A pre-disturbance soil survey by a geologist or soil scientist is recommended during the Site Assessment phase to map beneficial soil resources, soil liabilities, and relative geotechnical constraints.
These surveys can direct the location of buildings, infrastructure and environmental systems. For example, stormwater management areas and deep-rooted trees are best located on granular or allophanic soils.
Pre-disturbance surveys may also reveal suitable resources for bioretention practices (sandy loams) or wetlands (organic soils and peats). However, it is important to remember that Auckland soils vary over tens of metres, and unintentional mixing can potentially lend poor properties to 'good' soils.
Further sub-soil surveys may be undertaken if the infiltration rate identified in the pre-disturbance survey is low, or if planting is to take place on the cut faces of earthworked areas.
Discussion on soils can be found in Section B and TR2009/083 Auckland Regional Council Technical Report TR2009/083 Landscape and Ecology Values within Stormwater Management (Lewis et al., 2010).