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See below the our comments addressing the City Engineers comments regarding the house survey at <br /> 3227 Casco Circle in Orono, MN. <br /> I have reviewed the proposed survev for the new house at 3227 Casco Circle and have the followin� <br /> concerns: <br /> 1. From our conversation,the applicant is not doing any of the work shown in the 0-75' zone with <br /> the exception of installing the proposed drainage pipes. All other work not being proposed with <br /> this application needs to be removed from the survey. This includes removing the existing <br /> retaining wall and all work associated with the boathouse. <br /> All of the work within the 75' zone has been removed from the survey with the exception of the <br /> Proposed drainage pipe. <br /> 2. The survey shows a piped outfall from the low spot which discharges partially down the <br /> slope. This discharge does not show any erosion control measures to prevent erosion of the <br /> slope to the lake. Something will need to be installed down the slope probably all the way to <br /> the lake to prevent erosion. This may also need to be shielded from the lake. <br /> Based on our hydrocad model (see attached sheets) the speed of the water running through the <br /> drainage pipe during back to back 100 year rain storms is 1.07 feet per second. Sod will be <br /> sufficient to prevent any erosion. <br /> 3. There should be treatment of the runoff prior to entering the pipe. I would recommend a rain <br /> garden be installed which can handle the volume of runoff associated with at least a 10 yr event <br /> prior to water being directed into the pipe. <br /> The water discharging through the pipe is filtered through the lawn. <br /> 4. The engineer should provide modeling results of this low area which shows if back to back 100 <br /> yr. rain events or a 100 yr. snowmelt occurs,that the pipes can handle the volume of water <br /> without impacting the proposed house. <br /> Hydrocad modeling for a 100 year and back to back 100 year rainfall modeling results are <br /> included. <br /> 5. The installation of the pipe may very well disturb more than 10 CY of material within the 0-75' <br /> area which would trigger the CUP. If you look at the invert of the pipe at the 75' setback it will <br /> be approximately at 944.00 elevation and the existing topo point is at 951.3'. This is a 7' deep <br /> trench and when you have an OSHA approved trench it will be at least 1:1 slopes if the soil are <br /> acceptable. That means there will be a 14'wide trench and will disturb more than 10 CY and a <br /> CUP will be triggered. <br /> It is my understanding that the contractor will be boring in the pipe. <br /> 6. The grading along the west side of the property may be directing water onto the neighboring <br /> property. This runoff could affect the neighboring garage. The drainage should be directed to <br /> the east more to maintain the drainage on the property. Additionally, the applicant may want <br /> to consider installing some measures to slow or reduce the amount of water being directed <br /> down the property lines. By channelizing the runoff there is a potential of additional erosion on <br /> the slope. <br /> The grades along the west property line have been revised to show the water dissipating along <br /> the near the westerly property line. Sod will be sufficient to prevent any erosion. <br /> Please let us know if you have any additional questions or comments. <br /> Aaron J. Mages L.S. <br /> Stonebrooke Engineering <br />