths Grant, thence along the boundary line of Carruths Grant till it reaches the stream of Waiarohia and thence up the course of the Waiarohia to the point of commencement at Pongatahi. The Tapued ground at Tararau is not to be included in these boundaries.”

Figure 5: Whauwhau Block, (printed upside down).


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Some of the early settlers in what was then called Whauwhau Valley were William Hawken and his family, who arrived in 1859, and John MacDonald and his family, in 1860. The MacDonald family was part of the group of people from Nova Scotia who settled in the Whangarei area. The subdivision of the Whauwhau Valley is shown on SO 761, dated 1869 (Figure 6). This plan shows Francis Wood as the owner of allotments 60 and 61 (the subject property) with Joseph Griffin holding allotments 56 and 59 adjacent to the west. Roderick MacDonald is shown as the owner of Allotments 64, 66, 67 and 68 on the south side of Whau Valley Road.

Griffen was growing award-winning citrus and mandarins in particular by the 1880s (‘Citrus Camelia and Winter Fruit Show’, Northern Advocate, 30 July 1887) and Griffin was supplying seedlings from a 30 year old tree in the valley to the townspeople later that year (‘Miscellaneous’, Northern Advocate, 10 September 1887). In 1904 Griffin was offering his farm for sale, which at that time consisted of 159 well-watered and fenced acres including 10 acres of orchards, and a seven room hose and outbuildings (‘Auction Sales’, Northern Advocate, 12 February 1904).

Figure 6: Plan SO 761 (1869) showing the subdivision of Whau Valley.

The discovery of coal in the Whau Valley Stream by Jonny Rake, saw the beginning of coal mining in the Whangarei District. Rake had worked at the coalmines in Thames and when he recognised coal in a tributary of the Ketinikau Stream, he took it to Henry Holman for examination. Holman was running the flaxmill at what is now Mill Road and had some experience with minerals. He didn’t have the money to invest in mining the seam, which extended back into the hill behind the stream, and instead contacted Henry Walton to investigate a joint venture.


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The Whau Valley Coal Mines were opened in 1865 by Henry Walton and William Grahame, who took a 99-year lease on the land. Walton had leased the coalfield in 1862 from the Maori at Ketinikau (west Kamo), with the lease being signed by Chief Te Puia, which was five pounds for every acre of coal baring land.

He had originally tried to buy the land and arranged the survey and attempted to buy 53 acres of coal-baring land through John Grant Johnson, the local Government Land Commissioner, and had Henry Holman’s son Harry do the survey, during which time they discovered a 25 foot high waterfall on the stream composed of an outcropping coal. The Maori ultimately refused to sell outright and both parties opted for a lease.

At around the time Walton and Grahame started the mine operation Francis Wood offered a site for a new school on his land adjoining the coal fields (Daily Southern Cross 30 January 1865). It is not known if this offer was accepted but it appears no school was constructed on Allotment 61. Soon after Wood sold his Whau Valley farm and opened up a general store, which he operated with great success during the early years when the mine was prospering. Wood went on to build a steam-powered flourmill in the centre of Whangarei before retiring in 1884. He died in 1887 (Northern Advocate 12 March 1887).

A miner’s village was established with a butchers shop, bakery, and accommodation for imported Cornish labour and became known as Rowdy Town1 (Figure 7). Walton invested about 20,000 pounds in his venture but ended up shutting it down after three years due to water seepage into the workings. In that time the brought out almost 71,000 tons of coal.

Figure 7: Rowdy Town at Whau Valley, 1860s (Florence Keen Collection, Whangarei Museum). The first flats to be built in Whangarei are on the left of the photograph.

During 1865 a wooden tramway was built from the mine to the Hatea River so coal wagons could be pulled by horses to be loaded onto ships (Figure 9). Horse drawn trucks pulled coal down the tramway and long the

1 In 1933, Joseph Smith, a long-time resident of the area recalling his time spent in the Whau valley, reported that Rowdy Town was located on the farm of Mr Phil Going’s present farm (Auckland Star 26 January 1933). He was involved in gum digging in the area during that time (ca. 1868).


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east side of Kamo Road to a chute at the end of Donald Street, above the Hatea River, from whence it was loaded onto the Auckland coal cutters. The tramway was six feet wide with 4x4 timber bearers of Whau Valley sawn rimu. The full trucks were attached to a wire drum pulley and sent down the hill to a small wharf on the river. By July 1866 coal was shipped from the terminus on the Aquila and Elizabeth with the Daily Southern Cross stating that daily shipments were soon expected. Coal from the Whauwhau mine was advertised locally in 1875 at a rate of 10s. per ton (Daily Southern Cross 18 November 1875), and by 1885 annual output from the mine was 45,359 long tons (46,087t).

In the 1870s Alexander Love arranged a scheme to drain the flooded workings and opened up a mine halfway along Whau Valley Road. He operated for seven years before losing an arm in a winch accident.

