H2S threshold

May 24, 2021

landfill odor control

It goes without saying: landfill operators are forever working to stay on top of odors, especially when the community smells something and points to the landfill or when regulators come calling. This blog shares two odor stories: one around landfill gas and another around trash. Then it looks at what happened when an operator got a permit restriction over alleged hydrogen sulfide emissions; odor was not the problem here. It was a perceived health risk; learn how SCS proved a predictive model was off the mark.


Is Landfill Gas a Source of Community Odors? And Ensuring Compliance

Living up to landfill odor nuisance standards is tough. The underlying premise is that odors must limit peoples’ ability to enjoy life or property to create a public nuisance, but it’s a subjective call. How strong an odor is and sometimes even if it exists depends on perception, so the question becomes: when they aren’t sure what they are being measured against, how do operators comply and prove compliance?

SCS recently helped a client figure out how to accomplish this after receiving odor complaints from the community, ultimately leading to a state agency-issued violation.

“We needed to thoroughly investigate to identify and mitigate odors, then prove compliance to the state regulator. Making a strong, valid case without having a numeric standard to go by takes both creativity and a scientific approach,” says Pat Sullivan, SCS senior vice president.

Sullivan, a biologist and his team of meteorologists, air dispersion modelers, and engineers, had a good starting point. They knew landfill gas was the source of the problem. But they needed more data to get to the root of that problem, and the operator’s required surface monitoring did not tell enough of the story.


The team launched a series of studies relying on multiple investigative tools.

“When we may have to put in more gas collection components, as we did here, we want to be sure we install them exactly where they are needed. This entails going above and beyond the standard modeling with a more rigorous methodology to get a comprehensive landfill gas emissions footprint,” Sullivan says.

SCS began by bringing out a drone to reach more landfill areas than technicians on foot for better coverage. The drone can fly over slopes, areas too dangerous to walk due to constant movement of heavy equipment, and areas inaccessible because of snow and ice. As it flies, it shoots a laser, which identifies methane based on the light refraction by methane molecules—then incorporates the data into a map for a comprehensive, visual picture.

landfill odor

 Knowing methane concentrations at specific locations is important, but determining where to be more vigilant in controlling landfill gas also requires knowing hydrogen sulfide (H2S) concentrations. Sometimes overall methane levels are within acceptable limits, but the hydrogen sulfide in it is elevated, which could be a problem, Sullivan explains.

Getting a good grasp on H2S’s potential impact is tricky, as levels can vary radically from one area of the landfill to another. Pat Sullivan,  SCS senior vice president, has seen them range from 100 parts per million to as high as 100,000 at different locations.

SCS used a Jerome meter, a highly sensitive tool that precisely quantifies H2S down to low-level part per million levels. SCS took it across the landfill and then into the community in search of H2S hot spots.

At the same time that the team investigated surface emissions of H2S, they went deeper down, sampling each landfill gas extraction well for levels of this volatile sulfur compound to identify potentially problematic spots within the landfill gas system.

“For this, we used Dräger sampling tubes, a resourceful tool in that rather than sending 100 samples to the lab, we analyze them ourselves and get immediate results,” Sullivan says.

Technicians get accurate quantitative results within plus or minus about 20% and can view concentration readings out in the field. Results are recorded on field logs and entered into a database for future analysis.

SCS overlaid the methane data from the drone study with the H2S data on both surface emissions and wells to develop a roadmap to design a landfill gas system upgrade. It includes new wells and piping in focused areas and more blowers for increasing the vacuum to pull more gas.


“We saw immediate results,” Sullivan says.

“Total gas collected went up 15 to 20 percent. Complaints went down significantly, and our client has not received another violation since.”

Of course, as the landfill takes in more trash, it will generate more gas, so due diligence is ongoing.

“Problem-solving is a phased approach. You do what you determine to be most effective; evaluate; then do additional work to improve. We will continue to follow this site and fine-tune where needed to keep the system running efficiently and keep the community and regulators happy,” Sullivan says.


Taking Down Landfill Odors from Trash

New garbage on a landfill’s active face can be a source of offsite odors, but determining if the waste facility is responsible, and determining when, where, and how odors travel, takes forensic work. Landfill odor experts rely on multiple data sets and tools to understand what can be complex issues and ultimately devise the most effective odor mitigation program when necessary.

