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These percentages are approximate because of ambiguities in the post-mining survey data; however, they do indicate minimal planning or controls to ensure adherence to the mining depth limit. The preceding analysis suggests that some mining below the baseline channel elevation may have been deliberate. Lee Queen (of BLQ, Inc., a consultant for Sandco) stated that mining below the baseline level was not a problem because. the river would naturally refill such a depression with gravel during the following spring runoff (oral statement at Animas River Stakeholders meeting, 4/29/03); his statement implies that Sandco may have adopted this approach. 4.5 Changes in River Channel (Primarily from Mining) Since 1996-1997, the reach through the Dalton Pit has incised 1.9 ft on average; however, lazge variability is evident from maximum incision of 5.7 ft at section SC-1 and maximum aggradation of2.1 ft at SC-I4 (Table 5 and Figure 3}. Since 1977, available data suggest that the thalweg has incised 10-13 ft in the upper part of the pit and 6-10 ft in the middle and lower parts. Accuracy of the 1977 data is uncertain, but changes of this magnitude aze consistent with the relatively large height of the floodplain above the present channel. Aerial photos show long-term channel planform changes such as greatly decreased sinuosity and concentration of flow in a single channel, which is unusually wide in most places. 4.6 Suggested Modifications • Prohibit further mining in areas where thalweg is akeady below the 1996 or 1997 level. • Provide yearly late-summer orpre-mining surveys for all cross sections, as a minimum, in a timely manner • Annotate post-mining cross sections to make it more cleaz which parts of the section were actually mined. • Provide yeazly late-summer orpre-mining longitudinal sections through the entire pit, as a minimum. • Provide all survey data in both graphic and tabular numeric forms. • Provide estimated river mileage for all sections. • Indicate "look direction" on cross sections, for example by labeling east and west. • Provide complete tabular survey data for cross section SC-1 on Apri14, 2003 (data provided in letter from Dillon to Hellige on 10/21/03 appears incomplete when compared with the corresponding graph). • Determine whether Sandco has other pre-1996 survey data for this pit, and obtain all such data. • In any new permit issued for mining after November 30, 2004, require operator to mine in a manner that maintains a specific thalweg level. Gillam [o Hellige, Nov. 28, 2003 page Z O