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Page 17 <br />The fractures are very wide, and water conductivity is excellent in the caved zone. When <br />1 the aquifer is located in the caved zone, the water generally will not reappeaz once lost during <br />mining. <br />4.3 Evaluation Criteria <br />The evaluation criteria to be applied to the high-extraction solution mining option at the <br />White River Nahcolite, Inc. lease aze derived from the multiple-seam mining experiences and <br />other sources. For the discussion in this section, the criteria are divided into qualitative and <br />quantitative categories. <br />The qualitative criteria based on the caving mechanism described in Figure 4-1 are: <br />^ Solution mining impact to the protection of aquifer and minability of oil shale is <br />minimum if the strata of aquifer and oil shale aze located in the continuous defor- <br />mation zone. <br />^ Solution mining impact to the protection of aquifer and minability of oil shale <br />may range from insignificant to adverse if the strata of aquifer and oil shale are lo- <br />~ cated in the fractured zone. For the minor fractured zone, the impact should be in- <br />significant. For the severe fractured zone, the impact could be adverse. <br />^ Solution mining impact to the protection of aquifer and minability of oil shale <br />would be unacceptable if the aquifer or oil shale were located in the caved zone. <br />With 40% extraction of the nahcolite reserve, solution mining could yield approximately <br />16 ft of equivalent mining height (H). The caved zone is predicted to be from 32 to 128 ft (2 to 8 <br />H) with the fractured zone extending up to 144 to 176 ft (9 to 11 H) from the roof of the cavern. <br />The stratigraphy presented in Table 2-2 indicates that the interburden height from the dissolution <br />surface to the B-Groove is approximately 288 ft. Judging from this information, the impact is <br />most probably insignificant. <br />Quantitative criteria for aquifer protection are summarized in the SME Mining Engineer- <br />ing Handbook (SME 1992). The damage criterion is expressed in terms of horizontal strain and <br />is 0.005. No explicit quantitative criteria was found for the assessment of minability. However, <br />Chekan and Listak (1993) suggest that beds located in the caving zone (three to six times the <br />mining height) may not be minable. The strain criterion of 0.005 is also suggested for both the <br />assessment of impact to the aquifer protection and minability of oil shale. <br />Associates, Inc. <br />