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CFH-309448-3-441-V4

BEFORE THE ENVIRONMENT COURT CHRISTCHURCH REGISTRY ENV-2016-CHC-47

IN THE MATTER of an appeal under Section 120 Resource Management Act 1991

BETWEEN BLUESKIN ENERGY LIMITED Appellant AND DUNEDIN CITY COUNCIL Respondent

EVIDENCE IN CHIEF FOR MARK TAPIO WALROND

____________________________________________________________

GALLAWAY COOK ALLAN LAWYERS DUNEDIN

Solicitor on record: B Irving

Solicitor to contact: B Irving/C F Hodgson P O Box 143, Dunedin 9054

Ph: (03) 477 7312 Fax: (03) 477 5564

Email: [email protected] Email: [email protected]

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Introduction

1. My full name is Mark Tapio Walrond. I am a Senior Engineering

Geologist with GeoSolve Ltd, based in Dunedin. I hold MSc (Geol) and

BSc (Geol) degrees from the University of Otago. I have been involved

in geotechnical consulting for 12 years in Dunedin and the wider

Otago/Southland area. I also have experience in engineering geology

elsewhere in New Zealand and mineral exploration in both New Zealand

and Australia.

2. I have read the Code of Conduct for Expert Witnesses within the

Environment Court Consolidated Practice Note 2014 and I agree to

comply with that Code. This evidence is within my area of expertise,

except where I state I am relying on what I have been told by another

person. To the best of my knowledge I have not omitted to consider any

material facts known to me that might alter or detract from the opinions I

express.

Scope of Evidence

3. This evidence will cover the following matters:

(a) My prior involvement in this project;

(b) Geological characteristics of the application site.

Previous involvement in the Project

4. I prepared a preliminary report for the original three turbine application

on behalf of the applicant. That report was based on test pitting and

concluded that the proposed sites of the three wind turbines were likely

to be suitable from a geotechnical perspective for the construction of the

turbine foundations, subject to some additional testing work at the

detailed design phase. A copy of that report is attached at Appendix 1 to

this evidence.

5. Test pitting was chosen as the most appropriate method to initially

assess the properties of the soils and underlying rock at the turbine site

due to the obvious near surface boulders and adjacent exposures of

strong rock. There were also reports of shallow refusal during previous

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subsurface investigations. An engineering geological site appraisal has

been undertaken previously by GeoSolve Ltd. Test pitting was

undertaken at the locations proposed for the 3 turbines. Three test pits

were advanced to a maximum depth of 2.8 m. Scala Penetrometer tests

were also undertaken at selected locations at each test pit location

advancing to refusal.

Geological Characteristics of Application site

6. Porteous Hill is a Miocene volcanic centre. The published geological

mapping indicates that Porteous Hill comprises layered rock types of the

Dunedin Volcanic Group overlying sedimentary rock of both marine (e.g.

Caversham Sandstone) and non-marine origin (i.e. Older Floodplain

Conglomerate). Benson 19401 indicates that the volcanic rocks of

Porteous Hill are likely to be fed by volcanic vents rather than simply

comprising remnants of more extensive capping lava flows. The location

of deeper vents and the full extent of the volcanic rocks below the site is

currently unknown, however a significant cover of volcanic rock is

present based on the investigation work and adjacent mapping.

Assessment of revised proposal

7. I understand that Blueskin Energy now wish to amend the application to

provide for one 3 MW turbine of approximately 110 m height. I have

been provided with the specifications of the Enercon E83 turbine and

have reviewed the foundation requirements as set out in the foundation

data sheet supplied by the manufacturer. The required foundation is

circular concrete base with a diameter of 17.4 m and a thickness of up to

2.7 m, requiring 416 m3 of concrete and over 40 t of reinforcing steel.

The specification outlines details of the required dynamic stiffness

moduli, allowable tilting as a result of settlement and the soil bearing

pressure.

Geotechnical Characteristics of the Proposed Turbine Location

8. At the proposed turbine site the surface contains abundant sub-rounded

boulders of strong crystalline volcanic rock. Test pit excavation revealed

1 Landslides and Allied Features in the Dunedin District in Relation to Geological Structure, Topography and

Engineering, W.N. Benson 1940

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that the upper metre comprises similar boulders up to 700 mm in a

matrix of predominantly silt and clay. The upper metre is interpreted as

residual soil derived from advanced weathering of the volcanic rocks

beneath. Weathered volcanic rock is exposed beyond around 1 m depth

and comprises spheroidally weathered, fine grained crystalline volcanic

rock. The rock appears to be highly fractured, most likely as a result of

cracking induced by the process of lava cooling. Chemical weathering

processes associated with water infiltration have resulted in complete

weathering of the rock along these fracture margins and hence the rock

comprises “abundant core stones” or boulders of strong to extremely

strong volcanic rock bounded by thin zones of completely weathered

rock (stiff silty clay). Oxidation products are abundant such as orange

iron oxides and black oxides (possibly manganese oxide).

9. No Scala penetrometer testing was carried out in either the residual soil

or the underlying rock owing to obvious refusal likely on boulders or

core-stones at shallow depth. Dense to very dense soil conditions are

interpreted in the upper metre underlain by weathered volcanic rock

predominantly in strong condition or better.

10. The excavator was able to proceed to a maximum depth of

approximately 2.8 m at these sites with a toothed bucket owing to the

fractured nature of the rock, however excavation was difficult beyond this

depth probably indicating that stronger rock is present below about 3 m

depth.

Slope Stability of the Proposed Turbine Location

11. We note that Enercon require slope stability verification for foundations

near slopes. Owing to the proximity of landslide features locally, a

cautious approach should be adopted and further evaluation of slope

stability is recommended during detailed design. No major slope stability

issues are expected at the turbine site which is to be founded on strong

volcanic rock with no known landslide mapping or tectonic deformation

structures in the vicinity. Hence there is only a very low risk that slope

instability will affect project feasibility.

12. There are no potential sources of debris inundation, rock fall or rock roll

that could affect these hill crest sites from upslope sources.

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13. Owing to the extensive slope instability developed on the flanks of

Porteous Hill and the current uncertainty regarding the location of failure

planes and the vertical extent of the volcanic rocks (including vent

structures), a surveyor could be engaged to advise if historical survey

data can be used to confirm any movement of benchmarks that may be

available at the summit of Porteous Hill. If this is not possible then further

geological mapping and geotechnical investigation including drilling

should be considered to enable full confirmation of slope stability.

14. Attention will also be required to assess the slopes below the sites. We

note that the turbine site is adjacent to a steep slope. Cross sections

should be generated and slope stability analysis carried out once the

final platform is confirmed and following additional mapping and

subsurface investigations. These analyses should consider both static

and seismic stability.

15. Following excavation for pad foundations, no adversely oriented defects

are expected to affect the volcanic rock at foundation level. The rock is

known to be jointed and therefore standard construction observation will

be required during bulk earthworks when defects, if any, are fully

exposed. Careful mapping and evaluation of any defects and lineaments

encountered will be required within the foundation excavations, and

stability analysis should be carried out at that stage to confirm safety

factors. Defects should be checked to ensure there is no potential for

defect-controlled slope instability. If significant defects or other adverse

structures such as faults or landslide shear surfaces are encountered

then the site may require remedial stabilisation works (e.g. rock

anchoring).

