greater wellington regional council · 2009. 9. 17. · to peer review the applications by...

Greater Wellington Regional Council

REPORT: TECHNICAL REVIEW OF WELLINGTON CITY COUNCIL'S APPLICATION FOR AIR DISCHARGE PERMITS – DEWATERING & CENTRATE PLANT, AND DISPOSAL OF SLUDGE CONTAMINANTS

Report to Council FINAL Version 6 April 2008

The SKM logo is a trade mark of Sinclair Knight Merz Pty Ltd. © Sinclair Knight Merz Pty Ltd, 2006

Greater Wellington Regional Council

REPORT: TECHNICAL REVIEW OF WELLINGTON CITY COUNCIL'S APPLICATION FOR AIR DISCHARGE PERMITS: DEWATERING & CENTRATE PLANT, AND DISPOSAL OF SLUDGE CONTAMINANTS

Final Version 6 April 2008

Sinclair Knight Merz Level 12, Mayfair House 54 The Terrace PO Box 10-283 Wellington New Zealand Tel: +64 4 473 4265 Fax: +64 4 473 3369 Web: www.skmconsulting.com

LIMITATION: This report has been prepared on behalf of and for the exclusive use of Sinclair Knight Merz Limited’s Client, and is subject to and issued in connection with the provisions of the agreement between Sinclair Knight Merz and its Client. Sinclair Knight Merz accepts no liability or responsibility for or in respect of any use of or reliance upon this report by any third party outside of this specific resource consent process.

Report: Technical Review of Application for Air Discharge Permits – Dewatering & Centrate Plant, and Disposal of Sludge Contaminants

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Contents

1. Summary 1 1.1 Introduction 1 1.2 Location, Topography, and Meteorology 1 1.3 Sources of Odour within and outside of Carey's Gully 2 1.4 Key Odorous Contaminants Generated by Activities in

Carey's Gully 3 1.5 Evaluations of Carey's Gully Odour Emissions Carried Out

Since 2002 3 1.5.1 Sinclair Knight Merz Limited 4 1.5.2 GHD Limited and WaterCare Services Limited 5 1.6 Evaluation of Recent Odour Complaints 7 1.6.1 Thursday 6 September 2007 7 1.6.2 Wednesday 19 September 2007 8 1.7 Evaluation of Dewatering and Centrate Plant 9 1.7.1 Skip Bay Odour Emissions 10 1.7.2 Odour Emission from Skips in Transit 11 1.7.3 Odour Emission from Discharge of Centrate Black Boxes Aeration Air

to Atmosphere 12 1.7.4 Proposed Odour Management Plan 13 1.8 Landfilling of Dewatered Sludge 13 1.9 Tree Planting Programme 14 1.10 Health Impact of Odorous Contaminants 15 1.11 Conditions of Consents if Granted 16 1.11.1 Operation of the Dewatering and Centrate Plant 16 1.11.2 Landfilling of Sludge Contaminants – Discharge of Contaminants into Air 20

2. Introduction 22 2.1 Applications for Resource Consents 22 2.2 Complaints about Offensive or Objectionable Odour 23 2.3 Issues in Respect to the UWI Site and the Carey's Gully Complex 23

3. Section 92(1) Request by GWRC 24

4. Review of Application Documents and related Information 25 4.1 Introduction 25 4.2 Additional Information/Clarification 25 4.2.1 In Respect to the Sludge Dewatering and Centrate Plant 25 4.2.2 Down Wind Odour Assessments 26


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4.2.3 Reports Prepared by GHD and Watercare 26 4.3 Actual Activities to which the Application Relates 27

5. Sources of Odour within Carey's Gully 28 5.1 Location and Current Activities 28 5.2 Topography and Meteorology of the Carey's Gully Area 30 5.3 Sources of Odour within Carey's Gully 30 5.4 Key Odorous Contaminants Generated by Activities in

Carey's Gully 31 5.5 Sources of Odour outside of Carey's Gully 33

6. Evaluations of Carey's Gully Odour Emissions Carried Out

Since 2002 34 6.1 Introduction 34 6.2 Sinclair Knight Merz Limited 34 6.2.1 Introduction 34 6.2.2 Complaints and Comments from Residents 34 6.2.3 Qualitative Ambient Air Odour Assessments 35 6.2.4 Odour Sources within Carey's Gully 38 6.3 GHD Limited and WaterCare Services Limited 41 6.3.1 Carey's Gully Landfill 42 6.3.2 Dewatering and Centrate Plant 43 6.3.3 Composting Plant 45 6.3.4 Odour Mapping of Carey's Gully 49

7. Evaluation of Recent Complaints about Odour in Carey's Gully 52 7.1 Introduction 52 7.2 Thursday 6 September 2007 52 7.3 Wednesday 19 September 2007 53

8. Evaluation of Dewatering and Centrate Plant 55 8.1 Dewatering & Centrate Plant 55 8.2 Process Description: Dewatering Plant 56 8.3 Process Description: Centrate Treatment Plant 58 8.4 Process Control and Maintenance - Both Plants 60 8.5 Plant Improvements and Refurbishing 60 8.6 Adjacent and Down Wind Odour 61 8.6.1 Introduction 61 8.6.2 SKM 2002 Evaluations 62 8.6.3 GDH and WaterCare 2005 Evaluations 63 8.6.4 SKM Visit 30 August 2007 64


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8.6.5 Recent Odour Complaints 65

9. Dewatering and Centrate Plant: Adoption of the 'Best Practicable Option' of Odour Emission Prevention and Control 66

9.1 Introduction 66 9.2 Dewatering Plant Process Controls and Safeguards. 66 9.2.1 Raw Sludge Transfer from Moa Point and Handling at Dewatering Plant 66 9.2.2 Sludge Storage at Dewatering Plant 66 9.2.3 Sludge Dewatering Equipment 67 9.2.4 Transfer of Skips to and from Composting Plant 68 9.2.5 Containment and Ventilation to Odour Control Equipment 72 9.2.6 Odour Control Biofilter 73 9.2.7 Time Lines for Processing of Sludge and removal of Skips 74 9.2.8 Centrate Plant 74 9.2.9 Housekeeping 76 9.2.10 Use of Odour Neutralising Agents 76 9.2.11 Emission and Monitoring of Faecal Coliforms and Salmonella 76 9.2.12 Proposed Odour Management Plan 77

10. Landfilling of De-watered Sludge 78 10.1 Introduction 78 10.2 Proposed Method of Disposal to Landfill 78 10.3 Effects on the Air Environment from Landfilling Dewatered Sludge 79

11. Review of Submissions 81 11.1 Principal Issues Raised by Submitters to Notified Applications 81 11.2 Statement for Pre-Hearing Meeting 85 11.3 Health Impact of Odorous Contaminants 88

12. Suggested Conditions of Consent 99 12.1 Operation of the Dewatering and Centrate Plant 99 12.1.1 Relevant Conditions on Existing Permits or Conditions having Similar Intent 99 12.1.2 Suggested New Conditions or Matters to be Address by New Conditions 101 12.2 Landfilling of Sludge Contaminants – Discharge of Contaminants

into Air 102


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1. Summary

1.1 Introduction Sinclair Knight Merz Limited was commissioned by the Greater Wellington Regional Council (GW) to peer review the applications by Wellington City Council for air discharge permits for processing of sewage sludge and disposal of sludge contaminants by landfilling carried out within Carey's Gully.

A significant number of complaints about objectionable or offensive odour continue to be made to Greater Wellington Regional Council and (presumably) to Wellington City Council by residents of Brooklyn, Mornington, Kingston, Happy Valley, and Owhiro Bay. Many of these complaints implicate odour sources from within Carey's Gully, of which the Sludge Dewatering and Centrate Plant is one potential odour source.

The Dewatering and Centrate Plant is located within a physically defined area within Carey's Gully. Carey's Gully is owned by the Wellington City Council.

