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