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TO: <br />FILOM: <br />PUBEIC W0f3KS <br />PROJIsC'f RIsVIF,N' MisMORANDUh9 <br />Paul McKcc <br />Janc Zimnternum <br />/ " � <br />DA'l'L: � Decembcr 28, 2004 J ; <br />! . <br />SUB,TI?C1': Multiple Pamily Project at 9331 I R°i Ave W <br />I have the following review comments on the suhject submival: <br />D2AINAGL CALCULATICNS: <br />Gencral <br />Thc crcckhvctland corridor to thc immcdiatc c��st of this projcct ilows south, has an <br />upstrcam drainage basin ol� more than 100 acres, and has downstrcam restrictions to t7ow. <br />Thc f7nished (loor clevations af thc buildings on this sitc must be a minimum of 2 feet <br />above dic 100-ycar (lood clevalion. The applicant's engincer will be rcquired to definc <br />the upsu�cam druinage busin, detennine lhe 100-year creek flow, and conduct a backwater <br />analysis in order lo detennine the 100-year flaod elevation at this sile. <br />A sprcader trench is an acceptable means of discharging treatcd and detained stonnwater <br />runotT into the crcelJwedand corridor. However, instead of backfilling with native soil, <br />the 6 inclies above the mirafi 140 NL should also be washed rock, in order lo allow water <br />to over(low the trcnch. As sho�an, the lowest exit point is tl�e rim of catch basin #8, and <br />if thc runoff in thc trench does not infiltrate, iCs likely that thc grate of C[3 #8 �vill <br />bccume a poinl discharge. If the thrcc cutch basins arc provided, �hey should be equipped <br />with solid lids, or have a rim elevcuion at least G' higher Uian lhe washed rock surfacc of <br />the lrench, so as to enca�ragc dispersed shect 11ow out of the trench and through thc <br />buffer. <br />On thc calculation summaiy shect, thc allo���ablc rcicase appears to be �O�lo of thc existing <br />2-ycar runofCratc, but this faet should he stated explicitly, eithcr in section V of thc <br />report, or in the summary shcet. <br />The project is a multiple fumily projcct, and has a i,000 syuare f�oot threshold for runoff <br />treatment. RunofC treahnent must be provided in accordance �vith City standards. Per <br />Uiis projcct, the �'ollo�ving options exisC <br />a) a���etpond or constructcd wedand, designed in accordance with City standards <br />'�IG <br />s:A� zi mmcnn\���urdApr_ I Sth a��c <br />