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Report of Geotechnical Exploration <br />North Arm Bay Boat Launch; Mound, MN <br />April 10, 2023 <br />AET Report No. P-0016964 <br />AAMEMICAN <br />0.06 inches/hour. This infiltration rate represents the long-term infiltration capacity of a practice <br />and is not meant to exhibit the capacity of the soils in their natural state or recompacted (i.e. fill) <br />state. These values also assume a minimum separation of 3 feet between the bottom of the <br />infiltration practice and the seasonably high ground water table. <br />7.0 CONSTRUCTION CONSIDERATIONS <br />7.1 Potential Difficulties <br />7.1.1 Groundwater in Excavation <br />There is the potential for groundwater to appear in the infiltration trench excavations at this site. <br />The groundwater table will need to be lowered in the project area to allow construction in the <br />dry. It is the responsibility of the contractor to design the dewatering system. In our experience, <br />groundwater control in clayey and organic soils is generally accomplished using sump pits and <br />pumps, and groundwater control in sands is generally accomplished using well points or <br />dewatering wells. The project contractor should consider groundwater control, which will need <br />to be carefully planned and executed, as part of their installation process. The level of <br />groundwater drawdown should be achieved before the excavation reaches the planned <br />elevation, and maintained at least 2 feet below the lowest anticipated subgrade or subcut <br />elevation. The water table should not be lowered more than necessary to provide a dry <br />excavation, to reduce the risk of settlement of adjacent structures, pavements, and sewers. It is <br />the responsibility of the Owner and the designers of the dewatering system to assess the effects <br />of lowering the groundwater on adjacent structures, pavements, or sewers. <br />7.1.2 Disturbance of Soils <br />The on -site soils can be disturbed under construction traffic, especially if the soils are wet. If <br />soils become disturbed, they should be subcut to the underlying undisturbed soils. The subcut <br />soils can then be dried and recompacted back into place, or they should be removed and <br />replaced with drier imported fill. <br />7.1.3 Cobbles and Boulders <br />The soils at this site can include cobbles and boulders. This may make excavating procedures <br />somewhat more difficult than normal if they are encountered. <br />7.2 Excavation Backsloping <br />If excavation faces are not retained, the excavations should maintain maximum allowable slopes <br />in accordance with OSHA Regulations (Standards 29 CFR), Part 1926, Subpart P, "Excavations" <br />Page 4 of 5 <br />123 <br />