APPENDIX N RICHARD SIMONDS GROUNDWATER REPORT

Transcription

1 APPENDIX N RICHARD SIMONDS GROUNDWATER REPORT

2 Technical memo - Specialist Unit To: Nicola Broadbent, Team Leader - North West Resource Consenting Unit, Auckland Council From: Richard Simonds, Senior Specialist - Coastal & Water Allocation, Resource Consents, Auckland Council Date: 19 June APPLICATION DESCRIPTION Application and property details Applicant's Name/ Application Name: Panuku Development Auckland / America s Cup Wynyard Hobson Service Centre Application Number & Water Allocation Consent Number: Activity type: Site address: BUN & WAT The take and diversion of groundwater as a result of ground improvements along Brigham Street. Wynyard Point & Wynyard Wharf, Auckland CBD Application Documents 1.1 This report provides a regulatory review and assessment of the effects of taking and diverting groundwater associated with the America s Cup Wynyard Hobson resource consent application, which I refer to in this memo as the Application. 1.2 The following application documents are particularly relevant to this report: a) Application for Resource Consent: Assessment of Environmental Effects (AEE), America s Cup Wynyard Hobson, 13 April 2018, prepared by UNIO Environmental Limited (UNIO); b) Document 7 to the AEE, Applicant s Proposed Draft Consent Conditions, 13 April 2018, prepared by UNIO (the Applicant s Draft Conditions); c) Document 26 to the AEE, America s Cup Groundwater Technical Report for Resource Consent Application, Wynyard Hobson, 11 April 2018, prepared by Beca Limited (the Beca Groundwater Report). Consent: WAT

3 d) Document 9 to the AEE, America s Cup Physical Infrastructure Technical Report for Resource Consent Application, Wynyard Hobson, 11 April 2018, prepared by Beca Limited (the Beca Infrastructure Report). e) An received from UNIO dated 16 May 2018, providing an amended set of draft groundwater conditions (the Amended Groundwater Conditions). 2.0 PROPOSAL, SITE AND LOCALITY DESCRIPTION Aspects of the Proposal considered to be Permitted Activities 2.1 The proposed shallow excavations and filling activities required as part of the America s Cup Wynyard Hobson development comply with the Permitted Activity Standards E and E for the take and diversion of groundwater. 2.2 In relation to the proposed maritime activities such as coastal works and the Hobson Wharf extension, I concur with the statement in Section 1.2 of the Beca Groundwater Report that they will not have any impact on the groundwater regime and are therefore these activities are not considered further in this report. 2.3 In the Beca Groundwater Report the following activities are described that may encounter the groundwater table: a) Piling for buildings b) Ground improvements. 2.4 In relation to piling for buildings, Section of the Beca Groundwater Report states that piles of up to 600 mm diameter may extend to a depth of greater than 20 metres below ground level (mbgl). The Beca Report states: Driven and screw piles will not require any dewatering. Bored pile holes are expected to be cased and either locally dewatered for only very short periods (days) before concreting, or, will be constructed as wet pours with no dewatering. As the piles are not contiguous (overlapping) they are unlikely to result in any impedance of groundwater flow or mounding. 2.5 Based on these measurements, I consider that a consent for take and diversion of groundwater is not required in relation to piling for buildings. Aspects of the Proposal relevant to this permit/consent only 2.6 Development of the south-eastern portion of Wynyard Point is proposed to accommodate five bases as part of the America s Cup Wynyard Hobson Application. 2.7 Ground improvements, also referred to as stabilisation in the Beca Groundwater Consent: WAT

4 Report, are required for the proposal over approximately 230m of Brigham Street as shown on Figure 1 below, which also shows the Wynyard Point reclamation. 2.8 The term ground improvements has been defined at Section (page 11) of the Beca Groundwater Report as: improvements that will likely comprise cement-stabilised columns (or stone columns), placed in a lattice pattern and extending some 20 m landward of the existing seawalls. These columns are likely to extend to depths of 10 m to 15 m. Ground improvements could also include a cement stabilised raft in the upper few metres of the soil profile (i.e. more akin to the in-situ stabilisation used for roading upgrades in Wynyard Quarter) over the full extent of the lattice and / or piling at a diameter of up to 2 m. N Wynyard Point Reclamation Wynyard Wharf Proposed extent of ground improvements Figure 1 Consent: WAT

