Laserfiche WebLink
900 feet. Twentymile's consultant, Hydro-Geo, prepared a description of the potential impacts to the these creeks <br />• based upon the subsidence predictions for the Eastern Mining District. That information is presented above and in <br />the included exhibits. The conclusion of their analysis is that the respective creek channels will have selected <br />segments experience gradient changes, but these changes will not result in excessive erosion of the channel. The <br />study also included the installation of eleven monitoring wells, two of which were completed in a shallow bedrock <br />unit and the remainder in the Fish Creek alluvium. The monitoring of these wells showed that the shallow bedrock <br />well experienced localized dewatering over the mine workings, which had been predicted, and the subsequent <br />recovery to approximate premining conditions. The alluvial wells did not experience any significant dewatering <br />due to the undermining and subsiding of the valley floor. These data are summarized in Exhibit 7j. The water <br />quality in the wells was not significantly impacted by the subsidence that occurred in the study area. There was a <br />slight increase in some of the metals due to mobilization within the alluvium, but the concentrations were not high <br />enough to cause water quality problems. <br />The study is useful in demonstrating that undermining and subsiding of creeks and valley floors can be <br />accomplished without negative impacts. It is Twentymile's opinion that Middle and Foidel Creeks and their valley <br />floors will respond in the same manner as those in the study azea. <br />(ivl A elan based on the probable Itydrologic consequences <br />determination and baseline hydrologic and peologic information submitted to comply with 2.04.5, 2.04.6, and <br />2.04.7 for the collection, recording, and reporting of Around and surface water Duality and quantity data. The plan, <br />in accordance with 4.05.13, shall identify monitoring site locations, parameters, sampling frequency, and describe <br />how these data will be used to determine the impact on the hydrologic balance. At a minimum, the hydrologic <br />monitoring plan shall include: <br />• (A) Monitoring of at least total dissolved solids or electrical conductivity <br />corrected to 25° centigrade (specific conductance), pH, and iron; <br />(B) Monitoring of water levels, reported as feet above or below land surface <br />datum, for ground water plans; <br />surface water plans; and <br />(C) Monitoring of total suspended solids and flow rate measurements for <br />(D) Monitoring for additional water Duality constituents may be required b y <br />the Division based upon site-specific conditions, approved postminine land use, or for good cause sltotvn. <br />HYDROLOGIC MONITORING PROGRAM <br />TCC will conduct a program of surface and ground water monitoring in the Foidel Creek Mine Permit and adjacent <br />areas. A detailed discussion of monitoring procedures and the schedule for monitoring activities is presented as <br />Exhibit 14, Hydrologic Monitoring Plan. Monitoring activities will continue on a regular basis until the effects of <br />mining-related activities have been determined to have stabilized and are within acceptable limits as determined <br />from water quality criteria and until approved to be reduced or terminated by the Division of Minerals & Geology. <br />The monitoring program as proposed will conform with all applicable State and Federal laws and will provide a <br />continuing means of detecting and measuring any changes in the area hydrologic environment. Hydrologic <br />monitoring activities will address the quality and quantity of both surface and ground water systems. <br />Ground WaterMonitorint= <br />TR99-32 2.05-168 APPF3®E/~~ r[B C 'v 2000 11/15/99 <br />