Marion County has awarded SCS the planning, designing, permitting, bid phase services, construction quality assurance (CQA) services, and construction contract management for the approximately 50-acre baseline landfill cell No. 3 closure. The County sought a firm specializing in solid waste, with landfill closure experience in Florida to provide the required design and permitting services, and with the in-house capability to conduct the construction quality assurance (CQA) services required during construction. The entire project is estimated to take three years to complete, with construction spanning multiple rainy seasons.
Weather-related issues during closure construction are one of the critical factors to address. An overly aggressive contractor could strip too large of an existing vegetative area, try to place too much protective cover material over the barrier layer system; either can potentially cause significant erosion during rain events.
The County’s concern about CQA is to prevent placing the protective cover material over the newly installed barrier layer system. Should an unqualified contractor replace the protective cover material on the barrier layer, it will increase construction time and increase the potential for damage to the system. This damage is often not found until the contractor has demobilized from the site, and the facility begins to conduct the required surface emissions monitoring. The resulting repairs to the barrier layer are often a cost the owner incurs, not the contractor.
Based on decades of experience designing, building, and operating landfills, the SCS CQA professionals prevent these types of construction mistakes. Working closely with contractors to ensure construction events are thought through to the operations phases while providing recommendations if the construction plan may encounter potential issues.
“Our entire team is excited to have the opportunity to continue serving Marion County, especially with a project of this magnitude and importance to Marion County,” said Shane Fischer, a vice president with the SCS team. “Our professionals are committed to delivering the highest quality engineering and construction services possible for the long-term success of the project.”
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When the Glades County Sanitary Landfill No. 2 closed, the 6.5-acre Subtitle D landfill provided an opportunity to monitor leachate generation under controlled conditions. With ever-increasing disposal rates at wastewater treatment facilities, and the possibility of wastewater treatment plants refusing to take leachate, studying leachate generation in a controlled environment provided invaluable information.
During the 20-year life span, the facility contained primarily municipal solid waste with a limited quantity of construction and demolition debris. Yard waste and vegetative waste was never landfilled.
During the final cover construction, the geomembrane was welded to the bottom lining system, preventing water from entering the landfill. Due to its small size, only a few passive vents were necessary, creating conditions to trap the landfill gas condensate generated in the landfill.
In this WasteAdvantage article Leachate Generation Trend After Closure of a Subtitle D Landfill, co-authors Ali Khatami and Myles Clewner discuss the leachate generation data collected along with the pre-existing and closed conditions. The authors provide a wealth of information about the leachate generation rate that makes up a significant part of the post-closure financial assurance cost estimate. The data collected provides the opportunity to use a more reliable leachate generation number for cost estimating and prevent over-estimating the leachate disposal cost for the entire 30- year post-closure period.
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The Los Angeles County Board of Supervisors designated Alpine Village in Torrance, a Historic Landmark. The parking lot is a former landfill, and in the early ’70s, SCS Engineers designed building protection/sub-floor ventilation systems for several on-site structures. Once completed, SCS entered into contracts to monitor, maintain, prepare, and submit regulatory reports that the firm still performs well to this day.
“As we celebrate our 50th Anniversary, Alpine Village is an example of one of SCS’s oldest and longest continuously running projects,” said President and CEO Jim Walsh. We’re proud that we provide valuable environmental services to businesses and communities.”
Dave Ross, Senior VP (retired), said, “This certainly underscores SCS’s longevity and sustained superior client service. I can recall the elation when we won the first LFG [landfill gas] monitoring job there…I completed one of the earliest rounds of [air] sampling on the roof of the main building.”
Learn more about SCS Engineers and the award-winning environmental services this employee-owned firm provides.
… according to the experts, and continue through its active life. All along, operators should consider what they will need to show regulators once they are ready to install the final cap.
Choosing the right designer for liquids and gas management is critical. The complexity of landfills varies from site to site, and issues related to conflicts among gas and liquids pipes, and pipes and final cover geosynthetics vary depending on the geometry and other landfill features involved at each location. In short, your designers must understand and work closely with your operations and monitoring team.
The best way to resolve conflicts before the closure is to have a coordinated effort among parties involved in the design to discuss and find solutions to every conflict at the design stage.
The EPA Resource Conservation and Recovery Act (RCRA) requires landfill operators to maintain post-closure care for 30 years, though states will adjust the term according to when they determine ending this care will not threaten human health or the environment. Industry stakeholders say it’s not enough guidance because it does not provide how states should assess for impact on human health or the environment, nor how to determine when to transition from active post-closure care to custodial care. Regulators tend to default to an extension of terms. Again data collection plays a significant role in determining the post-closure care term.
