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Mr. Boryczka Page 2 engineers in Minnesota follow these standards. In situations where a permit from the MPCA is required, some of these standards are required to be followed, and the remaining standards are highly recommended or recommended. Therefore, TEI believes the City of Roseville should evaluate the proposed Oak Acres Biofiltration plan in light of the MPCA standards. Listed below are several areas where the Plan may fall short of the MPCA standards: 1. MPCA recommends that soil borings or pits be dug (in the same location and elevation as the proposed bioretention facility) to verify soil types and infiltration capacities and to determine the depth to ground water after initial soil evaluation. The minimum depth of the soil borings or pits should be five feet below the bottom elevation of the proposed bioretention practice. MPCA highly recommends that "the soil profile descriptions be recorded and include the following information for each soil horizon or layer (Source: Site Evaluation for Stormwater Infiltration, Wisconsin Department of Natural Resources Conservation Practice Standards, 2004): a. Thickness, in inches or decimal feet b. Mansell soil color notation c. Soil mottle or redoximorphic feature color, abundance, size and contrast d. USDA soil textural class with rock fragment modifiers e. Soil structure, grade size and shape f. Soil consistence, root abundance and size g. Soil boundary h. Occurrence of saturated soil, impermeable layers/lenses, ground water, bedrock or disturbed soil" A review of Ramsey County's website indicates the generalized soil type to be Urban Land - Kingsley Complex with 15-25% slopes over 62.5 acres. The Hydrologic Soil Group for this soil is B. However, infiltration testing is needed at each Bioretention site to verify specific soil types and infiltration capacities and determine depth to ground water. If the Bioretention facilities are constructed prior to obtaining this information, the Bioretention facilities may fail, not function properly or create higher Operation & Maintenance costs for the City. This testing is especially needed for these facilities because there is a pond about 60 feet east of the proposed facilities and the water elevation is about 3 feet above the proposed facility under-drain elevation which may mean there is seasonally saturated soils underlying the facility and the proposed location is unacceptable. Has the applicant provided the city with detailed soil boring information, as listed above, for city staff review? If not, the plan does not meet MPCA recommendations for determining soil types and infiltration capacities. Nor does it provide sufficient soil data to meet the requirements of City Code. T:\Projects\Gary BoryczkaUtr to Gary 8-27-07.doc Engineering and Environmental Solutions