report: response to auckland regional council request for ... · rule 10.5.2(i) existing stormwater...

S E C T I O N 4

Miscellaneous

4.4.6 Habitat Protection

Information Requested

ARC Q31. What special controls (besides sediment fences?), will be put in place to protect areas of salt marsh?

Response

To begin with, it is noted that in most cases salt-marshes located in the low-energy environments of the upper reaches of harbours and estuaries (such as in the Mangere Inlet) perform the role of an agent of active natural reclamation. In this role they trap and consolidate marine (and terrestrial) fine silts and sediments, to the extent that terrestrial processes can begin to take hold. This sediment entrapment and consolidation process is an entirely natural function of salt-marshes.

In specific response to the question above, it is noted that the occurrence of any saline vegetation in the immediate vicinity of the project is very small in extent. It furthermore involves only species and communities that are common and well represented elsewhere within the Mangere Inlet.

It is additionally noted that while silt fences will certainly be used on this project, it is recognised that they are but one option under the ARC Technical Publication guidelines that relate to erosion and sediment control devices and techniques. Additional comprehensive and effective erosion and sediment controls are an integral component of the Project.

For example, all construction activities (and zones) that have the potential to generate large volumes of sediment have been designed to include stormwater detention (and treatment) ponds. These will protect the salt-marsh areas from smothering by sediment.

In addition, vehicles and machinery will not be parked on or moved through the salt-marsh areas, and people will not be allowed to trample through it. The salt-marsh area will be cordoned off to make it clear to the construction team or other related people that entry into the area is not permitted. This will be reinforced with “tool-box” meetings with the construction crew in the early stages of the project.

4.4.7 Salt Marsh at Onehunga Harbour Road Temporary Reclamation


ARC Q31. Please explain the ecological basis for the expectation that a saltmarsh would extend into or thrive in the reinstated environment of the Onehunga harbour Road temporary reclamation. Please explain why an extended saltmarsh would be an enhancement of the environment if created in this location.

The proposed temporary reclamation in this area is now no longer proposed.

4.4.8 Contaminant Levels


ARC Q31. What are the existing contaminant levels in the marine environment and how will stormwater runoff from the bridge influence them?

Response

In response to this query, it is first noted that the project is located within a totally urban environment (both suburbia and industry), and for the most part simply seeks to widen an existing transport corridor. In this context, any effects on the receiving environments that the project may generate (at least in terms of contaminants) are more than likely already being made manifest.

MHX-RP-005 ARC S92 Response Amended 14 Sept.doc4-18

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Sediment samples collected by ARC from the Mangere sampling station, analysed for grain size, indicate that the sediment is dominated by fines, with approximately 80% silt, 4% clay and 16% very fine sand. Generally, the smaller the grain size, the higher the organic content of the sediment. Many contaminants are positively correlated with high organic content.

Sediment within the Mangere Inlet is contaminated with heavy metals (Zn, Pb, Cu, As, Cd, Cr), organochlorine pesticides (chlordane, DDT) and PAHs from past industrial discharges, landfill leachate and wastewater. Contaminant levels are highest in Mangere Inlet and decrease towards the Tasman Sea (Williamson et al., 1996).

ARC have reported in their marine sediment survey that the concentration of zinc, copper and lead in sediment from the Mangere site is within the Environmental Response Criteria (ERC) amber range and the concentration of dieldrin is higher than the ERC red level.

A survey of trace metal levels in fish from the Manukau Harbour was carried out by Winchester in 1988 and revealed the following concentrations in mg/kg fresh weight (gut tissue).

Species Cu Cr Zn Pb As Cd Mn Ni Co Flounder 75 0.9 66 9.6 1.9 0.6 21 34 1.4 Mullet 94 1.6 41 1.7 1.8 <0.2 83 1.6 1.2

These metal concentrations in fish tissue reflect the current state of the Manukau Harbour.

Stormwater from roads generally contains contaminants such as heavy metals and polycyclic aromatic hydrocarbons. The design of the stormwater treatment systems for this project indicates that carriageway runoff will be conveyed from the bridge to ponds and wetlands for treatment prior to ultimate discharge into the harbour. As such, in accordance with ARC TP108, runoff from the south side of the new bridge will be conveyed to a wetland, and runoff from the north side will be directed via a swale to another wetland. Treatment in the wetland ponds is designed to remove 75% of the sediment prior to discharge into the harbour.

