Whangarei Wastewater Treatment Plant Final€¦ · Whangarei Wastewater Treatment Plant: Application for Change to Consent 200404352(02) - Additional Information Final September 2011

Whangarei Wastewater Treatment Plant: Application for Change

to Consent 200404352(02) - Additional Information

Whangarei District Council

September 2011 – Final

Whangarei Wastewater Treatment Plant: Application for Change to Consent 200404352(02) - Additional Information Final

September 2011

AWT WATER LTD - AWT HOUSE, 131 NEW NORTH ROAD, EDEN TERRACE, PO BOX 109-601 NEWMARKET, AUCKLAND, PH 64 9 3741599, FAX 64 9 309 3209

Z:\TRIM\TEMP\CONTEXT.22860\11 79319 Whangarei Wastewater Treatment Plant Application for Change to Consent 200404352(02) - Additional Information. September 2011 - Final.DOC

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QUALITY RECORD SHEET

Document Whangarei Wastewater Treatment Plant: Application for Change to Consent 200404352(02) - Additional

Information – Final

Reference R:\Projects\1006 Whangarei DC - Whangarei WWTP Peak Flow Treatment Options Assessment\500 Deliverables\510 Reports\AEE\110915 WDC WWTP AEE FINAL.doc

Date September 2011

ORIGINATOR

Name Sarah Sunich

Title Senior Environmental Scientist

Organisation AWT Water Ltd

Signature

CHECKED

Name Rosanne Simpson

Title Senior Engineer


Signature

APPROVED

Name Steve Couper

Title Managing Director


Signature


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DOCUMENT CONTROL

The following organisation shall receive two (2) copies of this report on release:

ORGANISATION

Whangarei District Council

REVISION HISTORY

Version Publication Date Organisation

Draft Version 1 12 September 2011 AWT Water Ltd

Final Draft Version 1 14/15 September 2011 AWT Water Ltd

Final Version 15 September 2011 AWT Water Ltd

DISCLAIMER

This report has been prepared for the particular project described to us and its extent is limited to the scope of work

agreed between the client and AWT Water Limited. No responsibility is accepted by AWT Water Limited or its

directors, servants, agents, staff or employees for the accuracy of information provided by third parties and/or the use

of any part of this report in any other context or for any other purposes.

This report is for the use by Whangarei District Council only, and should not be used or relied upon by any other

person or entity for any other project.


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TABLE OF CONTENTS

EXECUTIVE SUMMARY ............................................................................................................................................................... V

1 INTRODUCTION .......................................................................................................................................................... 1

1.1 Purpose of this Report ................................................................................................................................................ 1

1.2 Proposed Change To s127 Application ...................................................................................................................... 2

2 BACKGROUND ........................................................................................................................................................... 4

2.1 WWTP Consent 2004 ................................................................................................................................................. 4

2.2 Okara Park Pump Station Consent 2010.................................................................................................................... 5

2.3 Whangarei WWTP s127 Consent Application 2009 ................................................................................................... 6

2.4 Wastewater (Improvement) Strategy 2010 ................................................................................................................. 6

3 EXISTING SYSTEM AND OPERATION .................................................................................................................... 20

3.1 Existing Plant ............................................................................................................................................................ 20

3.2 Current Situation....................................................................................................................................................... 23

3.3 Receiving Environment ............................................................................................................................................. 25

4 TREATMENT PLANT UPGRADE .............................................................................................................................. 28

4.1 Why upgrade is required .......................................................................................................................................... 28

4.2 What standard is needed .......................................................................................................................................... 33

4.3 Proposed Modifications to Treatment Processes ..................................................................................................... 35

4.4 Treatment Performance ............................................................................................................................................ 38

4.5 Works Programme.................................................................................................................................................... 38

4.6 Alignment with Wastewater Improvement Strategy .................................................................................................. 39

5 CONSULTATION ....................................................................................................................................................... 40

6 ACTUAL AND POTENTIAL ENVIRONMENTAL EFFECTS ..................................................................................... 42

6.1 Effect on Limeburners Creek and Upper Whangarei Harbour .................................................................................. 42

6.2 Submitters Concerns ................................................................................................................................................ 44

6.3 Mitigation .................................................................................................................................................................. 44

6.4 Monitoring ................................................................................................................................................................. 45

7 ALTERNATIVE METHODS ........................................................................................................................................ 46

8 CONCLUSION ............................................................................................................................................................ 47

9 REFERENCES ........................................................................................................................................................... 48

APPENDICES

APPENDIX 1 – EXISTING CONSENT

APPENDIX 2 – WDC – WHANGAREI WASTEWATER SYSTEM IMPROVEMENTS INTERIM REPORTS

APPENDIX 3 – WDC – INFRASTRUCTURE AND SERVICES COMMITTEE MEETING AGENDA ITEMS APPENDIX 4 – TECHNICAL REPORTS

APPENDIX 5 – CONSULTATION DOCUMENTATION


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APPENDIX 6 – WDC QUALITY MANAGEMENT SYSTEM CERTIFICATION

LIST OF FIGURES

Figure 1-1 Consented Ecoli loads versus Proposed Ecoli loads per minute of discharge (note logarithmic scale) ........................ 3

Figure 2-1 Wastewater Strategy – Vision, Mission, Goals & Key Principles ................................................................................... 7

Figure 2-2 UVT, solids compensated UVT and TSS during 23 January storm event. .................................................................. 15

Figure 3-1 Process schematic of Existing Flow Paths ................................................................................................................. 21

Figure 3-2 Site Layout with Existing Flow Paths ........................................................................................................................... 22

Figure 3-3 Whangarei WWTP inflow during Cyclone Wilma (instantaneous and flow totalised over a 24 hour period) .............. 23

Figure 3-4 Network Hydraulic Model Validation Event ................................................................................................................. 24

Figure 3-5 Monitoring of the Bypass discharge to Limeburners Creek from the Primary Clarifiers ............................................. 25

Figure 3-6 Effluent Flow Bypass Discharge location to Limeburners Creek ................................................................................ 25

Figure 4-1 Estimate of the effect of the WWTP discharge on harbour water quality during ex-tropical cyclone Wilma under

current treatment levels and a possible upgrade. ......................................................................................................................... 30

Figure 4-2 Simplified Process Flow Diagrams illustrating (a) existing situation (b) Option 2 treatment upgrade ......................... 36

LIST OF TABLES

Table 2-1 Summary of Current Resource Consent Requirements (sourced from MWH, 2010) ..................................................... 4

Table 2-2 UVT Values following a 116 MLD flow to the Whangarei WWTP ................................................................................. 15

Table 2-3 Options identified and evaluated for further investigation at 18 April 2011 workshop. .................................................. 17

Table 3-1 Maximum Extreme Flow Bypass Discharges to Limeburners Creek ........................................................................... 24

Table 4-1 Whangarei Harbour Modelled Activity Risk for Contact Recreation ............................................................................. 32

Table 4-2 Whangarei Harbour Modelled Activity Risk for Shellfish Gathering .............................................................................. 32

Table 4-3 WDC Proposed Disinfection Standard (sourced from MWH, 2010) ............................................................................ 34

Table 4-4 Indicative Extreme Flow Effluent Quality ..................................................................................................................... 38


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EXECUTIVE SUMMARY

Whangarei Wastewater Treatment Plant s127 Consent Application

In order to minimise wet weather overflows from the Okara Park Pump Station (Okara Park PS), the pump station was recently

upgraded. This has resulted in wastewater that previously spilt at OPPS now being pumped to the Whangarei Wastewater

Treatment Plant (WWTP), resulting in a maximum possible inflow to the treatment plant of approximately 124,000 m3/d (1,440

L/s) and with a potential for future increased flows up to 140,000 m3/d (1,620 L/s) as a result of pump station improvements.

The current resource consent (200404352 (02)) for the Whangarei WWTP does not explicitly impose a maximum daily flow rate

to the WWTP. However on review of the application for the consent it is implicit that the maximum flow considered by Northland

Regional Council (NRC) at the time of that application was in the order of 90,000 m3/d. An application to increase the maximum

daily discharge of extreme wet weather flows from the WWTP to Limeburners Creek from a limit of 90,000m3/d to 140,000m3/d

was therefore lodged with NRC in December 2009.

Independent hearings Commissioners were appointed by NRC to hear and determine the application by WDC to change

Condition 16 of Consent 4352(02). A hearing was held in June 2010 and the commissioners subsequently issued an Interim

Decision inviting WDC to formulate and adopt a comprehensive programme for the upgrade of the WWTP to treat wet weather

flows. In addition to the Commissioners considerations, the NRC is undertaking a separate review of the consent conditions in

accordance with Condition 28 of consent 4352. Any changes to the quality of the existing consented discharge volumes from

the WWTP can be assessed and addressed through this review.

The calibrated sewer model developed in 2010, which led to the development of the WDC Wastewater Improvement Strategy,

identified the Extreme flow bypass discharge from the Whangarei WWTP as the most significant point source discharged in the

Whangarei area, followed by overflows at Okara Park PS (now resolved) and Hatea SPS (currently being upgraded).

Proposal

To accommodate the increased peak flows within the WWTP, WDC propose a number of modifications to be made to the

existing structures and flow paths to enable all flows to receive tertiary treatment and a large portion of additional flows to

receive secondary clarification. It is proposed that an effluent target of 1,500 Ecoli/100ml (median) and 1.5 log reduction in

rotovirus levels will be achieved through the provision of UV disinfection.

Outcomes

By applying these wastewater discharge standards, it has been shown through dilution studies and hydraulic modelling that, in

considering only the treatment plant discharge, the contact recreation standards below the Port Rd Bridge and standards for

shellfish gathering at Onerahi, can be met. To assess the influence of other contaminant sources in addition to the WWTP

extreme flow discharge, such as network overflows and background water quality, it has been determined from undertaking a

Quantitative Microbial Risk Assessment that the upgrade works proposed will significantly improve the overall public health risk,

however not sufficiently to meet acceptable winter shellfish gathering standards. Therefore additional improvement works to the

network sewer and background water quality will also need to be undertaken. WDC have set out a strategy to undertake this

work.

The proposal will provide significant improvements to the upper Whangarei harbours water quality by greatly improving the

effluent quality of any extreme bypass flows through UV disinfection.


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1 INTRODUCTION

When it rains flow within the sewer network increases as stormwater makes its way into the sewer system. The volume of

stormwater that enters the network increases with the duration and/or intensity of the storm. In some cases the sewer network

cannot convey all the wastewater and localised spills from the network occur. During these events sewage pump stations run

at their maximum rate causing high flows to enter the wastewater treatment plant (WWTP).

Flows within the Whangarei Sewer Network are conveyed to the Whangarei WWTP on Kioreroa Road via four pumping stations

namely; Okara Park, Otaika Valley, Kioreora and Waverley. As a result of recent upgrades to the Okara Park pump station (in

2010), overflows to the Hatea River from that pump station no longer occur and the volume of „Extreme‟ flow (those flows

exceeding 57.4 ML/d or 664 L/s) at the WWTP has increased. This increase in Extreme flow at the WWTP triggered the need

for Whangarei District Council (WDC) to lodge an application for a change of consent conditions to allow an increase in the

discharge limit of 90 ML/d to 140 ML/d (lodged in 2009).

The WWTP has operating systems that divert high flow around various treatment units in times of wet weather flows. This is

normal in treatment plants and is done to protect the biological treatment process and recognises that the units that treat

wastewater during normal flows are not normally designed to treat dilute wastewater (mixture of wastewater and stormwater).

Currently under normal to medium flow conditions, ultraviolet light (UV) is used for effluent disinfection (pathogen kill) prior to

discharging to the wetlands in Limeburners Creek. However, flows greater than those capable of being treated by the existing

UV system (High to Extreme flows), bypass the UV system and discharge directly to the wetlands, or in very large storms,

directly to Limeburners Creek following screening and primary treatment. Although primary treatment is better than discharging

raw sewage, this High and Extreme flow fraction still contains pathogens.

The application for a change of consent conditions was heard in June 2010 and the Commissioners of the consent hearing

issued an interim decision on 27 August 2010, in which they invited WDC to formulate and adopt a comprehensive programme

for the upgrade of the WWTP to treat wet weather flows with particular focus on improving public health risk. As a result, WDC

have carried out a range of investigations (some in collaboration with NRC) to determine what effect sewage spills have on

harbour water quality and the relative impact of the various discharges, whether from sewer network spills or the WWTP

Extreme flow bypass. Sewer modelling work has identified that the Extreme flow is two to three times greater in volume than

the total of other overflows in the network. The exact proportion varies and is dependent on the nature of the storm. Therefore,

the WWTP Extreme flow now represents the single largest discharge of wastewater pathogens into the Hatea River.

Treatment of the WWTP Extreme flow bypass to reduce pathogen loads in the upper Whangarei Harbour has been identified as

the highest priority project as part of the WDC Wastewater Improvements Strategy. To ensure all flows from the WWTP have

been disinfected, upgrade works to the WWTP have been investigated. Options to treat these flows have been evaluated and

an option selected to carry forward as part of the Stage 1 works programme for 2011-2013.

1.1 Purpose of this Report

The 2009 WDC s1271 application to change consent 4352(02) Condition 16, proposed an increase in the volume of Extreme

flow discharged from the WWTP to that previously authorised (90ML/d increased to 140ML/d), and that this portion of Extreme

flow would be primary treated prior to discharge to Limeburners Creek. This report has been prepared to address the key

issues associated with the s127 application heard by the Commissioners as outlined in their Interim Decision. It is considered

that the key issues are:

Evidence presented at the hearing indicated that the discharge of primary effluent to Limeburners Creek has a more

than minor adverse effect on the public health of users of the harbour.

1 Resource Management Act 1991 – Section 127 – Change or cancellation of consent condition on application by consent holder.


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This report outlines how these effects may be addressed through an upgrade of the WWTP and further work within the

network.

The background water quality at the time of the Extreme flow discharge was impaired by other wastewater discharges

and other contaminant sources which made the impact of the treatment plant extreme flow difficult to assess.

This report outlines how other containment sources have been assessed and quantifies the impact of the WWTP

Extreme flow discharge before and after the proposed upgrade.

That the effects are associated with all primary treated wastewater that is discharged direct to Limeburners Creek via

the Extreme flow bypass, i.e. when flows exceed 57.4ML/d. However the matter before the Commissioners was

regarding flow in excess of 90ML/d.

This report puts forward a proposal to disinfect all flows and therefore has considered the effects of flow greater than

57.4 ML/d for completeness.

WDC have undertaken considerable investigations, consultation and strategising in the past year. The purpose of this report is

to present the details and results of this work, set out clearly any changes to the previous application in terms of what is being

sought as part of the consent change, and to clarify the effects of the proposed change to condition 16.

1.2 Proposed Change To s127 Application

1.2.1 Extreme Flow Bypass

As a result of the WWTP upgrade options investigations that have been carried out by WDC (discussed further in Section

2.4.5), this report undertakes to consider the volumes of Extreme wet weather flow between 57.4 to 140ML/d, rather than

limiting the upgrade options to the portion of flow being addressed by the 2009 change to consent application of 90ML/d

to140ML/d.

1.2.2 Higher Effluent Quality

The main effect of the discharge, as identified in the Commissioners Interim Decision, is related to the public health risk

associated with pathogen load in the harbour. Therefore, WDC propose an upgrade focused on tertiary treatment of the

effluent using UV disinfection to address this concern.

WDC has committed to all Extreme flows at the WWTP receiving screening, primary treatment and UV disinfection prior to

discharge to Limeburners Creek. In conjunction with this work, WDC also propose to undertake the previously consented Stage

2 UV disinfection upgrade works for all High flows (30.4 – 57.4ML/d). WDC propose to disinfect all flows such that, allowing for

mixing and die-off, the effluent will meet the MfE/MoH (2003) recreational contact guidelines at Port Rd Bridge and Shellfish

gathering guidelines upstream of Onerahi.

