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City auilding Tnapection )apartment <br />City of Everett <br />City hall <br />liverett, Washington 98201 <br />Attention: Mr. Ken Callahan <br />September 12, 1979 <br />30 <br />APR 9A 1982 <br />....................... <br />;ITY OF EVERETT <br />public Works 0ePt <br />cascade High School, Alterations and Additions <br />Gentlemen: <br />The following calculations are for the Retention/Detention Systems <br />Pt Cascade Iligh School. <br />RL•'fENTIOY/DETENTION SYSTEM #1 at AUTO SHOP <br />Post _Develo ent SYetam #ll <br />7,050 sq.ft. Paving <br />450 Sidewalk <br />7,000 " Roof Area <br />14,500 sq.ft. Total <br />pre Development Systsm_.±-1 <br />14,500 sq.ft. Grass Area <br />f>esign Storm: <br />Pre Development <br />frequency <br />1 in <br />10 years <br />Pont Development <br />frequency <br />1 in <br />25 ypare <br />,)oration <br />20 minutes <br />1.3 <br />in./hr. <br />IntensitN* pre <br />Development <br />1.6 <br />in./hr. <br />intensity post <br />Development <br />pre Development Design Runoff: <br />(.40) ( ) (12) 14,500 a .40(524) 210 C1'T <br />Post pevel�nt Runoff: <br />(.95)(136)(1/12) 14,500 - .95(645) - 613 CFT <br />Runoff Differential <br />