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~~ <br />U <br />Revised 04/20/90 <br />Section 7'80.18(b) Continued. <br />reestablished ephemeral drainages, permanent diversions, and <br />associated transition and flow control structures. <br />Reestablishment of effective drainage across or around disturbance <br />areas is the primary controlling factor in design of the postmining <br />topography. For each active pit area, Kerr reviewed premining <br />topography maps to determine drainage locations, density, <br />configuration, and gradient. Utilizing available backfill material, <br />Kerr then developed a design postmining configuration which most <br />closely approximates these parameters, providing effective drainage <br />within the constraints of operational and economic feasibility. <br />The postmining drainage configurations for Pit 1 and the 720 Pit are <br />• illustrated by the Kerr Mine Area Postmining Topography Map, (Map <br />37a), and detailed supporting design calculations are presented in <br />Exhibit 42, Drainage and Sediment Control Plan. <br />Overburden Samoling Program <br />Some elevated values for SAR and ESP have been identified from <br />overburden analysis results for samples from the Pit 2 area. Based <br />upon available information, there are indications that elevated <br />values are a reflection of bias due to sample contamination by <br />drilling fluids. <br />In order to further evaluate potential overburden toxicities, Kerr <br />is proposing an overburden sampling program for the Pit 2 area if <br />mine development proceeds. Sampling will focus on those intervals <br />previously identified as exhibiting elevated SAR or ESP values. <br />Within these intervals, Kerr will collect a minimum of two samples <br />for each compositing interval, with sample locations to be from 200- <br />. 500' apart. <br />780-70 aaa <br />