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Thatcher August 24, 2007 Gary Boryczka 2250 Acorn Road Roseville, MN 55113 Re: Biofiltration Trench Oak Acres Subdivision Roseville, Minnesota Dear Mr. Boryczka: C,,~.e, .,t,-= ~~~DU~ ~~~~$~ Thatcher Engineering, Inc. 3055 Old Highway 8, Suite 103 Minneapolis, MN 55418 p 612 781 2188 f G 12 781 2241 www. thatcher-eng. com Emailed to: ~rv(a~borvczka.com In accordance with your request, Thatcher Engineering Inc. ("TEI") reviewed the proposed Biofiltration Trench Plan ("Plan") to determine compliance with Roseville City Code requirements and Minnesota Pollution Control Agency Best Management Practices. TEI understands that Art Mueller seeks approval of the Final Plat and Public Improvement Contract for Oak Acres, a residential subdivision that redevelops 2201 Acorn Road into a 41ot single-family residential development which includes the construction of two Biofiltration Trenches. We also understand that the Biofiltration facility will be owned, operated, maintained and cleaned by the City. We also understand that the facility will be located on private property within a City easement. We reviewed the City Code and have the following observations: 1. The Code requires that all improvements shall be in accordance with applicable City standards (Subdivision Regulations Section 1102.07.B.). However, the Code does not have specific standards for Biofiltration. 2. The Code requires that each lot created through subdivision shall be suitable for the proposed use as defined by a suitability analysis. Suitability analysis shall consider soil limitations, and sufficient information shall be submitted by the applicant for the community to make a determination of land suitability. The information shall include at least adequate soil information to determine suitability for public utilities from field investigations such as borings or other methods (Shoreland, Wetland and Storm Water Management Section 1016.23). The Biofiltration Trenches included in the Plan are public utilities since they are a vital part of stormwater management and will be owned, operated, and maintained by the City. Thus the soil information required by this section must be supplied by the applicant. Since the City has no specific standards for evaluating the design of Biofiltration trenches, we look to other recognized standards. The Minnesota Pollution Control Agency (MPCA) has published Best Management Practices (BMP) for Bioretention as a part of its Stormwater Manual dated September 2006, which it recommends that local governments follow. Most T:\Projects\Gary BoryczkaVtr to Gary 8-27-07.doc Engineering and Environmental Solutions