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A Guide to the Revegetationand Environmental Restorationof Closed Landfills

Report

October 1999

Table of Contents

Preface

Chapter 1. Introduction

Chapter 2. Regulatory Background

• Regulatory Requirements for Vegetative Final Cover

Chapter 3. Elements of Restoration

• Definition of Vegetative Cover Layer• Role or Purpose of the Vegetative Cover• The Degrees of Vegetative Restoration• The Goals of Vegetative Cover Programs

Chapter 4. Types of Vegetative Communities

• The Vegetative Zones

Chapter 5. Precipitation and Moisture

Chapter 6. Aspects of California's Vegetation

• Plant Assemblage Profiles• Plant Communities• Compatible Plant Associations

Chapter 7. Landfill Vegetative Design

• Landfill Design Considerations

• Additional Uses for Vegetative Cover

Chapter 8. Considerations in Vegetation Selection

• Site-Specific Considerations• Planting Considerations• Vegetation Types and Considerations in Program

Planning

Chapter 9. Planting of Vegetation

• Seeding• Planting Small Seedlings, Cuttings or Saplings• Transplantation• Sources for Vegetation

Chapter 10. Six Concepts for a Successful Restoration

Chapter 11. Maintenance of Vegetation

• Irrigation• Water Supplies• Fertilizing and Plant Nutrition• Maintaining Plant Health

Chapter 12. Some Problematic Conditions

Irrigation Source Water ProblemsFalse Readings in Soil Water SamplesDrainage and Surface SettlingSoil Methane Gas ConcentrationsAdditional Considerations

Chapter 13. Conclusion

Appendix 1

Appendix 2

Resources

Bibliography

Acknowledgement

I thank my colleagues who volunteered their time and effort toreview this guide. I especially give thanks to those who encouragedme to press on, to make this resource available to them.— JacquesGraber, Author, Associate Engineering Geologist, Permitting andEnforcement Division, California Integrated Waste ManagementBoard.

LEA Central

Last updated: December 05, 2003

LEA Information Services http://www.ciwmb.ca.gov/LEACentral/Donnaye Palmer: [email protected] (916) 341-6321©1995, 2004 California Integrated Waste Management Board. All rights reserved.


A Guide to the Revegetation and Environmental Restoration of ClosedLandfills

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 localenforcement agencies with information on revegetation andenvironmental restoration in the closure of landfills. Thesetechniques also should prove useful to conservationists in restorationor other habitat reclamation.

The guide is intended to serve as a bridging document between twoState publications. These publications are Guide to VegetativeCovers for California Landfills, published by the California IntegratedWaste Management Board (IWMB); and WUCOLS, Water UseClassification of Landscape Species, prepared by the CaliforniaDepartment of Water Resources. These three documents shouldprovide the project coordinator with the essentials for revegetationor environmental restoration. This guide also provides listings ofother references and restoration resources in California.

The guide distinguishes between revegetation and environmentalrestoration as follows:

• Revegetation involves the placement of plants, horticultural ornative, on a project site. Relatively few, if any, otherenvironmental restoration techniques will be applied. The plantscan be an arbitrary choice of the project coordinator, with noregard for native species, their distribution or plant communitydesign. A landfill configured to engineering specifications and

planted with non-native grasses in regulatory complianceillustrates simple revegetation. Consideration for countyapproval of species should be made.

• Environmental restoration will invariably involverevegetation. But, it also involves the extensive design andnaturalization of project site contours, soil content andvegetative communities. The intent of environmental restorationis to create a seamless "repair" by emulating and supporting thenative floral and faunal communities adjacent to and on theproject site. The ultimate aim is for the project to be"assimilated" back into the surrounding environment.

Environmental restoration is characterized by these elements:

o A detailed reconstruction of the project site topography(elevations).

o Site geomorphology (surface features).o Soil types conducive to the native plants of the project area.o Surface hydrology (water features).o Native plant species, their diversity, and distribution.

Table of Contents

Chapter 1: Introduction

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

In the 1800s, waste disposal sites were selected based onconvenience, especially in the major metropolitan areas. Sites werenot selected to avoid negative environmental impacts. In SanFrancisco (population 149,000), two good examples of unsounddisposal practices could be found. One site was at a once existing

bay at the foot of present day Market Street, and a second site waslocated at the north area Marina district. Ships were scuttled in placeand 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 wereinstalled, debris freely scattered into the bay. Planned compaction ofthe wastes was not practiced at these sites. This activity led tocalamitous differential settling and damage to or destruction ofstreets and building foundations during the Great Earthquake andFire of 1906. Evidence of this disposal activity is discovered witheach new construction excavation that occurs in the Financial Districtof San Francisco.

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

As more municipalities applied this practice with its cumulative airimpacts, and other generators of air pollutants became moreprevalent, a new strategy in waste management had to be devised.Prompted by the development and implementation of the Clean AirAct 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 wastemanagement in California to a higher technical level. The end ofopen burning, the closure of these sites, and the opening of newlandfills created new demands on management policy. Managed andplanned closure procedures hap! to be developed to assure consistentclosure of landfills to protect the public health, safety, and theenvironment.

By the 1970s, the general public attained a heightened awareness of

the environment, which led to a more critical perspective on theclosure of disposal sites and their final appearance. The casualviewer sought a more harmonious result, visually and ecologically,from the closed landfill.

As a result, the concepts of revegetation and, finally, environmentalrestoration, including "bio-engineering," are becoming an acceptedpart of final closure. Even the use of vegetation as a moisture-regulating mechanism for the final cover is gaining some seriousconsideration.

Today's landfills are found in a spectrum of sizes (1 to 700 acres) asthe old ones close and newer, larger ones open. They are oftenlocated in more environmentally critical areas, either in sensitivehabitat or near urban residential housing. Each facility, when itcloses, results in a long-term visual and environmental impact onthe neighboring community or region.

By current regulation, a newly closed landfill is monitored for variousconditions (leachates, landfill gas, slope stability, etc.) for a period of30 years, possibly longer, following its final date of closure per Title27, California Code of Regulations (27, CCR), Section (§) 21180.These sites will remain as permanent monuments to our wastemanagement practices unless restoration is achieved.

Environmental restoration is used in the mitigation and restoration oflands damaged by open pit or strip mining operations and otherdevelopment projects involving sensitive lands. These techniques arecoming into their own in landfill closure practices. Research intorevegetation with native plants, and the concepts and practices ofenvironmental restoration, as practiced in these other venues, arebecoming important in the closure of landfills.

When a landfill closes, the primary intent of its design is to containthe waste and control the by-products resulting from itscontainment. These can include landfill gas, leachates, and thewastes themselves. The design insures the integrity of the externalcover from settling, wind and water erosion, slope failure, andseismic damage. The design protects the public from exposure to theconfined wastes.

If a planned postclosure land use is implemented, the landfill sitecan be designed to accept the appropriate land use. If no plannedpostclosure land use is intended (non-irrigated open space) or thepostclosure project entails a parkland, preserve, or golf course, thefinal role of the cover layers is to provide a veneer to preventerosion, support a viable plant community, and the chosenpostclosure use facility.

Landfills located in arid and desert regions would impose differentdemands on the cover. These landfill covers are expected to supportmore sparse vegetative communities or, as an alternative, to becovered with rock cladding. Cladding helps protect the landfill fromslope failures, or erosion, and in turn, can provide a limited aestheticvisual buffer. Even desert environmental restoration practices arebeing utilized with encouraging results.

With special soil surface treatment, using imprinters and appropriateplant types, a revegetation program in an arid or desert environmentcan provide a secondary use for the public in the surrounding region.Such a program could provide a desert wildlife area, and educationalpark for local schools and other visitors.

This guide is intended to provide practical information and methodsin the concepts of revegetation and environmental restoration asapplied to solid waste landfills.

Table of Contents

Chapter 2: Regulatory Background

To assure some degree of consistency in the development of finalvegetative cover in landfill closure design, regulatory standards weredeveloped by both federal and State agencies. These standardsprimarily apply to the thickness of the vegetative cover soil layer andits performance, and the vegetation planting and maintenanceprotocols. These regulations are concerned with the use of thevegetative layer as a protective element in the long-term integrity ofthe 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 forfinal cover can be a reasonably economical and durable slopeprotection method. Current research reveals that vegetation canserve as an effective soil layer binder and moisture transpirationcontrol system. Vegetation can extract excess moisture from thecover layer, reducing the potential for saturation and possible slopefailure, especially at the soils interface between the moisture barrierand the erosion or vegetative layer. Employing a planned plantcommunity and a successional plant population introductiontechnique may ensure successful establishment of the higher planttypes, creating a naturalized vegetation community.

Developing a more complex landscaped, or ecosystem-based, plantcommunity that is integrated into the surrounding natural vegetationecosystem will require more advanced planning, research, and efforton the part of the operator. Ultimately, the result can beeconomically advantageous and aesthetically rewarding throughreduced maintenance costs, improved plant survival, and possiblewildlife habitat enhancement.

There is no current regulatory requirement that states that nativeplants must be used in final vegetative cover, or that the landfillslope profiling and vegetative cover must reflect the naturalconditions in which the landfill is located. But, through practicalapplication of more natural slope design and vegetative cover inmine reclamation projects, the natural and native configurations ofplant communities can be more economical in the long run. Soilconditions and moisture may not support the non-native plants thatare introduced. Natural pests attack and destroy non-native plantslacking natural defenses against these pests, or the costs and effortsof maintaining the non-native vegetation, through irrigation and pestcontrol, are greater than they would be in using the nativecounterparts.

This practice should be applicable to landfills. In addition, the costsof configuring side-slopes and decks to more natural profiles shouldnot introduce significant costs, if these details are designed in theearly development of the landfill closure.

As the public's environmental awareness matures, and urbanizationexpands around existing closed landfills, or existing urban landfillsclose, placing greater demands on final closure appearances, therole of environmental restoration as an integrated part of final coverand vegetation design can assume greater significance. Additionally,new and larger landfills are being proposed in remote regions ofgreater environmental sensitivity. These restored areas couldrecover lost habitat or, increase available rare or endangered specieshabitat. This effort would not only improve the chances of survival ofnative or endangered species, but it could also enhance the publicimage of the agencies or operators that adopt this type ofrestoration program at these landfills. A project at Coyote Canyon,Orange County, is applying such a program for the CaliforniaGnatcatcher, (Polioptilia californica].

