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Subsurface Exploration and Foundation Evaluation Proposed Golden Oil Refueling Station Stoughton, Wisconsin PSI Project No. 0092822 Page 13 STORMWATER MANAGEMENT AREA CONSIDERATIONS As requested by the client, borings SW-1 and SW-2 were performed in the area of the proposed stormwater management area. It is understood that the proposed stormwater management area will consist of an underground storm retention basin. The size and bottom elevation of the basin was not known at the time of report preparation. The subgrade soils encountered in SW-1 and SW-2 have been visually classified in general accordance with the USDA textural soil classification system. They consisted of gravelly sand, gravelly loam, silt loam, loam, loamy sand, silty clay, fine sand, sandy loam, and sand. Groundwater was encountered during auger advancement at depths of about 16 and 11 feet (EL. 859.0 feet and EL. 863.4 feet) in borings SW-1 and SW-2, respectively. After the auger was removed, groundwater was observed in SW-2 at a depth of 8 feet (EL. 866.4). With regard to the above soil and groundwater conditions encountered at the borings, NR 151.124(4)(c)1 and 2 — Infiltration rate exemptions indicates that infiltration practices located in an area where the infiltration rate of the soil measured at the proposed bottom of the infiltration system is less than 0.6 inches per hour using a scientifically credible field test method; or where the least permeable soil horizon to 5 feet below the proposed bottom of the infiltration system using the USDA method of soils analysis consists of sandy clay loam, clay loam, sandy clay, silty clay or clay may be credited toward meeting the requirements, but the decision to infiltrate under these conditions is optional. In addition, NR 151.124(4)(b)1 — Separation distances indicates that infiltration practices shall be located so that the characteristics of the soil and the separation distance between the bottom of the infiltration system and the elevation of seasonal high groundwater or the top of bedrock are in accordance with the following Table (reproduced from NR 151.124): Table 3. Separation Distances and Soil Characteristics Source Area Separation Distance Soil Characteristics Industrial, Commercial, Institutional Parking Lots 5 feet or more Filtering Layer* and Roads Residential Arterial Roads 5 feet or more Filtering Layer* Roofs Draining to Surface Native or Engineered Soil Infiltration Practices 1 foot or more with Particles Finer than Coarse Sand Roofs Draining to Surface Not Applicable Infiltration Practices All Other Impervious 3 feet or more Filtering Layer* Source Areas