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Response to Public Comment
Listed below are summaries of comments by Dao Yang, followed by a response from USGS. The summary of each comment is linked to the original document submitted by Dao Yang.
Comments from Dao Yang
Complete letter from Dao Yang (pdf)
DY1. The potentiometric surface generated for the carbonate-rock aquifer is not acceptable.
Apparently, there are not enough well data available to generate the contour. Some contours were generated based on well data across different valleys and thus they are across mountains.
RESPONSE
The potentiometric-surface map was constructed from the best available data. The authors recognize that wells penetrating the carbonate-rock aquifer are few but heads in deeper wells in the overlying aquifers are thought to be similar to heads in the deeper aquifer and were used to generate the regional map. The coarseness of the contour interval also allows some flexibility in map construction. It has been long recognized that regional ground-water flow is driven by hydraulic gradients that are continuous over long distances and can be unconstrained by local topographic or drainage features (Bedinger and Harrill, 2005). The potentiometric surface map constructed for the BARCAS study was compared to published maps for consistency. These maps may be modified in the future as deeper test wells are constructed by SNWA and the Utah Geological Survey.
DY2. It is so strange the way the stored water was calculated.
It appears that it was tried to calculate how much water can be yielded from a 100-foot lowering of water level from the thick basin-fill aquifer and another confined aquifer beneath the basin-fill aquifer. It is not clear if the water from the confined aquifer represents the water yield from the carbonate-rock aquifer. If it is, that means that the extent of the carbonate-rock aquifer is the same as the basin-fill aquifer. This is contradictory with the presentation of the potentiometric surface map for the carbonate-rock aquifer.
RESPONSE
The comparison of water stored in aquifers between the unconfined basin-fill and confined carbonate-rock aquifer was based on the areal extent of the valleys for each hydrographic area. The differences represent the physics of gravity drainage versus rock/water compressibility in the release of water. Additional text has been added to the summary report (SIR 2007-5261) to clarify how storage was calculated.
