Landfills, especially large regional landfills, are huge enterprises with many different operations ongoing daily. A landfill’s tangible assets are equipment, buildings, machinery, construction materials in the ground, or stockpiled to support various operations. Of all these, the most significant asset is the permitted airspace. It’s undoubtedly a non-tangible asset when permitted, but gradually this asset gets consumed as it turns into revenue.
Creating landfill airspace during a design/permitting process involves the operator hiring a landfill engineer to develop the concept of the airspace, prepare an appropriate design with engineering methods, and obtain a permit for it through regulatory agencies. In a sense, a portion of your future revenue is in the hands of your landfill engineer. You depend on this engineer to create the maximum amount of airspace, generating the maximum amount of revenue for your operation over time. Your engineer is supposed to be your trusted partner, and you are investing an enormous amount of capital for the design, permit, and construction based on the work performed by the engineer.
In some instances, the operator leaves most of the technical decision making to the engineer. On other occasions, the operator is in the loop during the engineer’s design, but the operator is not heavily involved in the nuances of the disposal cell’s layout in consideration of the existing terrain. In either case, the engineer is significantly responsible for achieving the maximum amount of airspace. The multi-million dollar question is whether you could have had another 3 million or 5 million cubic yards of additional airspace in your permit. How do you check if your landfill engineer maximized airspace in the design?
Assuming proper training, most landfill engineers can design adequate landfills. Still, very few landfill engineers have the unique talent and experience that can maximize airspace within specific design parameters. You, as the operator want engineers with a proven track record of maximizing airspace in their landfill designs, and do not let relationships or political nuances affect your judgment during selection because tens of millions of dollars of additional revenue are at stake.
A trained landfill engineer may miss details that a highly qualified engineer would not. Incidentals here and there, if recognized and accounted for, can add significant airspace to the design. These details vary from site to site, and it’s up to the engineer to recognize the benefits of geometric and regulatory opportunities to add to the covered airspace. These details could be in the form of:
Special geometries for the landfill slopes,
The lateral extent of waste limits,
The landfill footprint placement within the terrain,
The extent of excavation for establishing bottom grades for disposal cells,
The relative position of base grades with respect to the groundwater elevations,
Combining leachate collection sumps among two or more disposal cells,
Steeper slopes to increase airspace while staying within the bounds of regulatory requirements,
Positioning peripheral systems in a different way to benefit from additional land to add to the landfill footprint,
Considering future expansion down the road and planning appropriately, and
Other nuances that an expert considers.
The operator chooses the project manager or the primary engineer for the design of a greenfield landfill or an expansion to an existing landfill, knowing that the work performed by the selected engineer could potentially add to or take away hundreds of millions of dollars from the bottom line of your enterprise. So, pick your engineer based on the engineer’s prior design track record and make sure the engineer is an expert in maximizing landfill airspace.
SCS is an expert, highly experienced landfill designer – relied on by many landfill operators as a trusted partner. Our culture is to serve our clients as if their project is our own, and we do not consider ourselves successful unless our clients are satisfied. These close relationships help us serve the majority of our clients on a long-term basis, with decades of continuous service and value.
SCS will gladly evaluate scenarios for your landfill expansions that you are planning to design and permit, and provide you with a preliminary estimate of airspace gain and revenue that an SCS design could bring, potentially increasing your primary asset by another tens of millions of dollars. Now that’s a value statement!
About the Author: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.
The industry is designing and building more substantive drainage features and larger collection systems from the bottom up, that maintain their integrity and increase performance over time, thus avoiding more costly problems in the future.
Waste360 spoke with three environmental engineers about what landfill operators should know about liquids’ behavior and what emerging design concepts help facilitate flow and circumvent problems such as elevated temperature landfills, seeps, and keep gas flowing.
The engineers cover adopting best practices and emerging design concepts to facilitate flow. They cover topics such as directing flow vertically to facilitate movement to the bottom of the landfill, drainage material, slope to the sump percentages, vertical stone columns, installing these systems at the bottom before cells are constructed, and increasing cell height to prevent the formation of perched zones.
