Ask The Operator: Gas Monitoring

John C. Anders

As you may remember from the World Wastes September issue, Lee Chate is responsible for the operation of the Anytown Sanitary Landfill, Anytown, U.S. Previously, he examined groundwater and surface water monitoring.

Lee's facility strives to protect its employees and the surrounding environment, so he must be certain that equipment functions properly, that traffic through the facility flows logically and smoothly and that site activities are closely monitored to ensure a safe and secure operation.

To help him manage his operation effectively, Lee often seeks the assistance of experts in his field. This month, Lee discusses landfill gas monitoring issues. Let's join him as he consults Len Cobb, civil engineer for the Public Works Department of Richmond, Va.

Lee: Len? Lee Chate at Anytown.

Len: Yes, Lee. What can I do to help you?

Lee: I plan to install gas monitoring probes and gas vents here at the landfill, and I'd like to know about the monitoring process after installing the equipment. Is it true that you monitor your own probes and wells?

Len: Yes. That's a regular occurrence for me.

Lee: Great, then you can tell me what I should be thinking about when planning for this.

Len: It is very important to consider your access to the monitoring points. Some of our sites are rather remote, so we often have to pack insect repellent and watch for poison ivy and ticks.

Lee: I'll probably have the same problem. Unfortunately, we have pretty big horseflies around here. I should probably think about some kind of protection from them. I've been bitten several times.

Len: That certainly wouldn't hurt. If your people can't get to the monitoring points, you're stuck. Also consider the presentation of the data from the monitoring. You will end up with a load of raw data that will need to be boiled down to a meaningful report.

Lee: What do you mean?

Len: Well, it's likely that you will distribute the data to various people in your local government. Many of these people will not be as intimate with the program as you are. Handing them a bunch of raw data will be worse than presenting nothing at all. I have been experimenting with a few ways to present the data graphically so that the reader can have a one-page overview of the results without having to dig through the raw data.

Lee: What kinds of data have you been reporting?

Len: Typically, I will report the methane concentration and compare it against the Lower Explosive Limit (LEL). That's the regulatory limit when a response or action is needed. But I also record weather data, oxygen content, pressure data and the moisture conditions within the well or probe.

Lee: Why so much data? Wouldn't the methane level against the LEL be enough?

Len: The other data becomes helpful when you are trying to analyze it over time. Getting as much data as possible will be particularly useful if you need to develop long-term connections between weather patterns and movements of gas through the ground or within the landfill itself.

Lee: Len, thanks for your help.

Len has made Lee aware of a couple of things that may seem trivial at first, but are actually quite important. The style of data presentation is critical. Whoever prepares the report must know who the audience is and what they are expecting from the report. Regulatory requirements must also be considered. Simply presenting a barrage of data may be ineffective. Len likes to boil the data down to a one-page, graphical summary that tells the story clearly.

Interior/Exterior Facilities Next, Lee calls Don Nuttall of Draper Aden Associates, Richmond, Va. Don has performed routine gas monitoring at numerous landfill facilities.

Lee: Don, Lee at Anytown.

Don: Lee, what can I do for you?

Lee: Don, I understand that you have monitored several landfills for gas. I'm going to be doing that soon at Anytown, and I'd like to hear your thoughts.

Don: You will have to monitor the interior and exterior aspects of your facility. For the exterior facilities, you will be most concerned with off-site migration of gas from the disposal cells. This monitoring can be handled by the use of monitoring probes around the periphery of your site.

Lee: What makes up the probes?

Don: The probes are very similar to groundwater monitoring wells, except they do not intentionally extend into the groundwater. You need to drill to the depth of interest and install the probe. Six-inch augured holes are the norm. Perforated tubes are placed at various levels and sealed off to allow monitoring of various strata within the probe depth.

Lee: Why is that important?

Don: There may be specific silt layers in the ground that would permit the migration of gas easier than other soil layers. This can be determined in the field by keeping a record of the drilling. Otherwise, a uniform screening of five- to 10-foot intervals can be used.

Lee: What concentration of gas would I be looking for?

Don: For exterior monitoring, the regulatory maximum is 5 percent methane at the site boundary. This is the LEL. For interior monitoring, the maximum limit is 1.25 percent methane, roughly 25 percent of the LEL.

Lee: What kind of interior monitoring will I be doing?

Don: For compliance monitoring, you should monitor buildings, scalehouses, equipment sheds, etc. You don't need to worry about leachate collection manholes or other similar structures. These structures need to be monitored for safe conditions if you intend to work in them.

Lee: What kind of equipment do I need to do the monitoring?

Don: The explosive gas monitors that are available commercially can be modified to allow monitoring for landfills. The equipment can get pretty exotic if you are monitoring to do a detailed evaluation of the data to understand the actual migration.

Lee: Don, this is good information. Any other thoughts?

Don: Yes, Lee. Consider setting an action level for your monitoring. The action level is usually some concentration less than the regulatory limit. At this level you begin taking a detailed look at your monitoring data. This provides a check on the situation before triggering the regulatory levels. Also, make sure access is always clear. The gas probes are typically very close to the ground, and vegetative growth can easily hide them. Mark them well so they do not become obscured.

Lee: Well, Thanks for your help, Don.

Don has made Lee aware of some of the details related to gas monitoring. In addition to considering hiring a consultant, Lee might also want to refer to literature such as, A Compilation of Landfill Gas Practices and Procedures by the Landfill Gas Division of the Solid Waste Association of North America.

Installing Gas Probes Now, Lee turns his attention to procuring the services of a company to install the gas probes. He calls Jim Belgeri, the vice president and branch manager of S&ME Inc., Blountville, Tenn.

Lee: Jim, this is Lee Chate, operator of the Anytown Sanitary Landfill. I'd like to install some gas monitoring probes at the landfill, and I'm interested in learning more about how your company might be able to help me. Do you have a few minutes to talk?

Jim: Sure, Lee, how can I help?

Lee: Gas monitoring seems to be a critical issue. I want to be sure that the company we hire is qualified. I certainly don't want to end up with an inexperienced driller.

Jim: Good precaution, Lee. You'll get the job done right if you make your selection based on qualifications, not on price.

Lee: What should I look for?

Jim: Lee, it is important that you look for an experienced professional and field staff, a health and safety plan, a company-wide medical monitoring plan and equipment that can do the job.

Lee: Why is the health and safety plan needed?

Jim: This plan describes how the job will be monitored. It is possible that you could be drilling into an explosive atmosphere. Your health and safety plan sets the course of action if unsafe conditions develop. It also outlines what to do with the solids and liquids you may encounter during the drilling.

Lee: I never thought of that. The solids can be put into the landfill, but liquids cannot.

Jim: That's right. The health and safety plan establishes what needs to be done. The medical monitoring plan is important, too. It establishes what the company does to monitor the health of their workers, both before and after a project.

Lee: That's good to know, Jim. Any other thoughts?

Jim: Yes. Consider doing only what is necessary at any one time. I don't mean the bare minimum, but you should limit the possibilities of drilling into a hazardous atmosphere. For instance, try to stagger the installation of your probes relative to your gas vents. Statistically, you will reduce your risk on the project if you can stretch or stagger the installations and not lump them all into one project.

Lee: Thanks, Jim. You were a big help.

Lee has received plenty of food for thought. He is now well-prepared to make the crucial decisions that will affect the safety and efficiency of his operation.

Landfill gas monitoring is serious business. The monitoring structures must be properly installed by qualified, safety-minded people, and the monitoring must be performed correctly. Once monitoring occurs, the data must be presented in a manner that satisfies the reader and tells the story in the most clear and concise way possible.