An Investigation into Underground Mine Interaction with Overlying Aquifers, Huntly East Mine, New Zealand

In recent years, Huntly East Mine has operated at a depth range of approximately 100 m to 220 m below a Quaternary aged clay, sand and silt aquifer that is connected to a nearby large river system (Waikato River). A key issue for mine planning and environmental management has been the development of mine design criteria to allow efficient mining of the reserves and to maintain the integrity of the aquifer. A case study and back analysis at Huntly East Mine is presented, which investigates the overburden conductivity and the impacts caused by mining-induced caving. The case study includes: i. computer modelling of the mine geometry, caving and overburden fracture networks created; ii. field investigation to develop an engineering geological model of the overburden within the goaf to validate the goaf geometry as defined by the computer generated model; iii. in situ field measurement of overburden conductivity in the pre- and post-mining condition; iv. interference testing across the goaf to determine the level of interconnectivity; and v. measured water pressure profiles above the mine.