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ExxonMobIl Global Services Page A-6 <br />Colony Shale Oil Project <br />ESR Reclamation Studies <br />. Weighing Lysimeter Perforn~ance 1990-2003 <br />Project No. 353 <br />To be used for water balance calculations, moisture movement in soIls needs to be measured <br />on a reasonably frequent basis, and a monthly frequency has become the minimum fiequency, <br />essentially coinciding with monthly summaries of precipitation, temperature, solaz radiation, and other <br />factors in the water balance. <br />In test plots and lysimeters operated by shale oil developers in to the 1970s, neutron probes <br />were commonly used to monitor seasonal moisture changes. These measurements are time <br />consuming and require an NRC licensed specialty contractor. Another drawback to the neutron probe <br />is that it senses moisture in a "basketball" sized zone, while this program was seeking to make soil <br />moisture distinctions on a tighter spatial basis, e.g., the break between the "mixed zone" ESR <br />combusted shale. Further, the neutron probe is incapable of distinguishing between hydrogen <br />molecules that are in the form of water or ice vs. hydrogen molecules that have become part of a <br />• hydration mineral and no longer participating in the seasonal moisture migration <br />When the ESR test plots were in the design phase, other researchers at the University of <br />Wyoming had successfully demonstrated the use of TDRs to measure moisture changes in soils and in <br />spent shales. The measurements in spent shales were more difficult because the salt content tended to <br />mask the changes in dielectric constant that the sensor was attempting to measure. The University of <br />Wyiming researchers had found that by using shorter probes (4'~, the moisture changes could be <br />measured in salty soils. <br />TDRs were installed in the weighing lysimeter and in most of the sloping plots and in the flat <br />plot, and are read monthly. The initial readings were calibrated against carefully mixed control boxes, <br />in the Colony lab/office building. The control boxes were also fitted with neutron probe access tubes. <br />Exxon's contractor Environmental Solutions, Inc. (ESI) was able to develop a reproducible algorithm <br />to transform the TDR readings into volumetric moisture content, starting with the known calibration <br />boxes at known moisture content in the lab. These readings are taken typically monthly, by a site <br /> <br />LACHEL FELICE & Associates <br />