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. Between the F seam and the 300 foot overburden contour WECC monitors 11 <br />wells: B-32, SOM-13, SOM-80, SOM- 45-H-1, C-76, 23-H-3, 23-H-4, A-1 and A- <br />2. WECC has prepared well hydrographs for these 11 wells and they are <br />attached as new Figures 2.8.1.D.1 through 2.8.1.D.19. Subsidence is not <br />expected to affect springs or surface water when the overburden thickness <br />exceeds 30 times the seam height (average seam height is 7 feet). To <br />present a more conservative case, WECC is using a 40 times seam height <br />factor to estimate subsidence effects and has generally rounded the <br />resulting overburden thickness of 280 feet (40 X 7 feet seam height) to 300 <br />feet. The use of the criteria of 30 times seam height is discussed in the <br />response to question 2 of the additional questions submitted by CML.ZD to <br />WECC on April 17, 1986. <br />S. What impact has mining in the present 5 year mine plan area had on the <br />water levels in the water monitoring wells in the Barren Member. Most <br />notably the wells installed above the test panels. If no effects were <br />noted please discuss the reason for this. <br />Impacts of mining on water levels in monitoring wells and piezometers are <br />described in Section 2.8.S.l.a under "Observed Groundwater Impacts." In <br />addition, two wells, B-32 and SOM-13 showed anomalous water level <br />fluctuations but these may not have been related to mining. From early <br />January 1982 [o early March 1982 water levels dropped about 8 ft. in well <br />8-32. This well is completed in the Barren Member appror-imately 900 feet <br />from the portal construction area. However, the same well showed a 12 ft. <br />drop in water level during the month of June, 1981 prior to the start of <br />• construction at Mt. Gunnison. <br />Water levels in Well SOM-13 dropped approximately 50 feet from the <br />beginning of August through the end of September 1981. This well is <br />completed in the Barren Member about 1200 feet from the portal construction <br />site. It is apparent that this decline was not associated with mining <br />because the decline preceded portal construction. Also, it is unlikely to <br />be the result of dewatering, since the low angle drains installed for that <br />purpose produced little water. <br />The attached hydrographs (new Figures 2.8.2.A through 2.8.2.x) show no <br />response that could be related to mining. Wells 23-H-3 and 23-H-4 show an <br />increase in water levels in the spring of 1984. Both wells are in the Dry <br />Fork of Minnesota Creek valley which has not been impacted by mining. <br />6. "Page 2-486 states that wells SOM-38-H-1 and SOM-38-H-2 were unsuccess- <br />fully pump tested using [he air lift method. Why weren't other methods <br />used to pump test these wells? Future wells should be pump tested with <br />alternative methods if airlifting can not be used." <br />These wells were tested using "slug test" methods. The results are includ- <br />ed in Appendix D-2, "1981 Slug Test Data." <br />7. "Pages 2-530 to 2-536 are calculations for mine inflow using the Jacob <br />and the McWhorter method. Given that the cone of depression will <br />extend to 5 miles after 5 years of mining how much water can be ex- <br />• petted to be removed from the Minnesota Creek Basin?" <br />V-3 <br />