Table of Contents

Regulatory Requirements for Vegetative Final Cover

The primary regulatory sources for State and federal standards forclosures are Title 27, California Code of Regulations (27 CCR), and40 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 forwaste piles and surface impoundments that are closed as landfills, allvegetation for the closed unit's vegetative cover shall meet therequirements of Section 21090(a)(3)(A)l, in cases where the unitdoes not utilize the mechanically resistant erosion layer per § 21090(a)(3)(A)2.

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

1. Erosion resistance via a vegetative layer. This layer consists ofnot less than one foot of soil which:

a. Contains no waste (including leachate).

b. Is placed on top of all portions of the low hydraulicconductivity 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 provideeffective erosion resistance with native or other suitablevegetation having a rooting depth not exceeding the depth tothe top of the low hydraulic conductivity layer described in § (a)(2). For any proposed vegetative cover, the discharger shallpropose a species mix which harmonizes with the proposedpostclosure land use and which requires little long termmaintenance as feasible by virtue of its tolerance to thevegetative layer's soil conditions.

2. Mechanically erosion-resistant layer. An erosion and ultra violetlight-resistant layer which, by virtue of its composition andfinished-and-maintained grade, resists foreseeable erosioneffects by wind-scour, raindrop impact, and runoff (e.g., a one-foot-thick layer of cobbles, the interstices of which are filled withgravel).

California Coastal CommissionShould a closure project be located within the jurisdiction of theCalifornia Coastal Commission, the regulatory standards andrequirements of that agency may have to be addressed (PRC13053.5(a)).

Department of Fish and GameShould a closure project be located within the jurisdiction of theCalifornia Department of Fish and Game, the regulatory standardsand requirements of that agency may have to be addressed (PRC13053.5(a)).

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

Federal

Final Cover Design—40 CFR § 258.60, Subpart F6.2.1 (a)(3). Minimize erosion of the final cover by the use of anerosion layer that contains a minimum 6 inches (60 cm) of earthenmaterial capable of sustaining native plant growth.

6.2.3. Design criteria for a finaLcover system should be selectedto ... improve aesthetics.There are alternatives to the Subtitle D prescriptive standard coverdesigns 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 theinfiltration as specified in paragraph (a)(2) above.

2. An erosion layer that provides equivalent protection from thewind and water erosion as.specified in paragraph (a)(3) above.

These alternatives provide an additional design choice that canbroaden the vegetative design options available to an operatorclosing a landfill.

U.S. Army Corps of EngineersBecause many existing landfills and sites for potential landfills arelocated near natural waterways or may be sites upon which arelocated sensitive wetlands or vernal pools, the Army Corps ofEngineers may have jurisdictional involvement under section 404 ofthe Clean Water Act. This jurisdictional authority may require aclosure project obtain a permit from the Corps, prior to initiating theproject. Dispute over Corps permit jurisdiction is requiring morescrutiny 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 thepurposes of State regulation, the vegetative cover layer can be

defined on the basis of compliance with all of the requirements of27, CCR.

Role or Purpose of the Vegetative Cover

When a landfill is closed, the final design of the structure mustincorporate various elements to serve several functions. The coverlayers form the containment and moisture barriers directly overlyingthe waste mass, providing the containment and barrier functionsabove the waste. This protects the contents from invasive moistureand protects the public from exposure. The final layer covering allthese preceding elements is the erosion, or vegetative soil layer.This layer, with vegetation, helps to prevent erosion, supports thevegetation, and provides some additional moisture protection.

The operations and containment layers below the waste and the finalcover foundation layer and moisture barrier layer above the wasteare intended to serve as barriers to moisture and gas migration intoor out of the landfill. The final vegetative layer's intended purpose, inaddition to preventing erosion and enhancing moisture protection, isto serve as a stable substrate for a surface-stabilizing plantcommunity on the final cover. The minimum standard vegetative soillayer thickness in California's Title 27 requirements is 12-inchminimum thickness. This layer can be thicker but it may not be anythinner than the minimum. This minimum standard supersedes the6-inch federal standard for Subtitle D for landfills in California.

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

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

Table of Contents

The Degrees of Vegetative Restoration

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

Environmental RestorationEnvironmental restoration is recreating, as completely as ispracticable, that portion of the ecosystem that was displaced ordisturbed by the project. Restoration takes into consideration thereconstruction or close approximation of the soil types and profile ortopography of the area that was modified. The reconstructed slopesand terrain will mimic, as closely as possible, the natural features ofthe surrounding land. If the landfill were placed in a canyon, theslopes would be designed to mimic a shallower canyon or broadslope; or a ridge, if fill material overfilled the original canyon terrain.Surface landfills in flatter terrain would be profiled to emulate hillslopes, if hills are nearby, or to emulate a hill though none are in thearea. Vegetation in such a restoration project would ideally reflectthe proportions of plant species distribution reflected in thesurrounding plant communities, utilizing the same species of nativeplants in the revegetation phase.

This type of restoration would serve three important functions. Itwould "repair" the ecosystem by replacing the project with theoriginal environmental composition displaced while the project wasoperating. It would provide a new natural environment to enhancethe local biotic community, improving species diversity andexpanding available habitat. Restoration could also providemitigative capacity in certain circumstances for mitigation ofendangered species by allowing custom fitting of special localizedhabitats for endangered species in an area into the surroundingnatural community. By using native plant species, the restorationproject serves in contributing to the local species gene pool byproviding more indigenous individuals to reproduce with theestablished local resident species.

Aesthetic Mitigation—Providing Compatible Postclosure UseOptionsIf environmental restoration is not a viable option for the operator,or a proposed postclosure land use development is intended for theformer project site, an aesthetically satisfying vegetation programcan be implemented on the site that approximates the localvegetation community. Such a vegetation option would be availablefor recreational parks or golf courses, or business park campuses. Inthis application, horticultural or nursery plant types and aestheticallydesigned landscaping are planned, not necessarily to emulate thenatural vegetation and local terrain. Native plants could also beutilized but with the landscaped accent required for the project plan.Generally, this type of project will serve two purposes:

• Space UseThe postclosure project will provide a viable natural environmentfor the public's enjoyment. It can provide an aestheticallypleasing landscape that will mediate visual impacts created bythe closed landfill. The project can still satisfy native plant needswhile exhibiting landscaped features.

• Mitigative NeedsThe project will provide an acceptable alternative that will satisfythe regulatory standards of 27, CCR and Subtitle D. It will alsooffset the past impacts of the previous landfill activities.

Regulatory Compliance—Satisfying Regulatory StandardsA vegetative program that is designed to satisfy the requirements ofTitle 27, CCR and Subtitle D will employ the simplest and most basicelements of final cover design, landfill slope profiling, and vegetationtypes. Slope profiles will assume the most basic engineered forms incompliance with the closure requirements. Overall cover structuresurfaces will generally be planar and obviously man-made. Theprimary functions of the vegetative cover will be to provide slopestability and soil binding, provide moisture control, control surfacerunoff flows, enhance evapotranspiration, reduce moisture intrusionand leachate production, and reduce landfill gas production.Vegetation will assume the more direct functional roles whileproviding the basic coverage to satisfy the requirements of Title 27.

In this application, landfill control systems will be least visuallyhidden. Gas control systems, vents, well heads, collection pipes,surface moisture control systems, and maintenance/access roads willbe 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 ordictated by the financial resources and priorities established by eachoperator, while complying with the regulatory requirements of CCRTitle 27 and 40 CFR, Subtitle D.

Restorative

The technically most complex project is the restorative vegetationplan. To properly implement restoration, the operator must construct(reconstruct) a final cover (erosion or vegetative layer) that providessoil conditions and topographic features closely duplicating thesurrounding soil types and geography. These preparations areintended to increase the chances that the replacement native plantcommunity that is reintroduced will survive. A restored vegetativeplant assemblage must duplicate the native plant profile in terms ofratios of species occurrence (distribution), correct native speciesselected and distribution of these species across the project site toclosely duplicate the plant distributions in the surroundingundamaged areas. Ideally, this restoration will create conditions thatwill provide a natural habitat to encourage re-population by nativeanimal species. In theory when this project has matured, it shouldprovide a seamless restoration with the surrounding land or create anatural native environment in mixed urban or suburban areas.

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

• Characteristics of a Restored SiteRestored sites use native vegetation indigenous to theimmediate area, or, for rare and endangered species mitigation,rare plant species that would be found within the ecologicalregion. They provide vegetation or unique habitat that isdepended upon by specific species of animals or insects for foodor reproductive needs or as a mitigative effort to increasepopulations of a rare or endangered plant.

oThey provide for a natural plant community profile, withrepresentative species distributions and correct profile ofunderstory plants, intermediate shrubs and overstory trees.

oThe reconstructed land surface closely mimics thesurrounding natural land features. This is accomplished byusing HDPE geogrid reinforcement, landform contour gradingand importing large rocks or cobbles and placing them on-site, These practices can be effected if the surroundingterrain demonstrates these features and if they can beengineered into the final cover design without compromisingfinal cover functions.

o Restored sites use bioengineering techniques for erosionrepair and slope stabilization efforts including straw logs,wattles, revetments, and other surface stabilizing structuresthat can employ living plant materials in the structures,aiding in slope profiling and stabilizing.

oThe primary projects employing habitat restoration ormitigation are wildlife preserves, natural parklands, wildlifemanagement areas, rare or endangered species mitigation,or natural public or educational parklands.

o Restored sites do not have planned postclosure land usesbeyond the role of parkland or preserve.

In terms of the restorative role of a site, a vegetation plandesigned around a recreational use would rank as a closesecond for environmental value. A choice of either nativeplants or compatible nursery varieties would still provide asignificant environment with both ecological as well asaesthetic merit.

A proposed postclosure land use following an initial

vegetation phase would influence plant selections moretoward a vegetation selection that would be less expensiveto plant and remove. This cover type would be lessenvironmentally mitigative than the first two options ofnatural parklands or native-or-non-native landscapedrecreation area.

