Landfill engineering and design readily lend themselves to an organizational approach directed toward analysis of the various systems comprising a landfill. The final product (an operational or construction permit application) can be organized in a matrix according to the required information cross-referenced to its presentation format. The matrix approach is facilitated by the fact that the design of each landfill system and the overall design effort follow a consistent sequence. This sequence determines the scheduling of the project tasks and resultant personnel assignments.
Each task belongs to a particular information category (landfill gas, geotechnical analysis, runoff and erosion control design, etc.) and produces this information in one or more formats (narratives, detail drawing, plan drawings, specifications, etc.) Individuals with appropriate skills and experience will be assigned as needed for each system design task. For example, many landfill engineers specialize in the design and layout of landfill gas collection and management systems. Others specialize in geotechnical analysis. The task schedule and skill requirements will define the appropriate team configuration and the most efficient allocation of engineering assets for the design effort.
Matrix Management Theory and Applications
The matrix model is a network of interfaces between teams and the functional elements of an organization. At the level of organization associated with the company itself, the matrix is typically formed between functional managers and project managers. Functional managers are responsible for how a task is done and who will do it. Project managers are responsible for what, when, and why tasks are done, as well as budgeting for, scheduling, and performing evaluations of those tasks. At the level of the landfill design project, functional tasks deal with the formats of the design presentation. The project tasks deal with design categories as each system element is treated as a small project within the overall design project effort.
When an engineering group is dealing with numerous projects, a matrix organization may be used where there are departments or individuals with well-established, specialized skills and capabilities for performance on a variety of projects. A matrix organization provides a flexible structure within which people and resources can be allocated as needed. The projects flow through the functional complex and receive the services of these specialized departments or individuals. The matrix organization represents a compromise between traditional functional organization and full-scale program management. Typically, engineering organizations maintain specialized design, laboratory, and field groups, which provide the necessary skills and experience.
To handle multiple projects, provisions are made for the establishment of project managers for each client program. The project manager has overall management responsibility for all project activities and directs these activities through project schedules, cost and quality control, system analysis and planning, engineering, and contract management. Engineers and technicians with specialized skills are assigned to participate in the project team for all or part of the project’s duration. Each individual may work exclusively on one project or provide support to several projects at the same time.
Solid- and hazardous-waste disposal-site permit applications require information concerning three broad areas of concern: general site layout and location information, geotechnical and hydrogeological information, and engineering design and analysis. This information is presented in three formats: narrative descriptions, graphic design, and attached support documentation. The information categories and presentation formats allow the permit application to be organized in a coherent matrix (see Table 1). This article will focus on the production and presentation of the engineering design and analysis portion of the permit application package.
| Table 1. Generalized Landfill Design Matrix | |||
| Areas of Concern | Narrative Descriptions (Function) |
Graphics Presentations (Function) |
Support Documentation (Function) |
| General site layout and location information (project) | Site description, legal property survey, location, setback restrictions, etc. | Topography, region site description features, property lines, easements, etc. | Natural bodies of water, private wells, utility locations, etc. |
| Geotechnical and hydrogeological information (project) | Hydrogeological and geotechnical investigation report(s) | Hydrogeological cross sections, fence diagrams, groundwater contours, etc. | Field records, boring logs, soil test results, etc. |
| Engineering design and analysis (project) | Design narratives, CQA procedures, operational narratives, etc. | Engineering plans and detailed drawings | Engineering analyses, and computation, specification, manufacturers’ documentation, etc. |
Landfill Systems Analysis
The first two projects, site layout and location information and geotechnical and hydrogeological information, provide the foundation for completing the third project, engineering design and analysis. The goal of the engineering design and analysis effort should be properly defined in terms of a systems analysis of the interrelated landfill components.
It would be a mistake to view a landfill as a static configuration of waste, geosynthetics, and engineered soils. While structural integrity is critical, its importance lies in ensuring the proper function of the landfill management systems and subsystems. The primary purpose of a landfill system is to manage and minimize the quantity and quality of water entering the landfill (from either the top as precipitation or from the bottom as groundwater). Water percolating through the waste becomes leachate and is handled by the leachate management systems. Secondary systems also exist to manage decomposition gases exiting the landfill. Feedback concerning the effectiveness of these systems is provided by various environmental monitoring subsystems (see Figure 1). In short, a landfill is a hydraulic system designed to manage both liquid and gaseous flows.
Surface-water management systems include final grades/cap and cover system designed to ensure positive surface-water runoff from the landfill and minimize percolation into deposited waste; surface-water runoff control structures to collect and channel the runoff so as to prevent sheet flow and reduce peak runoff amounts and flow velocities while minimizing scouring and erosion; sedimentation and erosion control systems to trap water-borne soils and prevent them from leaving the site; and intermediate grades/waste cell construction and operational procedures designed to ensure positive runoff away from the current work area.