Furthermore, upgrades to expand the WWTP capacity are being worked through, to enable flows greater than 57.4ML/d to

receive further levels of secondary treatment in addition to UV disinfection prior to discharge to Limeburners Creek.

The following graph illustrates what the plant is consented for in terms of pathogen kill (we have used here the indicator species

Ecoli) via the different flow streams within the WWTP compared to what is proposed as part of this revised s127 application.

Although the volumes of Extreme flow will increase from that previously consented, the number of Ecoli entering the receiving

environment during a peak storm event will be significantly reduced.


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Figure 1-1 Consented Ecoli loads versus Proposed Ecoli loads per minute of discharge (note logarithmic scale)

1.2.3 Connection With Condition 28 Resource Consent

WDC understand that the review by NRC will focus on the Extreme flow component of the discharge that is the proportion

greater than 57.4 ML/d (based on a meeting held with WDC and NRC representatives on 21 September 2010). The key

concern associated with Extreme flow discharges is the impact on public health and therefore the focus for treatment is on

removal of pathogens. As outlined in this report WDC and NRC have been working collaboratively to develop an agreed

discharge standard to be specified in the consent.

Other factors that may be included in the review are:

90%ile values for BOD and TSS for normal flows;

The date required by condition 3 of the consent to install the UV system to treat flows up to 57.4 ML/d. This date has

passed, and as per a letter from WDC to NRC, WDC propose the increase in UV capacity will now be amalgamated

into the 2011 – 2013 upgrades to disinfect all flows.

It is noted, that WDC is willing to include a wider group in the review process than provided for under condition 28 of the

consent, although NRC has indicated that legally the parties will remain the original four submitters to the 1997 application

(DOC, Royal Forest and Bird Protection Society, Northland Health, Waikaraka to Parua Bay Residents Association – the later is

no longer in existence).


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2 BACKGROUND

2.1 WWTP Consent 2004

The existing consent (CON200404352 – hereafter 4352) was granted in May 2004 authorising the following:

To discharge treated wastewater to Limeburners Creek. (01)

To discharge primary treated bypass wastewater to Limeburners Creek when flows to the treatment plant exceed

57,400 m3/day. (02)

To discharge contaminants to land as a result of the operation of the wetland treatment system. (03)

To discharge contaminants (primary odours) to air. (04)

To erect, place and use a bypass discharge structure in the Coastal Marine Area. (05)

Consent 4352 expires on 30 April 2022, please refer to Appendix 1 for a copy of the consent.

The WWTP is currently configured to treat flows via three flow paths as required under the current consent (i.e. normal,

medium/high and extreme flows). The flow paths are operated in parallel and progressively activate as the inflow to the WWTP

increases. These paths and the WWTP‟s process components are illustrated in Figure 3-2. The daily flow capacities

associated with each path align with the current plant consent as shown in Table 2-1 below taken from Conditions 1, 9 and 14

of 4352(01).

Table 2-1 Summary of Current Resource Consent Requirements (sourced from MWH, 2010)

Type of Flow Discharge

Flow (m3/d)

Treatment UV Dose

(mWs/cm2)2

BOD5

(mg/L)3

TSS

(mg/L)3

NH4-N

(mg/L)3

Enterococci

(#/100ml)5

Median

Normal Daily

Flow

< 21,000 All process units >30 < 10 < 10 < 5 <136 (median)

<277 (maximum)

Medium Wet

Weather

Flows

> 21,000 &

<30,400

All process units up to

secondary clarifier

stage1, UV & wetland

>30 <25 <25 <10 <136 (median)

<277 (maximum)

High Wet

Weather

Flows

> 30,400 & <

57,400

All process units up to

secondary clarifier

stage, UV & wetland

>40 <25 <25 <15 <136 (median)

<277 (maximum)

Extreme Wet

Weather

Flows

>57,400. Screen & Grit removal

only, discharge direct to

Limeburners.

Nil NS4 NS NS NS

Notes:

1. For medium and high wet weather flows treatment by ‘all process units up to secondary clarifier stage’ means preliminary treatment,

primary treatment, and treatment provided by first stage trickling filters and storm clarifiers.

2. Consent limit for UV Dose is a PLC-based dose that is calculated as a 10 minute average value and applies at all times. (Condition 9)

3. Consent limits for BOD5, TSS and NH4-N are median values and apply upstream of the wetland. (Condition 9)

4. NS – not specified.

5. Enterococci standards apply to water quality of Limeburners Creek measured at Port Road Bridge (Condition 14 g).

6. Consent includes other requirements such as maximum daily loads for flows up to 21,000m3/d and water quality requirements at Port

Road Bridge downstream of WWTP.


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The existing consent authorises discharges from the WWTP which by-pass the main treatment train, being that component

between 57.4 – 90 ML/day. There is no standard for this discharge and only rudimentary receiving standards are specified

(Condition 18).

The consent also includes a two-staged upgrade of the WWTP, agreed to as a result of a pre-hearing process, with different

treated wastewater requirements before and after each upgrade. The purpose of the staged upgrade was primarily to provide

UV disinfection of all wet weather flows up to 57.4 ML/d and passage of these flows through the wetland treatment system prior

to being discharged to Limeburners Creek. Stage one included upgrading the activated sludge plant to treat up to 21 ML/d and

upgrading the UV disinfection system to treat up to 30.4 ML/d with a PLC-based UV dose of 30 mWs/cm2. Stage one was

completed in 2004. Stage two includes upgrading the UV disinfection system to treat up to 57.4 ML/d with a PLC-based UV

dose of 30 mWs/cm2 for all flows up to 30.4 ML/d and a PLC-based UV dose of 40 mWs/cm2 for all flows greater than 30.4

ML/d. Stage two was scheduled to be completed by May 2011, however as noted in a letter to NRC2, this work has been

amalgamated with the planned WWTP upgrade work to disinfect all flows received at the WWTP. A revised works programme

is presented in Section 4.5.

2.2 Okara Park Pump Station Consent 2010

Okara Park Pump Station (Okara Park PS) was constructed in 1966 as part of the construction of the Whangarei WWTP and

conveys between 70 – 80% of the wastewater flow to the WWTP. The Okara Park PS has had a history of overflowing an

untreated mix of wastewater and stormwater to the upper Whangarei Harbour via a constructed overflow pipe and screen

during heavy rain events when the flow exceeded pumping capacity („wet weather overflows‟). These capacity related

overflows were authorised by a previous discharge permit (consent 7521), that expired on 31 May 20023. A renewal application

was lodged in November 2001, and was placed on hold while NRC sought additional information under section 92 of the RMA.

In September 2008, WDC submitted an amended short-term (5 year) consent application with NRC to continue with wet

weather overflows. This approach was taken with the vision of developing, during the sought five year consent period, a

detailed physical works programme and long-term service standards to reduce and manage overflows, through extensive

community consultation and monitoring/modelling. On making that application, the community spoke strongly about their

concerns regarding overflows, calling for long-term levels of service and performance standards to be developed as soon as

possible. The application was put on hold and WDC investigated various upgrade options.

As a result of submissions on its Long Term Council Community Plan (LTCCP) 2009 – 2019 and subsequent discussions with

the community, WDC upgraded Okara Park PS in early 2010, with the aim of eliminating all wet weather overflows. The

upgrade has enabled an initial increase in pumping capacity from 700L/s to 1,100L/s. As a result of this increase in pumping

capacity, no overflows are expected during wet weather, as the pumps can currently pump more water than can theoretically

flow into the station.

The Okara Park PS upgrade however, does not eliminate the risk of overflows as a result of causes other than the inflow of

wastewater during storms. Like all pump stations, factors such as loss of power (main and emergency standby); catastrophic

pump failure; vandalism; and acts of nature that cause damage, etc, may cause unplanned overflows, even with comprehensive

and robust contingency measures. Therefore in May 2010, a discharge permit was sought by WDC to authorise emergency

unplanned discharges of wastewater from the Okara Park PS to the Coastal Marine Area in accordance with Rule 31.2.1 of the

Northland Regional Coastal Plan (NRCP – July 2004). Consent was granted on 20 September 2010 with an expiry date of

2022.

2 WDC letter addressed to Rob Lieffering at NRC, dated 14 February 2011, Whangarei WWTP Resource Consent Condition 3: Upgrade of UV disinfection. 3 Consent 7521 authorised the discharge of up to 24,000 m3 of screened wastewater and stormwater per day during emergency stormwater conditions from the OPPS to the upper Whangarei Harbour.


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2.3 Whangarei WWTP s127 Consent Application 2009

By eliminating wet weather overflows from Okara Park PS, wastewater that previously spilt is now pumped to the

Whangarei WWTP. With the upgrade at Okara Park PS, the maximum possible inflow to the treatment plant, assuming all four

pump stations are operating at capacity, is approximately 124,000 m3/d (1,440 L/s) with a future potential of up to 140,000 m3/d

(1,620 L/s) as a result of further pump station upgrades.

The current consent (200404352 (02)) does not explicitly impose a maximum daily flow rate to the WWTP. However on review

of the application for the consent NRC determined that the maximum flow at the time of that application was in the order of

90 ML/d. An application to increase the maximum daily discharge of extreme wet weather flows from the WWTP to

Limeburners Creek from this limit of 90 ML/d to 140 ML/d was therefore lodged with NRC in December 2009. The

application sought to increase the flow-rates to match the planned peak capacity of the upgraded Okara Park PS plus the other

three pump stations. This application for a change of consent condition pertained only to Condition 16 of 4352(02) regarding the

use of the Extreme flow discharge.

In parallel to preparing the consent application WDC were also investigating options to improve the wastewater systems

performance. It was determined that the most effective improvement to the network, in terms of pathogen load to the harbour

and cost, was to treat the Extreme flow discharge volumes. However, before WDC could present this as part of the consent

application, Council approval was required and unfortunately the timing of this approval did not coincide with the consent

process. Approval has subsequently been given as discussed further in Section 2.4.

Independent hearings commissioners Doug Arcus and Hamish Lowe were appointed by NRC to hear and determine the

application by WDC and a hearing was held in Whangarei in June 2010. The commissioners subsequently issued an Interim

Decision dated 27th August 2010 (the Interim Decision). The reasons for the Interim Decision were based on the findings that

the proposed increase in Extreme flow discharge, based on the evidence presented at the hearing, would result in significant

adverse effects and was contrary to the relevant planning instruments and provision of Part 2 of the Resource Management Act

1991 (RMA). The Interim Decision invited WDC to formulate and adopt a comprehensive upgrade program for the WWTP

following which further clarification and investigation into the effects of increasing the maximum daily extreme flow discharge

from the WWTP would be provided to the Commissioners.

In addition the Interim Decision required progress reports to be submitted by NRC to the Commissioners. WDC have provided

progress reports to NRC on the Whangarei Wastewater System Improvements Strategy in November 2010, February, May and

August 2011 (refer to Appendix 2). NRC has subsequently provided progress reports to the Independent Commissioners Arcus

and Lowe on 4 November 2010, 4 February 2011 and 3 June 2011.

In addition to the Commissioners considerations, the NRC is also undertaking a separate review of the consent conditions in

accordance with Condition 28 of consent 4352. Any changes to the quality of the existing consented volumes of discharge from

the WWTP can be assessed and addressed through this review.

To accommodate the increased peak flows within the WWTP, WDC propose a number of modifications to be made to the

existing structures and flow paths. A full description of the works planned is included in section 4 of this report.

2.4 Wastewater (Improvement) Strategy 2010

The issue of stormwater infiltration into the Whangarei sewer system and subsequent sewer overflows and treatment plant

bypasses is an ongoing concern. The effect of sewer overflow and bypass discharges on the water quality in the harbour and

the community‟s and Council‟s reduced tolerance for sewage spills initiated development of a district wide Wastewater Strategy

(WDC, 2010). This strategy sets out the broad plan for the management of wastewater in the Whangarei District over the next

50 years.

A key purpose of the Strategy has been to define high level goals for the district‟s wastewater management and provide an

outline of how WDC intends to achieve these goals and identify likely challenges that could affect the achievement of such


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goals. This long-term strategy also provides guidance for the development of LTCCPs and direction for the development of the

Wastewater Asset Management Plan.

The following figure sets out the vision, mission, goals and principles of this strategy. For each Key Principle the Strategy sets

clear objectives; and presents a series of actions to achieve them.

Figure 2-1 Wastewater Strategy – Vision, Mission, Goals & Key Principles

The strategy has been driven by a number of factors that include:

Submissions on WDC‟s recent application for Resource Consent to increase the volume of primary treated effluent

discharge during storms;

Consultation with the community, key stakeholders and iwi/hapu;

The development and availability of a calibrated sewer network model which has enabled WDC to undertake a

quantitative assessment of the sewer systems performance during storms and therefore prioritise and analyse sewer

upgrade works (refer to section 2.4.3 below for more detail); and


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The outcome of the NIWA harbour model that demonstrates, due to tidal action, how discharges move through the

harbour (refer to Section 4.1.3 below for more detail).

The above factors and actions presented in the Strategy have lead to the development of a programme of works for the

wastewater system for the period 2010 – 2013 (Stage 1) and a preliminary programme for long term engineering works for the

period 2013 – 2019 (Stage 2). Stage 1 of the programme was adopted by WDC in the 14 July 2010 Infrastructure and Services

committee meeting (prior to the WWTP s127 consent hearing), with Stage 2 recommended for consideration for the 2012 –

2022 LTCCP. A copy of the Stage 1 Capital Works Programme for 2010-2013 is provided in the WDC February 2011 Interim

Report (provided in Appendix 2).

The key objective of Stage 1 is to eliminate/reduce sewerage spills from the three biggest overflow sources. Projects

associated with Stage 1 works include: Okara Park (PS) upgrade works to eliminate wet weather overflows to the Hatea River and re-directing these flows to

the WWTP for screening and primary treatment. This project is now complete and operational.

Increased capacity to store and treat wastewater at the Hatea sewage (PS). This project has commenced.

A programme to look at major sources of inflow to the sewers. This project has commenced and is ongoing.

Further monitoring of the sewer network. This project has commenced and is ongoing.

An upgrade of the treatment plant so that all wastewater is treated. This work includes an allocation of $4.0M for the

treatment of WWTP Extreme flows up to 140,000m3/day.

Stage 2 includes the long term engineering options to reduce spillage from the network. Expenditure has been estimated

assuming that:

Key infrastructure projects are developed so that they contain/prevent spills at a 1 in 5 year return period. This is the

case for Okara Park PS and future Hatea PS overflow treatment.

Network discharge overflows are reduced such that 80% of spills that are predicted to occur in year 2040, accounting

for growth, are prevented or treated in an annual storm event. This is in comparison to what would happen if no

investment took place.

No allowance has been made for Inflow and Infiltration (I/I) mitigation in this programme. This assumption will require

extensive review before committing to the proposed works programme identified in this strategy.

The Stage 2 capital works programme has an estimated cost of $34M and includes;

A new large pump station to the WWTP or alternative storage/treatment;

Further upgrade of the treatment plant;

Increase in capacity of key sewers; and,

Interconnection of sewers to maximise use of existing capacity.

There is currently insufficient funding within the LTCCP to complete this work. Furthermore, these works are a first

approximation and more investigations are required to refine the balance between inflow and infiltration works, network

upgrades and treatment.

WDC have confirmed the availability of funding to improve the treatment capacity at the Whangarei WWTP. From 2012 new

funding will be required and it is proposed this be sought through the 2012-2022 LTCCP consultation round as required.

The following sections provide further detail on the progress made by WDC with the Wastewater Improvement Strategy.


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2.4.1 Okara Park Pump Station

The first phase of the Stage 1 Capital Works Programme was to upgrade the Okara Park PS to stop wet weather overflows

from it and increase the capacity of the Whangarei WWTP so that increase in flows from the Okara Park PS could be screened

and primary treated. A summary of the history of the Okara Park PS is provided earlier in Section 2.2.