16. Cavities are not likely to be encountered at these sites as the subgrade

rock types are not calcareous and no active tectonic activity is mapped

in the vicinity.

Geotechnical Design and Construction Considerations

17. We recommend that geotechnical aspects such as rocking spring

stiffness, settlement calculations and bearing capacity should be verified

for the site by appropriate testing during the detailed design phase.

Laboratory testing of rock and soil samples may be required. We

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recommend that the manufacturer specify the type of testing required to

meet their requirements, based on the preliminary ground model

identified. The above work is conventionally carried out as part of the

building consent application.

18. Weathered volcanic rock is present at shallow depth. Deep foundations

are not likely to be required and the appropriate foundation solution is

likely to comprise undercutting any obviously weathered or fractured

rock prior to replacement with compacted AP65 aggregate and

construction of the manufacturer’s shallow foundation system.

19. On rock sites, such as these Enercon recommend that a suitable boring

should be made to at least 2 m below the base of the foundation and this

will be required. Deeper confirmatory drilling is recommended, as

discussed above, to verify the persistence of the volcanic layers, quality

of the rock and to ensure that weaker sedimentary rocks or landslide

mechanisms are not present at shallow depth. This is considered to be a

precautionary measure only to enable a full understanding of the ground

model and to evaluate the need for anchoring. Based on current

observations, we consider it a very low risk that such investigations will

reveal data that would affect the feasibility of the project.

20. For rock sites, such as these the manufacturer may specify shallow

foundations with grouted anchors. Enercon specify that for preliminary

design in this case, information is required on rock fissuring. At these

sites the rock is known to be relatively rippable (or easily excavated) to a

depth of at least 2.8 m owing to joint sets within the weathered upper

part of the rock profile. If anchors are required (following more detailed

drilling investigations) then further evaluation of the rock quality may be

required for anchor design.

21. Additional SPT or HDCP testing (i.e. standard testing to evaluate soil

density) is unlikely to be feasible at these sites as immediate refusal on

rock is likely. Rock is expected to predominate at subgrade level when

excavations are complete, however Scala penetrometer testing or other

appropriate methods should also be carried out to verify stiffness

requirements are met if rock is not universally encountered. Although I

considered this to be unlikely.

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22. Compaction of granular backfill (for both the crane platforms and under

any foundations) should be carried out in accordance with a specification

prepared by a geotechnical engineer with consideration of the

manufacturer’s requirements, however compaction and verification by

NDM testing in accordance with NZS 4431 is likely to be adequate.

23. Construction supervision of the foundation excavations and fill

placement is required and this should be carried out by a geotechnical

practitioner with documentation of approval via producer statements.

The foundation subgrade should be inspected by a geotechnical

practitioner to ensure that defects or other stability or bearing capacity

risks are not present.

24. We note that soil resistivity requires measurement in accordance with

the manufacturers guidance.

Groundwater Characteristics of the Location

25. The possible effects of turbines on the Porteous Hill Groundwater

system has been raised as a concern by some submitters. GeoSolve

has reported on these aspects in a report dated 30 May 2016

(appended).

26. The proposed development is located within the zone of infiltration that

recharges an unconfined aquifer at considerable depth below the crest

of Porteous Hill.

27. The shallow foundations for the turbine and limited hardstanding

proposed means that the development can be constructed without

creating any physical impediments to rainwater infiltration or

groundwater flow. Consequently the volume of spring flows is very

unlikely to be affected by this single turbine development.

28. The turbine would be founded on volcanic rock and hence there are no

potential vibration effects that could have an adverse effect on the

groundwater at depth.

29. Precautions will be required to minimise the possibility of accidental

chemical spills to ground during construction and future maintenance.

This can be managed through conditions of consent.

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Matters to be addressed for detailed design

30. Some further geotechnical work is recommended as part of the detailed

foundation design phase (as described above). This could be readily

addressed by means of consent conditions suggested below. The key

aspects are additional drilling work to confirm the ground model, further

confirmatory consideration of slope stability including slope analysis and

observational geotechnical involvement at the construction stage.

31. We have not considered the geotechnical aspects associated with

accessways or transmission line structures at this stage, however some

landslide terrain may be encountered and we recommend that these

aspects are addressed at an early stage to confirm the optimal locations

and risk considerations for roads and transmission line supports.

32. We recommend that a surveyor should be engaged to determine the

most appropriate alignment for the accessway and transmission lines.

Unless alignments require minimal cut or fill (less than 1.5 m high or

thick), cross sections at critical locations should be provided by the

surveyor showing cut and fill profiles. These cross sections should be

checked by a geotechnical practitioner to enable advice on any physical

support requirements and any need for site specific design for structures

founded on any active landslide areas.

33. Construction of the accessway and transmission structures should be

carried out under the supervision of a geotechnical practitioner. Any

seepage encountered will require appropriate drainage measures during

the earthworks.

Recommended Conditions

34. Suitable investigation should be made to at least 2 m below the base of

the foundation. This will be required as a minimum. Subsequent deeper

confirmatory drilling should be carried out, if considered necessary by

the geotechnical engineer, to verify the persistence of the volcanic

layers, quality of the rock and to ensure that weaker sedimentary rocks

or landslide mechanisms are not present.

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35. Further evaluation of slope stability should be carried out during the

detailed design phase, with reporting to confirm any appropriate design

revisions or remedial works.

36. Geotechnical aspects for all sites such as rocking spring stiffness,

settlement calculations and bearing capacity should be verified by

appropriate testing and analysis during the detailed design phase.

37. The turbine foundation subgrade should be inspected by a geotechnical

practitioner to ensure that defects or other stability or bearing capacity

risks are not present and to verify appropriate placement of any fills, with

documentation of approval via producer statements. Additionally any

seepage, spring flow or under-runners that may be encountered during

construction should be drained under geotechnical direction.

38. Compaction of granular backfill (for both the crane platforms and under

any foundations) should be carried out in accordance with a specification

prepared by a geotechnical engineer with consideration of the

manufacturer’s requirements

39. The optimal locations and risk considerations for access roads and

transmission line supports requires confirmation. A surveyor should be

engaged to determine the most appropriate alignment for these and to

provide cross sections showing cut/fill at critical locations. These cross

sections should be checked by a geotechnical practitioner who should

provide advice on any physical support requirements and any need for

site specific design for structures founded on any active landslide areas.

Conclusions

40. At this feasibility stage, the site appears well suited to the proposed

development, with volcanic rock available at shallow depth. Further

investigations are required for detailed design. In summary, our

evaluation of this site has not revealed any plausible geotechnical or

geohydrological issues that could be considered to place this project at

significant risk of imposing any adverse effect, if normal standards of

care are used during construction.

41. Extensive landslides have occurred on the flanks of Porteous Hill,

however the crest is clearly underlain by volcanic rock and appears to be

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stable with subdued topography. Owing to the proximity of landslide

features locally a cautious approach should however be adopted and

further evaluation of slope stability is recommended based on full

geotechnical review of existing and forthcoming investigation

information.

