Environmental Engineering Reference
In-Depth Information
study, specific attention is given to the possible risks associated with soil contamination
and ground water pollution. In order to understand the regulatory instruments and to
apply them correctly during the design and operational stages of this practice, basic
principles regarding the mechanisms of the transport of pollutants in soils and
groundwater are described. A specific case study of long-term irrigation of a pasture with
effluents and sludge is presented, and the impacts of such practice assessed in terms of
soil and groundwater quality. The study area is the same as the one discussed in Chapter
8, but here the assessment focuses on ground water quality, discussed in the context of
soils characteristics. In addition, a second assessment of pollution loads directed to the
area has been done during the year 2002, which allows for the comparison and trend
evaluation with respect to the material (sewage sludge and effluent mixture) used for
irrigation. Thus, in terms of the diffuse pollution of water resources, this chapter focuses
on ground water pollution as a result of long-term irrigation with sewage sludge. Usually,
such a type of diffuse pollution is classified as originated from agricultural activities and
is associated with rural areas. However, in the case of sludge land application, the most
common case is to develop the farm area close to the location of the wastewater treatment
plant, usually in the sub-urban areas. Thus, in cases of improper design or operation,
groundwater pollution from such activities becomes one separate aspect of the
management of aquifers in urban areas, and the related impacts on surface water through
base flow and recharge.
2 POLLUTION TRANSPORT IN SOILS AND GROUNDWATER
2.1 Soil treatment mechanisms
The soil has a large capacity to retain, transform and recycle some of the pollutants found
in municipal wastewater and hence is frequently used to provide both treatment and
disposal of wastewater (Ayers & Westcot 1985, Yadav et al. 2002). Wastewater
treatment in the soil occurs due to physical, chemical and biological processes that
include retention, transformation and destruction of pollutants. Some of the
Figure 9.1. Soil matrix zoning.
physical processes are infiltration, dispersion, and dilution, while vitalization, adsorption,
complexation, precipitation and photodecomposition are chemical processes that occur in
the soil matrix. Biological processes include biological oxidation (mineralization),
nitrification, denitrification, immobilization, and plant uptake (USEPA 1992).
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