The SRK UK water team undertook a water management study of the Kuusilampi pit at the Terrafame Mine, Finland between 2017-2020.
SRK recognises that careful management of water in the mining environment is important to ensure a safe and efficient operation, to limit unnecessary expenditure on removing and treating water and to minimise impacts to the environment.
The primary aim of this study was to predict inflows to the pit and pore pressure development in the pit walls as the mine expands and to gauge what impact these elements will have on future mine operation and pit slope stability.
In October 2018, SRK carried out a seepage assessment to identify and evaluate locations of groundwater and surface water inflows to the pit. This was followed by a hydrological study that included a detailed reconnaissance of the surface mine water facilities and surrounding natural catchments.
Hydrogeological fieldwork was completed between October and November 2019 and included:
- Installation of Vibrating Wire Piezometers (VWP), Smartwell and uPVC standpipe piezometers for monitoring pore pressures and water levels;
- Down-hole flow logging to characterise discrete groundwater flows linked to joints and faults;
- Packer testing using STX-60 packer equipment to identify the locations of permeable fracture sets and evaluate fracture permeabilites in the rock mass to the full depth of the future pit; and
- Short (2 hour), medium (1 day) and long (13 day) pumping tests to derive hydraulic properties of the rock mass (K, transmissivity and storativity [S]) and to identify boundary effects.
- Additionally, meteorological and hydrological assessments using both field and open source data were completed to produce representative climatic and river flow data that could be used to model and predict run-off, both within the pit and in the surrounding catchments.
Once this data had been collated, two models were produced:
- A surface water model using the Hydrologiska Byråns Vattenbalansavdelning (HBV) modelling procedure. The primary aims of the model were to determine a run-off coefficient for the natural catchments around the project site, develop Depth-Duration-Frequency (DDF) curves, produce initial calculations of peak flow rates and average monthly precipitation volumes for the catchment together with an estimate of recharge.
- A groundwater model using GMS (MODFLOW-USG). The purpose of the groundwater modelling component was to generate a detailed inflow schedule for the Kuusilampi pit and pore-pressures distributions for use in the geotechnical model.
Using the model outputs, SRK was able to produce a water management design that addressed the needs of the future mine expansion, including specific recommendations on pit dewatering design and future surface and groundwater level monitoring.
Close collaboration throughout the modelling and design stages between the SRK water and geotechnical teams to produce optimal slope angles was critical for the successful design of the future pit shell.
