Statement in opposition of the Oakleigh Meadows Tentative Planned Unit Development <br />Permit (PDT 13-0001) and Willamette Greenway Permit (WG 13-0001) <br />I believe the following sections of the report of the Planning Department lack a proper basis in <br />fact because no data has been presented to substantiate the conclusions reached : EC9.8320(9),' <br />EC 9.6791 through 9:6797. These sections deal with stormwater runoff from the project <br />Specifically, no analysis has been presented regarding the quantity of stormwater/ runoff to be <br />treated. Staff has required that all stormwater must be treated on-site and none enter the <br />City's storm sewers or be allowed to create standing water off of the project site. I quote from <br />page 25 of the planning report "The applicant proposes to direct stormwater runoff from the <br />proposed development to the abutting City parkland to the east. The applicant's stormwater <br />management system will -include treatment facilities that also provide for some detention." <br />What quantities of stormwater are we talking about? Here is some data for evaluation. <br />Eugene average rainfall: 50 inches (approximately). <br />Eugene Precipitation Jan F'eb Mar Apr May Jute: Jul Aug Sep Oct Nov '.Dec <br />7 .7 <br />?recipitation (inches) <br />7.9 [5.6;15.5 3A 12.2 [114 0.5 '3:4 8.3 86` <br />Assume the project results in 1 square acre of impervious surface (buildings, sidewalks, <br />driveways, streets) out of a total project size of 2.3 acres. This represents 43.47% of the total <br />area. Maximum density allowed by City code is 50%. <br />One inch of rainfall falling on 1 square acre of impervious surface yields 27,152 gallons of water to be <br />disposed of. The average of 50 inches of rainfall results in 1,357,600 gallons of water annually. This <br />assumes no stormwater retention on-site. Assuming the project is able to retain 10% stormwater results <br />in 1,246,276 gallons, 20% retention 1,180,701 gallons. Which creates another question: what will be <br />used to store these flows? Bear in mind that 1 gallon of water weighs 8.34 pounds, 1 cubic foot of water <br />contains 7.48 gallons and therefore weighs 62.43 pounds. <br />-Let's examine stormwater flows by month for the rainy winters: <br />October = <br />3.4" <br />x 27,152 <br />November = <br />8.3 " <br />x 27,152 <br />December = <br />8.6 " <br />x 27,152 <br />January = <br />7.9" <br />x 27,152 <br />February = = <br />5.6" <br />is 27,152 <br />March = <br />5.5" <br />x 27152 <br />Total <br />= 92,317 gallons of water <br />=221,362 <br />=233,507 <br />=214,501 <br />=152,051 <br />=149,336 <br />1,063,074 gallons <br />Average rainfall during this six-month period is 177,179 gallons/month. Assume a, minimum 10% on-site <br />retention level. This is 17,718 gallons of water and requires a cubic volume of 2,369 cubic feet <br />equivalent to a single cistern of 10 feet wide x 10 feet high x 23.60 feet long. If 20% retention is <br />918 <br />