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For information on landfill gas emissions, contact:
Bob Grefe
608-266-2178
Dennis Mack
608-275-3466

Landfill gas emissions

Much of the waste placed in municipal solid waste (MSW) landfills gets decomposed by bacteria, and this decomposition results in the production of landfill gas.

Basics

Landfill gas basics

Landfill gas (LFG), which by volume is roughly a 50/50 mixture of methane and carbon dioxide with trace amounts of many other compounds, has the potential to cause or contribute to a number of aesthetic, health and environmental problems if not captured and treated. These include odors, potential explosion hazards, ground-level ozone formation and global warming. Consequently, since 1988, Wisconsin's solid waste rules have required that MSW landfills extract and treat LFG. Many closed MSW landfills in Wisconsin and nearly all of Wisconsin's operating MSW landfills currently extract and burn LFG.

LFG extraction systems are required to be installed incrementally as waste placement progresses. Generally speaking, extraction systems should be installed in areas of landfills that began receiving waste several years prior. These systems generally consist of vertical perforated pipes installed within the waste and connected to a blower. Despite its name, a blower actually applies a vacuum to the perforated pipes and sucks the LFG out of the waste. Properly run LFG extraction systems are able to collect the majority of the LFG produced; however, they cannot prevent the release of all LFG.

For more than two decades, Wisconsin has required that the base and below-ground sidewalls of landfills be lined with multiple feet of compacted clay. Since 1998 the state has required landfill operators to place a thick plastic membrane over the clay. This creates a barrier to horizontal movement of landfill gas and greatly reduces the explosion risk to nearby structures.

A number of larger landfills route the collected gas to turbines or internal combustion engines and use the gas to produce electricity, and a few others pipe their LFG to nearby industries for steam production. Several landfills in Southeastern Wisconsin have been producing electricity for 20 years.

The non-regulatory initiative described below serves to supplement existing state and federal air and solid waste regulations pertaining to municipal solid waste landfills.

DNR initiative

DNR initiative

Several years ago, in an effort to help guide future policy efforts, the Waste & Materials Management Program held a number of listening sessions with our customers. A theme heard in those meetings was concern over LFG emissions. The general consensus was that the program's past efforts had been primarily directed at groundwater protection, and given the strides made in this area, greater focus can and should now be placed on the air impacts associated with landfills. The stakeholders were interested in reducing air impacts and, if possible, doing so in a non-traditional fashion that might lead to greater environmental results than regulation alone could achieve.

Based on these sessions and on other internal DNR meetings, the Waste & Materials Management Program is taking a new initiative. The goal of this initiative is to reduce estimated uncontrolled or “fugitive” LFG emission rates statewide by 15 percent per year.

This initiative involves no new regulations, and partially relies on voluntary actions by landfill owners. There are two main parts: 1) using the Internet to increase public access to monitoring results, and 2) working to ensure better adherence to specific aspects of approved landfill plans that could affect uncontrolled LFG emissions.

After this period of time, the goal will then be re-evaluated for appropriateness.

Part 1: Monitoring results on the Internet

There are two basic methods for attempting to evaluate fugitive landfill gas emissions, and both have limitations. The first is direct measurement. Since most fugitive LFG emissions occur through the top or sideslopes of a landfill, direct measurement is difficult given the many acres of surface area involved. Also, while concentrations of gasses can be measured immediately above the surface of landfills, emissions rates of fugitive gasses can't be determined.

The second method, chosen by the DNR, is to estimate LFG generation rates and subtract those rates from the rates at which gas is extracted and treated. Accurately estimating gas generation from landfills is difficult due to many factors, including variations in types of waste accepted by specific landfills and operational methods employed. In addition, measuring flow rates of gasses is challenging, and the accuracy of some readings may be questionable.

Even with these limitations, using the above method should provide an idea of how landfills are limiting fugitive LFG emissions. In addition, to help estimate LFG generation rates, we've chosen to use a model developed by the U.S. EPA. See LandGEM model [exit DNR].

For more information , please contact Bob Grefe (608-266-2178)

Part 2: Ensuring closer adherence to DNR-approved landfill plans

Our program has modified its landfill inspection forms and advised staff that each time a landfill visit is made, landfill phasing and gas system installation must be evaluated with respect to department-approved plans. A basic evaluation of the landfill gas extraction and control systems are also to be performed and documented. Staff observing problems will discuss the problems with the landfill owner and request taking further actions as necessary.

