Sampling flags on top of a landfill marking the areas under investigation
Sampling flags on top of a landfill mark the areas under investigation.

A significant portion of the solid waste generated in Missouri is disposed of in landfills permitted and regulated by the Missouri Department of Natural Resources. Modern day landfills are state of the art systems that attempt to store our wastes in a manner that will minimize risk to the public and to the environment. 

In Missouri, landfill owners and operators are required to monitor the groundwater around the fill area and monitor for the presence of decomposition gases. A robust monitoring system allows for early release detection and facilitates rapid corrective action.

Additional Information: 


Over time, water and other liquids seep into the landfill, react with the waste and absorb different contaminants as it moves through the wastes. This liquid, referred to as leachate, could contain contaminants in an amount that may be harmful to human health or the environment if released into the groundwater. Deterioration of water quality can cause detrimental effects, such as human or animal health impacts, vegetative stress or other environmental problems. Groundwater monitoring programs represent the last line of defense by ensuring any contaminants released to groundwater are discovered and cleaned up in a timely manner. 

Baseline Monitoring

Groundwater that has not been affected by leachate is called "unimpacted" or "background" water. Monitoring systems should be installed at proposed solid waste disposal areas to determine pre-existing groundwater quality. Monitoring systems are initially installed to characterize groundwater quantity, rates and directions of flow. Once potentials for groundwater flow are known, then chemical analyses can be obtained through several seasons to evaluate annual temperature and rainfall effects on groundwater quality and quantity. At least two years of data is needed to establish seasonal effects and verify consistent monitoring results in initial groundwater systems. However, background water quality data may require additional quarters of data, depending on the statistical methods used.  

Detection Monitoring

Once initial groundwater quality studies establish seasonal and temperature variations at a site, groundwater sampling continues in order to help detect changes in the “background” groundwater quality and flow directions related to constructing and operating the solid waste landfill. A statistically significant increase in the amount of any of the contaminants monitored would indicate a release might have occurred. Only water quality in distinct groundwater monitoring zones can be compared statistically. Representative and comparable analytical data and detailed records for groundwater monitoring programs are dependent on consistent and reliable sampling methods, detailed field observations and analytical techniques. For guidelines describing collection and handling procedures, review Collection, Handling and Reporting Procedures for Groundwater Samples - PUB0181. For a list of guidelines to address common sample collection errors, review Guidelines for Soil and Groundwater Sampling: Brownfields/ Voluntary Cleanup Program - PUB2432.

Department staff may also sample groundwater at solid waste disposal facilities to determine if the landfills are causing adverse effects on the groundwaters physical, chemical or biological attributes. Staff split groundwater samples with the facility’s contracted sampler to provide a quality assurance check against routine sampling conducted by active and closed solid waste landfills. Samples collected by department staff are returned to the department's Environmental Services Program laboratory.


Landfill owners and operators are required to conduct routine sampling on an established schedule. The resulting data must be submitted the department within 90 days of the sampling event. In order for data to be accurate it must be submitted in the exact same format each reporting period. To aid this, the department created several worksheets to ensure consistency.

Please follow the instructions in the Reporting Landfill Groundwater Data - PUB2943 fact sheet and email the data to


When solid waste breaks down in a landfill, decomposition gases are produced. Landfill gas is made up of roughly 50% methane and 50% carbon dioxide. Methane and hydrogen sulfide, a trace constituent, are the main constituents of concern in landfill gas. Due to its extremely small concentrations, hydrogen sulfide production does not normally cause as great of a concern or threat to public safety as does methane gas. Methane can cause dead or distressed vegetation, especially trees, by displacing oxygen and asphyxiating the roots. Higher concentrations of methane can become flammable and potentially explosive if it collects in confined spaces. If the methane moves and accumulates in buildings or other confined spaces, it can pose public health and safety risks. For more information, review Landfill Gas - PUB2370.

Detection Monitoring

The Missouri Solid Waste Management Law and regulations require landfill owners and operators to control decomposition gases on site. This has been a regulatory requirement from the date of the first solid waste regulations in Missouri. Currently, regulations require sanitary and demolition landfill owners and operators to design and implement gas monitoring programs capable of detecting gas migrating from its landfill. Gas monitoring wells are installed around landfills as a way to detect methane gas concentrations and movement. Landfill owners and operators are also required to monitor methane in all buildings located within the landfill's permitted boundary. For guidance regarding sampling procedures, review Procedures for Sampling Methane Gas Inside Buildings - PUB2052 and Sampling of Landfill Gas Monitoring Wells - PUB2053.


Landfill owners and operators are required to conduct gas sampling at least quarterly. The resulting data must be submitted to the department within one week of collection. The information to be included in the data submission and the format by which to submit the data is described in the Reporting Landfill Gas Data - PUB2942 fact sheet. Email the data to