UFC 3-280-02A Hazardous Waste Land Disposal/Land Treatment ...

Table 6-4. Requirements for Leachate Collection and Removal SystemsSection of 40 CFR 264 Describing Requirementssophisticated instrumentation is available for detectionsystems, direct collection in a porous medium, withremoval through slotted pipes, is a simple and reliablemethod. Design details for such a system are similar tothose for leachate collection and removal systems.c. Components of the leachate collectionsystem. Specific regulations concerning leachatesystems are summarized in table 6-4. EPA guidancedocuments recommend that the leachate collectionsystem consist of a drainage layer at least 1-foot-thickwith a hydraulic conductivity > 1 x 10-3 cm/sec, and aminimum slope of 2 percent. When installed over asecondary clay liner with hydraulic conductivity of 1 x 10-7 cm/sec, such a system provides the four-order-ofmagnitudedifference in permeability known tosignificantly increase drainage efficiency.(1) A drainage layer of clean sand, classified byUSCS as SP or SW (with less than 5 percent passing theNo. 100 sieve), and free of rock, fractured stone, debris,and cobbles, will also satisfy the EPA requirement for aminimum 6inch protective layer over synthetic liners. Asand layer or filter cloth should be provided over thedrainage layer if drainage rock is used to preventinfiltration of fines from the waste and subsequentclogging of the drainage layer. Sands which act as filtersmust meet filter graduation require-TM 5-814-7ments, such as those shown in chapter 5 of TM 5-820-2.(2) Nondegradable synthetic filter cloths andgeotextile fabrics have also been used to replacegranular materials in subdrain systems. However, thelong-term performance of such materials has not beenfirmly established; clogging and filter cake formation canreduce the perpendicular permeability of both geotextilesand filter cloths, and overburden pressures cansignificantly decrease in-plane permeability of geotextilefabrics.d. Leachate collection pipe. Leachate collectionpipe networks should consist of slotted or perforateddrain pipe bedded and backfilled with drain rock. Thenetwork should include collection pipes, installed aroundthe base of the fill and across the base. Layouts mustinclude base liner slopes >, 2 percent, pipe grades>0.005, and pipe spacing determined for the unit. Allpipes should be joined and, where appropriate, bonded.(1) Collection pipes must be adequately sizedand spaced to minimize the leachate head on the linersystem. Layouts which incorporate 4-inch-diameterpipes on 50to 200-foot centers are considered adequateby the EPA.(2) Procedures to evaluate and establish thespacing for collection drain pipes, based upon theanticipated maximum infiltration rate and the hydraulicK L M NDesign Requirements Surface Impoundments Waste Pile Land Treatment LandfillA leachate collection and removal system immediatelyabove the liner that is designed,con- structed, maintained, and operated tocollect and remove leachate from the unitThe Regional Administrator will specifydesign and operating conditions in the permitto ensure that the leachate depth over theliner does not exceed 30 cm (one foot) Theleachate collection and removal system mustbe constructed of materials that are:Chemically resistant to the waste NA 264.251(aX2) NA 264.301(aX2)managed in the unit and the leachateexpected to be generated; and Ofsufficient strength and thickness to preventcollapse under the pressuresexerted by overlying wastes, waste covermaterials, and by any equipment used atthe unit; and Designed and operated tofunction without clogging through thescheduled closure of the unitCANCELLEDWhile in operation, leachate collection NA 264.254(bX4) NA 264.303(bX4)systems should be inspected weekly andafter storms for the presence of leachate andproper functioning of the systemsAfter closure, continue to operate theno longer detected Adapted from 40 CFR 264 NA NA NA 264.310(bX3)6-12