The railway line between Kamo and Whangarei, opened in 1882 and to some extent the Kamo and then the Hikurangi Colliery eclipsed the Whau Valley operation, with Walton investing in 400 acres at Hikurangi when coal was discovered there. It wasn’t until 1919 that a siding was built to connect the Whau Valley mine tramway with the main railway line (Northern Advocate 11 June 1910).

Figure 8; Announcement of the establishment of the Whau Valley tramway (Daily Southern Cross 6 October 1865).

There were several subsequent attempts to re-open the Whau Valley coal mine, the last being in the 1940s. In 1944 the land occupied by the abandoned Whauwhau railway was vested in the Crown, the line itself had been managed by the Railway Department since 1895 when it was taken by the state, having been mortgaged to the Crown as security for a debt of £1177 (Auckland Star 22 November 1944). The location of the mines, tramways and roads in 1922 is shown in Figure 10.

Aside from the establishment of the mine and Rowdy Town, European settlement in the Whau Valley was centred on farming and some horticulture. In 1865 only ‘two to three’ homesteads were reported in the Whauwhau Valley (Daily Southern Cross 17 January 1865:2) and even by the turn of the century few buildings had been built on Whau Valley Road (Figure 8). In 1899 the residence of T. Sutton was destroyed by fire (and in 1911 an eight bedroomed house belonging to the McLeod’s2 burnt to the ground (New Zealand Herald 28 January 1911).

2 The McLeod’s owned allotments 71, 72, 74 and 75 on the south side of Whau Valley Road.


Geometria Ltd

Figure 9: Looking up the Whau Valley ca. 1900. Subject property right mid-ground with diagonal crop lines visible on the property (The Camera in Early Northland. Northern Advocate, 9 November 1974).

Whau Valley also became important as a source of fresh water as Whangarei grew. While Kamo and Maunu were supplied by springs, but there was no such supply available for central Whangarei. Large bush reserves were established in the western/Pukenui Hills to supply a number of small reservoirs. Investigations into the Whau Whau Stream as a possible source of water supply for Whangarei was conducted by the town engineer in 1898 (Northern Advocate 7 May 1898:6) with the Whau Whau found to have great superiority over other sources and the capital cost of works to establish the water supply estimated at £6343. The first Whau Valley reservoir was completed in 1921 but within a few decades was not sufficient, with a larger dam built in the 1960s to supply the growing city.

Figure 10: Whau Valley in 1922 (Ferrar and Harris 1922).


Geometria Ltd

4.2.3 Archaeological Background There are three pa sites recorded in the immediate vicinity of the subject property (Figure 11). Q06/240 was recorded by the Archaeological Site Recording Group in February 1979. It consisted of a pa or defended site on a knoll on top of the ridgeline north of the subject property, about 100m north of the subject property boundary and 200m north of Whau Valley Road, at approximately 120m above sea level. At that time the site was in good condition, being under native bush and built in an area of rocky soil that hadn’t been cleared, although it was within a farmed paddock. The site was mapped over two days using pace, compass and staff (Figure 12). The site consisted of a terraced knoll with six terraces and a summit platform, with larger level areas either side of the knoll containing storage pits up to 4 x 2 x 1m deep in size. The western side of the knoll was defended by a 4m high scarp while the eastern side was defended by two 1m deep ditches. No middens were noted in association with the site but a piece of ‘flint’ was picked up and local informants suggested other artefacts had been found there.

Q06/376 was recorded by G. Nevin on 17 March 1988. It was a pa on the end of the ridge above the bend in Whau Valley Road at the intersection with the Waiarohia and Waikahikatea Stream, and was contiguous with the features recorded as pa Q06/240. This places it about 200m north east of the nearest boundary of the subject property. The pa was visible in a 1983 aerial photograph but at the time of recording by Nevin, had been bulldozed. No further information is given.

Three hundred metres north of the northwest corner of the subject property is another pa, Q06/249. This site contains at least 12 storage pits up to 6 x 4m in size, on eight terraces and a large summit platform with associated midden deposits and lithic artefacts, and was also recorded in 1979 by the Archaeological Site Surveyors. Another ten sites are recorded between Whau Valley and Fairway Drive to the northeast, attesting to the dense pre- and protohistoric occupation of the area by Maori.

Q06/392, 400m north of the subject property is the site of one of the Whau Valley coal mining operations. While the site position in Archsite is well away from the subject property, the site record reports mining related features and artefacts spread along a kilometre of the Waikahikatea Stream, from the Ketenikau Cemetery to the Waiarohia Stream. The site includes tramway foundations and cuttings on both sides of the valley, collapsed shafts, terraces and platforms and machinery including a large boiler. The centre of Rowdy Town, the Cornish miners village is located 200m north east of the north eastern corner of the subject property (Figure 13).

