(Chapter7)Combined Hydrochemical and Isotopic Determinations in Groundwater to Assess the Effectiveness of Mitigation Measures

摘要

Active mitigation measures for groundwater are often applied to prevent potential infiltration from contaminant generating source discharge to aquifers. These discharges will disturb the natural composition of groundwater. The mitigation measures are, usually, placed downgradient of massive spoil rock piles, tailing dams, leach pads and other industry infrastructure or activity that may cause changes to groundwater. Active mitigation measures consist of diverting water before it comes into contact with groundwater (drains and diversion channels)or directly applied to groundwater when it has been already affected by infiltration (pump and treat). Water chemical composition often contain indicators that may be used as forensic tools, help to identify the source of potential contaminants, aid in the evaluation of remedial actions and adapt such remedial actions, strategically, for better results in reaching mitigation and remediation targets. One makes use of major ions, minor constituents, groundwater isotopes and isotopes from dissolved or suspended constituents as indicators of solute mass, chemical processes, aid in the identification of water sources and the fate of chemical constituents. Monitoring of the active mitigation measures and associated sampling points is required to assess the performance of the remedial actions and to make informed decisions. Long term monitoring provides data sets that indicate the status of the natural system, the potential impact of the installations and infrastructure and, together with additional process information, enables to establish correct water balances. Presented in this paper is a methodological approach on how to use the monitoring information for a correct assessment of the status of groundwater bodies and to establish their evolution. Potential infiltration of waters from massive waste rock spoil piles and tailings are assessed by hydrochemical mass balances and fast reaction measurements are proposed utilizing online measurements. Combined with direct, sophisticated determinations, such online measurements are an effective way to make informed decisions in real time.