In a couple of recent scenarios in Southern California, SCS combined complaint data, meteorological data, and smoke studies to get a full picture that verified the decomposing waste was the odor source. Then staff helped nail down specific times the problem occurred and under what conditions; providing a concise window can save operators labor and other resources because they can execute proactive measures only when needed.

“We look at complaint data to learn the location, day, and time of the complaint, but these accounts are not reliable by themselves. So, we overlay this information with meteorological data to determine the wind conditions during those days and times. Weather-related data is important in vetting offsite odors because if the landfill is not upwind of the location when the complaints happen, there likely is another source,” says Pat Sullivan, SCS senior vice president.

Sullivan and his team begin their investigations in two possible ways – setting up meteorological stations at strategic areas on the landfill to capture wind-related data or capturing data from already situated stations. Then they produce wind roses from their findings, which graphically represent wind speed; how often the wind blows from certain directions; and how these two correlate. In these two scenarios, graphing wind data times during each day helped determine exactly when specific wind conditions are prevalent.

landfill odors

In one of the two cases, odors occurred in the summer and almost always in the morning. The data not only showed where the winds were coming from at those times, but also showed they were traveling at low to moderate speeds.

“We matched that information to complaints and confirmed that the wind conditions were indeed driving the odors,” Sullivan says, explaining the speeds were just enough to carry the odor molecules into the community but not high enough to disperse and dilute them.

“Now we have painted a picture of wind conditions that we can focus on to get more information. We are getting closer to designing a multi-tiered odor mitigation program,” he says.

landfill odor neutralizer

The next step was a smoke study, which reveals how odors move offsite, identifying the exact pathways and movement trajectory. These details are important because to treat or disrupt odor molecules; operators need to intersect the odor plume before it leaves the site.

SCS odor experts release colored smoke at the time and location they believe odors are, based on the meteorological data. They film from a drone to get a bird’s eye view of the smoke plume as well as get a camera filming from a different angle, following the plume movement to identify its path out of the landfill. This method enables them to determine where to intersect the odors as they move through the air before leaving the site.


From this research came three recommended measures to take during unfavorable wind conditions:

  1. Spray an odor neutralizer on the waste and set up an odor mist system along the perimeter to create a barrier. Distributing the neutralizer with technology that atomizes the molecules creates small droplets, which increases the surface area for more of a reaction.
  2. Reduce the active face to the extent possible.
  3. Identify when odorous loads come in, relocate them, and bury and place a daily cover on the trash immediately, or move them to areas less likely to result in offsite odors.

One of the landfill operators now has the problem under control and has received no further violations.

The other site made many of the same changes and plans to open a second disposal area for smelly loads. This client has seen a significant reduction in complaints and violations, but it’s a work in progress. The next true test will come when Sullivan and his team reevaluate in the summer.

“We will see then if any improvements are needed and tweak the solution if needed.”

And as with our other clients, we are training operators on how to be proactive. We teach them how to identify and grade odors and how to follow set procedures. And we help them with strategy implementation,” he says.

Odor mitigation is an ongoing undertaking. The team continually assesses and quantifies emissions and potential impacts.

“We look for changes that will control odors or prevent them in the first place. And we provide clients with the know-how and support to stay ahead today and into the future. Landfills and waste volumes are growing and changing. It’s a dynamic scenario. And we continue to build on what we have proven and adjust to keep up to make more progress,” Sullivan says.


Showing That a Model Can Over Predict H2S Emissions

Hydrogen sulfide (H2S) can be problematic even at very low concentrations, so this volatile sulfur compound is on federal, state, and local regulators’ radar. Some jurisdictions require the evaluation of air toxic emissions to determine potential health impacts to nearby communities.

They are also calling for these evaluations during permitting or to decide when controls are needed. To make these impact determinations, regulators typically rely on standard H2S risk assessments leveraging air dispersion modeling that predicts concentrations at locations away from the source.

However, this methodology, which includes estimates of emissions and predicts offsite concentrations based on algorithms that mimic how air moves, is not always accurate. Inaccuracy proved to be the case at one SCS client’s site. The model overpredicted offsite measurements of H2S that the state and local agency classifies as toxic.

Ultimately, the client entered into an enforcement agreement with the state because the operator had a permit limit, based on results of the risk assessment that it could not meet.

“Respectfully, the agency came in maintaining that the levels were out of compliance; it came as a surprise and seemed questionable to our team given our experience. We felt that the air modeling and risk assessment results derived from this modeling were not accurate,” says Sullivan.

