Stressors and Soil Contamination - Sustainable Practices in Geoenvironmental Engineering - page 35

2.2.2 Soil Contamination from Chemical Stressors

Chapter 1 points out that good land management practice (a) minimizes and mitigates dele-
terious impacts to the land environment, (b) seeks optimal land use and beneit from the land,
and (c) preserves and minimizes depletion of geoenvironmental natural capital. Probably
the most signiicant stressor responsible for degrading the quality of the land, its ecosys-
tems, and especially the receiving waters (including groundwater) is the group of chemical
stressors. The impact from these stressors is contamination of the land environment and
its receiving waters by contaminants and hazardous substances, and as will be discussed
in the latter part of this chapter and the next chapter, the importance of protection of the
receiving waters cannot be overstated. Ground contamination—i.e., contamination of soil
mass and receiving waters—by these same contaminants and hazardous substances poses
threats to human health, other biotic receptors, and the environment. Our attention in this
chapter will be focused on the various aspects of ground contamination and land manage-
ment, together with remediation and restoration requirements needed to meet sustainabil-
ity goals. The later chapters in this topic will focus on actual technologies, procedures, and
tools to implement sustainable geoenvironmental engineering land management practices.
Once again, although it is recognized that depletion of nonrenewable resources and threats
to renewable resources render absolute sustainability an impossible goal, it is nonetheless
necessary and important to undertake measures for protection of the geoenvironment and
its natural capital and resources—and where necessary, to restore the geoenvironment to
its pre-impact state. Failure to do so will exacerbate the conditions that have already led to a
compromised geoenvironment. As with all the chapters in this topic, the actions discussed
and proposed in these chapters recognize the need to strive for measures and actions that
will relieve the adverse pressures and stresses on the geoenvironment.
Contamination of the land environment by hazardous substances, contaminants, and
noncontaminants results primarily from man-made activities and events mounted to meet
societal and industrial demands. Contamination from natural events can also occur. These
include, for example, deposition of ash from volcanic discharge and seepage of sulfuric
acid and iron hydroxide when pyrite (FeS 2 ) is exposed to air and water, according to the
following relationship:

4 FeS 2 + 15 O 2 + 14 H 2 O ↔ 4 Fe (OH) 3 + 8 H 2 SO 4 (2.1)

We can encounter more dramatic discharges of sulfuric acid in the phenomenon com-
monly referred to as acid mine drainage (AMD). In this instance, the contamination is
considered to be associated with anthropogenic activities associated with metalliferous
mining, as will be discussed in more detail in Chapter 5.
By and large, contamination due to anthropogenic activities is without doubt the great-
est contributor to overall contamination of the environment and especially the geoenvi-
ronment. Accordingly, we will pay particular attention to this problem in this chapter. We
use the term contamination to include contamination by contaminants, toxicants, hazard-
ous substances, and all substances foreign to the natural state of the particular site and
microenvironment. When necessary, the terms contaminants, toxicants , and hazardous sub-
stances will be used to highlight the substance under discussion or to lay emphasis to the
problem. It (contamination) poses the most signiicant challenge in the maintenance and
protection of the many land environment ecosystems and resources needed to support life
on earth. Figure 2.1 shows a simple tabular sketch of some of the effects of impacts from
contamination of the land environment—illustrated as concerns and issues, for land , receiv-
ing waters , and ecological system.