20 YEARS IN THE MAKING – CLEANING UP GREYMOUTH
Simon M cAulay Melvin D Sutherland Project Manager, MWH Global & Assets & Engineering Manager, Grey District Council Dunedin, NZ Greymouth, NZ
Abstract Grey District Council is nearing completion of its $38m sewerage scheme upgrade to provide new wastewater infrastructure that will realise a number of health and environmental improvements for the Greymouth community.
The plans for an improved wastewater collection, treatment and disposal system were developed around 20 years ago with a long-term vision of a plan to improve the quality of discharges on both sides of the Grey River.
This year sees the fruition of those plans with the separation of the existing combined storm and wastewater sewer and new sewerage for areas previously restricted to on-site disposal. A new wastewater only sewerage system has been installed comprising 65 km of new wastewater pipes, 22 new wastewater pump stations, a new wastewater treatment plant and a significant upgrade of an existing ultra violet treatment facility.
The programme of work has provided some interesting experiences in the areas of consenting, construction and commissioning and the paper examines and shares some of these. Of particular interest is managing the progressive connection of various areas of Greymouth to the new sewerage system and the use of a biological trickling filter to treat odorous air collected from various parts of the covered wastewater treatment plant.
Key Words Greymouth, sewerage, upgrade, wastewater, treatment, trickling filter, odour, covered.
Introduction infrastructure upgrade in an effort to clean up Greymouth. Greymouth is the largest town on the west coast of New Zealand’s South Island and the The Staged Solution most significant of the areas subject to the governance of the Grey District Council Greymouth’s original sewerage system was (GDC). The area’s main industries are combined with stormwater; hence developing mining, forestry and fishing and the town’s a separate ‘wastewater only’ system would major industrial dischargers include fish be both expensive and time consuming. A processing plants, the hospital and the iconic sewerage improvement proposal had been Monteith’s Brewery. Tourism is in a growth considered in the eighties by the former phase for the area. Greymouth Borough but did not proceed due to a combination of high cost and low Greymouth’s population of 10,000 sits either perceived need. side of the mouth of the Grey River and the town had been discharging untreated sewage The next proposal was developed in the late into the Grey River for over 100 years. With nineties after the introduction of the Resource the advent of the Resource Management Act Management Act. To help ensure a positive (1991), it was apparent that things must outcome, a two-staged sewerage change. The paper will follow a timeline improvement scheme was proposed. The key through the progress and development of the objective of making the scheme affordable to Grey District Council’s long term plan to the community would be achieved with a 27 construct a significant wastewater year long construction period for the sewer separation part of the project. The main through a public process, culminating in a objective of improving the quality of hearing before commissioners. discharges to the Grey River would be met with an initial stage of treatment at each of As part of the Stage 1 process, the GDC the three main combined sewer outfalls to the made a commitment to building a separate Grey River; Blaketown, Cobden and sewerage system to further improve the Johnston Street. This would be followed management and quality of wastewater around 10 years later by the second stage discharges by separating the previously works with two new wastewater treatment combined stormwater and wastewater plants being constructed at sites at Preston systems. Road and Cobden (refer to Appendix A for a location plan of referred to sites). Discharge permits for treated wastewater discharges to the Grey River were The completion of this separation project consequently issued for 10 years as the would enable effective wastewater commissioners considered this the management, stormwater management and appropriate term for what was effectively to eliminate combined overflows, resulting in be a temporary discharge, notwithstanding significant improvements to the quality of the anticipated 27 year construction discharges made to the Grey River. timeframe.
