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6. PRESERVATION OF NATURAL DRAINAGE SYSTEM <br /> The runoff from the PGIS improvements will be dispersed along the east side of the <br /> proposed improvements. By not grading or compacting the majority of the pervious <br /> surfaces to remain after construction in the area of disturbance a maximum amount of <br /> PGIS runoff from the developed project will be absorbed and infiltrated into the existing <br /> on-site soils. This will mimic the existing conditions by maintaining the existing direction <br /> and condition of flow from this site. <br /> 7. ON-SITE STORMWATER MANAGEMENT <br /> Per Section 2.5.5 of the 2014 DOE manual projects must incorporate On-Site Stormwater <br /> Management BMPs based on lists provided in that section. The applicable list for this <br /> project is List#1 since this project only triggers MR#1-5. <br /> When using List #1 each BMP must be considered in the order provided in the list. The <br /> first BMP determined feasible for each type of surface must be used. <br /> Lawn and Landscaped Areas: <br /> Post Construction Soil Quality (BMP T5.13) - Selected/Feasible <br /> Roofs: Not Applicable <br /> Other Hard Surfaces: <br /> Full Dispersion - Not Feasible <br /> This project is not able to protect 65% of the site area as forest or native conditions and <br /> still have a viable project. Therefore, BMP T5.30—Full Dispersion is Not Feasible. <br /> Permeable Pavement Rain Gardens or Bioretention - Not Feasible <br /> This project is located within the existing City R/W or in an area that has been <br /> extensively graded/filled in the past. So all infiltration type BMPs are therefore <br /> deemed Not Feasible. <br /> Sheet Flow Dispersion - Modified/Selected <br /> This project will allow the runoff from the west within the R/W along with the new <br /> PGIS for this project to continue to flow east off the new/replaced PGIS and into <br /> the existing BNSF R/VV. The dispersion will be along the downstream edge of the <br /> new/replaced pavement which is slightly different from the standard sheet flow <br /> dispersion BMP which tried to have the runoff dispersed along the entire edge of <br /> the pavement that runs parallel to centerline. However, the R/W grades do not <br /> allow for this in this case. <br /> • <br /> Based on this information provided above, the drainage mitigation was laid out using the <br /> Selected/Feasible BMPs. <br /> Royell Manufacturing 15-0714 <br /> July 2017 Page 10 <br />