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City of Mounds View Staff Report Planning Case No.477-97:D.W.Jones Property May 24, 1997 111) Page 3 SEH does not expect stacking on Silver Lake Road--both northbound and southbound--to be a problem. Stacking on the northbound side may affect access to Driveway D for southbound motorists who want to turn left into the gas station site. Stacking is not expected to block the service road, and therefore motorists have an alternative. Also, since Silver Lake Road is four lanes wide at this point,motorists who want to travel south will have a way to get around motorists waiting to turn left into Driveway D or the service road. The revised traffic volumes submitted by Biko are consistent with SEH's calculations. SEH has noted that conflict points on-site continue to be a concern, caused by having the entrance to the two drive-thru aisles just after motorists enter the site at Driveway D,the need to cross Driveway D to go from the gas pumps to the drive-thru aisles, and the driveway from the service road which cuts across the car wash stacking lane. Staff has discussed with the applicant the possibility of dropping the drive thru aisle for the fast food restaurant and they are willing to consider it. This issue is noted in the stipulations and would be resolved at the development plan review. Q Drainage system: The site plan indicates two NURP ponds to handle the predicted run-off from this development. Rocky Keehn with SEH Inc. has reviewed the drainage calculations and the proposed ponding and has made a number of conclusions in a memorandum dated May 22, 1997 (attached). First,the NURP pond located at the southeast corner of the site(the east pond)is not feasible because the wetland extends out toward Highway 10, separating the pond from the development. While it would be possible to convey the water to the proposed pond via ditches or piping parallel to Highway 10,this would entail an alteration to the wetland itself and approval from regulatory agencies. • A further complication arises in that there is an existing stormwater intake culvert running under Highway 10 that carries discharge from approximately 26 acres north of the development. Use of the Highway 10 drainage ditch to convey runoff from the development to the proposed NURP pond would require the NURP pond to be sized large enough to accommodate both the development and the additional 26 acres of runoff. These factors contribute to the east pond's lack of feasibility. The second NURP pond--the central pond-- between the senior building and restaurant, while properly located, appears to be too small to handle the runoff directed to it. There appears to be sufficient room,however,to expand the pond as needed. A pond is likely needed to handle the runoff from the senior building and its parking lot, and the most likely location is south of the senior building where the nature overlook is shown. The remaining issue then is accommodating the runoff from the proposed office building south of TJB Homes, which could be accomplished with a small pond or grassed swale immediately adjacent to the office building and its parking area. Staff feels that the size of the office building would have to be reduced in order to provide for the necessary ponding. This issue has been discussed with the applicant, and they are willing to consider reducing the building from 5,000 square feet to 4,000 square feet. This would reduce the impervious area by at least 1,740 square feet and perhaps more, depending on building configuration and whether a driveway connection is made to TJB Homes. Staff has changed the maximum building area for the office building at the south end of the site to 4,000 square feet in the PUD stipulations. The • final layout of this site and the density allowed would be addressed in the development plan review.