A Guide to the Revegetation and Environmental Restoration of Closed Landfills

Preface and Chapters 1-3

• Preface
• Chapter 1. Introduction
• Chapter 2. Regulatory Background
• Chapter 3. Elements of Restoration

Preface

This guide provides landfill managers, owners, operators, and local enforcement agencies with information on revegetation and environmental restoration in the closure of landfills. These techniques also should prove useful to conservationists in restoration or other habitat reclamation.

The guide is intended to serve as a bridging document between two State publications. These publications are Guide to Vegetative Covers for California Landfills, published by the California Integrated Waste Management Board (IWMB); and WUCOLS, Water Use Classification of Landscape Species, prepared by the California Department of Water Resources. These three documents should provide the project coordinator with the essentials for revegetation or environmental restoration. This guide also provides listings of other references and restoration resources in California.

The guide distinguishes between revegetation and environmental restoration as follows:

• Revegetation involves the placement of plants, horticultural or native, on a project site. Relatively few, if any, other environmental restoration techniques will be applied. The plants can be an arbitrary choice of the project coordinator, with no regard for native species, their distribution or plant community design. A landfill configured to engineering specifications and planted with non-native grasses in regulatory compliance illustrates simple revegetation. Consideration for county approval of species should be made.
• Environmental restoration will invariably involve revegetation. But, it also involves the extensive design and naturalization of project site contours, soil content and vegetative communities. The intent of environmental restoration is to create a seamless "repair" by emulating and supporting the native floral and faunal communities adjacent to and on the project site. The ultimate aim is for the project to be "assimilated" back into the surrounding environment.

Environmental restoration is characterized by these elements:

• A detailed reconstruction of the project site topography (elevations).
• Site geomorphology (surface features).
• Soil types conducive to the native plants of the project area.
• Surface hydrology (water features).
• Native plant species, their diversity, and distribution.

Table of Contents

Chapter 1: Introduction

The management and final closure of solid waste landfills in American society is a relatively new applied science. In 1795, Georgetown, Virginia, enacted the first ordinance for waste management in the nation. The ordinance prohibited the extended storage of refuse on private property or the dumping of it on a public thoroughfare. In 1873, Los Angeles (population 6,000) established a garbage and dead animal plot with burial of these wastes to be three feet below ground level.¹

In the 1800s, waste disposal sites were selected based on convenience, especially in the major metropolitan areas. Sites were not selected to avoid negative environmental impacts. In San Francisco (population 149,000), two good examples of unsound disposal practices could be found. One site was at a once existing bay at the foot of present day Market Street, and a second site was located at the north area Marina district. Ships were scuttled in place and wastes brought in to create the newly reclaimed waterfronts. This process continued until the desired fill area was constructed. Because no containment barriers for the waste products were installed, debris freely scattered into the bay. Planned compaction of the wastes was not practiced at these sites. This activity led to calamitous differential settling and damage to or destruction of streets and building foundations during the Great Earthquake and Fire of 1906. Evidence of this disposal activity is discovered with each new construction excavation that occurs in the Financial District of San Francisco.

Smaller rural communities inland generally located their waste disposal sites with an "out-of-sight, out-of-mind" philosophy. Often, these disposal sites would be located where wastes literally could be shoved over the edge of a canyon or ravine, lost from view and future concern. Eventually, this strategy would be outgrown as communities grew larger and the over-the-side technique to dispose of wastes became less manageable. Burning of wastes, especially at area fills, took on a more important role as a way to "reduce" the volume of waste remaining at a community disposal site.

As more municipalities applied this practice with its cumulative air impacts, and other generators of air pollutants became more prevalent, a new strategy in waste management had to be devised. Prompted by the development and implementation of the Clean Air Act of 1977, and the creation of local Air Pollution Control Districts, the practice of open burn dumps was brought to a close.

The Integrated Waste Management Act (1989) brought waste management in California to a higher technical level. The end of open burning, the closure of these sites, and the opening of new landfills created new demands on management policy. Managed and planned closure procedures had to be developed to assure consistent closure of landfills to protect the public health, safety, and the environment.