Carey's Gully is accessed by members of the public but their presence is transitory. Employees of other activities are present on a generally continuous basis throughout their working day. Some of these employees may be sensitive to excessive odours generated by the activities carried on (including from their own activities) and, if so, warrant protection from exposure to excessive odour irrespective of the source.

1.2 Location, Topography, and Meteorology An aerial photograph of Carey's Gully is presented as Figure 1.

In respect to Figure 1, north is up the page. Immediately to the north of the Dewatering Plant is the area used to stockpile compost etc. by Living Earth Limited. To the east of the Dewatering and Centrate Plant is the Stage 2 (historical) landfill. In addition, and not shown on the aerial photograph, are two landfill gas flares. The centrate & landfill leachate sewer runs down the Landfill Road valley to join up with the main sewer on Happy Valley Road.

The topography of the area is complicated by a series of roughly north-south trending valleys separated by steep ridges. Housing developments such as along Mitchell Street, Karepa Street, and Ashton Fitchett Drive, and in the Mornington and Kingston areas, are also located on ridges and their slopes. In some areas such as Happy Valley and lower Landfill Road, development is within a valley system.



Figure 1: Aerial Photograph of Carey's Gully (from MWH AEE April 2007)

Prevailing winds are northerly and southerly trending but, in places, the complicated local topography modifies the wind flow patterns, especially during relatively light wind conditions. Katabatic drainage (cold air flow down slopes at night when wind conditions are generally light and skies partially cloudy to clear – radiation temperature inversion conditions) is common, and is especially pronounced during autumn, winter, and spring. The direction of this cool air flow is frequently different to the synoptic air flow (normal wind direction above the immediate influence of the terrain).

During southerly wind conditions the air mass blowing in from the southern coast will have very low natural odour, not having the opportunity of mixing with air over extended vegetated areas and urbanised areas. In residential areas located close to the south coast during light southerly conditions, the air is virtually pristine and any odour transported from Carey's Gully may be immediately obvious to exposed residents if the odour is of sufficient intensity to be above the odour threshold. In this case the contrast between pristine air and slightly odorous air may well be marked.

1.3 Sources of Odour within and outside of Carey's Gully There are five activities with Carey's Gully that potentially have significant odour potential, either individually or collectively (cumulatively). They are:



Disposal of refuse including odour from leachate ponds;

Processing of sewage sludge piped from the Moa Point sewage treatment plant (Dewatering and Centrate Plant managed by United Water Industries (UWI));

Composting of green wastes, dewatered sewage sludge, and other organic materials (Co-composting Plant managed by Living Earth Limited);

Discharge of treated centrate (separated liquid portion of the sewage sludge), landfill leachate, and waste water from the composting plant to the dedicated sewer; and

Failure of the landfill gas collection systems and failure of the landfill gas flares (flares are managed by Novogas Limited).

There are also sources of odour outside Carey's Gully that could cause odour nuisance to residents. Of these, sewage odours discharging from sewerage system vents and from pumping station vents would be the most likely cause of odour nuisance from activities outside of Carey's Gully.

1.4 Key Odorous Contaminants Generated by Activities in Carey's Gully Odour is generated by decomposition of the organic content of sewage sludge and from its wastewater content; during composting of sludge and bulking agents; and from decomposition of refuse. Soluble sulphides in liquid wastes also generate hydrogen sulphide under certain conditions. Proteins and urea are the source of most odorous contaminants containing nitrogen such as amines, and proteins are the source of most of the sulphur-containing contaminants generated such as hydrogen sulphide, mercaptans, and organic sulphides. Carbohydrates, and fats and oils, are also sources of odorous contaminants.

Ammonia is a common odorous contaminant especially during the early stages of composting and if vegetation wastes go anaerobic before landfilling, but the smell of ammonia is usually only apparent close to the source. Amines, which have a fishy ammonia-like odour, can be detected in very low concentrations in air and may be emitted from all activities at Carey's Gully depending on circumstances. Hydrogen sulphide and organic sulphur compounds have offensive odours in very low concentrations in air. Their odour ranges from rotten eggs (hydrogen sulphide) to decayed vegetables including decayed cabbage, garlic, and skunk-like odours. These compounds are mainly generated under anaerobic conditions. Volatile fatty acids are typically generated by fermentation of vegetable matter such as grass, hay, and leaves under anaerobic conditions. Their smell ranges from pungent (acetic acid, which is the smell of vinegar) to the smell of stale perspiration.

1.5 Evaluations of Carey's Gully Odour Emissions Carried Out Since 2002 Two specific evaluations of odour emissions from activities with Carey's Gully have been carried out since 2002. Additional to these are numerous routine and complaint-specific evaluations carried out by officers of Wellington City Council and Greater Wellington Regional Council.



1.5.1 Sinclair Knight Merz Limited Sinclair Knight Merz Limited (SKM) was commissioned by Wellington City Council (WCC) in early April 2002 to evaluate odour emissions from activities within and outside of Carey's Gully. These evaluations aimed, amongst other things, to positively identify source(s) of odour observed down wind; to locate and assess any significant odour sources outside of Carey's Gully that could be confused with odours originating within Carey's Gully; and to evaluate activities within Carey's Gully in respect to odour generating potential. Evaluations were carried out from 17 April to 7 August 2002, and sporadically thereafter until completion of the Report.

During the period of our evaluation, the Mitchell Street area was the most affected by odours about which residents complained (or commented) about and these complaints mainly occurred during light southerly winds1 (generally south-south-westerly through to south-westerly). Complaints from Mornington and Kingston could not easily be related to wind direction as most of the complaints made to SKM from these areas occurred during virtually calm conditions or during periods of light variable winds. However, we believe that some of these complaints related to odours being transported from Carey's Gully, but we also suspect that on occasions an odour source to the south of the complainants may have been responsible. Unexpectedly, relatively few complaints to SKM were made from residents in the Happy Valley Road/Western Island Bay/Owhiro Bay area. A part of the reason may be that the remedial and upgrading work carried out on the Dewatering & Centrate Plant and on the centrate sewer, which was substantially completed towards the end of the evaluation period, had a positive effect for sensitive development in these areas. Only on a few occasions did our investigations correspond with odours that residents complained about.

We also evaluated odour within Carey's Gully and we made recommendations as to how the activities that had more than minimal objectionable odour potential could be improved.

We concluded that the two principal sources of odours complained about during the evaluation period were the Dewatering & Centrate Plant ("sewage", "sewerage", "cabbage water", and possible some other descriptors) especially earlier during the evaluation period, and the Composting Plant ("earthy" odours, and possibly some other descriptors including "sewerage"). However, since a major component of the compost is sewage sludge, the source of sewage sludge-type odours down wind from the Dewatering Plant and the Composting Plant could easily be confused. We believed that during the evaluation period, the Composting Plant was the most likely source of many of the odours complained about, that the Dewatering and Centrate Plant was a lesser source, and that landfilling activities were a minor contributor to public complaint outside of Carey's Gully (if these activities contributed at all, except possibly cumulatively).

1 Complaint/comment about objectionable odour during strong wind conditions was limited to one occasion during the evaluation period.



1.5.2 GHD Limited and WaterCare Services Limited In 2004 GHD Limited were contracted by Wellington City Council to carry out odour emissions monitoring at Carey's Gully. In November 2004 GHD contracted Watercare to develop and undertake an odour sampling and odour mapping programme.

GHD's commission included identification of likely odour sources within Carey's Gully and the monitoring of these to establish source strength and offensiveness, and mapping the site to determine local influence to the odour sources and to identify any unsuspected odour sources. Odour emission monitoring represented the first part of re-focussing of efforts on the management of odours arising from Carey's Gully by the Wellington City Council. GHD's 2005 Final Report builds on WaterCare's report, and other evaluations including a review of site activities. The activities evaluated were the Dewatering and Centrate Plant site, the Southern Landfill sites, closed landfill sites, and the Co-composting Plant site. The review of some activities such as comments about the Composting Plant's building "supply" and extraction ventilation fans and positive pressure within the building are, we believe, contested by LEL.