5 2.4 The key matters to note, for the purposes of assessing the permitted activities and the actual and potential effects of the Application, are as follows: a) Only shallow excavations, less than 1m below existing ground level are proposed to create level building platform or for the installation of services. b) The piling for buildings may require dewatering for very short periods (days) from within cased holes. c) The ground improvements will be permanent. d) The length of the area for ground improvements will be approximately 230 m and the depth of ground improvement will be approximately 13 m below groundwater level. e) The cement-stabilised columns or stone columns to be used in ground improvements may exceed 1.5 m in diameter. f) Site-specific geotechnical investigations across Wynyard Point indicate that the ground conditions consist of reclamation fill materials overlying a variable thickness of recent marine sediments and Tauranga Group alluvial deposits that have infilled an old valley system. East Coast Bays Formation rock is encountered at a variable depth, ranging from -15 m to -23 m Chart Datum (CD) with the axis of the paleo-valley inferred to run parallel to (and beneath) Wynyard Point reclamation. g) Groundwater levels and flow directions across the Wynyard Point reclamation are complex as a result of the heterogeneous nature of the reclamation fill and presence of seawalls (of a wide range of construction types), both of which result in varying local permeabilities, tidal lags and tidal ranges over relatively small distances. h) Where the outer reclamation walls are permeable, it is expected that groundwater levels will be principally controlled by sea level. Where the outer reclamation walls are impermeable, groundwater levels will be controlled by local soil conditions as well as the presence of service trenches which may act as preferential flow paths. i) Historic groundwater level monitoring of the former BP Hamer Street site located adjacent to the southern extent of Wynyard Wharf, indicates slightly elevated groundwater levels, at 2.0 to 2.5 m RL, however elsewhere on Wynyard Point, groundwater levels tend to be in the range of 0.0 to 1.1 m RL (1.9 m to 3.0 m below ground level, based on a typical ground level of 3 m RL). Background and site history relevant to this permit/consent only 2.5 No groundwater take and diversion consents have been or are held for the site or within 150m of the site. Consent: WAT

6 3.0 REASON FOR CONSENT GROUNDWATER DIVERSION Reasons for consent 3.1 The proposed ground improvements will encounter groundwater and will not fully comply with the following permitted activity standards in Chapter E7 of the Auckland Unitary Plan (Operative in Part) (AUP) relating to the Taking, using, damming and diversion of water and drilling : a) E (1)(c), which provides an exemption from the standards for piles up to 1.5 m in external diameter (as noted, the cement-stabilised columns or stone columns may be greater than 1.5m in diameter); and b) E (4), which provides that: Any structure, excluding sheet piling, that remains in place for no more than 30 days, that physically impedes the flow of groundwater through the site must not: (a) impede the flow of groundwater over a length of more than 20m; and (b) extend more than 2 m below the natural groundwater level. As noted, the length of the ground improvements will be approximately 230 m and may partially impede groundwater flow, and the depth of the ground improvements is approximately 13 m below natural groundwater level. 3.2 As such, the proposed activity of ground improvements will require a permit for the diversion of groundwater as a Restricted Discretionary Activity. The trigger for this can be found in Activity Table E7.4.1 at (A28). 4.0 TECHNICAL ASSESSMENT OF EFFECTS Effects that may be disregarded Permitted Baseline Assessment 4.1 It is difficult to separate effects of permitted activity scale development from that likely to result from this proposal. The permitted baseline does not therefore assist in this assessment. Assessment of Effects 4.2 I consider that : a) There are no adjacent ecosystems that may be adversely affected as a result of the groundwater related activities. In addition there are no nearby take and diversion of groundwater consents and therefore there are no cumulative Consent: WAT

