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i <br /> � <br /> 9. DFSIGN CRITERIA -The system has been designed to meet thc City of Evcrett <br /> water qualiry treatment rcquirements of dead storagc of 65�90 of the 2 year swcm <br /> A summary of design criteria regacxiing detention releuse rates,sto��ge volumes anJ wet J <br /> ( pond volumes are shown in Table 1, Seaway Blvd. Lot SB Design Criteria Summary. <br /> Tablc 1 Seaway Blvd. L.ot SB Dcsign Criteria Summary � <br /> IDesi n Criteria 2 Year Storm � <br /> Re d. TreaUnent Volume, 5,227 : <br /> I cf, of 0.0.12 af <br /> n Cc Stora c, c 4,443 <br /> reatment Cc Stora c, c '� a <br /> I 100 Year Dcvelopeci Pc � 1. 2 cfs ^A � <br /> Runoff Rate " � <br /> 25 Year Developed Peal: 1.11 cfs � (� <br /> Runoff Rate l <br /> � 85°l0 of the Water Quality SWrtn volume af 5,227 cf <br /> 2159b of thc Water Quality Stocm volume of 5,277 cf � � <br /> � � <br /> � � <br /> ]0. DESIGN CALCULATIONS - Appendix A includes the hydrological analysis of the �� <br /> sitc. The calculations show the 2,25 and 100 ycar flows routed th►ough the treatment l L� <br /> I facility. Othcr appropriatc data and calculations arc also providcd in thc appcndix. Two v � <br /> working drawings of the sitc are included in the appendia as fold outs. � �, <br /> � <br /> II 1. PROPOSED DRAINAGE SYSTEM -The proposed dnunage system is composed of � <br /> collection system,cast and wcst forks for pavement ,and a watcr qualiry pond to provide � <br /> I trcatment for the w�ater quality storm. An emergency spillway has been provided in the T� <br /> event the system becomes dysfunctional. The building rooftop runoff shall be collected 1 <br /> on the east sidc of the building and ►outed to the existing scdiment trap pond.That Ilow <br /> will bc introduccd into the cnvironmental arca using thc exisGng sprcader. <br /> IThc treztmcnt storagc has becn accommodated within the sedimcntauon pond previously <br /> conswcted. The existing pond has been separated into two sec:tions . The first decper <br /> � scction will be used as thc opcn ccll. Its stage stotage curvc is"DOEWQP".The bottom <br /> c(cvauon is 59'L.5'.Thc ma�imum clevation for open cell storagc can thcn be 598.5'.Thc <br /> stage storage curve for thc open cell was devclo usin AutoCadd area function for the <br /> I contours south of the conc�te divider wall.�he open cell cle��ation shall be set y <br /> acing a stcel platc along t�concrete H�all set to an clevation of 597.�70'.�T e s rage <br /> provi c m t e o�etr�e�tzvitt-bc c . e secon ce w� �raunent. The <br /> bottom of that ccll is 596.0'. The marimum ccll clevation for trcatment then can be <br /> I 598.0'.The cxisting ouUct is 597.47'.The trcatment siorage will be 2,275 cf. Its stagc <br /> storagc curvc was determineci by subuacting the opea cell curve from the total ccl!curve. <br /> Thc rip rap will be removed and rcptaced by a 6" luyer of top soil to support the plant <br /> growth.The slorage providcd sh�ll c�ceed thc required storage in all cases. The <br /> I estimated maximum watcr elevation for the Ueatment cell is 597.76 during the 100 year <br /> storm. Thc hydraulic control foi thc pond will be thc riser ouUe� The maximum berm <br /> hcight of G00.0 will providc a frecba�rd of Z:LS'. <br /> � <br /> I 98-012 Twa Rivers Engmeering <br /> Scaway Lot St3 3 <br />