This article discusses global air quality and how the collaboration between policy-makers and the scientific community can have a continued positive impact on air quality in the U.S. This collaboration has been the primary cause for the improvements observed in air quality over the past few decades.
U.S. Environmental Protection Agency (EPA) programs, such as the New Source Performance Standards (NSPS), New Source Review, and Maximum Achievable Control Technology standards, have all had a significant impact on improving air quality by lowering the ambient concentrations of NOX, VOC, CO, SOX, and PM.
Some areas, such as southern California, have committed to working toward electrifying the transportation network, implementing more stringent standards on diesel fuel sulfur content, and encouraging heavier utilization of public transportation.
Author: SCS Engineers’ Ryan Christman, M.S., is an air quality engineer and environmental management information systems specialist with experience in the oil and gas industry and the solid waste industry. He is just one of SCS’s outstanding Young Professionals.
Vapor intrusion (sometimes known as soil gas intrusion or soil vapor intrusion) is a potential environmental risk that can occur at a wide variety of properties, from former industrial facilities, shopping malls, and even residential properties. Knowing how to assess the risk and mitigate potential harm from soil vapor intrusion is critical to reducing health impacts and mitigating financial and other liability from potential exposures.
What is Vapor Intrusion?
Developers and the public understand that soil and water contamination can pose a health hazard, but vapor intrusion is an environmental health risk that can be overlooked. It is a hazard that can result from both heavy industrial operations and small “mom-and-pop” businesses so that it can be an issue both at industrial properties, suburban strip malls, and even residential developments.
Vapor intrusion is the migration of soil or water contamination from below structures into businesses or homes as a vapor. Common vapor intrusion contaminants from small businesses include benzene from gasoline and perchloroethylene (perc) from dry-cleaners, while large industrial facilities may have a wide range of industrial chemical contaminants. Less common vapor intrusion hazards are mercury, polychlorinated biphenyls, and pesticides.
Determining Whether Vapor Intrusion is an Issue
Environmental due diligence is key to determining whether vapor intrusion is a likely issue. An environmental site assessment (ESA) is critical in assessing the potential for vapor intrusion issues and the current state of vapor intrusion based on past site history. A Phase I ESA will review the current and historical use of the property and surrounding properties to determine where and when potential sources of contamination were present. Leaky underground gasoline storage tanks and poor chemical handling practices at dry cleaners lead to chemical contamination that can create vapor intrusion issues, so the “corner” gas station or the strip mall dry cleaner can be the source of vapor intrusion hazards.
Vapor intrusion can also come from groundwater plumes that originate outside the property boundary, so it is important that any assessment looks for potential contamination issues from nearby properties as well as on-site.
When the potential for a vapor intrusion issue exists, a Phase II ESA should be conducted to determine whether there is contamination, the extent and magnitude of the contamination, and whether the contamination poses a significant health risk. In the Phase II ESA, samples of soil and groundwater are collected from the property and analyzed for evidence of contamination.
If contamination is present, results are compared to screening levels established by regulatory agencies or a health risk assessment (HRA) can be prepared. Either of these strategies can potentially be used to demonstrate that health risks are not significant for the property’s current or future use or to determine the level of remediation necessary.
Dealing with Significant Soil Vapor Contamination
If soil vapor intrusion poses a significant health risk, there are ways to mitigate that risk. Mitigation can include removal of the contamination, active mitigation of the contamination source, and protection against indoor air exposure. The approaches are not mutually exclusive, and multiple risk reduction strategies may be used.
The most effective way of reducing soil vapor risk is to remove or treat the soil or water that is the source. This remediation is the most cost-effective for small sources of contamination and when that contamination can be easily accessed. It is often not feasible to remove the source when contamination originates offsite and moves onto the property in a groundwater plume. It may also be more cost-effective to mitigate risk through other means when the source of the vapor intrusion is extensive or difficult to remove.
In active mitigation, soil vapor intrusion is mitigating by reducing contamination at the source. Active systems can include soil vapor extraction, in which vapor is collected and removed; in situ treatment, which uses chemical reagents to transform the contamination into less toxic chemicals; and containment of the contamination source by some form of barrier. Under ideal conditions, these methods have the potential to be highly effective in reducing contamination but monitor treatment for effectiveness and to determine that the resulting contamination levels are acceptable.
It is also possible to mitigate indoor air exposure to soil vapor intrusion. Underground vents, membranes, and seals beneath the foundation and slab depressurization can reduce the flow of soil vapor into a building. This type of passive mitigation leaves the contamination source in place, which may limit future uses for the contaminated property, but it may be more cost-effective than active mitigation, especially in cases where contamination originates off the property. Regulatory agencies typically require that properties mitigating the movement of soil vapor into buildings monitor the ongoing mitigation on a continuous basis with sensors and alarms or periodic resampling.