7 effects occurring on the surrounding sites. I consider that there will not be any adverse effects on the underlying East Coast Bays Formation aquifer due to the proposed activities and hence the effects on any other users of the aquifer will be less than minor. b) Overall I consider there to be less than minor effects on the environment as a result of the proposed activities. I concur with the key findings of the effects assessment detailed in the Beca Groundwater Report at Section 7 (page 25), which I summarise as follows: c) The pile holes required for buildings are likely to be cased and either locally dewatered for only very short periods (days) or will be constructed as wet pours with no dewatering. d) There is negligible up-gradient driving head and groundwater levels under Wynyard Point are expected to be principally controlled by the tide and local soil conditions. e) The ground improvements will be parallel, or at an oblique angle to the direction of groundwater flow. Therefore, they are unlikely to act as a dam but may partially impede groundwater flow. f) Modelling of changes in groundwater level associated with previous ground improvements in the Wynyard Quarter area calculates typically less than 0.2 m of mounding (i.e. less than seasonal / tidal range in this area). g) Previous roading upgrades that have required ground improvements in the wider Wynyard Quarter area have resulted in negligible change in groundwater levels post-construction (i.e. previous modelling is conservative). h) Groundwater drawdown is not anticipated. In the unlikely event that groundwater mounding does occur, the groundwater levels will remain more than 1.2 mbgl and so no buoyancy effects on services or surface structures are anticipated. Monitoring 4.3 Section 6.1 Monitoring Considerations (page 22) of the Beca Groundwater Report states that No significant excavations are proposed and as such ground and building settlement is not expected to occur. For this reason, no survey monitoring (ground or building), or, building or utility condition surveys are proposed. I support this statement. 4.4 Beca Limited has however, proposed groundwater monitoring boreholes in order to more fully understand the groundwater regime adjacent to the area of proposed ground improvements. Groundwater level monitoring is proposed in standpipe piezometers installed in three new machine drilled boreholes (AC36_PZ01 to PZ03). The proposed locations of the groundwater monitoring boreholes are shown on Consent: WAT

8 Figure 5 (page 22) of the Beca Groundwater Report. 4.5 Beca Limited has recommended that the groundwater monitoring boreholes be installed as soon as practical, in order to allow for a sufficient period of baseline monitoring to confirm the tidal (and if possible seasonal ranges) at each site ahead of any ground improvement works or piling for buildings (thus constituting preconstruction monitoring). Beca Limited recommends that as a minimum, one month of baseline readings will be required. 4.6 The proposed groundwater trigger levels (alert levels 1 & 2) and rationale for the selection of the groundwater trigger levels is outlined at paragraph (page 23) of the Beca Groundwater Report. They indicate that final trigger levels for the groundwater monitoring will be set once baseline pre-construction groundwater monitoring data is available. I consider that the proposed scope of monitoring and trigger levels in the Beca Groundwater Report is appropriate. 4.7 In section 6.2, of their report, Beca Limited indicates that once all instruments have been installed and the results of baseline groundwater monitoring are available to set final trigger levels, a Groundwater Monitoring and Contingency Plan (GWMCP) will be submitted to Council for certification prior to any ground improvements commencing. Beca propose that the GWMCP will need to include the following: a) Confirmation of the nature of ground improvements. b) Final location and as-built details of piezometers. c) Results of baseline monitoring data taken in advance of works. d) Establishment of final trigger levels and appropriate contingency measures. e) Details of monitoring to be undertaken (type, frequency and review). f) Review and reporting requirements. g) Roles and responsibilities. h) A system of review to determine at what stage after construction, monitoring can be reduced or cease. 4.8 I consider that it would be appropriate for a GWMCP to be required as a condition of consent, if granted. In addition, I consider that the proposed contents of the GWMCP, as listed above, are appropriate. Submissions 4.9 None of the submissions received have raised any concerns regarding the groundwater diversion consent. Conclusions 4.10 I concur with the assessment of groundwater effects provided by the applicant and conclude that: Consent: WAT

