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SECTION 4 water Quality Eualuatiou <br />More detail regarding each of these three options and the methods that were used for developing <br />the CP conceptual designs and costs is provided as follows: <br />1) Pipe and Pre -treat Option — All of the drywell clusters were reviewed in terms of selecting <br />the best option for dealing with drainage resulting from decommissioning. Some of the drywells <br />were located in very close proximity to an existing storm drainage pipe and directing the <br />drainage to that pipe appeared to be the most cost - effective option. This option was selected for <br />the following 16 drywell clusters (the list includes the CP IDs that were assigned). It should be <br />noted that this is a planning level analysis and while preliminary invert elevations were <br />confirmed, the project level engineering analysis and design will need to confirm the viability of <br />piped options for decommissioning. <br />Willamette Overflow Subbasin <br />WO -I -UIC: <br />Green UIC Cluster <br />W04-UIC: <br />Taz UIC Cluster <br />WO -6 -UIC: <br />Poplar UIC Cluster <br />WO -7 -UIC: <br />Kendra UIC Cluster <br />WO -8 -UIC: <br />Kent UIC Cluster <br />A1- Channel Subbasin <br />Al-1-UIC: <br />Crocker 1 UIC Cluster <br />Al -3 -UIC: <br />Shirley 1 UIC Cluster <br />Al -5 -UIC: <br />Hamilton UIC Cluster <br />Al -6 -UIC: <br />Bushnell UIC Cluster <br />Al -9 -UIC: <br />Greenleaf UIC Cluster <br />Al -13 -UIC: <br />Korbel UIC Cluster <br />Spring Creek Subbasin <br />SC -I -UIC: Zinnia lUIC Cluster <br />SC -2 -UIC: Zinnia 2 UIC Cluster <br />SC -4 -UIC: Countryside UIC <br />SC -5 -UIC: Lodenquai UIC Cluster <br />Flat Creek Subbasin <br />FC -2 -UIC: Willowbrook 2 UIC Cluster <br />There were two methods used for developing conceptual pretreatment and pipe designs for this <br />category of CPs. The first, and more simple method was used if the drywell or drywells were <br />located in close proximity to an existing pipe system and within the delineated drainage subbasin <br />for that piped system. Given that the XP -SWMM hydrologic model to estimate future flows was <br />already run assuming no drywells (see Section 3.0), the hydrologic results from the model <br />already included flows from the area that would be associated with drywell decommissioning. <br />Therefore, the calculations that were performed to size the pretreatment and pipe system <br />included 1) delineation of the sub - drainage area associated with the drywell; 2) estimation of <br />flow from the sub - drainage area using the Rational Method; and 3) estimation of a pretreatment <br />0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 4 -9 <br />