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STORMWA'1'L•R SITti PLAN <br />TIADISON COMMUNITY CHURCIi <br />MAY'6, 2006 <br />PAGE• 8 <br />V. ANALYSIS AND DESIGN OF RUNOFF CONTROL BMP'S <br />DRAINAGE BASIN ANALYSIS <br />The site contains two drainage basins. The main basin, Site Basin, consists of the parking, <br />adjacent landscaping and roof areas �vill be collected and directed to the detention pond. The <br />second basin, the Bypass Qasin, consists of the new impervious area along Wetmore Avenue. <br />Included in the basin is the proposed improvements to the unopencd alley to the west. Sce Figurc <br />Dcvclopcd Site. <br />HYDROLO(71C ANALYSIS <br />The drainage design for the site �vas prepared using the requiremcnts of the City of Everett <br />Stortnwater Management Manual, (CEM Manual). SCS curve numbers were taken from the <br />CEM Manual. Stormshed, prcviously known as Waterworks, by Engenious, Inc was used to <br />calculate basin runoff and size the detention pond. <br />The rainfall events used in thc calculations arc the SCS type lA distribution of the 24 hour <br />rainfall evcnt for the 2, ] 0 and I 00 year rcwm periods. Total precipitation, from dic Table I-5.4 <br />of the CEM Manual, is as follows: <br />Return Pcriod Rainfall <br />2 Year 1.55 inches <br />10 Year 2.25 inches <br />100 Ycar 3.25 inches <br />SOIL DESCRIPTION <br />According to SCS the undcrlying soil is Alderwooc�Urban land complex. This soil is <br />moderatcly decp over a hard pan and is moderately well drained. Typically the surface layer is <br />very dark grayish brown gravclly sandy loam about 7 inches thick. "fhe upper part of the subsoil <br />is dark ycllowish brown and dark brown very b�ravelly sandy loam about 23 inches thick. The <br />lower part is olive brown very gravelly sandy loam about 5 inches thick. A weakly cemented <br />hardpan is at a dcpth of about 35 inches. Depth to hardpan ranges from 20 to 40 inches. <br />Penncability of ihe soil is moderately rapid above the hardpan and very slow through it. <br />According to thc DOL Manual, this soil is in hydrologic group C. <br />A gcotechnical report has been prcparcd for the site by Cornerstone Gcotechnical, Inc titled <br />Gcotec/inical Engi�ieering Report, Mndisori Communiry Church Addilio�ti dated March 7, 2006. <br />This report confinns thc prescnce of thc Aldenvood soils. <br />J'Oo�eny Par� Conmw. ;y Cn�rcn - SiR Ja-029'�D einage455P Alaaisan DOCDVh'll5flil <br />