What You Need to Know
Soil vapor intrusion is a potential environmental liability, but it is manageable. Environmental due diligence can significantly reduce unforeseen costs of vapor intrusion by identifying the issue for proactive management before development, which is always easier and more cost-effective than trying to address a problem after development. It is possible to mitigate health risk from soil vapor intrusion on developed sites. Developers should work with qualified environmental consultants to address vapor intrusion through each stage of the process to adequately minimize risk.
An essential part of landfills accepting organic matter is the gas collection and control system (GCCS) for controlling odors and landfill gas (LFG) emissions into the environment; the piping network. GCCS design and construction have evolved significantly over the past four decades, from passive venting trench systems to a sophisticated and elaborate piping systems with specialized components for handling LFG, landfill liquids, and condensate flowing through the piping network.
This detailed article discusses best practices and recommendations that GCCS designers keep in mind; careful attention to these details can potentially save landfill operators significant modification costs and inconveniences prior to and during construction of the final covers.
Read the full article published in MSW Magazine.
About the Authors: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. Srividhya Viswanathan, PE, is a Senior Project Manager with over 10 years of engineering experience. David Fisher is an SCS National OM&M Compliance Manager with 18 years of environmental experience.
Som Kundral is a Project Manager with the Miami office. He is currently managing a 500-acre C&D landfill redevelopment project involving multiple engineering disciplines. Som serves clients in the region by providing design and construction oversight of groundwater remediation and landfill gas management systems. He says redevelopment on old landfills pose interesting environmental challenges and can be complex given the heavy involvement of regulatory agencies.
Som was born in 1983 in India, raised in Karnataka, a state in southwest India on the coast of the Arabian Sea. He has two younger brothers, both of whom work in Information Technology. His parents are retired and live in India. He grew up in a typical middle-class family with an emphasis on tradition and culture, where one is taught to respect and obey elders and to protect the young.
As a child, he was curious about how things work and admits to destroying numerous gadgets attempting to reveal their secrets – so engineering was a natural career choice. His father is a Civil Engineer who influenced Som to get a Civil Engineering degree instead of a Computer Science degree. Som has a Bachelor’s degree in Civil Engineering and came to Miami in August 2010, to earn a Masters of Environmental Engineering. While at school, he says he fell in love with the place, the people, and the culture.
Som’s wife, also an engineer, moved from Houston after their wedding in 2012. They enjoy gardening, greenery, and farms. He also collects watches and gadgets. While enamored with motorcycles, once belonging to a biking group as an undergrad, he no longer bikes out of respect for his wife and says he misses it.
Som aspires to become a leader in the industry and wants to grow with SCS Engineers. Som’s mentor is SCS Vice President and Southeast Region Office Director Bob Speed, who states,
I’ve worked with Som for several years. Som accepts tasks regardless of the difficulty and completes each promptly. Our projects usually have numerous stakeholders; Som keeps them informed, so good communications play an important role in keeping our work on-task. I would describe Som as ‘humble, hungry and smart; he truly is an ideal team player for our clients and SCS.
Som is an enthusiastic member of the SCS team. We appreciate his contributions supporting clientele, enhancing our technical reputation, and contributing to our company culture of industry involvement.
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.
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.
It is challenging to restore properties with a past, but you can do it on time and on budget if you plan ahead to address contaminated historic fill. Follow these tips and use the brownfield redevelopment checklist to keep your next redevelopment on track.
Design Phase
Consider how contaminated historic fill impacts the following:
Site feature locations – You can reduce or even eliminate landfill disposal costs by carefully selecting locations for your building, underground parking, parking lot, utility, and green space.
Storm water infiltration – Do you know that storm water infiltration devices must be located in areas free of contaminated historic fill? Infiltration devices cannot be located where contaminants of concern (as defined in s. NR 720.03(2)) are present in the soil through which the infiltration will occur.
Subslab vapor mitigation system – Already know you have contaminated historic fill on site? Consider adding a subslab vapor mitigation system to the design of your new building. It is usually much cheaper to install this system in a new building than to retrofit one into an existing building. It can also mitigate radon gas.
Planning & Design
Determine if contamination requires the following plans to manage the construction phase:
Material management plan – It establishes how you will separate excavated contaminated material from material that is not contaminated. It also outlines how you will handle contaminated material, either by disposing of it off site in a landfill or reusing it on site in an approved area such as a paved parking lot. This plan also covers screening, sampling, and testing contaminated materials, if required.