The upgrade works involved the replacement of the two existing large pumps and two small pumps. The replacement large

pumps (each rated at 250kW) have a combined capacity of some 940 L/s when pumping through the new rising main and the

two replacement small pumps (each rated at 75kW), can generate a further 470L/s through the existing rising main under peak

load conditions.

The combined capacity of all four pumps operating is approximately 1,410 l/s, although the maximum rate of flow into the

station is 1,100 I/s.

A new 800mm external diameter PE (polyethylene) rising main has been constructed between the OPPS and the WWTP. The

overall result is a pipeline with more capacity, more resilience and a predicted longer life than the existing rising main.

The existing 600mm diameter rising main will remain in service and has been connected to the new small pumps. The lower

flows will reduce line pressures and extend the potential life of this asset. Having four operational pumps, a stand-by generator

and two rising mains provides a high level of flexibility and resilience for the upgraded pump station and the ability to absorb a

wide range of potential interruptions caused by asset failure or planned shut-down without overflows occurring.

The WWTP inlet works were upgraded in 2010 and have been constructed to treat all flows up to 100 ML/d, while flows above

this are screened in the existing inlet works channels and diverted to an Equalisation (flow balancing) basin.

The project was completed and operational in 2010 and has achieved four significant objectives:

1. Eliminated all wet weather overflows of untreated wastewater from Okara Park PS;

2. Renewal of the pumps and major electrical infrastructure to improve the pump stations reliability and efficiency and

restore its full operating functionality; and

3. Duplication of the rising main from the pump station to the WWTP.

4. Increased screening and primary treatment capacity at the WWTP capable of treating flows up to 100 ML/d.

United Civil Construction Ltd won the NZ Contractors Federation Construction Award for contracts in NZ between $1M and

$10M for its work on the Okara Park PS upgrade.

2.4.2 Hatea Storage Tank

The Hatea Sewage Pump Station (Hatea SPS) is located adjacent to the Hatea River on Whareora Road and receives

wastewater from the Tikipunga and Kamo catchments. The station pumps these flows into the WDC sewer system to be treated

at the Whangarei WWTP.

During extreme wet weather events the inflow to the station exceeds the pumping capacity, and untreated wastewater is

discharged into the Hatea River as an overflow event. The sewer network model identified the Hatea SPS as being the third

most significant point source discharge in the Whangarei area, after overflows at Okara Park PS (now resolved) and Extreme

flow discharges from the Whangarei WWTP.

The current Hatea SPS has limited contingency storage and several sewage discharges are likely to occur in an average year.

Furthermore, it is known that the site is flood prone and the existing pump station is inundated on average three times a year.

In order to mitigate the problems at this site, and as part of the overall WDC Wastewater Improvements Strategy, it is proposed

to undertake the following improvements:

Construct a new sewage pumping station;


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Construct a 1,000m3 emergency storage tank, which will provide storage of inflow for at least a 12 hour period in dry

weather, thus preventing spills due to maintenance breakdowns (this is required regardless of success in I/I mitigation)

and due to short duration high intensity storms;

Construct a treatment facility that passes any discharge amount in excess of the emergency storage capacity through

screening, settlement and UV disinfection;

Construct the proposed facility such that it is still operational if the site is flooded; and

Construct the proposal in such a way as to minimise environmental, cultural and social impacts associated with the

project.

This 1,000m3 storage facility will eliminate spills in small to moderate storms. For larger storms the wastewater will be treated

via chemically assisted sedimentation and disinfected before being discharged.

A $4.05M contract for the construction of a storage and treatment facility at the Hatea SPS has been awarded to United Civil

Construction Ltd. Work commenced in April 2011 and the facility is expected to be commissioned in early 2012.

An application for the emergency discharge of treated wastewater from the Hatea SPS has been lodged with NRC (Opus,

August 2011). WDC has undertaken a number of community consultation meetings to discuss the City‟s wastewater strategy

and has consulted with local residents in regard to the details of the proposal. Ngararatunua Marae Trust, in its capacity as

Kaitiaki, has provided a cultural impact assessment for the proposal.

2.4.3 Sewer Network Model

The detailed Whangarei sewer network model and associated options report was completed by AWT Water in August 2010.

The sewer model has been used to assess pipework capacities under a number of differing storm Annual Return Intervals (ARI)

and determine problem areas and likely upgrade works required. The model also shows, the location, frequency and volumes

of sewer overflow spills which has been used to quantify and prioritise the Stage 1 wastewater improvement works, i.e. WDC‟s

objective is to address the larger spills first.

Although the model is calibrated there are a number of areas in the network where more information is needed for it to provide

reliable predictions of wet weather flows commensurate with the level of funding proposed in Stage 2 of the Strategy. Further

model development is being carried out as part of the strategy and includes further work in the following areas:

Flow gauging. Long term flow gauging has been installed and additional short term gauges have been installed to capture winter storm events in 2011.

A detailed asset survey of the pump stations. This includes understanding the operation of each station as far as set

levels, indentify the volume of pumps and pump types (make and model) in each station, and measure wet well

dimensions.

CCTV programme. There are a number of cross-connections shown in the GIS and it has been identified that there

may be more that are not shown. These connections will have a major impact on the predicted overflows and general

network performance and should be identified when at all possible. WDC have commenced a CCTV programme to

identify areas of significant silt-build up, possible cross-connections, and identify degraded pipe work that could result

in infiltration.

Overflow Log. Council have further developed an overflow log to record in detail where the overflow has occurred,

when it occurred, and the possible cause. This also includes incorporating Northland Health‟s risk assessment and is .

provided live on Councils website.

WWTP Hydraulic Model. Development of a hydraulic model of the WWTP treatment process to optimise plant

configuration. This work has been completed and has been used as part of the concept design optioneering work

carried out by WDC.


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Incorporation into the sewer network model of the Whangarei Heads reticulation in more detail.

Sewer network model recalibration. A further round of model verification and recalibration will be carried out in late

2011, based on this additional flow monitoring results.

This above work will enable the model to be further refined to establish seasonal variation on dry weather flows and re-validate

the model to larger storm events. This will provide Council with a more accurate understanding of discharge locations, volumes

and remedial works and characterise the expected influent flows to the Whangarei WWTP during storm events.

2.4.4 Inflow & Infiltration (I/I) Programme

Although historically Inflow and Infiltration (I/I) reduction programmes have had mixed results, WDC have continued with I/I

mitigation to address major infiltration issues, and propose to use further sewer flow monitoring to assess network

improvements as a result of this I/I programme. Work has focussed on the areas identified as having high I/I, notably

Kensington and Vinetown. Investigations include CCTV assessments, additional monitoring, and possible smoke testing.

Council have also introduced a pressure sewer policy to mitigate I/I issues in new development areas.

The following work has been completed to date.

Household Gully Trap Inspections

In 2009 a project was initiated to check for low gulley traps and roof water connected directly into gulley traps in the Central

Business District (CBD). Of the 1,227 properties inspected there were 112 properties found with faults of which 79 were

repaired by customers resulting in a 70% success rate.

In 2010 the focus shifted towards targeting properties within flood plains, where flood waters could enter directly into sewers. As

part of this work, areas of the city suspected of flooding during rain events were identified. Around 2,800 private properties

were inspected and problems were identified in approximately 6% of the sites. These have been categorised as:

a. Easy to fix (e.g. down pipes into gulley traps): 20 properties identified with letters to fix sent. Re-inspection of the easy

to fix systems has shown all now comply.

b. Medium (e.g. ground/driveway drains into gulley trap): 180 properties identified with letters to fix and cost estimates to

be sent. Re-inspection of the medium difficulty problems has shown around 75% have been resolved with the majority

of homeowners utilising Councils recommended contractor.

c. Hard (e.g. stormwater system blocks and floods property): 50 properties identified with WDC Engineers to review the

issue with the homeowner. This work is ongoing.

Funding has been allocated in the wastewater service level improvement budget 2011/12 to continue the inspection programme

with particular focus on catchments where high I/I rates are identified from the sewer network monitoring.

Network Flow Monitoring

As a follow-on to the flow monitoring undertaken to develop the sewer network model in 2010, additional flow meters have been

installed over the 2011 winter period to collect further data on how the sewer system operates during storms. This information

has been used to further refine the sewer network model, due to be completed end of 2011, to assist detailing the Stage 2

works programme which is forecast to commence in 2012/13. Long term flow gauging will continue in key network catchments

to enable council to monitor network improvements as a result of the works being undertaken


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Pressure Sewer Policy

A pressure sewer system is a complete system wherein macerated sewage is conveyed under pressure generated by pumped

units located in each property to a wastewater treatment plant or other wastewater system. One benefit of selecting a Pressure

Sewer system for suitable developments is the reduced chance of infiltration and cross connections to the sewer network.

WDC has adopted a Pressure Sewer Policy which identifies where pressure sewers will be adopted by council (these areas

shall be identified on the Council Geographic Information System (GIS)), ownership of various components of the system,

general requirements, and roles and responsibilities of stakeholders (WDC, 2010). The areas identified for pressure sewers

have focused on new development areas where there are high water tables and unstable land and catchments where there is

high I/I and/or limited capacity in the downstream network.

2.4.5 Wastewater Treatment Plant Upgrade

With the upgrade of the Okara Park SPS, overflows to the Hatea River from that pump station no longer occur and the volume

of extreme wet weather flows at the WWTP has increased. Wastewater received at the WWTP goes through a range of

processes. Which processes the wastewater goes through varies depending on the flow rate into the plant. The fraction of flow

that exceeds 57.4 ML/d (664 L/s) is screened and primary treated. Although better than discharging raw sewage, this extreme

wet weather flow fraction still contains pathogens. The extreme flows which discharge from the WWTP now represents the

single largest discharge of wastewater pathogens into the Hatea River.

Treatment of the extreme flows from the WWTP to reduce pathogen loads in the Hatea River has been identified as the highest

priority project as part of the Strategy. WDC have initiated a number of options studies and data gathering exercises to

establish the most practicable engineering solution to disinfect all flows discharged from the WWTP.

A list of work undertaken in relation to extreme flow treatment options includes the following:

Disinfection and Treatment Options Assessments

MWH Ltd, Storm Flow Treatment Option Assessment, November 2010

AWT Water Ltd, Peer review of MWH Report, December 2010

AWT Water Ltd, Whangarei WWTP Peak Flow Assessment – Disinfection Options Assessment, June 2011

Storm Flow Quality Assessment

2010 monitoring programme (included in MWH‟s November 2010 report)

AWT Water Ltd, Re: Whangarei WWTP Peak Flow UVT Review, 16 March 2011 - discussing the findings of the

following;

o AWT jar testing

o UVT sampling by WDC during 23 January 2011 event

o Inline (s::can) monitoring January 2011

Inline (s::can) monitoring July 2011– ongoing

Treatment Options Assessment (focusing on hydraulics)

Options identification and evaluation workshop 18th April

AWT Water Ltd, Whangarei WWTP Peak Flow Options Assessment, September 2011

Beca, Peer review of draft Peak Flow Options Assessment Report, August 2011


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Disinfection and Treatment Options Assessments

In 2010 MWH were engaged to investigate the feasibility of UV disinfection of Extreme flows. The primary method for utilising

UV disinfection is to expose wastewater to a UV lamp. UV disinfection works by penetrating the cell walls of pathogenic

organisms and structurally altering their DNA, thus preventing cell replication and function. Because UV is not a chemical

disinfection method, it disinfects without altering the physical or chemical properties of water and no hazardous chemicals are

produced or released. However, UV efficacy is affected by suspended solids in the wastewater, which can scatter and absorb

light. Thus, UV disinfection is less effective in wastewaters with high total suspended solids (TSS) levels. MWH and WDC

investigated what was technically feasible in terms of UV treatment and associated pathogen kill numbers, based on national

and international experience. It was considered an Ecoli median of ~1,500 cfu/100ml and 1.5 log reduction in virus

concentrations could be achievable and this was further assessed by MWH (November, 2010) and peer reviewed by AWT

(December, 2010).

Storm Flow Treatment Option Assessment Report – MWH, November 2010

MWH oversaw an influent monitoring programme in 2010 during a summer „dry weather‟ period and a winter „wet weather‟

period to better understand wastewater quality during storm events. This information was drawn on to develop four technically

feasible options for disinfection of storm flows at the WWTP presented in MWH‟s report „Storm Flow Treatment Option

Assessment (2010). The four options included:

Option A – UV Disinfection upgrade. Upgrade existing UV facility for flows <80 ML/d, install a new UV disinfection

system on to the extreme flow bypass line downstream of the equalisation basin for flows >80 ML/d.

Option B – Plant Modification and UV Disinfection Upgrade. Modify the flow path through the treatment plant so that

~80 ML/d goes through the trickling filters and the balance goes as per Option A.

Option C - Treatment Process and UV Disinfection Upgrade. Upgrade existing UV facility for flows <80 ML/d and

install a new ballasted sedimentation and new UV disinfection system on the extreme flow bypass line downstream of

the equalization basin for flows >80 ML/d.

Option D - Storage Facility. Upgrade existing UV facility for flows <80 ML/d and install a storage facility to hold effluent

until it could be processed through the high flow path.

Particular interest was given to UV transmittance as this is the key parameter for designing and selecting UV systems. A range

of influent flows were then modelled from 57.4 ML/d to 170 ML/d. The output of the modelling was used to generate the

probability distribution for UV transmittance during the simulated storm events with and without treatment. These distributions

formed the basis of UV design in the options assessment.

The options assessment considered the following three flow scenarios for Options A to D:

Flow Scenario 1: UV Disinfection of flows between 30.4 ML/d and 57.4 ML/d (High Flow). The report assumed the

same requirement as the current consent; a PLC-based dose is required to be greater than a 10 minute average of

30 mWs/cm2 for flows up to 30.4 ML/d and greater than a 10 minute average of 40 mWs/cm2 for flows up to 57.4 ML/d

(from 2011).

Flow Scenario 2: UV Disinfection of flows between 57.4 ML/d and 80 ML/d (Extreme Flow). The report assumes the

effluent should be treated to achieve the disinfection standard of median 1,500 E.coli/100mL.

Flow Scenario 3: UV Disinfection of flows between 80 ML/d and 120 ML/d (Extreme Flow). With provision to extend to

accommodate flows up to 170 ML/d. The report assumes the effluent should be treated to achieve the disinfection

standard of median 1,500 E.coli/100mL.

The report commented that flows up to 57.4 ML/day cannot be accommodated in the existing UV channel as this would result in

excessive head loss.


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The report considered what dose rates could be achieved under each flow scenario taking into consideration modelled UVT

levels, assumed improvement in the EQ basin and any constraints regarding bulb spacing.

MWH‟s report concluded that Option A was considered the most cost-efficient option to meet the requirements of the current

resource consent and WDC‟s aim to protect public health, whilst being easiest to start-up operationally prior to storm events,

minimising disruption to the performance of plant during normal flows.

AWT Water, Peer Review of Storm Flow Treatment Option Assessment Report – MWH, November 2010

A peer review of MWH‟s feasibility assessment was undertaken by AWT Water Ltd in December 2010. The peer review

supported the report‟s findings that UV disinfection is feasible, subject to confirmation of the effluent quality, and further

hydraulic evaluation.

The main comments contained in the peer review were that; in the sampling and UV treatment modelling MWH may have been

over optimistic in simulating the diluting effect of stormwater using drinking water and that the effectiveness of the EQ basin in

reducing TSS needed further investigation.

AWT Water, Whangarei WWTP Peak Flow Assessment – Disinfection Options Assessment, June 2011

An options identification workshop was held with council‟s consultants on 18 April 2011. A number of disinfection options were

evaluated as part of the workshop and included:

UV Irradiation Disinfection;

Chlorine Disinfection using Chlorine gas or Chlorine Dioxide;

Ozone;

Natural UV Irradiation;

Membrane filtration.

The disinfection options proposed for further investigation were UV and Chlorine Disinfection.

An options assessment of the above disinfection options has been completed in draft to a conceptual design level (AWT,

2011b). The selection of a preferred option has been undertaken in line with the work carried out by NIWA using the same

target extreme flow discharge standards used in the NIWA modelling work.