42. We recommend that the manufacturer should be asked to specify the

type of testing required to meet their requirements, based on the

preliminary ground model described in the attached report.

43. Groundwater issues are not expected to result in geotechnical

constraints.

44. The outstanding matters can be addressed by way of conditions of

consent and will also be addressed as part of the detailed design

required prior to seeking building consent.

..............................................................

Mark T Walrond

Dated: ....................................................

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PreliminaryGeotechnical ReportWind Energy Development,

Porteous Hill,

Blueskin Bay, Dunedin

Report prepared for:

Blueskin Energy Limited

Report prepared by:

GeoSolve Ltd

Distribution:

Blueskin Energy Limited

GeoSolve Limited (File)

April 2016

GeoSolve Ref: 160201

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Preliminary Geotechnical Report, Porteous Hill GeoSolve ref: 160201Blueskin Energy Ltd April 2016

Table of Contents1 Introduction .............................................................................................................................. 1

1.1 General .............................................................................................................................. 1

1.2 Proposed Development ...................................................................................................... 1

1.3 Review of Previous Work and Geotechnical Specifications ................................................. 2

2 Site Description ......................................................................................................................... 3

2.1 General .............................................................................................................................. 3

2.2 Topography and Surface Drainage ...................................................................................... 3

3 Geotechnical Investigations ....................................................................................................... 3

4 Subsurface Conditions ............................................................................................................... 3

4.1 Geological Setting .............................................................................................................. 3

4.2 Stratigraphy ....................................................................................................................... 4

4.2.1 Turbine Sites 1 & 2 ..................................................................................................... 4

4.2.2 Turbine Site 3 ............................................................................................................. 4

4.3 Groundwater ..................................................................................................................... 4

4.4 Slope Stability and Sinkhole Potential ................................................................................. 5

5 Preliminary Engineering Considerations ..................................................................................... 7

5.1 General .............................................................................................................................. 7

5.2 Slope Stability Considerations ............................................................................................ 7

5.3 Site Preparation and Excavations and Earthfill .................................................................... 8

5.4 Foundation Recommendations........................................................................................... 8

5.4.1 General ...................................................................................................................... 8

5.4.2 Turbine Sites 1 & 2 ..................................................................................................... 8

5.5 Turbine Site 3 ..................................................................................................................... 9

5.6 Groundwater Issues and Drainage ...................................................................................... 9

5.7 Site Subsoil Category ........................................................................................................ 10

5.8 Other Considerations ....................................................................................................... 10

6 Neighbouring Structures/Hazards ............................................................................................ 11

7 Conclusions and Recommendations ......................................................................................... 12

8 Applicability ............................................................................................................................. 13

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1 Introduction

1.1 GeneralThis report presents the results of preliminary geotechnical investigations carried out in order todetermine near-surface subsoil conditions and provide geotechnical comment for a proposed windenergy development at the summit of Porteous Hill near Warrington, Dunedin.

Photo 1 – General view of Porteous Hill summit

The investigations were carried out for Blueskin Energy Ltd in accordance with GeoSolve Ltd’sproposal dated 27 May 2016, which outlines the scope of work and conditions of engagement.

1.2 Proposed DevelopmentWe understand that the proposed development is to establish three wind energy turbines to belocated at the summit of Porteous Hill. The project will utilise wind energy turbines manufactured byEnercon. The proposed facility will comprise 3 turbines. The full height of the turbines from groundlevel to rotor tip will be between 80-102m in height. Earthworks will be required for the project toconstruct access tracks and excavate foundations.

The locations of the three turbine sites are shown on Figure 1.

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Figure 1 – Proposed Turbine sites (Turbines 1-3) and locations of preliminary test pits (TP 1-3)

1.3 Review of Previous Work and GeotechnicalSpecifications

We have reviewed a geological and geotechnical report on the area prepared by Dr Virginia Toy1,based on initial subsurface investigations carried out in early 2016. This report recommendedfurther geotechnical engineering inputs prior to detailed design. The report provides acomprehensive overview of the site geology including reference to previous geological mappingwhich indicates that all of the turbine sites are located on land mapped as Dunedin Volcanic Group.Please refer to this report for further background on the geology of the site. Hand augering wascarried out and logs provided, however these investigations met with refusal at shallow depthindicating that the sites are underlain by relatively competent soils.

We have also reviewed the manufacturer’s requirements for geotechnical reporting on soil androck2. Enercon provide specifications for geotechnical data required for sites that are underlain byeither soil or rock. In the case of soils, the requirement is for drilling to cover all strata where there isa risk of settlement and which are relevant for stability considerations. In addition, cone penetrationtesting (CPT) or other probing/sounding tests are recommended. In cases where there is only aminimal layer of soil on rock, trial pits can be undertaken and evaluated.

Owing to the obvious near surface boulders of strong rock and the reports of shallow refusal duringprevious subsurface investigations, test pitting was chosen as the most appropriate method toinitially assess the properties of the soils and underlying rock at the tree turbine sites.

1 Toy V (2016), Geological and Geotechnical Report on Porteous Hill Wind Farm Site.

2 Enercon Catalogue of specifications for soil investigations (ref PM-CE-SP003) and rock investigations (ref PM-CE-SP004).

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2 Site Description

2.1 GeneralThe proposed development will take place on part of a 161 ha property shown as 147 Church Road,Merton. The property is accessed from Porteous Road and lies at crest of the hillslope north-west ofWarrington.

The site is currently undeveloped and being used as farm land. A wind testing mast has been erectednear Turbine Site 2. Vegetation comprises pasture and the property is bounded by mostly pastureland on all sides. There are no buildings in close proximity to the proposed turbine sites.

2.2 Topography and Surface DrainageThe site is located at an elevation of approximately 390m at the crest of Porteous Hill. The slopesadjacent to the proposed sites are variable, with some moderate to steep slopes, particularlyadjacent to Turbine Site 1. No cross sections have been prepared at this preliminary stage, howeverdetailed cross sections showing the full ground model should be developed as part of detaileddesign.

The site is naturally free draining and no spring flows are evident. Ephemeral watercourses andsprings are present in the gullies below the hillcrest.

3 Geotechnical InvestigationsAn engineering geological site appraisal has been undertaken with preliminary subsurfaceinvestigations. GeoSolve Ltd visited the subject property with members of the Otago UniversityGeology Department on 7 April 2016, undertaking geotechnical investigations comprising three testpits which were advanced to a maximum depth of 2.8 m. Scala Penetrometer tests were undertakenat selected locations at each test pit location advancing to refusal.

4 Subsurface Conditions

4.1 Geological SettingPorteous Hill, East Otago, New Zealand is a Miocene volcanic centre with sedimentary rocks at depthand the regional geology has already been described by Toy 2016.

