Laserfiche WebLink
3. OFFSITE ANALYSIS AND MITIGATION <br /> This site proposes to construct approximately 3,324 sf of new/replaced impervious <br /> surfaces. The following table summarizes the new PGIS and NPGIS proposed both on <br /> and off-site for this project. <br /> PGIS NPGIS Total <br /> (sf) (sf) (sf) <br /> Existing 3,372 1 ,758 5,130 <br /> Proposed 1 ,186 2,138 3,324 <br /> Removed 1,500 1,758 3,258 <br /> New/Replaced 1,186 2,138 3,324 <br /> The new impervious surfaces will be mitigated using on-site stormwater management <br /> BMPs including four splash blocks collected by a shallow swale with amended soils & soil <br /> management. The net increase in impervious surfaces for this project when accounting <br /> for the removal of the SFR and portions of the existing driveway is only 66 sf. <br /> A. UPSTREAM ANALYSIS <br /> During the site visit it was observed that the only runoff entering this site is from the south <br /> is from the neighboring landscaping. As a result none of these offsite flows will be affected <br /> by the proposed improvements on this site. <br /> B. DOWNSTREAM ANALYSIS <br /> Runoff from the proposed disturbance area of the existing site sheet flows over the <br /> northern property line. The runoff is collected in the 95th Ct SE roadway and directed east <br /> based on existing grades to a CB located approximately 50-feet east of the northeast <br /> corner of the site. The flows then travel east within a piped conveyance system to the <br /> detention system serving the development accessing off of the 95th Ct SE roadway. <br /> Based on the fact that the new NPGIS runoff will be dispersed with splash blocks and the <br /> PGIS will be dispersed using a transition zone to sheet flow any runoff over the future <br /> amended soils and landscaping before the runoff leaves the site and that this project only <br /> proposes to increase the total impervious surfaces on the site by less than 66 sf the <br /> developed flows will be slightly higher or equal to the existing conditions for this project <br /> and the offsite drainage systems in the downstream path for this site are large enough and <br /> accommodate such a large existing basin, any minor change in the flow rate from this <br /> project will not have an affect on the natural drainage system. During the site visit and <br /> review of the downstream system visited, no portion of the system appeared to be <br /> inadequate and there were no signs of erosion on-site or in any of the downstream areas <br /> visited. <br /> Fordham SFR 12-0906 <br /> Oct.2012 Page 5 <br />