07/25/2007 Env Bd Packet - Laserfiche WebLink

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• • The Area must achieve the runoff Volume requirements of the AUAR. A discussion of the water quality and quantity leaving the site before and after the project is built must be provided. One -foot contours must be provided. AUAR area development proposals should follow the guidelines of the AUAR document in having "no net release" total phosphorous. A P -8 predictive model should be submitted as a part of this discussion. Although RCWD seems to be satisfied with quantity and quality considerations, I would request that the City Engineer look at AUAR/RCWD Curve numbers for both grassland area and composite curves for this area as represented in our AUAR. The goal as stated in the AUAR of the implementation of best management practices such as rain gardens, infiltration galleries, buffer strips, designed wetlands, bio-swales, and sediment basins should be the no -net increase in total phosphorous leaving a given development site. The use of native plants in treatment areas play a vital role in creating preferential infiltration and ground water recharge pathways through hardpan layers. Hardpan layers are common under row crop land uses due to repeated tillage of soil at the same depth. Additional use of tree species planted through out the type C and D soils should be used to capture the 1st 0.1 inches to 0.4 inches of rain, and evapo - transpirate additional surface /and shallow ground water accumulations. Proof of MPCA requirements for infiltrating runoff volumes from the mean rainfall event (0.34 inches) within a 72 hour period be accomplished in a 48 hour period, and that there is a 3 foot separation between infiltration facilities and groundwater should be provided. In general, there should be a narrative addressing all of the mitigation strategies presented in the AUAR Landscaping Plant Schedule: Northwoods Red Maple should be replaced with a species that will tolerate heavy soils. Northern Blaze Ash should be replaced with a non - ash species. Little Leaf Linden should be replaced with American Linden such as "Redmond ", or "Boulevard ", or Basswood. More trees should be planted particularly in type C and D soils. All sodded or landscape areas must be shown on the plan as irrigated. All infiltration areas should be seeded with the city native seed mix. All Native seed mix areas should be planted by a contractor on the Minnesota Department of Natural Resources list of contractors. The native areas should be maintained for a minimum of 3 years by the approved contractor and if possible burned at the end of 3 years.