AREA A/B ENGINEERING REPORT - Waste Management

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final closure, proper grading, seeding, and maintenance of cover system soils and vegetation help
prevent long-term erosion and siltation problems during the post-closure care (PCC) period.
4.3.2 Post-Closure Maintenance
Subtitle D regulations require monitoring of groundwater and vadose zone gas
migration, and management and maintenance of the leachate management
system and cover. Performance of these systems during PCC is verified
through environmental monitoring at key locations around the landfill, and
PCC maintenance requires that the monitoring system (i.e., methane migration
and groundwater monitoring well network) remains intact and accessible. Most
post-closure maintenance is spent on the cover system since this is the main component of the
landfill exposed to the elements after closure.
Cover system maintenance at a closed landfill with a Subtitle D (or approved alternative) cover
typically involves:
• Inspection and maintenance of the final cover to verify that it is stable against erosion,
instability, and washout;
• Inspection and repair of stormwater management system features (e.g., removal of
sediment from ditches and ponds, or re-grading drainage swales or cover slopes to
promote drainage);
• Mowing and fertilizing/replanting of vegetation on the surface;
• Tree removal (unless a tree cover is approved);
• Repair in the case of subsidence of the landfill cover; and
• Remediation of seeps, breakouts, or other conditions causing discharge of leachate to the
ground surface.
Erosion control is particularly important during PCC to prevent clogging of toe drains and
exposure of the final cover system internal drainage and/or barrier components to unanticipated
physical and climatic stresses. For many final cover systems, erosion control via the establishment
of plant species may be aided by placing a natural or geosynthetic erosion control (GEC) matting
layer on the surface before seeding. Long-term cover performance is not necessarily linked to a
high level of post-closure maintenance. New performance-based designs for sustainable, low
maintenance, natural analog cover systems are providing increased longevity and stability, with a
performance equivalent to prescriptive Subtitle D covers. Such natural analog covers were
discussed in Section 3.4 and will be re-examined in Section 6.2. For managed landfills without
Subtitle D equivalent liner systems, cover maintenance, along with natural geologic barriers and
environmental performance monitoring, provide overlapping levels of environmental protection.
Managed care of the cover enables it to perform as designed, controlling liquid infiltration and
stormwater runoff, and remaining sufficiently stable to maintain its containment function throughout
the PCC period and beyond.
MD10186.doc 67 29 March 2009