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GEO►SYNTEC CONSULTANTS Page of 7' <br />Written by: JOE TAM Date: 22 -Oct -99 Reviewed by: 002 Date: i0 Z1' <br />Client: Allied Waste Project: Forward Landfill Project/Proposal No.: WS0264 Task No.: 01 <br />INPUT PARAMETERS <br />Rainfall Distribution <br />Per [USDA -SCS, 1986], Forward Landfill is located in an area classified with a Type I rainfall <br />distribution. See (3-1 ) A�+�tcl��,e F, <br />Design Rainfall <br />The design rainfall quantities were obtained from the hydrology manual provided by the flood <br />control district of the Department of Public Works in San Joaquin County. This information can be <br />found in Attachment A to these calculations. The design rainfall quantities used in the drainage plan <br />calculations for the partial closure of WMU B at Forward Landfill are presented below: <br />Storm Rainfall Source <br />2 -yr, 24 -hr 1.51 in. San Joaquin County <br />100 -yr, 24 -hr 3.36 in. San Joaquin County <br />s <br />Hydrologic Soil Groups <br />P <br />The vegetative layer for the final cover will consist of a silty sand (SM), clayey sand, and sandy silt <br />(ML) mixture. This composition is equivalent to a sandy clay loam according to the United States <br />Department of Agriculture (USDA) textural classification system for soils [Das, 1994]. Sandy Clay <br />Loam falls under the category for Hydrologic Soil Group "C", according to TR -55 [USDA -SCS, 1986], <br />and it is therefore assumed that all site soils classify in Hydrologic Soil Group "C". <br />See F�,yv�res S—Z k Z-3, A4+c,tti,M + . <br />Runoff Curve Number (CN) <br />The CN is obtained from [USDA -SCS, 19861 for Hydrologic Soil Group "C". All drainage areas <br />(i.e., areas on the final cover and on the site outside the landfill) are assumed to be "Open Space" with <br />50-75% grass cover, corresponding to a CN=79. This is based on the existing conditions of undisturbed <br />areas on site. See F_;,jk�,e 6-H,/ A44etc�\mt^'r S <br />Post -Development Drainage Areas and Parameters for the Time of Concentration <br />The drainage subcatchments are shown in Figure 1. The longest flow path in each subcatchment is <br />used to calculate the time of concentration. Parameters for these flow paths are shown in the HydroCAD <br />outputs and are listed below. SLL b c c.+c1ne-"'r5 ct r.e 5- �-�-, �, r; ��{ 'I,, <br />lure -5/ A4AL14VM74, `g. _n^e 1onyS�- -(_10,a fuA't-1 Q�run, +ec-S Ur �?ctc� <br />S'tbr,la c.t4mevt't" are 5—tc., A44-+acViV'he,4 g. <br />J: IALLIEDWASTETORWARD WMU MCLOSURE PLAMDRAINCALMSWIDOC <br />