Landfill gas (LFG) fired leachate evaporation is a novel technology attracting the attention of landfill owners because it can offer an operational win-win. The technology uses a readily available resource at landfills, LFG, to remove liquid from landfill leachate via evaporation, thus abating this environmental liability onsite, often at a lower cost than conventional leachate treatment options. In addition, combusting LFG to evaporate leachate converts methane, a highly potent greenhouse gas, to carbon dioxide, which reduces overall greenhouse gas emissions.
Landfill owners seeking to implement LFG-fired leachate evaporation must undergo the necessary air permitting and follow applicable emissions regulations. In this regard, air permitting and regulatory requirements for the combustion-related component of LFG-fired evaporation are similar to those applicable to conventional LFG flares. However, in addition, there are permitting considerations for evaporation-related emissions too. As this is uncharted territory for regulators, it is important to work closely with your agency to ensure you or your consultant is properly addressing these technology-specific requirements.
Read Landfill Leachate, Just ‘Evaporate’ the Problem …or Permitting Issues for Using Landfill Gas to Reduce Leachate Volume by David Greene, PE, SCS Engineers. Published by em, the Magazine for Environmental Managers, A&WMA, issue June 2019.
About the Author: David Greene is a project manager at SCS Engineers with a multiplicity of solid waste related environmental engineering experience, including air permitting, landfill gas, financial analysis, due diligence efforts, regulatory development and analysis, compliance planning, greenhouse gas monitoring, emission inventory including emission factor development, SPCC and SWPPP development. Mr. Greene also consults internationally in Southeast Asia focusing on the areas of planning and implementing training and evaluating the feasibility of LFG energy and renewable energy projects at solid waste disposal sites. He is a Professional Engineer in North and South Carolina.
Landfill operators are seeking new means to dispose of leachate generated at their facilities more economically. Rising costs of leachate treatment at publicly owned treatment works (POTWs) obliges landfill operators to look for alternative disposal means at a lower price. These situations encourage landfill operators and consultants to do more with less when designing preventative solutions to reduce leachate generation in the first place.
Upstream measures to reduce leachate generation range from standard operating procedures to innovative ideas with significantly high benefit to cost ratios. SCS compiled a list of our Top 10 measures to consider, including:
1. Grading – Creating landfill plateaus to maximize rainwater runoff toward perimeter storm water ditches, using low permeable soil to seal landfill slopes that will not receive waste for an extended time.
2. Caps & Covers – Using temporary geomembrane caps over areas that will not receive waste for a long time. Constructing final cover over landfill final slopes to eliminate rainwater percolation into landfill.
3. Swales – Constructing temporary and strategic swales on landfill outside slopes to capture rainwater runoff before causing soil erosion on the slope and to convey runoff water to perimeter ditches.
4. Berms & Downchutes – Constructing temporary berms and swales on landfill slopes that drain toward new disposal cells to capture water before reaching waste in the new cell and directing water to perimeter ditches. Also, constructing a berm at the crest of slopes to minimize the flow of rainwater runoff over slopes that are causing soil erosion. Constructing engineered temporary and sturdy downchutes for rainwater runoff from top areas of the landfill to the perimeter ditches.
5. Tarps – Installing rain tarp over a portion of a new cell that will not be in service for some time.
6. Exposure – Minimizing exposure of the active face while the remaining areas are properly graded to shed rainwater runoff to perimeter ditches.
7. Shedding – Grading the top area of each lift to shed rainwater runoff to outside slopes and the perimeter ditches.
8. Plantings – Installing sod or seeding on exterior slopes and those interior slopes that will not receive waste for an extended time to reduce soil erosion.
9. Roads – Constructing ditches adjacent to access roads to safely convey runoff water to the bottom of the slope – pitching access roads toward the ditch adjacent to the road, and building a proper road surface to minimize erosion during severe storms while lasting long under traffic loading.
10. Maintenance – Establishing routine maintenance protocol for the aforementioned measures because regular maintenance sustains long life and performance.
For facilities outside the landfill area, special measures, such as using floating covers on leachate ponds or canopies over operations that could potentially generate leachate without the canopy, also help reduce leachate generation.
Upstream measures are not necessarily limited to our Top 10 list but depend on the type and extent of operations at a facility. The will of the landfill operator and the expertise of the solid waste engineer can go a long way to reducing leachate generation at landfill facilities, and we all strive for that.
More about Liquids Management including case studies.
Many landfill operators and owners are now spending more than 10 or 20 cents per gallon for leachate management, which can become quite costly. One of the primary reasons that leachate management has become an expensive challenge in the United States is more stringent regulatory policies regarding the discharge of liquids into public waters. The regulations affect publicly owned treatment works (POTW), which has led some POTWs to require that leachate entering their plants have adequate pre-treatment to remove contaminants. Under these circumstances, some landfills are forced to collect and haul their leachate to a different POTW or to consider installation of pre-treatment equipment themselves.