Three hundred metres east of the subject property, around Huia and Halcyon Streets, several other sites have been recorded. Q06/387 is the site of two sod houses that were demolished prior to the construction of stockyards at 143 Whau Valley Road, to the west of Halcyon place. They were 12 x 10 feet in size with 9-inch thick walls, according to K. Strong who demolished them, and were probably associated with mid-19th century occupation of the area, possibly by Cornish miners. Q06/388 and 389 are the location of kumara storage pits destroyed during housing development on Huia Street, to the east of Halcyon Place. These sites were all recorded by G. Nevin in 1988 during her survey of sites in the Whangarei area, and were based on local informants’ knowledge of the area.

Given the nearby pa and the well-watered alluvial flats that comprise the subject property, it seems likely that some pre or protohistoric Maori activity such as gardening may have occurred in that area in association with the occupation of the higher ground. Plan ML 441 dated 1862, shows ‘old native cultivations’ on the slopes immediately north of the property in the vicinity of pa sites Q06/240 and 249 (Figure 14). Another plan, SO 761 (1869), shows the area including the subject property, as ‘Old Cultivations, Rich fern flat’ suggesting that while the area had previously been traditionally cultivated, it was now in the early stages of successional vegetation regeneration (Figure 15).

The European occupation of the Whau Valley from the early 1860s has also left its mark on the wider landscape and there may be mining or farming related features in the vicinity of the subject property.


Geometria Ltd

Table 1: Archaeological sites proximate to the subject property

NZAA No. Type/Name Date Recorded Notes Q06/240 Pa 5/2/80 Not revisited since recorded in 1979 Q06/249 Pa 5/2/80 Not revisited since recorded in 1979 Q06/376 Pa 11/1/89 Recorded from aerial photograph –

destroyed Q06/387 Sod Houses 12/1/89 Destroyed Q06/388 Pits 12/1/89 Destroyed Q06/389 Pits 12/1/89 Destroyed Q06/392 Coal Mines 12/1/89 Whau Valley coal mines and associated

features

Figure 11: Archaeological sites in the vicinity of the subject property (Archsite, accessed 15 July 2015).


Geometria Ltd

Figure 12: Q06/240 as mapped in 1979.

Figure 13: Q06/392 the Whau Valley Coal Mine in 1865.


Geometria Ltd

Figure 14: Overlay of ML441 showing ‘Old native cultivations’ (red circle) and trail (red arrows) proximate to the subject property (in blue).

Figure 15: Section of SO761 showing ‘Old cultivations – Rich fern flat’ (red circle) over the subject property, allotment 61 (in blue).


Geometria Ltd

4.2.4 Other Heritage Registers and Listings The Whangarei District Plan Schedule of historic buildings, sites places, trees and sites of significance to Maori, and the Heritage New Zealand Pouhere Taonga List of historic places and wahi tapu were reviewed and no sites are listed in the vicinity of the subject property.

4.2.5. Site Visit The subject property was visited by Russell Gibb on the 21st July 2015. The site is a flat fenced paddock currently in pasture bounded to the north by the ridgeline where pa sites Q06/240, 249 and 376, and the Whau Valley Mine remains Q06/392 are located (Figure 16-18). There are no apparent surface features on the paddock and probing across the front of the site indicated no obvious subsurface archaeological deposits such as midden, concrete or other detritus that might be expected.

Figure 16: View looking west over the subject site from Whau Valley Road.

Figure 17: Part of ridgeline where archaeological sites Q06/240, 249, 376, and Q06/392 are located.


Geometria Ltd

Figure 18: Looking south over the subject site from the northern ridgeline


Geometria Ltd

5.0 Archaeological and Other Values 5.1 Assessment Criteria

The archaeological significance of recorded archaeological sites on a subject property is usually assessed using two sets of criteria based on Heritage New Zealand guidance for significance assessments of archaeological sites.

The first set of criteria assess the potential of the site to provide a better understanding of New Zealand’s past using scientific archaeological methods. These categories are focussed on the intra-site level.

How complete is the site? Are parts of it already damaged or destroyed? A complete, undisturbed site has a high value in this section, a partly destroyed or damaged site has moderate value and a site of which all parts are damaged is of low value.

How diverse are the features to be expected during an archaeological excavation on the site? A site with only one or two known or expected feature types is of low value. A site with some variety in the known or expected features is of moderate value and a site like a defended kainga which can be expected to contain a complete feature set for a given historic/prehistoric period is of high value in this category.

How rare is the site? Rarity can be described in a local, regional and national context. If the site is not rare at all, it has no significance in this category. If the site is rare in a local context only it is of low significance, if the site is rare in a regional context, it has moderate significance and it is of high significance it the site is rare nationwide.

The second set of criteria puts the site into its broader context: inter-site, archaeological landscape and historic/oral traditions.