By the 1970s, the general public attained a heightened awareness of the environment, which led to a more critical perspective on the closure of disposal sites and their final appearance. The casual viewer sought a more harmonious result, visually and ecologically, from the closed landfill.

As a result, the concepts of revegetation and, finally, environmental restoration, including "bio-engineering," are becoming an accepted part of final closure. Even the use of vegetation as a moisture-regulating mechanism for the final cover is gaining some serious consideration.

Today's landfills are found in a spectrum of sizes (1 to 700 acres) as the old ones close and newer, larger ones open. They are often located in more environmentally critical areas, either in sensitive habitat or near urban residential housing. Each facility, when it closes, results in a long-term visual and environmental impact on the neighboring community or region.

By current regulation, a newly closed landfill is monitored for various conditions (leachates, landfill gas, slope stability, etc.) for a period of 30 years, possibly longer, following its final date of closure per Title 27, California Code of Regulations (27, CCR), Section (§) 21180. These sites will remain as permanent monuments to our waste management practices unless restoration is achieved.

Environmental restoration is used in the mitigation and restoration of lands damaged by open pit or strip mining operations and other development projects involving sensitive lands. These techniques are coming into their own in landfill closure practices. Research into revegetation with native plants, and the concepts and practices of environmental restoration, as practiced in these other venues, are becoming important in the closure of landfills.

When a landfill closes, the primary intent of its design is to contain the waste and control the by-products resulting from its containment. These can include landfill gas, leachates, and the wastes themselves. The design insures the integrity of the external cover from settling, wind and water erosion, slope failure, and seismic damage. The design protects the public from exposure to the confined wastes.

If a planned postclosure land use is implemented, the landfill site can be designed to accept the appropriate land use. If no planned postclosure land use is intended (non-irrigated open space) or the postclosure project entails a parkland, preserve, or golf course, the final role of the cover layers is to provide a veneer to prevent erosion, support a viable plant community, and the chosen postclosure use facility.

Landfills located in arid and desert regions would impose different demands on the cover. These landfill covers are expected to support more sparse vegetative communities or, as an alternative, to be covered with rock cladding. Cladding helps protect the landfill from slope failures, or erosion, and in turn, can provide a limited aesthetic visual buffer. Even desert environmental restoration practices are being utilized with encouraging results.

With special soil surface treatment, using imprinters and appropriate plant types, a revegetation program in an arid or desert environment can provide a secondary use for the public in the surrounding region. Such a program could provide a desert wildlife area, and educational park for local schools and other visitors.

This guide is intended to provide practical information and methods in the concepts of revegetation and environmental restoration as applied to solid waste landfills.

Chapter 2: Regulatory Background

To assure some degree of consistency in the development of final vegetative cover in landfill closure design, regulatory standards were developed by both federal and State agencies. These standards primarily apply to the thickness of the vegetative cover soil layer and its performance, and the vegetation planting and maintenance protocols. These regulations are concerned with the use of the vegetative layer as a protective element in the long-term integrity of the landfill cover rather than as part of a holistic, integrated, visual, and environmental reconstruction.

The use of vegetation as a soil and slope-stabilizing component for final cover can be a reasonably economical and durable slope protection method. Current research reveals that vegetation can serve as an effective soil layer binder and moisture transpiration control system. Vegetation can extract excess moisture from the cover layer, reducing the potential for saturation and possible slope failure, especially at the soils interface between the moisture barrier and the erosion or vegetative layer. Employing a planned plant community and a successional plant population introduction technique may ensure successful establishment of the higher plant types, creating a naturalized vegetation community.

Developing a more complex landscaped, or ecosystem-based, plant community that is integrated into the surrounding natural vegetation ecosystem will require more advanced planning, research, and effort on the part of the operator. Ultimately, the result can be economically advantageous and aesthetically rewarding through reduced maintenance costs, improved plant survival, and possible wildlife habitat enhancement.

