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Propased Improvements Summary <br />Threc rctail buildinas are proposcd for thc site. Stormwater for thc site will bc collected in a <br />convcntional pipc systcm (scc Shcct 4.0 in Appendis A). Stormwatcr quality trcauncnt will bc <br />provided by a cartridge mcdi:t filler syslcm (Stormfilter'"'). Delention for lhc silc ���iil be <br />providcd in a concretc vault undemcath thc parking lot. 3tormwatcr �ti•ill outfall to an cxistin, <br />3G-inch storm drain linc runnine along lhc north sidc of H,vdcson Road. � <br />Conve ance Design <br />Thc proposed storm drain systcm will convcy surfacc runoff from thc Mowuain Vicw Plaza <br />building roofs, p:u'riing lots, sidcwalks, and landscapc arcas. This storm drain systcm is <br />designcd lo convcy thc 24-hou�', 25-ycar stonn cvcnt, which has a rainfaU dcpth of 2.60 inchcs as <br />defincd in thc COL•' Storni��•arer Alnnagrment D1a�wnL Thc ration:d mcthod was uscd for pipc <br />sizing calculations. A sprcadshcet showing pipc sizc calculations is includcd in Appendix B. <br />Thc pipcs wcre sizcd to convcy thc 25-ycar runoff ���ithout c�ccedin� 90 perccnt capacity. Thc <br />12-inr.h pipc is adcquatc to com�cy thc runoff from thc parking lots and roofs. Thc Zd-inch <br />outf:dl line is sized to convcy the 2S-ycar runoff from �lountain View Plaza plus thc 25-ycar <br />runol7 from fuWrc dcvclopmcnt of Lot 2 to thc north. <br />Detention Design <br />Stonnwatcr ctctcntion (or thc sitc will bc providcd by an undcrground concretc vault. Thc vault <br />is siud match 50 percent of the existing 2-ycar flo��� and 100 percent o( the e�istin; l0 and <br />100-ycar flows per thc COE Srormtirarrr �1lmia� en�cnr ,Umiurd. Calcul:uions arc providcd in <br />rlppcndix B. <br />Water Quality Design <br />A Stormfiltcr'" cartrid,c mcdia filtcr vault will providc ���atcr yuality trcatmcnt for thc paved <br />arcas subjcct to vchicic�uaffic. Storm��atcr will p:iss throu_h thc dctcntion vault to providc <br />prcucaunent of xdimcnts :md trash bcforc cntcring thc 3tormfiltcr'". 'thc filtcis usc a CS� Lcaf <br />m�dia for scdimcnt, oil, solublc mctals, and tolal nutricnt rcmovnl. 1'hc fiitcr is sized to trcat thc <br />discharge fi�om the prin:.ny orifice from the detention vault using the StormfilterT"' Design <br />�Ie�nu:il mass lo:iding method nnd City of F,verett rcquirements for I'ilters located do���nstre.un cf <br />dctcntion. Runoff from builJin� roofs ��•as assumcd to not contrihutc to thc mass loadin�. Sec <br />Appcn�lix [3 for Stormfilter�`� sizing calculations. A I6 x S fuot ��;iult �vith 20 filtcr caru�id�es is <br />rcyuire�l. 'l�hc dctcntion system routin� �cas calculutcJ usin�: thc 5anta I3arb;iru Urban <br />hlounlain Vio-.v Plua May 2J, 2005 <br />Hydraulics Repart � �' <br />� <br />