The Original Programme A suite of 25 resource consents was subsequently issued to the GDC by the West The GDC engaged MWH Global to work Coast Regional Council (WCRC), including together to produce a suitable programme of all coastal permits, discharge permits and work. Following a feasibility and consultation land use consents required to authorise the period to assess viable and acceptable works and discharges. options the proposal developed was an ambitious long term plan covering a period of From this point onwards, consultations 27 years as shown in Figure 1. became more specific with key stakeholders. For instance, extensive consultation was Funding undertaken with Te Rununga o Ngai Tahu The capital cost of the stage 1 treatment and Kati Waewae Runaka and the works was estimated to be around $4m with Department of Conservation. As outlined later the sewerage separation and stage 2 in this paper, between stage 1 and the stage treatment works having an estimated cost of 2 consents there was change in approach $34m. which enabled the use of a biological trickling filter and as the preferred final treatment The Stage 1 Resource Consents solution. Maintaining strong consultation links with key stakeholders enabled these changes The resource consents necessary to achieve to be introduced, fully explained and agreed Stage 1 of the upgrade were sought in 2002 to through a “no-surprises” approach which enabled a smooth progress of the project. Figure 1: The Original Programme Years from Project Start 1-2 3-4 5-6 7-12 13-18 19-27
Obtain Resource Consents and Approvals
Sewerage Separation works
Stage 1 Treatment installed at three sites
Stage 2 Treatment installed at two sites Once resource consents and discharge objects larger than 3mm from the combined permit applications were lodged, the Council wastewater/stormwater, and to reduce the continued to consult with key stakeholders micro-organism content by UV disinfection. and submitters, through group meetings and An inlet screen captured solids and on an individual basis. automatically removed the screenings which were then dewatered by gravity, compacted The First Changes to the Solution and stored for disposal to landfill. The treatment process is shown in Figure 2. Between granting of the resource consents and the start of construction of the stage 1 The two treatment plants were tendered in Treatment works, Government funding late 2004 and through the combined efforts of became available and the solution changed. the GDC, the contractor and MWH Global, In 2005 the GDC secured a 29% (~$9m) were commissioned in August 2006. At the funding level from the Ministry of Health. This time this was an innovative solution. Whereas additional funding enabled the sewerage the use of milliscreen technology was well separation to be constructed in a shorter advanced for solids removal, the use of UV timeframe allowing the overall programme to disinfection on screened raw sewage was be significantly reduced from 27 to 10 years. essentially unknown (being typically This time frame was decided by Council and associated with treated effluent). There was was also in line with the duration of the overseas research that showed promising Ministry of Health’s Sanitary Works Subsidy results on screened and primary sewage, but Scheme which was only available for this also highlighted limitations regarding time period. suspended solids content which could shield pathogens from UV irridation. There were no Around the same time the GDC eliminated known examples of such systems in New the Blaketown outfall treatment facility. A Zealand, however some encouraging results reassessment of the engineering solution by from UV irridation of oxidation pond effluent MWH Global showed that there was a whole were available. Aware of the limitations of the of life cost benefit to instead install a new UV treatment of screened sewage, but also pump station and rising main and transfer the assisted by the then introduction of higher Blaketown flow to the Johnston Street powered and more efficient UV systems, treatment facility. which included auto cleaning mechanisms, a conservative performance assumption was The Implemented Stage 1 Solution adopted and with the assistance of a reasonable mixing zone in the river, To provide the quality improvements in the secondary contract recreational standards discharges to the Grey River, the objectives were predicted to be able to be met. of the Stage 1 treatment plants at Johnston Street and Cobden were to remove all
Figure 2: Stage 1 Treatment Solution at Johnston Street and Cobden
Combined Stormwater & Wastewater Flow 3mm Step Screen UV Disinfection
Gravity Discharge Low Lift Pumps to Grey River