A site that is strictly designed to comply with the regulatoryrequirements of 27, CCR and Subtitle D regulations wouldemploy the simplest vegetation plan and would be the leastcostly to install and maintain, while facilitating a visuallypleasing cover. A grassland type cover could still provide asatisfactory mitigative result; if the site uses Californianative grasses and is located within grassland or mixed openlands and forests (glade) or savannah.

Vegetative restoration should be compatibly designed to fitin with the surroundings. No radical selection of plantsshould be made that will make the site stand out. It wouldnot be prudent to place a grove of tall Eucalyptus (non-natives) on an above ground landfill in an open grasslandenvironment. It is unnatural, a non-native, and theunprotected stand of trees could be rendered vulnerable toblow-down from strong winds over time, damaging the finalcover and creating added repair and cleanup costs. Again,considerations must be exercised to fit the plantingappearance and the plant selections in with thesurrounding environment.

Aesthetic Restorations

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

• Characteristics of an Aesthetic RestorationoThe use of non-native plants compatible with the

environmental conditions where they will be planted and/oruse of native plants when desired. This cover could assumenatural plant profiles (grasses, shrubs, and overstory trees)when appropriate.

o Application of landscape architectural techniques to createnatural- looking or purposely designed landscapes.

o Aesthetically pleasing landscapes that serve man's needs orrequirements such as parks, golf courses, playing fields(baseball, soccer) or recreation areas, and/or minimizedvisual impacts to the surrounding community.

o Little potential for planned postclosure land use beyond theinitial planned use (although a secondary or tertiarypostclosure land use may not be ruled out).

Functional Sites

These landfill covers will have their primary function in ensuring theircompliance with the regulatory requirements of 27, CCR and SubtitleD. This type of cover is the most commonly employed, using astandard hydroseed mix of annual and/or perennial grasses. Somesmaller herbaceous plants such as legumes (vetch or lupine) mayalso be used. Natural invasion and succession by nearby plantspecies may play a role in the later years of postclosuremaintenance. Aesthetic or environmental mitigations would be of asecondary importance in their design function.

• Characteristics of a Functional SiteoThe use of climatically compatible native or non-native

plants in the vegetative cover. No significant effort isexpected in plant community profiling. Possible use ofgrasses and planted or volunteer plants such as small shrubsand, eventually trees, if the cover can accommodate them.

o Developing primarily engineered slopes and land featureswithout attempts at duplicating or mimicking surroundingland profiles or aesthetic landscaping.

o Function takes precedence over form. The function of thefinal cover design is to be in regulatory compliance. There

would be minimal land forming beyond required, engineeredstandards. Functional requirements would include:

1. Slope stabilization.2. Moisture control.

a. Water penetration into cover.b. Down-slope water flow control, drainagesystems, etc.c. Leachate control.

3. Reduced maintenance demand.

a. Low irrigation requirements.b. High reseeding characteristics or return seedreplenishment.c. Minimal maintenance or cleanuprequirements.d. High potential for postclosure use; thelandscape materials are "disposable" and can beeasily removed should a future postclosure usesuch as office buildings or warehouses be placedon the site.e. Minimum vegetation diversity. Grasses andpossibly larger herbaceous plants such aslegumes.

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LEA Information Services httpV/www.ciwrnb.jca^gov/LEACentral/Donnaye Palmer: [email protected] (916) 341-6321©1995, 2004 California Integrated Waste Management Board. All rights reserved.



Chapters 4-5• Chapter 4. Types of Vegetative Communities• Chapter 5. Precipitation and Moisture

Chapter 4: Types of Vegetative Communities

A "community" is defined as "an aggregation of living organismshaving mutual relationships among themselves and to theirenvironment."2 A plant community includes each element of thevegetation characterized by a dominant species. For restoration of aplant community to be successfully achieved for any project, anunderstanding of the basics of plant communities must be explored.For a project proponent to install a vegetation community that willhave the highest chance of succeeding, the planner must be awareof the types of plant communities that exist throughout Californiaand the one at his project site. The operator must consider climateconditions, soil types, and compositions in the project area anddemonstrate an awareness of the surface topography of the areasurrounding the project site where restoration will occur.

Even in using nursery stock instead of California native plant stocksin a revegetation project, soil types, climate, and equivalency inplant types are important to successful survival of the final planting.

Throughout the State of California, plant communities havedeveloped and evolved into distinct assemblages of plants anddistribution patterns. Coastal plant communities differ greatly fromdesert plant communities. Alpine conifer forests will differ fromvalley chaparral. Species of plants will differ from one northern oakwoodland community in northern California versus a southern oakwoodland community in southern California, although they may looksuperficially alike. Even the western coastal conifer makeup isdifferent from the conifer forests in the western Sierras. An

awareness of these subtle differences may help make the differencein a restoration or revegetation project being a success or a potentialfailure.

Table of Contents

The Vegetative Zones

California's vegetative communities fall within four major vegetativezones.3 (Micro-environments are found within each major zone,containing their own distinctive plant communities.) Following arethe four major zones.

Coastal Zone

This vegetation zone embraces the majority of northern Californiafrom Modoc County to the northeast, across the northern counties toinclude the mountainous areas of Siskiyou, Shasta and Trinitycounties. This zone includes the coastal counties from Del Nortesouth to San Diego County, bounded by the coastal ranges on itseastern margin.

Plants in this zone are varieties that are highly moisture dependent,preferring a more temperate average climate ranging from the 50s(°F) to the 90s rarely. Rainfall is abundant to moderately availablewhile frequent occurrences of fog from the marine air layer of thePacific Ocean increase atmospheric moisture levels. The conifersdominate the northern forests, including the Redwoods (Sequoiasempervirons) and Douglas Fir (Pseudotsuga menziesii}. Thesespecies dominate as the overstory species. Hardwoods (WesternHemlock, oak, and others) can be commingled in some areas,occupying the intermediate layer of vegetation.

Smaller shrubs fall in the understory at the closest to ground level.More southerly forests will be populated with coastal species ofhardwood (deciduous) forests. A pocket of alpine desert plantcommunities can be found in northern and eastern Siskiyou Countyand Modoc County.

Interior Zone

The Interior Zone includes the entire Central Valley and a narrowband that follows along the eastern slopes of the Coast Ranges,including the west halves of Los Angeles, San Bernardino, Riversideand San Diego counties. Climatic conditions in this zone are drierthan the Coastal Zone, being partially influenced by the initial rainshadow effect of the Coast Ranges. Temperatures can vary from thelow 30s (°F) into the 100-plus degree range. Atmospheric moistureis generally dry during the summer and fall months. A short periodof heavy rains occurs between September and March.

This region is dominated by grasslands and Oak Chaparralcommunities, often with higher concentrations of vegetation alongriver and creek channels (riparian environments). Many of theseriparian environments are dominated by cottonwoods (Populustrichocarpa or tremuloides) as well as willow (Salix subspecies) inthe overstory layer. Digger Pine (Pinus sabiniana) can be found inthe drier hilly areas of this zone. Embracing the San Gabriel and SanBernardino Mountains, the Interior Zone holds distinctive mountainplant communities in these ranges.

Mountain Zone

This zone includes the region running along the western slopes ofthe Sierra Nevada, from southern Modoc County, across all westernSierra counties southerly to Tehama County and including north KernCounty. Dry temperate to warm summers and cold, snowboundwinters at the higher elevations generally dominate climaticconditions in the Mountain Zone.

The western Sierra receives high volumes of rain, and thunderstormsare frequent. Much of the eastward migration of storm moistureconveyed to this point is precipitated out before crossing to the eastdesert regions. Vegetation in this area is dominated again byconifers such as Ponderosa Pine (Pinus ponderosa) and Fir (Abiesgrandis or A. concolor} in the overstory. These species of conifersare more tolerant of dryer, hotter climates than the conifers of thecoastal varieties. Oak savannah or chaparral may dominate thesouthern portion of this zone. Arid conditions may dominate in theextreme southern zone. Hardwoods such as Valley Oaks (Quercus

lobata} are found more at the lower elevations and as intermediatespecies at middle montane elevations.

Desert Zone

The Desert Zone takes in northern Modoc County, the areas north ofLake Tahoe, and all of the easternmost counties to the southernCalifornia border. This zone includes the area bordered by the eastslopes of the Sierra Nevada. The climate in this zone ranges fromcool winter days to extremely hot summer daytime temperatures.The climate is generally arid with relatively less snowfall than theMountain Region. Soil conditions are dry, sandy or stony, oftenforming a "desert pavement," creating harsh conditions for naturalplant growth. Precipitation is limited because of the rain shadow ofthe Sierra. What rain there is may come primarily as cloudburstscreating brief flash flood events. Vegetation in this region consists ofxerophytes—plants highly tolerant of harsh desert conditions.Junipers (Juniperis] including J. californica and J. communis in thenorth, and J. ostosperma in the Mojave region, succulents, creosotesand other shrubs, and assorted species of yuccas or other desertvegetation will dominate this plant community.

The desert environment is particularly sensitive to impacts fromman. Desert regions, both low-altitude and alpine, possess verysubtle features difficult to replicate. These regions take a long timeto "heal" after excavations have been performed, and the slow ratesof growth and relative sparseness of native plant species in thedesert region will reveal scarring longer than other impacted areas.Barren rocky regions may make restoration nearly impossible toachieve as desert pavement and the phenomenon of "desertvarnish," a dark glaze over the rocky surfaces, are difficult toreconstruct, requiring natural weathering to complete the process.Alpine desert areas as in central Siskiyou county display subtle signsof frost polygon-like forms in the soil, presenting cell-likearrangements of surface stones, surrounding low hummocks overlarge tracts of open grassland.

"Desert" refers to a natural environmental community created inevolutionary response to hot arid climates. Desertification is an

environmental condition, usually resulting from the adverse activitiesof man. These activities, such as mismanagement of irrigation water,salt leaching, and concentration of other minerals in the soil andwind erosion of soils from tilling operations result from agriculturalactivities in fertile or marginally fertile lands of the desert regions. Inthe arid soils, chemicals accumulate and the soil surface forms a thincrust, relatively impermeable to the sparse available rains of thoseregions. The result is conditions that are hostile to plants andanimals and loss of natural soil nutrients that inhibits revegetationefforts.

Figure 1Map of California Showing Vegetative ZonesRelative to Counties(21 KB)

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Chapter 5: Precipitation andMoistureThe types of plants to be selected and the irrigation plan intendedfor a specific landfill site will depend upon the average naturalprecipitation in a particular area. The project planner must take thisvariation into consideration. The precipitation pattern of California isatypical of most precipitation and climate distributions worldwide.

