A generalised geological cross-section through the waste disposal area is shown below. The basement geology of the site comprises predominantly rhyolite, with some dacite. Rhyolite forms the steep hills to the east of Storage 2 and all of Storage 1A. It grades from a completely weathered clay-rich surface to an unweathered rock. Dacite forms Black Hill and extends under the Ohinemuri River as far as the toe of the embankment of Storage 2.

A low lying ignimbrite flow is located in a paleochannel along the interface between the dacite and rhyolite. The whole area is covered with volcanic ash except for the gullies which are filled with alluvial materials washed down from the surrounding higher ground. Peat and swampy deposits are found in many of the lowland valleys.

For further information on hydrogeology see Waste Disposal Area: Hydrogeology

1. Black Hill 2. Ruahorehore Dome 3. Position of Waste Disposal Area 4. Ohinemuri River.
Schematic diagram only, not drawn to scale.