Leachate management systems include leachate collection systems to direct leachate to extraction points and minimize leachate head on the liner; leachate extraction and transmission designed to safely remove accumulated leachate from the landfill; leachate treatment and disposal facilities providing onsite or offsite treatment of the extracted leachate; and a liner system and stable foundation designed to contain leachate and prevent it from exiting the site.
Groundwater management systems are utilized to isolate the site from groundwater by either cutting off or lowering the elevation of the groundwater. Permanent systems include slurry walls and under drains, while temporary groundwater management can be provided by wick drains or well points.
Landfill gas management systems include landfill gas extraction, including wells (either passive or attached to an active system) and associated laterals, headers, and blowers; and landfill gas destruction or utilization provided by ignition, containment, or energy production systems.
Environmental monitoring systems include landfill gas probes, groundwater monitoring wells, surface-water runoff monitoring points, leachate samplings, collection lysimeters, and other leak-detection devices. These monitoring systems provide the information necessary to initiate self-correcting mechanisms to modify the construction or operation of the landfill.
Design Sequence for an Individual Landfill System
So how does matrix management tie in with system analysis in landfill design? The design and analysis of each landfill management system is treated as a sub-project of the overall engineering design and analysis project described above. Again, functional formats (narratives, graphics, and documentation) are assigned to each of these sub-projects. Each sub-project task associated with a landfill management system is completed in a similar fashion.
Each landfill system design begins with a conceptual detailing of the system. The initial conceptual design and subsequent final designs will be based on the information provided by external sources. These include governmental regulations (federal Subtitle D, state regulations, and local ordinances) and site owner/operator requirements and standards. The previous experience of the design engineer, while internal to the engineer, can be considered another external influence.
The goals and requirements are often in conflict. Owner/operator standards must meet the minimum governmental requirements or the site will not be permitted. The designer must keep in mind the owner/operator requirements to maximize site profitability and avoid over-engineering the design. The twin engineering goals of operational performance and ease of construction can also conflict which other.
Engineering computations are then performed on the conceptual detailed design to establish that it will meet required performance and environmental safety standards (e.g., infinite slope liner stability). If these standards are not met, the design is revised until it does.
The dimensions of the system defined by the detailed design are used to establish plan drawings of the systems and define them in terms of elevation contours. A second round of engineering computations is performed for the plan design (e.g., final refuse grades rotational slope stability). Revisions and regrading are also possible at this stage should the proposed plan fail to meet design requirements.
The above is a description of a highly formalized and idealized process (see Figure 2). In reality, an experienced designer can rely on past design results to shortcut this process, arriving at a design solution much faster than the formal approach would allow.
Overall Landfill Design Sequence
Though an experienced engineer can often design individual landfill systems without formal sequencing, the landfill design as a whole must follow a more regular sequence (see Figure 3).
Certain design features must be established before proceeding to the next system (e.g., foundation grade elevations must be established prior to design of the liner system, final grades designed prior to surface-water management structures, etc.). The landfill engineering design can be presented in a matrix format. Each system is described in terms of narratives, computations, details, and plan drawings (see Table 2).
| Table 2. Landfill Design Matrix | ||||
| Design Element | Narratives | Documents Calculations/ Attachments |
Graphics Details (*) |
Graphics Plan Drawings (**) |
| Conceptual layout | Introduction, site description, location restrictions, system elements | Preliminary airspace, preliminary earthwork truck queuing | Access roadways, service roadways, onsite buildings | Existing conditions, site layout, conceptual liner, conceptual cover |
| Groundwater management | Hydrogeological investigation report | Groundwater inflow rates | Slurry cut-off wall, interception drain, under drain, groundwater monitoring well | Groundwater management |
| Foundation analysis | Foundation CQA | Cut/fill volumes, uplift and heave, groundwater inflow, bearing capacity, rotational stability, mass block stability | Groundwater wells, leachate floor management, leachate slope management, tie-in to existing leachate, leachate separation berm, leachate construction limits, leachate toe drain, leachate cleanout riser, leachate sump, leachate pump, leachate extraction riser, leachate discharge vault | Base grade contours, site hydrogeology |
| Liner grades | Liner system design, liner system CQA | Settlement sliding stability, tensile forces, anchor pull-out block stability | Liner system grades | |
| Leachate management | Leachate system, leachate system CQA | HELP model, active HELP model, closed pipe, static loading pipe, dynamic loading pipe flow, capacity pump, operating head pump cycle time | Leachate management system | |
| Leachate disposal | Leachate treatment, leachate disposal | Force main flow capacity, storage tank capacity | Force main storage tank pretreatment | |
| Waste cells | Waste disposal operations contingency plan | Disposal volume, operational lifetime, daily cover volume, intermediate cover volume, intermediate rotational stability, intermediate mass, block stability | Typical refuse cell | Site development plan(s) |
| Final cap and cover | Final cap and cover, final cap and cover CQA closure and postclosure | Final rotational stability, final mass block stability, sliding stability, tensile forces, cover buoyancy | Final cap and cover | Final grades |
| Surface water | Surface-water runoff | Peak channel flows, grass peak channel flows, riprap culvert flows, impact structure flows, downslope pipe flows | Runoff diversion, channel runoff, collection channel runoff, discharge channel runoff, discharge pipe roadway swales, culvert and spreader flow, impact structure | Surface-water management |
| Erosion control | Potential erosion and sedimentation control | Soil loss estimate, active soil loss estimate, closed basin sizing, sedimentation basin sizing, detention primary spillway flows, emergency spillway flows | Temporary erosion controls, basin inflow, basin outflow | |
| Landfill gas management | Landfill gas system, landfill gas CQA | Gas well radius of influence, landfill gas production rate | Gas well well head assembly, header pipe, trench lateral pipe, condensate tank blower, flare pad | Landfill gas system |
| (*Includes plan views, cross sections, profiles, and schematics) (**Includes site cross sections and plan drawings) |
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Figure 3 and Table 2 provide a useful tool for establishing staffing and scheduling requirements, and for illustrating how a seemingly small change on a system design established early in the process can result in major revisions to all subsequent systems. For example, a change to the foundation grades will also result in changes to the liner design, and leachate management system design. Unless the individual members of the design team have multidiscipline experience, engineers with specialized knowledge in the various landfill systems will be brought into the project as needed.