Most climate patterns follow defined responses to geographicfeatures, resulting in gradated changes across a climate regime. Thisusually results in wetter coastal regions gradating to drier or aridenvironments inland. In California, the association between weatherand precipitation, the widely varied terrain and regionaltemperatures creates a far more intricate melange of environmentalzones. Precipitation may vary widely in two different areas eventhough they may both be within the same vegetation zone andgeographic regime.

California's terrain is divided lengthwise by two major mountainchains running the length of the state. Two regional mountainsystems are located in the north central state and a long, transverserange in southern California. The Central Valley occupies the mid-portion of the state, while low desert and high desert plateaus andmountain complexes occupy the northeast and easternmost marginsof California. The state's length results in a broad temperature rangefrom the north latitudes to the south. These wide-rangingenvironmental influences result in wide variation in temperaturesand precipitation, all within small distances.

As an example, in the coastal vegetation zone, precipitation variesfrom 10 inches average annually, southeast of Monterey, to 100inches or more north of Eureka; a 90-inch difference. Temperaturescan be very cold on the north coast, yet warm in Monterey.Precipitation in the Central Zone varies between 10 and 70 inches.The eastern flank of the Sierra and the south desert region (DesertZone) range from 2 to 20 inches average annual precipitation.

A balance must be developed between the natural precipitation andaverage temperatures, and the planned irrigation volumes for landfillrevegetation at a specific project site. (See Figure 2).

**•*'

-~b Figure 2Map of California Showing Average AnnualPrecipitation(63 KB)

— ~+f~fJl^Kr

.•4--.,(l*MWl Figure 3aMap of California Showing Locations of ActiveLandfills(14 KB)

Distribution of California's LandfillsCalifornians live throughout the state, in the most remote areas ofthe mountains, to the farthest reaches of the desert. Thisdistribution places these sources of waste within virtually everyclimatic, temperature and precipitation zone in the state. Figure 3a

shows the locations of the State's 186 active landfills. This widedispersal of landfills demonstrates the diversity of wastemanagement requirements and postclosure maintenance and landuse demands placed upon operators and postclosure re-vegetationprograms, both active and proposed.

~Y. Figure 3bMap of California Showing Locations of Activeand Inactive Landfills(15 KB)

Figure 3b shows 262 landfills, active and inactive, within California.The majority of these landfills have not employed an environmentalrestoration program. Most employ programs compliant withregulations, employing the basic techniques of vegetative cover andstandard engineering practice. Many employ aesthetic programs,incorporating golf courses or other recreational facilities in thepostclosure use plan.

Table of Contents | LEA Central


LEA Information Services http://www.ciwmb.ca.gov/LEACentral/Donnaye Palmer: [email protected] (916) 341-6321

2004 California Integrated Waste Management Board. All rights reserved.



Chapter 6: Aspects of California'sVegetationPlant Assemblage Profiles

Just as plants develop associations based on climate, moisture, andsoil type, the plant community can establish itself into a simple tocomplex interrelationship as a layered or stratified structure. As thenatural succession of a plant community develops through time, thelarger vegetation supersedes the previous pioneer plants. Pioneerweeds and grasses begin the succession, preparing the soil for thesucceeding plants. The pioneer weeds and grasses are eventuallyshaded out by larger shrubs. These shrubs are displaced ordominated by the larger trees. This system of layering providesenvironmental levels for wildlife and plants alike(Figure 4).

The main plant layers include the understory, intermediate, andoverstory layers.

Understory

This includes the smallest vegetation such as mosses, ferns,grasses, small wildflowers, and low ground coveringvarieties of herbaceous or woody plants.

Intermediate

This layer will include smaller and larger shrubs and smallerspecies of trees or young saplings of larger overstory treespecies. These plants may be adapted to softer light andcooler temperatures created by the shading effect of theoverstory canopy. Woody perennial plants dominate theintermediate story.

Overstory

This vegetative layer consists of the larger species of treesin the natural assemblage. This layer can create a canopythat influences the overall light availability and averagetemperatures at the lower levels. These trees can besparsely distributed or closely growing together to create atight canopy. Destruction of the canopy trees can adverselyaffect the understory environment, or provide a point ofopportunity for saplings to fill in. Not providing these trees ina poorly planned restoration project may jeopardize thesuccess of understory plant species growth and the project.

A landfill revegetation or restoration project would shorten some ofthis successional process, compressing the sequence into roughlyone step, with grasses, shrubs, and trees planted at the same time.Invasive plants, including pest weeds, would impose on this plan if amaintenance program to remove these invaders were not exercised.

Figure 4Plant Assemblage ProfilesJacques Graber 1999(81 KB)

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Plant Communities

Within each of the four vegetation zones, plants have establishedthemselves into assemblages or communities. Each community,when viewed as a whole, is an integrated system adapted to thatparticular environment. Similar plant communities may be found inthe Coastal and the Mountain Zones, the Interior Zone as well as theother zones. Though superficially resembling each other in function,two similar looking plant communities will have entirely differentspecies assuming similar ecological functions. Species aside, thesevegetative communities follow several basic patterns, such asgrasslands, wetlands, woodlands or forests, etc. Within these majorpatterns, though, is a whole spectrum of variation. Some of the

major plant assemblages most found in California include4:

Valley Grassland and Savannah

This vegetation community consists primarily of annual or perennialgrasses with, now, predominantly introduced annual grass speciesfrom Europe (Festuca and others), and annual or perennialwildflowers. Grassland or prairie generally lacks major trees andshrubs. Though species such as oaks may be dispersed throughoutthis community, they would generally not constitute a "forest."

Major streams or river channels that traverse grasslands or prairiesmay support dense stands of hardwood trees and shrubs as Riparianlands, being restricted to available water from the stream.Grasslands and the remnants of a once expansive riparianenvironment that existed along the major rivers and streamsdominate the Central Valley (Figure. 5a or b).

Coastal Prairie

Similar to prairie. Open temperate hill grasslands or glades, or baldhills on the west slopes of the outer and middle coast ranges inMendocino and Trinity counties, north, and scattered to countiessouthward to San Francisco County. In the past, native bunchgrasses and flowering herbs dominated coastal prairies. Because ofovergrazing, these native bunch grasses have been displaced byannual grasses and by intrusion by non-native grasses.

Chaparral

This vegetation community consists frequently of an understorygrass soil cover with wildflowers within which are distributed, invarying density, different species of shrubs and oaks or juniper asintermediate and overstory plants. Chaparral is predominantly a dryclimate plant community. Many of the trees naturally found in thisenvironment possess thick corky bark (cork cambium) and areadapted to the wildfires that raged through prior to humaninvolvement. These trees may include Interior Live Oak, Blue andWhite Oak, Manzanita and chamise. This plant assemblage occupiesareas along Central Valley and foothills regions of California from

Redding, along the western Sierras. Chaparral can be found in thesouthern California counties and along the eastern flanks of theCoast Ranges from Redding to the San Bernardino Mountains, aswell as distributions south to San Diego County (Figure 5b).

Forest

These vegetation communities consist of a complex understory andintermediate plant relationship, with high diversity in these layers innatural mature forests. Woodlands' overstory trees are representedby two dominant tree types, conifers and deciduous, with a mixtureof the two as environmental conditions may dictate. The dominantoverstory trees will be made up of either species of conifers in thehigher altitudes or deciduous trees at lower elevations.(Figure 5c).

Forest communities create the most impressive and oldest plantcommunities in their natural mature state as exemplified by theredwood and old growth forests of the northwest state, the Big TreesNational Forest in the central Sierra Nevada and the BristleconePines in the high Sierras. Conifers or deciduous (broadleaf) trees canwholly dominate the overstory canopy to the exclusion of the other,or they can share this niche in varying proportions depending uponclimate, elevation and soil conditions. Forest or Woodlands commandthe Coastal and Mountain Zones as well as the riparian environmentsin the Central Valley. Several divisions of the forest community arelisted here. Forest communities are characterized by the dominantconifer found in each of them:

• Closed Cone Pine Forest. This community is found atintermittent locations along the California coast from Mendocinoto Santa Barbara counties.

• Redwood Forest. Located along the west slopes of the CoastRange from Del Norte to Santa Cruz counties. Some small areasare found in Monterey County.

• Douglas Fir Forest. This community is found in the north CoastRanges from Mendocino County southward, with scatteredremnants to Sonoma and Marin Counties, easterly of theredwood forest regions.

• Yellow Pine Forest. Found in the North Coast regions, toSouthern California.

• Red Fir Forest. Found in the North Coast ranges to SouthernCalifornia.

• Lodgepole Forest. Found in northernmost California to thecentral Sierra.

• Northern Juniper Woodland. A variant of woodlandcommunity in which the dominant tree species is Juniper(Juniperus occidentalis). This community can be found in centralSiskiyou County, easterly to Modoc County and south to MonoCounty.

Desert or Arid

This plant assemblage will be found in those areas of Californiawhere moisture and temperature are at their extremes. Soilconditions are harsh and difficult for plants to grow in. The dominantplants, known as Xerophytes are deep-rooted, and slow-growing.Many plants in the desert community are defensive; producingterpines that will keep invasive plants away from their roots;blocking competition for valuable water. Leaves are thick andphysical defenses such as spines, thorns, and foul-tasting resinskeep herbivorous animals from destroying their slow-growingfoliage. Knowledge of these traits can help in planning desertrestoration projects, so as not to put these highly competitive plantspecies too close to each other. Alkali sink vegetation is found inpoorly drained alkali flats and playas on the floor of the CentralValley and arid regions on the east slopes of the Sierra Nevada.(Figure 6a).

Wetland or Estuarlne, Riparian, and Vernal Pools

These three aquatic plant communities constitute the vegetationassemblages found along natural water bodies throughout California.Some are extremely small and fragile, such as vernal pools, theircombined statewide total areas barely covering several acres.

Plants in these communities are highly moisture-dependent, yet theycan be adapted to intermittent dry cycles, going into dormancy.Many of these species are microscopic and may be sensitive and

vulnerable to minor changes in their conditions. They can also serveas effective bioremediation mechanisms, filtering out certain effluentcomponents in sewage treatment projects (Figure 6b, c).

