Development of appropriate site-specific triggers form part of proactive site management and provides a means of reviewing and assessing monitoring data to manage the impact of site activities that may impact on groundwater quality and levels. The proposed approach highlights essential steps employed to assess groundwater quality and to define groundwater triggers. Effective assessment of the impact on groundwater quality allows future management decision and development of mitigation measures.
It is important to have a good understanding of the conceptual hydrogeological site model. Potential sources associated with the site activities should be identified for both inactive and operating facilities. Potential pathways from the various sources should be identified with consideration of local hydrogeological conditions. Potential receptors typically include third-party bores and surface water features. The source(s), pathway(s) and receptors should be qualitatively and quantitatively characterised.
The next step in trigger development is to statistically evaluate the monitoring data. This step interrogates the data and identifies outliers or trends that can be removed from the data set. A number of site-specific conditions should be considered, for example, the location of the monitoring bores, geographic position in terms of the potential sources on site, potential groundwater migration and location of the potential impact to the receiving environment.
Compliance bores are intended to be monitored and assessed against site-specific trigger values, while diagnostic bores are used to collect information to inform the mine about the trigger limits of different facilities on site. Groundwater trigger limits are frequently used to inform the groundwater management plan and assesses the groundwater quality and groundwater levels at an operation for both compliance and diagnostic purposes. Trigger values should be fit for the purpose but also conservative enough that they provide an early warning of emerging potential impact on the quality of groundwater. If triggers and limits are set too low, natural variability can be mistaken for site impact on groundwater.