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• • External Memorandum. To: Nick Tomczilc Permit RCWD Date: September 1, 2009 cc: Chris Winter Jim Studenski .HOUSt011Engineering Inc. From: Brent Johnson, RE. 4-d-dal Subject: Paving of Rural Section Gravel Road—Pine Street HEI Project No. 5555-070.07 Introduction: The Cities of Lino Lakes and Columbus are cooperating on a road project along their common 'boundary. Pine Street is currently a rural section gravel surface road with right of way ditches adjacentto both shoulders Pine Street is to be paved under this plan from Lake Drive west to the end of the road at Station 116+30(2.2 miles), but the 'rural section' with adjoining right of way ditches will be preserved (ie. this project only paves the road surface and.does riot include the installation of curb and ,gutter or storrn sewer). Water Quality and Volume Control Rice Creek Watershed District-rule RMP-3 includes the City of Lino Lakes RMP-3 rule 3.D.ii indicates that for public linear roadway projects District Rule C-51 applies to the Pine Street Project. In addition, as per Rule C.11.d, 'The criteria of paragraph SO) are waived for a projed that paves rural section gravel roadway if right-of-way ditch is Maintained and does not discharge directly to wetland or another sensitive water body. Rice Creek Watershed District staff and the. District Engineer view "discharge directly° in this rule to mean 'to create a concentrated The We do not expectthe toad Or tight of way dftches within the generally flat lands along Pine Street to create a concentrated -flow. For example, the-Districrs Impervious Disconnection Guidance on page 3 of 5 indicates full credit would be given to a rural road section where the maximum flow length over impervious surfaces it 75 feet or lets, the pervious disconnection length is greaterthan the flow path over impervious and the pervious disconnection areas have a slope less than or equal -to 5%, The Pine Street impervious road surfaces would be considered disconnected-under this guidanc.e. The grade of the road and ditches are generally fiat, runoff frbm the road lbws to vegetated areas and is disconnected, dispersed and not concentrated, therefore, we interpret the Pirie Street Project to be exempt from Rule C.5.f. as per rule C.1 1.d. Rate Control Rule C6 requires rate control -Stonnwaterrunoff rates fQr the_proposed project at the site boundary, in aggregate, must not exceed existing runoff rates for the critical two-year and 100-year frequency events. Any increase in a critical event rate ate specific point of discharge from the site must be limited and cause no adverse downgradient impact-