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STORM�VA"CGR SITL- PLAN <br />\x�ATEPFQItD LA.T�'E <br />JUN6 22, 1005 <br />��ar_.F ii <br />V. ANALYSIS AND IiESIGN OF RUNOFF CONTROL BMP'S <br />DRAINAGC BASiN ANALYSIS <br />The sitc contains one drainage basin. Flow from dic development will be collected and conveyed <br />to the west side of the wedand comdor for trcatment and dctentioa The balance of the site, the <br />wedand and buffcr areas, �vill not bc impacted Uy thc proposed devclopment. All of the site <br />discharges naturally to the centrally located category ll ���etland. See ['igure 3: Deve!oped Sitc. <br />HYDROLOGIC ANALYSIS <br />The drainage design for die site was preparcd using the mquirements of thc City of Everett <br />Srorm���ater Managemcnt Manual, (CEM Manual). SCS curve numbers �vcre taken from thc <br />CEM Manual. StonnShedT", by Engenious, was used to calculate runoff. <br />The :ainfall events used in the calculations are the SCS type IA c'istribution of thc 24 hour <br />rainfall eveni for tl�e 2, 10 and 100 ycar rctum perods. Tctal precipitation, from thc Tablc 1-5.4 <br />of the CEM Manual, is as follows: <br />Return Period Rainfall <br />2 Year 1.55 inches <br />10 Ycar 2.25 inches <br />]00 Ycar 3.25 inchcs <br />SOIL DESCRIPTION <br />According to Ihc soi( mapping prcparcd by thc SCS in thc Sai1 Snrrcy of S�tohanisl� Comitr <br />Area, {�as/iington the sitc is underlain with Aldenvood-Urban Land Complcx, see attachcd SCS <br />Soils Map and Soils Descriptia� in Appendix B. As can bee secn on the soils map the <br />surrounding properties are also unJerlain with this same soil type. <br />7'he description of Aldenvood UrUan Land Complcx is as follows: This soil is moderatcly �cep <br />over a hard pan and is moderaiely well dmined. Typically die surfacc laycr is very dark grayish <br />brown gravclly sa�idy loam about 7 inches thick. The upper paR of the subsoil is dark yellowisli <br />bro�i�n and dark brown very gravclly sandy loam about 23 inches thick. "Che lower part is olivc <br />brown very gravclly sandy loam about � inchcs thick. A weakly cemcnted hardpan is at a dcpth <br />of about 35 inches. Depdi to hardpan ranges from ZO to 40 inches. Permeability of the soil is <br />modcratcly rapid abovc thc hardpan and vcry slo��� through it. According to die DOE Manual, <br />this soil is in hydrologic group C. <br />� �s� i .� � �-:,,�s � . �-, . u-.:yT .o .. . �.� c_ ��- �r, �-:: asr . _i�•n��e r,uc DWH/srm <br />