2009-05-21_GENERAL DOCUMENTS - C1981014

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previously mentioned, Newlin Creek's surface flow is diverted upstream via a pipeline owned and operated by the City of Florence. This reduces the significance of any depletion of the creek from mining. At the time of this permit renewal (RN-05) no stream depletion has been documented. During operation, the mine had sources of inflow in both the north and south sections of the mine. Quantification of total depletions to Newlin Creek is nearly impossible to make, since mining adjacent to this creek was conducted from 1900 through the 1970's. Most of these areas were sealed off and, therefore, could not indicate reliable inflows. However, the mine inflow study conducted by the operator did provide valuable data on impacts from the Southfield operation. The primary source of water entering the mine appeared to be from the abandoned workings nearby and above the mine. Quantities of mine inflows decreased from around 40 acre-feet in 1995-1997, to 10-15 acre-feet in 1998- 2000. According to the EFCI, this decrease was most likely due to the mine reaching equilibrium with the surrounding groundwater system such that water no longer rises into the accessible area of the mine. B. Surface Water Description and Consequences The permit area is dissected by three major drainages: Newlin Creek (a perennial stream), Magpie Creek and Second Alkali Creek (both of which are ephemeral streams). The streams flow to the northwest of the permit area where they empty into Hardscrabble and Coal Creeks. Hardscrabble Creek is an ephemeral stream while Coal Creek is perennial. These two drainages discharge into the Arkansas River, which is the major perennial drainage in the area. The base flow of Newlin Creek is diverted by the City of Florence upstream from the Southfield permit area. This water is carried across the permit area by a 12" pipeline. EFCI has monitored both the Newlin Creek streambed and the "Florence pipeline for subsidence since 1984. In 1999 minor subsidence occurred. The amount of subsidence measured at the eight subsidence monuments ranged from 0.06-1.66 feet. The maximum subsidence of 3.42 feet was still within the maximum expected and worst-case expected values of 2.79 and 4.36 feet, respectively. No subsidence has been reported at any of these monuments since that report. The Magpie Creek drainage was diverted around the mine facilities area by Dorchester in 1982. The drainage and diversion are discussed in the permit in Exhibit 19, "Drainage and Sediment Control". With the approval of Technical Revision 15, December 1993, designs for the permanent retention of Magpie Creek were incorporated into the permit. Monitoring of Magpie Creek to date has consisted of flow measurements upstream and downstream on sampling days once each quarter. Peak flows in Magpie Creek are measured to provide data for re-stabilization of the creek for permanent diversion status. Stipulation 14 was added to the permit to incorporate sampling of Magpie Creek into the permit. Page 26 of 36