Given that the majority of contaminants are bound to sediment, there will be a positive correlation between sediment removal and contaminant removal from stormwater flows. As a result of this level of treatment, and given the water quality state of the existing environment that this treated stormwater will ultimately be discharged into, it is considered that any effects on the marine environment will be no more than minor.

NOTE: Refer to references in Section 5 of this report.

4.5 Permitted activity baseline


ARC Q32. It does not appear that a Permitted activity baseline has been carried out for any of the proposed activities or structures. Where it is concluded that adverse effects on the environment will be no more than minor this should be justified by reference to the standards and terms of the Permitted activity rules relevant to the effects.

Where it is concluded that adverse effects on the environment will be no more than minor (such as in sections 6.9 Coastal Processes and 6.10 Ecology and Water Quality), please carry out a Permitted Activity Baseline assessment.

Response

Under Section 94A(a) a consent authority “may disregard an adverse effect of the activity on the environment if the Plan permits an activity with that effect”. This is for the purpose of making a decision under Section 93 as to whether there are minor or more than minor effects. In other words, whether an


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application should be publicly notified or not. A decision has already been made by Transit in consultation with the three consent authorities, that the applications will all be publicly notified. In fact, a new Notice of Requirement is always processed on a publicly notified basis, as is an application that involves a restricted coastal activity.

As such, the permitted baseline assessment is of limited relevance in a statutory sense. However, in order to answer this question, the following summary table has been prepared setting out all the activities that may be undertaken as a permitted activity in the areas proposed to be affected by the project.

Table 4-1: Permitted Activity Baseline

Relevant Activity – Rule relevant to this project Comment

Rule 10.5.2(i) Existing stormwater and wastewater structures occupying part of the CMA at 23 October 2001, and any subsequent upgrade to such a structure that forms part of a stormwater or wastewater network operated or managed by a stormwater or wastewater network utility operator. Activity status is subject to conditions.

Many of the stormwater outfall structures affected by this proposal are already existing, and therefore form part of the permitted baseline for this project.

Rule 12.5.1 The maintenance, repair or reconstruction of any existing lawful structure, subject to the following conditions: …

The seawalls around the existing Orpheus Drive reclamation can be repaired and maintained as a permitted activity. The difference between repairing the edge of the existing reclamation and adding a strip along the edge of the reclamation is a relevant comparison in order to quantify the effects from a permitted baseline perspective. It is noted that under the Rules in Section 13 of the Plan, no reclamation is allowed as a permitted activity (all reclamations require a resource consent).

Rule 12.5.3 Structures erected and placed entirely below the surface of the foreshore and seabed, by methods other than trenching, but not the occupation by those structures, subject to the following conditions:…

Piers for duplicate bridge are within the scope of the application lodged.

Rule 12.5.5 The erection or placement of any temporary structure, and any associated occupation, subject to the following conditions:…

Temporary works may occur in the CMA for up to 14 days consecutively, and must be removed in a way so that effects on the coastal environment are unnoticeable. Whilst the temporary works for this project will remain in place for significantly longer than 14 days consecutively, it is important to recognise that the Plan does allow for some temproaray works to be undertaken – for the purpose of the permitted baseline assessment.

Rule 16.5.1 Any disturbance of the foreshore and seabed for the purposes of removing litter or marine debris, provided that the disturbance shall not involve the removal of sediment from the foreshore, other than sediment that is reasonably attached to any litter or marine debris.

Rule 20.5.4 Discharges into the coastal marine area, which are not covered by another permitted activity rule, subject to the following conditions:…

Any permitted activity discharges cannot contain any contaminants that will cause more than minor effects, and cannot contain raw sewage or change the temperature of the water more than 3 degrees.

Under Section 10 of the Act some activities have existing use rights subject to certain conditions. Whilst existing use rights cannot apply to activities that require regional consents, existing reclamations that are now part of the District Council’s jurisdiction can have existing use rights and therefore can form part of the permitted baseline.

