2011-07-21_AgendaPacket - Laserfiche WebLink

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651 Hale Avenue North Oakdale, Minnesota 55128 telephone: 651.]]0.8448 facsimi l e: 651.]]0.2552 www.eorinc.com Date I July 19, 2011 To I GLWMO Board of Managers cc I Tom Petersen, GLWMO Administrator From I Camilla Correll Regarding I Scope to Conduct Stormwater Sampling in 2011 Background The Grass Lake Watershed Management Organization (GLWMO) acquired three (3) Isco 6712 Full -size Portable Samplers to monitor stormwater runoff in support of the Lake Owasso Use Attainability Analysis (UAA). These samplers were used to monitor water quantity (flow) and water quality (TSS and TP) at multiple locations in the watershed for 2007 and 2008. Monitoring locations include Galtier Street (2007), Dale Street (2008), County Road C (2007 and 2008) and West Owasso Boulevard (2007 and 2008). This stormwater monitoring data was used to calibrate the water quality model (P8 model) developed for the UAA. Update Given that the GLWMO is planning on initiating the TMDL /Restoration and Protection Plan in 2012 it would be helpful to collect additional stormwater monitoring data to strengthen the calibration of the P8 model. Given that the GLWMO already owns monitoring equipment and has the budget since the aquatic macrophytes survey for Lake Owasso was cancelled it is strongly recommended that the GLWMO consider adding tree months of stormwater monitoring in 2011. This monitoring would be in addition to the monitoring that is currently planned for 2012. The P8 model predicts the generation and transport of stormwater runoff pollutants in urban watersheds. Currently the GLWMO has monitoring data which can be used to calibrate the model after stormwater runoff is "transported" in the system: as it travels through wetlands, ponds and other treatment devices. What the GLWMO doesn't have information on is the characteristics of the stormwater runoff "generated" in the landscape. Collecting information about the volumes, TSS and nutrient concentrations will allow FOR to calibrate the first stage of the model. Information collected for the UAA and information collected in 2012 can then be used to re- calibrate or verify the calibration of the second stage of the model, the stormwater runoff quality after treatment. The approach that FOR proposes for collecting stormwater monitoring data will be a little different than what was conducted for the UAA: instead of collecting monitoring data downstream of the wetland or stormwater management (ponding) systems (and making adjustments to the calibration to account for internal loading), FOR proposes to identify representative neighborhoods upstream of wetlands /ponds with little to no stormwater treatment. This will provide the GLWMO with a good understanding of the stormwater runoff quantity and quality generated in the landscape. This information will then be used to strengthen the calibration of the P8 model. It should be noted that the Galtier Street site did collect this type of information (in 2007) by monitoring runoff from a fully developed subwatershed that did not have any ponds or treatment devices. This would be one of the locations that FOR proposes to monitor this year: two additional sites would have to be selected. An Equal Opportunity Affirmative Action Emmons & Olivier Resources, Inc. water I ecology I community