Ali Khatami, one of the engineers interviewed, has developed standards for building tiered vertical gas wells that extend from the bottom all the way up. He frequently blogs about landfill design strategies that his clients are using with success. His blog is called SCS Advice from the Field. Dr. Khatami developed the concept of leachate toe drain systems to address problems tied to seeps below the final cover geomembrane. These seeps ultimately occur in one of two scenarios, each depending on how the cover is secured.
Landfill Gas Header: Location and BenefitsBy continuing to design gas header construction on landfill slopes, all of the components end up on the landfill slope as well. You can imagine what type of complications the landfill operator will face since all of these components are in areas vulnerable to erosion, settlement, future filling, or future construction. Additionally, any maintenance requiring digging and re-piping necessitates placing equipment on the landfill slope and disturbing the landfill slope surface for an extended period.
AIRSPACE, the Landfill Operators’ Golden EggAirspace is a golden egg, the equivalent to cash that a waste operating company will have overtime in its account. With each ton or cubic yard of waste received at the landfill, the non-monetary asset of airspace converts positively to the bottom line of the …
Gas Removal from Leachate Collection Pipe and Leachate SumpKeeping gas pressure low in and around the leachate collection pipe promotes the free flow of leachate through the geocomposite or granular medium drainage layer to the leachate collection pipe and improves leachate removal from the disposal cell. Using gas removal piping at leachate sumps is highly recommended for warm or elevated temperature landfills where efficient leachate removal from the leachate collection system is another means for controlling landfill temperatures.
Leachate Force Main Casing Pipe and Monitoring for LeaksLandfill operators may add a casing pipe to their leachate force main for additional environmental protection. Consequently, the leachate force main is entirely located inside a casing pipe where the leachate force main is below ground. In the event of a leak from the leachate force main, liquids stay inside the casing pipe preventing leakage …
Pressure Release System Near Bottom of LandfillsPressure Release System Near Bottom of Landfills – Essential Component for Proper Functioning of the Landfill Drainage Layer. Landfill designers are generally diligent in performing extensive leachate head analysis for the design of the geocomposite drainage layer above the bottom geomembrane barrier layer. They perform HELP model analyses considering numerous scenarios to satisfy all requirements …
Landfill Leachate Removal Pumps – Submersible vs. Self-Priming PumpsSelf-priming pumps can provide excellent performance in the design of a landfill leachate removal system. Landfill owners and operators prefer them to help control construction and maintenance costs too. A typical system for removing leachate from landfill disposal cells is to have a collection point (sump) inside …
Welcome to the SCS Advice from the Field blog series.
Airspace is a golden egg, the equivalent to cash that a waste operating company will have overtime in its account. With each ton or cubic yard of waste received at the landfill, the non-monetary asset of airspace converts positively to the bottom line of the waste operating company’s books.
The larger the airspace, the larger the non-monetary asset, and the larger future cash potential in the account.
Therefore, it is extremely important to design landfill footprints optimally in consideration of planned operations at the site, and design landfill features maximizing airspace within the selected landfill footprint.
Optimization takes into consideration the land available for development, including the various facilities and systems necessary for operations. The type of design, depth of landfill, base slopes, leachate collection pipe slope, perimeter berm geometry and size, slopes of landfill side slopes, terraces on slopes, and many other parameters determine the airspace volume available to the landfill operator. The designer’s goal is to provide the most volume to the landfill operator.
How does the operator know that a proposed design is maximizing airspace?
If SCS is the site designer, the maximization of airspace is inherent in proposed designs for permitting. On numerous occasions, when SCS is not the site engineer, our designers have proposed a re-design of landfill features to maximize the airspace within its permitted footprint. Under these circumstances, it is not easy to convince a landfill operator of the benefits of SCS’s proposal. Naturally, one assumes a designer would not propose a lesser design on paper and carry it through the high cost of permitting, so it is common for the landfill operator to express doubts about our proposed changes. Once the operator and SCS review the technical design changes in detail, the demonstrated value becomes apparent. It is not a simple process, but on every occasion, we have successfully increased the airspace for the client, increasing potential revenue for millions of dollars beyond the originally permitted amounts.
