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ARCADIS <br />Return of RO Concentrate to the Mine Pool <br />Overview: Plans include returning the RO treatment residuals (also commonly referred to as RO <br />concentrate) back to the mine pool at approximately 24 gpm on average while periodically injecting <br />molasses and alcohols into the RO residual return water line to facilitate biological activity. This strategy <br />was developed as an alternative to constructing an approximately 3.4 -acre evaporation pond adjacent to <br />the creek. <br />It is stated in the Reclamation Plan that, without in -situ treatment, constituent concentrations in the mine <br />pool will increase by 15 percent as a result of dewatering and return of the RO residuals, whereas wall <br />rock runoff will cause the uranium concentration in the mine pool to double based on the original refilling of <br />the mine. In contrast, the Reclamation Plan states that concurrent in -situ treatment will reduce uranium <br />concentrations to less than 3 mg/L within a year or two, and possibly significantly less over time. The <br />treatment is also assumed to more than offset the 15 percent increase in concentrations due to placement <br />of RO treatment residuals back into the mine pool. <br />Data Adequacy: Detailed water quality modeling should be conducted to support the predicted change in <br />constituent concentrations over time prior to and as a result of in -situ treatment. <br />Recommendations: Development of a more detailed conceptual model and associated geochemical <br />predictive model would help to obtain a more quantitative assessment of changes in the mine pool water <br />quality over time. <br />Platoro Mine Overview <br />Overview: The success of the Platoro Mine pool water treatment strategy and applicability to the <br />Schwartzwalder Mine pool treatment approach is extensively referenced in the Reclamation Plan (pages <br />7, 41, and 48). To assist with the Reclamation Plan review and to help assess the applicability of the <br />Platoro Mine pool treatment to the Schwartzwalder Mine, the Platoro Mine is described in more detail <br />here. <br />The Platoro Mine is an underground gold - silver mine in the San Juan Mountains of Southern Colorado, <br />owned by Platoro Mining Company and Union Gold Inc. (Platoro Joint Venture). An on -site WTP treats <br />acidic mine drainage and seepage associated with the waste rock dumps under the site permit conditions <br />(CDPS Permit No. CO- 0038954) and is operated from April 1 to November 30 to provide hydraulic control <br />on the mine pool water levels. The plant includes an equalization pond, lime treatment plant (aeration, <br />flocculation, settling, and clarification), and a final pH adjustment stage. The treated water is discharged to <br />a polishing pond and /or one of five sludge ponds before being released to Wayne's Creek, which flows to <br />the Conejos River, both of which are "state waters ". <br />Page <br />9/16 <br />