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~.: ~ STREAf1FLOW ANALYSIS AfJO MONITORING PLAN Monitoring Plan To accurately measure any hydrologic impacts of subsidence on Dry Fork and the other streams, ARCO has developed a monitoring plan that will identify when there has been a change in water yields from any of the basins which have a potential to be impacted. The monitoring program will also be able to provide a timely determination of changes in channels flow within the permit area. - Continuous recording stream gauges are located near Horse Creek, South Prong, Lick Creek, Upper Dry Fork, and Lower Dry Fork. A gauge is also located on the East Fork of Minnesota Creek below Beaver Reservoir but above any discharge from affected areas. Baseline data is already being collected from these stations. The analysis of data from this net~,aork will provide the information that will identify whether there has been a change in water yields or timing of flows from streams originating in or flowing through the mine permit area. In addition to the existing network, a gauge will be located on the East Fork above its confluence with the Dry Fork of Minnesota Creek. The proposed location of this gauge is immediately above the Sweezy Turner Ditch but it is still subject to U. S. Forest Service approval. The gauge will be a 4 foot Parshall flume designed to measure low flows within 5X accuracy. This gauge is actually not necessary to determine the impact of subsidence on streamflow but it will provide additional information on streamflow from the remaining "unaffected" portions of the East Fork basin. Its utility as a control watershed is questionable because of diversion of flows above this point and other man induced chances in streamflow regime. One gauge relocation is proposed for the Ory Fork of tinnesota Creek station above the coal lease boundary but below the outlet of Deep (1~)