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May 22, 2019 C-1981 -022/Elk Creek Mine LDS <br /> <br />Number of Partial Inspection this Fiscal Year: 8 <br />Number of Complete Inspections this Fiscal Year: 4 <br /> <br /> Page 3 of 12 <br /> <br />and it may be necessary for Oxbow to take additional steps in future to stabilize the surface while vegetation is <br />becoming established (for example, by using straw wattles to reduce the effective slope length). Regular <br />monitoring of these slopes will continue throughout the liability period. <br /> <br />HYDROLOGIC BALANCE - Rule 4.05 <br />Drainage Control 4.05.1, 4.05.2, 4.05.3; Siltation Structures 4.05.5, 4.05.6; Discharge Structures 4.05.7, 4.05.10; <br />Diversions 4 .05.4; Effluent Limits 4.05.2; Ground Water Monitoring 4.05.13; Surface Water Monitoring 4.05.13; <br />Drainage – Acid and Toxic Materials 4.05.8; Impoundments 4.05.6, 4.05.9; St ream Buffer Zones 4.05.18: <br /> The Elk Creek channel was reconstructed in the winter of 2017/18, and the process was documented in <br />monthly inspection reports from that period. The channel design is specified in Exhibit 2.05-E3 of the PAP. The <br />design is based on the 100 year, 24 hour event, which gives a peak volumetric flowrate of 107 cubic feet per <br />second (cfs). The design specifies a minimum bottom width for the channel of 10 feet, with side slopes of 3:1 and <br />a total depth of 1.8 feet. The channel slope is specified at 3-5% in the upper section and 6-13% in the lower <br />section. The design calls for the channel to be lined with a geotextile beneath 12” riprap. <br />Flow in the channel was high at the time of the inspection, however an attempt was made to measure the <br />channel dimensions at four points (see table 1 for measurements and figure 1 for approximate locations). Width <br />was measured at the waterline. Water depth and freeboard were measured using a stick and a tape measure, giving <br />an approximate measurement of total channel d epth. <br />Table 1: Elk Creek channel measurements <br />Point Width (feet) Water Depth (inches) Freeboard (inches) Channel Depth (inches) <br />A 10 16 18-24 34-40 <br />B 12 13 36 49 <br />C 15 >12 24 >36 <br />D 12 >12 18-36 >30 <br /> <br />No attempt was made to measure the size of the riprap used to line the channel, however the material used <br />was clearly larger than that specified (D50 = 12”). <br />At several locations along the reconstructed channel, particularly in the lower section, large boulders had <br />been moved within the stream. It was also clear that water had flowed behind boulders lining the banks of the <br />channel in places, and that soil was being eroded. Oxbow had attempted to stabilize the bank near to point D using <br />straw wattles. <br /> <br />DOCUMENTS RECEIVED <br />N/A <br />OTHER (SPECIFY) <br />N/A <br /> <br />ENFORCEMENT ACTIONS/COMPLIANCE <br /> <br />No enforcement actions were initiated as a result of this inspection, nor are any pending. <br />