Laserfiche WebLink
ENVIRONMENTAL BOARD MEETING MAY 31, 2000 <br />Mr. Johnson stated the culvert under Apollo Drive is lower than the culvert under the <br />freeway by several feet and the pond is several feet under that. The outlet will then go to <br />another pond with a submerged outlet that is slightly lower than the elevation of Apollo <br />Drive which will force the water to leave the site at a different rate than exists today. <br />Trehus asked how much water will leave the site. Mr. Johnson stated he has made that <br />calculation but does not have that information available tonight. He estimated 34.5 acres <br />will be incorporated into this plan and drain through a ponding system and out of the site. <br />The rest of the acreage is kept in on-site ponds. Mr. Johnson advised of the Rice Creek <br />Watershed District restriction to not allow a higher run-off rate than exists today. He <br />estimated there will be 60% impervious surface. <br />Donlin asked how rain events would be handled that are similar to what occurred several <br />years ago where there were three back-to-back 100 -year events. Mr. Johnson reviewed <br />the criteria the ponds can handle and how that criteria is established <br />Mach asked if staff's concern is the volume of water or quality of water. Asleson <br />explained the NURP ponds are designed to store a volume of water for a certain rain <br />event but after large rain events, there is a peak of discharge <br />Davidson noted the NURP ponds remove about50% of the nutrients, whereas, it would <br />be ideal to remove a higher percentage. <br />Mr. Johnson explained that the;NURP pondsdo a good job of removing contaminants <br />from low rain events, such as a two-inch rainfall. He then explained how a larger rain <br />event impacts the NURP pond. He stated'their intention to address the drainage issues <br />rather than expecting the indi'vidu'al parcel owners to do so. <br />Donlin complimented .Mr. Johnson on his past work on these types of projects. <br />Mach asked if there is potential for reconstruction of some of the ponds to function to <br />hold the' flow and provide treatment. Asleson explained how the ponds have been <br />designed to do both; <br />Trehus stated he becomes concerned about any project that places more water into one of <br />the City's lakes. Asleson asked if they can look at the feasibility of placing the pipe <br />under Apollo Drive and possible methods of financing that cost. <br />Acting Chair Lanyon asked if there is a way to have Pond 1 service more acreage to <br />provide additional on-site infiltration, or if additional ponds can be placed. <br />Donlin noted a lot of infiltration will occur since the ponds will have a sand bottom, at <br />least until the pond silts up. Asleson commented on the importance of properly designing <br />these ponds to assure infiltration. <br />4 <br />