• Wetland or Estuarine. These plant communities includeCoastal Salt Marsh and Freshwater Marsh. They can be foundgenerally as bordering lands along bays (large or small) salt,and fresh water bodies, lakes and rivers. The largest singlewetland environment in California can be found at the northshore of Suisun Bay northeast of San Francisco. This plantcommunity can consist of vast expanses of rushes and grassesadapted to live in water-saturated soils and conditions ofbrackish to fresh water. Floating plants, including an introducedspecies of water hyacinth, can be found in areas of theSacramento and San Joaquin River Delta. Sloughs, lagoons, orriver channels are generally associated with the wetland orestuarine community. Many estuarine or wetland systems can beinfluenced by tidal conditions (Figure 6b, c).

• Riparian. The riparian environment is an ecologic communityincluding plants growing along an established stream or riverchannel and the floodplain associated with it. Riparian vegetationconsists of rapidly growing, moisture dependent species such aspoplars or willows, assorted thick-growing shrubs, vines andunderstory grasses or other smaller plants. The riparianenvironment can form a complex multi-layered vegetationcommunity. Dense forests of deciduous trees, understory shrubsand grasses can occupy areas embracing the stream channelwhile small wetland environments may be interspersed along theriver or stream.

Early in California's history, the riparian environmentdominated the Central Valley where flooding along theSacramento River floodplain was uncontrolled and frequent.Since western man's immigration to California began,approximately 98 percent of this vegetation community hadbeen destroyed by flood control programs, and byagriculture and other development.

• Vernal Pools. Endemic to California, the vernal pool is one ofthe smallest environments, and one of the most sensitive todamaging impacts. The vernal pool plays an elusive role inproject development and restoration issues. The discussion ofwhat constitutes a "vernal pool" has caused some debate andlegal consternation among developers and environmentalists.The ultimate indicator of what constitutes a vernal pool is thepresence of certain plants that are restricted locally or entirelyby this type of habitat.5

The vernal pool vegetation community can be very small inscale. A vernal pool is a water body often only severaldozens of square feet in area and only inches deep. Vernalpools are seasonally created when water collects in a naturalsurface depression that is rendered water retentive byhardpan, claypan, or other low porosity soils in the basin.The vernal pool is intermittent, evaporating several days orweeks after it reaches its fullest level. This characteristicmakes defining it even more confusing. The vegetalassemblage can consist of very small species of grasses,mosses, and some associated trees and/or shrubs.

Some rare or endangered species of vernal pool life such asfairy shrimp are found on the macroscopic and themicroscopic level. (Figure 6c). Many vernal pool inhabitantsoften hibernate during the dry seasonal cycles. Vernal poolscreate issue for their often being located on prime lands fordevelopment and for being temporary or "insignificant"causing debate over their importance both in theirdestruction as well as their mitigative significance. On theother hand, vernal pool "construction" can be a mitigativeopportunity for a project proponent, as vernal pools aresmall yet often of environmental significance.

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Compatible Plant Associations

When a closure project features a golf course, business park, or

recreational park, the operator may select nursery rather than nativeplants for the landscaping. Selection of plant communities for suchprojects would be based upon the dominant geographic, soils, andclimatic characteristics in which the project is located. Theseconditions would then determine the dominant plant types used. Themain difference is that the plants that are selected would not beCalifornia native species, but they would still be compatible with theenvironmental characteristics of the site to ensure survival.

This type of planting program may require a more intensivemaintenance regimen to control invasive plant species, pests,irrigation, and nutrient provision. Using plant volunteerism byneighboring native species to stock the site would not be employedto avoid competition with the introduced plants. If an aggressiveplant control program is not followed, invasive (volunteer) plantscould still establish themselves. Using the natural overstory-understory distribution concept could be applied to cultivated non-native planting.

Figures 5a, 5b, and 5cGrassland or Prairie, Chaparral, and MatureWoodland(47 KB)

Figures 6a, 6b, and 6cDesert or Arid, Wetlands or Estuarine, andVernal Pool(64 KB)

Figure 7General Plant Succession from Bare Soil toMature Hardwood Forest(23 KB)

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Chapter 7: Landfill Vegetative DesignAs a landfill approaches its waning years of active use, the operatorshould consider the details of the final closure and postclosure landuse planning for the facility. At this time, the operator must considerif the closure will include an integrated planned postclosure use suchas creating undeveloped land, a park, a playing field or preserve,golf course, business park, or industrial park. These "uses" will makea difference in the planned final cover design and possible slopedesign or contouring design for the decks and side slopes, irrigation,and drainage control. The more complex or structured the final landuse, the more complex will be the design requirements for the finalcover and revegetation planning. An undeveloped, open grasslandwill demand less from the final cover design than a plannedrecreational park or a business park. The final cover planning will bedictated by other conditions such as the final cover and moisturelayer components, physical aspects of the landfill site, and thesurrounding environments.

Costs and availability of materials such as soil and plantstocks will dictate the proposed design characteristics. Theelements to consider in the restoration or other final closure plan willinclude landfill design and additional uses for vegetative cover.

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Landfill Design Considerations

Proposed Postclosure Use

If there is an actual planned postclosure use or idea in mind for thesite, this aspect will have to be analyzed prior to any actual designplanning of the final cover. Different uses will impact the demandsplaced on the final cover, including its thickness, slope profiles, and,in considering revegetation or restoration projects, the quality andquantity of the vegetative layer soil that will be utilized.

Drainage and supplemental irrigation issues will have to beaddressed. If the final plan is to install a simple grass cover on thelandfill, a thin vegetative layer that is in compliance with theregulations (Title 27 or Subtitle D) may be all that is necessary. Ifmore complex plantings are proposed, berms, supplemental soils onbenches and other such enhancements to the vegetative layer maybe required to support deeper-rooted plants and to protect theunderlying moisture barrier from root penetration.

Some final closure plans are proposing the use of a monolithic coverinstead of the current multi-layer design in use on most landfills. Themonolithic cover proposals use a thicker, single soil layer that wouldprovide sufficient depths to include deep-rooted vegetativeplantings. One proposed plan incorporates moisture control elementsinto the monolithic cover by using poplars or other similar vegetationand a groundcover plant such as clover to wick off soil moisture byevapotranspiration.6

Whether planning for root depths to determine the vegetative coverthickness or planning root depths to best work with the planned soilthickness, either technique requires forethought in designing thecover and vegetative systems as a unit.

Development of contours of the final cover can be impacted by thefinal postclosure use. An operator who intends to create arestoration project may create more naturally compatible slopes andcontours to the adjacent landscape. Or, the operator may requirebasic contours in compliance with current regulations and theengineering needs of the final project.

• Natural Parks, Preserves, and Mitigation Sites. These usesrequire "permanent cover" of native plants that will not bedisplaced for a future land use such as a business park or otherstructures.

• Recreational parks and golf courses. These uses will entailpermanent or long-term post-closure use cover elements. Thesesites can be developed with "disposable" cover. The vegetationmay usually be nursery plantings, though natural plant speciesare optional. A potential for their removal exists, allowing re-use

of the site for a business park or other structured developmentat a later time.

Final Design of the Landfill

This will dictate what kind of planting and vegetative layer conditionswill be placed on the landfill final cover. Steep slopes on final coverwill require more aggressively rooted vegetative types than shallowslopes. Benches can provide planting areas for deep-rooted plants.These benches must be sufficiently wide to accommodatemaintenance vehicles in addition to the proposed plantings such astrees or large shrubs. A thin vegetative cover will restrict plantoptions to shallow-rooted varieties that will not penetrate moisturebarrier layers. Irrigation from natural rainfall will dictate the types ofvegetation available for use in dry or moist conditions. This mayrequire supplemental irrigation to support the desired vegetativecover, at least until the plants are strongly established. Slopes andnaturalized contours can provide alternative planning options forrevegetation projects with areas to enhance opportunities forvegetation planting.

• Benches. Benches can provide deep soil zones for trees if theyare wide enough to provide space for the vegetation andmaintenance activities, usually with the vegetation at the outsideedge of the bench, where soil is deepest. Grouping trees insteadof lining them up creates more natural "groves."

• Decks. If top layers of vegetative soil are sufficiently suppliedbeyond the minimum 12-inch requirement (preferably 48 inchesor more), larger plants with deeper roots can be supported.

• Berms. Berms add small areas of thicker vegetative soils as hillsor other raised land features (48 inches or more); the added soilcan provide sufficient depths for trees or large shrubs toenhance the natural vegetative appearances of the final cover,

Advanced planning of the landfill, taking the postclosure land useinto account at the very outset, can help the operator plan foradequate soil and topsoil supplies for the final cover. By planning thefinal elevations and contours of the cover layer in advance, theunderlying waste volume can be graded to within more precise

tolerances to conform to the projected design.

By designing the waste contours to closely match the finished designspecifications, less financial resource is expended on poor gradefoundation soil built to grade and, instead, can be used moreefficiently in providing greater volumes of adequate quality topsoil inthe vegetative layer. This could result in additional capital for otherclosure project costs or savings to the operator overall. (Figure 7 aand b).

Figure 7a, and 7bLandfill with Waste Configured to Basic

_-,:,-._. Elevations, and Landfill with Waste Configured•fe^zrri* to Postclosure Project Plan

(10 KB)

Figure 7a. A landfill with wastes that are not closely configured tothe planned final contours will require additional foundation soil toachieve design grades. Less funding will be available for theacquisition of useful fertile topsoil for the vegetation layer.

Figure 7b. A landfill with wastes more closely configured to plannedfinal contours will require less foundation layer soil to achieve grade.This allows for more funding to be allocated toward better quality,thicker topsoil for the vegetative layer. A thicker topsoil layer willallow for more vegetation design options and improve chances forplant survival.

Location of Landfill

Where the landfill is located will influence the type of vegetation thatcan be used on it. Landfills in hot, dry regions will supportappropriately selected vegetation for those climates. Irrigation canprovide added options for vegetation selection, but it is moreexpensive to include as a planned element in vegetation selectionand closure maintenance plans. In addition, atmospheric conditionscan affect plant choices. Revegetation in urban areas may pose achallenge because airborne pollutants can adversely affect somevegetation. Conifers in the Los Angeles basin and grape plants in theCentral Valley have demonstrated this sensitivity by loss of foliage

and higher mortality.