Driven by the success of our clients, it is our culture to serve our clients completely as trusted professionals making your challenges our own. SCS is proud to say that at the date of this publication, our designers have created over $400,000,000 of additional financial benefit out of thin air for clients at a dozen landfills with more efficient landfill base grades that maximize airspace and cost less to construct.
As we move toward our 50th year, we hope to continually improve, evolve, and strive to maximize airspace at more landfills, adding value to our clients’ bottom line. Contact our nearest office if you are interested in a landfill evaluation for maximizing airspace and reducing construction costs. As always, our SCS authors are available to answer your questions or comments.
About the Author: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.
When the Federal Coal Combustion Residual (CCR) rule went into effect in 2015, it was a new regulatory layer on top of a widely varying landscape of state regulations affecting CCR management in impoundments and landfills. Some states already had significant regulations on the books for CCR impoundments and/or landfills, while others did not.
Where state regulations existed, they varied widely from state to state. While a few states have moved toward closing the gap between state and Federal CCR requirements, many utilities continue to face confusing and conflicting requirements coming from different regulatory programs as they move ahead with managing their CCR facilities.
In her paper entitled State vs Federal CCR Rule Regulations: Comparisons and Impacts, Nicole Kron shares state-versus-federal regulatory challenges utilities have encountered during landfill design and management, impoundment closure, and groundwater monitoring and reporting since the implementation of the Federal CCR rule. For example, some sites have completely distinct groundwater monitoring programs under state-versus-federal rules, with different well locations, well depths, and monitoring parameters for the same facility. She highlights unique approaches to bridging regulatory gaps and resolving regulatory conflicts between state and Federal CCR requirements. Ms. Kron also provides insights gained on the long-term potential for regulatory resolution of these issues based on discussions with state regulators in multiple states.
SCS Engineers Hydrogeologist Nicole Kron, recently finished her second session of Skype a Scientist, a program in which she Skypes with classrooms and talks to kids about her work as a professional geologist and her journey to become a scientist.
About the Author: Nicole Kron has nearly a decade of experience in the environmental consulting field. Her experiences focus on groundwater quality analysis of sites contaminated with coal gasification byproducts, coal combustion byproducts, chlorinated solvents, petroleum products, metals, and PCBs. Her experience includes managing team task coordination, groundwater modeling, and statistical analysis of CCP/CCR sites. She is experienced in planning and performing soil and groundwater contamination investigations, air monitoring, well design and installation, and soil and groundwater sampling.
Today’s landfill design professionals can help eliminate unsafe configurations and institute features that can proactively warn of and minimize hazards for operator and customer safety. Designers consider subgrade conditions, geotechnical factors and regulatory requirements when specifying how steep a landfill may be constructed.
The practical aspects of landfill operations and maintenance play a significant role in slope configurations since the landfill must provide safe access to monitoring points, environmental control features, and mowing.
Bob Gardner highlights the most important features to consider for landfill cells, including the design and construction phases of the entire landfill’s infrastructure. Bob covers a broad range of topics including:
State regulations
Site monitoring
Signage
Site access and traffic considerations
Citizen convenience centers
Many states regulate the maximum design slope, and although these vary, it is up to the landfill designer to take practical, safety and regulatory considerations into account when establishing the slope configuration. Bob recommends working closely with the field staff to incorporate a design that is user-friendly, effective and safe.
It is a general misconception that leachate seeps stop or disappear when slopes receive the final cover. In fact, it is only true if the source of leachate is located directly below the cover, but in most cases, the leachate originates from another location. Continuing seeps eventually reach the bottom of the slope, where two scenarios can happen depending on how the final cover geomembrane is secured at the landfill’s perimeter.
In the first scenario, where the geomembrane is anchored in an anchor trench, liquids will gradually flow underneath the cover geomembrane in the anchor trench and enter the perimeter berm structure. Leachate entering the berm structure softens the berm’s structural fill adversely impacting its shear strength. Additionally, leachate gradually seeps through the berm structure and enters natural formations below the berm and possibly into the groundwater. The operator is alerted when monitoring shows a localized structural failure or a groundwater impact in a nearby groundwater monitoring well.
