Environmental Engineering Reference
In-Depth Information
6
Geologic
V
ulnerability
6.1 Introduction
We have control over the chemicals we use, and where and how we use them. Control over
the geologic environment, however, is beyond our means. Therefore, we must understand
the geologic environment where our urban areas are located and develop methods to min-
imize or eliminate the potential harmful effects of contaminants upon human health and
the environment. A logical first step to this end is through an
understanding
of urban geol-
ogy, followed by an
evaluation
of the extent that a given urban area's geology influences the
migration of contaminants. Since water plays a critical role in assessing a region's vulner-
ability to contamination, the analyses performed during the evaluation step require an
understanding of water occurring at the Earth's surface and beneath.
As demonstrated earlier, urban areas within the United States and throughout the world
share a geologic environment dominated by sedimentary deposits. Many of those sed-
imentary deposits are saturated with water and function as sources of drinking water
and/or as hydraulic connections to surface water and sensitive ecosystems. Given these
relationships, using a watershed approach during the assessment process is scientifically
sound because the geology of a region greatly influences the surface drainage patterns and
often contributes significantly to the baseflow of surface water. Moreover, as described in
Chapter 3, water is considered the universal solvent, so any contamination released into
the environment from anthropogenic or natural sources has the potential to migrate and
impair surface water or groundwater.
The factors controlling the severity of the damage are (1) the hydrogeologic environ-
ment, (2) the physical chemistry of the contaminants and amounts released, and (3) the
mechanism in which the release occurs (Rogers 1996; Murray and Rogers 1999a; Kaufman
et al. 2005). As noted in Chapters 4 and 5, there are several techniques available for inves-
tigating and managing the complexity of urban water pollution. For example, a signifi-
cant amount of detailed geologic and hydrogeologic information for many urban areas is
currently available to support environmental assessments. In addition, there are several
methods that enable access to contaminated locations for conducting fieldwork, and pro-
cedures exist to collect the relevant data without causing disturbance to any natural or
anthropogenic surface features.
Despite the availability of specific methods and procedures, the environmental assess-
ment of many urban areas can become a daunting task. This situation arises because the
near-surface geologic deposits in urban areas are poorly understood, difficult to study,
complex, have been anthropogenically disturbed, and exhibit high variability over short
distances. Therefore, to achieve any level of success in mitigating environmental contami-
nation, it becomes a prerequisite to understand the watershed's hydrology, and the fate
and migration of contaminants within its specific geology.
The focus of this chapter is to identify urban regions vulnerable to contamination and
those areas where widespread contamination is less likely. To accomplish this task, an
Search WWH ::
Custom Search