General wind conditions at site should be considered when designinga vegetation cover. Pollutant gases can collect in windward-facingvalleys or pockets, creating adverse atmospheric conditions injuriousto plants.

Excessively tall trees may prove vulnerable to blow-down ("wind-throw") if left unprotected. This can cause damage to the final cover,should the roots peel the soil layer up with the toppled tree. Natural,established tree groves in areas with a prevailing wind tend todevelop an airfoil-like profile, due to natural pruning. Smaller treesof the expanding grove tend to grow at the perimeter of the grovewith larger, mature trees in the center area of the grove. This dome-like form encourages airflow gradually over and around the treegrove (Figure 8a). Single-line hedgerow-like plantings or isolatedindividuals, especially at the edges of top decks and maintenanceroads or benches, place adult trees in a vulnerable position to strongwinds, encouraging wind-throw (Figure 8b). Planting shorter trees atthe perimeter of a grove around taller varieties or adult trees canprovide a windbreak by slowing wind velocities and directing airflowover or around the taller canopy layer.

Figure 8a and 8bAirflow over Natural Tree Stand and Airflowover Uncontoured Tree Stand(95 KB)

Plant Community

When a vegetative cover is installed, extensive planning must beexercised in laying out the details of the vegetative layer and thefinal plantings. This can be most complex when all vegetation isplanned at the initial planting. A strategy for interim maintenancemust still be instituted when the natural population process of avegetative cover is attempted. A planned vegetative community canbe designed and installed in a variety of ways, with threesuggestions as follows:

• Developing and providing all of the major elements of theplant community, such as grasses, shrubs and trees, atthe very outset of planting.

This procedure will require the most advanced planning butit should provide the greatest element of control in theoverall plant community design and final outcome. The finalplant community would be established and maturing early inthe revegetation, and postclosure maintenance program.Some invasive volunteerism by outside plants could occur ifthe operator does not exercise aggressive control efforts bykeeping them out. The initial hydroseeding of annualgrasses, or hand planting of native perennial grasses can beintroduced for slope stabilization with larger plants installedat later dates.

• Providing the proper environment and soil conditions toencourage plant growth and allowing natural invasion(volunteering) by native plants adjacent to the site.

This procedure provides the lowest element of control on thetypes of plants that may be introduced to the site. Thisprocess is the most dependent upon the unpredictablephenomenon of natural plant establishment and successionthat may take longer than the immediate plantingprocedure. Some sort of initial soil stabilization planting witha rapid growing annual and/or perennial grass or groundcover will still be required to prevent erosion of the soil cap.The plant succession process occurs as the selected areamatures.

Naturally, the pioneer plants, most adapted to the harshconditions of bare, usually poor quality soils, begin theprocess. This community usually consists of low growing orprostrate weeds and grasses with deep taproots. This initialplant association begins the soil nutrient construction andsoftening of the soil that provides the conditions moreconducive to the later succeeding plants to establishthemselves.

As the soil is broken up and softened, taller grasses gain afoothold and establish themselves. In time, legumes,herbaceous perennials and woody perennials can begin thelarger plant occupation as soil quality and nutrient contentimproves. Eventually, shrubs and the larger trees assumethe mature level on the location.

A landfill preferably will have an annual and perennial nativegrass planting in its earliest vegetation phase, which mayskip the pioneer phase of the succession. Some strongerinvasive weeds may still try to occupy the site.

Shrubs may not be allowed on the site to avoid rootpenetration, but after the postclosure maintenance programis complete, shrubs and trees may complete the progressionanyway (Figure 9).

Combining planned planting with volunteering byadjacent native species to create the final vegetationcover.

This technique can allow some control in the selection andestablishment of the larger plants with other plant selectionsand distributions left to chance. Efforts may still be requiredto control undesired pest plant intrusion, especially plantswith deep reaching taproots that could damage the moisturebarrier.

GeneralPlant Succession from

Bare Soil to Mature HardwoodForest

Pioneer Grasses Small Shrubs Soft Hardwoods ExpandingWeeds (Poplar, Willow) Saplings

Mature Hardwoods

Figure 9

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Additional Uses for Vegetative Cover

In addition to the obvious uses of vegetative cover that includeregulatory compliance, soil stabilization and aesthetic contribution tothe landfill site, vegetative cover has some specialized functions thatcan be used to advantage.

Bioremediation

Vegetative cover can be used in certain situations to attenuateconcentrations of certain chemicals, salts, trace metals, and othertoxic materials such as boron and selenium present in soils. Certaingrasses have the capacity of surviving in higher concentrations ofthese compounds than other vegetation candidates. In additionthese plants tend to store these compounds in their leaf and stemtissues while removing them from the soil. This process can be used

to advantage to prepare contaminated soils at problem sites forfuture population with less tolerant plants. By planting with thesesalt-tolerant species and mowing them at maturity, thecontaminants can be removed. The contaminated cuttings aredisposed at a different, appropriate disposal site as fill. Afterrepeated cycles, the salts are removed from the soil; the lesstolerant vegetation selections can be planted.

A pilot project at Mountain View Sanitary district wastewatertreatment facility employed conifer trees as a moisture exchangingevapotranspiration mechanism to process water. The trees transpirethe water into the atmosphere, and create a harvestable revenuecrop at maturity. This activity can provide a year-round operation asa serviceable alternative to conventional irrigation disposal systemsthat shut down during the winter months. This technique could beemployed at landfill sludge or septage ponds or possibly leachateponds, upon closure.

Cattails and similar estuarine plants can absorb certain materials insolution, utilizing them as nutrients. Where high concentrations ofthese substances in water from sludge or leachate could posepollution problems such as in leachate and certain liquid wasteponds, cattails and related water plants can mitigate thesesituations. With naturalized leachate ponds and cattails or similarrushes, natural looking artificial "wetlands" could be created. Thecleaned water from these ponds can be recycled as irrigation waterafter additional treatment. The City of Arcata, in Humboldt County,is employing this technique at the final stages of its wastewatertreatment process.

Landfill Gas

Remediation of landfill gas and detection of landfill gas can beaccomplished using surface vegetation. Some landfill gas in lowconcentrations in soil can be absorbed and attenuated by thenitrogen fixing properties of certain legumes and other plant speciesthat possess such bacteria or fungi in their roots. If gasconcentrations do become excessive, plants are sensitive to thesegases and their abnormal appearance, loss of leaves, usually will

alert the operator to a potential gas problem that will need attention.This condition must be responded to quickly before permanentdamage is caused to the impacted vegetation, or the gas migratesand spreads further from the initial site.

Extreme exposures of vegetation to high gas concentrations can leadto stunting of growth or defoliation in some instances, or plantdeath, requiring subsequent removal and replanting.

Leachates

Leachates that develop at a landfill and accumulate in areas shallowenough to impact plant roots can be detected by plants. Loss ofleaves and die-off of vegetation on or in close proximity to thelandfill site may indicate signs of a possible leachate problem. Withthe right conditions and leachate composition, bioremediation (seeabove) can be employed to reduce leachate impacts.

Remediation of Nitrogen Deficiency

Certain plant groups, the legumes particularly, have a natural ability,through nitrogen-fixing fungal symbiotes, to fix nitrogen in the soil.This nitrogen-fixing ability aids in improving the nutrient quality ofthe soil that will encourage other plants to grow.



LEA Information Services http://www.ciwmb.ca.gov/LEACentral/Donnaye Palmer: [email protected] (916) 341-6321

2004 California Integrated Waste Management Board. All rights reserved.



Chapter 12: Some ProblematicConditionsDesigning and installing a vegetative cover, whether it is a naturalrestoration or a landscaped terra-form using nursery plant stocks,requires detailed planning. Several issues as previously discussedmust be addressed before construction begins. Some cases involvingproblems or successes with the more unusuaMssues will be coveredin this section.

Irrigation Source Water Problems

For a landfill vegetation program to succeed, not only must theirrigation hardware design (sprinklers, piping, etc.) be considered,but the source water and its source(s) must be addressed. If thechemical makeup of the source water is not analyzed, there may besome complications that may require expensive remedial actions.Such a problem occurred with a landfill revegetation project at a BKKClass I landfill in West Covina, California. The landfill cover consistedof a 5-foot thick erosion (vegetative) layer that required irrigation tomaintain proper moisture content. The landfill's surface featuresincluded several benches and sideslopes, totaling 118 acres with atop deck of 42 acres (160 acres total). Water for this moisturemaintenance was procured by using effluent outflow from a nearbyleachate treatment plant and a power plant cooling tower watersystem effluent.

Total Dissolved Solids (TDS). Sodium and boron are included inthis water. Concentrations of these compounds leached into the soilduring the irrigation program and attained dangerous levels thatcould adversely affect many less tolerant species of plants that hadbeen planted on the site. Because of this contamination, a newrevegetation (remedial) program was initiated. Plant selections for

the new vegetation program were limited to those plants tolerant tothe high boron and salt concentrations.

Existing grasses and small herbaceous plants would be removedfrom the landfill cover and replaced with ice plant initially, followedby larger shrubs and trees in test plots. All candidate plants are non-native. This choice was made as the salts left behind by the effluentwater irrigation made the soil intolerable for other plant selectionsincluding native candidates.

A new potable water source was selected to replace the previouswater source with hopes of avoiding continued salt contamination.Water would be distributed on the site with overhead sprinklers aswell as drip systems. Water volumes for the new program would becontrolled using a computation based on area, averageevapotranspiration rate, plant water needs, gallons conversion, andirrigation efficiency.

This model would determine the volume of water required to irrigatethe cover satisfactorily. Soil moisture sensors on site would providefeedback on the moisture content of the soil cover. This wouldenable the operator to monitor soil moisture content and to regulatethe amount of irrigation needed to maintain the proper moisture.

This is intended to reduce the chance of excess moisture penetrationinto the waste, which could lead to unwanted gas production andleachate generation.

In tandem with this project is a series of proposed options to treatthe effluent water from the leachate treatment plant and the powerplant cooling water to irrigate the landfill. Five process options totreat the water for salts and boron are being addressed includingreverse osmosis, electrodialysis, distillation, and ion exchange. Theleast costly process (reverse osmosis) is estimated at 1 milliondollars to construct, while ion exchange would exceed 2 milliondollars to build. (Evaluation of Treatment Options for Removal ofTDS and Minerals from LTP and Power Plant Effluents, Invirotreat,Inc., June 17, 1996). The project was being reviewed in 1996.