The stage 1 discharge consent limits were be areas that were already in need of repair set at a median discharge quality of 30,000 or replacement with some construction of a faecal coliforms (cfu) per 100 mL of more strategic nature. wastewater and an 80 th percentile target of 120,000 cfu/100mL. Results obtained were Further Changes to the Solution better than anticipated with a median of around 20,000 cfu/100 mL. Following the commissioning of the two stage 1 treatment facilities the GDC and MWH Constructing a New Sewerage System Global carried out a review of the proposed stage 2 wastewater treatment plant (WwTP) Construction of a new wastewater only solution. As a result of this review several sewerage system alongside the existing significant changes were proposed. combined collection system is a mammoth undertaking. Logistically the GDC needed to In assessing the stage 2 wastewater install some 65 km of new wastewater pipes, treatment solution the GDC aimed to provide 870 new access structures/chambers and 22 treatment to as high a quality as possible new wastewater pump stations of varying whilst balancing practicable, economic and capacities and depths. And once that operational constraints (termed the Best infrastructure was in place each and every Practical Economic Option) before household and business would then need to discharging it to the Grey River. Moving from connect to the new system. two to a single WwTP location met all of those objectives and so it was decided to When planning the work several centralise wastewater treatment to a single considerations needed to be balanced: treatment plant at Preston Road for greater efficiency, effectiveness, control and • Greymouth residents faced many years of consistency. This would also allow the in-road construction so traffic disruption Cobden stage 1 facility to be was to be minimised. decommissioned and the Cobden outfall to • The condition of the existing combined be used solely for stormwater discharges. system meant that some areas would benefit by having the new sewerage In addition to the centralization of wastewater infrastructure available sooner. treatment the treatment solution itself • Preferably, residents should be able to underwent a major change. make connections to the new sewerage system as soon as it is installed. This At the time of the stage 1 consents requires that, once connected, the submissions, the original stage 2 treatment wastewater flow has somewhere to go solution composed screens, a biological and so may require use of temporary trickling filter (BTF), a clarifier, a wetland and catchment cross connections and a sludge holding tank. temporary pump stations. There would be benefits if complete catchments are able The subsequent construction of the Hastings to be constructed. WwTP in 2008 signified an agreement with • The construction would need to be IWI of the ability of a BTF to transform human packaged into suitable tenders that were waste into bacterial biomass. This paved the manageable by contractors and matched way for acceptance of a similar simplified the GDC programmed spend profile of the treatment process at Greymouth that required overall sewerage upgrade scheme. only screens and a BTF with no solids handling required - a massive advantage Some parts of the new sewerage system over the more traditional process planned at were installed in parallel with the stage 1 stage 1. treatment plant construction. This tended to
The Stage 2 Wastewater Treatment m3/hr required to maintain the proper Plant environment for the bacteria. While this is the normal operation of the odour control system, The stage 2 wastewater treatment plant the GDC have the option of passing the (WwTP) that was finally implemented is collected potentially odorous air through a based around a 7m high, 26m diameter carbon filter prior to it being mixed with the biological trickling filter (BTF) to treat both clean air make-up and blown into the BTF wastewater and potentially odorous air. roof space. This provides an additional layer of protection should exceptionally Wastewater collected in the newly malodourous wastewater enter the WwTP constructed sewerage system will be and additional safety when operators need to collected in 6 terminal pumping stations enter the BTF roof space for maintenance serving each of the main areas of Greymouth activities. and the outlying communities. Flow is then pumped to the new WwTP to arrive in a small Both the wastewater and odour treatment inlet chamber where the inflows are designed streams are indicated in Figure 3. to be turbulent to encourage odorous gas to be released. From here flow passes through WwTP Design Capacity 2mm band screens and into the BTF feed The stage 2 WwTP is designed to treat a pump wet well. Collected screenings are design population of 14,000 population dewatered and stored ready for off-site land- equivalents. The capacity is based on fill disposal. The BTF feed pumps lift the flow population equivalents as most of the to the top of the BTF where the distributor wastewater load is from domestic sources. arm rotates to spread the wastewater over This capacity includes an allowance for the surface of the contained hundreds of connections from the outlying communities of thousand plastic media petals. As the Karoro, Taylorville, Dobson and Kaiata. wastewater trickles down through the BTF it comes into contact with the biomass attached The communities of Taylorville, Dobson and to the media which transforms organics from Kaiata have a combined population of around the wastewater by adsorbing and assimilating 800 and are situated adjacent to the Grey the soluble and suspended constituents. The River some 5km upstream of Greymouth. liquid discharge from the base of the trickling The properties in these communities have filter is collected