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Marc , 1 <br /> Me. Jane 2lmmerman <br /> City of Everett <br /> Public Works Departm ±nt <br /> 3200 Cedar Street <br /> Everett� WA <br /> Dear Me. Zimmf�rman: <br /> we are eubm:ttinq the revised storm retention syetem and <br /> calculatione; for your raview. We have modified the system <br /> to a gravel tzr_nch instead of e pond utilizinq a percolation <br /> rate for 1►ldetwood eoila of 15 minutea per inch in <br /> accordance with your reqL�iremente. The calculations are <br /> organized as followes <br /> Time of concentration. <br /> Hydrograph, 25 ��ear. <br /> Storm retention system data. ' <br /> Routinq datas 25 year intensity, 24 hour storm through <br /> the 9ystem: bnse �levation = 662.50j top elevntion = <br /> 665. 50 maximum elevatian of water with 25 year etorm <br /> ia 665.12. Siza of syetem ie 11 ft wide hy 1601f lonq <br /> by 3' deep. poroeity of the qravel ie 0.30. No <br /> storage is coneidered for the pipe. <br /> We have also added the vault and oil separator ae requeated. <br /> Maximum pondinq time ie 8.7 hours (see print out) . <br /> City notes have been added to the plane for the infiltrntion <br /> eystem. <br /> The other itema ih your letter have been rQeolved by phone. <br /> Please feel free to call if we may answer any additional <br /> questiene you may have. <br /> Sincere , <br /> �� / � <br /> Donald K. Scarb .r`ry, P.E. <br /> Manager Civi�gineerinq <br /> NelBon-Bourd es Inc. , P.S. <br /> 90U5C <br /> NELSON-BOURDAGES, INC., P.S. <br /> Cons�hing F.ngine�•r�• I141I NE. 17AIh S�rcet. Sulte ?30 � Klrkland. WA 9P030 • 70b/BI3�6A67 <br /> FAX I2�1 R70-09A7 <br />