Each landfill needs a solution to its leachate management issues that depends on applicable regulatory restrictions, the capability of the local POTW, and the leachate composition. Due to chemical reactions and biological activity inside the landfill, the leachate’s temperature is frequently warmer than area groundwater. Also, leachate is odorous, and generally brown in color, with colloidal suspended solids. The composition of leachates depends on the composition of a landfill’s waste, the landfill’s decomposition stage, and weather conditions. Many factors are evaluated to arrive at an efficient and economical treatment method for disposal of landfill leachate.
There are some treatment alternatives available to reduce the high organic and nitrogen loads in leachate. For some leachate applications, the treatment methods are sufficient to allow the POTW to process the leachate safely. If treatment is not possible, or cost prohibitive another alternative is to pre-treat the leachate, lowering the contaminant load to prevent subsurface precipitation, and then dispose of it using deep well injection. Some states require little or no pre-treatment before discharging leachate to deep injection wells.
The following technologies are available for the pre-treatment of landfill leachate: biological processes for wastewater treatment such as membrane bioreactors, sequencing batch reactors, activated sludge processes plus reverse osmosis. Wet oxidation processes, activated carbon adsorption, as well as precipitation, coagulation, and flocculation techniques are also used, depending on the contaminants and their concentrations. These two counties are using a combination of treatment technologies for their leachate management strategies.
Effective leachate management applies unique combinations of technologies which most adequately address the previously mentioned factors. To provide a truly sustainable solution to leachate management, SCS suggests another approach, which is to consider the landfill design and operations as part of the solution. By using the existing landfill design and operations, SCS develops an integrated approach to leachate management that is preventative. The benefits of using an integrated approach are that they are often a more cost-effective solution in the long-term, sustainable, working with the existing landfill’s infrastructure.
Waste Management is using an integrated approach at Monarch Hill Landfill in Pompano Beach, Florida. Monarch Hill Landfill is a 385-acre landfill with a waste flow of 5,000 tons per day. SCS helped decrease leachate formation as part of overall landfill design and operation. Waste Management reduced leachate formation using the following methods:
Temporary caps – SCS designed and provided monitoring services during installation of a 10-acre temporary geomembrane cap over a portion of the top intermediate plateau of the landfill. It reduced leachate generation, decreased odors, increased gas collection efficiencies, and addressed leachate seeps on the slope, as well as making surface water runoff over the top of the landfill easier and more efficient.
Final covers – SCS designed, permitted, and provided monitoring services during construction of six partial closure projects. The final covers were equipped with leachate toe drain systems below the final cover geomembrane, enabling leachate seeps to be collected and disposed of efficiently. The design also allowed collection of gas from the lower portion of the slope after completion.
Rainwater Toe Drain Systems – SCS designed a toe drain system above the final cover geomembrane that enabled water to be collected and diverted to the landfill perimeter ditches, preventing pore pressure build up and keeping the system stable.
Tack-on Swales – SCS designed tack-on swales that were implemented to catch runoff and convey water to downchute pipes. The swales could be easily adjusted based on the size of each partial closure and the overall management of stormwater.
Our approach is to develop a robust, tailored liquids management program comprised of the most appropriate technologies and engineering design to tackle the unique set of challenges facing each landfill client. In an era of doing more with less, clients find our programs are more cost-effective because they are more efficient and well designed.
Darrin Dillah: Landfill Leachate – Upstream
Ron Wilks: Landfill Leachate – Downstream and Evaporators
Monte Markley: Deep Well Injection
Bob Speed: Dewatering
Ali Khatami: Landfill Engineering and Construction Impacts on Liquids Managment
Sam Cooke: Industrial Wastewater Treatment
As a designer, I’ve been hired to correct inconsistencies between the gas system and the landfill too many times. Today’s blog is about the most important factors that all landfill gas designers should consider for a gas system to coordinate efficiently with the landfill design as permitted. This is a partial list of best practices developed at SCS Engineers.
Considerations for Design of Gas Collection Systems for Landfills:
1. Include the final cover layers in the gas design details where gas wells are installed near the landfill final surface. This inclusion will help the designer to specify proper heights for gas wells, proper depths for gas headers and lateral pipes, and proper heights for condensate sumps within the lined area of the landfill. Otherwise, locations of these elements may end up being in conflict with the location of various layers of the final cover system to be constructed later.
2. Always leave pipes exiting the liner boundary at the perimeter of the landfill at least 1 ft above the anchor trench shoulder. When the final cover is installed, it would be impossible to install a geomembrane boot over at the cover geomembrane penetration point of a pipe that is in contact with the bottom lining system geosynthetics over the anchor trench shoulder.
3. If flow control valves are located below the final cover near the perimeter of the landfill, design a vertical casing around the valve tall enough that future final cover can be booted to the vertical casing and access to the valve would be possible. Do not use corrugated material as casing because it would be difficult to place a geomembrane boot over corrugated casings. The designer should require sealing the void inside the casing pipe to prevent landfill gas release or oxygen intake through the void. If the control valve is located above the final cover, the designer should specify a proper height for the casing pipe that access to the valve stay above the final cover surface.