WaterCare's programme consisted of measuring odour intensity (concentration), odour offensiveness, and chemical fingerprinting of sampled odour sources. The monitoring programme was carried out in February and March 2005.

Odour samples taken on three days in February 2005 indicated that the Dewatering and Centrate Plant wet well and its bioreactors (Black Boxes), and the Dewatering Plant Skip Bay, had much higher odour concentrations (odour units per m3 of air sampled) than the other Carey's Gully sources (landfilling activities and operation of the Composting Plant). However, presuming that the sample odour concentrations are realistic, the concentration of odour at source does not indicate the rate of odour emission. For example, the very high wet well odour concentration relates to a very small volumetric flow from the wet well lid to atmosphere, thus only represents a moderate rate of odour emission. Another example is the Dewatering and Centrate Plant Skip Bay odour concentration in relation to the rate of odour emission of this foul air to atmosphere. Given effective ventilation of the Skip Bay to the odour control biofilter and adequate building tightness, this odour source is only important when the Skip Bay doors are open. It is also interesting to note that during various visits by SKM personnel to the plant during 2002, the odour in the Skip Bay and immediately outside of the Skip Bay when a door was open had been relatively mild. This does not mean to say that under abnormal circumstances the odour will not be very high – the very high odour concentrations recorded in February 2005 (if valid) suggests sludge of particularly poor quality (very anaerobic).

The concentration of odour determined in the Black Boxes ventilation stream, if valid, was high, but when related to an assumed rate of ventilation of 170 m3/hour only results in a moderate odour emission. However, if the rate of ventilation of the Black Boxes was much higher during testing than assumed, then rate of emission of odour would be very much higher than indicated.



GHD also calculated the rate of odour emission (odour units per second) based on the average odour sample concentrations multiplied by the assessed or assumed volumetric flow rate of odorous air to atmosphere. This indicated that the Dewatering and Centrate Plant had a relatively minor contribution to overall odour emission from facilities surveyed in Carey's Gully on the days sampling was carried out in February 2005 based on a number of assumptions. The rate of odour emission from the Dewatering Plant Skip Bay when a roller door is opened could not be calculated or estimated by GHD but this may at times be significant, especially if the door was left open for an extended period when sludge quality is poor. The rate of emission from the Composting Plant building was high on the days sampled based on the contested assumption of positive pressure within the building (however, it may give a good indication of impact down wind if a building roller door is opened especially during windy conditions). The rate of odour emission from the Composting Plant's biofilter (which was high) may give a good indication of odour nuisance potential down wind especially during light wind conditions when air mixing is relatively poor. The calculated rate of odour emission from the landfill face was higher than calculated for the Dewatering and Centrate Plant but much less than that calculated for the Composting Plant.

GHD commented that odour mapping of the site to determine the local influences of odour sources and to identify any unsuspected odour sources based on hydrogen sulphide as the key contaminant was of very limited value. Only relatively low levels of hydrogen sulphide were detected and those only very close to sources (LEL biofilter and the Centrate Plant wet well), and it dispersed very quickly. The issue was identified by GHD as steady breezes on the monitoring days were probably partially responsible but also access to some areas (for example, close to the tip face) was not available for safety reasons. WaterCare noted that odour mapping was attempted on three days in March 2005. WaterCare's file notes are presented in their report. They note amongst other things that the landfill tip face odour was strong over the entire site down wind (south) of the tip face and persisted as far as Carey's Gully administration buildings. WaterCare also noted that a strong landfill leachate odour was detected from the leachate stream and pond area, and this odour could be detected as far as the road between the Composting Plant and the refuse transfer station.

Much of the information provided in the Watercare and GHD reports is very useful and generally gives a good indication of operation of the activities in Carey's Gully over the period sampling was being carried out (3 days in February for odour sampling, and three days in March for odour mapping).

Only a very limited number of odour samples were taken during the survey period thus sampling covers only limited time duration. This is understandable given the cost of odour sampling and analysis and the logistics of the exercise (including transport of odour drum to Auckland for analysis within 30 hours of sampling, and that the number of samples that each odour assessment team can process in a day is around 4 to 5).

The issue of degradation of samples in transit before analysis is carried out is not addressed in the reports. Certain contaminants rapidly degrade in the presence of oxygen in sampled air. Degradation



of Carey's Gully odour in air sample constituents is liable to change the odour of the sample before olfactometry is carried out (the odour concentration may not change, may increase or may decrease), and the concentration of some contaminants in an odour sample will decrease before mass spectrometry analysis was carried out. This issue should be kept in mind when interpreting odour and other sampling results.

It is unfortunate that odour sampling was not supplemented by good observational data – the actual perceived odour character and strength of sources at various distances down wind in Carey's Gully at the time source sampling was being carried out. Perceived odour down wind then could be correlated with measured odour concentrations and assumed rates of odour emission. The descriptions of the odour of samples were provided by the assessment panel in Auckland, not by the testing and support personnel. However, we appreciate that assessing odour qualitatively down wind of activities in Carey's Gully is not easy because of difficult topography and meteorology. In addition, odour comprising a number of contaminants in various concentrations may have a different smell to the individual components, unless one contaminant such as hydrogen sulphide dominates. The smell may also change as distance increases from the source (with increasing dilution) depending on the odour thresholds and concentrations of the components.

In at least one case (the Black Boxes), the odour sampling results and the concentration of contaminants in sampled odour are difficult to understand.

With the exception of the Dewatering and Centrate Plant wet well, no comment is provided by GHD as to whether or not operations at the time of odour sampling was normal operation, or if not normal, what the circumstances were.

It is essential that when sampling is undertaken that source flow rates are also accurately determined as far as practicable to do so.

1.6 Evaluation of Recent Odour Complaints SKM has been advised about two series of complaints about activities in Carey's Gully since we were commissioned to assist GW with the applications for resource consent.

1.6.1 Thursday 6 September 2007 GW received nine complaints about offensive odour from Carey's Gully between 5.20 and 7.30pm. Evaluations by an officer were carried out in the Mitchell Street area of Kowhai Park (no odours noted); at Ridgeway School, Mornington (no odours noted); but in two locations in Kingston a strong sewage/compost smell and a strong biofilter-type odour was continuously present. The officer concluded that odour at these Kingston residential locations was verging on objectionable or offensive. The officer also noted that the odours were a definite Composting Plant smell, and another distinct but unidentifiable odour.



The officer then assessed odour within Carey's Gully to assist identifying the source of the Kingston odours. A very strong sludge-type smell was noted outside of the Dewatering and Centrate Plant but no malfunctions were noted but there was a small quantity of spilt sludge on the concrete pad outside one of the doors. The odour from the active landfill area was moderate from landfill gas and landfill leachate, but no refuse-type odours were detected, and daily cover seemed adequate. Outside of the Composting Plant there was a very strong sweaty sock-type odour from the biofilter.

The Composting Plant biofilter may have been the dominant odour source within Carey's Gully given its high rates of ventilation, but if the area was subject to a radiation temperature inversion during the complaint period then the consequent cold air drainage should have carried odorous air from the sludge Dewatering Plant and from the Composting Plant down Landfill Road to Happy Valley Road (and this odour should have been observed by the investigating officer). Given the location of Stage 3 of the landfill it is unlikely that landfill face and leachate odour would be a significant contributor. Since we do not understand the mechanism of odour being carried from Carey's Gully to Kingston during light southerly wind conditions and during radiation temperature inversions, we cannot indicate from information provided the likely source of the Kingston odours with any certainty.

1.6.2 Wednesday 19 September 2007 GW received six odour complaints from Brooklyn residents between 3:20 pm and 3:37 pm about offensive odour from Carey's Gully. Two GW officers investigated these complaints and conducted some odour surveys throughout Brooklyn, but could not detect any significant odour (perhaps some small whiffs) until they left the area at 4:55 pm.

