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I -35E Corridor Final AUAR September 26, 2005 The majority of the AUAR area faces many obstacles to effective stormwater management. In many cases agricultural ditch and tile networks have significantly altered drainage basins and changed sub - watershed divides. The drainage capacity of these existing tile networks will be insufficient to convey stormwater runoff from further residential, commercial, or industrial development. The recommendations made within this AUAR document are intended to improve post - development runoff water quality; attenuate runoff release rates downstream and drainage infrastructure capacities for both frequent and occasional rainfall events; and enhance groundwater recharge as the AUAR area is developed. Stormwater management areas (SMAs) will play a critical role in mitigating potential impacts from stormwater following development of the AUAR area. Appropriate design, construction, and maintenance of these areas will enable development to occur without compromising the integrity of the region's aquatic resources. The stormwater management approach outlined in this Final AUAR provides adequate detention of runoff for post - development conditions. It also provides a framework for water quality enhancement and increased groundwater recharge. The stormwater detention facility design will provide hydraulic properties appropriate for native plant species to thrive. All of these factors will help mitigate potential water quality problems associated with development in the AUAR area. The most effective approach to addressing stormwater issues is by implementing an integrated system of stormwater management elements. The Conservation Design Framework provides an appropriate layout for the regional implementation of an integrated system (see Figure 10 -3). Within the greenway corridors shown in the Framework, bio- swales, wet prairie, and wetlands can be oriented in series to effectively retard runoff rates, reduce stormwater volume, and enhance water quality. Runoff rates and volumes are decreased due to increased infiltration, evapotranspiration, and increased friction imparted on the flow. These decreased rates also reduce the ability of runoff to generate and carry sediment and associated pollutants. The runoff volume into the receiving waters will likely increase with development due to the increased impervious area constructed in the AUAR area. However, with the stormwater management requirements outlined in this document, the peak runoff release rates will be decreased from storms of 1 -, 10 -, and 100 - year recurrence intervals and runoff volumes will be no less than 80% and no more than 150% of existing conditions. The recommended large area stormwater management elements will result in relatively small water level fluctuations, provide area to enhance the groundwater recharge necessary to provide base flow to the receiving streams, and provide the detention time necessary to cleanse the runoff of contaminants and meter the increased runoff volume in compliance with Rice Creek Watershed District (RCWD) Rules. Regional Sanitary Sewer Infrastructure Capacity The city has met with Metropolitan Council Environmental Services (MCES) staff on several occasions from 2003 through Spring 2005 to discuss existing and future MCES service to Lino Lakes. The MCES is in the process of updating their comprehensive planning for the "Northeast Region," which includes Lino Lakes, Centerville, North Oaks, Forest Lake, Hugo, White Bear Lake, and White Bear Township. They anticipate the need to provide additional capacity in the Forest Lake Interceptor and downstream facilities to serve the future needs of those communities. Currently, MCES is engaged in plans to construct additional capacity support for the Forest Lake Interceptor. Following a series of meetings in early 2005, MCES agreed to construct an additional interceptor to serve the easterly portion of Lino Lakes. The MCES intends to construct this pipe in 2006, in conjunction with a proposed county highway improvement project. The new interceptor should be designed to convey the excess flow not accommodated by the existing Centerville Interceptor. Assuming the existing interceptor can handle 1.7 MGD, the new pipe should be designed to convey flows ranging from 1.3 MGD for Scenario One to 2.5 MGD for Scenario Three (see full discussion under Item 18). xiv