UV Irradiation has been selected as the preferred method for disinfection of the Wastewater. It is noted that UV has a number

of advantages over Chlorine disinfection which include; (i) the systems are generally simple with no moving parts, (ii) no

Disinfection-by-Product (DBP) formation, although other toxic by-products can be formed (iii) Greater efficacy regarding virus

control. A disadvantage to UV can be the susceptibility to particle blinding, reducing the UV dose and its efficacy.

Further Storm Flows Quality Assessment

AWT Water, Peak Flow UVT Review –March 2011

In addition to the influent characterisation work performed by MWH in 2010, AWT Water undertook jar testing in December

2010. Subsequently WDC carried out further sampling and s::can monitoring during January 2011 (capturing a peak storm flow

of 116MLD).

The results of; the jar testing, comments on the effluent quality assumptions in MWH‟s report and discussion of sampling results

from two subsequent significant storm events, in January 2011 are contained in a letter report from AWT Water, Re: Whangarei

WWTP Peak Flow UVT Review, dated 16 March 2011.

UV transmissivity was also measured during the 23 January event by taking grab samples at various points within the WWTP

site and were found to agree with the assumption that it is possible to disinfect the Extreme flow bypass using UV. The sample

UVT values exceeded 50%.


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Table 2-2 UVT Values following a 116 MLD flow to the Whangarei WWTP

Location Time Sampled TSS

(mg/L)

Filtered UVT

(% UVT)

Unfiltered UVT

(% UVT)

Inlet to the Equilibrium Basin 0645h 74 70.4 49.7

Effluent from the Equilibrium Basin 0645h 43 72.1 51.5

Effluent from the Equilibrium Basin 0920h 42 71.6 52.0

Storm Clarifier Effluent 0650h 26 71.7 56.2

Storm Clarifier Effluent 0925h - 72.1 58.5

Primary Effluent 0700h 61 70.7 70.7*

UV Influent 0705h 19 71.6 54.6

Hatea Pump Station Overflow 0830h 159 69.4 37.1

*This sample appears anomalous.

During the event of 23 January it was found that the EQ basin, when operating as a clarifier, had a solids removal efficiency of

40%. This supported the assumptions presented by WDC during the hearing on the effectiveness of this unit to act as a primary

clarifier. Results did however indicate that previous assumptions regarding 20% improvement in UVT across the EQ basin are

likely to be over optimistic.

An s::can unit monitoring UVT and TSS was installed just ahead of the 29 January event. The graph below shows the data

collected from the 29 January event.

Figure 2-2 UVT, solids compensated UVT and TSS during 23 January storm event.

The 29 January 2011 (cyclone Wilma) event was estimated by NRC to have a 12 hour rainfall intensity ARI of 80 years and 24

hour rainfall intensity ARI of greater than 30 years. During this event:

The peak instantaneous flow into the treatment plant was 1,340 L/s (approx rate of 116,000 m3/d)

90ML/day


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The 24 hour accumulated flow was 99,000 m3.

Okara Park SPS operated at full capacity without overflow, pumping around 1,100 L/s.

The 29 January results showed that incoming storm flows can have UVT as high as 60 – 70% due to the dilution effects of the

wastewater from stormwater infiltration, although there does appear to be a drop in UVT at the peak of the incoming flow that

indicates the quality of the storm flow suffers from a „first flush effect‟. Post secondary treated effluent showed on average a

UVT of 47.8% which is considered typical for a secondary treated wastewater (AWT, 2011b).

The data obtained from this event has enabled WDC to further confirm flow rates into the treatment plant, carryout further

influent and effluent quality analysis specific to UV treatment to check assumptions made in the UV assessment reports, and

undertake an assessment of EQ basin performance as a clarifier. In light of the monitoring carried out during this event the

Extreme flow volume estimates previously presented to the hearing committee and those being used for analysis of effects of

the discharge appear conservative on review of these results.

Further UVT Sampling

The design of the UV disinfection process is dependent on the clarity of the water, represented by its UVT. While earlier

investigations have supported the feasibility of treating the water with UVT there has not been sufficient information to detail the

exact configuration of the treatment processes. The following issues require clarification:

Management of the first flush.

The UVT data shows a deterioration of UVT at the onset of the storm, likely due to undiluted sewage that is stored within the

network being pushed quickly into the plant. The best way to manage this first flush requires further work, but it is likely to

include maximising the use of storage in the equalisation basin and maximising flow rates through the treatment process.

Understanding the characteristics of different storms

Under dry weather conditions the trickling filters build a thicker than normal slime layer on the rocks. During high intensity

storms after dry weather it appears that the rapid increase in flow rate causes this slime layers to dislodge and potentially

overload the storm clarifiers. During such storms it is likely that the clarity of water that passes through the equalisation basin is

of better quality than that that passes through the trickling filters. This does not appear to be the case during wet weather when

the trickling filters receive regular higher flow rates. This indicates that some flexibility is needed in the way the plant operates

during wet weather to ensure that the effluent receives the highest UV dose.

Since the monitoring of the 29 January event, WDC have reinstalled two inline monitors to attempt to collect further storm water

quality data. One unit was installed in the outlet channel of one of the storm clarifiers on 19 July 2011. The other unit was

installed after the EQ basin on 31 August 2011 and at the same time the first unit was moved to the inlet works.

The data that WDC has collected to date strongly suggests that extreme storm flows with some primary clarification are

treatable with UV. Collection of further data will aid WDC in confirming the best UV arrangement and engineering solution.

WDC also collects UVT data at the existing UV channel using an inline monitor which is part of the existing UV system.

Treatment Options Assessment (focusing on hydraulics)

WWTP Hydraulic Model

A hydraulic model of the WWTP was built to gain a better understanding of; the existing hydraulic performance of the

Whangarei WWTP, evaluate the hydraulic validity of WWTP upgrade options, and determine the most appropriate

configuration to be adopted for disinfection of the effluent. The model was checked using a single event that occurred on

21st March 2011 and reached the current WWTP capacity of approximately 57.4 ML/d.


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Options Evaluation Workshop

An options identification workshop was held with council‟s consultants on 18 April 2011. During this meeting 6 options were

identified for evaluation with the purpose of identifying 3 options to take forward for more detailed evaluation.

Table 2-3 Options identified and evaluated for further investigation at 18 April 2011 workshop.

Option Description Score

Opt1 Option 1 - Disinfect > 57.4 ML/d directly from EQ Overflow 27.0

Opt2 Option 2 – 80 ML/d through existing plant with the remainder as per option 1 29.0

Opt3 Option 3 – 125 ML/d through existing plant 26.0

Opt4 Option 4 – Same as option 2 but increase flows through activated sludge system 29.0

Opt5 Option 5 – 80 ML/d through existing plant and the rest store in pond near wetland 28.5

Opt6 Option 6 – 57.4 ML/d through existing plant and the rest through EQ and new mega wetland (combination of both existing wetlands)

21.0

The options were scored 1-5 against:

Uses existing assets

Process risk

Ease of operability

Potential for upgrade/ staging in future

Relative land requirements

Robustness to changes in hydraulic flow

Robustness to changes in influent characteristics

Effluent quality

Options 1, 2 and 5 were selected for further investigation. Option 4 was considered a variation on Options 2 that could be

investigated separately. AWT Water were engaged to carry out this options assessment work which is described below.

During the workshop disinfection options were also selected for further investigation. AWT Water carried out this work which is

described above. The final outcome was that UV disinfection would be taken forward.

AWT Water, Whangarei WWTP Peak Flow Options Assessment, September 2011

As a result of the 18 April 2011 options workshop the following options were hydraulically modelled, and an assessment of risks

and benefits and cost estimated carried out. A brief description of each option and its estimated cost is below.

Option 1: (Extreme flow disinfected) $3.0M

Fully treat flow < 57.4 ML/d and discharge to the wetlands through existing processes. Disinfect flows 57.4 ML/day –

125 ML/d directly after primary treatment in the EQ basin via a new disinfection system with discharge to continue to

Limeburners Creek;

Option 2: (Increased treatment) $4.0M

Upgrade the WWTP to primary treat, clarify and disinfect flows < 90 ML/d. Flows between 90 ML/d – 125 ML/d to be

primary treated in the EQ basin then UV disinfected via a new disinfection system. Following disinfection, flows


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<57.4ML/d to be discharged via the existing wetlands, and the remaining flow to be discharged to Limeburners Creek.

This would effectively lift the existing High Flow ceiling from where it is currently at 57.4 ML/d to 90 ML/d;

Option 3: (Lagoon) $5.5M

Upgrade the WWTP to primary treat, clarify and UV disinfect flows < 90 ML/day. Direct flows between 90 ML/d – 125

ML/d to a 15,000 m3 balancing pond after primary treatment within the EQ basin. Following disinfection, flows

<57.4ML/d would discharge via the existing wetlands, and the remaining flow would discharge to Limeburners Creek.

Pump out the storage pond after the storm recedes for full treatment. This proposal would effectively eliminate the

Extreme Flow portion as this would be pumped back into the treatment plant as the influent flows reduce. It may be

necessary to have some overflow from this storage basin during rare events, such as large sequential storms. It is

proposed that the storage pond would be built on land opposite the treatment plant owned by Council.

The ability of each option to cope with up to 140 ML/d in future has also been considered for each option.

Option 2 is the preferred Option because it maximises the use of existing process units by passing as much storm flow through

the process units at possible with the aim of improving quality of storm flows before discharge. All flows up to at least 125

ML/day will be UV disinfected before discharge to the wetlands or Limeburners Creek.

At an estimated cost of $4.0M Option 2 is considered the best option as it is less expensive than Option 3 and ensures all

discharges will be disinfected.

While initially Option 3 was the preferred option, a more detailed investigation into its viability has raised a number of risks

associated with the lagoon option and as it also has a higher cost estimate it is considered that this option not be pursued.

Investigations involved further network modelling using the last thirty years of rainfall data, a peer review of the concepts with

BECA engineers, and discussion the consenting requirements with NRC. A number of issues with Option 3 have arisen from

this work, including:

Lagoon cleaning difficulties of the large base area following storm events. While the water that enters the lagoon will

be screened, settled and dilute, some organic matter will drop out of suspension creating odours when the lagoon is

drained. The size of the lagoon will make odour control difficult.

NRC have advised that the existing air discharge consent would need to be changed to include this lagoon and

obtaining such a consent in this location may be challenging.

The modelling work indicates that under Option 3 the lagoon size proposed will over top (spill) on average around once

per year. This may be directed to the wetland, however this water would not be disinfected and therefore the goal of

100% treatment would not be achieved. A larger pond is not feasible on the land area available.

Option 2 will allow for some flexibility in how the water is routed through the plant as very intense rainfall events, and the

corresponding rapid increase in wastewater flow rates, can cause short term scouring of the trickling filters, deteriorating the

quality of water to be disinfected. The path through the EQ basin in this case will be more effective.

To help address hapu/iwi concerns in relation to land contact of the wastewater the option of passing treated effluent through

the existing wetland has been evaluated. It has been determined, based on WWTP hydraulic modelling, that the option to direct

flows of up to 125,000m3/d to the wetlands is technically feasible and environmentally preferable as the wetland may offer some

further treatment before discharge into the harbour (AWT, 2011). NRC has advised that installing this option may require

further changes to the existing consent and therefore further consent hearings. The current proposal is to continue to work on a

direct discharge to the Limeburners Creek, however, options to discharge the treated wastewater via a wetland are still being

investigated in consultation with NRC and iwi/hapu.


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Based on the findings of this study, Council have resolved4 to progress Option 2, at a cost estimate of $4.0M. Further to this

work it is necessary to increase the capacity of the inlet screening system over and above that provided for by the recent

upgrade. This work is planned to occur in parallel to the overall upgrade project

2.4.6 Quality Management System

Council operates a Quality Management System to international standard ISO 9001:2008 that sets out the operating

procedures for the „collection, conveyance and treatment of wastewater and stormwater to comply with resource consent

conditions‟. A copy of this certification is provided in Appendix 6. The system follows the standard Plan, Do, Check, Review

cycle for Quality Management which results in continuous process improvement. Council also intends by 2014, as part of the

Wastewater Strategy, to have prepared and adopted an Environmental Management System to ISO 14000 for Council‟s

wastewater treatment and disposal schemes in order to provide a structure system to minimise the impacts of the wastewater

activity on the environment.

Through the setting of quality and environmental targets for the wastewater infrastructure and following the process for

continual improvement, will lead to enhanced outcomes for both quality and environmental performance.

A copy of Council‟s accreditation certificate is appended.

2.4.7 Level of Service and Monitoring Results

Council also sets performance measures for the wastewater activity and consults on these as part of the Annual Plan and

LTCCP planning processes.

2.4.8 Whangarei Harbour Integrated Management Strategy

As a result of the consultation WDC has carried out with the community on wastewater issues, it is clear that there needs to be

a wider focus on water quality in the harbour as a whole. Work has begun to identify what information both Regional and

District Councils hold on the health of the harbour and where there may be gaps. The development of a strategy to address

harbour water quality, will need to be developed collaboratively and take an integrated approach.

4 WDC, Infrastructure and Services Committee meeting in August 2011


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3 EXISTING SYSTEM AND OPERATION

3.1 Existing Plant

The Whangarei Wastewater Treatment Plant (WWTP) services an area extending to Dairy Flat in the North, Maunu in the west,

Raumanga in the South and Onerahi / Whangarei Heads in the east.

The current WWTP was originally constructed as a relatively simple Trickling Filter/Clarifier plant in 1966 and was essentially

doubled in size and capacity in the early 1980s. Since then the normal flow treatment capacity has been considerably

enhanced through the addition of an activated sludge process, disc filters and UV disinfection of effluent under normal flow

conditions.

The WWTP currently comprises:

Inlet works

Preliminary treatment in the form of screening and grit removal.

Flow balancing, provided by Equalisation Basin (EQ basin).

Primary sedimentation, provided by three 25m diameter primary clarifiers configured in parallel.

Secondary treatment provided by two-stage trickling filtration and activated sludge processes. Under normal flow

conditions there are two trickling filter trains configured in parallel, each with two, 25.5m diameter first stage and two,

25.5m diameter second stage trickling filter, and one activated sludge basin. The activated sludge basin is currently

operated at 21 ML/d and typically operates with a solids retention time of between 10 and 12 days.

Secondary sedimentation, provided by two 25m diameter clarifiers configured in parallel.

Tertiary treatment provided by disc filtration, UV disinfection, and constructed wetlands. The UV facility is an open

channel low pressure high output system with one channel, two banks of lamps per channel, 6 modules per bank and

8 lamps per module (i.e. 96 lamps in total). There are two constructed surface flow wetland systems configured in

parallel. Effluent either gravitates to Wetland 1, which comprises two discrete ponds in series, or is pumped to

Wetland 2, which comprises three discrete ponds in series.

High flow treatment processes, including two storm clarifiers configured in parallel and an Extreme flow bypass

discharge point immediately downstream of the EQ basin.

The WWTP is currently configured to treat flows via three flow paths. The flow path used is dependent on flows received at the

plant. These flow paths are shown in Figure 3-1 and Figure 3-2 summarised below:

Normal Flows (up to 21 ML/d (<243L/s)). Water flows into the inlet works. A preset amount is directed into the

treatment process (via a flow control penstock) and any excess is directed into the EQ basin to achieve side stream

balancing. Water is pumped from the EQ basin as needed to ensure a stable flow enters the treatment plant.

Medium and High flows (from 21 ML/d up to 30.4 ML/d (243 – 352L/s) and 30.4 ML/d up to 57.4 ML/d (352-

664L/s)). This proportion of flows bypasses the second stage trickling filters and activated sludge processes, passing

instead through two 25m diameter storm clarifiers. Currently the UV disinfection process has a capacity limited to 30.4

ML/d. Under the current resource consents the UV process is required to be increased in capacity to 57.4 ML/d by

May 2011. In February 2011 WDC requested that this work be delayed so the upgrade could be amalgamated with

other upgrade works.

