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Mr. Travis Marshall <br />Mr. David Bird <br />Division of Reclamation, Mining, & Safety <br />May 11, 2011 <br />Page 6 <br />evaluate the potential for vertical flow relative to the overlying WBIs. <br />For instance, consider a hypothetical situation where a well in each of <br />two aquifers each has the same water level elevation. All things being <br />equal, there is no potential for either aquifer to flow upwards or <br />downwards into the other aquifer. However, if water in one of the <br />aquifers is colder than the other, then the colder fluid in that aquifer <br />would have the potential to flow into the warmer aquifer due to the <br />greater density of the colder fluid. By similar measures, again <br />considering two hypothetical aquifers with identical water level <br />elevations, the aquifer with denser fluid (e.g. higher TDS) would have <br />the potential to flow into the aquifer with the lower density fluid. By <br />measuring the fluid densities and temperatures in the aquifers, and <br />"correcting" them to fresh water equivalents at 20°C, then using a <br />reference point at the base of the L5 WBI for the deeper and higher TDS <br />L4 and L3 WBIs, the potentiometric surfaces were compared to the L5 and <br />overlying WBIs with respect to the potential for up-flow or down-flow <br />across the regional R5 "seal." Temperature, to a much lesser degree, and <br />TDS affected density corrections are also required to properly evaluate <br />horizontal flow directions in an individual WBI where the TDS affected <br />density varies significantly, as is the case for the L4 and L3 WBIs near <br />their respective nahcolite Dissolution Surfaces. This methodology and <br />detailed description has previously been provided to the BLM, and will <br />also be published soon as a paper in the proceedings of the Colorado <br />School of Mines / Colorado Energy Research Institute 30th Oil Shale <br />Symposium held on October 18-22, 2010. <br />4. Section 5.4.1 discusses iron sulfide dissolution in shallow Uinta groundwater and <br />shallow Parachute Creek Member ground water. Is there knowledge of the redox <br />potential in all units of interest, and of redox potential gradients and how did this <br />knowledge affect the prediction of sulfide dissolution? <br />Redox measurements in Piceance Basin wells in the Parachute Creek <br />Member are very typically unreliable due to persistent degassing that <br />occurs during sampling. Biogenic C02 and CHq are significant enough to <br />cause cavitation in pumps during hydrologic testing, and this <br />phenomenon persists from sampling event to sampling event. As a <br />result, redox measurements at the surface provide widely fluctuating <br />readings, so direct redox measurements are not possible. Evidence of <br />iron sulfide dissolution is based on (1) observation of elevated <br />sulfate concentrations in ground waters close to the surface (Uinta <br />and L7, depending on depth of the L7) and (2) sulfur isotopic <br />measurements of dissolved sulfate compared with published iron sulfide <br />measurements. <br />5. I am unable to locate on any map the well cluster 138-4-298. Please indicate where in <br />the application package this information may be found; otherwise, please show the <br />location of this well cluster on a map so that we can verify its position as a satisfactory