The existing reclamations in the area of Orpheus Drive are part of the existing environment and are likely to enjoy existing use rights.

In summary, the permitted baseline for the project, as it applies to the coastal marine area, largely comprises the existing environment. A limited range of activities are allowed as permitted activities in the


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CMA and these form part of the permitted baseline, but the majority of the activities proposed are not permitted.

The existing environment has already been well described in other parts of this report and in the original resource consent applications.

4.6 Coastal Processes


ARC Q33. Please describe the tidal characteristics and the geomorphology of the area. Please identify the wind field (wind rose: direction, strength, and frequency) the fetches, and then predict the wave climate. In addition, a discussion of any interactions between the proposed structures and coastal processes is required.

Please describe the potential adverse effects of the proposed works on the Tararata Creek and in the low energy environment where tidal flushing is less than in the main channel.

Please submit designs of the Duplicate Bridge, the new Mangere footbridge and the proposed Fender structure showing the number and spacing of piles.

The report indicates a number of design matters have not been determined, e.g. actual number and location of bridge piers to be determined at design phase, the level and location of pilecaps, and detail of temporary reclamations. Nevertheless it is considered in the report that the potential effects on tidal flows, and ultimately in terms of environmental effects, will be minor, or expected that they will be minor. Overall, this leaves ARC in a position of uncertainty.

Furthermore, it appears no site specific information has been collected, e.g. on page 13 ...there is some evidence from the marine chart that tidal current flows take place ... (page 14) The Marine Chart states that the current direction…….

Please provide assessments of the effects of these proposed structures on coastal processes in the inlet. Numerical modelling of the Duplicate Bridge should be carried out now and submitted as part of the application.

Please describe how the design will ensure that changes in the flow energy between bridge piers and fenders would not result in more than minor effects on the tidal currents and hydraulics of the CMA?

What effect will the structures, including the new pedestrian cycle bridge, have on the hydrodynamics of the inlet?

Please describe what remedial measures can be taken to deal with the build up of sediment behind the breakwater. What are the predicted effects of the reclamations on this sedimentation process?

Response

Refer to Appendix B and the earlier response to Question (17).

4.7 Monitoring


34. Part 3.5 (Appendix 22 p20) of the suggested conditions of consent deals with Monitoring. Please explain how compliance with these suggested conditions will avoid, remedy or mitigate adverse effects on the environment arising from the project.

The design of the project incorporates measures to avoid, remedy or mitigate adverse effects on the environment. As with other major construction projects, a suite of conditions will apply to the works to:

1. Ensure that work is carried out generally in accordance with information submitted with the applications; and


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2. To ensure that appropriate methods and controls are in place before, during and after construction to minimise potential adverse effects.

ARC Q34. A photo record is proposed. It is not clear what its purpose is, or how useful it would be. Please explain what it would achieve.

It is intended that regular aerial photographs will be taken at key stages throughout the project. The present aerial will serve as a baseline for comparison during and after construction of the project. The photo record will (for example) identify any new areas of sediment buildup or new tidal flow patterns, record any changes to the seabed, record any changes around the bridge piers and stormwater outfalls.

A series of photographs from land will also be taken throughout construction of the project.

4.8 Navigation and safety


ARC Q35. It is suggested that navigation is unlikely to be affected. Presumably that will be dependent on the nature and location of the various piles/structures that are to be placed in the CMA.

Please explain the navigation and safety aspects of the project.

Response

Refer also to Appendix B.

The general elevation and plan of the existing motorway bridge is attached. This is as-built drawing 1/87/10/7144 sheet 7. The existing bridge has eight sets of piles within the CMA, seven of which are situated within the main channel. This figure shows the existing bridge was designed taking into account potential enlargements to the port with the provision of a shipping berth and an additional navigation channel to enable passage to Pikes Point as well as a significant reclamation that provided additional port land, a motorway extension and a cooling water outlet.

Discussion with the Property Manager for the Port has indicated that there are no immediate plans for enlarging the existing port area, although they are constrained for space and would like additional land area. However, they wish to retain the possibility of navigation access to Pikes Point for barges and tugs at some time in the future.