From about 5.30 pm onward, 26 complaints were officially recorded but there could have been 35 complaints when accounting for direct contact made with one of the investigating officers. Officers investigating this series of complaints noted objectionable or offensive odour at and around Mitchell Street, and then noted odour opposite the Brooklyn Bagel factory that was also judged objectionable or offensive. The officer stated that the character of the odour was consistent with odours he had previously observed from the Composting Plant.

Two officers noted very strong odour behind the Composting Plant during a light but constant wind from a south-easterly direction, and that the odour was the same as that they had independently experienced outside of Carey's Gully. The officers then individually completed a 360 degree walk-around of the plant in opposite directions. The reporting officer noted that he also detected the strong compost/sweaty sock type odour all of the way along the eastern boundary of the plant. However, at the south-east corner of the plant when the wind was blowing from the direction of the Dewatering and Centrate Plant and the Stage 2 landfill area no odour could be detected. At the front entrance to the Composting Plant and along the road that separates landfills Stage 2 from Stage 3 an intermittent landfill gas odour was noted. The reporting officer did not feel that it was contributing greatly to the odours observed off-site.



The officers noted a strong pungent sewage type smell in the immediate vicinity of the Dewatering and Centrate Plant, but this was not observed during the earlier observations from the south-east corner of the Composting Plant. The Dewatering and Centrate Plant was not considered to be a major odour source that evening.

It appears that the cause of odour nuisance that evening was primarily due to the operation of the Composting Plant and may have been connected with the operation of the plant’s biofilter. From comments provided by the reporting officer, it seems unlikely that the odour of landfill gas and the odour observed close to the Dewatering and Centrate Plant as reported were significant contributors to odour nuisance outside of Carey's Gully on that occasion.

1.7 Evaluation of Dewatering and Centrate Plant The Dewatering Plant was installed to de-water liquid sludge pumped through a dedicated underground pipeline from the new wastewater treatment plant at Moa Point. The Centrate Plant is a more recent addition to treat the water (centrate) removed from dewatering of sludge before it is discharged into the sewer. The Dewatering and Centrate Plant operates for seven days per weeks (subject to sufficient sludge being available) for all year except on four public holidays.

Following dewatering, sludge is continuously and automatically transferred to one of eight skips in the Skip Bay to a pre-determined level, followed by filling of the next skip. Full skips are transferred by truck by LEL to the Composting Plant via the weigh bridge at the Kiosk, emptied, and returned to the Dewatering Plant Skip Bay. We understand that skips containing sludge are organised to be transferred to the Composting Plant on a seven day/week basis except for the public holidays referred to above.

The processing time for sludge is stated as being between 18 and 72 hours. UWI indicates that the optimum time for processing sludge is 18 hours and the average processing time is estimated to be less than 24 hours. Time additional to 18 hours is when the filled skips are not moved promptly to the Composting Plant. In addition, it is possible that a skip can stand overnight or, on rare occasions, over a weekend. UWI accept that odour emissions increase when filled skips are not removed promptly (although quantifying this is difficult) but the key issues are ensuring filled skips are removed to the Composting Plant as soon as possible and they do not remain in the Skip Bay overnight and certainly not over a weekend.

The Centrate Plant treats centrate to reduce suspended solids and biochemical oxygen demand before centrate is discharged into the sewer.

Ventilation air from activities in the Dewatering Plant Building that are highly odorous, and from the raw sludge tanks and from the Centrate Plant pump station (wet well), is extracted to a very effective biofilter for odour control.



The Dewatering and Centrate Plant is highly automated and can largely function unattended for long periods of time. Automatic control is via a programmable logic controller (PLC) that receives input signals from a large range of process sensors. While the plant is not continuously manned, input into the plants functions can also be made when the plant operator is present, and made from the Moa Point Wastewater Treatment Plant control room.

The areas of concern that we have are as follows:

That on occasions, the processing time from receipt of raw sludge to transfer of de-watered sludge to the Composting Plant somewhat exceeds 24 hours thus de-watered sludge may be anaerobic. This could cause odour issues when a Skip Bay roller door is opened and possibly odour from transferring odorous sludge to the Composting Plant (and handling of anaerobic sludge at the Composting Plant).

The discharge of aeration air from the Centrate Plant Black Boxes direct to atmosphere if the quality of centrate is poor.

1.7.1 Skip Bay Odour Emissions In respect to processing time and odour in the Skip Bay, while UWI tries to ensure that raw sludge is processed and transferred to the Composting Plant within 18 to 24 hours of receipt of raw sludge, this does not always occur. The issue is not the odour levels within the Skip Bay as such (although it is desirable to minimise odour generation) because this facility appears well contained when doors are shut and ventilated to odour control equipment. It is the escape of odour (fugitive discharges) when a roller door is open to remove a full skip and return an empty skip, and also leaving a roller door open for extended periods. Removal and return of skips is the responsibility of Composting plant personnel, not UWI. While we believe that fugitive odour discharges from the Skip Bay when a roller door is open for access and is then closed promptly is not an issue as a direct source of odour nuisance outside of Carey's Gully when the quality of de-watered sludge is good, this is not always the case. In addition, even when the quality of sludge is good, the emission of odour if a roller door is left open for an extended period may be important, at least cumulatively.

We have reviewed possible methods to minimise the emission of odorous air from the Skip Bay when a roller door is opened. The alternatives evaluated were:

Improve quality of de-watered sludge so that odour emission is reduced and, in particular, that poor quality sludge is not generated or sludge of good quality does not significantly degrade within the Skip Bay. This could include the addition of an appropriate oxidising agent to the raw sludge to reduce the concentration of soluble sulphides to minimise the generation of hydrogen sulphide.

Modify the Skip Bay door system to access each of eight skips through individual roller doors to minimise the open cross-sectional area during each access.

Increase rate of extraction to minimise escape of odorous air when a roller door is opened (additional biofilter capacity to treat additional ventilation air would be required).



Replace the skip transfer system with an enclosed and ventilated belt conveyor from the Skip Bay to the Composting Plant (additional biofiltration capacity would also be required).

Introduce an airlock system for each Skip Bay roller door; with airlock ventilation to the biofilter (additional biofilter capacity would also be required).

We doubt that modifying the roller door system will be practicable and cost-effective, nor is increasing the rate of ventilation of the Skip Bay without substantially solving the roller door fugitive emissions worth pursuing. Installing an airlock on each roller door is practicable but will be very expensive.

Our view is that the best method at this stage to is to process sludge when it is as 'fresh' as possible and to minimise hold time until transfer to the Composting Plant (and then process as quickly as possible), and monitoring of doors. The addition of a suitable oxidising agent to raw sludge upstream of the centrifuges should be evaluated by the Wellington City Council. The practicability of replacing skip transfer by an enclosed belt conveyor or a similar conveying system with the conveyor and transfer points ventilated to a biofilter should also be evaluated by the Council.

1.7.2 Odour Emission from Skips in Transit Skips transferred to and from the Skip Bay to the Composting Plant are not covered. There are logistical issues in covering skips, and whether such action is needed is debatable. The issues are:

Is odour from transfer of skips from the Skip Bay to and from the Composting Plant an odour issue?

Is it practicable to cover skips, and if so, what method of covering is the most cost-effective?

What other methods are available to minimise odour emission from skips being transferred to and from the Composting Plant?

Will covering skips or treating the surface of sludge cause other issues?

It is very unlikely that odour from transfer of skips from the Skip Bay to and from the Composting Plant is a primary cause of odour nuisance outside of Carey's Gully. Transfer will cumulatively add to other odour from Carey's Gully activities but not, we think, significantly. It will at times cause an odour issue within Carey's Gully, especially if sludge quality is poor. In our view the issue is when sludge quality is poor, but we accept that poor sludge may only occur for a small percentage of the time (but it may occur much more frequently).

It is practicable to provide some form of cover on the skips. While hinged steel lids are fitted to the skips that are transferred to and from the Karori WWTP to the Composting Plant, we do not know if these lids can be closed or opened within the Carey's Gully Dewatering Plant Skip Bay. However, while less effective, hinged lids can be closed/opened outside of the Skip Bay (Bay door closed). An alternative is to cover the top of the skip with an impervious tarpaulin and tie it down but while this (presumably) could be done inside of the Skip Bay and has a low capital cost, the method is more labour intensive than closing hinged lids.