Extreme Flows (Flow in excess of 57.4 ML/d (>664L/s)). During extreme flows all wastewater is passed through the

screens and grit removal process, although a provision is available to bypass this in an emergency (such as a power

cut, or mechanical fault). When the flow to the plant exceeds 57.4 ML/d and the EQ basin level is high the mixer in the


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EQ basin is turned off and the basin acts as a storm clarifier. Flow in excess of 57.4 ML/d then overflows a weir in the

EQ basin and discharges to Limeburners Creek. Solids that settle in the EQ basin are returned to the primary

clarifiers.

Figure 3-1 Process schematic of Existing Flow Paths

Whangarei Wastewater Treatment Plant: Application for Change to Consent 200404352(02) - Additional Information Error! Reference source not found.Error! Reference source not found.

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Figure 3-2 Site Layout with Existing Flow Paths

The flow rates used set out in the existing consent describe the theoretical capacity of the WWTP if it was to operate at this flow rate for the full 24 hours (e.g. 21 ML/day, 57.4

ML/day). In practical terms this will not actually occur as network flows, under both normal and storm conditions, will vary during the day. The flow to, and through the WWTP will

reflect this as there is no significant storage in the system to smooth the flows other than the EQ Basin. Therefore, while the WWTP might record a flow volume of 21,000 m3 for

the day, which translates to an instantaneous flow rate of 243 litres per second, the actual flow-rates through the plant during the day may exceed this at times of peak flow and will

be less at other times. Similarly, while the total daily flow to the WWTP might be only 15,000 m3 there may be periods during the day when the instantaneous flow rate exceeds

243 l/s. As such the description of the plant operating at 21,000 m3/day is more descriptive of an operating mode than an exact flow rate.

Storm Clarifier


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3.2 Current Situation

Influent Flow Rate Analysis

At the time the s127 application was heard in 2010 the actual flow to the treatment plant with the new Okara Park PS was

unknown, as the pump station upgrade was incomplete. Since completion of this project a number of events have

occurred that indicate that the maximum inflow rate is presently around 1,340 L/s (excluding a spike to 1,470 which

appears erroneous). The theoretical maximum daily flow (assuming the pumps run 100% for 24 hours) is therefore around

120,000 m3. To date the maximum 24 hour cumulative inflow has been 99,000 m3. This occurred during cyclone Wilma, a

storm during which the 24 hourly rainfall totals had an estimated annual return interval greater than 30 years. The figure below

provides a record of the peak instantaneous flow rate to the plant and 24 hourly cumulated figures.

Figure 3-3 Whangarei WWTP inflow during Cyclone Wilma (instantaneous and flow totalised over a 24 hour period)

Using the sewer network model, featuring the new upgraded OPPS and other contributing pump stations, AWT Water have run

a time series of rainfall data from 1996 to present (14 years). Based on the OPPS passing forward flows of up to approximately

125 ML/day to the WWTP, and bypass events occurring when inflow to the WWTP exceeds 57.4 ML/day, the model estimates

an average of approximately 5 spills per year. Using the model it is difficult to put an accurate figure on how many bypass

events would have occurred historically. Between Feb 2007 and July 2011, 19 bypass events have been sampled for effluent

quality (on average 4.2 events per year). However it is known that not all bypass events are able to be sampled, and some

events will be missing from those records (see Figure3-5 below for bypass quality sampling records).

AWT Water undertook a second validation of the sewer model based on the 29th January 2011 event, and found that the model

performed well, although note that the model appears to over-estimate at the height of the storm event.


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Flo

w m

3/s

28/01/2011 12:00:00 AM 30/01/2011 12:00:00 AM 1/02/2011 12:00:00 AM-0.5

0

0.5

1

1.5

2

ModelMeasured

Figure 3-4 Network Hydraulic Model Validation Event

AWT have modelled five distinct synthetic wastewater events simulating inflow and infiltration to the wastewater network and

into the WWTP from which the amount of the Extreme flow required to discharge directly to Limeburners Creek, has been

derived. The total Extreme flow discharge, volume and duration for each event is given in the Table 3-1 below. As shown, the

modelled frequency of the event for which consent is sought is in excess of five years.

Table 3-1 Maximum Extreme Flow Bypass Discharges to Limeburners Creek

Wastewater Event,

modelled frequency

Total Extreme Flow Volume

(m3)

Extreme Flow Bypass

Discharge Duration (hrs)

Maximum discharge

volume over 24 hours (m3)

3 month 35,083 31 30,066

6 month 44,302 34 37,109

1 year 53,093 38 41,150

2 year 64,819 42 46,856

5 year 84,787 46 56,162

There is limited data available on wastewater composition during storm flows, primarily due to the limited occurrence of these

events. The data available is summarised in Figure 3-5. The data available does not correlate well with size of storm flows.

This is likely to be due to a number of factors including the limited number of total samples, only one grab sample taken during

each event, timing of grab sample taken relative to duration of event and timing of storm event relative to diurnal flow.


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Figure 3-5 Monitoring of the Bypass discharge to Limeburners Creek from the Primary Clarifiers

Note: Samples are triplicate, taken 5 mins apart; EQ basin was installed August 2010, prior to this, the influent was directed to the PSTs

where it overflowed to Limeburners. We note flow monitoring data peaks at 70 ML/d due to limitations with the flow metering.

3.3 Receiving Environment

The discharges from the WWTP including the Extreme flows are directed to Limeburners Creek, the Upper Harbour and

ultimately the wider harbour which is heavily used by the public for recreational activities. The location of the WWTP and the

bypass outfall relative to Limeburners Creek is shown below in Figure 3-6.

Figure 3-6 Effluent Flow Bypass Discharge location to Limeburners Creek


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Limeburners Creek is located in the upper reaches of the Whangarei Harbour and drains a watershed area of 1,189 hectares,

southwest of the Whangarei CBD. The creek is an area long compromised by a well established industrial area on its fringes,

WWTP discharges and upstream catchment runoff.

The creek is designated under the Northland Regional Coastal Plan as a “Mixing Zone for Major Discharge”. This means that it

has no applicable water quality standards. The mixing zone ends at Port Road Bridge.

The Upper Harbour is a secondary receiving environment for Extreme flow discharges as a result of the mixing and dilution

effects in Limeburners Creek. The Upper Harbour covers an area of approximately 4.2km2 and runs generally in a north/south

direction from Onerahi to the marina approximately 5.5km from the harbour entrance. Upstream of the Limeburners Creek

confluence the harbour at high water is typically 80 to 100 metres wide, but widens downstream to between 140 to 160 metres.

At low water, a shallow navigation channel meanders between extensive exposed mud banks. The tidal prism between Mean

High Water Spring (MHWS) and Mean Low Water Spring (MLWS) is in excess of 8,000,000m3 for the Upper harbour and

499,000m3 for Limeburners Creek.

The harbour in the vicinity of the Limeburners Creek confluence is estuarine in character. The margins to the estuary in the

vicinity of the Limeburners Creek confluence are heavily developed with industrial and commercially zoned land and a large

amount of historical reclamation. There is a reasonably intact fringe of mangrove habitat on both sides of the estuary, although

this is broken in places.

Waters of the Upper Harbour are classified under the Northland Regional Coastal Plan5 as a Marine 2 (Conservation)

Management Area. Coastal water quality standards also apply under the NRCP, for the Upper Harbour, with a Contact

Recreation Standard (CB) applying to the area upstream of Onerahi, and a General Quality Standard (CA) applying to the area

downstream of Onerahi. The criteria for these Coastal water quality standards are summarised as follows:

No conspicuous oil or grease film, scums or foams, floatable or suspended materials, or emissions of

objectionable odour.

CB - Based on not fewer than 5 samples within any 30 day period, a median faecal coliform count of

<150cfu/100 ml and an 80 percentile count of <600cfu/100ml.

CA – Based on not fewer than 10 samples within any 30 day period, a median faecal coliform count of

<14/100ml and a 90%ile <43/100ml.

In addition, the Ministry for Environment and Ministry of Health Microbial Guidelines for Marine and Freshwater

Recreational Areas (June, 2003) also stipulate the following water quality standards:

Contact Recreation Standard - <260 enterococci/100ml

Shellfish Gathering Standard - <10% of samples exceeding MPN of 43/100ml faecal coliforms

3.3.1 Background Water Quality

The Commissioners were satisfied from the WDC/NRC evidence presented that water quality standards in the receiving

environment were not being met, with major contributors being wastewater discharges from various sources. Concerns

however were raised about the monitoring points, and their potential to be influenced by intertidal movements, and therefore the

relevance of the water data used in the s127 application.

No further water quality monitoring or analysis of the NRC state of the environment monitoring has been undertaken since the

2009 application, other than a viral study NRC did to accompany the QMRA investigation. Other harbour investigations

undertaken are discussed further in Section 4.1

5 See Northland Regional Coastal Plan Map C16


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3.3.2 Ecology

The most recent comprehensive assessment of Limeburners Creek was undertaken in 1999 by Brian T. Coffey and Associates

Ltd. This was used in support of WDC‟s existing consent (Harrison Grierson, 2002) and summarised in the 2009 s127

application.

Poynter & Associates Environmental Ltd also prepared a report in 2008 that describes the existing ecology, water and sediment

quality in the Upper Harbour within the vicinity of Okara Park PS, this was also summarised in the previous 2009 s127

application.

We have therefore not repeated the findings here and refer the reader to the 2009 s127 consent application supporting

documentation. No further ecological assessments have been carried out in the past year.


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4 TREATMENT PLANT UPGRADE

4.1 Why upgrade is required

During the June 2010 hearing, it was established clearly that the water quality standards in the harbour were not being met at

all times, with a major contributor being wastewater discharges from various sources in the WDC wastewater reticulation

system. The calibrated sewer model (discussed earlier) has since confirmed that the Extreme flow bypass is two to three times

greater in volume than the total of other overflows in the network. The exact proportion varies and is dependent on the nature of

the storm. For example heavy steady rain can result in high treatment plant inflow with little network overflows, while very heavy

storms when the soil is wet, can cause a higher proportion of network spills. The previous proposal to primary treat the extreme

flows only was considered by the Commissioners to be a minor improvement on raw wastewater quality, and did not

satisfactorily address their concerns regarding risks to public health.

A range of investigations have since been undertaken to determine what effect sewage spills have on harbour water quality and

the relative impact of the various discharges, whether from network spills or the Extreme bypass. These investigations have

included:

- NRC‟s State of the Environment and Virus monitoring

- PDP Dilution Study

- NIWA Harbour Dispersion Modelling

- NIWA Quantitative Microbiological Risk Assessment (QMRA)

Furthermore these investigations were undertaken to help determine an appropriate treatment standard to meet recreational

contact standards downstream of Port Rd Bridge and shellfish gathering standards at Kaiwaka Point, Onerahi.

4.1.1 Virus Monitoring

NRC‟s environmental monitoring shows elevated levels of pathogens in the upper harbour during storms that are consistent

with sewage discharges and show an elevated concentration downstream of the WWTP.

A virus monitoring run in May 2011 also showed very high levels of Norovirus in Limeburners Creek from the WWTP,

particularly from the Extreme flow fraction, that was associated with a Norovirus epidemic in the Whangarei District at the time.

NRC has completed an assessment of catchment landuse types of the Whangarei harbour, and developed a comprehensive

GIS database, to assist in assessing potential point-source and non-point source contaminant sources that maybe affecting

background water quality in the harbour.

4.1.2 Dilution Study (October 2010)

The initial approach taken to determine an appropriate discharge standard was one whereby a back calculation was done

taking into account dilution from both coastal water and freshwater inputs. WDC engaged PDP to calculate dilution factors and

the NRC had these calculations reviewed by NIWA.

PDP (2010) undertook an analysis of a range of discharge events to determine the expected dilution factors for the Extreme

flow bypass from the WWTP for two locations: Port Rd Bridge at the confluence of Limeburners Creek and the Hatea River (the

CB area defined in the regional plan): and, the Upper Harbour boundary of the CA classified area west of Onerahi. PDP

acknowledged the complex process of dilution and simplified the dilution process by only considering the volumetric factors of

stormwater runoff and the tidal prism and assumed the modelled wastewater overflows were fully mixed within those volumes6.

6 It was assumed the discharge and the receiving water was fully mixed and in addition, it was assumed that the stormwater runoff did not mix with the harbour volumes below MLW and the tidal dilution calculations were based on an assumption of no stormwater runoff


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The dilution factors were calculated by comparing the five modelled Extreme flow discharge volumes, with their corresponding

rainfall event volumes, as well as the available tidal prism volumes.

Stormwater runoff dilution factors of 16 to 19 for Limeburners Creek and 185 to 206 for the Upper Harbour were calculated by

comparing the various WWTP extreme overflow events against the corresponding storm events (i.e. 2 year Extreme Flow

volume overflow versus 2 year ARI rainfall event. Consideration was also made to the fact that there could be less dilution if

part of the storm volume discharges past the Port Road Bridge prior to the Extreme flow commencing. Assuming less than 10%

of the storm volume occurs prior to the discharge commencing this was not considered to significantly reduce storm dilution

resulting in storm dilution factors of 15 and 175 in Limeburners Creek and the Upper Harbour respectively.

The neap and spring tidal prisms were utilised to determine the tidal dilution. Assuming full mixing, the tidal dilution factors

ranged from 3, for the 5 year discharge event in Limeburners, to 233 for the 3 month discharge event during a spring tide. An

allowance was made for partial mixing across the intertidal areas within the harbour of 50% mixing with a 60% shall area extent.

This resulted in a neap harbour tidal dilution factor of between 101 to 42, depending upon the wastewater event size. For full

tidal dilution to occur it is expected to require several tidal cycles within the Upper harbour. As the Extreme discharge occurs

over 31 to 46 hours, the tidal dilution factors calculated are based on mixing occurring over two to four tidal cycles.

Although the storm runoff and tidal dilution factors have been calculated independent of the other, in reality, the dilution process

is likely to be a combination of tidal flushing, mixing effects, retention within the harbour and dilution by stormwater discharges.

In order to asses this the use of a hydrodynamic harbour dispersion model is necessary. As the storm runoff volumes are larger

than the tidal prism volumes and the Extreme flow duration is shorter than the storm runoff duration, PDP recommended the

dilution factors using the volumetric approach should be based on the storm runoff volumes.

Further dilution in the tidal prism is likely to occur, however the extent of this could not be accurately assessed without utilisation

of the NIWA harbour model. An effluent quality was derived from these figures such that the bathing standard at Port Rd Bridge

and the shellfish gathering standard at Onerahi could be achieved based on freshwater dilution only (excluding die off and

dilution in the tidal prism, but including an adjustment for incomplete mixing). An effluent quality with a median of 1,500 E coli /

100 mL was proposed, and consistent with the effluent quality considered technically feasible to achieve by UV disinfecting the

Extreme flow (discussed earlier in Section 2.4.5).

PDP, and subsequently NIWA, in a peer review of PDP‟s report, recommended that the standards derived from the dilution

estimate be assessed using the dispersion model due to the questionable validity of some of the assumptions, particularly

mixing.

4.1.3 Harbour Dispersion Modelling (February 2011)

To help assess the effects of network overflows and WWTP bypass flows, NIWA developed a 3-dimensional particle dispersion

model (NIWA, 2011a). The model predicted the flow paths of pathogens associated with these discharges down the harbour,

the time of travel and bacteria concentrations/dilutions at various points of interest. Important locations considered were; the

Town Basin, Onerahi boat ramp and beach (used for swimming and boating activities), Kissing Point (easy access, used for

rafting etc), Snake Bank (shellfish farming) and Mair Bank (shellfish farming). A copy of the report is provided in Appendix 4.

This model indicated that point source discharges of sewage from Okara Park PS and the WWTP have a significant detrimental

impact on water quality in the harbour, and the effects can extend seaward of Onerahi in large events.

