Appendix 18 Stage 2 Refined Options Technical Memo Summary of Capex and Opex

Transcription

1 Appendix 18 Stage 2 Refined Options Technical Memo Summary of Capex and Opex

2 Memorandum To: Wolfgang Kanz Date: 4 July 2017 From: Rachael Shaw Our Ref: Copy: Garry Macdonald Subject: Gisborne Stage 2 Refined Options Technical Memo - Summary of Capex and Opex Background The Banks St WWTP s discharge consent requires GDC to establish the most appropriate longterm management option for Gisborne s wastewater by assessing the feasibility and level of community acceptance of upgrading the treatment plant with either a conventional solids removal and disinfection system or an alternative wastewater management system, which may involve a range of alternative use and disposal (AUD) options. As such GDC, in conjunction with NIWA, has been pilot trialling a series of enhanced pond and wetland stages to provide tertiary treatment of the effluent and solids streams following discharge from the existing Biological Trickling Filter plant (BTF). Two concept designs were developed and presented to the WTAG in October Option 1 was for a scaled up natural treatment system based on the processes that have been pilot trialled at the Banks St WWTP. Option 2 was for conventional clarification and solids handling at the Banks St WWTP. The capital cost estimate for Option 1 was significantly higher than Council or the WTAG had anticipated and as such the value engineering workshop undertaken with the WTAG identified a number of permutations of both the conventional treatment and natural treatment process for further development. Order of magnitude capital and whole of life estimates were developed for each of the identified options, described as Options A through K. The options were developed to a level suitable for comparing and screening options. Following presentation to the full Council in December, Council decided to reconvene the WORG and extend the development of the options into an option refinement phase with the objective of presenting the refined options to Council in August Through a series of technical workshops with Council staff, stakeholders and technical specialists, the options were further refined with a change in focus to the alternative treatment being provided through either treatment wetlands or polishing wetlands as opposed to the high rate algal ponds and sludge treatment reed beds evaluated in the pilot trial. Ten refined options have been developed. All are premised on the Banks St site being upgraded to provide as a minimum solids clarification, thickening, dewatering and disposal to a local vermicomposting site. For all refined options, the settled municipal effluent would undergo UV disinfection prior to discharge to either the ocean outfall or the wetlands. Receiving Environments The Waipaoa River, Waikanae Stream, Awapuni Streams, and Taraheru River ecological assessment and hydrodynamic modelling confirmed that even with a very high level of nutrient removal the discharge to a surface water was unlikely to be consentable due to an increase in nutrient loadings. CH2M Beca // 4 July 2017 // Page 1

3 Previous work undertaken by Opus investigated the feasibility of land disposal in the region and concluded that it was not viable as a year-round disposal solution due to the vast areas of land required. Additional work was undertaken by Beca assessing the potential to irrigate wastewater to the Dunes. The assessment concluded that it is unlikely that the dunes could accommodate the full wastewater volume, but could be potentially utilised for disposal of some of the volume. No further work has been undertaken at this stage to progress this option further, although it is noted that it could be considered as part of an integrated reuse and disposal scheme in the future. Given the results of the surface water assessment and the dune irrigation assessment, the options identified for refinement were all based on continued discharge to the marine outfall in the short to medium term. However it should be noted none of the options preclude the potential for future connections to allow reuse or alternative disposal for example irrigation to land in a reasonable proximity, should a suitable market or demand be identified. Basis of Estimates The purpose of these estimates is to provide Comparative Cost Estimate values to support the evaluation and selection of the optimal WWTP solution. Notably, the comparative values for the respective options are not necessarily the expected Total Cost of the option but more likely an indicative outturn cost. These estimates are preliminary and still undergoing internal verification. They are included as a progress update. Please refer the Refined Options Final Report (to be issued) which provides a summary of the level of design development supporting the estimate, the methodology in preparing the estimate, the source and general status of rates applied, assumptions, inclusions and exclusions and the expected level of accuracy associated with these inputs. Option Description Ten refined options were identified and are presented in this report. Three of the options are presented as sub options A or B, depending on whether land for the wetlands is purchased or leased. The options are broadly described below and shown graphically in Figure 1. Option 1 Default Consent Variation (DCV) This option is based on the consented requirement to disinfect wastewater (which comprises the installation of UV in this case) if AUD does not proceed. Solids settlement is required to achieve reliable disinfection to the consented standard. Sludge thickening, dewatering and associated building and storage tanks are required to process the solids to a product which can be transported to a local vermicomposting facility. The option also includes a new pump station to lift the flows to the clarifiers as well as significant ground improvements due to the challenging ground conditions at Banks St. A provisional sum to repossess the remaining portion of the Council owned and designated site (currently occupied by Archives, the Council field office and VTNZ) has been included. Included in the cost is a $1M capital allowance to provide some additional redundancy measures should the BTF need to be taken offline for an extended period for scheduled maintenance or unscheduled repairs. This is intended to cover the costs associated with carrying critical spares, as well as some modification to the clarification process and downstream solids handling, in order to allow the clarifiers to operate as primary clarification process in the event of an extended outage (i.e. several weeks). CH2M Beca // 4 July 2017 // Page 2

