56    REGULATIONS FOR POST-CLOSURE MONITORING OF
LANDFILL GAS
Suresh R. kikkeri, Environmental Engineer
Edward P. Hagarty, Vice President
CC. Johnson & Malhotra, P.C.
Silver Spring, Maryland 20902
INTRODUCTION
Gas production in closed sanitary landfills is affected by many variables, including, among others,
depth of landfill, composition of the waste, moisture content of the waste, period of operation and
temperature. The principal gases produced from the decomposition of solid waste consist of methane
and carbon dioxide. When methane is present in the air in concentrations between 5% and 15%, it is"
explosive. The release of landfill gas (LFG) from a closed sanitary landfill may pose certain hazards to
nearby residents or landfill monitoring personnel. Until publication of the "Final Rule" by the federal
agency during the end of 1991, federal regulations regarding post-closure monitoring of LFG were
almost non-existent. State regulations differ throughout the country and they lack uniformity. This
paper presents an overview of current state regulations and the impact of the new federal regulations
on post-closure monitoring of the LFG.
Quantity and composition of municipal solid waste (MSW) have been studied in detail by several
investigators. The United States Environmental Protection Agency (EPA) estimates that approximately 180 million tons of MSW are produced each year in the U.S.' Table I shows the composition of
typical MSW.
Microbial reactions in landfills control the quality and quantity of LFG produced. LFG is produced
as a result of anaerobic decomposition of organic biodegradable components in solid waste. Decomposition in a sanitary landfill occurs in three distinct phases. The first phase is an aerobic phase where
biodegradable organic materials undergo aerobic decomposition, utilizing the oxygen trapped during
the landfilling process. This phase generates carbon dioxide and water. After the available oxygen is
depleted, the second phase of decomposition begins. In this phase, aerobic organisms die off and
anaerobic organisms proliferate. During the third phase, anaerobic organisms are predominant and
the anaerobic decomposition produces mainly methane and carbon dioxide. Additional gases in small
amounts found in landfills include nitrogen, carbon monoxide, hydrogen sulfide, hydrogen, ammonia and oxygen. In most cases, over 90 percent of the gas volume produced from the decomposition of
solid waste consists of methane and carbon dioxide.2 Typical LFG composition is shown in Table II.
The heat value of typical LFG is about 500 British Thermal Units (BTU) per standard cubic foot.
The heat value of methane is about 1000 BTU per standard cubic foot. The gas yield from landfills
has been estimated by various investigators and these numbers vary widely. For example, according to
O'Leary and Walsh,3 the ultimate gas yield under ideal conditions is 16,600 cubic feet per ton of solid
waste whereas according to Willumsen,4 the ultimate gas yield ranges from 11,200 cubic feet per ton
to 12,800 cubic feet per ton of solid waste. It is important to note that various environmental factors
Table I.    MSW Materials by Weight Generated in 1988'
Component Quantity (million tons)
Glass 12.5
Food waste 13.2
Plastics 14.4
Metals 15.3
Rubber, leather, textiles, wood 20.8
Yard waste 31.6
Paper 71.8
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.