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n u ADDENDUM RESPONSE TO HINED LAND RECLAMATION DIVISION CLARIFICATION OF HYDROLOGY ISSUES AT THE ALMA PLACER NINE After a site meeting with personnel of the Mined Land Reclamation (NERD) on June 19, 1990, some issues were raised regarding the pro projects, drainage patterns and water use. This brief report is i address those issues. Most of the data presented herein has pre vi presented in submittals to the MLRD staff, most particularly the o Application and the engineering report that were attached to a let John Schmuck (of J. Remper Will) to Larry Oehler (of MLRD) on June entitled "Response to Mined Land Reclamation Division, Hydrology C the Alma Placer Mine". The following discussion clarifies the out items known to us at this time. AFFECTED AREA DRAINAGE As stated in the June 8 report and referred to previously, runoff f disturbed area rill be directed to the recirculating ponds, which 1 • downstream of nearly all areas designated as "affected areas". A m portion of the northernmost affected does not have surface topograp currently would direct surface runoff to ponds. Hoxever, it rill n without drainage modification. Mining rill progress in a northerly which inherently creates a drainage pattern that directs any surf ac from the mined areas to the recirculating pond. vision sed mining ended to sly been gins! r from 1990 terns at anding the that be mined irection runoff -In response to a specific request from the MLRD on June 19, this dr inag pattern has been shoxn as a "Water Collection Channel" on Plate lA. The channel will be constructed as part of the mining process and refle is disturbed area topography drainage, not existing surface topography rai The northxard-progressing mining will naturally create a south-drat ing channel. 25-YEAR FLOOD MLRD has expressed concerns that the 25-year flood will not be rout the site without causing damage. To clarify, the 25-year flood of Fork of the South Platte River is not being rerouted. It passes by in its existing channel, and the mine operators are protecting agai possibility of flood damage from the 25-year flood in its existing The 25-year flood at this location is approximately 600 cubic Feet (cfs) as discussed in our June 8 report and prior submittals. This the entire drainage area above Highway 9, which is just downstream site and essentially at the south end of Alma. This encompasses Bu • Creek and other tributaries to the !fiddle Fork of the South Platte As stated in our June B and prior submittals, we then assessed the flow in the vicinity of the recirculating pond embankments. Using equation, the standard calculation method in the hydrology/hydrauli around e Middle he site t the cation. r second ncludes the mine skin ver. pth of nning's