What is the context of the site within the surrounding archaeological sites? The question here is the part the site plays within the surrounding known archaeological sites. A site, which sits amongst similar surrounding sites without any specific features, is of low value. A site, which occupies a central position within the surrounding sites, is of high value.

What is the context of the site within the landscape? This question is linked to the one above, but focuses onto the position of the site in the landscape. If it is a dominant site with many features still visible it has high value, but if the position in the landscape is ephemeral with little or no features visible it has a low value. This question is also concerned with the amenity value of a site and its potential for on-site education.

What is the context of the site within known historic events or people? This is the question of known cultural association either by tangata whenua or other descendant groups. The closer the site is linked with important historic events or people the higher the significance of the site. This question is also concerned with possible commemorative values of the site.

An overall significance value derives from weighing up the different significance values of each of the six categories.

In the case of the subject property, there are no specific values to assess.


Geometria Ltd

6.0 Assessment of Effects There are no obvious archaeological features on the property at 274 Whau Valley Road and thus no specific effects of the water treatment plant proposal. However, proto-historic or historic period Maori gardening activity occurred in the vicinity and a historic trail is shown on a survey plan for an adjacent property, which may have transited the subject property. Subsurface archaeological features such as made or anthropogenic garden soils created by the addition of other material to the natural humus, stone garden alignments or mounds, and the bases of earth ovens or hearths, and field shelters may survive below the turf and may be modified by the water treatment plant. Such features are amenable to identification and analysis during preliminary earthworks. 7.0 Discussion There is no surface archaeological evidence on the subject property however archival research suggests the Whau Valley area was gardened by Maori in the early to mid-19th century, prior to European land acquisition.

The exact form of this gardening, described as ‘Old Cultivations’ or “Old native cultivations” by European surveyors on their land plans, remains unknown. Typically, archaeological features associated with Maori horticulture elsewhere in Northland include stone rows, mounds, large complexes of garden rows and structures based on the use of stone in the inland Bay of Islands, slope trenches and garden boundaries, and the extensive ditch systems of Awanui, Oruru, Motutangi Taumatawhana and Matakohe-Limestone Island. Gardening evidence is concentrated around the coast, around inland areas where fertile volcanic soils are present and on the islands. Storage pits are widespread, reflecting that much of Northland provided suitable conditions for growing crops, and such pits are present on the pa sites recorded above the subject property.

Subsurface archaeological evidence of Maori gardening can include areas of burning or fires from initial vegetation clearance as forest is cleared and gardens are established and maintained (Johnson 2002: 35), ‘made’ or anthropogenic soils whereby sand, shell, charcoal, shingle, subsoil or other ‘mulch’ is added to or mixed through otherwise less than suitable soils to improve fertility, drainage, soil temperature or other growing conditions, or the soil is artificially deepened for similar reasons (Furey 2006: 46).

Structures associated with Maori horticulture and which may be present below the modern and otherwise modified existing ground surface include the bases of stone garden mounds (which may be simple clearance piles or more complex piles of stone and soil that were gardened upon), walls and alignments used to delineate garden plots and paths, hearths or earth ovens used for warmth or cooking meals while working in the gardens, and structural features associated with field shelters erected to provide shelter while working in the gardens and consisting of postholes for posts, drains and stone windbreaks. Such features have been found in other parts of Whangarei where surface archaeological features have not been present but Maori gardening was known from historic sources, such as around the State Highway 1 Kamo Bypass, where subsurface archaeological features were recorded during the first stage by Johnson (2001), and during the second stage by Shakles and Phear (2011). Fire scoops recorded by Phear near the new Kamo Road/State Highway 1 intersection redeveloped in 2010 have provided the earliest radiocarbon dates for the Whangarei area.


Geometria Ltd

It is possible that evidence of European horticulture may also be present, associated with the late 19th century occupation of the area and its use as a farm or orchard by Joseph Griffin. This might include subsurface remains of farm fences and outbuildings.

8.0 Recommendations and Mitigation 1) Whangarei District Council should apply for an archaeological authority under Section 44 of the Heritage New Zealand Pouhere Taonga Act 2014.

2) Whangarei District Council should consult with the Tangata Whenua as part of the archaeological authority application process.

3) An archaeological management plan and on-call procedures to manage accidental discoveries should be prepared to manage the archaeological effects of the development.

4) Preliminary earthworks i.e. the removal of turf and topsoil prior to the development of the site should be monitored by an archaeologist.

9.0 Summary Geometria Ltd was commissioned by G. Sands of the Whangarei District Council to undertake an archaeological survey and assessment of the proposed new water treatment plant at 274 Whau Valley Road, Whangarei.

There is no archaeological impediment to developing the water treatment plant on the property. No Maori archaeological features were observed on the property, although two pa sites are recorded on the ridge to the north and it is adjacent to two areas of gardens attested to in historic land plans, to the south west and north and probably associated with the nearby pa. It is also adjacent to historic archaeological features associated with the Whau Valley coal mine.

