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DocuSign Envelope ID: EBE28081-13782-41342-13AD13-D8C9313687131B <br />TOXICITY REDUCTION EVALUATION — LINES OF INVESTIGATION <br />Design Basis <br />remove the cleaning chemicals and brought back into service with pretreatment mine water. Individual <br />cleaning cycles must be done for each type of fouling component which can include mineral and/or <br />biological foulants. Citric acid, sodium bisulfite, and calcium hypochlorite are included as potential <br />chemicals needed for cleaning on an assumed quarterly basis. <br />Residual Handlina <br />Brine from the NF system entails a significant challenge as the concentrate reject stream flowrate of <br />approximately 30 gpm has to be stored in a pond for evaporation. Evaluation of site conditions shows that <br />a net evaporation of 6.7 inches annually is expected. Additionally, this evaporation is limited to a relatively <br />short window of the year which means that the pond must store residual waste brine without significant <br />evaporative losses from October to April. Without enhanced evaporation, the resulting evaporation pond <br />size is approximately 90 acres which accounts for storage during the winter months and evaporation of <br />this stored amount plus inputs during the evaporation season. Precipitation and continued residual brine <br />inputs from the NF system are expected to result in roughly 9.9 million gallons (30.4 acre-ft) over the <br />course of the wet season (the period when net evaporation is near zero or less). Additional investigation <br />and modeling will be done during the value engineering stage to optimize this sizing if this is pond <br />evaporation remains the primary option for concentrate brine management. <br />Several mechanical evaporators were considered to manage either the full mine water volume or the <br />reduced and NF concentrate brine volume. Of the potential mechanical evaporation approaches <br />considered, the most cost effective is a header and branch droplet spray system that is installed within <br />the envelope of the pond. Each sprinkler head is expected to evaporate roughly 8% (assumed to be <br />Senninger Supersprays) of the solution pumped through it. Pressurized concentrate from the NF system <br />will be regulated down to 80 psi and then sent through the first stage of sprinklers with the remaining, <br />non -evaporated, water settling into the pond. These sprinkler heads also reduce the potential for <br />overspray impacting vegetation in nearby areas. <br />Collected water within the pond will be pumped into a header that feeds into the sprinkler branches. Each <br />sprinkler branch and sprinkler head are assumed to be placed at 40-foot intervals to eliminate overlap of <br />sprinkler spray which is expected to encompass a 30-foot diameter. At the 8% evaporation rates, 255 <br />sprinkler heads are expected to be installed to meet the evaporative requirements over the approximate 6 <br />month long dry season. This correlates to an approximate 10 acre pond area. The location of this storage <br />evaporation pond has not yet been determined. The pond location would be determined in a later design <br />stage if this option for brine solution management is chosen by Colowyo. <br />Solids accumulation in the pond over the course of several seasons would need to be cleaned and <br />sprinkler heads cleaned or replaced to ensure optimum operation. Due to this cleaning requirement, it is <br />recommended that two cells be constructed and cleaned in alternating years. The evaporation pond <br />elevation must be kept above the flood plain and out of runoff drainages. <br />Operational Control Approach <br />Each aspect of the NF process can be automated to minimize operator intervention during normal <br />operation. The raw mine water pH is adjusted through addition of sulfuric acid using a peristaltic dosing <br />dpg \\us0321-ppfss011shared_projectsV33001407\reports\4_tre lines of investigationitre lines of investigation_20200320_ifra.docx 2.6 <br />