The published geological mapping indicates that Porteous Hill comprises layered rock types of theDunedin Volcanic Group overlying sedimentary rock of both marine (e.g. Caversham Sandstone) andnon-marine origin (i.e. Older Floodplain Conglomerate). Benson 19403 indicates that the volcanicrock of Porteous Hill are likely to be fed by volcanic vents rather than simply comprising remnants ofmore extensive capping lava flows. The location of deeper vents and the full extent of the volcanicrocks below the site is currently unknown.

McCahon et al (1993)4 states that the earthquake hazard in Dunedin is dominated by relativelyinfrequent moderate to large earthquakes (magnitude up to 7.5) in eastern Otago, and large to verylarge earthquakes in the much more seismically active Fiordland and Westland regions.

3 Landslides and Allied Features in the Dunedin District in Relation to Geological Structure, Topography and Engineering,W.N. Benson 1940

4 The Earthquake Hazard in Dunedin I F McCahon, M D Yetton, D R L Cook (EQC report 91/56 - June 1993)

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The nearest trace of any mapped active fault is near Mosgiel approximately 25 km from PorteousHill.

Active fault traces were not observed at the site or in the vicinity. However, significant seismic riskexists in this region from both local faults in East Otago and potentially from ground shaking likely tobe associated with a rupture of the Alpine Fault, located along the West Coast of the South Island.There is a high probability that an earthquake with an expected Richter magnitude of 8 will occur alongthe Alpine Fault within the next 50 years.

4.2 StratigraphyA preliminary geological model for the near-surface geotechnical conditions at the three turbinesites has been developed. Turbine Sites 1 & 2

At two of the sites (Turbines 1 & 2, Fig 1) the surface contains abundant sub-rounded boulders ofstrong crystalline volcanic rock. Test pit excavation revealed that the upper metre comprises similarboulders up to 700mm in a matrix of predominantly silt and clay. The upper metre is interpreted asresidual soil derived from advanced weathering of the volcanic flow rocks beneath. Weatheredvolcanic rock is exposed at approximately 0.5 to 1m depth and comprises spheroidally weathered,fine grained crystalline volcanic rock. The rock appears to be highly fractured, most likely as a resultof cracking induced by the process of lava cooling. Chemical weathering processes associated withwater infiltration have resulted in complete weathering of the rock along these fracture margins andhence the rock comprises “abundant core stones” or boulders of strong to extremely strong volcanicrock bounded by thin zones of completely weathered rock (stiff silty clay). Oxidation products areabundant such as orange iron oxides and black oxides (possibly manganese oxide).

No Scala penetrometer testing was carried out in either the residual soil or the underlying rockowing to obvious refusal likely on boulders or core-stones at shallow depth. Dense to very dense soilconditions are interpreted in the upper metre underlain by weathered volcanic rock predominantlyin strong condition or better.

The excavator was able to proceed to a maximum depth of approximately 2.8 m at these sites with atoothed bucket owing to the fractured nature of the rock, however excavation was difficult beyondthis depth probably indicating that stronger rock is present below about 3m depth.

4.2.1 Turbine Site 3The subsurface conditions at Turbine Site 3 differ significantly to those at the above sites. There is noboulder field evident at surface and the subsoils comprise cohesive silty clay deposits with rarecobbles, gravel and sand. Slickensides and oxidation mottling of the soil was evident below 0.6 mdepth. The slickensides indicate that the soil is likely to comprise landslide debris and this persistedto at least 2.4m depth. The full extent of the debris and depth to bedrock requires confirmation andfurther drilling investigations are required to fully define the ground model at this site.

The soil types are stiff to very stiff as indicated by Scala penetrometer testing.

4.3 GroundwaterNo groundwater seepage was observed in any of the test pits during investigations. The soilsobserved were predominantly dry to moist in condition.

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We understand that an unpublished thesis held by the University of Otago (Rekker 19915) describesa perched groundwater system which is developed on Porteous Hill, and is summarised as follows:

The aquifer material is jointed olivine basalt, porous lapillistone and lapilli tuff, and an oxidisedmarine silty sand named the Green Island Loose Sand. Aquicludes are marine mudstones, infilled andcemented tuff-breccia, and phonolite intrusions. The aquifer is reported to be unconfined except atsome of the lower margins. The aquifer is recharged by rainfall infiltrating through the soil in theupland fields of Porteous Hill. Ground waters usually flow out of the aquifer as springs just above thelower contact of the aquifer rock types with the aquiclude rock types.

This illustrates that the soils/rock developed at crest of Porteous Hill is likely to be relativelypermeable, with a very low probability of artesian groundwater conditions at depth (owing to theunconfined nature of the aquifer).

The permeability of the soil and rock types at Turbine Sites 1 & 2 is expected to be relatively highand these materials are expected to represent the recharge area for the aquifers described byRekker 1991. The soils at turbine Site 3 are expected to be of lower permeability. Permeabilitytesting can be readily carried out if required for the purposes of detailed design.

4.4 Slope Stability and Sinkhole PotentialDunedin City Council’s geotechnical advisor (MWH NZ Ltd) notes that the turbine tower locations aresituated outside the known extents of mapped landslides, however they point out that the volcanicsmay be underlain by weak sedimentary rocks and that the northern-most tower lies within 20m ofan ancient landslide boundary. They note that in spite of nearby instability, the area of the proposedtowers is underlain by volcanic rock and that the proposal would not create or exacerbate instabilityon this or adjacent properties.

Slope stability considerations have also been discussed by Toy 2016 with similar conclusions on theglobal stability of the sites. However one recommendation of that report was that cross sectionsshould be generated and slope stability analysis carried out.

Landslides are numerous around Porteous Hill and groundwater flow (e.g. the perched groundwatersystem described by Rekker 1991) is likely to be the dominant trigger for slope failure. The landslidesare likely to be developed at and below the zone where the perched groundwater level intersectswith topography and numerous transient spring flows are likely to be developed at these locations.Rekker considered that fluctuation in hydraulic head is the dominant transient factor in thecontinuing failure and creep of major slides and slumps on the flanks of Porteous Hill. Movement ofthese landslides is likely to be associated with periods of higher than average rainfall.

A detailed published hazard map showing landslides (Stout 19716) in the Kilmog-Seacliff area hasbeen consulted and this shows that the turbine sites were mapped outside any areas of recent orancient landslide (see Figure 2).

5 Rekker, Jens, “Hydrogeology and related geological aspects of Porteous Hill, East Otago, New Zealand,” PGDipsci - 1991

6 Landslide map of the Seacliff-Kilmog Area, M.L. Stout 1971

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Figure 2 – Proposed Turbine sites (Turbines 1-3) in relation to landslide mapping by Stout 1971. Yellowindicates active landslide and red indicates ancient landslide.

The slickensides observed in the subsoils at Turbine Site 3 indicate that the area is likely to havebeen subject to ancient landslide activity and that the area mapped by Stout 1971 may requireextension to include Turbine 3. The topography of the Turbine 3 site is very subdued with gentleslopes and therefore the debris is likely to have originated from ancient landslide activity (as mappedby Stout in adjacent areas), with subsequent erosion and no apparent reactivation in recent times.In order to confirm the ground model at this site (including identification of shear surfaces andbedrock if applicable) further drilling investigations are required. We recommend that a review ofstereoscopic aerial photography should be carried out to better delineate the extents of slopeinstability.

