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HR Green, Inc. <br />Project B2204225 <br />October 3, 2022 <br />Page 11 <br /> <br /> <br />routine maintenance, such as seal coating and crack sealing. The actual pavement life will vary depending <br />on variations in weather, traffic conditions and maintenance. <br /> <br />Many conditions affect the overall performance of the pavements. Some of these conditions include the <br />environment, loading conditions and the level of ongoing maintenance. With regard to bituminous <br />pavements in particular, it is common to have thermal cracking develop within the first few years of <br />placement, and continue throughout the life of the pavement. We recommend developing a regular <br />maintenance plan for filling cracks in exterior slabs and pavements to lessen the potential impacts for <br />cold weather distress due to frost heave or warm weather distress due to wetting and softening of the <br />subgrade. <br /> <br />C.4. Stormwater <br /> <br />We estimated infiltration rates for some of the soils we encountered in our soil borings, as listed in Table <br />4. These infiltration rates represent the long-term infiltration capacity of a practice and not the capacity <br />of the soils in their natural state. Field testing, such as with a double-ring infiltrometer (ASTM D3385), <br />may justify the use of higher infiltration rates. However, we recommend adjusting field test rates by the <br />appropriate correction factor, as provided for in the Minnesota Stormwater Manual or as allowed by the <br />local watershed. We recommend consulting the Minnesota Stormwater Manual for stormwater design. <br /> <br />Table 4. Estimated Design Infiltration Rates Based on Soil Classification <br />Soil Type <br />Infiltration Rate * <br />(inches/hour) <br />Clayey sands and clays 0.06 <br />*From Minnesota Stormwater Manual. Rates may differ at individual sites. <br /> <br /> <br />Fine-grained soils (silts and clays), topsoil or organic matter that mixes into or washes onto the soil will <br />lower the permeability. The contractor should maintain and protect infiltration areas during <br />construction. Furthermore, organic matter and silt washed into the system after construction can fill the <br />soil pores and reduce permeability over time. Proper maintenance is important for long-term <br />performance of infiltration systems. <br /> <br />This geotechnical evaluation does not constitute a review of site suitability for stormwater infiltration or <br />evaluate the potential impacts, if any, from infiltration of large amounts of stormwater. <br /> <br />44