Laserfiche WebLink
Planning Commission <br />September 5, 2007 <br />Page Four <br />5. Please complete a survey so that the entire drainage area for the project site <br />is encompassed. <br />6. As noted previously the individual lot infiltration trenches will not be allowed <br />for inclusion in the storm water calculations for the site. Please eliminate <br />these infiltration areas from the stormwater calculations. <br />7. Post-West 1 stormwater calculations should be routed thru Post-West 2. The <br />stormwater runoff route for Post-West 2 cannot change from the existing <br />conditions route since there is no grade change from the pre to post <br />conditions. <br />8. It appears as if the time of concentration used for subcatchments Post-West <br />3 and Post-West A are longer than actual conditions show. Please review <br />these time of concentrations and adjust accordingly. <br />9. Please run the stormwater calculations showing an infiltration rate for the soil <br />separating the infiltration rock area and the bottom of the proposed ponds. <br />Also provide the documentation on how the infiltration rate was determined. <br />10. Please provide additional stormwater calculations that show the pond levels <br />and corresponding discharge rates under the conditions of no infiltration into <br />the pond rock infiltration trench. These calculations shall be run at 2-year, <br />10-year, and 100-year storm events. Rate control for the development must <br />be less than or match pre-existing conditions without accounting for <br />infiltration. <br />11. It appears as if the pipe material used for the east pond outlet is incorrect. <br />Please review this and change as necessary. <br />12. Please revise the routing of the outlet for the east pond. The EOF should be <br />classified as a secondary outlet. <br />Miscellaneous <br />1. The site is over one acre; therefore a storm water pollution prevention plan <br />should be submitted for review and approval. <br />2. A landscaping plan should be submitted. <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 />itc. ~~~ <br />Lee Elfering, P.E. <br />City Engineer <br />cc: Bill Dircks, Public Works Director <br />Ltr-090707-PC <br />10062 Flanders Court NE, Blaine, MN 55449 -Phone: (763) 780-0450 -Fax: (763) 780-0452 <br />