Benson 1968 (published geological map) suggests that the crest regions of Porteous Hill withsubdued topography are likely to comprise olivine basalt. These rock types are not mapped aslandslide terrain however the volcanic rock types underlying the basalt comprise dolerites, basaltsand basaltic breccias that do appear to be affected by landslide activity. It should be noted that thegeological exposure appears relatively limited in the areas mapped as landslide, however furthermapping should be carried out to more fully delineate the rock types that are susceptible to slopeinstability.

No mining has been carried out in the vicinity of the site and there is a very low likelihood of anynatural subterranean cavities in the rock types on site. The rock types in this area are volcanic withno likelihood of calcareous sedimentary rocks at shallow or moderate depth. Consequently thelikelihood of encountering sinkholes or other cavities associated with chemical weathering isconsidered very low. However, any cavities encountered during excavations will require specificgeotechnical inspection and possibly further investigations followed by remedial works.

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5 Preliminary Engineering Considerations

5.1 GeneralThe recommendations and opinions contained in this report are based upon preliminary groundinvestigation data obtained at discrete locations and historical information held on the GeoSolvedatabase. The nature and continuity of subsoil conditions away from the investigation locations isinferred and cannot be guaranteed. Further investigations are required to confirm assumptions fordetailed design.

5.2 Slope Stability ConsiderationsWe note that Enercon require slope stability verification for foundations near slopes. Slope stabilityis discussed above (Section 4.4). Owing to the proximity of landslide features locally a cautiousapproach should be adopted and further evaluation of slope stability is recommended.

There are no potential sources of debris inundation, rock fall or rock roll that could affect these hillcrest sites from upslope sources.

No major slope stability issues are expected at least for Turbine Sites 1 & 2 as the sites are likely tobe founded on strong volcanic rock with no known tectonic deformation structures in the vicinity.

Owing to the extensive slope instability developed on the flanks of Porteous Hill and the currentuncertainty regarding the location of failure planes and the vertical extent of the volcanic rocks(including vent structures), it is recommended that a surveyor should be engaged to advise ifhistorical survey data can be used to confirm any movement of benchmarks that may be available atthe summit of Porteous Hill. This would enable a cost-effective determination, however if this is notpossible then further geological mapping and geotechnical investigation including drilling should beconsidered to enable full confirmation of slope stability.

Attention will be required to assess the slopes below the sites. We note that Turbine Site 1 isadjacent to a steep slope, Turbine Site 2 has been identified by Council’s geotechnical advisor asbeing in close proximity to mapped landslide and Turbine Site appears to be underlain by someancient landslide debris. We agree with Toy 2016 that cross sections should be generated and slopestability analysis carried out once the final platforms are confirmed and following additionalmapping and subsurface investigations. These analyses should consider both static and seismicstability.

Following excavation for pad foundations, no adversely oriented defects are expected to affect thevolcanic subgrade Turbine Sites 1 & 2 however the rock is known to be jointed and therefore furtherassessment will be required during bulk earthworks when any defects (if any) are fully exposed.Careful mapping and evaluation of any defects and lineaments encountered will be required withinthe foundation excavations, and stability analysis should be carried at that stage to confirm safetyfactors. Defects should be checked to ensure there is no potential for defect-controlled slopeinstability, particularly where turbines are located adjacent to steeper slopes (e.g. Turbine 1). Ifsignificant defects or other adverse structures such as faults or landslide shear surfaces areencountered then the sites may require relocation or remedial stabilisation works.

Further investigations are required for Turbine Site 2 in particular to verify the depth of soil coverand to determine if the landslide debris identified presents any slope stability design constraints.

Cavities are not likely to be encountered at these sites as the subgrade rock types are not calcareousand no active tectonic activity is mapped in the vicinity. We note that geophysical wavemeasurement procedures can also be used to identify voids for detailed design (as opposed todrilling) however in this case it is unlikely that this is required.

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5.3 Site Preparation and Excavations and Earthfill· During the earthworks operations all topsoil, organic matter, fill and other unsuitable

materials should be removed from the construction areas in accordance with therecommendations of NZS 4431:1989.

· The rippability of the soils has been determined to some degree during test pitting and itappears that standard excavation equipment should be sufficient to enable the platforms tobe established to the depths required by the manufacturer.

· All fill that is utilised as bearing for foundations should be placed and compacted inaccordance with a specific earthfill specification (possibly in accordance with therecommendations of NZS 4431:1989) and certification provided to that effect. An earthfillspecification can be provided on request.

· We recommend site stripping and subsequent earthworks be undertaken only when asuitable interval of fair weather is expected, or during the earthworks construction season.

· Construction recommendations for the foundation excavations can be verified as part ofdetailed design, however relatively steep batter angles will be appropriate in rock and stiffsoils and significant over-break is not expected to be required.

· Bulk earthworks should be supervised by a geotechnical practitioner.· Water should not be allowed to pond or collect near or under a foundation slab. Positive

grading of the subgrade should be undertaken to prevent water ingress or ponding.

5.4 Foundation Recommendations

5.4.1 General

· We recommend that geotechnical aspects for all sites such as rocking spring stiffness,settlement calculations (if applicable) should be verified by appropriate testing during thedetailed design phase. Laboratory testing of rock and soil samples may be required. Werecommend that the manufacturer should be asked to specify the type of testing required tomeet their requirements, based on the preliminary ground model described in this report.

· Compaction of granular backfill (for both the crane platforms and under foundations) shouldbe carried out in accordance with a specification prepared by a geotechnical engineer withconsideration of the manufacturer’s requirements, however compaction and verification byNDM testing in accordance with NZS 4431 is likely to be adequate.

· Construction supervision of the foundation excavations and fill placement is required andthis should be carried out by a geotechnical practitioner with documentation of approval viaproducer statements. The foundation subgrade should be inspected by a geotechnicalpractitioner to ensure that defects or other stability or bearing capacity risks are notpresent.

· We note that soil resistivity requires measurement and this can be arranged via a testingcontractor.

5.4.2 Turbine Sites 1 & 2

· At Turbine Sites 1 & 2, weathered volcanic rock is available at shallow depth. Deepfoundations are not likely to be required and at these two sites the appropriate foundationsolution is likely to comprise undercutting any obviously fractured rock prior to replacementwith compacted AP65 aggregate and construction of the manufacturer’s shallow foundationsystem.

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· On rock sites, such as these Enercon recommend that a suitable boring should be made to atleast 2m below the base of the foundation and this will be required as a minimum. Deeperconfirmatory drilling is however recommended, as discussed above, to verify the persistenceof the volcanic layers, quality of the rock and to ensure that weaker sedimentary rocks orlandslide mechanisms are not present at shallow depth.

· Additional SPT or HDCP testing is unlikely to be feasible at these sites as immediate refusalon rock is likely.

· Rock is expected to predominate at subgrade level when excavations are complete, howeverScala penetrometer testing or other appropriate methods should also be carried to verifystiffness requirements are met if rock is not universally encountered.