The model has allowed specific discharges to be investigated in isolation of background water quality. This has allowed the

effects of the WWTP in its current configuration and future upgrade options to be assessed.

Figure 4.1 provides an image of the maximum bacteria concentrations that the NIWA dispersion model predicted would have

occurred during ex-tropical cyclone Wilma, January 2011 as a result of Extreme flows experienced at the WWTP. The model

was run for two scenarios, (i) current treatment levels and (ii) assuming all flow leaving the WWTP is disinfected to an average

of 1,500 E coli per 100mL.


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The model predicts large improvements in water quality in the harbour from the proposed upgrades. The estimated bacteria

concentrations are within the bathing quality and shellfish gathering standards for the upper harbour and outer harbour

respectively when considering the WWTP discharge only.

Figure 4-1 Estimate of the effect of the WWTP discharge on harbour water quality during ex-tropical cyclone Wilma under current treatment

levels and a possible upgrade.

It was acknowledged by NIWA that because the model was designed to predict the effects of the discharge in the wider

harbour, i.e. far-field, that for the purpose of analysis being required, the model resolution was too coarse.


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4.1.4 Quantitative Microbiological Risk Assessment (June 2011)

NIWA were also engaged by NRC, in collaboration with WDC, to estimate the risk wastewater discharges pose to public health

while people are swimming, undertaking other recreational activities (e.g. Waka-ama), and eating raw shellfish collected from

water at various locations.

NIWA developed a Quantitative Microbial Risk Assessment (QMRA) and estimated the probability of specific pathogen, in this

case a virulent virus (rotovirus) predominantly found in sewage, making its way into the harbour and making people ill either

through contact recreation at the Port Road Bridge or through shellfish collection at Kaiwaka Point, Onerahi (NIWA, 2011b).

Due to the virility of the virus chosen, NIWA considers this allows a conservative representation of a range of pathogenic

organisms. A copy of the report is provided in Appendix 4.

It should be noted that Kaiwaka Point was selected as the risk assessment site for shellfish gathering because it is located „on

the line‟ shown on the Water Classification Map within the Regional Coastal Plan for Northland below which the water quality

should be protected for shellfish gathering purposes in terms of bacteriological standards. However, shellfish in Whangarei

Harbour are commonly collected in the lower harbour (below Parua Bay) but rock and pacific oysters may be collected as far up

harbour as Waikaraka, which is located ~4 kilometres down-harbour from Kaiwaka Point. There are no known shellfish

beds/sites of any significance up-harbour of Waikaraka. This means that while individual illness risks have been calculated for

Kaiwaka Point, these should be considered to be very conservative given the location of actual shellfish gathering sites in the

harbour.

A total of 72 scenarios have been modelled using a 1-dimensional model (the QUEST model), comprising combinations of

various degrees of wastewater treatment and storage at the WWTP and at Network overflow sites and varying degrees of

contamination from other (non-monitored) sources. Details of importance are summarised here:

The assessment took into account rotovirus input from three sources; treatment plant discharges, network overflows

and background sources of pollution. Some scenarios were run without any background contribution to enable the

effects of the WWTP to be analysed in isolation (i.e. what would the effects/risks be if the WWTP were the sole

contributor of bacteria/viruses, similar to the approach taken in the PDP dilution study and NIWA harbour modelling).

The model incorporated a time-varying and season-varying microbial inactivation of faecal microbes in the River and

Harbour water to examine cases where overflows may begin at night and therefore subject to minimal natural UV

disinfection for some hours and compare predictions of microbial concentrations for summer versus winter conditions

(less UV in winter).

The model was run assuming dry weather, a small storm and a large storm (1 in 5 year storm).

The quality of the Extreme flow discharge in the large storm event varied from current (screening only and no UV

disinfection) to treated applying the three WWTP upgrade options discussed in section 2.4.5 above. Options 1

involves disinfection of flows >30.4 ML/d to achieve a 1.5 log reduction in virus concentrations, Option 2 involves

upgrading the WWTP to treat and disinfect flows <90 ML/d and disinfection flows >90 ML/d similar to Option 1, and

Option 3 involves upgrading the WWTP to treat and disinfect flows <90 ML/d with the remainder stored in a balancing

pond/wetland before being returned for treatment i.e. no bypass discharge in a large storm (1 in 5 year storm).

The network overflow volumes were based on the wastewater model estimates of what happens in a 5 year frequency

storm currently. In addition, all the scenarios were re-run with an improved background water quality to reflect longer

term water quality improvements that may be able to be achieved within the catchment as a result of Stage 2

improvements to the wastewater reticulation system. The stage 2 works is expected to eliminate spills at key sites for

a 1 in 5 year storm event and an 80% reduction in volumes from other sites.

The output from the model is the risk of illness from undertaking activities in the harbour at the two locations nominated. NIWA

have determined what would constitute an “acceptable” or “good” beach quality at these sites in accordance with MfE/MoH

(2003) national water quality standards. The determination recognises that all natural water bodies have a small health risk


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associated with contact recreation or shellfish gathering and that this risk increases as the water quality deteriorates. The

threshold for this investigation was a 5% probability that a person was exposed to an infectious dose. Therefore, a risk less

than 5% was deemed acceptable, greater than 5% deemed unacceptable.

The results of the QMRA can be summarised as follows:

Under all scenarios, including the previously proposed bypass regime7, the risks to users of the upper Whangarei

Harbour for contact recreation purposes, including swimming, are acceptable8 both in summer and in winter.

Table 4-1 Whangarei Harbour Modelled Activity Risk for Contact Recreation

Contact Recreation Summer Winter

Current With Improvements Current With Improvements

Upper Harbour Acceptable Acceptable Acceptable Acceptable

Wider Harbour Acceptable Acceptable Acceptable Acceptable

Under all scenarios, including the previously proposed bypass regime, the risks to persons collecting shellfish below

Kaiwaka Point (Onerahi) are acceptable in summer but not during winter.

Table 4-2 Whangarei Harbour Modelled Activity Risk for Shellfish Gathering

Shellfish Gathering Summer Winter

Current With Improvements Current With Improvements

Upper Harbour Acceptable Acceptable Unacceptable Acceptable

Wider Harbour Acceptable Acceptable Acceptable Acceptable

During winter wet weather conditions the individual illness risks associated with eating shellfish collected from below

Kaiwaka Point are reduced from ~14% (current regime) to ~9.8% by upgrading the WWTP under options 1-3 and no

further catchment or network improvements are done. This is a significant reduction but still in excess of what is

considered acceptable. This is due to the impact network overflows have on water quality, on top of the effect of

underlying water quality.

Improvements to the network and background quality will also significantly reduce the individual illness risk associated

with eating shellfish collected from below Kaiwaka Point but the risk will still be in excess of what is considered

acceptable (~12.8%).

The background water quality during a very large storm in winter without any sewage discharge, poses a risk for

shellfish consumption estimated at 2.9%, and therefore contributes between 20 and 30% of the individual illness risks.

However it is the discharge of untreated wastewater from the wider reticulation network and the WWTP which poses

the greatest risk to both contact recreation and shellfish gathering.

Therefore, in order to achieve an acceptable winter shellfish consumption risk the QMRA work indicates that an

upgrade of the WWTP, in addition with network improvements, are needed. It has been anticipated that through long

term improvements to the network, the spill volume can be reduced by 80%. This reduction in spill volume has been

assessed in conjunction with the WWTP upgrade options. The differences in risk associated with the 3 upgrade

options, 5.4% Option 1, 5.4% Option 2 and 4.9% Option 3 is minimal and within the uncertainty of the model

predictions.

7 Previously proposed bypass regime is that applied for under the s127 application – all bypass flows remaining untreated.

8 For the purposes of the QMRA „acceptable‟ means an individual illness rate of <5%.


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The data therefore indicates that with the network upgrades, WWTP upgrade and some general improvement in

background water quality the target of 5% can be achieved.

Although not specifically the subject of the s127 application, the QMRA also indicates that achieving acceptable limits in relation

to shellfish consumption at Kaiwaka Point requires a reduction in the load of pathogens from wastewater network overflows and

improvement in background freshwater quality.

4.2 What standard is needed

The Commissioners, as indicated in their interim decision, want to be satisfied that this proposed increase in Extreme flows will

not result in the receiving water beyond the Port Road Bridge to be unsuitable for contact recreation and the receiving water

beyond Kaiwaka Point (Onerahi) unsuitable for shellfish gathering. The Commissioners have emphasised in their Interim

Decision report that they consider the major impact of the proposed volume increase in Extreme flows is on public health and

other contaminants such as suspended solids are of less significance. Therefore the focus of treatment option investigations,

have been to address public health protection through targeted pathogen reduction in the Extreme.

The existing consent authorises Extreme flow discharges from the WWTP (57.4 – 90ML/d) which by-pass the treatment train

without any specific target discharge quality standards applied (with exception to Condition 18). NRC and WDC have been

working collaboratively to determine an appropriate discharge standard and hence treatment standard for the Extreme flow

discharge.

As discussed above in Section 3.3, there are a number of appropriate standards that need to be considered, including the

MfE/MoH (2003) contact recreation and shellfish gathering standards, and the NRC Coastal Plan, CB and CA Water Quality

standards. As noted in the Interim Decision (pg28), the monitoring programme to assess compliance against the CB water

quality standards, i.e. requirement for 5 samples to be taken over a 30 day period, provides an indication of long term water

quality, however is not suitable to assess public health risk. It was therefore highlighted that the MfE/MoH contact recreation

standard approach was more appropriate. Based on existing uses of the upper harbour (i.e. swimming as well as boating

activities) and in consultation with NRC, WDC proposes to disinfect all Extreme flows such that, the effluent, taking into account

dilution and die-off and excluding background water quality, will meet the MfE/MoH recreational contact guidelines at Port Rd

Bridge and Shellfish gathering guidelines downstream of Onerahi during any event.

To assist in determining what a suitable treatment level is, two activities have been undertaken. The first was to propose a

standard that was technically realistic utilising industry experience, and see how this would impact water quality in the harbour

assuming freshwater dilution only (no die-off or tidal dilution) and checking this via the NIWA hydraulic dispersion model. The

work indicated that an effluent with a median of 1,500 E coli/100ml would be diluted sufficiently at both the Port Road Bridge

and CA/CB coastal boundary to achieve the recreational bathing and shellfish gathering standard respectively. Note that this

estimate only considers the wastewater discharge (no background effects).

The second investigation involved NRC and WDC engagement of NIWA to undertake a Quantitative Microbial Risk Assessment

(QMRA) of sewage discharges into the harbour. The results of this study are presented in Section 4.1.4. The aim of this work

was to help overcome some of the limitations of the use of Standards in assessing intermittent discharges when the background

water quality is affected by other contaminant sources.

The results of the QMRA indicated that during winter the risk for shellfish gathering at Kaiwaka Point is not acceptable without

improvement works. Kaiwaka Point is in Onerahi and near the CA/CB coastal water boundary. The model also indicated that

despite the water quality not meeting the MfE/MoH Standards at Port Rd Bridge the health risk to recreational users is currently

within acceptable limits, similarly for shellfish gathering at Kaiwaka Point during summer.

To address the shellfish gathering risk at Kaiwaka Point the QMRA model indicated improvements to both the WWTP and

overflow volumes and/or quality is required.

The model also indicated that the Council needs to consider the cost benefit of its improvement works. There is a diminishing

return on treating the effluent at the treatment plant to higher and higher standards during storms as the other contaminant


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sources (overflows and background) quickly dominant the overall harbour water quality. A balance is needed that addresses the

effects of the discharge yet allows for funding to mitigate other discharges.

The suggested treated wastewater quality targets at the discharge point to Limeburners Creek have been summarised in Table

4-3. As discussed within the report there is likely to be a change in effluent quality through the progression of a wet weather

event, due to a change in wastewater characteristics (for example the UVT of the water improves the longer the storm

progresses). How the suggested standards would be imposed and monitored requires further discussion with NRC as outlined

below. The suggested targets may also need revision following the outcome of discussions on the use of the wetlands as a

discharge point during storm events.

Table 4-3 WDC Proposed Disinfection Targets

Description Contact Recreation Shellfish Gathering

Freshwater Marine Marine

Compliance

Standard1 at zone

boundary

Port Rd Bridge

260 E.coli/100ml

(95 percentile)

Port Rd Bridge

140 Enterococci/100mL

(95th percentile)

Onerahi

14 Faecal Coliform /100mL

(90 percentile)

Dilution Factor2 12 – 19 12 - 19 >200

Discharge Quality

Requirements

3,120 to 4,940 E.coli/100ml

(95 percentile)

1,680 to 2,660 Enterococci/100ml

(95 Percentile)

>2,800 FC /100ml

(90 percentile)

Proposed

Disinfection

Targets

Median 1,500 E.coli/100ml

90 percentile 3,000 E.coli/100ml

1. Based on MfE/MoH Microbiological Water quality Guidelines for Marine and Freshwater Recreational Areas

2. Based on Dilution Study undertaken by PDP 2010.

Comments relating to the Table

The dilution factor used is based on the fresh water inputs into Limeburner‟s creek, further dilution will be provided

from sea water.

WDC would prefer to standardise, for monitoring purposes, on one indicator organism and suggest that E Coli be used

for this purpose as it is the largest subset of the Faecal Coliform group. It is a valid indicator organism for freshwater

systems, which will be the key dilution factor during an extreme flow event. We also consider that there will be a

relationship between EColi and Enterococci and thus standardising on one indicator organism will make monitoring

more simplistic.

All three indicator organisms evaluated show a similar numerical value in the final effluent once the dilution factors are

applied; in particular the Faecal Coliform requirement for shellfish gathering given the lower number but greater dilution

available is similar in magnitude at the point of discharge to the E Coli requirement for Contact recreation.

The shellfish gathering standard applied is a 90th percentile rather than a median as applied in the NRC Coastal Plan

and MfE/MoH guidelines and therefore enables a more conservative assessment to be made.

The contract recreation compliance standard for marine waters is far more stringent than the existing Enteroccoci limits

on the consent for the downstream discharge point at Port Road Bridge (136/100mL as a median and 277/100mL as a

maximum). This again provides a conservative approach taken by WDC.


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We also understand that the NRC Coastal Plan contact recreational standard is based on sampling over a number of

(30) days however our compliance is likely to be evaluated for single events thus introducing a more stringent

requirement for WDC.

Technology Requirements and Monitoring

A number of technologies were found that could provide this level of disinfection however the most cost effective and least

environmental impact was using UV disinfection

NRC are also undertaking a review of the consent and have identified that it is impractical to separate out the existing and

proposed wet weather components of the Extreme flow and propose that a single discharge standard consistent with a standard

imposed as part of the s127 should be applied to the entire Extreme flow. WDC are in agreement with this approach.

The current resource consent includes PLC-based UV dose limits but not microbiological limits in the treated discharge for flows

up to 57.4 ML/d and has no limits for flows above 57.4 ML/d. For consistency with the existing resource consent, it is

recommended any target disinfection standard that applies to storm flows is based on the above microbial standards and

associated dilution factors.

WDC propose monitoring against the above effluent quality standards at the plant outlet for specific events with reference to the

Extreme flow bypass periods. Monitoring for the remainder of the consent requirements will proceed as normal (it is noted that

the volumes to which the current monitoring apply may be revised through either this application assessment or review, to

provide for an increase in flows to the wetlands as currently being discussed with NRC and iwi).

WDC will seek to establish a range of UV dose requirements for the different levels of flow passing through the system based

on UVT sampling work currently being undertaking and:

The removal requirements for indicator organisms;

The improvement to UVT across the process units under various flow/load conditions;

The dilution of the wastewater with storm water;

Performance of different proprietary UV equipment.

From this WDC will be purchasing UV disinfection equipment using a performance based specification that identifies the

appropriate UV dose for all flow scenarios across the range of 30.4 – 125 ML/day.

Sampling and Compliance

We propose to develop a sampling program for compliance with NRC based on the above indicator organism levels in the final

effluent during the Extreme flow events as opposed to a UV dose consent parameter. We will use UV dose as an operational

control mechanism however, to ensure that the above bacteriological levels can be maintained as required.