“The whole purpose of the post-closure care term is to provide enough time for landfills to become stable. One way to assess is by determining if functional stability has been achieved, which entails looking at performance metrics like leachate management, settlement, landfill gas control, and groundwater monitoring,” says Bob Gardner, of SCS Engineers.
Looking at these metrics, once it’s determined that functional stability has been achieved, these active systems may be able to be turned off, with only passive controls like cover remaining in place.
Monitoring may be done less frequently or not at all. “EPA acknowledges that back in the 1980s, it did not know how systems, primarily liner systems, would perform under new Subtitle D rules. But based on monitoring of these systems over the past 25 years, we know that they perform well to prevent migration of contaminants to groundwater,” says Gardner.
Read the Waste360 article Stakeholders Call for More Certain Landfill Post-closure Care Terms
Investigate why over 600 landfills use SCS eTools® to track, report, and store important data.
Even the simplest impoundment closures come with design challenges. It is a challenge to navigate project constraints, whether technical, regulatory, or financial, to design and implement an effective closure strategy. Cost often helps to determine the “balance” between project constraints when the future end use of a closed CCR surface impoundment or the property it occupies is undefined. When a post-closure end use is defined, finding balance among project constraints to best serve that future use provides rewarding challenges.
SCS Engineers has navigated this balancing act on impoundment closure projects during generating facility decommissioning. Through a presentation of case studies, you can learn how this team has approached ash pond closure planning and execution where the future use of the impoundment site ranged from undefined to the home of a new solar photovoltaic installation. Examples also include potential future industrial use or property sale.
Case studies will highlight how geotechnical, hydrological, regulatory, or simple physical constraints have influenced the design and implementation of CCR surface impoundment closures.
EUEC 2019 in San Diego, February 25-27, 2019. Conference details here.
As more and more landfill closure projects were built using geomembranes as the final cover barrier layer over the past 20 years, the issue of handling water in the final cover drainage layer became more prominent. Precipitation on closed portions of a landfill leaves the landfill basin in three ways: (1) runoff; (2) percolating into the final cover upper soil layer and then evaporating back out into the atmosphere by evapotranspiration; and (3) percolating into the final cover upper soil layer and reaching the final cover drainage layer, flowing through the drainage layer to the bottom of the landfill slope, and leaving the landfill basin through discharge points to the landfill perimeter ditch. Addressing the runoff component is relatively straightforward because for decades engineers have been designing various types of conveyance systems to handle surface water runoff. Mother Nature takes care of the second component.
The third component, however, took many years to be engineered properly. SCS developed one of the best-engineered systems over 18 years ago and perfected the design over the following five years. The perfected design has been incorporated into the permits of many landfills and implemented at many closure construction events. As a commitment to the efficiency of the design, SCS has been monitoring the performance of many of these closure projects during rain events to gather data and ensure that nothing unexpected occurs during the more severe storm events.
SCS’s system involves a perforated collection pipe embedded in gravel, wrapped in geotextile, and placed in a depression created by a geomembrane flap near the bottom of the slope. The geomembrane flap is welded to the final cover geomembrane and supported in a depressed shape by the upper soil layer of the final cover system. The drainage layer geocomposite ends at the bottom of the depression, delivering the water in the geocomposite into the pipe-gravel-geotextile positioned inside the depression. Installation of the geomembrane flap is at a sloping grade; therefore, the collection pipe ends up sloping toward a low point where a drain pipe that is perpendicular to the perforated pipe takes the water out of the depression and delivers it to the landfill perimeter ditch. The system is fairly easy to install and almost guarantees proper removal of water from the final cover drainage layer. Although other engineers have designed many varieties of such systems, the SCS system has a proven track record with no glitches or side effects at the bottom of the landfill slope.
Some other systems, because of the inherent shortcomings in the design, either don’t remove all of the water from the geocomposite drainage layer, or they clog at the discharge point. Sometimes the water coming through the system adversely affects other landfill components, such as the perimeter berm integrity. Additionally, complexities during construction of the system can conflict with the storm water down chute pipes or landfill gas pipes that may exist above the cover system geomembrane.
In addition to writing the SCS Engineers blog series SCS Advice from the Field, Dr. Khatami speaks about SCS blog topics at SWANA national and local chapter conferences. His webinar Design Leachate Collection Pipes to Eliminate Clogging of Geotextiles will be presented on June 29, 2016. Use the links below to learn more about Dr. Khatami’s advanced landfill designs which last longer and help prevent common operational challenges over time.
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.
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 in the design and permitting of civil and 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. He is also involved in 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.
If you are looking to design a final cover for your landfill, please contact SCS. We will review your particular needs and the existing conditions at your facility and will recommend a proper design that suits your site conditions. SCS will also provide you with construction recommendations and an estimate for construction of the system. Furthermore, SCS will gladly incorporate the final design into your facility permit and prepare construction drawings for implementation of the system.