Author:Edda Kalbus, Laura Buckthought, Angela Perks, Jamie Boyle
Source:Auckland Council Research and Evaluation Unit, RIMU
The Auckland Council regularly monitors groundwater levels and quality (physical, chemical and microbiological properties) within some of the region’s aquifers as part of its state of the environment (SoE) programme. The primary purpose of the SoE groundwater programme is to provide information on the status and long-term trends of groundwater at a regional scale, thus providing evidence for availability and the sustainability of water allocation. The results enable Auckland Council to assess if the groundwater is suitable for potable supply, supporting plant and animal life when discharged as baseflow to rivers, saline intrusion risk and how groundwater quality changes over time.
Groundwater availability in the Auckland region originates primarily from rainfall, which percolates down through porous rock, fractures, or unconsolidated sand, gravel or silt materials. Aquifers in the Auckland region are an important water source for many rural areas and for some industries, and also supply a small proportion of Auckland’s drinking water. The primary aquifer types, as used in the Auckland region, include the Waitematā aquifers, Auckland volcanics, south Auckland volcanics, Kaawa formation, greywacke, Quaternary sediments, and geothermal aquifers.
The purpose of this report is to summarise and analyse the groundwater data, assess the current state of groundwater levels and quality across the Auckland region, and identify long-term trends. For the purpose of this report, Auckland’s aquifers were grouped into five areas; North-East, North-West, Waiheke Island, Central and South.
Groundwater levels were generally stable with only small fluctuations observed in many bores over time. There were exceptions however, such as the Mt Richmond volcanic aquifer, which had substantial fluctuations over time. Declining trends in water level were observed in Omaha Waitematā, Karaka Waitematā, Waiau Pa Waitematā and Parakai geothermal, aquifers. Increasing trends in water levels were observed in the Manukau Waitematā, Clevedon East Waitematā, Bombay volcanic, Pukekohe central volcanic and Bombay-Drury Kaawa aquifers.
The state of groundwater quality is generally good, with the exception of nitrate which exceeded the maximum allowable value (MAV) for drinking water in four of the thirteen bores situated in Southern aquifers. Two of these sites, BP Bombay and Rifle Range Road Shallow, showed an increasing trend for nitrate for the Bombay volcanic and Pukekohe central volcanic aquifers respectively. Of the few significant and environmentally meaningful trends, the most common were for total and soluble iron and manganese, with both increasing and decreasing trends.
Auckland Council technical report, TR2017/034