Geologic Data

Figure 8.3: Example of a Geologic Map

Credit: National Atlas, US Geological Survey

Why we need it

Geologic data provides siting engineers with the information they need to determine earthquake and foundation design requirements for towers. Geologists and environmental scientists use the geologic data to determine what type of rock underlays the route and whether this rock has characteristics that could cause environmental concerns if exposed or disturbed.

Two examples come to mind. The first is an overhead electric transmission line constructed by a major electric utility through Panther Valley in western North Carolina. During the construction of the transmission line, acidic rock was exposed. When exposed to air and water, this rock created acidic runoff impacting otherwise pristine streams. Action by the utility company to mitigate this rock exposure prevented widespread surface water degradation. A second, and more costly, example is the construction of Interstate I-99 through Central Pennsylvania. During I-99 construction in 2003, Pennsylvania Department of Transportation (PennDOT) crews first dug into the sulfur-bearing rock material (pyrite) in the Skytop section, near State College, and then continued to dig, using some of the million cubic yards of pyrite-laced sandstone as fill under the new highway and leaving the rest in spoil piles along the road. Seven years later, in 2010, after I-99 excavation exposed a massive amount of sulfur-bearing rocks, officials said the cost to undo the environmental damage totaled $100 million! Here is just one link to the I-99 problem: NY Times article

Figure 8.4: I-99 Acid Rock Remediation

Credit: Mining Waste Treatment Technology Selection

Where to find it

• The National Geologic Map Database is a USGS maintained catalog of geologic and geoscience maps and data.
• Additional sources of digital geologic data can be obtained from many individual State Geological Survey websites. Here is an example from the Maryland Geological Survey.