The longer spans on the existing bridge make allowance for eastern expansion of the Onehunga Wharf (Port) and a navigation channel in the deepest part of the Harbour. The 45m wide channels, as envisaged in the original design, are shown on drawing 5001 included in Section 2.2 of this report, even though plans for the inner harbour development have diminished

The shorter spans of the existing bridge make allowance for Onehunga Harbour Road and the Onehunga Branch Rail line.

The pier locations proposed for the duplicate bridge avoid the navigation and berthing channels, as originally proposed, and still provide for clearance to Onehunga Harbour Road and the Rail line. In doing so the duplicate bridge remains faithful to the original designers intention but in a way that reflects modern bridge design practice.


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4.9 Sedimentation


ARC Q36. Significant potential adverse effects would appear to be related to sedimentation (as also referred to the coastal ecology/water quality report). Please describe the extent of maintenance dredging POAL carry out in the adjacent port area, and how the proposal may affect or be affected by that.

Refer to the earlier response to Question (17).

ARC Q36. What will the efficacy of sediment control be during construction and will it be adequate to prevent environmental degradation?

Refer to the earlier response to Question (31).

ARC Q36. How will sediment plumes generated from the suspension of material from the seabed be controlled during the construction and/or removal of structures?

There is likely to be a temporary generation of sediment during installation of sheet piles and then again during removal. Sheet piles are proposed around the main bridge piles and all works associated with bridge pile construction will be contained within the bounds of the sheetpiling.

4.10 Stormwater and Earthworks

4.10.1 Stormwater Management


ARC Q37. The PARP:ALW (Policy 5.4.4 (e) (ii)) requires that that when considering a Resource Consent to Divert and Discharge Stormwater the ARC requires the applicant to adopt the Best Practicable Option (BPO) for the diversion and discharge of stormwater. This shall be determined by having regard to, the level of stormwater quality treatment provided for existing impervious areas to ensure the greatest extent practicable of TSS removal is achieved on an average annual basis.

Whilst it may well be that the current level of TSS removal is the Best Practicable Option for stormwater management, without a thorough options analysis there is no way for the ARC to make this assessment. In this regard, please provide an options analysis of the proposed stormwater treatment devices to demonstrate the differing levels of TSS removal that can be achieved (in accordance with Policy 5.4.4). This analysis should include at least 3 options for different levels of contaminant removal. The benefit to the receiving environment, cost and practical implementation of each option should be considered and compared.

Please when providing maps / plans show representative sizes of the devices.

The Application must have sufficient detail to provide a level of confidence that the proposed stormwater management devices can be constructed. This should include information about:

• re-suspension issues considered;

• in areas where levels are an issue further details should be provided;

• feasibility of device specifically looking at key issues of each device (if any).

• constructability / feasibility of the proposed measures.


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Response

The request for an options analysis arose from the fact that the submission documentation proposed a level of treatment that achieved ARC TP10 guidelines for 75% sediment removal with respect to new pavements, but not with respect to total contributory catchment areas.

Further analysis undertaken post lodgement and refinement of stormwater management proposals has enabled the outcome that a level of treatment that achieves ARC TP10 guidelines for 75% sediment removal can generally be achieved for total contributory catchment areas. Appendix C provides the basis for this outcome.

On the basis of this improved outcome, an options analysis is no longer considered necessary.

4.10.2 Erosion and Sediment Control


ARC Q37. It is understood that the erosion and sediment control plans are indicative, however additional information is required. Please provide catchment boundaries for the proposed sediment control devices.

Response

Following discussions with ARC staff, it appears that this concern relates more to the extent of the site apparently treated by lower efficiency control measures rather than by the more sediment retention efficient chemical treatment systems. The indicative erosion and sediment control plans (ESCPs) previously submitted to the ARC have been reviewed in this light and the revised plans are attached (Drawings D-041-5001 to 5007).

