General Overview of Project

The coal tar that is currently being removed from the former Oneonta Manufactured Gas Plant site is being done so by certified professionals who approach the clean up using certified and closely monitored methods. The pits that are dug by the engineers are done so after careful calculations are made based on where the left over coal tar is and where it has moved to. In order to decide where the pits are dug it is imperative to take the geology and hydrology of the area into consideration.

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The above image displays where the remediation site is located within Oneonta New York

            The geology of an area does not just include the rocks, but the unconsolidated overburden (soil and unconsolidated sediments). Differences in geology can drastically change the way viscous mediums, like water, oil or in this case the coal tar, move though the ground. For example, water will move more easily though gravel (larger sediment) than it will clay or silt (smaller sediment). This is because there are large spaces in between each gravel grain and there are very small spaces in between clays and silts. Imagine having a container of gumballs and a container of baking flour. If you were to dump equal amounts of water into the containers the one with the gumballs would have water reach the bottom first. Using this information we can calculate an estimate of approximately how fast liquids are moving though the ground. We get geologic information of what is below ground from well logs. When a well is put into the ground a record is made of all the geology that the well passes through.

            The hydrology of the area includes all things having to do with water. This includes rivers, streams, lakes, rain and water wells. The hydrology of the area is important, especially the ground water, because some of the components of the coal tar dissolve in water. Water infiltrates though the overburden (soils/sediment) and down to a saturated zone in the soil, or the aquifer. The aquifer stores water, but the water is constantly moving. The ground water moves considerably slower than surface water in a river or stream does. Water is known as the universal solvent, meaning that almost everything dissolves in water, so if there is dissolution taking place then is an important factor in the proper clean-up. The water table (the top of the area saturated with ground water) changes during the year, so it is very important to know how deep the water table is. For example, if you need to dig a hole 25 deep but the water table is only 20 feet below the ground, you may have some issues.

            Another piece of the puzzle is the geography of the area, or the topography and general shape of the land in the area. This includes the hills, flat flood planes and other terrain. The topography is based on the geology of the area and the geologic processes that happened in the past. For example glaciers carved out the U-shaped valleys that we see today in Oneonta.  The ground water will flow much like surface water, from areas of high elevation to areas of low elevation, only much slower.

            Overall, digging the coal tar out of the ground is a complex job that could not be done properly without an understanding of the geology and hydrology of the area. For example, what would happen if they started to dig a hole with an excavator and encountered sandstone bedrock 5 feet down? The excavator could not be used to take out bedrock, so they would need to find a different way to clean up the site. The contaminant and ground water would have traveled though the ground differently if it was moving though sandstone bedrock instead of unconsolidated sediments. Engineers would not know how far the coal tar has traveled over a period of time, where it has gone or what it has done if they did not know what type of geology it is moving though. They also would not know if ground water was affecting its transport. The geology and the hydrology of an area are interconnected and are impetrative information in order to make the clean-up effort successful.

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