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28,2002 -5- 003-2203 2.0 WATER BALANCE MODEL -GENERAL DESCRIPTION A revised water balance analysis was completed to quantify the probable volume of solution within the VLF over time due to normal processing, water gained by precipitation, lost to evaporation, and moisture retained in the ore matrix. The monthly model was developed for the period from January 1995 through January 2020 for the entire VLF. The last 8 yeazs of the model simulates the cyclic climatic conditions that could develop when the facility is being leached, rinsed, and the loss of moisture to ore wetting no longer occurs. As identified in Amendment No. 8, the water balance model is based on the following equation: where: BS+p+OMoEL=E+OMFC+PS BS = the barren solution applied to the ore P = the precipitation that falls directly onto the ore OMoet,= moisture contained in the matrix of the ore delivered to the VLF E = evaporation loss from the active and inactive leaching areas OMFC = moisture contained in the matrix of the ore at field capacity after leaching and draindown PS = pregnant solution pumped from.the PSSAs to the ADR. The water balance equation was set-up as an Exce1T"' spreadsheet model to track solution flow within the Phase I, Phase II, Phase III, and Phase IV areas of the VLF. Since precipitation and evaporation vary month by month and from yeaz to year, a probabilistic approach was used for the water balance. This variability or uncertainty in the amount of precipitation from month to month was accounted for in the water balance model through the use of an internally linked, variability-based softwaze program (Crystal Ba11T"'). Probability distribution functions were developed for precipitation and evaporation using actual historic climatological data, combined with recent site climatological data from the Cresson Project. maoazo~w,oo~rxawrxenwsaaoo3zzo~.Oaoo.oJ6zo.000 Golder Associates