Función del cuidado del medio ambiente

Landfill A is located in the United Kingdom - a developed country with stringent regulations governing landfill management. The 9.2 ha conventional landfill site is operated strictly in accordance with the EU Landfill Directive (1999/31/EC). The EU Landfill Directive introduced requirements for member states to reduce the amount of biodegradable wastes disposed of untreated to landfills. This restriction aims to prevent and reduce as far as possible negative effects on the environment, in particular the pollution of surface and groundwater, soil and air as well as any resulting risk to human health. Furthermore, the Landfill Directive requires high standards of engineering and operational practices consistent with best modern practices. Unauthorized entry to the landfill site is prohibited. This is achieved by a fence that has been constructed around the site and a gated entrance. The landfill site is split into four

phases (Figure 4.1). Phases 1 to 3 are complete (closed), capped, and currently undergoing aftercare. Current disposal activity is confined to Phase 4, which is divided into smaller cells.

Landfill A accepts a wide range of wastes including domestic, commercial, industrial and special wastes including hazardous (i.e., asbestos) and low level radioactive wastes (LLW), which are disposed of separately. Over 90 % of waste disposal at the site is residual waste collected from households and businesses. The low level radioactive waste makes up less than 10 % of the total waste. The effect of the EU Landfill Directive, which bans the disposal of liquid wastes and sets targets for member states to reduce the amounts of biodegradable waste sent for disposal (e.g., UK targets are 75 %, 50 % and 35 % of 1995 levels for the years 2010, 2013, and 2020, respectively) is visible at Landfill A. The quantities of waste landfilled have declined from 800,000 tons when the site opened in 1986 to 100,000 tons in 2012 and only 50,000 tons were expected to be disposed of at the end of 2013 (Walker, 2013 Pers.

Comm., 14^th June).

Figure 4.1: Aerial View of Landfill A

Engineering Designs (Containment System) - A key engineering requirement under the EU Landfill Directive is a geological barrier for all landfills. This is required up the landfill sides as well as across the base and must provide sufficient attenuation to prevent potential risks to soil and groundwater. When operations have ceased, a final cap is required to be installed at the top of a landfill (Figure 4.2).The EU Landfill Directive further requires that a landfill site be situated and designed so as to meet the necessary conditions for preventing pollution of soil, surface and groundwater and ensuring efficient collection of leachate as and when

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required. As shown in Table 4.1, the changes in EU landfill legislation can be seen from the way the top and bottom compartments (liners) for Phases 1-3 and Phase 4 have been designed.

Phases 1 -3 were developed on a ‘dilute and attenuation' basis comprising earthen material (clay) as the only bottom liner (barrier). At the time of construction, it was generally believed that attenuation and buffering capacity of the natural barrier (i.e. geologic conditions) was sufficient to prevent seepage of leachate into groundwater. This understanding may have led regulations not to require the installation of low permeability barriers. However, Phase 4 (active area of landfill), which is more recent and subject to existing EU legislation, has been developed on a full containment basis with composite lining and leachate collection systems.

In addition to liner requirements at the bottom, a 10 m deep slurry wall encapsulation has been built around Phase 4, which in addition to accepting general wastes, accepts low level radioactive-waste (LLW). The slurry wall prevents the flow of contaminants into and from the landfill site. As shown in Table 4.1, a low-permeability top cover (final cap) is now required at all modern landfills after closure.

Figure 4.2: Sketch of a Containment System Requirement under EU Regulations (Adapted from EA, 2009)

Table 4.1: Design of Top and Bottom Containment Systems at Landfill A Landfill Phase

(Area of landfill)

Landfill Base(Liners) Landfill Final Cover

Phase 1-3 (Closed cells)

Low permeability earthen barrier

100 mm top soil

300 mm stone drainage layer 1200 g/m geotextile material 2 mm impermeable HDP membrane

500 mm engineered mineral liner

Geological barrier and artificial sealing liner

Engineered cell separation structure

Leachate collection System

Empty cell

Waste Disposal Process - The landfill operator/owner operates a tracking system that enables the identification of areas within a landfill cell where a particular waste load will/has been disposed of. Waste disposal is confined to active tipping areas of Phase 4. Inert material is used as daily cover to prevent odour, windblown litter and particulates, and scavenging by birds. Waste accumulation at the site is only permitted for a maximum of 14 days before disposal. The accumulated waste is subject to conditions requiring containment against weather; any accumulated waste is covered by a mat. Low level radioactive wastes (LLW), which come packaged in sealed containers are disposed of by digging a trench into conventional wastes that have already been disposed of. After disposal, the container is covered with approximately 50 cm of non-radioactive materials and approximately 150 cm of non-radioactive cover is placed on top the same day of disposal.

Landfill Gas Management and Monitoring - Landfill gas management is a requirement under the EU Landfill Directive. Annex 1 Paragraph 4.1 of the Directive requires that appropriate measures be taken to control the accumulation and migration of landfill gas.

These measures include the requirement to collect and treat the gas through the production of energy and where this is not possible, the gas must be flared. Landfill gas at the landfill site is collected and transported to a treatment facility by a network of gas pipes that have been installed (Figure 4.3). The collected gas is treated by generating approximately 2.8 MW of electricity using CAT engines. The generated electricity is fed into the local electricity grid.

The absence of odours at the landfill site is attributed to existing good management (collection and treatment) of landfill gas, which is a requirement under the EU Landfill Directive.

Furthermore, in accordance with the issued permit, landfill gas monitoring is carried out on a monthly basis. The trigger levels have been set at 1.0 (% v/v) for methane and 6.1 (% v/v) carbon dioxide.

83 | P a g e Figure 4.3: Gas collection pipe at landfill A (Author, 2013)

Leachate and Water Management - It is a requirement under the EU Landfill Directive to sample and collect the generated leachate at representative points within a landfill site.

Leachate sampling and measurement (volume & composition) must be determined separately where leachate is discharged from the site. Furthermore, the EU Landfill Directive requires surface water to be monitored at not less than two points: (i) upstream; and (ii) downstream of a landfill. The above management requirements are being met at Landfill A. Leachate arisings are collected and pumped into two lagoons where methane is removed by air-stripping (bubbling air). The methane stripped leachate is sent to a nearby wastewater treatment plant for further treatment before it is discharged into the environment.

Groundwater is monitored on a monthly basis both upstream and downstream of the landfill site while surface water is monitored at three points: (i) upstream; (ii) downstream; and (iii) at the outfall. Ammoniacal nitrogen is the surface water determinant parameter whose trigger level has been set at 5.31 mg/l.

Aftercare Management - Article 13 of the Landfill Directive requires member states to undertake aftercare of closed landfills. The Directive has given powers to national regulatory agencies to determine the aftercare period on a site specific basis. In accordance with this requirement, Phases 1 to 3 at Landfill A have all been rehabilitated/restored and were now being used as pasture land for sheep while parts of Phase 4 that had closed have been rehabilitated and were undergoing aftercare. The components being managed during the aftercare period include landfill gas, leachate, and top cover.