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Mayor & City Council <br />October 14, 2008 <br />Page Three <br />6. For the proposed Subcatchments it appears that some have a composite <br />curve number. A breakout of the areas within the Subcatchment and <br />corresponding curve numbers should be provided. In addition, the time of <br />concentration used for the proposed Subcatchments should be reviewed and <br />more detailed information provided. The areas vary in size considerably and <br />it appears that the numbers should vary in time. <br />7. For the Stormtech ponds documentation should be provided for the <br />exfiltration rate that was used. Proposed calculations should also be <br />provided that do not account for any exfiltration. The comparison of existing <br />and proposed rate of discharge will be compared using the calculations that <br />do not account for exfiltration. <br />8. A maintenance agreement must be provided and approved for the Stormtech <br />system, which includes an inspection and maintenance schedule. The City <br />standard agreement can be provided upon request. <br />General Comments <br />1. There is over one acre of disturbance for the redevelopment and therefore a <br />Ramsey Washington Metro Watershed District and National Pollution <br />Discharge Elimination System (NPDES) permit will need to be obtained. <br />Documentation of the permit approvals will be required prior to any work. <br />Please contact me if you have any questions regarding the above information at (763) <br />780-0450 ext. 13. <br />Sincerely, <br />ELFERING & ASSOCIATES <br />~~~~~ <br />Lee Elfering, P.E. <br />City Engineer <br />cc: Bill Dircks, Public Works Director <br />Ltr-101408-PC <br />10062 Flanders Court NE, Blaine, MN 55449 -Phone: (763) 780-0450 -Fax: (763) 780-0452 <br />