3. Summary of contamination assessment

3.1 Overview

Contamination investigations conducted to support obtaining the necessary planning approvals for the CRL works in the Karangahape Station area are documented in the following reports:

City Rail Link: Contaminated Land Assessment July 2012, prepared by AECOM; Auckland City Rail Link: Aotea Station to North Auckland Line Construction and CRL Operation Contaminated Land Assessment May 2016, prepared by Golder Associates; and Auckland City Rail Link: Aotea Station to North Auckland Line Construction and CRL Operation Water Quality Assessment May 2016, prepared by Golder Associates.

The contaminated land assessments undertaken in the Karangahape Station area comprised an assessment of soil and groundwater. For accessibility and logistical reasons, the soil and groundwater investigations did not necessarily target specific locations but were positioned to provide an overview of potential ground contamination constraints.

3.2 Geology and hydrogeology

A summary of the available geological information indicates the general vertical stratigraphic sequence in the area comprises the following:

Fill - generally varying in thickness between 2 - 3 m along the Beresford Square and Mercury Lane construction areas, but increases up to 4 m thick just south of the ridge crest at Karangahape Road and 5 - 6 m thick towards the lower slopes and towards Central Motorway Junction; Tauranga Group - local alluvium deposits infill the heads of paleo-tributary gullies south of the ridge crest; East Coast Bays Formation (ECBF) - the thickness of the weathered and residual ECBF varies in the area. The residual ECBF underlies the fill (where no alluvium deposits are present), ranging from 4 - 8 m and 3 - 6 m along Beresford Square and Mercury Lane respectively. The thicknesses of the weathered ECBF vary similarly, before grading into unweathered ECBF at depths between 46 and 54 m RL.

Hydrogeological studies and historic groundwater monitoring data from piezometers installed in the region of Beresford Square and Mercury Lane indicates the presence of a shallow or perched groundwater level, varying between approximately 2 m below ground level (bgl) to 6 m bgl. The perched water level fluctuates between these maximum and minimum levels in response to rainfall events, particularly in the Beresford Square area. Beneath the perched groundwater zone (at depths varying between approximately 8 to 10 m bgl), seasonally permanent saturation of the fill/alluvium/residual ECBF is assumed to occur, representing the top of the regional groundwater system in this area. This regional hydrogeological regime is relatively complex, with up to four regional groundwater levels conceptualised in the hydrogeological model of the area.

Further details on the geology and hydrogeology are provided in the ‘Groundwater and Settlement Monitoring and Contingency Plan’ prepared for the Karangahape Station main works.

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3.3 Soil quality

The intrusive investigation work has been undertaken on public land and within road reserves around the CRL project alignment and has not specifically assessed potential contamination on private properties. The investigations identified that significant soil contamination was unlikely to be encountered during land disturbance activities.

Soil quality testing undertaken in and around the Karangahape Station is limited and has largely focused on potential contaminants of interest likely to be associated with the urban land use. Soil analysis comprised the following common contaminants considered appropriate for fill with unknown origin and road infrastructure:

• Asbestos; • Metals; • Polycyclic aromatic hydrocarbons (PAH); and/or • Total petroleum hydrocarbons (TPH). No olfactory indications for contamination were reported within fill; however, car parts, brick, metal and glass were observed in fill at borehole EB312 (corner of Mercury Lane and Canada Street) between 0.1m and 2.74 m bgl. The NES Soil regulations provide a set of chemical specific soil contaminant thresholds that define an adequate level of protection for human health for a range of differing land-uses in New Zealand (referred to as soil contaminant standards or SCS). For the Karangahape Station works, the NES SCS for commercial/industrial land use has been adopted. All results complied with the adopted NES SCS. Nickel and zinc concentrations in several samples exceeded the Auckland Council criteria for discharges to the environment (previous and current adopted criteria). Cadmium, chromium, copper, lead, zinc and PAH concentrations within fill material also exceeded the published background concentrations for non-volcanic soils in Auckland as described in the Auckland Regional Council Technical Publication 153 –Background Concentrations of Inorganic Elements in Soils from the Auckland Region (TP153). Asbestos is likely present in the underground services due to the age of the utility network. Asbestos in soils was tested for in one sample within the Karangahape Station work areas (BH134 at 0.1-0.2m bgl located towards the north-east end of Beresford Square) with laboratory results reporting asbestos not detected within the sample. Fill material will be removed during the works and will require appropriate disposal (refer Section 4.4).

3.4 Groundwater quality

Groundwater information is available for a number of locations on public land and within road reserves along the CRL project alignment. Available groundwater results in and around the Karangahape Station works area were compared to the 95% trigger values of the Australian and New Zealand Environment Conservation Council Guidelines for Fresh and Marine Water Quality (ANZECC Guidelines, 2000). Marine trigger values have been used for comparison for the northern part of the catchment draining to the Waitemata Harbour and freshwater trigger values for the catchment draining west to Motions Creek, with result findings summarised as follows:

Except for boron and copper concentrations within a shallow well in Mercury Lane (BH312), the dissolved trace element data groundwater quality in and around the Karangahape Station was generally lower than the relevant ANZECC Guidelines 95% trigger values; and

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Results of total concentrations for arsenic, boron, cadmium, chromium, copper, lead nickel and zinc exceeded ANZECC Guidelines 95% trigger values. These concentrations are considered attributable to very high concentrations of suspended solids present in groundwater samples.

Groundwater will be encountered during the Karangahape Station main works. Site water (surface and groundwater) during construction requiring discharge will be managed through a water quality monitoring programme to ensure discharge quality is met prior to disposal (refer Section 4.6 and the ESCP prepared for the Karangahape Station main works).

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