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They are made by drilling a hole to the desired depth, and then pumping down fresh water to dissolve the salt, slowly raising the fresh water injection elevation, and pumping the salt water out of the cavern, until the desired diameter and height has been achieved. To illustrate how giant these structures are, compare them to the Empire State Building in New York City. which is 1,250 feet (381 meters) tall. And these salt caverns are only a fraction of the height of the salt domes.
Over a couple of years in the mid-1990's I did a detailed integrated interpretation of two small 3-D seismic surveys and a regional 2-D seismic section over the Boling Salt Dome in Wharton County, Texas. The objective of this study was to show there was not a significant salt overhang on the north side of the salt dome. If there was a significant overhang, then the proposed dissolution caverns would be too close to the edge of salt, and it would not make sense to make the caverns. The caverns were proposed for storing low grade toxic waste. One of the waste byproducts from hydrocarbon refining is long chain hydrocarbons, which are a toxic waste. The planned approach was to mix this waste with cement, then grind it up, and put the resulting mixture in salt caverns for permanent storage. A map of the top of the caprock, and a cross-section made from integrating the three seismic surveys is shown in Figure 46. This was an interesting geotechnical study, with very interesting political and social dynamics. To my knowledge the group paying for the study never got permission to proceed with the project from the State Regulatory Agency. The issues regarding what to do with these toxic wastes is like a vitriolic religious discussion. NIMBY's (those who say "Not In My Back Yard") put on their polyester clothes, leave their plastic stuffed houses, and drive their SUV's to protest placement of a toxic waste site in their county. And they do not seem to see the contradictions. There are, of course, two sides to every story. Proximity to the Gulf of Mexico (see Figure 47) and associated concerns about flooding were key considerations by the State Regulatory Agency.
Note that Figure 47 also shows the general location of the Katy salt domes, where the West Delta seismic section (Figure 44) and the general area where the Fairfield Salt Domes (Figure 45) are located, as well as where the Boling Salt Dome is (Figure 46).
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paradoxes
