HYDRO23780 - Laserfiche WebLink

Home Browse Search

l~ Mr. Dan Jackson .tune 24, 1999 Page 2 ~' ~ 2. P. 3, Par. 4, P. 20, last Paz.The volume of saline minerals removed can be calculated with reasonable accuracy, but the method of identifying the shave of the cavity, which is critical to structural integrity, is not described. Some method of monitoring the migration of the solution front into pillars via the saline beds is needed. PP. 5-7 Hydrogeology. Water quality in the Parachute Creek Aquifer. The high concentrations of salt noted aze anomalous compared to past results of cazeful drilling/testing by the USGS at the US Bureau of Mines' Horse Draw site and at Fault Draw, and at the White River Nahcolite site (then aMulti-Mineral Corp. operation) (see reference, attached letter). These USGS results indicated TDS concentrations of a few 1,000 mg/L in the Lo~Ner Aquifer orily a few ]0's of feet above the dissolution surface. A common practice during drilling is to sample drill return water as a hole is deepened, as a way to estimate aquifer water quality. However, isolated Nahcolite nodules commonly occur in the oil shale section, where the near-impermeable rock has protected Nahcolite from solution by groundwater. When the drill penetrates such nodules, the resulting return water is charged with dissolved Nahcolite until the nodule is completely dissolved, thus leading to mis- interpreting this water as characteristic of the aquifer. The USGS evidence clearly indicates that the Pazachute Creek aquifer meets criteria for a US DW. 4. Monitoring Leakage of injection fluid, caving, subsidence, and wide excursions of the solution front (cavity shape) can best be detected early on by monitoring wells. Cavity leakage can readily be detected by Piezometers with ] 0-30' of perforations bottomed at the dissolution surface. Measurement of water level changes aze inexpensive, very sensitive, and may well be the first indication of leakage. Monitoring wells in pillazs would detect major solution extrusions laterally. P. 16. Injection Interval. A minor point, there are several aquifers below the Green River Fm (none likely to be affected). 6. P. 17, Par. 102 Because oil shale is not a strong rock, injection fracturing pressures can be significantly less than the normal 1 psi/ft. rule of thumb. See Item 2, P. ] of my 3-8-99 attached letter. Such hydrofracturing will result in small, probably insignificant earthquakes at the locus of fluid movement. The high pressures within cavities will promote brine flow along any fractures into the overlying aquifers.