This problem demonstrates the importance of source water quality

testing to reduce the potential for salt contamination. Soil testing forsalts would be recommended prior to planting. This will enable theoperator to select vegetation according to salt tolerance capacity, toselect a less salt-contaminated water source, or to apply remediationtechniques to bring concentrations to more tolerable levels. As theproject goes into the maintenance stage, continued soil sampling isadvised. This will allow for potential salt build-up problems in thefuture, catching the problem before it causes damage to vegetationor the soil. This is most important in sites using recycled water oreffluent water for irrigation.

Below are listed two methods for salt testing in soil.

1. Electrical Conductivity (EC).2. Sodium Absorption Ratio (SAR).

Several grasses are good candidates for soils with high salinity.These are listed in the following tables.

Tolerant

Tall Wheatgrass

Basin Wild Rye

Russian Wild Rye

>Alkali Sacaton

Weeping AlkaliGrass

Elitrigia pontica

Leymus cinereus

Psathyrostachysjuncea

Sporobolusairoides

Puccinelladistans

Moderately Tolerant

Tall Fescue Festucaarundinacea

Stream bankWheatgrass

Lymuslanceolatus

Some of these grasses are not California natives.

Some tolerant legumes include:

• Koa haole Leucaena leucocephela. Strawberry clover Trifollum fragiferrum (moderately

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False Readings in Soil Water Samples

When monitoring soil water samples at a landfill as part of anirrigation maintenance program or other data gathering activities,attention must be paid to the characteristics of the landfill's coversoil makeup including any amendment materials added to the soil orplants and their debris. Note that some amendments like tree barkcan generate chemical compounds that can mimic certain manmadehydrocarbons. Because of false results from natural compounds,they could lead to unnecessary testing and remedial activities tocorrect the "problem."

False sample results involving detected hydrocarbons in groundwatermonitoring samples revealed the production of terpenoids by waterpassing through a natural tree bark fill material at Caspar Landfill, inMendocino County, owned by Louisiana Pacific.11 This conditionproduced chemicals that resembled diesel and hydraulic fluid thatcould be detected in groundwater samples. Thorough testing wasconducted for certain components in the diesel test samples, thehydraulic fluid test samples, and the tree bark test samples. Testchromatograms for these samples revealed that the hydrocarbonsgenerated at the Caspar site were of biological origin. Certain treespecies with high terpene concentrations (eucalyptus) could create asimilar circumstance if bark and plant debris is allowed toaccumulate on the landfill.

Table of Contents

Drainage and Surface Settling

The efficient and complete removal of water on a conventional drylandfill is vital to its proper function and the integrity of the cap. Thepresence of excessive moisture in a landfill can lead to downwardmigration of water through the landfill cover into the underlyingrefuse. When the refuse is exposed to the invading moisture,accelerated degradation of the wastes can occur. Since this moisturewould be uncontrolled, degradation of wastes will be uneven withvaried settling rates across the landfill.

If a landfill experiences variable settling, the cap material may crack,compromising the function of the cap in containing landfill gas,moisture exclusion and surface runoff drainage functions. Low spotsin a landfill cover can encourage ponding of water, causing addeddrainage problems and moisture invasion. Leachate can form asmoisture collects. These leachates can seep out of the side slopesand contribute to soil weakness or erosion. Leachate with highconcentrations of waste residuals can injure or kill vegetation if itpenetrates the root zone. As with gas, leachates will damage plantroots, affecting viability. Leaves will brown and drop off. Growth willbe impacted.

Sustained exposure to leachates causes defoliation and plant death.Remediation of the leachate problem would be an expensive project,requiring removal of the contaminated soil or possibly washing thesoil and replacing it at the site.

Variable surface settling can create problems for surface facilitiessuch as parks or golf courses located on the landfill. Gas collectionand irrigation systems can be seriously affected by the differentialsettling of landfill covers. Piping for gas collection, surface waterrunoff and irrigation systems can be damaged if the top layers areseverely distorted enough to break pipes or induce leakage. Surfacedrainages can be disturbed significantly, changing slopes andinterfering with surface runoff. Extreme surface distortions resultingfrom settling can damage wires for lighting or electronic monitoring

systems. Structures such as access vaults, maintenance sheds orother buildings that may be located on the landfill may sufferfoundation damage or shifting, possibly encouraging gas entrapmentin their enclosed spaces.

Golf courses can be significantly, adversely affected by improperirrigation and drainage control. If uncontrolled settling occurs on agolf course, the affected section can be rendered unplayable andrequire reconstruction. This can involve regrading and expensivereconstruction to correct.

Landfill cover integrity is highly dependent upon the moisture anddrainage design elements in the final landfill plans. This moisturecontrol should reduce the potential for uncontrolled settlementacross a landfill.

A recreational facility at Industry Hills in San Bernardino County,California, is located on top of a closed landfill. The center includes amajor hotel, swimming pool, tennis and gym facilities, two golfcourses, horse and pedestrian trails. This extensive facility mustinteract with the postclosure landfill behaviors that accompany anaging landfill. Landfill gas is collected from wells throughout the siteand is fed into their combustion facility for space heating and wateruse. All aspects of the facility are monitored and maintained throughan aggressive program to maintain constant gas production, withconsistent BTU (heat) production, irrigation and water control.

Table of Contents

Soil Methane Gas Concentrations

When landfills are completed, a clay moisture barrier layer orsynthetic barrier and a final erosion or vegetative layer are placed onthe structure to provide a means to keep excessive moisture fromreaching the wastes contained within. In addition to keeping excessmoisture out of the landfill, the clay and erosion layers are intendedto provide a capture layer to prevent landfill gas from escapinguncontrollably into the atmosphere. If a gas recovery system isemployed, the clay layer enhances the system's efficiency.

Construction of the cap and incorporating a landfill gas collectionsystem of wells and lateral piping systems to recover the gas forburning or flaring helps to reduce fugitive gas released to theatmosphere.

The erosion or vegetative layer is placed on top of the final landfillcap, serving both as part of the gas trapping function and as asubstrate to support the planned vegetative cover. To comply withthe minimum requirements of Title 27 and Subtitle D, in mostinstances, the vegetative cover may be a minimum of 12 inchesthick. Due to leakages in the clay layer from non-uniform settling,side slope movement, cracking and breaches in the cover, volumesof landfill gas may escape through the clay layer and linger in thevegetative layer soil, as well as escape to the atmosphere. Thesegases can be produced in quantities to build Up lethal residualconcentrations that remain trapped in the vegetative layer. Thesesoil gas concentrations can affect the root zone of the vegetationplanted on the cover. If these gas concentrations exceed thetolerance levels of the overlying vegetative layer, the plants can beadversely affected to the point of impaired growth or death.

The concentrations of landfill gas can impact the natural soil gasconcentrations that are essential to proper plant metabolism,displacing vital oxygen and other resident gases usually found in thesoil and replacing it with methane and carbon dioxide.12 This soil gasdisplacement can adversely affect the roots of plants and theirsymbiotic fungal associations that aid in nutrient and gasassimilation.

Initial signs of this impact on vegetation include stunted growthrates over time, brown patches in turf, partial loss of foliage, or totalloss of foliage and plant death.

A golf course in Utah experienced a situation in which landfill gaseswere invading the vegetative layer and residing in the root zone ofthe cover. As the gas concentrations built up to critical levelsimpacting plant survival, there were apparent signs of damage tovegetation. Green turf areas became covered with brown and deadpatches. Trees and shrubs also displayed signs of impaired growth

and poor establishment, with partial loss of leaves. These signsrevealed a potential gas leakage problem.

Gas concentration tests were performed at two locations in whichextensive areas of brown patches were found in the turf. Studieswere undertaken to observe methane flux emissions and methaneoxidation rates in the soil. The greens were constructed with an 80percent and 20 percent peat soil mixture, following United StatesGolf Association standards. To maintain gas exchange, greensmanagement staff carried out remedial aeration procedures but thiseffort failed. After using a corer to prepare the holes, gas samplerswere installed at 6 to!4 inch depths. The soil plugs were reinstalledbehind the gas probes to allow natural gas concentrations toreestablish.

Gas samples were taken from the plugs and they were "determined"with gas chromatograph tests. Laboratory testing on the samplesrevealed high methane concentrations where turf was injured.Diffusion rates at four sample sites reached 212 Ib./ac/hr, 23Ib./ac/hr, 88 Ib./ac/hr and 16.5 Ib./ac/hr. Areas with no signs of turfdamage revealed no methane concentrations in the soil. It wasdetermined that methanotrophic bacteria were displacing oxygen inthe soil. This eliminated oxygen from the soil environment, creatinganaerobic conditions and resulting in damage to roots and turf. Insituations where soil gas is found, usually methane is in the highestconcentration with carbon dioxide, hydrogen, and nitrogen in lesserconcentrations.

Correcting a soil gas problem is often an expensive and intensiveoperation for a golf course operator to undertake. Soil gas must beeliminated which requires installation of efficient gas collectionsystems. Retrofitting such a system will require trenching to installhorizontal gas collection lines or drilling wells for vertical gascollection systems. These steps can be expensive and demanding ofplanners to work around existing surface features as are found ingolf courses.

The best alternative to retrofitting is planning and installing the gascollection system while the final cover is being constructed or while

the landfill is first being designed and constructed. Grading thewaste to near final planned contours will reduce the need for usingadditional topsoil to build up to planned elevations. This willconserve soil resources for the project. Proper and completecompaction of wastes during filling may improve waste settlingbehavior, ideally promoting uniform settling of decomposing wastesand reduced breaches in the cap. Good design and installation of thefinal cover layer, and the erosion layer should provide the protectionagainst escaping landfill gas and efficient recovery via the gasrecovery system to prohibit soil gas problems.

