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L1. . WHEELER <br />ASSOCIATES, INC. <br />Water Resources Engineers WWW.WWWHEELER.COM <br />3700 S. INCA STREET I ENGLEWOOD, CO 80 1 1 0-3405 <br />303-761-4130 1 FAx 303.76 1 -2a02 <br />TECHNICAL MEMORANDUM <br />October 31, 2017 <br />To: Brandon Beggs <br />From: Doug Maclaren, P.E. <br />Re: 1333.01.11 Henderson Mill Seepwater Collection System Piping Hydrostatic test <br />On October 17 and 19, 2017, the discharge pipelines for Phase III of the Henderson Mill <br />Seepwater Collection system were hydrostatically tested. Phase III consisted of two new wells, <br />MLEX-4 and -5, along with the associated vaults and pipelines, etc. The two new wells were <br />drilled, and vaults and discharge pipelines were installed earlier in the summer/fall of 2017. Well <br />MLEX-4 is connected to the existing well pipeline system that includes wells MLEX-1 thru -3, <br />which discharges into the storage pond at the base of the tailing dam. Well MLEX-5 uses a <br />separate discharge line that discharges the flow directly into the sump at Ute Park Pump Station. <br />Due to their locations, the two well systems use separate discharge lines and were therefore <br />tested independently. The discharge line from MLEX-4 was a 4 -inch and from MLEX-5 a 3 -inch <br />HDPE line was installed. A line sizes used are adequate to handle the expected flow rate from <br />either of the wells. <br />The line from well MLEX-5 was hydrostatically tested first on October 17. 2017. The end of the <br />new pipe where it is to be connected to the existing discharge box was closed off with a blind <br />flange, which was modified to add a pressure and fill port. The 1-112 inch valve in the concrete <br />vault was closed and the 4 -inch HDPE line pressurized with water to between 85 and 90 psi. For <br />the next 4 hours the line was kept at this pressure by adding water as required. Once the line <br />was determined to be holding pressure, Wheeler was contacted and visited to the site to witness <br />the 1 -hour hold period, which is the most important part of the test procedure. After being <br />pressurized to a minimum of 85 psi for 4 hours, the line pressure was reduced to 75 psi and no