Table 5.14 (continued) Maximal and Entry-level or Residual risk assessment precommissioning residual simplified assessment (operational) risk assessment and recovery rates Verification of monitoring flow – cumulative recharge – and discharge volumes watertable elevation – Monitor observation • well in target aquifer • at critical control points (beneath and M adjacent to the recharge basin or gallery), and at a well further away, to t provide early warning of excessive mounding and discriminate between causes Monitor control • system to detect a potential failure Continue monitoring Implement • Operational until unsaturated zone groundwater level monitoring na = not applicable. monitoring as early as and aquifer behaviour possible before is well understood. commissioning, to generate Ensure that flow and Estimate or • background data water-quality measure seasonal monitoring are or annual coordinated injection and See verification • recovery volumes monitoring and validation monitoring above. 5.9 Contaminant migration in fractured rock and karstic aquifers In fractured rock aquifers, most water flows through cracks in the rocks, and thus may only interact with a very small percentage of the rock mass. The effective porosity of fractured rock aquifers is much less than for aquifers in which flow is predominantly through interconnected pores throughout the porous medium. Water is conveyed through connecting fractures, and may zigzag through aquifers in three dimensions. Hence, the water injected into a fractured aquifer will travel further from the ASR well than the same volume would travel in a porous aquifer. The distribution of recharged water is therefore much more difficult to predict, which has implications for
Table 5.14 (continued) Entry-level or simplified assessment Maximal and precommissioning residual risk assessment Residual risk assessment (operational) Verification monitoring • and recovery rates of – flow – cumulative recharge and discharge volumes – watertable elevation • Monitor observation well in target aquifer at critical control points (beneath and adjacent to the recharge basin or gallery), and at a well further away, to provide early warning of excessive mounding and discriminate between causes • Monitor control system to detect potential failure Operational monitoring na = not applicable. • Estimate or measure seasonal or annual injection and recovery volumes • Implement groundwater level monitoring as early as possible before commissioning, to generate background data • See verification monitoring and validation monitoring above. Continue monitoring until unsaturated zone and aquifer behaviour is well understood. Ensure that flow and water-quality monitoring are coordinated 5.9 Contaminant migration in fractured rock and karstic aquifers In fractured rock aquifers, most water flows through cracks in the rocks, and thus may only interact with a very small percentage of the rock mass. The effective porosity of fractured rock aquifers is much less than for aquifers in which flow is predominantly through interconnected pores throughout the porous medium. Water is conveyed through connecting fractures, and may zigzag through aquifers in three dimensions. Hence, the water injected into a fractured aquifer will travel further from the ASR well than the same volume would travel in a porous aquifer. The distribution of recharged water is therefore much more difficult to predict, which has implications for a M t
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