Laserfiche WebLink
<br />4. Page G-8: top. The Operator concludes that "the only aquifer at the Piceance site that meets <br />the definition of a USDW is the Uinta Formation (upper) portion of the Upper Aquifer. This <br />conclusion is apparently based on TDS measurements in a single well, number 20-3. The <br />conclusion implies, though i[ does not state explicitly, that the upper part of the Uinta is the <br />only aquifer that needs USDW protection. <br />There are other actual TDS measurements from this and other wells. Moreover, conductivity <br />data were collected at a somewhat high frequency. Given the controversy over water quality <br />in the upper and the lower aquifers in the region, the Operator should make a more detailed <br />attempt to quantify conclusions about aquifer quality for the lower part of the upper aquifer <br />and the lower aquifer. Provided the relationship between TDS and conductivity can be <br />substantiated, then all conductivity values from all the local wells should be used to construct <br />a conductivity-based TDS facies map, or other such construction, to identify the boundaries <br />of waters with greater than 10,000 mg/L TDS. <br />6. Page G-10, ~[ 3. The DMG agrees that there is a tendency toward supersaturation and mineral <br />precipitation when solute-laden fluids cool. We question whether cooling alone will promote <br />precipitation of the solids that will be dissolved by hot water that will be injected into the <br />saline zone. Depending on the amount of water added, the saturation index might not be <br />reached, even at surface temperatures, unless part of the water evaporates from the solute. <br />Kinetics of precipitation also may play a role. <br />In [he present case, the potential adverse effects of fluid escape are considered to be minimal <br />on the assumption [hat the dissolved nahcolite will reprecipi[ate upon cooling and heal <br />fractures in the Uinta formation aquifer, thereby preventing injections of saline fluids into the <br />upper aquifer. Given the low TDS in the upper aquifer, we consider this doubtful, but do not <br />have enough information to evaluate the conclusion. <br />If temperature-controlled reprecipitation of dissolved solids is to be considered a means to <br />control leaks of process water into the upper aquifer, or other USDWs, the DMG would need <br />to see evidence that such solids will form. We would anticipate that American Soda has <br />conducted enough experiments to know with some degree of accuracy the temperature and <br />solute concentrations that control nahcolite precipitation, and would be able to provide that <br />information to support their conclusions. In any case, the DMG needs to know whether such <br />a process is deemed to be a necessazy means to control contamination of the USDWs. <br />