Other possible methods to minimise the emission of odour from sludge in skips being transferred is to liberally spray the sludge surface with a reputable odour neutralising agent designed for surface application and that does not have excessive 'perfume'. Movement of the sludge load during transit may break up the surface and render the application less effective. Covering skips containing rejected sour raw materials at rendering plants with a 50 to 60 mm layer of green (damp and chemically untreated) sawdust seems to minimise odour emission during transit to landfilling. This method will be more labour-intensive than using odour neutralising agents.

Covering of skips or treating sludge surface while the truck is present in the Skip Bay would extend the time the roller door is open – very undesirable and must be avoided. To minimise door open time any covering/uncovering or surface treatment should be carried on out of the Skip Bay with door closed.

Our view at this stage is that the best method in respect to transferring skips to and from the Composting Plant (and landfill) is to carry out this process as quickly as possible.

To minimise potential odour nuisance to employees and the public in Carey's Gully, all skips (but especially those containing poor quality sludge) despatched from the Dewatering Plant location should be covered. As a possible alternative to covering, a trial should be carried out by spraying the sludge surface with a reputable odour neutralising agent having a low perfume. If spraying of odour neutralising agent is encouraging, this method could then displace covering of skips.

To minimise the time the Skip Bay doors are open, covering of skips or spraying the sludge surface with odour neutralising agent (unless this can be done quickly) should be carried out just outside the Skip Bay.

Before skips are returned from the Composting plant, they should be thoroughly washed out with cold water.

1.7.3 Odour Emission from Discharge of Centrate Black Boxes Aeration Air to Atmosphere

The Centrate Plant appears to be well managed and maintained and UWI demonstrate a good understanding of the process and its variability and how best to operate it to maximise the quality of plant effluent. UWI believe that the odour nuisance potential of Black Box aeration air is relatively low.

In respect to the discharge of odour into air, the questions in 2002 were that under upset operation, will the emission of odour cause nuisance outside of Carey's Gully either directly or cumulatively with other Carey's Gully odour sources, and if so, what would the frequency be? These questions are still current.

Odour samples collected by Watercare in February 2005 indicated at that time aeration air had high odour intensity (although the calculated rate of odour emission was relatively low by assuming a rate



of air emission of only 170 m3/hour). If those odour concentrations are valid, and if they are multiplied by currently advised aeration rates (1,200 to 1,500 m3/hour in total) then the rate of odour emission could have been as high or higher than 239,000 OU/s based on the 23 February 2005 sample – a rate of odour emission around 75% of the Composting Plant's biofilter odour emission rate. Unfortunately, WaterCare did not determine the volumetric flow of the Black Boxes aeration air at the time of sampling nor provided observations about the degree of offensiveness of the odour emissions at source nor comment about odour down wind of the plant. There is also an inconsistency between odour concentrations and the chemical species present in an odour sample as determined by mass spectrometry.

While we accept that for probably most of the time the rate of odour emission from the Black Boxes is relatively low, indications are that at times odour emissions are high. Consequently, we recommend that the range in rate of aeration of the Black Boxes be determined with some precision, and if volumetric flow rates exceeds around 300 m3/hour then aeration air from the Black Boxes be directed to odour control equipment such as a separate biofilter designed to tolerate occasional foaming.

We appreciate that given the current paucity of quantifiable information about rates of odour emission from the Black Boxes, that requiring venting of the Black Boxes to an effective odour control system may be seen as only a precautionary measure.

1.7.4 Proposed Odour Management Plan We fully support the intention of the applicant to prepare an Odour Management Plan which will be independently peer reviewed in the draft stage. Critical headings are included in Section 7.2 of the AEE.

We recommend that this Plan be formatted in a way that the actions and other requirements can be easily incorporated into UWI's standard operating procedures, and that the Plan be able to be easily updated to reflect any changes in processing or control procedures as a result of experience.

1.8 Landfilling of Dewatered Sludge Wellington City Council has applied for consent to landfill sludge contaminants. (Note: the application we are dealing with here relates only to the disposal of sludge from the dewatering plant; the disposal to land of de-watered sludge from the composting plant is covered by another consent which is not part of this process.) Sludge contaminants are either dewatered sludge from the Dewatering Plant or dewatered sludge that has been processed through the Co-composting Plant but which has a dry solids content of less than 50% by mass.

Disposal of sludge contaminants to the landfill has been necessary on only two occasions since the Composting Plant was commissioned – on one occasion due to a breakdown of the plant, and the need to dispose of off-specification compost on the other occasion. However, the applicant is concerned that in future there may be more need for disposal to the landfill. For example, if the supply of green wastes declines, or if circumstances change that disposal of sludge to the composting plant does not



continue, or for disposal of off-specification sludge, and delivery by mistake of a skip of sludge to the landfill.

Disposal of sludge contaminants will take place during normal landfilling hours with the disposal of refuse at a mixing ratio of 4:1 of bulking agent to sludge. Quarried material will be used to make up any shortfall in refuse. This mixing of sludge with bulking agent is to ensure even compacting of materials, to minimise odour, to avoid creating boggy areas, and to maximise waste decomposition.

The applicant proposes to use the following mitigation measures to minimise the emission of odour when landfilling sludge contaminants (see Section 7.3 of the AEE):

Ensure availability of sufficient quarried material to achieve the minimum mixture ratio and for daily cover.

The application of odour neutralising agents directly onto the sludge/refuse mixture.

Use quarried material as an interim seal over the sludge/refuse mix prior to compaction.

The availability of a mobile water blaster to clean vehicle wheels on leaving the tipping face (a fixed wheel wash unit is also available in Carey's Gully).

A water cart to wash down the approach roads.

The use of quarried material to resurface vehicle approach routes and the unloading area.

The above measures are appropriate and should minimise the emission of odour from the activity.

We support the proposed measures to minimise odour when sludge contaminants are disposed by landfilling. Care is needed when mixing sludge contaminants with bulking agents especially if mixing aerates the blend. If the sludge contaminants are anaerobic, the application of a suitable odour neutralising agent during mixing may be appropriate.

Additional to the measures proposed we recommend that the mobile water blaster should also be used to clean down the internal surfaces of emptied skips. The spraying of odour neutralising agents onto the refuse/sludge mix if the sludge is not anaerobic should not be necessary if interim covering with quarried material is prompt. However, if the sludge is anaerobic, spray application of an appropriate odour neutralising agent onto the sludge surface should be carried out. The effectiveness of odour neutralising agents depends on the type and the quantity applied, and the sprayed surface should not be disturbed until the interim cover is laid.

1.9 Tree Planting Programme The Wellington City Council advised at least one complainant in early 2005 that one of the initiatives was an extensive tree planting programme. Trees are known to adsorb odours and to disrupt air flow to cause deposition of particulate matter containing adsorbed odour. In late October 2005 the Council advised the same complainant that tree planting was only moderately successful and the Council intended to replant during next planting season (autumn 2006). At this stage we are not aware of the outcome of this programme.



Shelter belts and other vegetation plantings adsorb odour, but their effectiveness is dependent not only on the species but on being able to intercept the flow of odorous air. The principal issues are having sufficient vegetation coverage down wind of odour sources and that the height of the vegetation is sufficient for the purpose. In respect to Carey's Gully, we expect that mature plantation belts in strategic locations would result in a significant reduction in odour under some circumstances but, because of the confused topography and meteorology of the area, we would be surprised if all odour episodes would be mitigated. In any case, it will be some years before tree plantings are sufficiently mature to be fully effective.

