Plenary: Urban geological mapping: pushing the frontiers of science below parks concrete, industry, businesses, and residences

Conducting geological mapping in urban settings is perhaps the most challenging mapping and the mapping exercise least desired by mappers. Logistics of where to obtain new subsurface information can be extremely limited, and sometimes depending on neighborhoods, not a safe working environment. Existing data, while often times plentiful, can be very difficult to obtain due to confidentiality restrictions. Just mobilizing from one location to the next location, considering traffic, pedestrians, and other urban travelling restrictions and obstacles is sometimes near to impossible. However, urban paved-over settings are some of the least understood geological environments, and perhaps the most deserving of our mapping attention. Indeed our city’s subsurface hosts deep foundation pilings and basements, underground tunnels for drinking water and waste water, sewage lines, pipes, electrical and fiber optic lines, as well as subsurface modes of transportation in the form of tunnels and subways. Urban land is a myriad of streets, parks, ecological restoration areas, industrial holdings, waste disposal and contaminated sites, surface and subsurface infrastructure development, and residential/commercial establishments. It is within the above context that high resolution 3D geological mapping will reveal “what lies beneath”. Only through a deep understanding of the subsurface environment can we truly assess contamination of the soil, contaminant mobility and pathways of contaminant movement with groundwater, as well as understanding the depth to, thickness, distribution, character, and continuity of deposits including aquifers, as well as address numerous other urban issues. Land-use and development decisions require knowledge of the subsurface for evaluating: 1. The local movement of contaminants because the soil holds wastes, spills, and debris from generations of habitation, and many areas have been redeveloped into parks, playgrounds, and areas of urban agriculture, and pose a real hazard. 2. Costs of cleanup of contaminants and long-term performance of waste disposal sites, as well as effectiveness of large-scale groundwater flow models to assist in pump and treat decontamination processes. 3. The ability of groundwater to recharge aquifers and how knowledge of geologic material variability helps to coordinate efforts to increase recharge/decrease runoff. 4. Foundation conditions that support a city’s skyline and infrastructure. 5. The extent and favorable/unfavorable construction conditions that assist in construction designs, bidding accuracy, and avoiding natural hazards, and this leads to cost-effective plans with future lower liabilities for economic development, environmental protection, and remediation. 6. The nature and distribution of geologic deposits that directly impacts the susceptibility of a city to urban hazards and geologic processes such as building settlement, piping, flooding, and earthquake shaking. 7. Brownfield reclamation and redevelopment. 8. Costs of excavation and fill, required for infrastructure, depend on the nature and thickness of surficial deposits and rock at construction sites. 9. Development of underground space to quarry rock, tunnels for transportation or drainage control, or create warehouse space. 10. Where the highest quality, closest, and least expensive sand, gravel, and rock can be obtained for building and infrastructure upgrades. These resources are becoming depleted in areas closest to cities. 11. Coastal issues of shoreline erosion, protection, and redevelopment strategies, sedimentation, beach replenishment. 12. Suitability of land for preservation, restoration, or creation of open spaces, wetlands, and surface water bodies. 13. Cost and long-term performance of waste disposal sites. 14. Ability of groundwater to recharge aquifers that is a function of the variability of geologic materials and land use. Knowing where these materials occur would allow land-use planning to better coordinate efforts to increase recharge/decrease runoff. Numerous land-use and development decisions are made on a daily basis within our urban environments, and each decision is associated with a potential liability, whether it be a failed foundation, unexplained cracks in concrete, contaminated soils and neighborhoods, unanticipated piping, or the mere encountering of unexpected subsurface conditions. All of these situations can result in increased costs to the developer, a municipality or other government entity, a landowner, and ultimately the tax paying public. Through 3D geological investigations that reveal a detailed knowledge of the subsurface, liabilities are greatly reduced just through anticipatory knowledge and situational planning that accounts for the unexpected and pursues planning and development endeavors that can take advantage of favorable conditions and avoids or is able to mitigate regions with unfavorable conditions.