First, his team tried to adjust model inputs and variables that would yield what they believed would be more accurate data. Even though they could show improvements, the model adjustments could not obtain readings that showed compliance with the risk-based limits.

Next, they began going out monthly and measuring real concentrations at receptor locations. The team used a Jerome sensor, a highly sensitive handheld device that detects H2S down to single-digit parts per billion levels with good accuracy.

When they compared the predictions from the standard model to their readings on the same days of each month and same times of day, they confirmed the concentrations were well below the acceptable risk threshold.

“Because we did this over an extended period, we have continuous readings and a large data set from many locations that give a history and statistical validity,” Sullivan says. Every monitored value was substantially lower than the values predicted by the model.

“What that means is we could show that while there were onsite emissions, they were not escaping the landfill at levels that would exceed risk-based thresholds. That was useful in proving to the regulators that the landfill was actually in compliance with the standard, even when the model suggested it was not,” Sullivan says.

Now SCS is asking for revising its client’s permit and that the limitations are made more flexible based on real-time, longer-term findings. While the team is still waiting on the final permit decision, they’re confident they have proof that the site complies with the risk-based limit.

The outcome of this project has potential beyond possibly changing one permit for one operator, Sullivan surmises.

“We think the data developed from this study showing how the models can overestimate real-world conditions can ideally help other operators build a sound case in circumstances where they truly are in compliance.”


Related Resources

Staying Ahead of Odor Management at Solid Waste Facilities – This video recording is from a live session about the challenges of odors, including measuring them and the science behind them. Throughout the recording, the speakers’ field questions as they make recommendations for assessing and avoiding odors, regulatory issues, litigation, and responding to complaints.

The presentation and Q&A run for 1 hour 41 min. It’s well worth your time, with plenty of questions posed by solid waste facility operators, landfill managers, and composting operators answered.

SCS Engineers encourages you to share this video or any from our Learning Center. You can embed them at events and use them for in-house training. Look for our .









Posted by Diane Samuels at 6:00 am

March 2, 2021

landfill regulatory changes


On March 1, 2021, the New Jersey Department of Environmental Protection (NJDEP) proposed several amendments to air quality regulations pertaining to the regulation of New Jersey Hazardous Air Pollutants (NJHAPs) as well as fumigation operations.  The NJHAP regulations changes could significantly impact MSW landfills because they include proposed changes to hydrogen sulfide regulation as a NJHAP.

Key changes are summarized as follows:

  • The NJDEP is proposing to regulate hydrogen sulfide as a NJHAP;
  • Proposing a reporting threshold for H2S of 90 lbs/yr,
  • Proposing a State of the Art (SOTA) threshold for H2S of 10,000 lbs/yr (5 tons/year).

Several potential implications could result from these proposed changes, including:

  • Facilities with existing Title V Operating permits would be required to calculate the potential to emit (PTE) emissions of H2S for existing sources. If H2S emissions are above the very low reporting threshold of 90 lbs/yr, the H2S PTE emission rate would need to be added to the Title V Operating permit during the next permit renewal or the next permit modification.
  • Facilities subject to Emission Statement reporting and emitting H2S in an amount greater than or equal to 90 lbs/yr would have to include H2S emissions in their annual emissions statements.
  • For sources with potential H2S emissions of 90 lbs/yr or more, risk screening would be needed as part of (1) an initial operating permit for a new major facility or (2) for a minor or significant modification to an existing operating permit.
  • For sources with potential H2S emissions of 10,000 lbs/yr (5 tons per year) or more, a SOTA analysis would be required with certain permit applications. A SOTA analysis involves evaluating and potentially implementing available control technologies to reduce emissions and considers both technical feasibility and economic impact.  The proposed changes could lead to the need to implement additional landfill gas collection, control, and potentially treatment systems at some landfills.


A virtual public hearing regarding the proposed changes is scheduled for April 8, 2021, at 4:00 PM (ET).  A link to the virtual public hearing will be posted at http://www.state.nj.us/dep/aqm/curformp.html.

Written comments are due no later than April 30, 2021, to  www.nj.gov/dep/rules/comments.

View the proposed changes may be viewed at https://www.nj.gov/dep/rules/proposals/20210301a.pdf


Please direct questions to your SCS Project Manager or one of our local professionals:










Posted by Diane Samuels at 5:41 pm