9 a) There have been adequate on site geotechnical investigations to provide appropriate and suitably conservative geotechnical and groundwater level data for an adequate assessment of effects. b) On the basis of the effects assessment, a GWMCP is required to ensure that groundwater levels remain within the predicted envelope. c) The effects of the proposed take and diversion of groundwater are considered to be less than minor for neighbouring buildings, structures and services and less than minor for the environment. 5.0 STATUTORY CONSIDERATIONS Objectives and policies of the AUP 5.1 The objectives and policies relevant to the groundwater diversion aspects of the application in relation to the AUP are provided in Chapter E7 Taking, using damming and diversion of water and drilling, in particular Standards E7.2 & E7.3 and in Chapter E2 Water quantity, allocation and use, in particular Standards E2.3 (6), (7) and (23). Whilst the assessment of objectives and policies is a matter for the Council s reporting planner, I have read the objectives and policies stated above, and as I have set out in Section 4 of this memo from a technical perspective, subject to implementation of the project in a manner consistent with best practice and adherence to the recommended conditions of consent, I consider the proposal to not be inconsistent with them. Other relevant matters 5.2 There are no other matters considered relevant and reasonably necessary to consider with respect to the proposed groundwater take and diversion. Duration of consent: Section It is considered appropriate to set a term of 35 years for the groundwater diversion consent because the groundwater diversion will occur in the long-term and effects on the environment will be less than minor. 6.0 RECOMMENDATION AND CONDITIONS Recommendation 6.1 The assessment in this memo does not identify any reasons to withhold consent and the aspect of the proposals considered by this memo could be granted consent subject to recommended conditions set out below. Draft Consent Conditions 6.2 Conditions concerning groundwater were provided as Conditions 93 to 102 of the Consent: WAT

10 Applicant s Draft Conditions. Subsequently an was received from UNIO on 16 May 2018 with a set of Amended Groundwater Conditions. 6.3 I have reviewed the Amended Groundwater Conditions and consider that they are appropriate with the exception of the following: (a) (b) (c) Throughout the groundwater conditions reference is made to the Team Leader Central Monitoring. This is not the correct role description. The correct role description is Team Leader Compliance Monitoring Central and the groundwater conditions should be amended accordingly. Delete the monitoring location plan from condition 96(a) (condition 4(a) in the Amended Groundwater Conditions), and replace it with a cross-reference to Figure 5 in the Beca Groundwater Report. The text following the table in condition 99 should be amended as follows, for consistency with other groundwater conditions, which generally refer to stabilisation : The monitoring frequency may be changed as part of the certification process by the Team Leader Compliance Monitoring Central Monitoring. Any change shall be specified in the GWMCP. In addition, the 6 month monitoring period post Completion of Dewatering/Stabilisation may be extended, by the Team Leader Compliance Monitoring Central Monitoring, if measured groundwater levels are not consistent with inferred seasonal trends or predicted groundwater movement. Advice Note: If groundwater level measurements show an inconsistent pattern immediately prior to the Commencement of Dewatering/Stabilisation (for example varying more than +/-200mm during a month), then further readings may be required to ensure that an accurate groundwater level baseline is established before dewatering commences. (d) The Amended Groundwater Conditions employ a number of terms and expressions, which I consider should be defined. I recommend that the following definitions be inserted in the definitions condition (condition 1): Definitions Words in the groundwater diversion conditions have specific meanings as outlined in the table below. Alert Levels Specific groundwater levels at which actions are required as described in the conditions. Consent: WAT

11 Commencement of Dewatering/Stabilisation Completion of Dewatering/Stabilisation Means when ground improvements commence. Means when all ground improvements are complete. GWMCP Monitoring Station Means Groundwater Monitoring and Contingency Plan. Means a groundwater monitoring borehole. Seasonal Low Groundwater Level Means the annual lowest groundwater level which typically occurs in summer. Services Include fibre optic cables, sanitary drainage, stormwater drainage, gas and water mains, power and telephone installations and infrastructure, road infrastructure assets such as footpaths, kerbs, catchpits, pavements and street furniture. Damage Includes Aesthetic, Serviceability, Stability, but does not include Negligible Damage as described in the table below: Table 1: Building Damage Classification Category of Damage Normal Degree of Severity Description of Typical Damage (Building Damage Classification after Burland (1995), and Mair et al (1996)) General Category (after Burland 1995) 0 Negligible Hairline cracks. Aesthetic Damage 1 Very Slight Fine cracks easily treated during normal redecoration. Perhaps isolated slight fracture in building. Cracks in exterior visible upon close inspection. Typical crack widths up to 1mm. 2 Slight Cracks easily filled. Redecoration probably required. Several slight fractures inside building. Exterior cracks visible, some repainting may be required for weathertightness. Doors and windows may stick slightly. Typically crack widths up to 5mm. Consent: WAT

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