In the second scenario, where the final cover geomembrane is welded to the bottom lining system geomembrane, leachate seeping out of the slope reaching the toe of the slope accumulates at the toe because it has nowhere to go. Accumulation of leachate behind the final cover geomembrane forces water to gradually move laterally along the landfill perimeter berm behind the final cover geomembrane damaging a larger area behind the final cover. Vertically, more of the area above the toe of the slope becomes engaged by the accumulating leachate. The two obvious consequences are the softening of the soil layer below the final cover geomembrane at the toe of the slope and the water-bedding effect of the area near the toe of the slope.
In the first scenario, the operator has to handle a non-compliance issue, either a failure in the slope or impacts to groundwater. In the second case, the leachate remains contained, but the operator has to address the issue by opening the final cover and removing leachate accumulated behind the final cover geomembrane. The geomembrane opening is closed, and final cover soils are restored after liquids are removed. Both are costly and complicated solutions. Moreover, the problem does not end after completion of the repair because the source of leachate seep is not eliminated.
Landfill operators can require their engineers to design a leachate toe drain system located at the toe of the slope and connected to the leachate collection system at the bottom of the landfill before the final cover geomembrane is installed. The leachate toe drain system is the only way to collect and route leachate to a location at the bottom of the landfill constructed for removal of leachate.
If you are closing a portion of your landfill slope and you find no leachate toe drain system in the construction plans, you can ask for a system to be added to the design plans before the commencement of the construction project.
SCS has significant experience with various types of leachate toe drain system constructed at different locations under various conditions. If you like to know more about the design of leachate toe drain systems or if you are looking for an experienced engineer for the design of your next final cover contact SCS.
Landfill base grades not only make leachate collection and removal possible but also have a significant impact on the amount of landfill airspace. For landfill operators, airspace is the primary asset, because it represents the level of revenue the operator can expect. Airspace is a commodity to be maximized.
Operators expect to get the most airspace from their landfill designer and depend on the engineer to design the grades to maximize it. Placing your trust in an engineer is a noble matter, but as the operator, you check, verify, and confirm that what the designer has engineered is what is needed to provide you with the expected value. An experienced landfill designer looks for ways to provide airspace above and beyond the operator’s expectations.
SCS has been in the business of designing landfills for nearly half a century. We have significant experience in optimizing landfill designs and maximizing airspace. SCS is often retained to design a new expansion to an existing landfill. Upon starting work we analyze the entire facility holistically to see all of the potential ways to maximize airspace around and above the existing landfill. Every cubic yard of additional airspace is a big achievement for our clients and in turn for us.
SCS often evaluates permitted, yet to be developed, base grades for operators. The intent is to determine whether additional airspace can be achieved by applying a different design to the base of the landfill. SCS has turned the science of geometry into mathematical models utilized to quickly evaluate base grades. Specific parameters of the currently permitted base grades are plugged in the mathematical model along with those of the alternative and the model provides quantitative values (cubic yards) of the difference between the permitted grades and the alternative. The values are quickly returned. After modeling, the operator may decide to modify the design to gain the additional airspace based on the alternative design. Contact us to work with our landfill design experts to assist you with an evaluation.
Sometimes geosynthetic material specifications for a specific project, i.e., lining system or final cover system, is a performance-based specification which does not specify the type of product for use in construction. What does the engineer need to do when the selected contractor submits a product for approval in accordance with a performance-based specification? What should the engineer do when the owner purchases the material and identifies a product for use based on the performance-based specification?
Specifications that SCS has prepared are performance-based and include a qualifying procedure whether the product is introduced by a contractor or owner. This qualifying procedure is specifically left to the engineer to carry out by laboratory testing of typical samples of the specific product for use in construction. Typical reported values by the manufacturer or test results submitted by the contractor or owner are not acceptable under these procedures. Since the engineer is taking the liability of accepting a specific type of product for his or her project, the engineer should have the right to perform laboratory testing before the product is approved for use in the project, that only makes sense in the world of taking liabilities!
