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Minnetonka Custom Homes STS Project 99189 June 24, 2003 Page 3 the entire height of the basement walls would slow or stop the flow of infiltrating water to the drain pipes. This could lead to a build-up of hydrostatic pressures against the walls, and contribute to seepage through the walls. The subgrade masonry walls should be thoroughly braced internally prior to backfilling. The soil used as exterior basement backfill for a distance of at lest 18 inches from the walls should be a free draining sand or sand and gravel mixture with less than 7% passing the No. 200 sieve. On-site clay soil should only be used to cap the backfill at the surface. Wall backfill should be compacted sufficiently so that it does not settle after construction, but it should not be over-compacted or it could create excessive lateral stresses against the walls. Roof drainage should be carefully controlled. Basement walls backfilled with a thin layer of sand surrounded by sandy clay should be designed to resist the lateral pressure exerted by an equivalent fluid having a density of 52 pounds per cubic foot. Slope Stability Analysis We performed a slope stability analysis, using a limit equilibrium procedure. In this analysis, we also factored in an allowance for a footing load on the soil of 2,000 psf. Based on our analysis, the minimum factor of safety is about 3.1. Usually, for a slope of this type, a minimum of factor of safety against failure of 2 is considered adequate. Thus, in our opinion, this slope is stable. We wish to caution, however, that care should be taken to avoid excessive erosion of the slope. Thus surface runoff water that drains over the top of the slope should be channeled or controlled in such a manner as to avoid erosion of the soil. A graphical depiction of our slope stability analysis is appended. Construction Safety All excavations must comply with the requirements of OSHA 29 CFR, Part 1926, Subpart P "Excavations and Trenches". This document states that excavation safety is the responsibility of the contractor. Reference to this OSHA requirement should be included in the job specifications. The responsibility to provide safe working conditions on this site, for earthwork, building construction, or any associated operations is solely that of the contractor. This responsibility is not borne in any manner by STS Consultants, Ltd. Field Observation and Testing We recommend that the earthwork and footing installations for this project be observed and tested by a geotechnical engineer or qualified engineering technician to determine if the soil and groundwater conditions encountered are consistent with those anticipated based on our exploration. Foundation subgrades should be tested to check for adequate bearing conditions. Subgrades for slabs, pavement and new structural fill should be test rolled and unsuitable areas improved. Fill placement and compaction should be monitored and tested to determine that the resulting fill conforms to specified density, strength or compressibility requirements. Structural materials should also be tested for conformance to specifications. STS would be pleased to provide the necessary field observation, monitoring and testing services during construction.