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GEM SERVICES <br /> Dawson Project—Tailings Characterization Page 26 <br /> 5 Summary <br /> The two components of the FTSF, development rock and tailings,have been characterized to <br /> assess their potential to produce acidic drainage and metal leaching. All tailings and development <br /> rock are classified as non-potentially acid generating. Only 1 development rock sample contained <br /> sulfide sulfur above the detection limit. <br /> Metal release from tailings was measured directly by analyzing tailings filtrate. Tailings filtrate <br /> quality meets the groundwater quality standard,with the exception of manganese. Manganese <br /> concentration is less than in background groundwater at the site. Tailings filtrate has a neutral <br /> pH. <br /> Long term metal release from tailings was assessed using the humidity cell test. The tests were <br /> run for 25 weeks until sulfate concentrations were stable near the detection limit. Humidity cell <br /> leachates maintained neutral to slightly alkaline pH throughout the test. Alkalinity increased <br /> throughout the test and acidity and sulfate decreased to near detection limits. Very few metals <br /> were detected in the leachates. Detected metals that have groundwater quality standards include <br /> aluminium,manganese and selenium. All three metals maintained a decreasing concentration <br /> trend throughout the test. It is notable that many common heavy metals, such as copper, lead and <br /> zinc,were not detected during the test. <br /> Metal release from the development rock is generally low. Many metals were less than the <br /> detection limit in shake flask extraction tests. Sulfate was also less than the detection limit. The <br /> shake flask extraction results are consistent with the lack of metal enrichment in the development <br /> rock. <br /> FTSF seepage quality during operations was estimated. The metal release from development <br /> rock and tailings were combined on a mass balance basis using conservative assumptions. <br /> Seepage quality is dominated by tailings filtrate quality and as a result its characterization is the <br /> same. Seepage quality meets the groundwater quality standard,with the exception of manganese. <br /> However, manganese is less than the concentration in background groundwater. <br /> FTSF seepage produced during operations is not expected to require treatment prior to discharge. <br /> The FTSF seepage quality is suitable for discharge via the sedimentation/stormwater pond. <br /> Leachate from the FTSF is not expected during post-closure. Seepage is expected to drain from <br /> the sand and gravel layer during storm events;however,this seepage is not expected to contact <br /> tailings. Seepage quality will be similar to infiltration through soil. <br /> DDS/dds Zephyr_Dawson_Teilings_Charactedzation FinaL_Report,Feb.3,22,1:1 B PM Feb 2022 <br />