The landfill design sequence has two potential work paths once the facility layout has been determined: one associated with the “top” of the landfill (phasing, final grades, cap and cover, surface water, erosion, and landfill gas), the other with the “bottom” of the landfill (foundation, liner, leachate collection, leachate extraction, and leachate disposal).
In general, the flow of the landfill design effort can be described as follows: Once the maximum extent of the landfill has been determined by location restrictions and geotechnical features, a conceptual layout can be drawn. Additional hydrogeological information will then be used to design the first task of the “bottom of the landfill” work path, layout of a groundwater management system (if necessary). Foundation grades and liner/base grades are then designed in accordance with groundwater and other geotechnical concerns, and provide the basis for design of the leachate collection system. The leachate collection system (drainage layer, pipes, and sumps) is then extended into a transmission system for movement of the leachate beyond the boundaries of the landfill. The transmission system connects the collection elements to the leachate disposal media (sewer pipelines, temporary storage tanks, and/or a pretreatment system).
Once the conceptual layout has been determined, the first task of the “top of the landfill” work path, phasing and the general site development sequence, can be established. It is important to establish the phasing sequence early since this will directly impact the sequence of construction and flow direction of both the surface-water runoff and landfill gas management systems designs. Final grades are developed next and are used as the basis for designing both the surface-water and landfill gas systems. Erosion/sedimentation control structures are designed in accordance with the surface water systems flow estimates. Finally, both work paths converge at the end to develop an environmental monitoring plan.
This is not to say that both paths are completely independent of each other. For example, the ability of the leachate collection pipes to withstand static loadings depends on the maximum refuse final grades. The depths and production rates of landfill gas wells depend on their allowable depth as defined by the base grading plan. The cap configuration will greatly impact anticipated leachate production rates, affecting the design of all the leachate management systems. Multiple iterations may also be required to achieve a design goal. For example, a landfill must maximize size while leaving enough area for a sedimentation pond. The size of the pond depends on the amount of surface-water runoff, which in turn depends on the size of the landfill, etc. But the two work paths do suggest that an optimum design team consists of two engineers, each with the multidiscipline training required to simultaneously complete each work path (see below).
Landfill Design Disciplines and Skill Requirements
It is the skills needed for the design of each landfill system, and the position of the system in the landfill design sequence, that determine the staffing and scheduling matrix required for landfill design planning. In addition to a working knowledge of hydrogeological issues (necessary for interpreting the results of site investigations and their impact on the design effort), various hard engineering skills will be needed by the design team. These include hydrology (surface-water runoff, erosion and sedimentation, flow through permeable soils); hydraulics (piping systems, pumps, liquid and gaseous flows); geotechnical (consolidation, slope stability, foundations); and geosynthetic engineering and materials science. Only the last can be considered a specialized skill required for landfill engineering, though geosynthetics have extensive uses outside of landfills.
The computer-aided design and drafting (CADD) and clerical production cycles and associated skills should not be neglected, as these will determine the presentation quality of the final product. Traditionally, an engineer provides a document (either a pencil sketch or handwritten narrative) to the CADD operator or word processor for input to electronic medium. However, as engineers become more directly fluent in CADD and word-processing software, the tendency is for the engineer to directly design or write in electronic medium, thus reducing the time for the first step and leaving the second step exclusively for revision, polishing, and production of the document.
Potential Landfill Design Team Configurations
The landfill design team should be as small as possible given the anticipated project requirements. Team members should have sufficient cross-training t