The most effective chemical treatment system is that which is installed on sediment retention ponds, but the construction of most sediment retention ponds requires a significant area of land. One of the characteristics of this project is the lack of room along the route on which to place sediment retention ponds and, in some places, there is simply no room available to construct a pond. In addition, there are some very flat sections along the route where concentrating runoff and directing it to sediment retention ponds will be difficult (e.g. next to Onehunga Bay). Therefore, not all site runoff will be able to be directed to sediment retention ponds, either through a lack of room on which to construct a pond or because the site is too flat to obtain fall.

The review of the ESCPs has resulted in a change in location and type of some of the sediment control measures along the route. In summary, reassessment of the ESCPs has resulted in an additional 4 hectares of site runoff being directed to a chemical system for treatment. Approximately 6 hectares of land remain for which would be difficult to direct runoff to conventional chemical treatment systems. Indicative sediment control facilities for these areas are proposed to be super silt fences, decanting earth bunds and similar.

The primary erosion and sediment control facilities and their catchments are shown on the attached ESCPs, Drawings D-041-5001 to 5007.

A revised USLE assessment for the new ESCPs has been undertaken and is attached. Allowing for 95% sediment retention efficiency of chemical treatment systems, and 50% for other measures, the assessment indicates that approximately 20 tonnes or so of sediment is likely to be discharged from the proposed works during construction. This is a slightly higher figure than that derived in an earlier USLE assessment provided to the ARC despite more of the site being treated by the higher efficiency chemical treatment systems. The higher assessment is due to a more detailed break-down of the site, lower efficiency levels assumed for sediment retention measures other than chemical treatment systems, and the adoption of a more conservative P value in the USLE model.


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Information Reqested

ARC Q37. Please provide a detailed erosion and sediment control plan and methodology for the proposed reclamations and including the removal of material associated with the temporary reclamations.

Response

Only one area of reclamation is proposed as part of the project works, this being a permanent reclamation at Orpheus Drive as indicated on Project Drawing Number P-181-5004. The reclamation works will be undertaken in progressive stages with small areas worked on and completed before the next stage is commenced. Material will need to be imported to construct the reclamations and this material would be granular rock. The reclamation fill would be brought up to final height and erosion protection measures installed on the outside face to protect it from wave damage. The final erosion control measure, probably rock rip rap, would be installed on the outside of the permanent reclamations.

Temporary sediment control during construction would be undertaken with floating sediment curtains although only low levels of sediment are likely to be produced during this operation.

There are a number of methodology options that can be undertaken for the reclamations and two scenarios that relate to different site conditions are discussed below. Note however that the actual method(s) of reclamation may vary from that outlined below.

Option 1

This option would relate to areas with little overlying unconsolidated marine muds, a firm underlying substrate, and a relatively small width of reclamation e.g. less than 20m distance from the present shoreline.

A combination of rock granular fill and geogrid could be placed directly on these areas. The works would be undertaken progressively along the shore, perhaps in 20 metres stages, with the fill progressively brought up to a level where it would be protected against storm damage. Little or no unconsolidated material would be expected to be “squeezed” out from under this filling operation because little of this material is present. No material will be removed from the site under this operation and rock material only will be imported. Little sediment is expected to be generated. Temporary sediment control and permanent erosion control measures have been discussed above.

Option 2

Loose unconsolidated marine muds and a relatively wide width of reclamation e.g. 30m or more distance from the present shoreline.

In this situation, a likely construction scenario would be the construction of a narrow causeway along the outer edge of the reclamation and which would slowly extend along the length of the reclamation. This causeway would be made with rock fill and constructed to full height with erosion protection placed on the outer face to protect against wave action. At the same time as this causeway was being constructed, rock bunds would be pushed out from the shore line to join with the causeway and so create small “cells”. These cells would then be filled with rock fill.

There would be expected to be a limited amount of loose marine material pushed out seaward by the construction of the outer causeway but this should be restricted to the outer half of the causeway (the inner half would be pushed out landward and into the eventual cell). That pushed out by the bunds would also be contained by the cells. Once the cells have been formed, the unconsolidated marine muds contained within the causeway and bund could either be removed off site, or stabilised (e.g. with cement) and geogrid laid down interspersed with compacted rock fill. Water contained within the cell would be pumped to a tank or to a sump in the adjacent cell once it, in turn, has been isolated from the sea. This


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water would then be tested for excessive turbidity or cementitious material (from any cement or other stabilisation works), treated as required and then discharged from the site. Details associated with the testing and treatment methodology would be expected to form part of the eventual chemical management plan for the project.