There is no current regulatory requirement that states that native plants must be used in final vegetative cover, or that the landfill slope profiling and vegetative cover must reflect the natural conditions in which the landfill is located. But, through practical application of more natural slope design and vegetative cover in mine reclamation projects, the natural and native configurations of plant communities can be more economical in the long run. Soil conditions and moisture may not support the non-native plants that are introduced. Natural pests attack and destroy non-native plants lacking natural defenses against these pests, or the costs and efforts of maintaining the non-native vegetation, through irrigation and pest control, are greater than they would be in using the native counterparts.

This practice should be applicable to landfills. In addition, the costs of configuring side-slopes and decks to more natural profiles should not introduce significant costs, if these details are designed in the early development of the landfill closure.

As the public's environmental awareness matures, and urbanization expands around existing closed landfills, or existing urban landfills close, placing greater demands on final closure appearances, the role of environmental restoration as an integrated part of final cover and vegetation design can assume greater significance. Additionally, new and larger landfills are being proposed in remote regions of greater environmental sensitivity. These restored areas could recover lost habitat or, increase available rare or endangered species habitat. This effort would not only improve the chances of survival of native or endangered species, but it could also enhance the public image of the agencies or operators that adopt this type of restoration program at these landfills. A project at Coyote Canyon, Orange County, is applying such a program for the California Gnatcatcher, (Polioptilia californica).

The primary regulatory sources for State and federal standards for closures are Title 27, California Code of Regulations (27 CCR), and 40 Code of Federal Regulations (40 CFR), Part 258 (Subtitle D).

State

Title 27, CCR Requirements (formerly 14, CCR and 23, CCR)
Subchapter 5, Article 1, Section (§) 20950(e). For landfills and for waste piles and surface impoundments that are closed as landfills, all vegetation for the closed unit’s vegetative cover shall meet the requirements of Section 21090(a)(3)(A)1, in cases where the unit does not utilize the mechanically resistant erosion layer per § 21090(a)(3)(A)2.

Section 21090 (a)(3)(A)1. Closed landfills shall be provided with an uppermost cover layer consisting of either:

1. Erosion resistance via a vegetative layer. This layer consists of not less than one foot of soil which:
   
   a. Contains no waste (including leachate).
   b. Is placed on top of all portions of the low hydraulic conductivity layer described in § (a)(2).
   c. Is capable of sustaining native or other suitable plant growth.
   d. Is initially planted and is later replanted as needed to provide effective erosion resistance with native or other suitable vegetation having a rooting depth not exceeding the depth to the top of the low hydraulic conductivity layer described in § (a)(2). For any proposed vegetative cover, the discharger shall propose a species mix which harmonizes with the proposed postclosure land use and which requires little long term maintenance as feasible by virtue of its tolerance to the vegetative layer’s soil conditions.
   
2. Mechanically erosion-resistant layer. An erosion and ultra violet light-resistant layer which, by virtue of its composition and finished-and-maintained grade, resists foreseeable erosion effects by wind-scour, raindrop impact, and runoff (e.g., a one-foot-thick layer of cobbles, the interstices of which are filled with gravel).

California Coastal Commission
Should a closure project be located within the jurisdiction of the California Coastal Commission, the regulatory standards and requirements of that agency may have to be addressed (PRC 13053.5(a)).

Department of Fish and Game
Should a closure project be located within the jurisdiction of the California Department of Fish and Game, the regulatory standards and requirements of that agency may have to be addressed (PRC 13053.5(a)).

California Environmental Quality Act (CEQA)
All projects in California must be reviewed in accordance with the California Environmental Quality Act (CEQA) to determine whether the project may have a significant impact on the environment. If the project might have a potential significant impact, mitigation measures may have to be incorporated into the project to avoid the impact.

Final Cover Design––40 CFR § 258.60, Subpart F
6.2.1 (a)(3). Minimize erosion of the final cover by the use of an erosion layer that contains a minimum 6 inches (60 cm) of earthen material capable of sustaining native plant growth.

6.2.3. Design criteria for a final cover system should be selected to ... improve aesthetics.
There are alternatives to the Subtitle D prescriptive standard cover designs which regulatory agencies can consider and approve (40 CFR §258.60(b)). The alternatives include:

1. An infiltration layer that achieves an equivalent reduction in the infiltration as specified in paragraph (a)(2) above.
2. An erosion layer that provides equivalent protection from the wind and water erosion as specified in paragraph (a)(3) above.

