Selected trace elements in Stockton, New Zealand, waters

Abstract

Ni, Mn, As, Pb, Cd, Cr, Cu, Hg, Se, Al, Zn, Fe, SO42, hardness (calc.) in addition to pH, total dissolved solids (TDS), and total suspended solids (TSS) were measured at 18 (11 surface and 7 subsurface) sampling sites (which were each assigned a semi-quantitative Mudstone Index (MI)) from 20 days over 9 months in the waters which drain the Stockton coal mine area on the Stockton Plateau, New Zealand. Trace element, TDS and TSS concentrations were found to be elevated and pH depressed consistent with acid mine drainage (AMD) and were characterised by significant variability due to environmental processes. Frequent concentration spikes in surface and subsurface waters occurred which sometimes exceeded maximum acceptable values (MAV) and/or aesthetic guideline values (GV) including a number of toxic trace elements. Mean concentrations of Ni and Mn in both surface and subsurface waters and As and Cd in subsurface waters exceeded MAVs. Mean concentrations of Mn, Al, Fe, SO42, and pH in both surface and subsurface waters exceeded GVs. There tends to be higher trace element and TDS concentrations where there are more mudstones (higher MI) with lower pHs. It is recommended that any further studies focus on geographic distribution, concentration fluctuation factors, movement, and possible exposure issues. © 2002, Copyright Taylor & Francis Group, LLC.