2011-09-08_REVISION - M1977342 (39)

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• (Page 2) MINE ID # OR PROSPECTING ID # 1(- 77-342 INSPECTION DATE 10/30/95 OBSERVATIONS INSPECTOR'S INITIALS ACS New Water Treatment Pond e-! Henderson Mine is constructing an additional treatment pond that will be used in series parallel with the existing pond system used to treat water collected and pumped from t underground workings. The mine dewatering and water treatment system at the Henderson Mi has been designated an Environmental Protection Facility in the Environmental Protection Plkiti submitted for the Henderson Mine, and currently under review by the Division. Dent drawings and information for the pond were submitted for Division review on September 1995. in a telephone conversation on September 5, 1995, the Division provided acceptance the proposed pond as an Environmental Protection Facility component, based on the drawin and information provided. The Division stipulated that the operator analyze a representati sample of the pond foundation soils for shear strength in order to verify design assumptio regarding stability of the pond side slopes. It was agreed that a consolidated /undrain triaxial test with pore pressure measurement would be conducted on a sample of the pon foundation coils. Titan Environmental, Englewood, Colorado is the design, quality assurance, and certifying engineer for the pond installation. John Lupo, with Titan Environmental, was present for part of this inspection. Colorado Lining Company, Parker, Colorado is the lining contractor for the pond installation. Michael Bait, with Colorado Lining Company, was present for part of this inspection. The pond had been excavated and bermed at the time of this inspection, but liner installation had not yet commenced. John Lupo reported that the pond had been installed to the approximate lines and grade detailed in the design drawings. Changes in the design incorporated during construction are addition of a flume at the pond inlet works, and incorporation of a diversion box at the outlet works that allows pond effluent to be directed to either of the existing ponds 1.1 or 2. The new pond is primarily an incised pond, with only some low berming on the north and east sides. John Lupo reported that the pond berms were constructed by placing thin horizontal lifts, and compacting with heavy equipment and a sheepefoot until the berme were brought to design grade. The material removed from the pond excavation was piled in several locations around the site. Anne Ih:lenfeldt reported that the piles will be seeded this year, and silt fences will be erected around the piles. Characterization and final disposition of the piled material will occur next year. Some of the dirt may be suitable for use as a top dressing /plant growth medium for. reclamation. The pond will be lined using 40 Mil HDPE, which will be anchored into trenches 3 feet deep by 2 feet wide, located 5 feet from the pond in -slope on the pond perimeters. Pressure testing of fusion welds, and vacuum testing of extrusion welds was discussed with Michael Bair. For fusion weld pressure tests, the Division requires verification that an intact air channel exists for the length of the weld being tested. This can be accomplished by blowing air into the channel, and verifying that the pressurized air is exiting the opposite end, also by sealing the channel at both ends, pressurizing the channel and metering the.pressure at one end, then cutting a slit in the channel at the un- metered end and verifying that the pressure immediately drops at the meter, or, as suggested by Michael Hair, in thinner liners, such as the 40 Mil HDPE to be used here, the channel will visibly bulge when pressurized and the technician can verify that the bulged area is continuous. For vacuum testing, the Division requires that technicians carefully overlap inspected areas when the vacuum testing apparatus is moved, so that absolutely 100 percent of each extrusion weld or suspect area is examined through the vacuum apparatus glass. The pond subgrade preparation was reviewed. Laborers were removing rocks from the coarse sand subgrade at the time of this inspection. The Division requires that the prepared subgrade be smooth and free of all rocks, stones, sticks, roots, sharp objects, or debris of any kind. No standing water or excessive moisture is allowed in the liner subgrade. The installation contractor shall certify in writing that the surface on which the membrane is to be installed is acceptable before commencing work, and this certification must be included in the final certification report to the Division. Also, the operator will provide a plan - view depicting the location and configuration of each BDPE panel as it was installed.