These alternatives provide an additional design choice that can broaden the vegetative design options available to an operator closing a landfill.

U.S. Army Corps of Engineers
Because many existing landfills and sites for potential landfills are located near natural waterways or may be sites upon which are located sensitive wetlands or vernal pools, the Army Corps of Engineers may have jurisdictional involvement under section 404 of the Clean Water Act. This jurisdictional authority may require a closure project obtain a permit from the Corps, prior to initiating the project. Dispute over Corps permit jurisdiction is requiring more scrutiny of project content and project location.

Table of Contents

Chapter 3: Elements of Restoration

Definition of Vegetative Cover Layer

Although there is no specific definition identified in the CCR, for the purposes of State regulation, the vegetative cover layer can be defined on the basis of compliance with all of the requirements of 27, CCR.

Role or Purpose of the Vegetative Cover

When a landfill is closed, the final design of the structure must incorporate various elements to serve several functions. The cover layers form the containment and moisture barriers directly overlying the waste mass, providing the containment and barrier functions above the waste. This protects the contents from invasive moisture and protects the public from exposure. The final layer covering all these preceding elements is the erosion, or vegetative soil layer. This layer, with vegetation, helps to prevent erosion, supports the vegetation, and provides some additional moisture protection.

The operations and containment layers below the waste and the final cover foundation layer and moisture barrier layer above the waste are intended to serve as barriers to moisture and gas migration into or out of the landfill. The final vegetative layer’s intended purpose, in addition to preventing erosion and enhancing moisture protection, is to serve as a stable substrate for a surface-stabilizing plant community on the final cover. The minimum standard vegetative soil layer thickness in California’s Title 27 requirements is 12-inch minimum thickness. This layer can be thicker but it may not be any thinner than the minimum. This minimum standard supersedes the 6-inch federal standard for Subtitle D for landfills in California.

The vegetation that is planted on the final cover is intended to serve as a protective soil binding and stabilizing element. The vegetation can also serve as an attenuator; the canopy absorbing damaging rainfall velocity before it strikes the soil.

This function of the vegetation aids in reduced impact erosion on the soil layer and improved moisture capture. Vegetation also serves as a moisture control through evapotranspiration by removing excess moisture from the soil, an aesthetic mitigation and an ecological mitigation by providing a reconstructed vegetative habitat for local animal species as well as rare or endangered plant or animal species.

Table of Contents

The Degrees of Vegetative Restoration

When a landfill is finally closed and the operator is preparing the final vegetation layer and the vegetative cover, there are three options to consider: restoration, aesthetics, and function.

Environmental Restoration
Environmental restoration is recreating, as completely as is practicable, that portion of the ecosystem that was displaced or disturbed by the project. Restoration takes into consideration the reconstruction or close approximation of the soil types and profile or topography of the area that was modified. The reconstructed slopes and terrain will mimic, as closely as possible, the natural features of the surrounding land. If the landfill were placed in a canyon, the slopes would be designed to mimic a shallower canyon or broad slope; or a ridge, if fill material overfilled the original canyon terrain. Surface landfills in flatter terrain would be profiled to emulate hill slopes, if hills are nearby, or to emulate a hill though none are in the area. Vegetation in such a restoration project would ideally reflect the proportions of plant species distribution reflected in the surrounding plant communities, utilizing the same species of native plants in the revegetation phase.

This type of restoration would serve three important functions. It would "repair" the ecosystem by replacing the project with the original environmental composition displaced while the project was operating. It would provide a new natural environment to enhance the local biotic community, improving species diversity and expanding available habitat. Restoration could also provide mitigative capacity in certain circumstances for mitigation of endangered species by allowing custom fitting of special localized habitats for endangered species in an area into the surrounding natural community. By using native plant species, the restoration project serves in contributing to the local species gene pool by providing more indigenous individuals to reproduce with the established local resident species.

