Leachate and Gas Emissions

The production of contaminated leachate is a possibility with most disposal sites. Leachate consists of water that has become contaminated by wastes as it passes through a waste disposal site. It contains waste constituents that are soluble, not retained by soil, and not readily degraded chemically or biochemically. Therefore, new hazardous waste landfills require leachate collection/treatment systems, and many older sites are required to have such systems retrofitted to them. Leachate is collected in perforated pipes that are embedded in granular drain material. 

The best approach to leachate management is to prevent its production by limiting the infiltration of water into the site. Rates of leachate production may be very low when sites are selected, designed, and constructed with minimal production of leachate as a major objective. A well-maintained, low-permeability cap over a landfill is very important for leachate minimization. 

If leachate is released from a hazardous waste landfill, it may be necessary to install a leachate treatment system. Such a facility is a sophisticated wastewater treatment system using biological, physical, and chemical treatment processes as described in Chapter 5. 

Gas emissions may be produced from hazardous waste disposal sites. In some cases, gases come directly from materials disposed of in the site. If biodegradable wastes are present, the anoxic biodegradation of biomass, represented by CH2O, may produce significant quantities of CO2, explosive CH4, and toxic H2S  

These gases may carry volatile wastes, such as benzene and chlorinated hydrocarbons, from the disposal site into the atmosphere and cause air pollution problems or pose health hazards near the site. In some cases, it may be necessary to collect the gases and treat them as discussed in Section 16.24. Filtration over activated carbon can be employed, and in some cases the gases have been pumped with intake air into internal combustion engines where they are destroyed by combustion. 

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Table 11.8. Monitoring recommended for leachate and gas emissions (Draft EEC Directive 1995)...

In 1947 the Town and Coxmtry Planning Act was passed. This required all new landfill sites to obtain planning permission. The new legislation did not apply to existing sites and there was still no consideration of managing leachate or gas emissions from sites and no effort to control the types of waste accepted. 

Waste deposited in landfills undergoes biological, chemical and physical transformations that cause changes in solid, liquid (leachate) and gas phases. As much as 90% of the carbon that is released during the decomposition of organic matter in the waste migrates to landfill gas in the form of CH, COj and various hydrocarbons, whereas only 10% enters the leachate (Huber-Humer, 2007). The complex composition of the gas emitted from landfills and its uncontrolled emission into the atmosphere poses multiple threats and problems at different levels of coverage. 

Anaerobic. Moisture is added to the waste mass in the form of recirculated leachate and from other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects. 

Remediation of landfill leachate plumes has, in most cases, focused on source control. This is due to the fact that landfills are so large that the mass of pollutants contained in the landfill body would be able to sustain the leachate plume for centuries making a remedy focusing on the plume a long and costly approach. Additional reasons for focusing on the source are that the landfill also may be a time bomb containing chemical waste in drums subject to corrosion, landfill gas emission needs to be controlled, improvements of landscape value is requested by the community, and potentially new landfilling capacity is in demand. 

In the history of the barrier development (Ryser 1989), initially only the site location was considered in the next phase, landfdl liners were added as surface covers and base liners to facilitate leachate collection (during the 1970s). Since the early 1980s, attempts have been made to control reactions inside the landfdl, for example by waste compaction and gas collection. In the early the 1990s, it became evident that in order to effectively minimize landfill emissions, the prior separation of contaminants was necessary. The culmination of this development will be reached, when the inert- and residual landfill will become the norm. 

Just two years after the Deposit of Poisonous Waste Act was passed it was replaced by the Control of PolluHon Act 1974. Earlier legislation on waste disposal had been led by a public health perspective with no concern for the wider environmental issues related to leachate and landfill gas. There was no classification of waste and no control over what types of waste were deposited in landfill sites. There are numerous stories of dead cows, chemical drums etc. being deposited in landfill sites. Sites were usually capped off with a layer of soil to cover the waste and without any thought of controlling gas emissions or rainfall infiltration. 

Gas and Leachate Movement and Control Under ideal conditions, the gases generated from a landfill should be either vented to the atmosphere or, in larger landfills, collected for the production of energy. Landfills with >2.5 miUion cubic meters of waste or >50 Mg/y NMOC (nonmethane organic compounds) emissions may require landfill-gas collection and flare systems, per EPA support WWW, CFR 60 Regulations. The leachate should be either contained within the landfill or removed for treatment. 

DPE suits, and butyl rubber (NRC, 2001b). The levels were 0.0002 to 0.0008 ng/m3, three orders of magnitude below the EPA criterion of 0.2 ng/m3 for dioxin emissions from incinerators. In the test with neat GB, the product gas contained 0.01 to 0.06 percent phosphine. As noted previously in the section on methods development testing, phosphine can interfere with the measurement of GB. Based on results from the EPA s toxicity characteristic leachate procedure, stabilization would be necessary only for solid wastes derived from DPE suit material, because the cadmium and lead criteria were not met by the treated dunnage in some tests (NRC, 2001b). 

Typical concerns relate to visual impact, noise, and landscaping, and for landraising to be effective, such concerns must be balanced against the potential environmental benefits. Because of the facility for increased control over emissions, e.g. collection and treatment of gas and leachate, landraising may also allow landfill development in areas otherwise considered to be too vulnerable for landfill development. Vulnerable sites include those located above aquifers, while those sited above, for example, clay could be considered as being suitable for development either with or without a complementary lining system. Other potential advantages include ... 

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