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Memorandum Montgomery Associates 11 <br /> Page 2 Resource Solutions.LIC <br /> Proposed erosion control methods are shown on Sheet 2. The Universal Soil Loss Equation was used to <br /> evaluate soil loss for the representative worst-case scenario.This scenario is described by disturbance of silt <br /> loam(k-factor of 0.43)on a slope of 5%with a slope length of 150 feet from September 15,2016 to January <br /> 15,2017,with final stabilization on May 15,2017.The WDNR Soil Loss&Sediment Discharge Calculation <br /> Tool for Construction Sites,with manufactured perimeter control from beginning to final stabilization <br /> ,calculated a soil loss of 3.0 tons/ac/year, this is less than the threshold of 5.0 tons/ac/year.As such,this <br /> disturbance does not require additional BMPs.USLE calculations are included in Appendix A. A stone <br /> construction entrance will be placed in the proposed driveway area. <br /> Erosion Control Construction Cost Estimate <br /> Item <br /> No. <br /> Material QT) Units Unit Rate Cost <br /> Stone <br /> 1 Construction 1 EA $1,000.00 $1,000.00 <br /> Entrance <br /> 2 Silt Fence 410 LF $2.00 $820.00 <br /> Total Costs $1,820 <br /> Stormwater Management <br /> Applicable Performance Criteria <br /> Applicable County stormwater performance standards for this development site are as follows: <br /> • Retain soil particles greater than 20 microns on the entire site(40%reduction)resulting from a one- <br /> year 24-hour storm event,according to approved procedures, and assuming no sediment <br /> resuspension. <br /> • Post development infiltration volume shall be at least 75%of the pre-development infiltration <br /> volume,based on average annual rainfall. <br /> OR <br /> If more than(1%)of the site is required to be used as effective infiltration area,the applicant may <br /> alternately design infiltration systems and pervious systems to meet or exceed average annual <br /> recharge rate of(7.6 inches per year). <br /> • Installed practices must comply with all standards and specifications described in s.11.13. <br /> Site Evaluation <br /> To determine the soil conditions,the site was located on the NRCS Web Soil Survey.The soil survey of Dane <br /> County characterizes the site soils as St.Charles silt loam.The infiltration rate of these soils is characterized <br /> P:11744 Kieran Montgomery House\Reports\STORMWATER MEMO6-16.docz <br /> 119 South Main Street • Cottage Grove. WI 53527 ph 608.839.4422 fx 608.839.3322 • www.ma-rs.org <br />