The key advantage of using a numerical standard for an indicator organism at the point of discharge as opposed to

measurements in the environment will be ease of access during specific events to a greater number of samples, and the ability

to build up over time better information of the system performance.

By logging UV dose over time certainty relating to the applied UV dose against the actual numbers of indicator organisms

achieved can be established.

4.3 Proposed Modifications to Treatment Processes

As discussed in section 2.4.5, WDC propose to pursue with Option 2 of the Options assessment carried out by AWT in

August 2011.

This option involves installing two new UV disinfection systems to ensure all flows including Extreme flows up to 125ML/d are

tertiary treated. The proposed system will be able to be upgraded in future to treat flows up to 140ML/d in the event further


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upgrade works on the reticulation occur. It also involves a proposed increase in treatment plant capacity to enable greater flow

volumes to pass through the trickling filters and secondary clarification processes, and by doing so, enhancing treatment to a

greater volume of flow received by the WWTP. The exact flows to pass through the upgraded WWTP have yet to be confirmed,

although, hydraulic and process engineering investigations carried out to date have assumed flows of up to 90ML/d. Flows up

to 57.4ML/d will continue to discharge to the existing wetlands, while the remainder of the flow will discharge via the

existing overflow pipe to Limeburners Creek.

A simplified process flow diagram is provided below illustrating the proposed configuration of Option 2.

(a) Existing Situation

(b) Option 2 Treatment Upgrade

Figure 4-2 Simplified Process Flow Diagrams illustrating (a) existing situation (b) Option 2 treatment upgrade

Inlet Screen and Grit Removal

New inlet works were installed in 2010 and have were constructed to treat all flows up to 100 ML/d, while flows above this are

screened in the original inlet works channels and diverted to the EQ basin. The existing inlet works are in poor condition and

will be replaced in this financial year to treat storm flows.

Primary Settling Tanks

Incoming flows would be split equally between the three PSTs. Based on flows up to 90 ML/day calculations indicate that

hydraulic retention times and flow rates through the PSTs would be above the normal design range. There is likely to be lower

than usual total suspended solids (TSS) in the incoming wastewater during these higher flow events, however, with a low

hydraulic retention time in the PSTs there may be reduced TSS removal and UVT improvement. A more frequent de-sludge

cycle will be required during storms to reduce the risk of solids carry over due to high up flow rates.


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Trickling Filters

Two modes of operation are proposed for the trickling filters. Under normal flow conditions trickling filters 1 & 2 act as first stage

trickling filters and 3 & 4 as second stage trickling filters. Under storm conditions the four trickling filters would be operated in

parallel with flow split between TF 1, 2 and 3 with flow to TF 4 capped initially at 21 ML/d. The hydraulic loading rate on the

trickling filters has been calculated as acceptable for a flow rate of up to 90 ML/day.

The above process changes will require the existing weir in the distribution chamber to be lowered and controls added to the

Archimedes Screw pump so that the operation can transition between 2 sets of trickling filters in series to 4 trickling filters in

parallel during storm events. Flow measurement instruments and control mechanisms will be installed to provide the

appropriate flow split to the four trickling filters and to ensure the activated sludge system is receiving the correct volume of flow

(currently a maximum of 21ML/day).

Storm Clarifiers

As the flow through the activated sludge system is restricted to 21 ML/day the balance of the flow needs to pass through the

two storm clarifiers. As the flow increases the loading rate on the clarifier‟s increases. It is likely that the storm clarifiers will be

operating at the recommended peak design loading rate when the flow into the treatment plant reaches 60 ML/d. As the flow

rate exceeds these rates the performance of the clarifiers will reduce.

A more frequent de-sludge cycle should be implemented during storms to reduce the risk of carry over, as well as ensuring

flexibility within the operation of the plant system to manage storm flows on a case by case basis. Management will include

utilisation of clarification capacity in the EQ basin and maximising flow to the activated sludge process.

A 900mm diameter pipe from the storm clarifiers to the new UV system will be required to convey the higher flow rates

Equalisation Basin

The equalisation (EQ) basin will continue to act as a clarifier when inflow to the WWTP exceeds 57.4 ML/day or as required to

maximise effluent quality. Sampling during the 23 January 2011 storm event indicated that the EQ basin removed 40% of

incoming TSS, further performance monitoring is ongoing.

UV Disinfection

The existing UV disinfection system (Trojan UV3000 Plus in channel UV system installed in 2006) will be upgraded from 30.4

ML/day to 50 ML/day by installing additional UV lamps. Furthermore, WDC propose to install a new UV channel adjacent to

the existing with a capacity of up to 50 ML/day. Additionally a new UV channel is proposed on the line between the EQ basin

and the Limeburners Creek outfall. It is proposed that this UV channel would have the ability for installing extra capacity in case

inflow to the WWTP was increased in future.

In accordance with resource consent 4352, the minimum UV dose delivered is:

30 mWs/cm2 for flows up to 30.4 ML/day; and

40 mWs/cm2, when the effluent flow exceeds 30.4 ML/day but does not exceed 57.4 ML/day.

Although the existing consent 4352 does not specify a UV dose for flows greater than 57.4ML/d, WDC propose to ensure a

minimum UV dose from the new UV systems of:

40 mWs/cm2, when the effluent flow exceeds 57.4 MLd.

Wetland

Although it is possible to increase the volume of treated flows discharging to the wetlands, at this time, WDC plan to continue to

discharge the consented maximum of 57.4 ML/day to the wetlands.


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It is possible to achieve this by reinstating an abandoned 750mm diameter pipe between the wetland discharge pump station

and Limeburners Creek out fall.

Other Improvements

As part of the sensitivity analysis flows up to 140ML/day were modelled to understand how the proposed upgrades would

perform if the terminal pump stations in the network were upgraded. In general the analysis showed that 140ML/day could be

accommodated by increasing the flow through the EQ basin and allowing spare capacity in the proposed, post EQ basin UV

channel.

There is a risk that directing flows of up to 90 ML/day through the WWTP may cause carryover of solids that have settled in the

bottom of the PSTs and storm clarifiers. De-sludge cycles may need to be altered during storm events to reduce this risk as

discussed above. Ultimately WDC may choose to run the plant at less than 90 ML/day (but no less than 57.4 ML/d as per the

consent) and direct more flows through the EQ basin if this will result in better quality treated storm flows.

There is a risk that high flow rates in the EQ basin and storm clarifiers, may cause difficultly in achieving an adequate

effluent quality for successful disinfection. In this case WDC would consider the options of chemically assisted dosing

(CAS) or the installation of lamella plates to improve settlement rates in either the EQ basin or storm clarifiers.

4.4 Treatment Performance

All Extreme flow bypass events that currently occur at the Whangarei WWTP result in screened wastewater being discharged to

Limeburners Creek. With the proposed upgrades in place, future events with a total volume less than 90 ML/d will be conveyed

through various treatment stages of the WWTP including UV disinfection. Future events with a volume greater than that

processed within the treatment plant will be screened, primary treated and UV disinfected prior to discharge to Limeburners

Creek.

As discussed above in Section 3.2, the estimated frequency of overflows based on historical rain data, post Okara Park PS

upgrade is difficult to accurately state, however from running the network model we have estimated an average frequency of

five extreme flow events per year. Furthermore, it has been predicted that the modelled frequency of the event for which

consent is sought (<140ML/d) is in excess of five years.

Based on the very limited effluent quality data available for the Extreme flow bypass (refer to earlier Figure 3.5), we have

determined (see Table 4-4) an indicative effluent quality based on this data and the work discussed earlier regarding the likely

pathogen numbers to be technically achievable through UV disinfection. These numbers have not accounted for any potential

improvement in effluent quality as a result of a portion of the Extreme flow bypass receiving secondary clarification as proposed

as part of the Option 2 upgrade.

Table 4-4 Indicative Extreme Flow Effluent Quality

BOD5

(mg/l) TSS (mg/l)

NH4-N (mg/l)

Ecoli (cfu/100ml)

Median 41 72 10 <1,500

90th%ile 84 117 24 <3,000

The data shows that the primary clarifiers/EQ basin can achieve, during high flow events, on average a BOD and TSS reduction

of ~40%, which supports the findings by WDC from their recent monitoring of the equalisation basin.

4.5 Works Programme

WDC provide an indicative construction programme for the proposed upgrade works:

Existing UV upgrade complete by March 2012.

Capacity Upgrade complete by November 2012.


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New UV complete by April 2013.

4.6 Alignment with Wastewater Improvement Strategy

The proposed works at the Whangarei WWTP form part of the overall improvement works identified in the Whangarei

Wastewater Improvement Strategy. As part of the strategy, reduction of infiltration and inflows to the system are also being

managed, however is it noted that this is unlikely to significantly address the Extreme flow issues.


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5 CONSULTATION

The Resource Management Act (1991) requires under the Fourth Schedule that if any consultation is undertaken that it is

included in the Assessment of Environmental Effects.

WDC fully comprehends the interests of the Whangarei community and particular interest groups in relation to wastewater

discharges and its effects and has been regularly engaging with individuals and groups on wastewater matters relating not only

in regards to the Whangarei WWTP but also in terms of wastewater more broadly in the Whangarei area.

WDC have developed a draft communications/consultation programme to facilitate input from key stakeholders and the

community in regards to the handling the extreme flows at the Whangarei WWTP, NRC 2011 consent review, and wider

Whangarei sewer network improvements and Wastewater Management issues. The draft Wastewater Strategy

Communications/Consultation Plan is provided in Appendix D of the WDC February 2011 Interim Report (refer to Appendix 2).

This plan is currently a “live document” that is being developed in conjunction with community, the new Council and Mayor, and

covers a range of activities over a number of years.

In the meantime WDC staff have continued to engage with key stakeholders, Iwi/Hapu/Marae and submitters in relation to the

overall wastewater strategy. The following provides a summary of the consultation carried out in the past year and a record of

this consultation is provided in Appendix 5 to this report..

In terms of consultation with Iwi on the wastewater strategy and WWTP, discussion has formed part of consultation meetings

held between WDC and the Iwi Hapu Practitioners Group. It is understood that this group contains a member from each Iwi and

Hapu that has input on consent activities. The meeting held on 19 May 2010 provided an update on the proposed wastewater

improvements to be undertaken by WDC including discussions around the Whangarei WWTP upgrade project. The general

consensus from the meeting was understood to be encouragement from the Group to proceed with the improvements proposed

but being mindful that discharge to land is the best method. Similar meetings have subsequently been held on 16 August 2010,

10 November 2010 and 15 July 2011 to distribute and update information on wastewater improvements and seek input from the

Iwi / Hapu Group. A hui was also recently held at the WWTP on 1 September 2011 with a number of members from the Iwi /

Hapu Group to discuss the condition and future use of the wetlands. Agreement by all that putting greater wet weather flows

through the wetlands is preferred that a direct discharge to Limeburners.

In addition to Iwi, meetings have also been held with other key stakeholders and interest groups in regard to WDC proposals for

wastewater improvements, including the Whangarei WWTP and requests for feedback on the Draft Wastewater Strategy.

Public meetings, held at Forum North on 18 November 2010 and 28 March 2011 have been attended by groups such as Save

our Harbours, Department of Conservation (DOC), Northland Health District Board (NHDB), Mania Health, NRC, Northland

Chamber of Commerce, RMA Practitioners Group, Forest and Bird, Iwi, Transition Towns, Whangarei Harbour User Groups

and others. Other smaller meetings have been held

It is noted that the Save our Harbour Group also had direct audience with WDC to discuss Whangarei wastewater in July 2010

and a more recent meeting was held on 25 August 2011. Meetings have also been held between WDC and DOC, NDHB, NRC

and Forest and Bird either individually with or as a group of interested parties. Meetings have been held on 22 July 2010, 16

May 2011 and 19 May 2011. Most of this correspondence is summarised in Appendix 5.

In regards to the consent review process being carried out by NRC, a meeting with DOC, NHDB was undertaken on 19 April

2011 to discuss the reasons for the review, the link between the review and the s127 application in respect of dealing with the

entire wet weather flow as a single component, the QMRA work and discharge standards. It is noted that representatives from

Forest and Bird and Save the Harbour were unable to attend.

In addition it is noted that for the wider public, the WDC has also consistently provided updates to the community in local

newspapers and on the WDC website as to the commitment of the WDC to wastewater improvements and the direction and

steps being undertaken to achieve this. A survey was undertaken at the A&P show of what the community‟s harbour water

quality focus is and it was noted most responses were associated with mangroves. Council has extended its Drain to Sea


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school education programme to include wastewater topics. Appendix 5 contains some of the media releases demonstrating this

information dissemination.

The need to consider wider harbour health issues has been a key issue in discussion with key stakeholder and community

groups. Council is currently reviewing options to manage wider harbour water quality issues. Development of this has been

incorporated in the consultation strategy, although it is envisioned that this will be separate to the wastewater projects to ensure

wastewater issues remain in focus.

Overall WDC has effectively engaged with the many parties interested in wastewater management in Whangarei and also those

with a particular interest in the Whangarei WWTP. WDC has demonstrated that the Council is listening and responding to

concerns and making best efforts to resolve issues relating to the effect of wastewater discharges. Generally the feedback

received regarding the project is that most parties are in support of the proposal and wish to see the improvements in place

quickly.


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6 ACTUAL AND POTENTIAL ENVIRONMENTAL EFFECTS

6.1 Effect on Limeburners Creek and Upper Whangarei Harbour

6.1.1 Public Health

Limeburners Creek is not known to be used for recreational or food gathering purposes. Moreover, industry, extensive

mangroves and the Port Road Bridge create a general physical barrier to public access. However, as the NIWA model shows,

the effects of the WWTP discharges extend well beyond the Upper Harbour. The Upper Harbour is subject to high public use

ranging in recreational activities such as; boating, waka ama, and downstream towards Onerahi, swimming and shellfish

gathering. While more overflows would generally be expected during winter months with higher average rainfall and higher

base flows, the system is also susceptible to the more intense summer storms, which occur during the period of more extensive

recreational use of the harbour.

As surmised from the Interim Decision, the main concern raised by the Commissioners was in regard to the effects of the

previous proposal on public health protection and that “direct discharges of untreated or minimally treated wastewater… should

be avoided… only then can public health effects be avoided”. The impact of wastewater discharges is generally a risk of

intestinal infectious illness as a result of ingesting contaminated water or consuming contaminated shellfish flesh.

Over the past year, WDC have evaluated a number of treatment options, with the intention of providing disinfection to all flows

through the plant, including the Extreme flows. Based on the options evaluation and further receiving environment

investigations discussed earlier in Section 4.1, WDC have committed to a $4.0M WWTP upgrade that will provide UV

disinfection to treat wastewater to a quality target of median1,500 Ecoli/100ml and 1.5 log reduction in rotovirus levels. In

addition, the proposed upgrade is to include an increase in treatment plant capacity to enable greater flow volumes to pass

through the trickling filters and secondary clarification processes, and by doing so, enhancing treatment to a greater volume of

flow received by the WWTP. The exact flows to pass through the upgraded WWTP have yet to be confirmed, although,

indications are that flows of up to 90ML/d may be technically feasible.

A number of studies carried out by PDP and NIWA have indicated that the level of treatment proposed will enable the MfE/MoH

recreational contact guidelines to be met downstream of Port Road Bridge, and for shellfish gathering standards to be met at

Onerahi. The QMRA, which has considered other contaminant sources such as network overflows and harbour background

quality as part of its assessment, confirms that the proposed upgrade option will significantly reduce the risk to public health.

However without any further network improvement works the risk of illness will remain in excess of what is considered

acceptable during winter. Therefore, in order to meet the acceptable water quality standards, WDC will need to carry out further

network improvement works in conjunction with the WWTP upgrades and as proposed through their Wastewater Improvements

Strategy. The QMRA has provided confidence that the treatment plant upgrade being proposed will be suitable to achieve the

goal of public health protection.