The property is level and well-watered and would have been suitable for Maori horticulture. Related archaeological features may be present below the ground surface but are not amenable to pre-emptive testing or identification. These may be accidentally encountered during the development of the water treatment plant and a recommendation has been made to apply for an archaeological authority under Section 44 of the Heritage New Zealand Pouhere Taonga Act 2014, with associated recommendations for consultation with tangata whenua, management plan, and monitoring preliminary earthworks.


Geometria Ltd

10.0 References Furey, L., 2006. Maori Gardening: An Archaeological Perspective. Department of Conservation,

Wellington.

Johnson, L., 2002. Archaeological Monitoring of the Kamo Bypass and Investigation of Site Q06/486. Unpublished report for Opus International Consultants by Northern Archaeological Research, Auckland.

Keene, F., 1966. Between Two Mountains. A History of Whangarei. Whitcombe and Tombs, Auckland.

Pickmere, N. 1986. Whangarei: The Founding Years 1820-1880. Nancy Preece Pickmere, Whangarei.

Shakle, R and S. Phear, 2011. Archaeological Monitoring of the Kamo Bypass Stage 2 Works, Kamo, Northland: Recording and Investigation of Sites Q06/581, Q06/607 AND Q06/616. Unpublished report for the NZ Transport Agency, Clough and Associates, Auckland.

Turton, H. H., 1877A. Maori Deeds of Land Purchases in the North Island of New Zealand: Volume One. George Didsbury, Government Printer. Wellington.

Turton, H. H., 1877B. Plans of Land Purchases in the North Island of New Zealand. Volume One: Province of Auckland. George Didsbury, Government Printer. Wellington.


Geometria Ltd

Appendix A - Site Record Forms

SITE COORDINATES (NZTM) Easting: Northing:1717281 6048882 Source: CINZAS

Finding aids to the location of the site

Scale 1:2,500

IMPERIAL SITE NUMBER: METRIC SITE NUMBER:N20/103 Q06/240

Brief description

PA

Q06/240NZAA SITE NUMBER:

SITE TYPE:

SITE NAME(s):

Pa

DATE RECORDED:

Site Record Form

Recorded features

Other sites associated with this site

09/07/2015Printed by: jonocarpenter

1 of 6

NEW ZEALAND ARCHAEOLOGICAL ASSOCIATION

Statement of condition

Site description

Condition of the site

Current land use:

Threats:

Q06/240NZAA SITE NUMBER:SITE RECORD HISTORY


2 of 6


Q06/240NZAA SITE NUMBER:SITE RECORD INVENTORY

Supporting documentation held in ArchSite


3 of 6



4 of 6



5 of 6



6 of 6




Scale 1:2,500


Brief description

PA


SITE TYPE:

SITE NAME(s):

Pa

DATE RECORDED:

Site Record Form

Recorded features



1 of 3



Site description


Current land use:

Threats:



2 of 3





3 of 3




Scale 1:2,500


Brief description

COAL MINES


SITE TYPE:

SITE NAME(s):

Mining - coal

Whau Valley Mines

DATE RECORDED:

Site Record Form

Recorded features

Mine



1 of 9



Site description

Updated 15/07/2015 (other), submitted by jonocarpenter Grid reference (E1716881 / N6049181)

Name added from SRF - 6/2/2014, Rick McGovern-Wilson


Current land use:

Threats:



2 of 9





3 of 9



4 of 9



5 of 9



6 of 9



7 of 9



8 of 9



9 of 9




6519113 // NZ1-11649715-4 0.4 // page 47

Appendix H

On-site Dewatering Assessment Memo

CH2M Beca // 7 September 2015 // Page 1

6519113 // NZ1-11278458-5 0.5

Memorandum To: Mark Shaw Date: 7 September 2015

From: Philip La Roche Our Ref: 6519113

Subject: 274 Whau Valley Rd - On site dewatering assessment

1 Introduction

Whangarei District Council (WDC) is proposing to build a new water treatment plant (WTP) 274

Whau Valley Rd.

The feasibility study of 274 Whau Valley Rd has proposed to recycle filter to waste, recycle filter

backwash following settlement, in order to maximise the treated water produced, due to the limited

raw water resource available, as well as minimising waste stream disposal issues. The clarifier and

backwash sludge waste stream will need to be managed and residual solids disposed.

It is proposed to enable discharge of plant overflows or off spec water to the river, via a buffer pond.

The purpose of this memo is to compare the costs and benefits of discharging waste directly to

sewer versus on site dewatering.

2 Discharge to Sewer

The process design assumes filter to waste is recycled, filter backwash is recycled following

settlement and clarifier and settled backwash sludge is discharged to sewer.

The following table summarises the expected discharge flows to sewer. Note these flows would be

significantly less than the existing plant discharge with the proposal to recycle settled backwash

waste.