1.10 Health Impact of Odorous Contaminants Exposure to odorous contaminants at concentrations many times less than the lowest concentrations that are observed to cause irritation or other classical physical health symptoms appear to cause health effects in some people. The complex relationship between physiological, behavioural, and psychological factors, is not fully understood. It may be possible that a mixture of odorous contaminants could generate adverse heath effects even when the concentration of the individual components is very much lower than that recognised to cause physical health affects, but this has not received much scientific attention. However, it is becoming widely accepted that odours, even at low concentrations in air, may cause physical health effects in susceptible people such as nausea, headaches, irritation, stress, and mood changes.

Mechanism for health symptoms occurring from exposure to odours at concentrations that are above odour thresholds but are not irritating is not well understood but several factors appear to be involved. Humans are genetically coded so that pleasant and unpleasant odours activate different parts of the brain (alerts humans to potentially unsafe food and air). Sensitivity of the human nose to some contaminants (for example, hydrogen sulphide) may be a protective mechanism to prevent upsetting certain metabolic processes. Unpleasant odours can change breathing patterns. Exposure to objectionable odours may also cause stress and mood changes and these changes may cause illness or worsen existing illness. In some cases health symptoms from odour at non-irritating concentrations may be due to innate or learned aversions. The distinction between adverse physical health effects and social and mental well-being has become blurred due to the policy of many environmental and public health authorities accepting that good health includes a good quality of life not just the absence of disease or infirmity. That some researchers link odours and physical health effects may have reinforced the public view that objectionable odours and health problems are closely linked.

Some of the odorous contaminants emitted into air from activities in Carey's Gully have objectionable smell in very low concentrations. Some of these have associated ambient air contaminant guidelines published by jurisdictions such as the N.Z. Ministry for the Environment, the World Health Organisation (WHO), and the Texas Commission on Environmental Quality. Many of these guidelines are now based on odour effects rather than being derived from the lowest concentrations causing irritation and other physical health effects. Such guideline values are many times lower than they would be if derived from irritation and other physical health effects data. For example, in respect to



hydrogen sulphide (rotten egg odour), the WHO ambient air guideline based on irritation (0.10 ppmv) is 20 times higher than the MfE guideline (0.0047 ppmv – which is the same as the WHO odour guideline) based on odour effects. This is in recognition that good health is not just the absence of disease or infirmity but also includes social and mental wellbeing.

Some of the odorous contaminants emitted from Carey's Gully activities have reported physical irritation thresholds. Of these, most have irritation thresholds significantly higher than their odour thresholds. In our view, it is highly unlikely that contaminants having objectionable odour will be present in ambient air outside of Carey's Gully at concentrations approaching their physical irritation thresholds.

The relationship between reported odour thresholds and workplace exposure standards (WES's) are also evaluated. For those contaminants having assigned WES's, all but three have odour thresholds substantially lower then their WES. Of those that don't (ammonia, benzene, and n-butanol), these contaminants are highly unlikely to be smelt outside of Carey's Gully. Even if the WES's are adjusted to concentrations applicable as public exposure levels, it is unlikely that the concentration of contaminants that have significant odour nuisance potential when accounting for their likely presence in areas frequented by the public will approach levels in air which pose a direct risk to the public in respect to physical irritation and other physical health effects.

It is important not to lose sight of the fact that the primary issue down wind of Carey's Gully is objectionable and offensive odour. If odour nuisance to the public can be substantially eliminated then other adverse effects will also essentially be eliminated.

1.11 Conditions of Consents if Granted We recommend that if the consents sought are granted then they be subject to conditions that cover or include the following aspects.

1.11.1 Operation of the Dewatering and Centrate Plant Relevant Conditions on Existing Permits or Conditions having Similar Intent

Standard conditions imposed on all air discharge permits.

The operation of the activity to be generally in accordance with the application for consent and its associated documents lodged with Greater Wellington Regional Council and additional information dated 20 August 2007, and any additional information lodged with the consent authority up to the time of completion of the resource consent hearing including evidence. If there is any conflict between information lodged and conditions of the permit, the conditions prevail. [Similar to the existing condition.]

There shall be no discharges to air arising from the exercise of this permit that are noxious, dangerous, offensive, or objectionable, at or beyond the boundary of the area that the resource consent applies to. [Essentially an existing condition.]



The permit holder shall prepare an Odour Management Plan to ensure that there are no discharges to air arising from the exercise of the permit that are noxious, dangerous, offensive, or objectionable, at or beyond the boundary of the area that the resource consent applies to.

The Odour Management Plan shall include but not be limited to addressing all matters relating to complying with the conditions of this permit, and shall also include contingency and precautionary measures covering upset or other abnormal operation or circumstances including when biofilter active media is being refurbished or replaced. The Odour Management Plan should be constructed in a way to enable incorporation of provisions into the Plants Standard Operating Procedures.

The draft Odour Management Plan shall be submitted to the Manager, Consents Management, Greater Wellington Regional Council, for approval not later than three months after the date of granting this permit. The Odour Management Plan shall be reviewed by the permit holder at least annually, and any changes to the Plan having a bearing on the discharge of contaminants to air shall be submitted to the Manager, Consents Management, Greater Wellington Regional Council, for approval as soon as practicable after completion of the review. [Expanded existing condition.]

All processes shall be effectively monitored to assist optimising their operation and, as appropriate, to provide a record of operation. Monitoring records shall be kept for at least 12 months on a rolling basis and shall be provided to the Manager, Consents Management, Greater Wellington Regional Council, on request as soon as practicable to do so. [Modified existing condition.]

Any incident that could result in an adverse effect on the environment that is more than minor or is likely to cause noxious, dangerous, offensive, or objectionable discharges to air, including odour, at or beyond the boundary of the area that the resource consent applies to shall be notified to the Manager, Consents Management, Greater Wellington Regional Council, as soon as practicable or within one hour of knowing the incident, has occurred. Within five working days the permit holder shall report in writing to the Manager, Consents Management, Greater Wellington Regional Council, on the reasons for the incident, measures taken to mitigate the incident and to minimise the risk of recurrence. [Similar to an existing condition.]

The permit holder shall notify the Manager, Consents Management, Greater Wellington Regional Council, of any complaints received alleging adverse effects for the exercise of this consent within 24 hours of the complaint being received. [An existing condition.]

The permit holder shall monitor air quality in the vicinity of the Dewatering Plant and its biofilter to determine the concentrations of faecal coliforms and salmonella (if any) in air. The sampling method and locations, sampling frequency, and method of notification are to be agreed by the Manager, Consents Management, Greater Wellington Regional Council. [An existing condition.]

In the event that officers of the Greater Wellington Regional Council confirm any discharges to air from the Dewatering Plant or from the Centrate Plant or from ancillary activities, that are noxious, dangerous, offensive, or objectionable to such an extent there is or is likely to be an adverse effect on the environment that is or could be more than minor, the permit holder shall take



all reasonable measures to avoid, remedy, or mitigate such adverse effects of the discharge to air. These measures may include but not be limited to:

(a) Measures to minimise or prevent the emission of odour from the Skip Bay when being accessed to transfer skips.

(b) Covering or other measures to minimise the emission of odour from skip contents when skips are transferred from and to the Skip Bay.

(c) Requiring Centrate Plant bioreactor (Black Boxes) aeration air to be routed to effective odour control equipment.

(d) Changes to housekeeping measures.

[To be reviewed.]

The Greater Wellington Regional Council may review any or all conditions of this permit by giving notice of its intention to do so pursuant to section 128 of the Resource Management Act 1991 at any time within six months after the commencement date of this permit, and thereafter at yearly intervals, for the following purposes:

(a) To deal with any adverse effect on the environment which may arise from the exercise of this permit, to which it is appropriate to deal with at a later stage.

(b) To review the adequacy of any or all conditions of this permit.

(c) To review the adequacy and implementation of the Odour Management Plan required by this permit.

[Simplified version of an existing condition.]

Suggested New Conditions or Matters to be Address by New Conditions

As far as practicable and subject to the supply of raw sludge, the Dewatering and Centrate Plant shall be operated continuously throughout each year except for the following four public holidays: New Years Day, Good Friday, Easter Sunday, and Christmas Day.

