2007-12-19_REVISION - M1988112 (12)

Home Browse Search

A transient model, which corresponds to the condition of irrigating as described in this permit amendment, was then created from the steady-state model using a stress period of six months representing the irrigation season. The final ground water level configuration from the steady-state model was used to define the initial condition in the transient model. A summary of the transient run is presented in Appendix F. Using MODFLOW to simulate ground water flow, a solute transport model was then constructed using MT3DMS to evaluate the fate and transport of fluoride in ground water with time. MT3DMS is designed to be used in conjunction with MODFLOW. The inputs used in MT3DMS related to advective and adsorptive characteristics are presented in Appendix F. The model was run until solute concentrations achieved steady-state within the model domain (Figure G.3-2). Results of the steady-state ground water modeling indicate that ground water flow is to the southwest in the vicinity of the irrigation pivots at Salazar Ranch. This result is consistent with the regional ground water system as presented in the RGDSS. However, for purposes of this evaluation, the nearest location of current ground water use is to the south at the Town of San Luis. Therefore, in order to assess the potential affects to current ground water use in the vicinity of the irrigation pivots, the focus of the solute transport analysis is at the southern boundary of the Salazar Ranch (and permit boundary). The results of the solute transport model indicate a probable increase in ground water fluoride concentration of approximately 0.46 mg/L in the vicinity of SLM-2 (Figure G.3-2). Other locations show variable fluoride concentrations depending on proximity to the irrigation pivots and location relative to ground water flow direction (Figure G.3-2). Ambient fluoride concentrations in ground water at the Salazar Ranch are approximately 0.5 mg/L, which results in a total projected concentration of 0.96 mg/L at SLM-2, which will not adversely affect any current or reasonably foreseeable future use of ground water, given that the projected ground water fluoride concentration is well below any established beneficial use standards. Battle Mountain Resources, Inc. 37 P:\Pmjwts\212-Now t(SenGris)\SanLuis\Pe t Amendment - West Pit MsmgemendVS Report & PDFs\Text\Pe`mitAmendmem_v5o-d- December 2007