Environmental Management
Pit Lakes
Numerical Modeling
Project Permitting

A lake forms naturally when ground water and precipitation are permitted to flow freely into the open pit left after activity has ceased at a mine site. Depending on the size of the pit and the rate of inflowing water, complete filling may take weeks, months, or many years. Typically, pit lakes are much deeper relative to their surface area than are naturally occurring lakes. This is important in determining the rate of mixing and vertical stability of the water in the lake. Other factors that can influence pit lake properties include:

  • Surface heating / cooling
  • Precipitation, snowfall, and ice formation
  • Groundwater inflow / outflow
  • Surface inflow of diverted water / sludge
  • Sub-surface removal of water via pumping
  • Surface winds
  • Water chemistry

Pit lakes have the potential to contribute a wide variety of deleterious substances to the surrounding environment. Therefore, it is important to anticipate changes in chemical and physical properties as a pit lake ages. In some cases the chemical composition of the pit lake may not be important and only the physical properties need to be considered. In other instances, geochemical properties are crucial to developing an effective pit lake management strategy.

Lorax utilizes several computer models to simulate the formation and subsequent evolution of pit lakes, including:

  • DYRESM: Developed and maintained by the Centre for Water Research at The University of Western Australia. It is widely used for pit lake stability simulations. It currently does not include geochemical properties of pit lakes or surface ice formation.
  • PITMOD: Developed and maintained by Lorax, PitMod incorporates the PHREEQC chemical speciation model for detailed geochemical calculations. It also includes an ice formation sub-model.