Ample soil thickness can improve options for landscape design andselections for vegetation. Thicker soil can also promote better gascontainment. A thin erosion layer will limit vegetation options tosmaller grasses or herbaceous plants with shallow roots. Thiscondition can also allow greater chances of damage to the clay layeras less differential shifting can more readily breach a thin soil layer.Potential for soil gas impacts on vegetation and the outsideenvironment can be greater with a thinner soil layer by placing theplants in closer proximity to the underlying soil gas zones. Odorproblems will be more possible, which is a concern when planning agolf course or other high use recreational facility.

Deeper soil overall or planned berms of deeper soil from 3 to 5 fivefeet thick, in addition to the 12-inch vegetation/erosion layer, willpermit larger shrubs or trees to be used. This can also help bufferthe root zone from the underlying barrier layer and the refuse or gasbelow. These soil enhancements should be large enough toaccommodate the planned plants' root systems.

Table of Contents

Additional Considerations

Cover minimizes the percolation of surface water into thewaste layer. Since the applied demand for final cover is to prohibitexcessive moisture entering the upper soil layer, some compaction isdone on the erosion layer. The compaction will reduce porosity anddownward water migration. This may interfere with irrigation of

vegetation and promote surface water runoff.

Vegetation maximizes evapotranspiration with irrigationbalancing evaporation. If soil moisture is critical to the integrity ofunderlying clay layers in the cover, vegetation can accelerate theevaporation of moisture back out of the cover and clay layer.Without proper monitoring of the soil/clay moisture, desiccation ofthe clay layer can lead to cracking and loss of the moisture barrier'sfunctional integrity. This can allow excess moisture into the landfillduring wet weather seasons and landfill gas escape year round.

Vegetation selection should address fire safety issues. Certainvegetation can promote fire hazards, either due to growth cyclessuch as the dry period in grasslands in late summer or excessiveplant debris accumulations such as bark, leaf and branch debris.Some deciduous species allow their leaves to dry and remain ontheir branches, prior to shedding. These materials combined with dryconditions can present a high fire hazard. An aggressivemaintenance program of large sized debris removal can reduce thisdanger. In addition, the large debris (branches, broken-off treetops)can be ground up and recycled as mulch, a savings incentive formaintenance budgets.

The topsoil medium for plants to establish on is usuallyminimal in depth and of poor quality. Most closure projects arelimited by the costs of the closure operation. In most instances, thecost of obtaining, transporting and installing quality topsoil for thevegetative layer can be high. Unless a free or low cost source of soilcan be found close to the facility, the soil layer will be constructed tothe minimum standard of 12 inches thickness in compliance withSubtitle D or Title 27 regulations. This thickness can support grassesand maybe smaller perennials such as vetch or lupine, but it wouldnot be sufficient for larger shrubs or trees. Inferior soil quality willnecessitate fertilizer and soil supplements to aid plant establishmentand growth.

The best situation is to remove the native topsoil andstockpile it on site for eventual replacement as the vegetativecover when the landfill is closed.

Use of supplemental fertilizers to encourage vegetationgrowth can be undertaken, but these supplements can beexpensive to obtain and spread on site. These materials canalso accumulate in soil, causing potential future problems.Preparing the new topsoil with supplements such as manure,composts or mulches and amendments prior to planting canfurther the success of the vegetation project.

Compaction of the topsoil layer with a relatively smoothsurface makes it difficult for roots to penetrate through thesoil, and for plants to become established. Since the finalerosion layer is placed on the final cover, the nature of itsplacement, grading, and sloping will increase the tendency towardscompaction. The use of heavy earth moving equipment, inducingcompaction, will reduce loft and the ability for the soil to absorbmoisture and rapid root penetration, which is vital to plantestablishment and growth. Texturing the soil with a sheep's foot orgrid roller, or an imprinter in arid or desertified environments, canimprove the soil conditions to some extent and will provide surfacepockets to retain seed and fertilizer. Without texturing of the soilsurface, water runoff and wind erosion can occur, causing soil loss,as well as loss of plant seed and accompanying nutrients.

Little organic material is available for plants in most landfillcover. In many cases, the "topsoil" used in the final erosion layermay actually come from subsoil layers moved in excavation. Thismaterial may not be of the same grade or quality of true topsoil,lacking the organic materials found in the original topsoil of theproject area. With a lack of organic material or vital nutrients in thesoil, the likelihood of a successful revegetation project isjeopardized. An option is to scrape the actual topsoil layer to the "A'horizon (topmost layer) and to stockpile it, replacing it as a finallayer when closure and final grading are completed.

Irrigation systems often can be poorly designed, providinguneven coverage. Germination and survival of the plants willclosely reflect the irrigation pattern. Dry areas where water is notreaching will limit the possibility of new plantings to survive theirinitial establishment. Poor management of irrigation systems can

create the same situation resulting in soil moisture loss, desiccationof vegetation and death. Excessive soil moisture can result inpossible leachate and gas development or slope erosion or failure, aswell as distressing young vegetation.

Invasion by weeds or other undesirable pest plants creates acompetitive pressure, removing valuable water and nutrientsfrom the cover vegetation. An active program of selective weedabatement can reduce the competitive pressures of weeds on thevegetation.

Side slopes at landfills can be steep, making irrigation andmaintenance difficult. Steep grades, if not properly engineered ortextured, can encourage excessive surface runoff. Steep slopes canmake seeding and seed establishment difficult. Seeds can have atendency to be washed off by accelerated water flows during stormsand by strong winds.

Geotexturing can be used if site conditions require it or if thesurrounding topography reflects an aggressive terrain.Geotexturing employs variable grade slope faces in its appearance;achieving 45 degree slopes. The variable grade creates a morenatural face. These angles can be achieved through use of HDPEgeogrids. Forming a subsurface foundation, the geogrids provide aninternal subsoil structure to support the soil layers above, inhibitingdownslope migration. Vegetation can be hand planted on these areasonce they are prepared. A site at Spanish Hills Golf and CountryClub, Ventura County employed this technique. Such slopes wouldrequire foundation soil analysis studies for slopes greater than 1.75(H): 1 (V). Various soil stabilization products such as those producedby American Excelsior Company and others can assist in steep slopestabilization.

Soil temperature can vary throughout the soil cover and canbe detrimental to healthy plant growth. In some areas wheretemperature extremes may occur, these extremes can affect seedgermination, reducing seedling population. This variation inextremes can be affected by north-facing slopes (cooler, moremoist) or south-facing slopes (hotter, drier).

External pressures from the local community can impact theaesthetics of the landfill site. A local community can elect toinfluence the vegetation choices a developer may put on a landfill.The choice, though functionally adequate, might not be aestheticallyor, environmentally, the wisest choice. This must be emphasizedwhen community members become involved in the landfill designprocess.

Cost Analysis: Determine the costs and availability ofmaterials and resources. Conserving and stockpiling topsoilremoved from the site will save future costs in procuring new soiland transporting it to the site. This may hold true for stockpilingvegetation stock. It may be less costly to transplant small trees andshrubs on the site to a holding nursery and then transplant themback at the closure phase. Different projects will be more costly thanothers will. Recreational parks and open or natural field projects maybe cheaper than playing fields, or golf courses.

Two Golf Course Cost Analyses13

Golf Course on Conventionally Closed Landfill

Landfill Closure Costs (20-acre site, conventionalburial, and maintenance)

Construction at $100K/Acre

Maintenance at $50K/Yr., 30-Yr. Period

$2,000,000

1,000,000

Golf Course Costs

Construction of Course, 25 PercentCost Premium

Maintenance at $100K/Yr.

$2,250,000

2,000,000

Total $7,250,000

Golf Course on 50 Percent Reclaimed Landfill

Landfill Reclamation Costs (Landfills "mined" ofwastes, recycling.)

Reclaim

Cap10Acres

10 Acres

(Construe

(Mainten<

$1,500,000

:tion) 1,000,000

ance) 750,000

Golf Course Costs

ConstructionPercent Cost

Maintenance

of Course, 12 $2,025,000Premium

at $50K/Yr./NPV j 1

Total 1

,000,000

$6,225,000

18-Hole Golf Course 10-foot average depth of waste175-Acre Site 300,000 Cu/Yd of waste-.̂ /v i jr-ii • i*-^-ii r ,--4. Construction cost average @20-Acre Landfill in Middle of Site ^,nni//u ,$100K/nole.

This scenario would involve a landfill in which most of the wastes areremoved, "reclaimed" or "mined" for their recyclable value in metals,etc.

Costs of supplemental materials such as geotextiles and other slope

re-enforcement/erosion control systems can vary for differentsystems that may accomplish the same things within the sameperformance standards. Below is a comparison of several erosioncontrol systems from the least expensive and simplest up to themost complex and costly.

Long Term Erosion Control Systems 14(3)

Type Description FlowVelocity

Range (fps)(i)

InstalledCost

($/Cu Yd)

VegetatedGeocellularContainment

Polymerichoneycombshape, 3-dcell systemfilled withsoil andvegetation.

4-6 $20-$40

UltravioletStabilizedFiber RovingSystems

Strands ofpolypro- orfiberglassfiber blownonto thegroundsurface, thenanchored inplace usingemulsifiedasphalt.

6-9 $l-$2

TurfReinforcementMats

3-dimensionalmatrix of PP,PE, or nylonfibers

10-25 $6-$15

stitched,woven orthermallybonded .Designed tobe seeded,then filledwith soil.

VegetatedConcreteBlock

Articulatedor hand-placedconcrete

10-25^ $40-$60

GeocellularContainmentSystems

Polymerichoneycombcells filledwith gravelor concrete.

$30-$60

Fabric FormedRevetments

Geotextilesfilled withgrout orslurry.

15-25 $15-$30

ConcreteBlockSystems

Articulatedor hand-placedconcreteblocks.

15-25 $40-$60

Gabions Rock-filledwire basketsor frames.

15-25 $45-$75

Riprap Quarriedrock ofsufficientdensity

6-30dependingupon meandiameter

$15-$80

(1) Some systems with greater mass and/or ground covermay exceed these upper limits.

(2) Depending on infill material.

(3) Shear stress ranges have been omitted because ofcomprehensive data for the range of materials is not readilyavailable. Manufacturer may have specific performance andcost data.

PP, Polypro-= PolypropylenePE=PolyethyleneUV=Ultraviolet



LEA Information Services http://www.dwmb.ca_,gov/LEACentral/Donnaye Palmer: [email protected] (916) 341-6321©1995, 2004 California Integrated Waste Management Board. All rights reserved.

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