Urban Geologic Mapping - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 166

the prime transport mechanism for contaminants. This combination of complex sedimen-
tary deposits and flowing water is why the shallow geologic environment beneath urban
areas must be understood at a level of detail at least equal to, or even greater than other
areas of the Earth, because these places are where we live and form the tightest bonds
between nature and society.
Geologic maps thus form the foundation for ecosystem management (USGS 1998). The
natural environment and the humans within it acquire an imposed organization resulting
from the geologic framework at any given location. Geologic maps provide us with knowl-
edge of that framework. Specifically, a geologic map facilitates the basic means for evalu-
ating resources, evaluating hazards, and environmental data relative to human activities
(Thomas 2004). As noted in Chapter 2, 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 how contaminants behave
and affect people. Constructing a geologic map of a region or a specific site is critical and
should be the first step in evaluating the development or redevelopment potential of an
urban region or site (USGS 1998; Berg et al. 1999; Berg 2002). It is therefore not an exaggera-
tion to say that sustainable urban environments cannot be achieved without accurate and
usable geological maps.
5.2 Geologic Mapping in an Urban Environment
Mapping the geology of urban areas increases our understanding of their fundamental
natural processes and identifies the types and locations of anthropogenic impact to con-
sider during the sustainable development and redevelopment of city cores and outlying
areas. Standards exist for geologic mapping (USGS 2010a) and always require that exten-
sive field work be completed when constructing a geologic map of a desired area (Maley
2005). However, many urban locations are not accessible, often making it imperative to
gather and evaluate as much reliable historical data and information as possible from mul-
tiple sources. The next nine sections present a sequence beginning with the collection of
relevant information and ending with the preparation of the final urban geologic map.
5.2.1 Information and Mapping Challenges
Mapping the geology of an urban region presents many challenges to geologists and can be
more difficult than mapping other regions (USGS 1998). Some of these challenges include
• Maintaining safety. Conducting field activities in urban areas poses many safety
concerns, including physical hazards from equipment, machinery, automobiles,
and other mechanical equipment. In addition, there may be other hazards such as
heat stress and related hazards imposed by weather conditions and the require-
ment for wearing specialized personal protective clothing to prevent exposure to
contaminants.
• Inaccessibility due to legal aspects of trespass and private property. Many loca-
tions of interest are not on public property and can only be accessed by receiving
permission from private property owners.
• Areas covered with buildings and other anthropogenic structures obscure origi-
nal features and eliminate the possibility of physical inspection.