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Mr. Michael Cunningham <br />CDRMS <br />November 26, 2013 <br />Management Plan (SWMP). This document has been prepared by UMC, and provides <br />the basis of our response to this query. <br />Figure 6 -2 (see Attachment 2) has been updated to show our planned upland diversion <br />measures. In general, the design will handle a 200 year, 24 -hr rainfall event (2.47 <br />inches, per NOAA database), diverting runoff around disturbed areas, reporting in <br />detention ponds in some areas, and onto natural existing drainages. Water within <br />disturbed areas will report to the TSF. <br />The following excerpt from the SWMP describes and addresses aspects of the upland <br />diversion design. <br />"There are two distinct portions of the Mill property. The northern portion of <br />the property is a moderately steep south facing slope and drains to the south. <br />The average grade of the northern slope is 25% and the hill slope on the <br />property ranges from an elevation of 9,760ft to 9,730ft. The southern portion <br />of the property is a gently sloping area that drains toward the southwest and <br />west. The average grade of the southern slope is 3% and the hill slope on <br />the southern portion of the property ranges from 9,730ft to 9,700ft at the <br />southwest property corner. <br />An unnamed 1ft to 3ft wide drainage channel enters the property on the <br />eastern boundary, adjacent to the northwest corner of the Leadville Sanitation <br />District polishing pond. This channel generally flows to the southwest across <br />the property, crossing under two access roads. The channel flows into what <br />appears to be an old soil conservation drainage ditch in the southwest corner <br />of the property and the water then flows along the contour to the northwest, <br />exiting the property on the western boundary. Undisturbed area runoff water <br />to the north of the unnamed drainage channel reports to the unnamed <br />channel. The flows are limited and the culverts under the road are 12in <br />culverts, with no evidence of overtopping or wash outs. The water exits the <br />property into an existing road drainage network, flowing to the Highway 24 <br />drainage network and then to California Gulch. <br />Undisturbed area runoff water south of the unnamed channel does not report <br />to a drainage channel, and overland flows through trees, and vegetative <br />cover, leaving the property along the southern boundary. <br />One type of soil classification exists within the property's drainage basin <br />according to the Lake County Soil Survey. The soil series is Leadville sandy <br />loam (LeE). This is a woodland soil. The predominate tree species on the <br />property is Lodgepole Pine. <br />During operation, runoff and flow patterns in the property drainage basin are <br />designed to generally follow the same paths as the historic basin. Soil <br />characteristics are identical to those of the historic basin, except for <br />impervious building, impoundment and road improvements. Vegetation <br />characteristics will not change in the undisturbed area of the project. Swales <br />and inlets are designed to handle the 100 -year 24 -hour peak flow. <br />During operation, a stormwater management plan and best management <br />practices (BMPs) will be implemented and maintained. Disturbed area <br />measures will include silt fence, erosion control logs, construction entrances, <br />river rock (or on -site cobble) sediment traps as required in swales or <br />