As a geology major, it was my goal to propose a realistic question that would infuse both geology and geography. The world population continues to grow exponentially each year, causing waste and land management problems. Americans produce more than 200 million tons of garbage a year, creating a need to find safe locations to dispose of the waste without jeopardizing the surrounding population.
The question I chose to answer was: "What are the best locations in Travis County, Texas to create a new landfill?" In real life, it is a requirement that the base of a landfill be lined with clay to prevent possible leakage from entering the groundwater. As a result, one parameter considered was that the location had to be within a low permeability geologic unit such as clay. In addition, it was also established that the location had to be 300m from any wells or rivers, and outside any federal reserve lands. Furthermore, the location had to be economically reasonable so I created a parameter requiring the landfill to be within 1 mile of a highway.
The intended audience of this project is the county board of Travis County, Texas. This information is incredibly useful when considering the safest, yet economic place to put a new landfill.
Data Sources:
I knew the hardest aspect of this project would be finding geology data, so I decided to search the Esri 2013 USA database. There was no accessible geologic data, so I decided to utilize data provided with the Mastering Arcgis textbook by Marybeth Price. The Austin Geodatabase provided geologic data for seven counties in Central Texas, but I chose Travis County because it was the only county that also provided well locations in the area. I also needed to find data regarding rivers, and obtained it from the Esri 2013 database for the entire continental U.S. This was an extremely large file which made it difficult to work with. Other data obtained from the Esri 2013 database included U.S highways, U.S Federally protected land, and counties.
My biggest concern with this data was mixing U.S data such as rivers and highways with local data such as Travis County wells and geology. This presents a problem because it is likely that the U.S data was mapped at a very small scale and is over generalized when compared to the locally mapped well and geology data. Another concern is with regards to the geologic data used. One of the geologic units considered was titled "Del Rio Clay and Georgetown limestone; undivided". This indicates that not all of the area mapped is necessarily the Del Rio Clay, and in reality would need to be double checked before deciding to place a landfill in that geologic unit. Lastly, I was also concerned with the differences in map projection. As a result, I decided to change all features to the NAD 1983 HARN, Central Texas State Plane projection.
Methods:
I chose to use model builder within Arcgis to complete project (Fig. 1). Even though it was not a requirement to project each feature class into the same projection, I did so anyway to mimic a real world problem. I chose the NAD 1983 HARN, Central Texas State Plane projection because the area of interest (AOI)) fell entirely within that State Plane boundary. Using a local coordinate system reduces map distortion and increases the accuracy of the data. After projecting the data, I had to find a way to trim my U.S data to only the AOI. To do so, I first created a new feature class by isolating Travis County from the U.S County attribute list. Next, I intersected the Travis County Feature class with the highway, river, geologic, and federal preserve land data to cut out all data outside of the Travis County border. This made small scale data easier to work with, and allowed me to proceed with buffering the highway, river, and well data according to the original parameters. Furthermore, because the landfill was required to be within a clay unit, I had to isolate those areas (Walnut Clay and Del Rio Clay) from the rest of the geologic units by using the select by attributes tool. From there, I was able to use the erase tool to remove the well and river buffer areas that overlapped the clay units. Similarly, I then used the intersect tool to remove the area of clay that did not intersect the highway buffer. Lastly, I erased the clay area that fell within federal preserve land which produced the final objective.
Result:
As seen from figure 2, the resulting feature class (dark blue) shows area inside a clay geologic unit, within 1 mile of a highway, at least 300m away from rivers and streams, and outside of federal preserve land. The data shows there are relatively few options that fit all the criteria, which in it of itself adds value to this project. Placing landfills is a delegate situation due to the potential ramifications on environment and quality of life of those living near it.
Evaluation:
This project allowed me to utilize knowledge from two fields of science that I am interested in, while also creating a map that could be useful to the Travis County board.
It is acknowledged that not all the aspects of selecting a landfill location have been acknowledged in this project due to lack of available zoning data. As a result, it is very possible that a large majority of the area within the Del Rio Clay is within the city of Austin, which would not be a good location for a landfill. Furthermore, for the sake of this project, it was established that the landfill location had to be within a clay geologic unit. Although this is convenient, it is not always true. In reality, County boards will often use clay from another location to line the base of the landfill. If I were to do this project again, I would set the parameter that the landfill must be within two miles of a clay unit, which would drastically increase the available land area. In addition, I would need to obtain zoning data from the city of Austin so that it is not accidentally recommended that a landfill be built downtown.
My biggest struggle with this project was working with the large River and Highway data sets. Projecting the data into a new coordinate system caused the program to stop responding on multiple occasions, and took a very long time when it did work. If this were an actual project, I would use locally obtained data regarding streams and highways to provide a more accurate map and make the data easier to work with.
Sources:
Price, M., (2014). Mastering ArcGIS, Sixth Edition. McGraw-Hill Companies, Inc., mgisdata.
ESRI Database
www.EPA.gov/epawaste/nonhaz/municipal/
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