Table 1: Sewer discharge





3 Allowance for raw water suspended

solids plus coagulant

Percentage solids in clarifier sludge 0.2%

2,000 g/m3 Could design clarifier so that solids

were up to 1% concentration

Total solids per day with average flow 130,000 g/d

Clarifier and backwash sludge to discharged directly to sewer at average plant flow

65 m3/d

Total solids per day with max flow/average solids

293.8 kg/d

Clarifier and backwash sludge to be 147 m3/d

Memorandum


6519113 // NZ1-11278458-5 0.5


discharged directly to sewer at max plant flow

Peak flow (approximate nominal) 5.1 L/s 3 times estimated peak day/average solids flow

The nearest public sewer is approximately 250m from the 274 Whau Valley site. A gravity waste

pipeline would be constructed from the WTP site to the sewer network outside 264 Whau Valley

Road. Here a 150NB waste pipeline gravitates to an existing sewer pump station south of the one

way bridge. The volume of waste to be discharged to sewer would utilise around 25-50% of the

existing 80 NB rising main. Hence depending on the utilisation of this pump station by the existing

catchment, the existing sewer pump station and rising main may need to be upgraded. The cost

estimates presented in section 4 allow for these upgrades.

Issues with disposal to sewer include:

n Increased risk of sewer fouling – this is particularly a risk with high doses of polyelectrolyte

and high sludge concentration. Discharge of clarifier sludge, as opposed to thickening this

sludge, is expected to make sewer fouling risks manageable.

n Phosphate Precipitation – a positive benefit of disposal of alum sludge to sewer is phosphate

removed will be improved, with lower levels of this nutrient being discharged with the liquid

effluent stream from the wastewater treatment process. Hence disposal of sludge to sewer, with

the volume minimised, is environmentally beneficial. WDC’s trade waste policy allows for

“Incentive rebates for discharging materials beneficial to the council sewerage system”. This

may be a case where the WTP could argue a justification for a rebate on the trade waste costs.

n Reliance on Sewer Operation – the disposal is reliant on the sewer pumping and conveyance

system being operational. In the event of failure (including power outage) a contingency such as

storage, discharge to the site pond and/or improved reliability of power supply to the waste pump

station may be needed.

3 On Site Dewatering

As with the discharge to sewer option, filter to waste would be directly recycled, filter backwash

would be recycled following settlement, however clarifier and settled backwash sludge would be

dewatered to produce a sludge that can be handled as a solid material. Dewatering would consist of

a gravity sludge thickener followed by centrifuge dewatering. Centrifuge centrate would be

recommended to be discharged to sewer and thickener supernatant water recycled. The centrifuge

centrate would be discharged to the existing sewer network as described in section 2, however

given the smaller volume of waste discharged, the existing sewer pump station and rising main

would not be expected to need upgrading.

Table 2: On site dewatering





3 Allowance for raw water suspended

solids plus coagulant

Percentage solids in settled backwash sludge 2%

20,000 g/m3

Memorandum


6519113 // NZ1-11278458-5 0.5


Percentage solids in centrifuge sludge 16%

160,000 g/m3

Total solids per day with average flow 130 kg/d

Sludge to centrifuge at 2% solids at average flow

6.5 m3/d

Solid sludge to waste at 16% solids at average plant flow

0.8 m3/d

Centrate to sewer at average plant flow 5.7 m3/d

Total solids per day with max flow 293.8 kg/d

Sludge to centrifuge at 2% solids at max flow

14.7 m3/d

Solid sludge to waste at 16% solids at max plant flow

1.8 m3/d

Centrate to sewer at max plant flow 12.9 m3/d

Peak flow 0.5 L/s Assumes 8 hours/d dewatering

Issues with on-site dewatering include:

n Noise – centrifuges are noisy, and the control to very low levels will be necessary in the

residential area where the plant is located, and as the sludge plant would inevitably be located

close to a boundary. Noise control is complicated with a sludge plant by the desire to maintain

good ventilation and keep condensation down.

n Odour – probably a lesser issue than noise, but water treatment plant sludge, particularly during

periods of high algal activity can have a mild odour, and due to the location in a residential area

any significant odour could create complaints.

n Recycled Water Quality Risks – the risks from recycling such as elevated soluble manganese,

taste and pathogens are increased from recycling of sludge supernatant. Centrifuge centrate is

assumed to still go to sewer due to the low quality of this stream.

n Increased Operator Input – Dewatering processes typically require significant operator input,

significantly increasing the manning requirements for the plant.

n Waste to Sewer – the smaller volume of waste discharged to sewer means upgrading of the

sewer system is unlikely to be required.

Memorandum


6519113 // NZ1-11278458-5 0.5

4 Cost Comparison

Capital and operating cost estimates are presented in the table below. Note that these are based on

concept level information and are comparative costs only. The costs below do not allow for 250m of

new sewer pipework to connect the WTP to the existing network as this pipework is common to

both options.