Aesthetic Mitigation—Providing Compatible Postclosure Use Options
If environmental restoration is not a viable option for the operator, or a proposed postclosure land use development is intended for the former project site, an aesthetically satisfying vegetation program can be implemented on the site that approximates the local vegetation community. Such a vegetation option would be available for recreational parks or golf courses, or business park campuses. In this application, horticultural or nursery plant types and aesthetically designed landscaping are planned, not necessarily to emulate the natural vegetation and local terrain. Native plants could also be utilized but with the landscaped accent required for the project plan. Generally, this type of project will serve two purposes:

• Space Use
  The postclosure project will provide a viable natural environment for the public’s enjoyment. It can provide an aesthetically pleasing landscape that will mediate visual impacts created by the closed landfill. The project can still satisfy native plant needs while exhibiting landscaped features.
  
• Mitigative Needs
  The project will provide an acceptable alternative that will satisfy the regulatory standards of 27, CCR and Subtitle D. It will also offset the past impacts of the previous landfill activities.

Regulatory Compliance—Satisfying Regulatory Standards
A vegetative program that is designed to satisfy the requirements of Title 27, CCR and Subtitle D will employ the simplest and most basic elements of final cover design, landfill slope profiling, and vegetation types. Slope profiles will assume the most basic engineered forms in compliance with the closure requirements. Overall cover structure surfaces will generally be planar and obviously man-made. The primary functions of the vegetative cover will be to provide slope stability and soil binding, provide moisture control, control surface runoff flows, enhance evapotranspiration, reduce moisture intrusion and leachate production, and reduce landfill gas production. Vegetation will assume the more direct functional roles while providing the basic coverage to satisfy the requirements of Title 27.

In this application, landfill control systems will be least visually hidden. Gas control systems, vents, well heads, collection pipes, surface moisture control systems, and maintenance/access roads will be most visible. A general grass vegetative cover will be in place. Still, native grasses can be employed in this situation.

The Goals of Vegetative Cover Programs

The goals of vegetative cover programs may be based upon or dictated by the financial resources and priorities established by each operator, while complying with the regulatory requirements of CCR Title 27 and 40 CFR, Subtitle D.

Restorative

The technically most complex project is the restorative vegetation plan. To properly implement restoration, the operator must construct (reconstruct) a final cover (erosion or vegetative layer) that provides soil conditions and topographic features closely duplicating the surrounding soil types and geography. These preparations are intended to increase the chances that the replacement native plant community that is reintroduced will survive. A restored vegetative plant assemblage must duplicate the native plant profile in terms of ratios of species occurrence (distribution), correct native species selected and distribution of these species across the project site to closely duplicate the plant distributions in the surrounding undamaged areas. Ideally, this restoration will create conditions that will provide a natural habitat to encourage re-population by native animal species. In theory when this project has matured, it should provide a seamless restoration with the surrounding land or create a natural native environment in mixed urban or suburban areas.

An alternative project may involve creation of special habitat for rare or endangered species that both mitigates the project and provides new habitat. Conditions may warrant preparation of the site with special vegetation types that are present in that area that are attractants of local rare or endangered species, especially insects, such as certain species of butterfly or beetle, small reptiles, or mammals.

• Characteristics of a Restored Site
  Restored sites use native vegetation indigenous to the immediate area, or, for rare and endangered species mitigation, rare plant species that would be found within the ecological region. They provide vegetation or unique habitat that is depended upon by specific species of animals or insects for food or reproductive needs or as a mitigative effort to increase populations of a rare or endangered plant.
  
  • They provide for a natural plant community profile, with representative species distributions and correct profile of understory plants, intermediate shrubs and overstory trees.
    
  • The reconstructed land surface closely mimics the surrounding natural land features. This is accomplished by using HDPE geogrid reinforcement, landform contour grading and importing large rocks or cobbles and placing them on-site, These practices can be effected if the surrounding terrain demonstrates these features and if they can be engineered into the final cover design without compromising final cover functions.
    
  • Restored sites use bioengineering techniques for erosion repair and slope stabilization efforts including straw logs, wattles, revetments, and other surface stabilizing structures that can employ living plant materials in the structures, aiding in slope profiling and stabilizing.
    
  • The primary projects employing habitat restoration or mitigation are wildlife preserves, natural parklands, wildlife management areas, rare or endangered species mitigation, or natural public or educational parklands.
    