Subject to the Dewatering Plant and the Co-composting Plant operating, skips containing de-watered sludge shall be transferred to the Co-composting Plant on a seven days/week basis with a timetable to ensure as far as practicable that the time taken to process raw sludge from its receipt to dispatch of de-watered sludge from the Dewatering Plant is as short as possible and in any case does exceed 24 hours.

If the Dewatering Plant is operating but the Co-composting plant is not operating [because of breakdown] then de-watered sludge shall be disposed of by landfilling as far as practicable to keep within the 24-hour timetable above.



The containment and ventilation of the odorous areas of the Dewatering Plant building, the raw sludge tanks, and the Centrate Plant pumping station (wet well) shall be optimised to minimise fugitive odour emissions to atmosphere. The total rate of ventilation of these facilities to the existing biofilter not be less than 5.75 m3/s other than when maintenance of the biofilter media requires a section of the biofilter to be bypassed. During maintenance of the biofilter the rate of ventilation of the Dewatering Plant building shall be as high as practicable.

As a part of the permit holders review of building ventilation extraction being carried out in 2007, an evaluation of Dewatering Plant building tightness shall be carried out and this evaluation include as far as practicable a study of negative pressure in the Skip Bay when one access roller door is open and an estimation of Skip Bay air flow under various wind conditions as a consequence. This evaluation of building tightness shall be provided to the Manager, Consents Management, Greater Wellington Regional Council, no later than 6 months following the granting of this permit.

The Skip Bay access doors and other building access doors shall be continuously monitored and a warning system (or systems) operated to ensure as far as practicable that no Dewatering Plant building door remains open longer than necessary for access. The effectiveness of this monitoring programme shall be reviewed by the permit holder and this review provided to the Manager, Consents Management, Greater Wellington Regional Council, no later than 6 months following the granting of this permit.

To minimise fugitive odour emissions from the Skip Bay when an access door is open, and from transfer of de-watered sludge to the Co-composting Plant, the permit holder shall:

(a) Evaluate the feasibility (including advantages and disadvantages) of adding a suitable oxidising agent to raw sludge upstream of the centrifuges.

(b) Evaluate replacing skip transfer by an enclosed belt conveyor or a similar conveying system, with the conveyor and transfer points ventilated to a biofilter.

(c) Evaluate equipping the Skip Bay roller doors with an airlock system to minimise the discharge of fugitive odours during transfer of skips.

Reports of these evaluations shall be provided to the Manager, Consents Management, Greater Wellington Regional Council, no later than XXX months [timing under review] following the granting of this permit.

To minimise potential odour nuisance to employees and the public in Carey's Gully, all skips [and especially those containing poor quality sludge] despatched from the Dewatering Plant be covered. Before skips are returned from the Co-composting plant or from the Southern Landfill if contents are landfilled, skips must be thoroughly washed out with cold water.

As a possible alternative to covering skips, a trial can be carried out by spraying the sludge surface with a reputable odour neutralising agent having a low level of perfume. If spraying odour neutralising agent on sludge surface is sufficiently encouraging to be an effective alternative to



covering skips the report of evaluations shall be provided to the Manager, Consents Management, Greater Wellington Regional Council, who may then approve the use of odour neutralising agents as an alternative to covering skips.

That the discharge of aeration air from the Centrate Plant bioreactors (Black Boxes) be determined with more precision, and if volumetric flow rates exceed 300 m3/hour then aeration air from the Black Boxes may be required to be directed to effective odour control equipment such as a separate biofilter designed to accept the highest rate of air flow expected and to tolerate occasional foaming. [proposed condition is still under review]

The level of housekeeping shall be optimised to minimise fugitive discharges of odour.

[Note: In view of the fact that spraying odour neutralising agents into ambient air, notwithstanding their inherent odour, is unlikely to cause significant annoyance within Carey's Gully and won't cause nuisance outside of Carey's Gully, we make no recommendation in respect to its use – whether to use ONA's or not, is a decision for UWI.].

1.11.2 Landfilling of Sludge Contaminants – Discharge of Contaminants into Air Standard conditions imposed on all air discharge permits.

The operation of the activity to be generally in accordance with the application for consent and its associated documents lodged with Greater Wellington Regional Council and additional information dated 20 August 2007, and any additional information lodged with the consent authority up to the time of completion of the resource consent hearing including evidence. If there is any conflict between information lodged and conditions of the permit, the conditions prevail. [Similar to an existing condition.]

There shall be no discharges to air arising from the exercise of this permit that are noxious, dangerous, offensive, or objectionable, at or beyond the boundary of the area that the resource consent applies to. [Essentially an existing condition.]

Sludge contaminants shall be defined as:

(a) Dewatered sewage sludge, or

(b) Any material which includes dewatered sewage sludge;

any of which has not completed processing through the Co-composting Plant or does not have a dry solids content of at least 50 percent by mass. [Existing condition]

The permit holder shall prepare an Odour Management Plan to ensure that there are no discharges to air arising from the exercise of the permit that are noxious, dangerous, offensive, or objectionable, at or beyond the boundary of the area that the resource consent applies to.

The Odour Management Plan shall include but not be limited to addressing all matters relating to complying with the conditions of this permit, and shall also include contingency and precautionary measures covering abnormal activities or circumstances including storage of sludge contaminants during the period the landfill is closed. The Odour Management Plan should be



constructed in a way to enable incorporation of provisions into the Southern Landfill Standard Operating Procedures.

The draft Odour Management Plan shall be submitted to the Manager, Consents Management, Greater Wellington Regional Council, for approval not later than three months after the date of granting this permit. The Odour Management Plan shall be reviewed by the permit holder at least annually, and any changes to the Plan having a bearing on the discharge of contaminants into air shall be submitted to the Manager, Consents Management, Greater Wellington Regional Council, for approval as soon as practicable after completion of the review.

Any incident that could result in an adverse effect on the environment that is more than minor or is likely to cause noxious, dangerous, offensive, or objectionable discharges to air, including odour, at or beyond the boundary of the area that the resource consent applies to shall be notified to the Manager, Consents Management, Greater Wellington Regional Council, within one hour of knowing the incident, has occurred. Within five working days the permit holder shall report in writing to the Manager, Consents Management, Greater Wellington Regional Council, on the reasons for the incident, measures taken to mitigate the incident and to minimise the risk of recurrence.

The Greater Wellington Regional Council may review any or all conditions of this permit by giving notice of its intention to do so pursuant to section 128 of the Resource Management Act 1991, at any time within six months after the commencement date of this permit, and thereafter at yearly intervals, for the following purposes:

(d) To deal with any adverse effect on the environment which may arise from the exercise of this permit, to which it is appropriate to deal with at a later stage.

(e) To review the adequacy of any or all conditions of this permit.

(f) To review the adequacy and implementation of the Odour Management Plan required by this permit.

[Modified existing condition]



2. Introduction

2.1 Applications for Resource Consents Sinclair Knight Merz Limited was commissioned by the Greater Wellington Regional Council (GW) under section 92(2) of the Resource Management Act 1997 to peer review the applications by Wellington City Council for air discharge permits for the Dewatering and Centrate Plant and for the disposal to land of sludge contaminants. The Dewatering and Centrate Plant is located in Carey's Gully and managed by United Water Industries (UWI).

The terms of reference for the peer review and GW's expected outcomes were specified in a letter dated 1 August 2007 and are summarised below.

Review the document "Carey's Gully Sludge Dewatering Plant and Sludge Disposal at the Southern Landfill Assessment of Effects on the Environment" which is the AEE prepared by MWH New Zealand Limited in April 2007. Identify any areas in the document which are not consistent with the actual effects on the environment and those presented by the applicant.

To assess whether further information is required from the applicant additional to further information under section 92 of the Resource Management Act 1991 (RMA) sought on 25 July 2007 to enable a full understanding of the nature of the proposal and its likely effects on the environment.

Review the operation and management practices with respect to avoiding adverse odour effects beyond the site boundary; and to assess whether odour emissions at the site are being controlled using 'best practicable option' technology. GW drew attention to the large number of complaints attributed to the Carey's Gully Complex which contains a collection of different odour sources. GW also advised that odours that are potentially objectionable or offensive may be produced during operation of the plant.

