TM 5-814-7CANCELLEDFigure 6-5. Typical leak detection systems and leachate collection drains6-13
conductivity of the drainage layer material available, arepresented in EPA SW-873, EPA SW-870 and EPA625/1-81-013.e. Leak detection and leachate collection drains.As shown in figure 6-5, trench installations can be usedfor leak detection drains in secondary clay liners.Projecting installations should be used for syntheticliners. Slopes for bedding should be no steeper than theangle of repose of the drainage layers and all slopebreaks should be rounded. Collection drains oversynthetic liners should incorporate a 4-inch-minimumbedding of clean sand (SP) to satisfy requirements forliner protection. Drain rock used over synthetic linersshould be rounded pea gravel. Geotextile fabrics mightbe evaluated to serve as an alternative protectivemeasure.f. Leachate collection sump and riser. Thecurrent state-of-the-art in leachate collection systemdesign uses sumps or basins at low points on the baseof the fill to which the leachate collection networkdischarges. A riser pipe extending from the sump to theground surface enables leachate removal. The lowersegment of the riser pipe in the drain rock of the sump isslotted, and can be connected to a slotted header pipe inthe sump to allow a higher rate of flow to, and withdrawalfrom, the riser pipe.(1) The riser must be of a diameter that willaccommodate a pump suction line or submersible pump.The riser pipe can be installed in a trench excavated inthe wall of the clay liner, or bedded in suitable soil on thesurface of the synthetic liner.(2) Leachate collection networks for landfills,which must remain functional during the 30-yearpostclosure period, should include pipe cleanoutsextending from major collection drains to the groundsurface, to enable system inspection and/or cleaning.g. Design considerations. In designing aleachate collection system, one must consider resistanceto chemical attack, prevention of clogging, and pipestability.(1) All components of leachate collectionsystems must be able to withstand the chemical attackwhich can result from waste or leachate. Plastic (PVCand polyethylene) and fiberglass piping are usuallyselected for such systems; however, if solvents in thewaste stream contain organics capable of attackingcollection pipes, sumps or risers, an alternative to theuse of plastic or fiberglass piping might be concrete orcast iron. Any geotextile filter cloth or fabric used in theleachate collection system shall be evaluated for itsability to withstand attack from the hazardous waste andthe leachate generated from that waste.(2) The drainage layer, any geotextile filter clothor fabric, drain rock, pipe slotting, and waste fines mustbe evaluated to determine the ability of the system totransmit leachate without clogging. Although6-14TM 5-814-7the EPA guidance document recommends use of agranular layer above the drainage layer, if clean sand isused for the drainage layer, it will serve to precludeplugging and possibly eliminate the need for a filter clothor fabric.(3) The pipe used in leak detection and leachatecollection systems must be of sufficient strength andthickness to withstand the pressures exerted by theweight of the overlying waste, the cover materials, andany equipment to be used on the waste unit. Slotting willreduce the effective strength of pipe and its ability tocarry loads and resist pipe deflection under loading. Thecapacity of buried pipe to support vertical stresses maybe limited by buckling and by the circumferentialcompressive strength of the pipe. Information ondeflection, buckling capacity and compressive strengthmay be obtained from the pipe manufacturer.(a) Even when correctly designed to withstandwaste loading, piping can fail from equipment loadingduring construction or operation of the waste unit.Moving loads result in impact loading one and one-half totwo times greater than stationary loading. Therefore,equipment should, if possible, not cross leachatecollection drains installed in projecting installations or intrenches with shallow cover. When equipment must berouted across a drain, impact loading should beminimized by mounding material over the pipe to anadequate depth to prevent pipe failures.(b) Specific design procedures and examplesused to determine loads resulting from the waste filland/or construction equipment are provided in appendixV.2 of SW-870.6-5. Surface water run-on and run-off controlsystemsa. Regulatory requirements. Surface water runonand run-off control systems are required for landfills,waste piles and land treatment units and indirectly forsurface impoundments. Regulatory requirements forsurface water control at land disposal facilities aresummarized in table 6-5. While federal regulationsrequire control systems for 24-hour, 25-year storms,state regulations may require sized control for stormswith a return frequency up to 100 years. In such cases,the more stringent requirement should be considered insizing surface water run-on and run-off control facilities.The designer must also size collection and holdingfacilities, and develop specific management proceduresto enable all run off from active disposal areas to beretained for treatment prior to its evaporation ordischarge to natural drainage courses or back to anapproved hazardous waste facility.b. Types of control systems. Run-on and runoffcontrol systems at hazardous waste units utilize avariety of structures for control of surface water,including conveyance, barrier and control/retentionsystems.CANCELLED
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