REP29179 - Laserfiche WebLink

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1 1 1 1 A 10-in diameter EIDPE pipe extends from the leak detection sump invert to the crest of the pond. This lower 6-ft of the pipe is perforated with 1/4-in holes and enveloped with a Filter fabric sock. The pipe continues from the pond invert up the slope and extends approximately 2-ft above the pond crest. The pump sump is located in the far southeast corner of the pond adjacent to the leak detection sump. The pump sump contains three 24-in diameter HDPE pipes which act as pump casings for submersible return water system pumps. The 24-in HDPE pipes have a factory manufactured 90 degree elbow which extends from the invert of the sump 5-ft upward. This allows the pumps to have the 5-ft of head required for proper operation when the pond water Level is low. The submersible pumps for the water return system are located in the invert of the 24-in IiDPE pipe 90 degree elbow. The three solution riser pipes extend from the sump invert up the slope to the crest of the pond. The pipes are located directly above the primary liner and are backfilled with a Type 3 silt material. No penetration of the primary liner occurs. The riser pipes and Type 3 backfill are encapsulated with a layer of 60 mil HDPE material which is attached to the pond primary liner system. A sensor pipe with the pump high level and low level sensors is installed in the auxiliary 24-in riser pipe. 3.4 Collection Ditches and Channel The collection ditches and channel collect the tailings seepage water from the impoundment liner and under drain system and transfer it to the collection pond for return to the impoundment surface water ponds. The ditches extend along the entire length of the downstream toe of the main embankment and are approximately 1,700-ft in length. The collection channel routes the surface flow from the collection ditches and transfers it to the collection pond. t The collection ditches have a double synthetic liner system with a leak detection layer. The secondary liner (lower layer) consist of a layer of 40 mil VLDPE liner which is an continuation of the impoundment liner system. The leak detection layer consist of geogrid. The primary liner ' (upper liner) is a layer of sixty mil HDPE liner which is extrudate welded to the impoundment liner system approximately 18 fines under the downstream toe of the main embanlgrtent fill. The ' downstream side of the ditch liner system is anchored along the crest of the ditch in a standard anchor trench. Ttvo small leak detection sumps were installed at the lower end of north and south collection ditches just upstream of the collection channel ' The wllection channel has a double synthetic liner system with a leak detection layer. The ' secondary liner (lower liner) consist of a layer of 60 mil IiDPE which ties into the impoundment 40 mil VLDPE liner system at the upstream end of the channel and laps onto the collection pond ' 14 1