Again rock material would be used for fill.

Universal Soil Loss Equation – Indicative Soil Loss Estimation

Table 4-2: Universal Soil Loss Equation Factors

A = R K LS C P

Where R = 67 (75 mm – 2yr 24 hour rainfall - ARC TP 108).

K = 0.54 (bare soil)

0.34 (60-75% rock. Conservative as this includes an allowance for loose sediment on the rock surface).

LS = 0.41 (3% slope, 100m length).

0.27 (3%, 25 m length)

0.20 (2%, 30m – Reclamations)

5.41 (33%, 10m – Batters)

C = 1.0 (bare).

P = Assume 1.1 during works

Sediment control efficiency = 95 % for chemically treated TP 90 ponds,

50% for other measures

Sediment delivery ratio = 0.5

Earthworks period = I year for carriageway works, 2 months for batters and reclamation works

Table 4-3: Stage 1 - Estimated Soil Loss

Location Area (ha)

R K LS C P Time (yr)

sdr Efficiency (%)

Total yield (tonnes)

Carriageway 19.1 67 0.54 0.41 1.0 1.1 1.0 0.5 95 7.8 Carriageway 2.2 67 0.54 0.27 1.0 1.1 1.0 0.5 50 5.9 Batters 0.6 67 0.54 5.41 1.0 1.1 0.16 0.5 50 5.1 Reclamation 2.1 67 0.34 0.2 1.0 1.1 0.16 0.5 50 0.4 Total 24.0 19.2


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4.11 Coastal stormwater outfalls


ARC Q38. Please provide one plan identifying all existing and proposed stormwater outfalls in the project area. Show which have existing resource consents and any existing outfalls that do not have consent. Please explain how new and existing stormwater outfalls will be integrated to serve the whole area. Please identify the ownership and maintenance responsibilities of each outfall.

Response

The stormwater report in Appendix C presents the detail of the revised design of the proposed motorway drainage and runoff treatment systems. This is based on the design originally presented with the application, but refined on the basis of the greater detail of information now available.


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References

5 References

Allen, D., 2006. Discussion with Dave Allen at Ministry of Fisheries regarding fish species in the Manukau Harbour.

Gibbs, M. & Hewitt, J., 2004. Effects of sedimentation on macrofaunal communities: a synthesis of research studies for ARC. ARC Technical Publication No. 264, Auckland Regional Council.

Hewitt, J., Hatton, S., Safi, K., Craggs, R., 2001. Effects of suspended sediment levels on suspension feeding shellfish in the Whitford embayment. Prepared for Auckland Regional Council. NIWA Client report ARC00205.

Lowe, M., 2006. Unpublished data. NIWA, Auckland.

Morrison, M.A., Francis, M.P., Hartill, B.W., Parkinson, D.M., 2002. Diurnal and tidal variation in the abundance of the fish fauna of a temperate tidal mudflat. Estuarine, Coastal and Shelf Science, 54, 793-807.

Nicholls, P., Hewitt, J., Halliday, J., 2003. Effects of suspended sediment concentrations on suspension and deposit feeding marine macrofauna. ARC Technical Publication No. 211. Auckland Regional Council.

Thrush, S.F., Hewitt, J.E., Cummings, V.J., Green, M.O., Funnell, G.A., Wilkinson, M.R., 2000. The generality of field experiments: interactions between local and broad-scale processes. Ecology, 81 (2), 399-415.

Williamson, R.B., Van Dam, L.F., Bell, R.G., Green, M.O., Kim, J.P., 1996. Heavy metal and suspended sediment fluxes from a contaminated, intertidal inlet (Manukau Harbour, New Zealand). Marine Pollution Bulletin, 32 (11), 812-822.

Winchester, R.V., 1988. Trace metal levels in fish from the Manukau Harbour, Auckland, New Zealand, related to a water pollution incident. New Zealand Journal of Marine and Freshwater Research, 22, 621-624.

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