Laserfiche WebLink
2002 -7- 003-2203 <br />used previously and were found to generally exceed the mean evaporation values used in the <br />water balance. <br />During operations, annual average evaporation losses were estimated to be 2 percent of <br />solution applied by drip emitters, which is consistent with that used in Amendment No. 7 and <br />Amendment No. 8. During the eight-yeaz post operations period, losses were estimated to be <br />5 percent of the solution applied during the summer months (June through September), <br />consistent with Amendment Nos. 7 and 8. This accounts for higher evaporation from <br />wobblers, which will be used during post operations. A monthly distribution was developed <br />for the solution application evaporation losses by multiplying annual average evaporation by <br />a monthly weighting factor. This factor was determined by dividing monthly lake <br />evaporation by the average annual lake evaporation. Evaporative losses on the inactive <br />portions of the VLF were modeled by conservatively assuming that 25 percent of the <br />monthly precipitation that falls on the inactive area was lost to evaporation, which is also <br />consistent with that incorporated in the water balance model presented in Amendment No. 7 <br />and Amendment No. 8. No evaporation losses from precipitation falling within the active <br />azea under leach was assumed, which is also consistent with that incorporated in the water <br />balance presented in Amendments No.7 and No. 8. Past experience with modeling <br />evaporative losses on baze granular surfaces with the HELP computer model has shown that <br />between 40 and 75 percent of precipitation is evaporated. The 25 percent value was chosen <br />to conservatively overestimate precipitation gains to the system for PSSA sizing purposes. <br />The field capacity moisture content of the ore was modeled at 7.5 percent of dry weight, <br />based on data provided by CC&V. Data pertaining to the ore field capacity are presented in <br />Appendix C. The moisture content of the ore during active leaching will exceed the static <br />field capacity. The excess moisture is excluded in the water balance model, as the volume of <br />solution exceeding static field capacity will drain from the VLF when leaching ceases and the <br />moisture content of the ore returns to static field capacity. <br />t:\00@203W0001PH<N'TRBAL0503\0032303.0000.03fi30.DOC Golder Associates <br />