May 5, 2009 City Council packet - Laserfiche WebLink

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Mr. Kyle Klatt April 10, 2009 Page 2 Comments on Final AUAR The following paragraphs list the VBWD's comments and the corresponding AUAR question number and page number. Executive Summary, Stormwater Volume Control, Page x This section states, "The city will work with developers to provide runoff volume facilities adequate to maintain existing runoff volume or the 100-year rainfall event...." As summarized in other sections of the AUAR, the City needs to require that developers not increase the stormwater runoff volumes for the 100-year rainfall event. Question 17, Water Quality— Surface Water Runoff, Pages 67-79 While the VBWD does not agree with all of the assumptions (including curve numbers for existing conditions) of the various runoff volume analysis scenarios, the response to this question concludes on page 78 that the runoff volume control facilities will be constructed to not increase runoff volumes from existing conditions for the 100-year event, as calculated by the VBWD simple calculation for landlocked basins. (This basically means that a volume equal to six inches times the new impervious surface must be infiltrated.) Following the City's proposal, permit applicants will need to provide proof that • the runoff volume difference between proposed and conditions (as calculated by the VBWD simplified method) is captured, • the proposed infiltration facility can infiltrate at the designed rate, and • the runoff volume can be infiltrated within 48 hours. The VBWD is currently updating its Rules and Regulations and may include this requirement for projects within the Downs Lake watershed.