· For rock sites, such as these the manufacturer may specify shallow foundations with groutedanchors. Enercon specify that for preliminary design in this case, information is required onrock fissuring. At these sites the rock is known to be relatively rippable to a depth of at least2.8m owing to joint sets within the weathered upper part of the rock profile. If anchors arerequired (following more detailed drilling investigations) then further evaluation of the rockquality may be required.

5.5 Turbine Site 3· Rock was not identified at this site during shallow test pitting. Further drilling investigations

are required for Turbine Site 3 to: (1) verify stability considerations (see above), and (2)determine the depth of soil cover and confirm if any piles are required to enable loads to betransferred to rock or other bearing layers at depth. This appears unlikely as the surface soilsobserved to date are in stiff to very stiff condition.

· The loading from the foundation pads is relatively low, however strong materials of highstiffness are required in order to minimise cyclical loading under wind loading and alsopotential earthquake loading. Consequently further testing as well as laboratory testing isrequired.

· The manufacturer’s requirement is for drilling to cover all strata where there is a risk ofsettlement and which are relevant for stability considerations. In addition, cone penetrationtesting (CPT) or other probing/sounding tests are recommended.

5.6 Groundwater Issues and DrainageNo groundwater was encountered and hence the foundation type “shallow without buoyancy” islikely to be applicable at sites 1 & 2 at least. The manufacturer’s requirement is that accumulatedwater cannot develop in the foundation excavation (i.e. bathtub effect). We note that sufficientpermeability testing may need to be addressed for detailed design, however the hill crest location ofthe sites as well as the fractured nature of the rock subgrade indicates that groundwater levels areunlikely to rise. Near-surface piezometers have been installed to enable ongoing monitoring duringheavy rainfall and winter conditions. The assumption of sufficient permeability can also be verifiedby site-specific permeability testing if required during detailed the design phase. In any case, passivedrainage solutions could be readily designed if unexpected groundwater issues do emerge.

The regional watertable is expected to lie well below the indicated finished foundation levels and amajor perched groundwater system has been described by Rekker 1991. The aquifer appears to beunconfined and hence no artesian pressures are expected to generate deep-seated slope instabilityin this setting. A full review of Rekker 1991 is recommended to better understand the ground model.

Dewatering or other groundwater-related construction issues are therefore unlikely to be required.It is important that a geotechnical practitioner is contacted should there be any seepage, spring flowor under-runners encountered during construction.

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No flood hazard is applicable at these hill crest sites and there are no water-courses in closeproximity to the sites. Cut-off drains can be constructed if runoff from any minor upslope extentsappears problematic.

5.7 Site Subsoil CategoryFor detailed design purposes it is recommended the magnitude of seismic acceleration be estimatedin accordance with the recommendations provided in NZS 1170.5:2004.

Following excavations to expose rock subgrade at Turbine Sites 1 & 2, these sites are expected to beat least Class B (rock) and probably Class A (strong rock sites) in accordance with NZS 1170.5:2004seismic provisions. The site for Turbine 3 may be Class C (Shallow soil site) however this requiresfurther confirmatory investigations as rock may be relatively shallow.

The sites are not subject to liquefaction.

Some testing may be required to verify stiffness to the manufacturer’s requirements and to confirmif any strength loss applies in the case of cyclic loading.

5.8 Other ConsiderationsWe have not considered the geotechnical aspects associated with accessways or transmission linestructures at this stage, however some landslide terrain may be encountered and we recommendthat these aspects are addressed at an early stage to confirm the optimal locations and riskconsiderations for roads and transmission line supports.

We recommend that a surveyor should be engaged to determine the most appropriate alignment forthe accessway and transmission lines. Unless alignments require minimal cut or fill, cross sections atcritical locations should be provided by the surveyor showing cut and fill profiles. These crosssections should be checked by a geotechnical practitioner to enable advice on any physical supportrequirements and any need for site specific design for structures founded on active landslide areas.

The accessway should be contoured appropriately to allow surface runoff to fall to a contour drainor equivalent in order to intercept any surface runoff.

Construction of the accessway and transmission structures should be carried out under thesupervision of a geotechnical practitioner. Any seepage encountered will require appropriatedrainage measures during the earthworks.

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Head Office: 70 Macandrew Road ô Phone 64 3 466 4024 ô PO Box 2427, South Dunedin, 9044 Email: [email protected]

GeoSolve Ref: 16020130 May 2016

Blueskin Energy Ltd1121 Mt Cargill RdWaitatiDunedin

Attention: Scott Willis

Dear Scott

GroundwaterConsiderationsforWindEnergyDevelopment,PorteousHill,BlueskinBay,Dunedin

1 IntroductionThis letter presents engineering geological comment in response to concerns that have been raisedregarding potential adverse effects on groundwater aquifers as a result of a proposed wind energydevelopment at the summit of Porteous Hill near Warrington, Dunedin.

Photo 1 – General view of Porteous Hill summit

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Groundwater Considerations, Porteous Hill GeoSolve ref: 160201Blueskin Energy Ltd May 2016

The work was carried out for Blueskin Energy Ltd in accordance with GeoSolve Ltd’s proposal dated27 May 2016, which outlines the scope of work and conditions of engagement.

2 Proposed DevelopmentWe understand that the proposed development is to establish three wind energy turbines to belocated at the summit of Porteous Hill. The full height of the turbines from ground level to rotor tipwill be 90m. Earthworks will be required for the project to construct access tracks and to excavatefoundations.

Based on initial test pitting investigations, the foundations of the turbines are likely to compriseshallow (2-3m deep) concrete pads (subject to confirmatory geotechnical drilling investigations) of11m diameter. At this stage no deep piling or anchoring is expected to be required.

The access track would be approximately 5m wide and will involve undercut of near-surface soils toapproximately 300mm depth followed by placement of permeable compacted granular fill to form apavement for vehicles that will be required for construction and maintenance.

The locations of the three turbine sites are shown on Figure 1 & 2.

Figure 1 – Proposed Turbine sites and access roads (map view)

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Figure 2 – Proposed Turbine sites and access roads (schematic view)

3 Nature of ObjectionsThe Dunedin City Council planner has recommended that the Resource Consent application for theabove development be declined for reasons that include uncertainty over the effect installingturbines would have on nearby groundwater springs.

Several objections have been received in regard to perceived potential adverse effects on springflows in the Porteous Hill area. The objections raised above can be summarised as follows:

1. Concerns relating to physical effects on the groundwater system such as reducedgroundwater flow, disruption to groundwater flow paths and changes to thelocations and discharge rates of spring flows.

2. Concerns relating to contamination of groundwater by the development.3. Concerns relating to land instability.

The following are examples of opposing submissions that specifically mention the above concerns:

2. Andy Barratt, 317 Apes Road, RD1 9471, Karitane. "… there are also hydrologicalimplications of the work involved in providing foundations for the windmills. Myunderstanding is that the proposed site is a source of spring water which supplies water toneighbouring properties for both domestic and farming use. At the very least, this proposalwould need to be supported by expert evidence that these rural activities would not be putat risk by the proposed development, which would contravene the proposed and existingDistrict Plans"

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3. Eric Neuman, 392 Coast Road, 9471, Warrington. "We get some of our water from a springbelow the proposed turbines and we are concerned that the excavation and placing of lotsof concrete will disturb the fragile structure, and destroy our water supply, (and 11 otherhouseholds which share this spring and resulting stream)."