Table 3: Capital and operating cost comparison

Item Cost Basis

Discharge to sewer

Capital Cost

Allowance to upgrade existing sewer pump station by one way bridge

$50,000 May not be required; can be determined during detailed design.

Allowance to upgrade 80 PE sewer rising main

$100,000 430m of sewer rising main.

May not be required; can be determined during detailed design.

Opex Cost

Trade Waste Charges

Volume $28,000 24,000m3/year at $1.17/m

3

Solids $25,000 48t/year at $0.51/kg

Labour – 0.5 hour per day $13,400 $75/h including overheads

Maintenance $2,000 2% of capital cost

Total Capital Cost $150,000

Total Operational Cost $68,300

NPV Cost (25 year, 5% disc rate) $1,099,370

On site dewatering

Capital Cost

Dewatering Plant $1,020,000 Sludge thickener and centrifuge dewatering

Opex Cost

Sludge to landfill $4,000 45t/year at 16% solids at $75/tonne

Trade Waste Charges

Volume $6,000 5,000m3/year at $1.17/m

3

Solids $2,000 2.4t/year at $0.51/kg

Polyelectrolyte Note that both discharge to sewer and on site dewatering will use poly in the proposed backwash clarifier, but as this cost is applicable to both options, it is not included in this comparison table.

Thickener $120 0.5g/m3 of poly added to thickener

at 24,000m3/year of flow to

Memorandum


6519113 // NZ1-11278458-5 0.5

Item Cost Basis

thickener at $10/kg

Centrifuge $3,000 5kg of poly added to centrifuge per tonne of solids in centrifuge at $10/kg

Labour – 2.5 hours per day $67,000 $75/hour including overheads

Maintenance cost $20,000 2% of capital cost

Total Capital Cost $1,020,000

Total Operational Cost $102,120

NPV Cost (25 year, 5% disc cost)

$2,439,468

The capital cost of on-site dewatering is high and estimated operational costs also higher than

disposal to sewer.

Memorandum


6519113 // NZ1-11278458-5 0.5

5 Summary and Recommendation

The following table summarises the key costs, benefits and risks of the two options.

Table 4: Summary

Discharge to sewer On-site dewatering

Capital cost $150,000 (if sewer upgrade required) $1,020,000

Operating cost $68,300 $102,120

Noise Sewer pump station – low noise risk in comparison to centrifuge dewatering

Higher noise risk, but could be managed with an acoustically designed dewatering building

Odour Sludge transferred immediately to sewer, removing source of odour from site

Sludge pile before collection by truck could produce odour – typically mild but may increase with algal blooms

Recycled water quality stream

Lower risk Some risk of iron, manganese and algal by-products in thickener supernatant

Water lost 24,000 m3/annum estimated

(0.65% of plant production)

2,100 m3/annum estimated

(0.06% of plant production)

Discharging to sewer is recommended as when compared to on-site dewatering it has:

n Significantly lower capital cost and operating costs

n Less risk of impact on the neighbourhood from noise in particular

n Simplified plant operation

n Positive benefit of reduced phosphorous in the wastewater treatment plant treated effluent.

We support WDC’s requirement to allow for space for the future addition of an on-site dewatering

system should drivers change and this be justified in the future.

Philip La Roche

Technical Director - Water Engineering Direct Dial: +64-9-308 4888 Email: [email protected]

mailto:[email protected]



6519113 // NZ1-11649715-4 0.4 // page 49

Appendix I

Flood Hazard Assessment

21 Pitt Street PO Box 6345, Auckland 1141, New Zealand T: +64 9 300 9000 // F: +64 9 300 9300 E: [email protected] // www.beca.com

Our Ref: 6519113

NZ1-12077409-2 0.2


Private Bag 9023

Whangarei 0148

New Zealand

Attention: Andrew Venmore

15 February 2016

Dear Andrew

274 Whau Valley Road Flood Assessment

Whangarei District Council is proposing to construct a new water treatment plant at 274 Whau Valley Road.

The extent of the site is shown in Figure 1 outlined in red with the green square representing the approximate

location of the water treatment plant building and structures. The purpose of this letter is to review the

proposed development with respect to flooding risks to determine both the risk of flooding to the proposed

treatment plant and whether the development could increase the flood hazard to any other properties in the

catchment.

The site is located in a sub catchment of the Waiarohia stream. An unnamed tributary of the Waiarohia

crosses the northern part of the site and this tributary drains a catchment of approximately 47.5 Ha to a

culvert located on the eastern boundary of the site that conveys flows beneath a local access road.

Northland Regional Council (NRC) have undertaken flood modelling of the catchment. Figure 1 shows the

extent of flooding represented by the NRC model in both the 10 year and 100 year ARI storm events. This

information has been sourced from the NRC Flood Map. The dark blue represents the flood extents in a 1 in

10 year ARI storm event with the light blue representing the flood extents in a 1 in 100 year ARI storm event.

