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ATTACHMENT 5 Geological Assessment (Tonkin & Taylor) Job No: 1007709 10 January 2019 McConnell Property PO Box 614 Auckland 1140 Attention: Matt Anderson Dear Matt Orakei ONF Assessment 1- 3 Purewa Rd, Meadowbank Introduction McConnell Property is proposing to undertake the development of a multi-story apartment building at 1 - 3 Purewa Road, Meadowbank. The property is located within an area covered by the Outstanding Natural Feature (ONF) overlay of the Auckland Unitary Plan. The overlay relates to the Orakei Basin volcano located to the west of the property. The ONF overlay requires consent for the earthworks and the proposed built form associated with the development of the site. McConnell Property has commissioned Tonkin & Taylor Ltd (T+T) to provide a geological assessment of the property with respect to both the ONF overlay and the geological characteristics of the property. The purpose of the assessment is to place the property in context of the significant geological features identified by the ONF overlay, and to assess the geological effects of the proposed development. Proposed Development The proposal (as shown in the architectural drawings appended to the application) is to remove the existing houses and much of the vegetation from the site, and to develop the site with a new four- storey residential apartment building with a single-level basement for parking. The development will involve excavation of the site, which will require cuts of up to approximately 6m below existing ground level (bgl). The cut depths vary across the site, resulting in the average cut depth being less than 6m bgl. Site Description The site is located at the end of the eastern arm of the ridgeline that encloses the Orakei Basin (Figure 1). The property is set back approximately 25 m from the edge of the Orakei Basin and is currently occupied by two semi-detached houses (Figure 2). The property slopes moderately towards the west. Immediately west of the property boundary the topography steepens significantly as it descends to the Purewa Creek. This is illustrated in a sketch cross-section through the property presented as Figure 3. Tonkin & Taylor Ltd | 105 Carlton Gore Rd, Newmarket, Auckland 1023, New Zealand PO Box 5271, Wellesley St, Auckland 1141 P +64-9-355 6000 F +64-9-307 0265 E [email protected] 2 Some modification of the site appears to have occurred as a result of developing these houses and sub-basement levels. Published Geology The Orakei Basin represents the flooded remains of an explosion crater formed from a phreatic (steam) eruption bought about from basaltic magma encountering groundwater at a relatively shallow depth. The explosion(s) created the existing 800 m diameter explosion crater through a combination of material being ejected into the air and from the surrounding country rock and ejecta collapsing back into the crater as a series of landslides. The ejected material was deposited upon the surrounding landscape to form a tuff ring approximately 1 km wide. The published geology of the Orakei Basin1 and its surrounds is shown in Figure 4. It can be seen that the subject property is located with the inside edge of the tuff ring. The tuff ring itself extends approximately 700 m further to the east of the property. In total the tuff ring covers an area of approximately 6 km2 and covers parts of Meadowbank, Orakei and Remuera. The Orakei Basin volcano appears to have ceased activity upon the completion of the phreatic eruption stage of the basaltic eruptive sequence, not advancing to the stage of scoria cone or lava flow development. There are a number of other similar explosion craters in Auckland such as the Panmure Basin, Onepoto volcano, Tank Farm volcano, Pukaki volcano and Mangere Lagoon volcano. Orakei Basin Volcano A 3D topographic model of the Orakei Basin and surrounding area is presented in Figure 5. It illustrates the following notable features: The explosion crater is approximately circular in shape and defines the general size and shape of Orakei Basin; The inside slopes of the tuff ring have collapsed back into the explosion crater. This is particularly clear in the southern part of the crater; The Purewa Creek developed or re-established its main west-east channel and its southern tributary channel around northern and eastern edges of the explosion crater once eruption activity ceased; Erosion along the flanks of the Purewa Creek appears to have removed the northern and eastern sides of the explosion crater to below current sea level. Recently completed geotechnical boreholes undertaken by T+T at the subject property has proven the presence of variably welded tuff to a depth of at least 11 m. It is apparent from this, the topography model (Figure 5) and the view from Kepa Road (Figure 6) that the property at 1-3 Purewa Road is located within the tuff ring but lies some distance outside of the original explosion crater. The most distinctive topographic feature associated with the