by an underdrain system individual onsite wastewater disposal and gravitates back to the pumping station. systems. In 2010 the GDC secured a 50% Some of the treated wastewater is funding level (based on an overall deprivation recirculated back onto the BTF and the index of 7.1) to install a gravity sewerage remainder flows into a wet well to be pumped collection system in each of these through to Johnston Street for UV treatment communities and transfer the flow to prior to discharge to the Grey River through Greymouth. The timing for application for the Johnston Street outfall. funds was again influenced by the MoE Sanitary Works Subsidy Scheme. As part of the odour management plan, the inlet chamber, screens channels, pump wet The $7m project includes 3 pumping stations wells and the BTF are all covered. The air and rising mains that transfer collected from these spaces is sucked through ducts wastewater from Taylorville to Dobson, from by a large fan and blown into the roof space Dobson to Kaiata and from Kaiata through to of the BTF. Four smaller fans around the the Greymouth WwTP at Preston Road. The circumference of the BTF draw this air down route of these rising mains provided some through the media and blow the treated air interesting engineering challenges, requiring into the atmosphere via chimney like suspension over the Grey River and structures. In addition to the 3,000 m3/hr of negotiating an active slip zone. potentially odorous air collected the odour fan also draws in clean air such that the combined flow into the BTF is the 10,000 Figure 3: Stage 2 Greymouth WwTP
Greymouth WwTP
Discharge to
Odour collection atmosphere and Treatment Odour Fan
BTF odour fans
BTF feed pumps Inlet 2mm Band (recirculation ) Chamber Screens
UV feed pumps
Terminal Pump Johnston Street Stations transfer Upgraded UV flow to WwTP Disinfection Gravity Discharge Wastewater collected in to new sewerage system Grey River
Karoro currently has its own WwTP that upgraded Johnston Street facility should be treats flow collected from the 900 population. able to achieve the proposed 5,000 cfu/100 Currently, decommissioning of the Karoro mL limit under normal operating conditions. WwTP and transfer of the wastewater to the Greymouth WwTP is not a project that the Re-use of the Johnston Street facility would GDC have plans to fund. mean a significant capital cost saving could be made. However, there remained a risk Stage 2 UV Treatment that the lower limit “should” was not a definite and so the design of the stage 2 WwTP MWH Global initial design assessment allowed for a possible future retrofit of UV determined centralization would require new treatment and the GDC allocated a UV treatment at the new WwTP. Further contingency sum should this be required. For detailed studies were carried out in the purposes of the stage 2 resource consent conjunction with the UV supplier and it was the GDC proposed to monitor the determined that if the existing Johnston performance of the Johnston Street UV Street UV facility was upgraded it could treatment system and if a median of 5,000 achieve a residual median concentration of cfu/100mL was not achieved after a period of faecal coliforms of approximately 7,000 stable operation of the plant (expected to cfu/100 mL. The proposed stage 2 discharge occur once the plant is commissioned and consent limit was to be 5000 cfu/100mL. The there are sufficient sewer connections to the 7,000 cfu/100 mL design figure was checked new WwTP) then a new UV system that will against actual results being achieved at deliver a higher dose of UV treatment would Hastings WwTP and it was agreed that an be installed at the stage 2 WwTP.
Stage 2 Expected Discharge Quality Predictably, the main issue raised at the Improvements public hearing was the potential of offensive odours being released from the WwTP. As a Stage 1 wastewater treatment had a very result, having listened to the main concern of limited effect on dissolved solids, BOD 5 and the submitters, the GDC decided to install a ammonia. The stage 2 treatment system roof on the BTF as part of the baseline provides primary and secondary treatment WwTP solution. This would mean that all of wastewater and will reduce TSS, BOD 5 areas of plant subject to wastewater flows and ammonia resulting in equal or lower were covered and the air from under these contaminant concentrations, and achieving covers could be abstracted and treated. a lower contaminant load in discharges to the Grey River. The secondary treatment In addition to this, as part of the WwTP will significantly reduce soluble BOD 5 and consent, the GDC instigated a community will remove at least some of the ammonia in liaison group (CLG). This group is largely the influent. made up from submitters and people with businesses close to the WwTP. The CLG met Table 1 – Comparison of Expected Discharge formally prior to commissioning of the WwTP Quality to discuss and comment on the proposed operation and maintenance plan and, in particular, the odour management plan. Since Stage 1 Stage 2 the plant has been in operation (August BOD 5 200 70 2014) the CLG group meet every 3 months. (mg/L) To date there have been no confirmed odour TSS 200 <140 complaints at the WwTP and general (mg/L) feedback from the CLG