The locations where the levels are shown represent the flood model results received from NRC for a 100

year ARI design storm and includes and allowance for climate change. The modelled flood levels range from

RL 77.2 m to RL 80.1 m across the proposed site.

Page 2 15 February 2016

Our Ref: 6519113

NZ1-12077409-2 0.2

Figure 1: Northland Regional Council Flood Mapping

Information presented by Whangarei District Council (WDC) GIS Mapping shows that part of the site has a

flood susceptible area variation proposed on (Figure 2). We understand this variation has not yet been

accepted by WDC and therefore the Flood Susceptible Area rules do not apply.


Our Ref: 6519113

NZ1-12077409-2 0.2

Figure 2. Flood Susceptible Area (Variation) represented on the Whangarei District Council GIS

Flood Assessment

A preliminary analysis has been undertaken to review the 100 year peak flow from the catchment and flood

levels on the site as indicated by the flood modelling undertaken by NRC. Survey data for this analysis is

based on a survey undertaken on the 24th August 2015 by Boundary Hunter Ltd on behalf of Whangarei

District Council.

An estimation of the 100 year peak catchment runoff to the culvert beneath the access road at the eastern

extent of the site, was determined based on the method outlined by the Department of Scientific and

Industrial Research (1989), ‘Flood Frequency in New Zealand’ giving a peak flow rate of 6.6 m3/s. This

compares well with the peak flow of 6.4 m3/s obtained from the flood modelling undertaken by NRC for the

same catchment.

An assessment of the backwater effects upstream of the 1500 mm diameter culvert at the eastern extent of

the site was undertaken to confirm the flood level at the proposed site of the water treatment plant upstream.

A headwater level was first determined at the inlet to the culvert which was calculated as RL 77.4 m. The

stream through the site has a fairly regular section with grass coverage and the flood plain area adjacent to

the site is pasture land with relatively short grass. Therefore, a mannings ‘n’ value of 0.05 has been adopted

in the calculation. Considering the channel and the vegetation in this area, such a mannings ‘n’ value would


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be considered relatively conservative. Four channel cross sections through the site were analysed as shown

in Figure 3.

Figure 3. Locations of Channel Cross sections included in the Flood Assessment

The flood level at cross section 3 was determined as RL 78.6 m and at cross section 4 at the western side of

the site was determined as RL 79.6 m. A sensitivity check was undertaken to understand the potential effect

on the flood level should the values adopted for mannings be different or if the flow is underestimated. For a

flow of 6.4 m3/s with a mannings ‘n’ value of 0.04 the flood level at section 4 would be RL 79.5 m. In the

event that the flow is underestimated and a flow of 7.0 m3/s be adopted with a mannings ‘n’ value of 0.05 the

flood level at section 4 would be RL 79.7 m.

These flood levels are typically less than those taken from the NRC flood model. The analysis undertaken as

part of this review is relatively simplistic and the NRC model is more detailed. Different survey information

was also used. Across the site, the 100 year ARI flood levels are not dissimilar and reasonably reflect the

flood extents represented on the NRC flood map shown in Figure 1.


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1.1 Stormwater Runoff from the Site

Stormwater runoff from the development on the site, an area of 0.65Ha, will be contained within the site by a

low bund approx. 0.75m in height and will be collected in the proposed stormwater / water retention pond,

prior to being discharged to the stormwater network via a new connection. The proposed retention pond is

required to have a minimum capacity of 60 – 120m3, however a larger volume is proposed to be provided to

allow additional attenuation, and cater for process flow discharges from the treatment plant. The pond will be

designed in general accordance with Auckland Council’s Technical Publication 10 - Stormwater Treatment

Devices Design Guideline Manual (TP10), which is currently recognised as industry best practice in

stormwater treatment device design. The pond will provide treatment and flow attenuation storage, resulting

in minimal change to the existing downstream flow as the discharge of peak flows will be delayed mitigating

against any increase in flood levels or additional flow downstream during large storm events.

Conclusion

In summary, the proposed development and any associated bunding will be located away from the flood plain

resulting in minimal change to upstream or downstream flood levels due to the construction of the new water

treatment plant. The expected flood level across the site is likely to range between RL 77.2 m – RL 80.1 m.

The proposed finished floor level for the water treatment plant is RL 80.3 m, therefore a minimum freeboard

of 0.4 m is provided adjacent to the building. Runoff from the site will be attenuated by means of a

stormwater pond and will be released slowly and conveyed by a new pipe along the northern side of Whau

Valley road to be discharged at the Wairarohia bridge on Whau Valley road.

Yours sincerely

Eilis Byrne

Civil Engineer on behalf of

CH2M Beca Ltd

Direct Dial: +64 9 300 9709 Email: [email protected]

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Anna Lewis, Beca

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