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Explanation of a Methane Gas Area of Concern (MGAOC) <br />The MGAOC is defined as the area of land surrounding a mixed municipal solid waste <br />(MSW) IandfiII waste footprint where the presence of certain activities, such as construction <br />of enclosed structures, may be impacted or precluded by subsurface migration of methane <br />gas. Methane gas is an odorless gas produced when MSW decomposes, and can be <br />explosive in confined spaces such as basements when mixed in air. The MGAOC is used <br />to inform the public about the risks to current and future land owners regarding certain uses <br />they may want to consider. Any questions about developing land within the MC/\[)C <br />should be addressed to the MPCA Closed Landfill Program (CLP) staff assigned to that <br />particular landfill. <br />Methane Gas Area of Concern around Anoka/Ramsey Landfill <br />Soils in the vicinity of the Anoka/Ramsey Landfill are generaily coarse sands. Depth to the <br />groundwater table is approximately 20 feet below ground surface. The IandfiII waste <br />footprint is approximately 65 acres and contains approximately 5,700,000 cubic yards of <br />waste. A low permeability cover system is in place. The northwest corner of the waste <br />footprint is approximately 240 feet from a residence. Other residences are located greater <br />than 300 feet from the waste footprint <br />The cover system has 43 vertical gas extraction welis connected to an enclosed <br />blower/flare unit. All 16 gas monitoring probes Iocated around the landfiII perimeter have <br />had zero percent methane measured in them for more than 5 years, indicating that there <br />likely 15 no gas migrating off the property. An investigation of the waste quality conducted <br />in 2011 found the waste to be very dry, confirming that the lower gas generation rate being <br />extracted by the flare system was not due to fouled gas weUa, but rather a slower <br />degradation rate due to lack of moisture. <br />Based on the Iarge mass of waste present, the highly hly permeable soils in the area, the <br />potential for an extended shutdown of the gas extraction system due to unforeseen <br />circumstances, the dry waste present, and recognizing the potential for gas to migrate <br />under seasonal low permeable (frozen) conditions, the MGAOC is revised down from the <br />previous estimate to extend 250 feet beyond the waste footprint. <br />Existing Land Use Controls <br />Local ordinances may exist and should be checked for applicability to control the building of <br />structures within the MGAOC. <br />January 23, 2012 <br />