4. Geraldine Tait, 33 Reservoir Road, RD1 Waikouaiti, 9471, Warrington. "There are nogeological or hydrological reports. The whole North Coast area is prone to slips and is part ofthe hazard zone in the draft 2GP. Any work on the road, access track and site preparationcould result in serious land movement. Major excavation is required to create a platform forthe concrete bases, as the underlying geology is not known the depth and extent of thisexcavation may be considerably more than has been anticipated. The hill has anunderground network of streams which come to the surface as springs, all the local farmersand many of the lifestyle blocks totally rely on spring water for household and stock water.Disturbance at the top of the hill could lead to pollution of this water or diverting ofunderground streams away from where they are presently utilized. Due to issues associatedwith land movement and water, a Resource Consent should also be required from the OtagoRegional Council."

5. Grant Boyle, 235 Coast Road, 9471 Warrington. "There is no study on the potential effectsthe site earth works and foundations will have on the stability of the land or the groundwater. A number of people who farm in the area have raised serious concerns over thesuitability of building such large structures on this land."

6. John Thom, 58 Reservoir Road, 9471 Warrington. "There is little information on bird life,geotech & environmental effects. Effects on springwater for households and stock."

7. Murry Cumming - Raises the possibility of contamination of water supply and disruption ofspring flows.

8. Polly Higham, 392 Coast Road, 9471, Warrington. "We get some of our water from a springbelow the proposed turbines and we are concerned that the excavation and placing of lotsof concrete will disturb the fragile structure, and destroy our water supply, (and 11 otherhouseholds which share this spring and resulting stream)."

9. Simon Ryan and Jennifer Ashby, 90 Pryde Road, Merton – Express concerns relating toeffects on spring flows.

10. Thomas and Linda Thompson, Rapid 5, Porteous Road, RD1 Waikouaiti, 9471. "The groundat Porteous Hill is unstable and massive excavation plus ground vibrations when towers areoperational will have an unknown effect, varying from nil to possibly catastrophic to theentire hillside."

11. Nathan Parker, CMB103 Warrington, Otago 9449, "If the turbines are built of Porteous Hillthere seems to be no guarantee that they will not have any adverse effect on local aquifers -this hill with its mix of basalt and loess is highly unstable. Local farmers report problems withland subsidence, slips and significant damage from only small disturbances to the land - thisis historic for the area. From around Porteous Hill aquifers flow - in the past they were usedas the main water supplies in Seacliff, Warrington, Omimi, Evansdale and Mertoncommunities. Many of the farms are reliant on these continuing to flow. Our ability to beresilient/autonomous communities will diminish significantly if these aquifers/springs aredamaged and so will our ability to grow food be limited with no water!"

12. Lyndon and Kirsty Clayton, PO Box 12044, Maori Hill, Dunedin, 9043 [they live at 22 PrydeRoad] – Express concerns on the possible impacts that excavations could have on sensitivesprings and underlying aquifers that are utised for domestic and stock water.

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4 Site DescriptionThe proposed development will take place on an approximately 24 hectare property legallydescribed as Lots 1 and 2, DP 473199 and OT 646829. The property is accessed from Porteous Roadand lies at crest of the hillslope north-west of Warrington. The site is currently undeveloped andbeing used as farm land. A wind testing mast has been erected near the NW turbine site. Vegetationcomprises pasture and the property is bounded by mostly pasture land on all sides. There are nobuildings in close proximity to the proposed turbine sites.

The site is located at an elevation of approximately 390m at the crest of Porteous Hill. The slopesadjacent to the proposed sites are variable, with some moderate to steep slopes, particularlyadjacent to the SE turbine site. No cross sections have been prepared at this preliminary stage,however detailed cross sections showing the full ground model should be developed as part ofdetailed design.

The site is naturally free draining and no spring flows are evident at the crest of the hill. Ephemeralwatercourses and springs are present on the slopes and in gullies well below the hillcrest.

An engineering geological site appraisal has been undertaken with preliminary subsurfaceinvestigations. GeoSolve Ltd visited the subject property with members of the Otago UniversityGeology Department on 7 April 2016, undertaking geotechnical investigations comprising three testpits which were advanced to a maximum depth of 2.8 m. Scala Penetrometer tests were undertakenat selected locations at each test pit location advancing to refusal.

5 Subsurface Conditions

5.1 GeologyPorteous Hill, East Otago, New Zealand is a Miocene volcanic centre with sedimentary rocks at depthand the regional geology has already been described by others.

The published geological mapping indicates that Porteous Hill comprises layered rock types of theDunedin Volcanic Group overlying sedimentary rock of both marine (e.g. Caversham Sandstone) andnon-marine origin (i.e. Older Floodplain Conglomerate or Kaikorai Leaf Beds). Benson 1940 1 indicatesthat the volcanic rock of Porteous Hill are likely to be fed by volcanic vents rather than simplycomprising remnants of more extensive capping lava flows. The location of deeper vents and the fullextent of the volcanic rocks below the site is currently unknown.

At this preliminary stage, the site appears well suited to the proposed development from thegeotechnical point of view, with volcanic rock available at shallow depth at two of the three turbinesites. Further investigations are required for detailed design and this work is planned as well asmapping of the spring flows and development of geotechnical and groundwater cross sections.

5.2 GroundwaterNo groundwater seepage was observed in any of the test pits during investigations. The soilsobserved were predominantly dry to moist in condition. However, there are well known spring flowsthat emerge on the lower slopes of Porteous Hill and the groundwater system has been considered

1 Landslides and Allied Features in the Dunedin District in Relation to Geological Structure, Topography and Engineering,W.N. Benson 1940

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in an unpublished thesis held by the University of Otago (Rekker 19912) which describes a perchedgroundwater system summarised as follows:

The aquifer material is jointed olivine basalt, porous lapillistone and lapilli tuff, and an oxidisedmarine silty sand named the Green Island Loose Sand. Aquicludes are marine mudstones, infilled andcemented tuff-breccia, and phonolite intrusions. The aquifer is reported to be unconfined except atsome of the lower margins. The aquifer is recharged by rainfall infiltrating through the soil in theupland fields of Porteous Hill. Recharge is likely to also occur through the Tertiary sedimentary rocks.Ground waters usually flow out of the aquifer as springs just above the lower contact of the aquiferrock types with the aquiclude rock types. The springs emerge from landslide debris on the SW side ofPorteous Hill at about 200-220m elevation and also from the base of the volcanic rocks.

This illustrates that the soils/rock developed at crest of Porteous Hill is likely to be relativelypermeable, with a very low probability of artesian groundwater conditions at depth (owing to theunconfined nature of the aquifer).