LandGEM model

LandGEM model

In running the LandGEM model and preparing the graphs to be placed on the web, we've made the following assumptions.

  • Only the tons of putrescible or decomposable waste accepted by a landfill have been entered into the model. (If you're familiar with the waste categories we use for annual tonnage reporting, we've defined this as categories 1, 3, 5, and 6.) The model was originally calibrated by EPA based on inclusion of all waste tonnages. However, for the purposes of emissions estimation, EPA now allows use of only putrescible waste tonnages.
  • Two key variables in the model are the methane generation rate constant (k) and the methane generation potential per volume of waste (Lo). For emissions estimation, EPA recommends that k to be set at a value of 0.04/year and Lo at 100 m3/megagram of waste. These are the values that we've used in applying LandGEM to all MSW landfills in Wisconsin. Values of .05/year and 170 m3/megagram respectively are required by EPA to be used for determining the applicability of federal air rules pertaining to larger landfills. Use of these higher inputs to the model approximately doubles an operating landfill's estimated LFG generation. The Waste and Materials Management Program will be reviewing our choices for k and Lo as time progresses. Other values may subsequently be chosen for specific landfills based on evaluation of actual gas extraction rates and information contained in landfill organic stability plans required under s. NR 514.07(9)(a), Wis. Adm. Code.
  • The only LFG extraction rate information we currently have for most landfills are instantaneous measurements taken periodically as required by their approved plans. In these cases, we've averaged each year's instantaneous measurements and applied this average extraction rate 24 hours per day for the number of days in that year that the landfill gas extraction and treatment systems were operational.
  • Because the LandGEM model assumes methane concentrations in LFG equal to 50% by volume, we've adjusted the LFG extraction rate information from landfills to 50% methane as well. For example, if a landfill reported that it was extracting 500 ft3/minute of LFG at a methane concentration of 43% by volume, we would adjust the extraction rate as follows:
    • 500 ft3/min (43/50) = 430 ft3/minute, or
    • if the measured methane concentration was, for example, 55% by volume, the adjustment would then be:
      500 ft3/min (55/50) = 550 ft3minute

Results

Landfill gas generation & extraction results for individual landfills (by region)

From 2004 to 2007, our calculations indicate a 14 percent increase in modelled gas production, a 32 percent increase in measured gas collection, and a 39 percent decrease in estimated release of fugitive landfill gas.

We believe that these significant reductions are a result of several factors: real improvement in gas extraction and treatment by landfill operators; greater attention to reporting of landfill gas extraction monitoring results to the department; and accelerated landfill gas generation rates at larger landfills practicing leachate recirculation or accepting substantial quantities of sludges or other high moisture content wastes.

We'll be looking at this last issue in greater depth over time and may make adjustments to the modeling assumptions for certain landfills. Nevertheless, the estimated decreases in fugitive landfill gas emissions is a marked improvement, and the hard work and partnerships made by landfill operators in this initiative should be noted.

View the results [PDF] for each of the five DNR regions and a statewide summary.

Northeast DNR Region
Northern DNR Region
South Central DNR Region
Southeast Region
West Central DNR Region

Landfill owner comments

Over the past several years, the DNR has spent many hours with landfill owners attempting to work through the legitimate concerns they've raised regarding proper application of the LandGEM model and the potential for misuse of information placed on the Internet. We've considered all issues raised and have made several modifications to our initial plan. Although we believe that we've fairly addressed all concerns raised, some landfill owners remain very much opposed to our use of the LandGEM model for this purpose and to placing the results on the Internet. Other stakeholders don't believe that this initiative goes far enough.

Because this remains a controversial initiative, we've agreed to allow our customers to provide their perspectives on this web page. Landfill owners provided specific comments on the graphs for their landfills and Republic Services, Inc. provided separate comments [PDF].

During the several years of deliberation with landfill owners on this initiative, the waste management industry brought in a consultant with expertise in landfill gas management. This expert, Mike Michels, prepared a paper with Gerard Hamblin of Waste Management of Wisconsin, Inc. The paper uses the LandGEM model to estimate aggregate LFG generation at Wisconsin MSW landfills and compares it to measured LFG collected.

Last Revised: Monday April 29 2013