has been Total Ammoniacal 50 20 encouraging. Nitrogen th (95 percentile mg/L) The stage 2 resource consents were issued Faecal Coliforms 30,000 5,000 to the GDC by the WCRC in June 2013. (median cfu/100mL) Discharge Quality Performance to Date In addition to the improvements in the quality of the discharge at the Johnston Street outfall The wastewater treatment plant was the GDC is able to eliminate over 20 commissioned in August 2014. While the combined sewer overflow discharges with the treatment plant is yet to receive its full design change from a combined system to a load (until all areas of Greymouth are stormwater only system - a significant separated and properties are connected to achievement with regard to lowering the the new sewerage system), the results potential for negative environmental impact. obtained in samples of the treated effluent have been promising as shown in Figure 4. The Stage 2 Resource Consents In general, the quality of the water discharged The resource consents necessary to achieve from the Johnston Street outfall has lower stage 2 of the upgrade were sought in 2012 faecal coliform levels than the recently through a public process which, similar to the measured background concentrations that stage 1 works, culminated in a hearing before already exist in the Grey River… on that commissioners. front, we are successfully cleaning up Greymouth. In preparation for submission for the discharge consents, MWH Global carried out extensive odour dispersion modelling at the WwTP site and dilution modelling of the treated effluent discharge into the Grey River at the Johnston Street outfall. Figure 4 – Wastewater Treatment Performance (cfu/100ml)
WwTP - Pre BTF 100,000,000 WwTP - Post BTF Discharge Consent Limit Johnson St - Post UV 10,000,000
1,000,000
100,000
10,000
1,000
100
10
1 18-Sep-14 17-Dec-14 17-Mar-15
Challenges Faced staff rising to provide pro-active management of the stage 2 works. In addition to the need for the GDC to be adaptable to the changes that would One of the unforeseeable effects on the inevitably occur over such a long term plan stage 2 works was the impact of the there were several challenges worthy of Christchurch rebuild on the availability of mention. contractors and their consequential pricing of tenders. Post-earthquake Christchurch has With such a significant programme of works tended to draw in Contractors from wider- for this project (which included the $7 million afield, including from the West Coast area. for the Taylorville-Dobson-Kaiata reticulation Hence, the GDC has seen fewer contractors and link main and other capital works interested in bidding on stage 2 tenders and associated with upgrading drinking water the price of those tenders has tended to be quality at its water supply plants) on the significantly higher than the estimates. horizon, in addition to the myriad of regular Several times the GDC have been in the issues that council staff are required to attend predicament where they must choose to, it would have been helpful if the GDC between tried and tested local contractors assets and engineering department staffing who are drawn thin with also servicing the levels could have been increased. Naturally, extra opportunities in Christchurch and those the reality of circumstances left the contractors who are not so proven. With the department with lower staff levels than prior volume of works to complete the GDC have to manage the imminent stage 2 works. found it necessary to go forward with both of Fortunately the challenge was well met with these options and both have encountered less than favourable results. Some of the couple of the BTF roof panels. Overall the set tried and tested local contractors proved to back to the roof was minimal but the same be drawn too thinly and have been unable to couldn’t be said for the BTF media. Wind complete works on time, the worst offenders speeds estimated at 120kph sucked plastic being almost 12 months late on a 4 month media petals out of the BTF and distributed contract. The GDC have also suffered quality them around the treatment plant site, the issues with a not so proven contractor with adjacent road and garden centre. In the the Engineer to the Contract recommending aftermath clean up the locals rallied round to the Client (the GDC) that the contractor and between them retrieved an estimated was not fulfilling their obligations and the 250,000 of the plastic media petals, of which contract being terminated. This has left the around 95% were able to be reused, returned GDC with no option other than to employ new into the BTF. contractors to fix up the problems and complete the works. Note that aside from Aside from the final areas to be separated works not being completed on time, there has and the availability of contractors one been upwards of 60 contracts awarded for challenge in particular remains for the GDC, various components of the scheme and only to get the community to connect to the new one contract that has had to be terminated. sewerage system. The connection of However, this one contract was significant at individual households to the new sewerage $1.2m. The overall effect on the GDC was system is the responsibility of the owners and several-fold; the higher cost impact on rate