Dewatering plan – If the development requires excavation through contaminated historic fill to depths below groundwater, you will need a dewatering plan to properly manage discharge of the water. You may be able to discharge the water to the storm sewer or the sanitary sewer depending on the type and concentration of contaminants. You must determine local and state permit requirements before implementing your dewatering plan.
Demolition plan – The demolition plan for removing existing structures during redevelopment should include handling, removal, and disposal of potential contaminants such as lead and asbestos. The demolition plan should also address recycling and reuse of existing on site materials like concrete. You may be able to save money by crushing and reusing concrete on site as fill material, or by hauling and crushing it off site to reuse it as fill at another property. This approach can save you considerable money compared to landfill disposal.
Ready to start saving time and money addressing contaminated historic fill at your next redevelopment? Contact Ray Tierney for help evaluating your options in the Upper Midwest, or using the SCS Brownfield Redevelopment Checklist .
Live in another part of the country? SCS Engineers offers brownfields, remediation, due diligence, and all appropriate inquires services nationwide. Contact us today at .
Learn more about these services at SCS Engineers; read our case studies and articles:
Brownfields and Remediation
Due Diligence and All Appropriate Inquiries
Temporary Landfill Caps
Temporarily capping landfill slopes is becoming a common measure for landfill operators. There are many benefits to closing landfill slopes with geomembrane on a temporary basis. One of the benefits is delaying construction of the final cover. Following is a discussion of the steps that should be taken to determine whether temporarily capping the slope with geomembrane and postponing the final cover construction is a better financial/operational decision.
Cost Burden
Constructing the final cover is costly, and it is considered an unavoidable expense that has no return on the money spent. Therefore, some operators perform a financial evaluation to determine whether the final cover construction costs can be delayed (provided, of course, that such delays are acceptable to the regulating agency). When evaluating whether to delay the final cover, the cost of maintaining the slopes during the postponement period should be considered. The operator must look at the financial aspects of either closing the slopes with a temporary geomembrane or of leaving the slopes open during the postponement period.
Temporary Landfill Capping Option
The benefits of temporarily capping the slopes during the postponement period may include:
The other side of the coin is the expense associated with the temporary cap. There may be repair costs associated with the geomembrane every few years in order to ensure that the temporary cap remains intact.
Leaving Slopes Open Option
The option of leaving the slopes open during the postponement period involves maintenance expenses such as:
The benefits of leaving the slopes open are twofold: first, the operator will save the costs of constructing the temporary cap; and second, the operator will gain additional airspace as waste settles during the postponement period.
Experience with the Temporary Capping Option
As discussed above, both options provide the benefit of gaining additional airspace during the postponement period. Constructing a temporary cap involves the costs of materials and installation, including the geomembrane and the ballasting system that keeps the geomembrane in place. Generally, the financial and non-tangible benefits of a temporary cap that remains in place five years or longer are more attractive than leaving the slopes open; therefore, most operators choose to install a temporary cap. The next step in the financial evaluation should be comparing the costs of the temporary cap to permanently closing the slopes without postponement.
Final Step in the Financial Evaluation
The next question is whether it makes financial sense to postpone the construction of the final cover.
Waste settlement during the postponement period and the resulting airspace are considered the determining financial factor in choosing the right option. If the present worth value of the airspace generated from waste settlement during the postponement period is greater than the cost to construct the temporary cap at the present time, then the temporary cap option would make financial sense; otherwise, the final cover should be constructed without postponement.
It should be noted that the length of the postponement period plays a very important role in this financial equation. Longer postponement periods have the potential for a greater gain in airspace. Another incentive that should be factored into the financial evaluation is the potential return on the money set aside for the final cover construction during the postponement period.
To assist with this financial evaluation, landfill operators are encouraged to discuss these options with their landfill engineers. Settlement models can be performed to calculate the amount of airspace that may be generated during the postponement period as well as the present worth value of the generated airspace. The returns on the final cover construction costs during the postponement will just be “icing on the cake.”
Read the related Advice From the Field blogs from the landfill and LFG experts at SCS Engineers:
Contact the author: Ali Khatami or your local SCS Engineers’ office.
Typical Conditions
The organic matter that is placed in landfills goes through a decomposition process that is exothermic and releases heat inside the landfill space. There are also other exothermic processes such as metal corrosion, hydration, carbonation, and acid-base neutralization that contribute to the heat generation phenomenon in landfills. Municipal solid waste has a relatively low heat conductivity characteristic, which means the heat is not as easily conducted through the waste keeping the landfill interior generally warmer than the areas near the landfill exterior.
