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~ ~~ • (Page 2) MINE ID / OR PROSPECTING ID ~` M-77-342 INSPECTION DATE 10/30/95 INSPECTOR'S INITIALS ACS OBSERVATIONS New Water Treatment Pond Henderson Mine ie constructing an additional treatment pond that will be ueed in aeries or parallel with the existing pond system ueed to treat water collected and pumped from the underground workings. The mine dewatering and water treatment system at the Henderson Mine has been designated an Environmental Protection Facility in the Environmental Protection Plan submitted for the Henderson Mine, and currently under review by the Givieion. Design drawings and information for the pond were submitted for Division review on September 5, 1995. In a telephone conversation on September 5, 1995, the Division provided acceptance of the proposed pond ae an Environmental Protection Facility component, based on the drawings and information provided. The Division stipulated that the operator analyze! a representative sample of the pond foundation soils for shear strength in order to verify design assumptions regarding stability of the pond aide elopes. It was agreed that a consolidated/undrained triaxial test with pore pressure measurement would be conducted on a sample of the pond foundation soils. Titan Environmental, Englewood, Colorado ie the design, quality aseuranaa, and certifying engineer for the pond installation. John Lupo, with Titan Environmental, was present for part of this inspection. Colorado Lining Company, Parker, Colorado ie the lining contractor for the pond installation. Michael Bair, 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 aides. John Lupo reported that the pond berms were constructed by placing thin horizontal lifts, and compacting with heavy equipment and a eheepsfoot until the berms were brought to design grade. The material removed from the pond excavation was piled in several locations around the site. Anne Ih:~enfeldt 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 ae 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-elope on the pond perirtieters. Pressure testing of fusion welds, and vacuum testing of extrusion welds was diecut~sed with Michael Bair. For fusion weld pressure teat e, 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 t:he opposite end, also by sealing the channel at both ends, pressurizing the channel and metering the.preeeure at one end, then cutting a alit in the channel at the un-metered end and verifying that the pressure immediately drops at the meter, or, as suggested by Michael Bair, 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 ie continuous. For vacuum testing, the Division requires that technicians carefully overlap inspected areas when the vacuum testing apparatus is moved, eo 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 Band subgrade at the time of this inspection. The Division requires that the prepared subgrade be smooth and free of all rocks, atones, 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 ie 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 HDPE panel as it was installed.