Any changes to the quality of the discharge from the WWTP would be able to be assessed and addressed through the review of

consent conditions which is currently also taking place.

6.1.2 Ecological Effects

The Commissioners concluded in the Interim Decision that “no compelling evidence was presented by any party, be it applicant,

submitters or NRC, that the discharge of untreated wastewater causes an adverse biological effect on the local ecology” (pg

32). Furthermore, it was noted, that the “effects appear to be largely secondary, relating to the use of ecology as a food source

i.e. harvesting of shellfish and catching of fish”. As a result of these conclusions, WDC have not undertaken any further

ecological assessments, and have addressed the public health concerns regarding shellfish gathering in Section 6.1.1 above.


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6.1.3 Social and Amenity Effects

As concluded in the Interim Decision and through recent consultation by WDC, untreated wastewater discharges are of great

concern to the community, particularly the social and amenity impact of the discharge. The main social impact in the past has

been harbour closures, where for periods of the year the community have been unable to carry out their recreational activities

within the harbour (waka-ama, shellfish gathering, swimming etc…). A degree of apathy towards signage and warnings about

the health risks of being in or near the water during harbour closures was indicated by some submitters and is concerning when

exceedences in critical water quality standards are known to have occurred, therefore emphasising the risk to public health from

untreated wastewater discharges.

WDC considers the proposed increase in treatment level of Extreme flow discharges, from that previously proposed, will

significantly improve the adverse social and amenity effects. By expanding the treatment capacity of the plant, more flows will

receive at least secondary clarification prior to UV disinfection, while a small portion of the larger flows that are likely to be

dominated by stormwater will receive primary settlement and UV disinfection. It is therefore considered that any conspicuous

oil, or grease films, scums or foams, or floatable materials in the discharge are unlikely to occur in the receiving environment.

Furthermore, it is noted that after reasonable mixing there is unlikely to be any conspicuous change in colour or visual clarity

especially as the Extreme flows will likely occur following storm events when the background water colour and clarify will be

significantly degraded as a result of stormwater runoff.

6.1.4 Cultural Concerns

As acknowledged during the 2010 hearing of the s127 application, the discharge of wastewater (untreated and treated) directly

to water is an affront to tikanga Maori. WDC have subsequently undertaken consultation with hapu/iwi on the matters

surrounding the WWTP upgrade and overall wastewater improvements strategy.

As a result of extensive consultation with the hapu/iwi, it is understood that iwi would like to see the system provide contact with

Paptuanuku (land). As discussed earlier, to assist in addressing hapu/iwi concerns in relation to land contact of the wastewater

the option of passing a greater volume of treated effluent through the existing wetland has been evaluated. It has been

determined that it is technically feasible to discharge up to 125 ML/d of tertiary treated effluent to the wetlands and is

considered by WDC to be environmentally preferable as the wetland may offer some further treatment before discharge into the

harbour. NRC has advised that proceeding with this option may require further changes to the existing consent and therefore

further consent hearings and is outside the scope of the s128 review. Therefore at this time, the current proposal is to continue

to work on a direct discharge to the Limeburners Creek (worst case), however, options to discharge the treated wastewater via

the wetlands or new wetland are still being investigated with NRC and iwi/hapu.

WDC‟s intention is that, the proposed upgrades, will go some way towards addressing iwi/hapu concerns, and have committed

to long-term engagement with iwi/hapu and other key stakeholders about future wastewater matters to be addressed as part of

the Wastewater Improvements Strategy and proposed Whangarei Harbour Integrated Management Strategy.

6.1.5 Financial Effects

As highlighted in the Interim Decision, “adverse impacts were directly felt not only by recreational fishermen but by also

commercial fishermen, especially shellfish harvesters” due to harbour closures triggered from wastewater discharges resulting

in restrictions in shellfish harvesting (pg 31). The outputs from the NIWA harbour model, has provided considerably assistance

to WDC, NRC and Northland Health in understanding the extent of discharges from the WWTP and sewer outfalls, which can

be used to improve public health notification processes and harbour closures. These notification process/procedures are

currently being worked on by WDC and Northland Health.

6.1.6 Odour Effects

The applicant considers that there will be no change to odour effects from the existing activity. That is, any effects from the

discharge of contaminants to air as odour are considered to be minor.


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6.1.7 Cumulative Effects

Based on the sewer modelling work undertaken by WDC, it is clear that there are multiple point-source discharges of untreated

wastewater from the network. The effects of these sewer overflows on the harbour water quality, in conjunction with the WWTP

extreme bypass flow and background water quality have been considered and addressed in the NIWA QMRA. Based on the

findings of this study, the QMRA has determined that carrying out the proposed upgrade works to the WWTP will not, on its

own, achieve an acceptable level of risk in terms of shellfish gathering in winter. Therefore other improvement works to the

sewer network and background quality levels are also needed to meet acceptable water quality standards. Although separate

to this application, WDC have shown commitment to undertaking further network improvements as part of Stage 2 of the works

programme, and these works will be further refined and agreed upon as part of the 2012 – 2022 LTCCP process.

6.1.8 Positive Effects

Although the volume of discharge to the WWTP will have increased as a result of this proposed consent change, the overall

quality of the discharge will be significantly improved due to the upgrade works WDC have committed to in their 2010-2012

LTCCP. As illustrated earlier in Figure 1-1, the overall quantity of pathogenic bacteria in the discharge to Limeburners Creek as

a result of the increased Extreme flow volume (57.4 – 140 ML/d), will reduce significantly to that currently authorised by the

existing consent as a result of the proposed tertiary treatment via UV disinfection. In addition, the results of the QMRA provide

confidence that the treatment plant upgrade being proposed will be suitable to achieve the goal of public health protection.

6.2 Submitters Concerns

As noted in the Interim Decision, a number of submitters to the hearing were opposed to wastewater being discharged to the

harbour, however the majority appeared to be opposed only to the level of treatment previously proposed (primary treatment

only). As acknowledged earlier, iwi are opposed to waterway discharges with a preference to land application, although some

tangata whenua submitters did recognise that while not ideal, waterway discharge could be acceptable providing a sufficient

level of treatment was provided, including passage through a wetland. It was therefore concluded by the Commissioenrs that

“adoption of an appropriate level of treatment would enable issues raised by most submitters to be addressed as part of this

consent application”.

WDC trust that the increased level in treatment being proposed as part of the WWTP upgrade option chosen, will assist in

addressing the majority of submitters concerns. Indications from the community, key stakeholders and iwi as part of the

extensive consultation undertaken suggest this is the case, although it is noted that WDC are continuing to work with hapu/iwi

and NRC to further investigate increasing discharges of the treated wastewater through the wetlands rather than direct to

Limeburners Creek.

6.3 Mitigation

Mitigation measures proposed by the applicant include a significant upgrade to the WWTP, including:

An upgrade to the existing UV disinfection system to enable flows of up to 57.4ML/d to be disinfected;

Installation of a new UV disinfection system to tertiary treat Extreme flow bypasses prior to discharging to Limeburners

Creek;

An upgrade of the WWTP process to enable primary treatment and secondary clarification for a portion of flows greater

than 57.4ML/d;

Other mitigation measures being carried out by WDC in the wider city area relating to overall wastewater improvements,

include:

Extensive I/I investigations to minimise stormwater infiltration into the network (ongoing);


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Upgrades to Hatea pump station to store and treat overflows (commencing);

Extensive sewer network modelling to assist council in confirming a long-term network improvement works programme

that would require resolution by Council when preparing the 2012-2022 LTCCP to provide the additional funding likely

to be required.

6.4 Monitoring

It is anticipated that extreme flow discharges will continue to be monitored during discharge events along with a revised

monitoring programme in the receiving environment. This monitoring programme will be developed in conjunction with design

of the treatment process and NRC‟s consent review, and is intended to monitor improvements resulting from the upgrade.

As discussed in Section 4.2, WDC propose monitoring against effluent quality standards at the plant outlet set out in Table 4-3,

for specific events with reference to the Extreme flow bypass periods. Monitoring for the remainder of the consent requirements

will proceed as normal. Furthermore, WDC will seek to establish a range of UV dose requirements for the different levels of

flow passing through the system based on UVT sampling work currently being undertaking


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7 ALTERNATIVE METHODS

The Wastewater Improvement Strategy identifies additional measures that will assist in achieving the wastewater improvement

outcomes identified. These other methods can in a broad sense be viewed as alternatives to this project however; they are

best applied as supporting measures. Such a measure is the Inflows & Infiltration Management. This is a measure that has

extensive application and considerable cost attached, and achieving full compliance unlikely given the number of variables and

the condition of the wastewater infrastructure (both private and public). Despite the noted difficulties this measure continues to

be applied. However, storage and treatment of wastewater is viewed as a more reliable method of addressing wastewater

concerns at this time.

Council is investigating different technologies to help reduce the impact of wet weather on wastewater flows. Pressure sewer

systems have been highlighted as a possible alternative to gravity sewers in appropriate locations and a pressure sewer policy

was adopted at the December 2010 Council meeting.


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8 CONCLUSION

It is concluded that this revised proposal does not significantly differ from the scope contained in the 2008 consent application

for Extreme flow discharges from the WWTP. Following a number of investigations, options assessments and consultation,

WDC now propose that all flows will receive UV disinfection, and through increasing WWTP capacity, a greater portion of flow,

will undergo secondary clarification prior to discharge. The above proposal provides a greater level of treatment than previously

applied for.

A number of investigations have been carried out to better understand the effects of the discharge on the harbour water quality.

These have been discussed in detail in Section 4 above and provide support for the proposed upgrade option. This proposal

reflects the intents and purposes of the Wastewater Improvement Strategy (June 2010).

Extensive consultation has been undertaken, and WDC anticipate the revised proposal has assisted in addressing the concerns

of most submitters, at least at this time. A consultation plan has been implemented to direct WDC on engaging the community

in ongoing participation in wastewater matters and harbour water quality management.


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9 REFERENCES

Arcus C.D. (August 2010) Interim Decision of Hearings Commissioners - Application to Change Condition 16 of Resource

Consent 4352(02), Relating to Discharge of Wastewater from Whangarei Wastewater Treatment Plant Kioreroa Road into

Limeburners Creek Whangarei Harbour, Northland Regional Council.

Arcus C.D. (July 2011) Procedural Decision and Directions of Hearings Commissioners - Application to Change Condition 16 of

Resource Consent 4352(02), Relating to Discharge of Wastewater from Whangarei Wastewater Treatment Plant Kioreroa Road

into Limeburners Creek Whangarei Harbour, Northland Regional Council

AWT Water Ltd (December 2009) Application to Change Condition 16 of Consent 200404352(02): Supporting Documentation

and AEE, prepared for Whangarei District Council.

AWT Water Ltd (May 2010a) Okara Park Pump Station Emergency Discharge: Resource Consent Application and Supporting

Information, prepared for Whangarei District Council.

AWT Water Ltd (December 2010)b Whangarei Wastewater Treatment Plant, Improvements of peak flow treatment, Peer

Review of Stormflow Treatment Options Assessment Report, memorandum prepared for Whangarei District Council.

AWT Water Ltd (March 2011a) Re: Whangarei WWTP Peak Flow UVT Review, letter report prepared for Whangarei District

Council.

AWT Water Ltd (June 2011b) Whangarei WWTP Peak Flow Treatment Disinfection Options Assessment Draft, report prepared

for Whangarei District Council.

AWT Water Ltd (August 2011c) Whangarei WWTP Peak Flow Treatment Option Assessment, report prepared for Whangarei

District Council.

Brian T. Coffey and Associates Limited (August 1999) Whangarei Wastewater Treatment Plant: Assessment of Effects of

Discharge to Limeburners Creek, Whangarei Harbour

Harrison Grierson (September 2002), The Discharge of Effluent from Whangarei Wastewater Treatment Plant to Limeburners

Creek: Resource Consent Applications and Assessment of Effects on the Environment, prepared on behalf of Whangarei

District Council.

McBride, G. and G. Reeve (June 2011) Predictions of Human Health Effects Associated with Wet Weather Flows in Whangarei

– Effects on primary and secondary water contact, and consumers of raw shellfish, NIWA report prepared for Northland

Regional council, NIWA Client Report No HAM2011-069.

MfE and MoH (June 2003) Microbiological Water Quality Guidelines for Marine and Fresh Water Recreational Areas.

MWH (November 2010) Storm Flow Treatment Option Assessment, prepared for Whangarei District Council.

NRC (December 2010) Northland Regional Coastal Plan.

NRC (May 2004) CON200404352

NRC (June 2011) Progress Report – Whangarei District Council Main Wastewater Treatment Plant Resource Consent.

OPUS (August 2011) Whangarei District Council Hatea Storage Tank Project – Resource Consent Application, prepared on

behalf of Whangarei District Council.

Poynter & Associates Environmental Ltd (January 2008) Okara Pump Station & Butter Factory Lane Emergency

Wastewater/Stormwater Discharge: Ecological Effects Report

PDP (November 2011) Extreme Flow Bypass – Addendum to Discharge Dilution Investigation, letter report prepared for

Whangarei District Council.


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Reeve, G. (February 2011) Whangarei Harbour Hydrodynamic and Dispersion Model – Contaminant Dispersion Simulations

Supplementary Scenarios, NIWA report prepared for Whangarei District Council, NIWA client report HAM2011-006.

WDC (June 2010a) Waste & Drainage Wastewater Strategy, prepared by VK Consulting Environmental Engineers

WDC (July 2010b) Whangarei City Wastewater Reticulation: Service Level Improvements 2011 – 2019, Infrastructure and

Services Committee Meeting Agenda Item.

WDC (October 2010c) Whangarei District Pressure Sewer Policy.

WDC (November 2010d) Whangarei Wastewater System Improvements – Interim Report.

WDC (February 2011a) Whangarei Wastewater System Improvements – Interim Report.

WDC (May 2011b) Whangarei WWTP – Whangarei Wastewater System Improvements Interim Report May 2011, letter

prepared for NRC.

WDC (July 2011c) Whangarei Wastewater Treatment Plant: Extreme Wet Weather Flows, Infrastructure and Services

Committee Meeting Agenda Item.

WDC (August 2011d) Whangarei Wastewater Treatment Plant: Extreme Wet Weather Flows, Infrastructure and Services

Committee Meeting Agenda Item.

APPENDIX 1

EXISTING CONSENT

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-1-Existing-consent.pdf

APPENDIX 2

WDC – WHANGAREI WASTEWATER SYSTEM IMPROVEMENTS

INTERIM REPORTS

Interim Report May 2011

Interim Report February 2011

Whangarei WWTP Resource Consent Condition 3: Upgrade of UV Disinfection, February 2011

Interim Report November 2010

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-2-Interim-report-2011.pdf

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-2-Interim-reports-2010.pdf

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-2-Interim-report-May-2011.pdf

APPENDIX 3

WDC – INFRASTRUCTURE AND SERVICES COMMITTEE MEETING AGENDA ITEMS

Agenda Item – 10 August 2011

Agenda Item – 1 July 2011

Agenda Item – 17 May 2011

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-3-agendas.pdf

APPENDIX 4

TECHNICAL REPORTS

NIWA, Predictions of Human Health Effects Associated with Wet Weather Flows in

Whangarei, June 2011.

NIWA, Whangarei Harbour Hydrodynamic and dispersion model – Contaminant dispersion

simulations: Supplementary Scenarios, February 2011.

PDP, Extreme Flow Bypass – addendum to Discharge Dilution Investigation, October 2010.

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Predictions-of-human-health-effects.pdf

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-4-contaminant-dispersion-model.pdf

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Extreme-flow-bypass.pdf

APPENDIX 5

CONSULTATION DOCUMENTATION

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-5-Communications-Plan.pdf

APPENDIX 6

WDC QUALITY MANAGEMENT SYSTEM CERTIFICATION

http://wdc.govt.nz/WaterandWaste/Wastewater/Documents/WWTP-Application-Appendix-6-Certification.pdf