Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 21

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Geology o fUrbanWatersheds
2.1 Introduction
We walk on a history topic every day, yet most of us are not fully aware of its signiicance.
The arrangement, thickness, and composition of the sediment layers beneath our feet
have a profound influence on where cities are located, how buildings are constructed,
where roads are built, and perhaps most important to the development and redevelop-
ment of our urban centers—how contaminants behave and how they affect the environ-
ment and people.
Geology is the science dedicated to the study of the history, structure, and composition
of the earth (Flint and Skinner 1974). The study of anthropogenic or human impacts on the
geologic environment is termed environmental geology (Bennett and Doyle 1997). For the
most part, the study of geology has been conducted for purely scientific and academic pur-
poses, natural resource exploitation, and geologic hazard evaluation and avoidance. Only
recently has the geologic environment in urban areas become of interest to geologists and
other scientists. The extreme upper portion of the lithosphere is affected by human activi-
ties, and this near-surface geologic environment frequently acts as the migration pathway
for contaminants to travel from a specific point of release to a point of ecologic or human
exposure. In many cases, this pathway goes undetected because the contaminants migrate
beneath the surface of the ground, and cannot be observed or detected until it is perhaps
too late.
The study of the near-surface geologic environment will become increasingly important
in the future. The world's human population is increasing in urban areas at a rate greater
than the human population as a whole. Nearly 3 billion people currently live in urban
areas. By the year 2030, the human population in urban areas is projected to be nearly
5 billion or 60% of the 8.6 billion people on the planet. The current level of population has
placed enormous pressure on our environment—including the geologic environment—
and the projected increases are likely to cause additional stress. Therefore, a thorough
understanding of the subsurface geologic environment is critical in order to understand
and protect the cities and places we live.
The environmental problems we face in the typical urban setting can in part be attrib-
uted to the poor understanding of the subsurface geology. Lack of attention to this area
of inquiry by the scientific community is one factor contributing to this knowledge gap.
Geologists generally have not spent very much effort or time studying shallow unconsoli-
dated geologic deposits beneath urban areas for environmental reasons because they
• Do not typically contain natural resources of high economic value.
• Have only become important in the last 30 years with the onset of significant envi-
ronmental regulations.
• Are covered by buildings and roads and other human-constructed surfaces.