The permeability of the soil and rock types at the SE and NW turbine sites is expected to be relativelyhigh and these materials are expected to represent the recharge area for the aquifers described byRekker 1991. The soils at the NE turbine site are expected to be of lower permeability. Permeabilitytesting can be readily carried out if required for the purposes of detailed design.

The groundwater system is understood to be a primary source of private water supply for the area,(however a previous public water reservoir is now understood to be redundant).

6 Discussion

6.1 Concerns relating to physical effects on thegroundwater system

Some objections relate to concerns such as reduced groundwater flow, disruption to groundwaterflow paths and changes to the locations and discharge rates of spring flows.

The objectors do not provide any specific details or arguments why the development wouldphysically impede or alter groundwater flows. Many concerns appear to be based on an assumptionthat the foundations of the turbines will involve volumes or depths of concrete large or deep enoughto physically affect the water flows or that the foundations will affect a fragile groundwater system.Some mention the possibility that the development could result in diversion of underground streamsaway from where they are presently utilized. At least one objector has specifically mentionedpotential effects from vibrations during turbine operation.

The recharge catchment for the Porteous Hill groundwater system coincides with the access roadsthat will be required as well as the foundations of the turbines and transmission structures. Wehave considered the potential for foundations and access roads to affect the groundwater system inthis zone of recharge as follows:

· Owing to the presence of rock at shallow depth, the foundations will most likely comprise 3concrete pads of 11m diameter, founded at 2-3m depth. The likely concrete volume istherefore minor and we consider that there is no credible possibility that this will result inany disruption to groundwater infiltration. Percolation of groundwater is unlikely to beimpeded as the areas of impermeable seal are limited and where present these can be

2 Rekker, Jens, “Hydrogeology and related geological aspects of Porteous Hill, East Otago, New Zealand,” PGDipsci - 1991

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designed to direct flow to the adjacent recharge zones, with no net reduction in rainwaterinfiltration. It therefore follows that the development will have no potential to reducecurrent spring flow volumes because there is no significant sealing of the recharge areaupslope of the springs.

· The concrete placed will have no potential to influence the perched groundwater system atdepth, as rainwater that infiltrates the volcanic rock at the crest of Porteous Hill will belargely conveyed to depth by the permeability of the fractured rock. The water then percheson low permeability layers below the volcanic rocks and is then conveyed to the areas ofspring flow. As no part of the proposed structures will be at such depth, there is no physicalimpediment to the groundwater flow at depth and hence no mechanism by which thegroundwater flows can be diverted or cut off by the proposed structures.

· In terms of potential effects from vibration, the turbine foundations are designed toaccommodate cyclical loading associated with wind loading (as well as earthquake loading).The design requires that the subgrade is suitably stiff to accommodate such rocking motionsto prevent structural failure of the turbines. Consequently the subgrade requirementsinclude the need to confirm adequate stiffness. The sites are predominantly volcanic rockand hence not significantly susceptible to deformation under cyclical loading. In addition,the turbine foundations are not within the saturated zone of the aquifer (i.e. they are in thezone of recharge above) and hence any vibrations would not be within the saturated zone ofthe aquifer at depth. Blasting is not likely to be required and hence there is no potential forvibrations sufficient to impose any credible change to the transmissivity of the aquifer soilsby densification/ consolidation.

· No groundwater draw from the aquifer is required to develop or operate the wind energydevelopment.

6.2 Concerns relating to groundwater contaminationSome objectors perceive that groundwater contamination could occur as a result of thedevelopment. One objector is concerned that disturbance at the top of the hill could lead topollution of spring water.

The recharge catchment for the Porteous Hill groundwater system coincides with the access roadsthat will be required as well as the foundations of the turbines and transmission structures. Wehave considered the potential for contaminants entering the groundwater system in this zone ofrecharge as follows:

· Apart from the access roads and turbine foundations, the development would result inminimal change of land use (i.e. we note that the area would continue be used for similarfarming activities to those currently).

· The placement of concrete (even if deep piling or grouted anchors are required) has nopotential to contaminate groundwater at depth as there are generally no toxins involved instandard cured concrete.

· There is some potential that accidental spills of diesel (and possibly other contaminants)could occur during the construction phase, however such matters would be straightforwardto address, readily monitored and corrected with appropriate conditions of consent. Wenote that construction equipment and contaminants are regularly used in the rechargezones of aquifers. We therefore conclude that standard precautions during construction arelikely to provide sufficient assurance and that this aspect can be managed.

· The turbines do rely on lubricants and potentially there may be some leakage. Themanufacturer is likely to have measures to mitigate such a possibility, however astraightforward contingency would be to create a simple isolation bund as part of the

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concrete pad structure with sufficient volume and correct placement to contain the volumeof oil that could potentially leak. We assume that if such a spill were to occur, this wouldresult in shut-down of the turbine and any oil or other contaminants can be cleaned up fromwithin the containment bund. We recommend that the manufacturer should commentfurther on the possibility of oil or other chemical leakage and standard measures to preventground contamination.

· A full record of the chemicals that are required for operation of the turbines as well asduring construction and future maintenance should be compiled, and an appropriatemanagement plan developed to ensure that the chemicals cannot be released to ground.

6.3 Concerns relating to land instabilitySeveral objections relate to uncertainty in regard to land instability. The Porteous Hill groundwatersystem is a major cause of the slope instability on the flanks of Porteous Hill. The crest of the hillwhere the turbines would be located is not however mapped as landslide according to Councilhazard maps and comprises extensive volcanic rock. However, further consideration of slopestability has been recommended for detailed design, including drilling investigations to confirmstratigraphy at depth.

Whilst movement of the major landslides that surround Porteous Hill is likely in future, it should benoted that the wind energy development would not be located on the unstable soils and thereforethere is no potential for the development to directly cause such slope instability.

7 Conclusions· The proposed development is located within the zone of infiltration that recharges an

unconfined aquifer at considerable depth below the crest of Porteous Hill.· The shallow foundations and limited hardstanding proposed means that the development

can be constructed without creating any physical impediments to rainwater infiltration orgroundwater flow. Consequently the volume of spring flows is very unlikely to be affected bythis development.

· The turbines would be founded on volcanic rock and hence there are no potential vibrationeffects that could have an adverse effect on the groundwater at depth.

· Precautions will be required to minimise the possibility of accidental chemical spills toground during construction and future maintenance.

· Based on engineering geological mapping, slope stability considerations are not expected toaffect the sites of the proposed turbines, however further confirmatory investigations areplanned for detailed design, and if any concerns remain, consent conditions could readilyinclude submission of satisfactory geotechnical inspection reports at each stage.

· In summary, our evaluation of this site has not revealed any plausible geotechnical orgeohydrological issues that could be considered to place this project at significant risk ofimposing any adverse effect, if normal standards of care are used during construction.

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8 ApplicabilityThis report has been prepared for the benefit of Blueskin Energy Ltd with respect to the particularbrief given to us and it may not be relied upon in other contexts or for any other purpose withoutour prior review and agreement.

GeoSolve Ltd

Geotechnical Engineering Consultants

Prepared by:

..........................................................

Mark Walrond

Senior Engineering Geologist

Reviewed by: Dr Graham Salt, Technical Director

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