1989-10-10_REVISION - M1988112 (12)

Home Browse Search

benches will be provided where the disposal area slopes exceed 5H:1V. The liner placement, anchoring and welding details are shown on Figure C-5. D.6.5.3 Drainage Laver Design Tailings water collection will be employed directly over the liner using a subdrainage system beneath the deposited tailings. This system will be constructed of coarse-grained native soil materials and perforated ADS pipe placed over the VLDPE liner. Within the disposal area the drainage layer will be two feet thick while beneath the splitter embankment the layer will be three feet thick. Drainage system characteristics for the main embankment are discussed in detail in Section D.6.5.4. To facilitate collection, perforated ADS pipe wrapped in filter fabric will be placed in a network over the liner surface within these pervious materials and routed to collection laterals running beneath the main and splitter embankments. The subdrainage layers and pipes will discharge • into a lined collection ditch along the downstream toe of the main embankment. The ditch will then route flow to the lined collection pond. A pump and pipeline system wild be used to reclaim the water from the pond and return it to tihe free water pool in the tailings disposal area. The drainage network is shown in plan view on Figure C-6. Drainage network details are shown on Figure C-5. The collection ditch and pond are discussed in detail in Section D.6.5.6. Inclusion of surface drainage pipes above the liner will limit the hydraulic head on the liner. Drainage of interstitial water and consolidation of the tailings immediately above the drain layer will result in a zone of low permeability above the drainage layer. The combined affect of liner drainage system and lower permeability of the tailings will further minimize the hydraulic head on the liner and minimize potential seepage from the facility. The drainage layer will be • D-33