Source of information: http://www.gfredlee.com/Groundwater/lf-conta.htm
Municipal solid waste landfill leachate contains a wide variety of hazardous chemicals, conventional contaminants, and non-conventional contaminants. Contamination of groundwater by such leachate renders it and the associated aquifer unreliable for domestic water supply and other uses; "remediation" treatment does not restore their quality. Focus must be placed on prevention of pollution of groundwater by MSW landfill leachate.
Increasing recognition is being given to the pollution of groundwaters by municipal and industrial "non-hazardous" solid waste landfills. The US EPA estimates that there are about 55,000 landfills in the US, on the order of 75% of which are polluting groundwaters. The majority of those landfills are what are called "sanitary" landfills in which there was little or no regard given in their siting, construction, operation, and closure for the potential impact of leachate generated within the landfill on groundwater quality. Today the US EPA and state pollution control agencies are recommending and/or requiring that sanitary landfills be situated above the watertable. According to recent federal regulations (US EPA, 1991), the minimal municipal solid waste (MSW) landfill requirements include a composite liner of compacted soil and plastic membrane, a leachate collection and removal system (LCRS) designed in concept to remove leachate generated in the landfill, and a low-permeability cover to be placed on the landfill when filled. While widely being adopted and used in some parts of the US, this approach is widely recognized as a stopgap measure which will only postpone the day in which groundwater pollution occurs by leachate generated within the landfill. Lee and Jones (1991a, 1992a) and Lee and Jones-Lee (1993) reviewed many of the numerous mechanisms which prevent "dry tomb" landfills from providing long-term protection of public health and groundwater quality.
Proponents of the "dry tomb" MSW landfill approach often assert that groundwater pollution by such landfills will not be a significant problem. However as discussed by Lee and Jones (1991a, 1992a), such assertions are based on an inaccurate description of the nature of the materials and processes that occur within MSW landfills that lead to leachate generation. This paper reviews the landfill processes that lead to leachate formation, the pollutional tendencies of leachates associated with MSW landfills, and the inability of the typical groundwater monitoring programs to provide reliable detection of leachate migration from the landfill and groundwater pollution by it before widespread pollution has occurred.
There is a common misconception that since the materials placed in MSW landfills are basically household wastes, they are relatively "safe" and would not likely adversely affect public health and groundwater quality. One need only consider the proposition of drinking the ooze that develops at the bottom of a garbage can or the water used to clean a garbage can to understand that it is not desirable to have municipal solid waste leachate in one's drinking water. Even adding a drop of such garbage-can-derived liquid to a glass of drinking water, i.e., highly diluted leachate, would not be considered desirable. Yet this is what happens when municipal solid waste landfill leachate is allowed to contaminate water that is or could be used for domestic supply. A similar comparison can be made with regard to construction and demolition debris and rubble (sometimes classified as inert wastes) that some try to advocate as "safe" for land burial with minimal restriction.
There are three broad types of contaminants present in municipal landfill leachate that need to be considered in evaluating the public health and groundwater quality impacts of MSW landfills. These are the group of what are called "hazardous chemicals," "conventional contaminants," and "non-conventional contaminants." Table 1 (from Lee and Jones, 1991b) presents a compilation of information from the literature on the chemical composition of municipal landfill leachates focusing on many of the conventional, more common contaminants.
| Parameter | "Typical" Concentration Range | "Average" |
| BOD | 1,000 - 30,000 | 10,500 |
| COD | 1,000 - 50,000 | 15,000 |
| TOC | 700 - 10,000 | 3,500 |
| Total volatile acids (as acetic acid) | 70 - 28,000 | NA |
| Tota Kjeldahl Nitrogen (as N) | 10 - 500 | 500 |
| Nitrate (as N) | 0.1 - 10 | 4 |
| Ammonia (as N) | 100 - 400 | 300 |
| Total Phosphate (PO4) | 0.5 - 50 | 30 |
| Orthophospate (PO4) | 1.0 - 60 | 22 |
| Total alkalinity (as CaCO3) | 500 - 10,000 | 3,600 |
| Total hardness (as CaCO3) | 500 - 10,000 | 4,200 |
| Total solids | 3,000 - 50,000 | 16,000 |
| Total dissolved solids | 1,000 - 20,000 | 11,000 |
| Specific conductance (mhos/cm) | 2,000 - 8,000 | 6,700 |
| pH | 5 - 7.5 | 63 |
| Calcium | 100 - 3,000 | 1,000 |
| Magnesium | 30 - 500 | 700 |
| Sodium | 200 - 1,500 | 700 |
| Chloride | 100 - 2,000 | 980 |
| Sulphate | 10 - 1,000 | 380 |
| Chromium (total) | 0.05 - 1 | 0.9 |
| Cadmium | 0.001 - 0.1 | 0.05 |
| Copper | 0.02 - 1 | 0.5 |
| Lead | 0.1 - 1 | 0.5 |
| Nickel | 0.1 - 1 | 1.2 |
| Iron | 10 - 1,000 | 430 |
| Zinc | 0.5 - 30 | 21 |
| Methane gas | 60% | |
| Carbon dioxide | 40% |
Regulations and regulatory agencies give primary attention to the so-called "hazardous chemicals" which are typically represented by the "Priority Pollutants." The group of Priority Pollutants was somewhat arbitrarily selected as part of a court order, by representatives of environmental activist groups and several individuals within the US EPA associated with the litigation. The list was not peer-reviewed within the US EPA, much less by the technical community as a whole and focused heavily on chemicals that were suspected of having the potential to cause cancer in man; largely ignored was a wide variety of chemicals that are known to have significant adverse impacts on domestic water supply water quality.
Conventional contaminants include parameters such as total dissolved solids, hardness, alkalinity, chloride, sulfate, iron, manganese, and hydrogen sulfide. In addition, this group includes a variety of non-differentiated organics measured as COD (chemical oxygen demand), BOD (biochemical oxygen demand), and TOC (total organic carbon). These are common components of a waste stream, traditionally analyzed to provide an overview characterization of the waste stream. They are typically present in elevated concentrations in landfill leachate and can thus often indicate the presence of leachate in unsaturated or saturated groundwaters. However, if present in sufficient amounts, conventional contaminants can cause severe degradation of groundwater quality and preclude its use for domestic water supply purposes. For example, organics measured as BOD, COD, or TOC can cause taste and odor problems and oxygen depletion in the groundwater. The chemicals that comprise those parameters may also adversely affect public health. Some of those organics can serve as co-substrates for microorganisms that can facilitate the conversion of hazardous chemicals to even more hazardous forms. An example of the latter is the conversion of TCE, a suspected human carcinogen, to vinyl chloride, a highly potent, known human carcinogen. The contamination of groundwaters by municipal landfill leachate contributes to the anoxic (oxygen-free) conditions that promote the conversion of TCE to vinyl chloride. Under anoxic conditions, bacteria in groundwater systems convert TCE to vinyl chloride.
Non-conventional contaminants are largely organic chemicals that have not been defined, and whose potential hazards to public health and groundwater quality are not known. Typically the organic Priority Pollutants, those organics that are identified and quantified, represent a very small fraction of the total organic matter present in leachate as measured by chemical oxygen demand and total organic carbon. It is estimated that from 90 to 95% of the organic materials in municipal landfill leachate are of unknown composition. Those chemicals have not been identified and obviously their potential impacts on public health and groundwater quality are unknown.