Contamination Delivery Work Plan
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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