4 Option 2 Default Consent Compliant This option is based on the consented requirement to disinfect wastewater (which comprises the installation of UV in this case), and the associated need for solids separation, as well as the consented requirement to reduce the BTF BOD loading to < 0.4kg/m3, should AUD not proceed. It has the same features as the option 1, as well as provision of a new BTF. It does not include the BTF redundancy measures. Option 3a DCV & Polishing Wetland (PW) with Land Lease (LL) This option is based on Option 1 being initially implemented. Following which a new pump station at Banks St, new pipelines to and from the wetland site and a return pump station at the wetland site would be constructed. The 10ha wetland is based on three parallel trains constructed at a site approximately 2.3km from Banks St. This site has been considered as presenting the more conservative (higher end) costs both with respect to pumping and pipeline costs and wetland construction. Following treatment in the wetland, the effluent would be returned to Banks St for discharge to the marine outfall. Lease costs are included in the opex. Option 3b DCV &PW with Land Purchase (LP) As per option 3a but assuming land is purchased. An allowance of $100K per hectare has been included for land purchase. Option 4a DCV & PW with LL & Future Wetland Aeration As per Option 3a but assumes that supplementary aeration will be added to the wetland in the future to encourage greater nitrification. Option 4b DVC & PW with LP & Future Wetland Aeration As per Option 4a but assumes land is purchased. Option 5 DCV & PW with LL & Future Wetland Aeration & wood chip filters (WCF) As per option 4b but includes the future addition of aeration and woodchip filters to the wetland to encourage increased nitrification and denitrification. Option 6 DCV & PW with LL & Future Wetland Aeration & WCF& wetland extension As per Option 5 but includes an extension to the wetland to allow a further 5ha of polishing treatment. Option 7a DCV & PW with LL & Future Second BTF As per Option 3b but allows for the future addition of a BTF for additional treatment and redundancy. Option 7b DCV & PW with LP & Future second BTF As Per Option 7b but assumes land for wetland is purchased. Option 8 DCV & PW with LL & Future second BTF & WCF As per Option 7a with the addition of wood chip filters to the wetland for increased denitrification. CH2M Beca // 4 July 2017 // Page 3

5 Option 9 DCV & PW with LL & Future second BTF & Denit Sand Filter As per option 7a but with the addition of denitrifying sand filters at Banks St for increased denitrification. Option 10 DCV & PW with LL & Future second BTF & WCF & wetland extension As per Option 8 but with the addition of a further 5ha of wetland for further treatment and polishing. As per the value engineering options presented in 2016, the refined options have been developed as building blocks so as to indicate how the capital and operating costs of the individual building blocks combine to give an overall scheme cost. These building blocks are summarised in Figure 1 over page. Each capital cost has been escalated to Depending on how or if Council decides to stage the works, the escalation allowance will need to be re-evaluated to match. This is particularly critical for the wetlands which will likely be constructed over a series of years as well as the longer term building blocks such as the wood chip filters and wetland aeration. Also note, some of the options have been developed to greater cost accuracy than others. The cost certainty associated with each building block is also shown in Figure 1. A summary of the refined option capital and operating costs are provided in Table 1. Table 1: Refined Options Summary of Capex and Annual Opex Option Capex (2020) ($M) Annual Opex ($M) 1 Default Consent Variation (DCV) $24 $ Default Consent Compliant $35 $1.57 3a DCV & Polishing Wetland (PW) with Land Lease $38 $1.84 (LL) 3b DCV &PW with Land Purchase (LP) $39 $1.76 4a DCV & PW with LL & Future Wetland Aeration $39 $1.84 4b DVC & PW with LP & Future Wetland Aeration $40 $ DCV & PW with LL & Future Wetland Aeration & $42 $1.84 wood chip filters (WCF) 6 DCV & PW with LL & Future Wetland Aeration & $46 $1.94 WCF& wetland extension 7a DCV & PW with LL & Future Second BTF $49 $1.96 7b DCV & PW with LP & Future second BTF $50 $ DCV & PW with LL & Future second BTF & WCF $52 $ DCV & PW with LL & Future second BTF & $54 $2.46 Denitrifying Sand Filter 10 DCV & PW with LL & Future second BTF & WCF $56 $2.06 & wetland extension CH2M Beca // 4 July 2017 // Page 4

6 Location Outfall Total Cost Banks Street Remote site Banks Street Remote site Option Key benefits Banks St Land Space for expansion Additional BTF redundancy, resilience By 2020 By 2028 Redundancy measures (no 2nd BTF) Redundancy Clarification, solids, composting AUD, Overall water quality incl. disinfection, biotransformation, resilience UV Disinfection Conveyance (pipes and pumps) to/from Transferring water Polishing wetland (10 ha) Emerging contaminants, metals, resilience, water storage for AUD, cultural aspects, some disinfection Land (purchase) Required for wetland Land (lease) Required for wetland Denitrifying Sand Filter removal Long term (if required for wetland values / AUD / redundancy) Additional BTF redundancy, resilience Aeration in wetland emerging contaminants Denitrifying Woodchip Filter (2 ha) emerging contaminants Additional Wetland Area (5 ha; total = 15 ha) Greater benefit for emerging contaminants, metals, resilience, water storage for AUD, some disinfection, cultural aspects Short Term Relatively low risk treated wastewater disposal option Long Term Relatively low risk treated wastewater disposal option CAPEX ($ M) OPEX ($ M) Average annual cost to ratepayer ($ M) (Consent default) a b a b a b CAPEX Cost ($ M) including escalation OPEX Cost ($ M) Cost confidence -30/+50% -15/35% -30/+50% -15/35% -15/35% -15/35% TBC TBC TBC -15/35% -15/35% -30/+50% -30/+50% -30/+50% Year escalated to Figure 1 Refined Options Matrix CH2M Beca // 4 July 2017 // Page 1

7 Rachael Shaw Technical Director - Project Management Direct Dial: rachael.shaw@beca.com CH2M Beca // 4 July 2017 // Page 2