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Pilot Test for Mapping of Solution-Mined Cavern Using <br />NSA's Seismic Reflection Technology, TRTT"" <br />Section 1.0 Introduction <br />American Soda, L.L.P. conducts solution mining to recover nahcolite from <br />Federal lands located in northwestern Colorado. American Soda <br />contracted NSA Geotechnical Services, Inc., to (1) evaluate the <br />effectiveness of using NSA's seismic reflection technology, TRTTM, to <br />estimate of the size and shape of the caverns resulting from this solution <br />mining, and (2) recommend a system and procedure for the evaluation of <br />other caverns based on the outcome of the test. <br />At the time of the survey, the cavern of Well 28-21 was filled with brine <br />heated to a temperature of approximately 200 to 275 degrees Fahrenheit. <br />The crown of the cavern was estimated to be at 1,680 feet below the <br />surface, and the floor of the cavern was estimated to be at 2,150 feet <br />below the surface. Specifically, the objective of this project was to <br />produce two- and three-dimensional tomographic images of the average <br />cavern perimeter as defined by seismic energy reflected from the cavern <br />boundaries. <br />This report includes a description of the test procedures, data analysis, <br />and a brief interpretation of results. <br />TRTTM Background <br />TRTTM uses seismic waves to identify structures within the rock mass that <br />reflect seismic waves. The technique is based on acoustic impedance <br />contrasts (the product of density and seismic velocity) that occur at <br />boundaries between geological layers or discontinuities. These <br />discontinuities act as imperfect mirrors, returning part of seismic energy to <br />a detector; this energy is then analyzed to determine the location and <br />nature of the reflecting boundary. A transition from a material with lower <br />acoustic impedance to one with a higher value results in a positive <br />reflection coefficient, and vice versa. Features such as fractured zones <br />within a more solid rock mass will also give rise to reflections. The larger <br />the acoustic impedance contrast, the larger the reflection coefficient, <br />and the easier it is to detect the echo. <br />A typical TRTT"^ survey uses a fixed array of about 10 sensors (receivers) <br />and seismic sources (blasts or hammer blows) initiated at different <br />locations. For each source, a seismograph records a data file that <br />