The testing performed by the engineer for qualifying a product do not count toward conformance testing of materials delivered to the site. The qualifying procedures are solely for accepting a certain type of product to be used in the project, but the specific rolls of pre-qualified product manufactured for use in engineer’s project must go through the required conformance testing specified in the specifications before use in the project.
The process of qualifying a product, ordering the qualified product, and performing conformance testing on the pre-qualified materials takes time. Engineers need to consider the amount of time necessary for the involved stages of approval into the construction schedule. If using material purchased by the owner, the owner needs to keep the timeline in mind to allow the engineer to carry out all necessary testing for the approvals to be in place before construction begins.
Repeating the qualifying procedure for a product from one project to the next depends on how the performance-based specification is written. Sometimes, the engineer accepts a product that was qualified for use in a prior project as long as the product has not changed since last used in accordance with statements by the manufacturer. If the performance-based specification includes such options, SCS highly recommends identifying the period between a prior project and the next project in the specification. In some cases, this means the product must go through a qualifying process even if it has not changed for many years but the previous set of qualifying data is older than a certain number of years. The period is based on the engineer’s judgment, but most professionals normally use five years in their specifications. During a five-year period, if the product changes or there are indications that the product might have changed due to recorded changes in certain reported values by the manufacturer, the qualifying process must be followed irrespective of the number of years passed since a recent past project to maintain quality and minimize risk.
Landfills are getting larger in height and greater in footprint area, but the location of leachate tanks, leachate ponds, or discharge points to an on-site or off-site leachate treatment plant usually don’t change.
A larger footprint means leachate force mains are getting longer and pumps have to work harder to push leachate through the system to a target point. Some operators carry on with the same pumps for decades and don’t monitor the performance of the pumps after expanding the landfill footprint.
SCS highly recommends that you evaluate the performance of the existing pumps again. Such an evaluation may require hydraulic analysis of the entire network of pipes along with pumps, or whatever segment of the network that is affected by the expansion. The effort is minimal in retrospect, but the operator makes sure that the system will function in an optimized zone with minimal wear on the pumps.
Sometimes the hydraulic evaluation may require up-sizing all or certain pumps in leachate sumps because not enough flow can go through the force main due to high friction loss in the expanded leachate force main. Up-sizing pumps may be achievable depending on the type of the leachate sump, i.e., riser system or vertical manholes. If the up-sized pump in a riser system is too long to fit inside a riser system or too long to the point of making routine maintenance too cumbersome, your engineer needs to come up with another idea.
Booster pumps along an expanded leachate force main can certainly be an option. Booster pumps can be the inline or offline type. Install the inline pumps on the actual force main, and position the offline type on the side so that liquids go through bends and elbows to reach the pump, and again through bends and elbows to get back in the force main. In either case, the booster pump adds hydraulic energy to the flow inside the force main to push the liquids at a higher pressure and velocity through the remainder of the force main and to the target point.
Operators need to be aware of the dynamic nature of the leachate piping network and the role of booster pumps in dynamic environments. After landfill expansion, with new cells coming online -increasing leachate generation, and when closing landfill slopes -decreasing leachate generation over time, the flow in the force main may change. Sometimes booster pumps have to be up-sized or down-sized depending on flow and pressure in the system.
We continue SCS’s Advice from the Field blog series with guidance from an article in MSW Magazine by Daniel R. Cooper, Jason Timmons, and Stephanie Liptak.
Planning a landfill gas collection system before collection is required can increase the long-term benefits for multiple stakeholders.
The authors of a recent article in MSW Management Magazine present engineering ideas that provide for more efficient construction of a GCCS. Gas system operators will benefit by having fewer pumps to operate and maintain and shallower headers that are more easily accessible. Odor management will be easier along with other benefits.
Read the full article here to learn about the design elements for maximizing long-term benefits, impacting: bottom liners, location of the blower/flare station, leachate risers, extraction well targets, and external header piping.
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About the Author: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.
