Journal of Hydrology (NZ) 47 (2): 85-106 2008 © New Zealand Hydrological Society (2008) Identifying leakage to groundwater from Lake Rerewhakaaitu using isotopic and water quality data Robert R. Reeves1, Uwe Morgenstern2, Christopher J. Daughney2, Michael K. Stewart3 and Dougall Gordon4 1 GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand. Corresponding author: R.
[email protected] 2 GNS Science, Avalon, P O Box 30368, Lower Hutt 5040, New Zealand 3 Aquifer Dynamics Ltd, 20B Willoughby St, Lower Hutt 4 Environment Bay of Plenty, PO Box 364, Whakatane 3158, New Zealand Abstract Introduction Stable isotopes (18O, 2H), water dating, and The quality and quantity of recharge to a major anion and cation water chemistry groundwater system can affect the sustainable of springs, groundwater bores, a stream use of groundwater resources, particularly and a lake have been used to identify areas where groundwater is used for domestic or of discharge from Lake Rerewhakaaitu. public water supplies, because public health Groundwater aquifers and spring discharges can be affected by contamination. Thus, to the north and west of Lake Rerewhakaaitu identification and safe management of the are found to contain up to 79% lake water. source of groundwater recharge is essential Hierarchical cluster analysis is used to for protection of groundwater resources. group sites into three clusters based on Natural sources of groundwater recharge to the major anion/cation water chemistry. the groundwater aquifers include streams, Defining meaningful hierarchical clusters was rivers, lakes and rainfall. difficult due to the similarity of the chemical Groundwater is used extensively in New compositions between sites.