subject property is the west-facing slope that extends to the Orakei Basin. Although this slope appears to be a continuation of the explosion crater when viewed from across the basin, this slope is set back from the explosion crater and is entirely non-volcanic in origin. The topography of the site, and the west facing slope in particular, has in fact been formed by the southern tributary of the Purewa Creek cutting down into the tuff ring. The land surrounding the Orakei Basin has been developed with residential housing. Because of its urbanisation, the presence of the wider tuff ring is almost entirely obscured and is indistinct from 1 Kermode, L.O. 1992. The geology of the Auckland urban area. Scale 1:50,000. Institute of Geological and Nuclear Sciences. Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property 3 the surrounding undulating terrain underlain by the marine sediments of the East Coast Bays Formation (ECBF). Orakei Basin ONF The Outstanding Natural Features (ONF) and Outstanding Natural Landscapes (ONL) overlays are included in Chapter D10 of the Auckland Unitary Plan – Operative in part (AUP). The extent of the Orakei Basin volcano ONF overlay is shown on Figure 7. Its eastern boundary has been set to align with the western limit of Puroto Street. The northern boundary of the ONF has been set within the railway corridor, thus incorporating Purewa Road. The ONF includes the eastern bank of the southern tributary of the Purewa Creek, even though this is a non-volcanic topographic feature formed after the cessation of volcanic activity. It can be seen from a consideration of the geological deposits (Figure 4) and the extent of the ONF (Figure 7) that the ONF encloses only a small part of the overall tuff ring. Its outer boundary corresponds to property and road boundaries and not geological features. Schedule 6 of the AUP presents details of the overlay that are specific to each ONF. This is reproduced in Table 1. From the description provided in Schedule 6, it appears that the Orakei Basin volcano ONF reflects the presence of the explosion crater and part of the surrounding tuff ring, but not specific geological features of note such as an exposure or outcrop. The property is located some 230 m north-east of the nearest exposures of the explosion crater. There are no outcrops or exposures of the volcanic deposits that are visible to the public, with the exception of those limited exposures present within the southern cliffs of the explosion crater and the limited number of small exposures adjacent to the pedestrian path that follows part of the basin edge. There are no exposures present within the subject property or any other unique or notable geological features. Table 1: Entry in Schedule 6 of the AUP for the Orakei Basin volcano ID Name Location Site Description Unitary Type Plan Criteria 143 Orakei Orakei V Ōrākei Basin is a volcanic explosion crater and a, c, d, e, f, Basin Basin large tuff ring (1km in diameter). The tidal h, i, l, b, k volcano inlet was formed when the sea entered Purewa Creek valley and breached a former freshwater lake that occupied the crater. Subsequently, the basin was closed off by the railway embankment and the water level and flushing of the basin is now controlled. Sediment cores taken from Ōrākei Basin revealed 90 ash layers deposited by eruptions from other volcanoes over the past 90,000 years Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property 4 Assessment Scheduling of the Orakei Basin Volcano ONF The factors set out in B4.2.2(4) of the AUP have been used by Council to schedule ONF’s. Council has assessed that criteria a, c, d, e, f, h, i, l, b, k (underlined below) apply to the Orakei Basin volcano ONF: a) the extent to which the landform, feature or geological site contributes to the understanding of the geology or evolution of the biota in the region, New Zealand or the earth, including type localities of rock formations, minerals and fossils; b) the rarity or unusual nature of the site or feature; c) the extent to which the feature is an outstanding representative example of the diversity of Auckland's natural landforms and geological features; d) the extent to which the landform, geological feature or site is part of a recognisable group of features; e) the extent to which the landform, geological feature or site contributes to the value of the wider landscape; f) the extent of community association with, or public appreciation of, the values of the feature or site; g) the potential value of the feature or site for public education; h) the potential value of the feature or site to provide additional understanding of the geological or biotic history; i) the state of preservation of the feature or site; j) the extent to which a feature or site is associated with an historically important natural event, geologically related industry, or individual involved in earth science research; k) the importance of the feature or site to Mana Whenua.

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