as such the work needs to be organised by payers being immediately obvious, but also and paid for by each individual owner. The the additional draw on the already scarce estimated cost of connection varies between contracting resources, the additional time and $1,000 and $5,000 depending on the extent energy needed to be invested by council of the work required. While this amount may staff, and the combination of the prolonged appear small in the sense of council construction related disruption to the engineering projects, the cost for owners can community and the delayed availability of be significant and for some of the lower separated sewers to that community. decile areas it will be considered prohibitive. From when it becomes available, households While the GDC is still under some time have a period of three years to connect to the pressures to get sewers separated to meet new system. Beyond that time period there consent requirements, the solution are enforcement options available to the recommended by its staff is to slow down the GDC – none of which are desirable. So far rate of tenders with the aim to better match there have been about 40% of property forward works with available contracting owners who have taken the initiative to resources. separate their onsite stormwater and connect to the new sewerage system. The second significant external challenge came from Mother Nature. A significant storm A consequence of the nature of connections occurred during the construction of the to the new sewerage system being gradual wastewater treatment plant. The timing of the over time and random with regard to location storm was particularly cruel with the is the ongoing need to address potential construction of the BTF Roof almost scenarios that may result in odour complete and ready to be lifted into place. generation. For example, if only one Fortunately staff from the GDC and MWH household in a street is connected to the new Global had the presence of mind to use items system there is the potential that self- of plant at the site to hold down the 26m cleansing velocities will not be met with diameter domed roof. Even with tie backs to possible accumulation and generation of trucks and excavators the power of the wind odour. Predicting the likely locations of such was enough to lift the roof off its temporary events is little more than guesswork and so supports and drag one attached truck the GDC developed a suite of odour sideways by a foot or so. A contractor’s site mitigation measures ranging from the most cabin was not restrained and was thrown effective, ‘proactive property connection to around by the wind, causing damage to a the new sewerage system’, to more reactionary responses to be used if required, such as use of chlorine tablets and flushing of sewers and rising mains.
Conclusions
Long term plans that stage infrastructure spend to enable implementation of solutions to be economic can be a useful tool for smaller councils to achieve costly infrastructure projects. Such long term plans should be entered into with the knowledge that regular reviews will be required, and with an acceptance that changes are likely and being adaptive to new technologies should be embraced. Stakeholder communication is a key facet with such council projects and early and ongoing communication can enable the process to occur more smoothly.
Acknowledgments
Cleaning up Greymouth wouldn’t have been possible without the input of the community; Iwi; the West Coast Regional Council; the Ministry of Health; the Department of Conservation; Councillors (past and present); Contractors and the efforts of MWH Global and Grey District Council staff.
References
The majority of information contained in this paper is taken from the many reports authored by MWH Global for Grey District
Council over the past 20 years. We decided not to provide an extensive list herein. If required, further details are available from the authors.
Appendices
Appendix A: Greymouth Sewerage Scheme - Stage 1 and Stage 2 Treatment Plants and Outfalls Locations
Author Biography & Photograph
Simon M cAulay Melvin D Sutherland [email protected] [email protected]
Simon has spent the majority of the last 21 Mel has spent almost his entire 30 year years working in the wet infrastructure career on the West Coast of New Zealand industry on a wide range of potable water, and is currently a member of the executive stormwater and waste water projects in management team of the Grey District both the UK and NZ. Council.
While in the UK Simon worked mostly on He is involved in a wide range of the United Utilities ‘AMP’ programme of infrastructure and community facilities work. He also worked on the Channel management and engineering. He has and Tunnel Rail Link project, focusing on the continues to be involved in a number of track drainage and the tunnel fire-fighting capital improvement projects in these system design. areas.
For the past 11 years Simon has been Recently he has had an involvement with based in Dunedin as project manager with the West Coast Wilderness Trail and is MWH. He currently manages an ongoing currently involved with the Westland portfolio of infrastructure projects for both Recreation Centre. city and district councils and for private enterprises.