Environmental factors affecting choice of disposal sites for harzadous and toxic substances

Considering the effects that harzadous waste disposal sites exert on their surrounding ecosystem and environment, these sites should be located in places with the minimum destructive effects and the lowest environmental impacts.

The following are methods used for the disposal of hazardous wastes; land disposal of wastes, incineration, dumping in the sea, underground disposal, and deep well injection.

Landfill siting for harzadous and toxic waste is an  extremely  difficult  task to  accomplish because  the  site selection process  depends on different  factors and  regulations.

Environmental factors are very important because  the  landfill  may affect  the  surrounding biophysical  environment  and the  ecology  of the area.

The following geological environmental factors affect choice of disposal sites for hazardous and toxic wastes;

Land Use: The landfill footprint must not be located within 500m of an existing or planned sensitive land use (EPA, 2000). Sensitive land uses include, but are not limited to: schools, residences, hotels, restaurants, food processing facilities, churches, and municipal parks. Land uses such as heavy industry, forestry operations, mining, railways/rail yards, etc. are not considered sensitive land uses.

Ecological  value  of the  flora and  fauna: The  direct and  indirect  spatial use  of a  landfill will destroy  the actual  vegetation and  fauna.  When  making  a decision,  the ecological  value of  the  actual vegetation and  fauna  should  be evaluated carefully  for  the candidate area. Ecological value  is  based on  diversity,  naturalness and  characteristic  feature.  An example  of  indirect  use  is  the  disturbance  of the  quietness in  the  surroundings caused  by the activities on  the  landfill.

Topography: This has to do with the natural and physical features of the area. It is desirable to have a topographic surface that tends to shed water in order to reduce ponding and infiltration. Karst topography is a landscape formed by the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. Sanitary landfills should not be constructed on karst topography.

Steep Slope: A completely flat area is exposed to accumulations of water during raining seasons and a very steep slope can be easily eroded. If the slope is too steep, it is difficult and costly to construct the landfill. Slope is a very important factor when siting a landfill; hence higher slopes would increase surface runoff of pollutants from the landfill and thereby contaminate areas that are further away. The landfill area having steep gradient (where stability of slope would be problematic) should not be selected.

Groundwater level and Surface water bodies: The groundwater level of a designated site for landfill construction should be sufficiently below the base of excavation. Also landfills should be sited in areas where beneficial uses of groundwater is minimal because groundwater contamination by leachate is difficult to remediate. Landfills should not be sited close to surface water because contamination of water bodies could be hazardous to aquatic lives.

In essence, distance from surface and groundwater, access routes, residential areas, industries, power transmission lines, flood-proneness, faults, slope, and distance from gardens and agricultural lands are all geographical environmental factors that are considered during site selection for hazardous and toxic wastes so as to prevent or minimize the harmful effects of such wastes on the environment.