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Knight Pidsold <br /> CONSULTING <br /> Question 3: In Section 2.1 it is stated that the samples were collected as bulk grab samples. Please <br /> provide more details of how this sampling was conducted. Additionally, if the samples were <br /> surficial in nature there is the potential of oxidation zoning in the piles where the surface has <br /> reacted and the more interior of the pile unreacted. Ideally sampling of the piles should have <br /> been done using a 5-point composite and sampling at depth within the pile. <br /> KP Response: <br /> Attachment 2 includes the photos taken during the sampling program. The samples were collected from <br /> each of the three piles that were accessible using a backhoe to remove the first five to six feet of the exterior <br /> of the pile and them taken a composite sample of the material. At each location, a fifty-gallon drum was <br /> collected and then sent to laboratory where representative splits were analyzed. <br /> Question 4: There are three historic draining mines with acid mine drainage that have been <br /> identified by the Abandoned Mine Lands(AML)within a two-mile radius of the site.Two of those <br /> mines, Silver Cycle and Big 5 Tunnel, have seen partial to complete restoration and the third <br /> site, Rockford, is currently draining.Given the site is located in a known region to produce acid <br /> mine drainage, the paste pH values of the piles range from 4.4 to 4.7 and NNP values being <br /> between -20 and 20 kg CaCO3/ton additional kinetic testing should be completed. <br /> KP Response: <br /> The piles located on the Gladstone site have been in place since the late 1800s with no significant acid <br /> rock drainage being generated, as the kinetic testing program would only be 4 weeks, it is Knight Piesold's <br /> professional opinion that kinetic testing would not benefit by adding additional information to the length of <br /> time to generating acidity to the existing piles. In addition, these piles will be removed as part of project <br /> development and as such this would reduce any existing environmental liability at the site. Lastly, the low <br /> paste pH of the material is likely in part due to the residual ferric oxyhydroxides that contain enough residual <br /> acidity to register the pH values seen in the testing program. <br /> Question 5: The report notes that in the GARD Guide, 2014, that sulfide-sulphur contents of less <br /> than 0.1% wt sulphide-S are not considered to be acid generating. Typically, this approach is <br /> used when the complete mineralogy of the samples and area are well documented.Mineralogical <br /> work provides a framework for interpreting geochemical tests. To date the mineralogy of <br /> samples and waste rock piles are not well documented. Please recalculate the NNP using the <br /> more conservative total sulphide content. <br /> KP Response: <br /> Calculating Net Neutralization Potential (NNP) based on total sulfur results in the following NNPs: <br /> • Pile 1: -13.1 kg CaCO3/t <br /> • Pile 2: -5.9 kg CaCO3/t <br /> • Pile 3: -7.3 kg CaCO3/t <br /> June 29,2021 <br /> DV-21-0775 2 of 5 <br />