If 'best practicable option' is not being used, to make recommendations in respect to operations and management that can be undertaken to adopt the 'best practicable option'.

Suggest consent conditions that may be appropriate if the consent were to be granted. GW made specific reference to conditions in respect to the 'best practicable option' to prevent or mitigate potential or actual effects on the environment of objectionable or offensive odour beyond the site boundary.

Prepare a report to address the issues outlined above.

The application documents and other related information were reviewed by Ron Pilgrim, Principal Consultant, Air Quality & Air Pollution Control, SKM Limited, Wellington.



2.2 Complaints about Offensive or Objectionable Odour A significant number of complaints about objectionable or offensive odour continue to be made to Greater Wellington Regional Council and (presumably) to Wellington City Council by residents of Brooklyn, Mornington, Kingston, Happy Valley, and Owhiro Bay.

Many of these complaints implicate odour sources from within Carey's Gully, of which the Sludge Dewatering and Centrate Plant now operated by United Water Industries is one potential odour source.

2.3 Issues in Respect to the UWI Site and the Carey's Gully Complex The Dewatering and Centrate Plant is located within a physically defined area within Carey's Gully, on land owned by Wellington City.

The application to GW for air discharge permits gives the legal description of the land as Lot 1 DP29398 and Lots 1 and 2 DP29742 being all of the land in CT 21D/612 (Wellington Registry) which, according to the Schedule of Legal Descriptions, encompasses some 861 hectares. This parcel of land is nearly all of the land owned by the Wellington City Council in Carey's Gully. Consequently, on this basis, we presume that the "site" of the Dewatering and Centrate Plant is Lot 1 DP29398 and Lots 1 and 2 DP29742 being all of the land in CT 21D/612 (Wellington Registry), and not the land more or less within the security fence around the plant. If this is the case then it could be argued that issues relating to any adverse effects on the air environment are only relevant outside of the boundary of the Council-owned land in Carey's Gully and not within Carey's Gully. This, of course, is a legal issue.

Irrespective of the normal practice of assessing effects of air discharges on the environment to beyond the boundary of the industrial or trade premises, we are not aware of any provision in the Resource Management Act 1991 that limits the Act in respect to effects on the environment from the discharge of contaminants into air to outside of an industrial or trade premises except for a regulation in the National Environmental Standards. Regulation 14(2) of the Resource Management (National Environmental Standards Relating to Certain Air Pollutants, Dioxins, and Other Toxics) Regulations 2004 provides, in the context of those regulations, that if the discharge of a contaminant is permitted by a resource consent, the ambient air quality standard for the contaminant does not apply to the area that the resource consent applies to.

Carey's Gully is accessed by members of the public but their presence is transitory. Employees of other activities are present on a generally continuous basis throughout their working day. Some of these employees may be sensitive to excessive odours generated by the activities carried on (including from their own activities) and, if so, warrant protection from exposure to excessive odour irrespective of the source. The question is whether the RMA, in respect to the effects on the environment of discharge of contaminants into air from industrial or trade premise, applies within the boundary of the land owned by the Wellington City Council at Carey's Gully or only outside of these premises.



3. Section 92(1) Request by GWRC The following information relevant to the application to the application for an air discharge permit for the Dewatering and Centrate Plant and landfilling of dewatered sewage sludge was requested by GW on 25 July 2007.

A copy of the Sewage Sludge Dewatering & Disposal Operational Management Plan 1998 referenced in the AEE.

Details of how the processing time for sludge (between 18 and 72 hours) can affect the amount and intensity of odour generated.

The operating parameters of the Sludge Dewatering Plant including: total volumes and flow rates (design capacity); current operating rate and volume; estimated increase in volume and flow rates that will be handled in 10, 15, 20, and 25 years; and the average and range of processing time of sludge entering and leaving the facility.

The mass balance flow rates (current and design capacities) of each individual section of the facility, including: the biofilter (extraction volumes & residence time within the media, and total air volumes); the MBR bioreactor (Black Boxes) in respect to air volumes discharges and centrate volumes handled; the centrate wet wells with respect to centrate volume handled; the centrifuge units with respect to sludge volumes handled; and the landfill skip bins and filling process with respect to dewatered sludge volumes and air discharge volumes.

Details of the current site odour management procedures, and further operational practices not otherwise specified.

Monitoring results of bioaerosol contaminants that may have an effect on human health.

An outline of the proposed odour management plan and what mitigation measures will be used to achieve a decrease in levels of discharged odour.

In addition, GW requested information about the circumstances that will necessitate the disposal of dewatered sludge directly to land at the landfill; and a detailed assessment of the potential environment effects of the disposal of sludge to land at the Southern Landfill.

MWH responded on 20 August 2007 and provided detailed information to address the information requests.



4. Review of Application Documents and related Information

4.1 Introduction We reviewed on 20 August 2007 the applicant's Assessment of Effects on the Environment dated April 2007 prepared by MWH for the Wellington City Council.

Generally, there was sufficient information in the assessment to enable us to have a full understanding of the proposal and its effects on the environment. This is because we reviewed this plant in 2002 as a part of a survey carried out on behalf of the Wellington City Council relating to the odour nuisance potential of activities in Carey's Gully.

There were, however, some areas where additional information and clarification would be helpful. In addition, the AEE refers to two reports that we did not have a copy of.

4.2 Additional Information/Clarification

4.2.1 In Respect to the Sludge Dewatering and Centrate Plant In Section 6.3.3 on pages 45 and 46 of the AEE, various comments are made relating to the operation of the moving bed bioreactors ('Black Boxes") such as:

Air blowers provide a total of 170 m3/hour of air to the black boxes;

The black boxes are fully enclosed and this provides a satisfactory level of odour control (and in Section 7.1.1 it is stated that the centrate black boxes are effectively enclosed).

Bunding was constructed to prevent foam and overflows from contaminating the immediate environment (this suggests that the black boxes are not fully enclosed, at least not at the time the bunding was installed).

Variable speed control of the black boxes air blowers was installed in Match 2007 to improve effluent quality and further reduce air emission rates.

Air is extracted from the centrate wet well and is ducted to the biofilter for odour control.

In 2002 when we reviewed this plant, the operator (then Anglian Water International) and Wellington City Council were debating the merits of ventilating the black boxes to an odour control biofilter, and if so, who would pay for it. There was considerable reluctance to ventilate the black boxes to the dewatering plant biofilter to avoid any potential overload, thus a stand-alone biofilter was being considered.

At the times of our various visits, the centrate treatment plant emitted at times an obvious odour apparent at the adjacent eastern boundary fence under certain wind directions, the odour being a mixture of typical sewage treatment plant influent sewage odour with at times an overtone of hydrogen sulphide, and a typical centrate odour. Generally this was not very obvious more that 25 m down wind of the boundary fence adjacent to the Centrate Plant but at other times the odour was



relatively strong. At the time of our visits, only the Centrate Plant "pump station" (the wet well system) was ventilated to the Dewatering Plant odour control system (the biofilter). New covers had just been fitted to the Black Boxes and while these were fitted with vent extensions to enable venting to odour control equipment, this had yet to be agreed to by the WCC and Anglian Water. The actual rate of air blowing of the Black Boxes was not known at the time of our visits during 2002 but the data submitted with the first application for an air discharge permit was 1,500 m3/hour.

At the time we evaluated the current AEE we were uncertain if the Black Boxes aeration air is still discharged to atmosphere, or if it piped to the centrate wet well to be extracted with the wet well ventilation air to the plant biofilter; and what the rate of air blown into the Black Boxes is. In addition, there was also some uncertainty about the type of contaminants that are discharged from the Centrate Plant.

These uncertainties have now been clarified following discussions with UWI staff.

In the first sentence of the last paragraph of Section 6.3.3 on page 46, the AEE states that "However, some possible improvements have been identified." We presume