4. Locating flow control valves near the landfill perimeter and within the lined area should be in consideration with the future location of a rainwater toe drain system at the toe of the slope that will be constructed when the final cover is constructed.
5. Condensate sumps installed before construction of the final cover should be tall enough to accommodate construction of the final cover system around the condensate sump with sufficient space to boot the final cover geomembrane to the exterior walls of the condensate sump. Miscellaneous stub outs on the condensate sump should be designed in consideration of having enough space for the geomembrane boot in the future.
6. Pipes connected to a condensate sump (such as compressed air line, discharge force main, power conduits, etc.) should be positioned such that boots can be placed on each line at the penetration point of the pipe through the final cover geomembrane. Boots may not be placed on pipes clustered together. If boots are placed on a pipe cluster, the designer should require sealing the voids between the pipes within the boot to prevent landfill gas release or oxygen intake through the voids.
7. Gas pipes located above the final cover geomembrane and crossing terraces on landfill side slopes may create conflict with rain water toe drain at the terrace. The designer should design terrace crossings such that future conflicts can be avoided.
8. Gas pipes crossing an access road on the landfill slope may cause conflict with a ditch adjacent to the access road at the final cover surface. Location of the gas pipes, either below or above the final cover geomembrane, should be designed in consideration of the final cover features that will exist in the crossing area in the future.
9. Gas pipes located above the final cover geomembrane and crossing an access road on the landfill slope may cause a conflict with a rainwater toe drain system above the final cover geomembrane running parallel to the access road at the toe of the slope next to the access road.
10. Gas pipes located above the final cover geomembrane and crossing the access road on the landfill slope may cause road grade problems at the final surface. Specific depressions across the access road width may have to be designed for larger pipes to prevent grades problem at the finish surface.
11. Gas pipes located above the final cover geomembrane may cause conflict with storm water downchutes that will be installed above the final cover geomembrane. Special depressions may have to be designed to place downchutes below gas pipes on the slope. Placing gas pipes above downchute may cause a problem with the flow of condensate in the line.
12. Sometimes horizontal gas collection pipes come out of the landfill side slopes and extend down the slope to a gas header or some other component of the gas system. If the pipe segment on the slope is going to be below the final cover geomembrane, then it must be placed deeply enough in the waste that it would not have any conflict with the final cover system components, such as leachate toe drain systems, terraces, access road ditches, etc. If the pipe segment is going to be above the final cover geomembrane, extension of the horizontal pipe connecting to the pipe segment on the slope will be designed such that the horizontal pipe can penetrate the final cover geomembrane and extend down the slope while located above the final cover geomembrane. Extension of the pipe on the slope above the final cover geomembrane should not cause any conflict with the final cover components, such as rainwater toe drains at terraces or at the toe of the slope next to the perimeter berm, downchute pipes, terrace or access road grades, etc. The elbow at the connection of the horizontal pipe to the pipe segment on the slope and above the cover geomembrane is critical because a geomembrane boot must be installed at the penetration point.
13. If tack-on swales are used on the landfill slopes, gas pipes on top of the final cover geomembrane may cause conflict with the flow line inside the tack-on swales. Large headers should cross tack-on swales at the high-end point of adjacent swales to prevent flow problems in the swale.
14. If tack-on swales are used, the location of wells for drilling purposes should be chosen to be outside the tack-on swale structure.
15. If a gas header located above the final cover geomembrane and crossing a terrace or access road where the terrace or access road is sloping toward the landfill, condensate flow through the gas header may become an issue. Special depressions across the terrace or access road may need to be designed such that condensate can flow in the proper direction.
SCS Engineers is a leader in the design of landfill gas and landfill lining and final cover systems. We evaluate these issues and many others during our landfill gas design work; our clients pay only once for construction of the system and do not have to spend additional money in the future to fix a system that could have been constructed correctly in the first place. Learn more here.
Dr. Khatami has acquired extensive experience and knowledge in the areas of geology, hydrogeology, hydrology, hydraulics, construction methods, material science, construction quality assurance (CQA), and stability of earth systems. Dr. Khatami has applied this experience in the siting of numerous landfills and the remediation of hazardous waste contaminated sites.
Dr. Khatami has been involved with the design of gas management systems, hazardous waste impoundments, storage tank systems, waste tire processing facilities, composting facilities, material recovery facilities, landfill gas collection and disposal systems, leachate evaporator systems, and liquid impoundment floating covers. He has also been involved in the design and permitting of civil/environmental projects such as surface water management systems, drainage structures, municipal solid waste landfills, hazardous solid waste landfills, low-level radioactive waste landfills, leachate and wastewater conveyance and treatment systems.
Contact Dr. Khatami directly to answer questions and comments.