  • Restored sites do not have planned postclosure land uses beyond the role of parkland or preserve.

In terms of the restorative role of a site, a vegetation plan designed around a recreational use would rank as a close second for environmental value. A choice of either native plants or compatible nursery varieties would still provide a significant environment with both ecological as well as aesthetic merit.

A proposed postclosure land use following an initial vegetation phase would influence plant selections more toward a vegetation selection that would be less expensive to plant and remove. This cover type would be less environmentally mitigative than the first two options of natural parklands or native-or-non-native landscaped recreation area.

A site that is strictly designed to comply with the regulatory requirements of 27, CCR and Subtitle D regulations would employ the simplest vegetation plan and would be the least costly to install and maintain, while facilitating a visually pleasing cover. A grassland type cover could still provide a satisfactory mitigative result; if the site uses California native grasses and is located within grassland or mixed open lands and forests (glade) or savannah.

Vegetative restoration should be compatibly designed to fit in with the surroundings. No radical selection of plants should be made that will make the site stand out. It would not be prudent to place a grove of tall Eucalyptus (non-natives) on an above ground landfill in an open grassland environment. It is unnatural, a non-native, and the unprotected stand of trees could be rendered vulnerable to blow-down from strong winds over time, damaging the final cover and creating added repair and cleanup costs. Again, considerations must be exercised to fit the planting appearance and the plant selections in with the surrounding environment.

These mitigative projects provide a vegetative cover that supports a plant community similar to surrounding native plant communities but which derives its plant makeup more from nursery plant species. The plant profile could employ trees, shrubs, and grasses assuming similar ecological roles as their native counterparts. The final result could range from natural appearing, to landscaped, both cases presenting a visually satisfying product. A compromise form would employ native plants, but with the landscaped appearance.

• Characteristics of an Aesthetic Restoration
  
  • The use of non-native plants compatible with the environmental conditions where they will be planted and/or use of native plants when desired. This cover could assume natural plant profiles (grasses, shrubs, and overstory trees) when appropriate.
    
  • Application of landscape architectural techniques to create natural- looking or purposely designed landscapes.
    
  • Aesthetically pleasing landscapes that serve man’s needs or requirements such as parks, golf courses, playing fields (baseball, soccer) or recreation areas, and/or minimized visual impacts to the surrounding community.
    
  • Little potential for planned postclosure land use beyond the initial planned use (although a secondary or tertiary postclosure land use may not be ruled out).

These landfill covers will have their primary function in ensuring their compliance with the regulatory requirements of 27, CCR and Subtitle D. This type of cover is the most commonly employed, using a standard hydroseed mix of annual and/or perennial grasses. Some smaller herbaceous plants such as legumes (vetch or lupine) may also be used. Natural invasion and succession by nearby plant species may play a role in the later years of postclosure maintenance. Aesthetic or environmental mitigations would be of a secondary importance in their design function.

• Characteristics of a Functional Site
  
  • The use of climatically compatible native or non-native plants in the vegetative cover. No significant effort is expected in plant community profiling. Possible use of grasses and planted or volunteer plants such as small shrubs and, eventually trees, if the cover can accommodate them.
    
  • Developing primarily engineered slopes and land features without attempts at duplicating or mimicking surrounding land profiles or aesthetic landscaping.
    
  • Function takes precedence over form. The function of the final cover design is to be in regulatory compliance. There would be minimal land forming beyond required, engineered standards. Functional requirements would include:

1. Slope stabilization.
2. Moisture control.
   
   a. Water penetration into cover.
   b. Down-slope water flow control, drainage systems, etc.
   c. Leachate control.
   
3. Reduced maintenance demand.
   
   a. Low irrigation requirements.
   b. High reseeding characteristics or return seed replenishment.
   c. Minimal maintenance or cleanup requirements.
   d. High potential for postclosure use; the landscape materials are "disposable" and can be easily removed should a future postclosure use such as office buildings or warehouses be placed on the site.
   e. Minimum vegetation diversity. Grasses and possibly larger herbaceous plants such as legumes.

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Last updated: April 18, 2008