It’s apparent that today’s engineers have the necessary technical expertise to design a safe landfill that meets federal, state and local regulations. But do consultants consistently and effectively consider the needs of the owner/operator? Do engineers account for local site conditions such as soils, climate and contractor capabilities, or do they apply the same suite of design strategies to every site? Landfill design that considers owner preferences, local conditions and “constructability” will ensure the long-term profitability of the facility and create a successful client/consultant relationship.
Whether the landfill design project is a greenfield site or an expansion, making the owner’s and engineer’s project goals work together is a critical component of a successful design. An engineer cannot assume to know all of the owner’s project goals right off, but a seasoned consultant knows of a few obvious objectives, including:
- to have the project come in under budget with no change orders;
- to have no surprises during the design process;
- to have the project completed on schedule;
- to receive a design that offers constructability and operational efficiency; and
- to have a facility that maximizes airspace.
- is technically correct;
- meets permit requirements;
- minimizes client construction costs;
- minimizes comments from regulatory agencies; and
- keeps the client happy.
An engineer can maximize his potential to meet client goals through effective communication, good project management practices, and, arguably the most important factor, applying actual field experience to the design.
Are You Experienced?
Field experience is paramount to effective landfill design. It’s a common practice in the solid waste consulting industry to hire entry-level engineers or geologists and place them immediately in the field for a few years. Construction quality assurance projects are a great way for young engineers to gain valuable field experience. It’s also a good way to weed out those that may not be interested or motivated to pursue a career in the solid waste industry. There are few ways to more effectively test a new employee’s work ethic and dedication than to have him document geosynthetic liner placement in the summer heat, or log the temperature and waste composition of a gas well installation.
With time spent on multiple sites, engineers can also gain a better understanding of facility operations, how they vary from site to site, and which operational aspects are more effective than others. This experience will improve the engineer’s dialog with the owner during the design phase and enable the designer to provide alternative approaches that the owner may not be accustomed to. Engineers who have spent time in the field understand the importance of constructability and how those designs are the most cost-effective to build.
A landfill owner expects engineers to know the basic technical requirements of landfill designs as well as applicable local, state and federal regulations. What is not known for a specific project is the owner’s preferences for the landfill design components. It’s critical that engineers talk to owners before the design process begins to get their ideas and discuss how they will be incorporated into the project. Avoid taking the “cookie cutter” approach and work with the owner to come up with solutions that will work for them.
Generally, landfill design can be subdivided into eight categories: base liner, final cover, leachate collection, landfill gas (LFG) collection and control systems, surface water management, phasing, and general facility areas. Owners will have specific preferences concerning each of these components that must be considered for the long-term success of the facility.
Consideration of airspace requirements, foundation soils, bedrock and groundwater proximity, soil balance or excess, maximum excavation depth, stockpile areas, and owner or contractor equipment capabilities are all important aspects to base liner design. Site geological and geotechnical investigation provides the design engineer with the necessary soil information to set base liner grades. The owner needs to be consulted regarding his target airspace and tolerance for a positive or negative soil balance. Minimizing the stockpiling of liner soils and their hauling distance are also important considerations. The ability of the available construction equipment should also not be overlooked, especially if the owner will be performing construction and has limited equipment capabilities.
Climate and soil availability can dictate final cover design. Low-maintenance final cover reduces erosion and efficiently sheds stormwater while reducing the owner’s long-term costs. Owner preferences for final cover drainage berms, other stormwater management features and access roads also need to be taken into consideration. Climate considerations will dictate vegetation type, if any, and the owner may have a preference for natural prairie, shrubs or shallow-rooted trees. Geomembrane, solar and armored covers should also be brought to the owner’s attention as these technologies may be a viable option for the site.
Leachate Management System
The construction and operation of leachate management systems result in significant capital and operating costs for landfills, so the engineer should consider ways to reduce these costs. Leachate generation can be reduced by directing stormwater away from active fill areas and the proper application of intermediate and final cover. Additionally, engineers must consider the owner’s experience and preferences for leachate management system components. Many different designs are in operation in landfills today. However, all of the designs have the same goals: to efficiently collect, extract, temporarily store, convey and treat leachate, and to minimize the head on the base liner. A myriad of design variations can be applied to the following leachate system components:
- Sumps. A designer needs to ensure constructability of the design slopes, depths, and soil and geosynthetic components while providing for adequate leachate collection.
- Riser pipes. A wide variety of sizes and configurations are used. Most variations function the same so owner preferences should be a guiding consideration.
- Riser vaults. If riser vaults are required, many owners will have designs that they like, sometimes involving local equipment suppliers.
- Forcemains. Location of the forcemain in the perimeter berm or access road shoulder is typically an owner-determined item.
- Pumps. Make sure to discuss with the owner his experience with leachate pumps. He may have strong opinions on what works and what doesn’t.
- Control Panels. Owners generally use a local electrician to set up pump control panels so a discussion with the owner’s electrician may be necessary.
- Control Logic. Can be sophisticated or simple depending on owner preference and regulations.
- Storage Tanks and Controls. Location of tanks and leachate loadout stations are critical to continuing site operations. Adequate leachate tanker truck turning radii need to be taken into account in the design.
LFG Collection and Control System
LFG management systems have many variations depending on gas quality and volume, regulations and owner preference. The waste depth, age, temperature and composition also dictate design of these systems. Design components for which the engineer should seek owner input and preferences include gas well material (HDPE, PVC, etc.), wellheads, flare type and a potential gas recovery plant. Systems for controlling LFG during operational phases of the site — such as horizontal collectors — need design input from the owner since they may interfere or complicate daily operations. Since it is common for the owner to perform the operations and maintenance of the LFG system, it is very important to consult with the owner to ensure a design with which they are comfortable and satisfied.
Surface Water Management System
There is a great degree of both regulatory and design variability with surface water management systems. Many counties and municipalities have adopted surface water management plans that may impact system design and performance criteria. Additionally, owners typically have specific design preferences that have historically performed well for their facilities and required minimal maintenance. Low-maintenance surface water features that minimize erosion are important for owners in reducing operating costs.
Operational phasing of landfills is critical for efficient management of airspace, soil, stormwater, and truck and construction equipment traffic. Incoming waste volumes and soil balance are two aspects that dictate phasing design. Interim storm water controls, borrow areas, temporary haul roads, rain flaps/intercell berms and temporary leachate sumps should also be discussed with the owner. Almost every landfill owner has a different idea of what the ideal phase development plan should be, and, therefore, the engineer needs to ensure consistent client communication while performing the phasing design for the landfill.
General Facility Areas
Facility areas include maintenance buildings, entrance and access roads, scale house and scales, and administrative buildings. Prior to designing these areas, the engineer must consult with the owner to understand their specific needs and preferences for the facility layout. Having adequate turning radii and appropriate queueing distance for haul trucks are vital for operational efficiency.
Landfill owner involvement in the design process is critical. An owner’s preferences may not always mesh with the engineer’s point of view and experience, but they need to be considered in order to build a site that the owner will be comfortable constructing and operating.
John Puls, senior project engineer, and Andy Nickodem, senior consultant, are with Golder Associates Inc. in Green Bay, Wis.