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. ,. <br />GLEN A. MILLER <br />2264 Willow Wood Road ~ <br />Grand Junction, CO 81503 <br />Home 970-245-4347 - Work 970-243-1642 <br />March 8, 1999 <br />Mr. Larry Schults <br />USDI, BLM, WRRA <br />73544 Highway 64 <br />Meeker, CO 81641 <br />Dear Mr. Schults: <br />RE: Comments on EIS <br />Yankee Gulch Sodium Minerals Project <br />My comments are limited to the impacts of caving/subsidence <br />related to proposed solution mining. Some general ini`ormation on <br />this is contained in the late 80's EIS for the White River <br />Nahcolite Site. <br />The EIS is lacking in many details, these general ~:omments are <br />based on past mining-hydrologic experience in Piceance Basin, and <br />on the applications of geohydrologic principles to the' site. <br />One detail in particular: when adequate studies have been <br />done, the data indicate that the groundwater quality '_n the Lower <br />Aquifer, except for a few 10's of feet immediately overlying the <br />dissolution surface, contains TDS at concentrations less than a few <br />thousand mg/L (e.g., Dale & Weeks, 1978, USGS WR1 78-28, found the <br />Lower Aquifer contained about 1,500 mg/L at Horse Draw, adjacent to <br />this site). Similar results were obtained during earl~~ hydrologic <br />testing at what is now the White River Nahcolite Site. High TDS <br />water typically is reported while drilling throug:z residual, <br />hydraulically isolated Nahcolite, when drilling water is sampled <br />before the nodule is dissolved. This oe not result in a <br />representative sample. <br />The following summary comments are based on the information in <br />the EIS, more details on the operation are needed. The <br />externalized costs of the project on water and miner~~l resources <br />appear to be significant, and are not fully addressed in the EIS. <br />1. Subsidence/caving will occur as noted, but almost <br />certainly will have more significant ei`fects than <br />described in the EIS. <br />Rich Oil Shale/Nahcolite is not noted for great rock <br />strength, and the 150-foot sill pillar above each mining <br />well site eventually will cave (and could fracture during <br />mining under proposed pressures), thus allowing brine to <br />enter the Lower Aquifer. Any significant: caving or <br />movement during mining could interfere with the well <br />system. The high pressures proposed are in the rock- <br />fracturing range determined by Wolff & Bredehoeft (1974, <br />RMAG Guidebook to Energy Resources of Color~~do). <br />This degradation of groundwater and progressively upward <br />fracturing would adversely affect future oil shale mining <br />(and aluminum recovery) because: <br />