Urban Geologic Mapping - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 172

Chapter 2. The investigator should pay attention to these deposits during the informa-
tion gathering phase of the mapping process. Then, he or she can make a determination
whether the deposits are sufficiently large in scale compared to the map being developed,
and if they contribute to the history and understanding of the area being mapped.
5.2.4 Fieldwork
Information gathered and evaluated from the sources listed in Sections 5.2.2 and 5.23 will
assist the geologist in understanding the area to be mapped before extensive field work
begins. The geologist must be skilled in understanding sedimentary processes and in
identifying the difference between a natural and anthropogenic deposit. This is some-
times difficult even when there is a detailed understanding of the geology of a site or
region. An example is the anthropogenic deposition of dredge materials noted in Section
2.6.2, which can take on the appearance of a natural deposit due to the common presence
of bedding layers indicating a stratified sequence of deposition. Complications such as this
in many urban areas may require several rounds of fieldwork, literature search, and his-
torical forensic review before sufficient understanding can be achieved to construct a map.
Based on the authors' review of large volumes of historical information and the con-
struction of numerous conceptual geologic models, fieldwork in urban areas is usually
concentrated at the following locations:
• Areas with limited or no information, or areas with gaps or missing information
in the existing data set
• Locations with geologic irregularities or complexities
• Areas with extensive anthropogenic disturbance
• Areas of geologic significance such as formation contacts and unconformities
• Areas where geologic processes of formation overlap or are located in close
proximity
• Locations requiring confirmation of previous interpretations
• Areas not easily accessible
• Areas of ecological significance
• Areas with a high potential of encountering contamination
Geologic mapping in an urban area often requires the geologist to excavate through poten-
tially disturbed soil profiles to reach material representing naturally occurring deposits.
This fieldwork is often a dangerous activity due in part to broken glass, metal fragments
and other debris, underground pipes, and the existence of potentially harmful contamina-
tion. There may also be other hazards present, such as high vehicular traffic. Therefore,
extreme care and proper planning should be employed, and the geologist should perform
the following actions before conducting geologic mapping activities in the field:
• Conduct a reconnaissance of each area or location of interest
• Prepare a written scope of work for each desired location, including
• Purpose and objective
• Activities to be conducted
• Equipment list