Landfills expel the heat in different ways; propagating through the waste mass to the air, ground, leachate, and gas heat sinks. The heat escapes the landfill at its boundaries by convection to the air above the landfill surface and by conduction to the ground below the waste. Heat can also escape from landfills through liquids and gases removed from the landfill. For example, by conduction, via leachate that flows through the waste and is removed by leachate sumps and by convection, and via gases generated inside the landfill that are removed through the gas collection system.
Special Conditions
The large majority of landfills in the country show no signs of special conditions indicating too much heat. The characteristics noted in this blog have been observed in a few large, deep, wet landfills. Field investigations at landfills with high temperatures revealed that the highest temperatures are generally located at mid-point to the two-thirds depth of waste from the top surface. Temperatures as high as 250 °F have been recorded by specialized measuring devices.
Under certain conditions, elevated temperatures may occur inside a landfill, and the excess heat changes the character of chemical reactions taking place in the landfill, such as the decomposition process of the organic matter. Other documented changes that may take place in accumulated heat conditions are: leachate becoming stronger with higher BOD, lower pH, higher carboxylic acids and salts; concentrations of certain acids increasing; carbon dioxide and carbon monoxide generation increasing; the ratio of methane to carbon dioxide decreasing; hydrogen generation increasing; landfill odors changing to a significantly pungent character; landfill settlement rates increasing; gas generation and gas pressure increasing; leachate generation increasing; along with other changes.
Research
Heat generation in landfills is studied by researchers, reported in technical literature and scientific papers by academia and the industry. A summary of the findings related to the amount of heat generated from municipal solid waste in landfills is presented in Table 1 of Heat Generation in Municipal Solid Waste Landfills posted on the California Polytechnic State University, Robert E. Kennedy Library website.
Since the issue of high temperatures in landfills is of extreme importance to landfill operators with respect to compliance, operations, and financial aspects of these cases, finding out the cause and sources of excess heat is a hot subject in the field of landfill science. The largest research grant supporting the on-going research in this field was awarded by the Environmental Research & Education Foundation (EREF) in December 2014. So far, three parts of a technical article explaining chemical mechanisms through which organic matter decomposes and generate various types of other chemicals and heat have been published by the researchers of the above grant in Waste360. The research is on-going, and more information will be published in future. Links to the first three parts of the above article are provided here:
Prevention, Diagnosing and Managing ETLFs
SCS was involved in the preparation of standards for large, deep and wet landfills for a major waste operator in 2016. The intent of the standards is to implement measures to prevent elevated temperature conditions in large, deep, and wet landfills. SCS’s experience at such landfills and its in-depth knowledge can be valuable to those waste operators who are either experiencing elevated temperature conditions in their landfills or want to prevent conditions forming in their landfills proactively.
About the Author: Dr. Ali Khatami
Join SCS Engineers at the Global Waste Management Symposium to learn more, or click these links read about our landfill and landfill gas to energy services, clients, and articles.
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Discovering unexpected pockets of soft soils at the time of construction can delay your project and drive up costs for landfills, support features, and many other types of construction. If you don’t find them, building over them can result in unexpected settlement affecting a structure or building, or cause a slope stability problem for a berm or stockpile. You can avoid both of these scenarios with early investigation and appropriate construction planning.
While landfill development investigations typically require numerous soil borings within the proposed waste limits of the landfill, it’s common to overlook perimeter areas. Pockets of soft soil deposits can be associated with nearby existing wetlands, lakes, or rivers; with wind-blown silt or ancient lake deposits from periods of glaciation; or with fill placed during previous site uses.
The landfill perimeter areas may contain tanks for leachate or fuel, buildings, perimeter berms for screening or landscaping, stockpiles, and other features. A tank or building constructed over soft soils could experience unexpected settlement affecting the performance and value of the structure. The potential for a slope stability problem can increase for a large berm or stockpile built on soft soils.
The first step to avoid these problems and identify problem soils is to include perimeter areas in your subsurface investigation. Perform soil borings or test pit excavations at the locations of the proposed perimeter features such as tanks or berms. If you encounter soft soils, address them like this:
Contact SCS’s geotechnical engineers for more information on how to find and test soft soil areas early in a landfill’s project schedule, so you can effectively address associated construction issues in a way that considers cost and minimizes unexpected project delays.
Pat Sullivan discusses two case studies that provide examples of two different approaches to odor management. The proactive approach resulted in a more positive outcome than the reactive approach. Although the odor issues never go away completely, the proactive facility has avoided lawsuits and regulatory enforcement and continues to have a positive working relationship with the community.
SCS Engineers freely shares our articles and white papers without imposing on your privacy.
Click to read Part I of this two part series. We’ll let you know when Part II is published soon.
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