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Drywall Supply, Inc. Project No. BBXX- 02 -0 .IOB April 24, 2002 Page 2 Foundation Support Consideration for Future Development Although the existing fill has likely been in -place for a long time, the existing fill and underlying organic materials are not considered suitable for building support, i.e. foundations and slabs. While the existing fill could be removed and replaced with compacted fill, the underlying organic deposits are too compressible to support new fill, footing and slab - induced loads. The lacustrine soils below the organic deposits are also soft and considered compressible such that tolerable settlements would be exceed as a result of the new fill needed to achieve design grades and overall building loads. Without soil corrections and /or alternative foundation systems, rather large settlements and differential movements can be expected over time as the existing fill, and underlying organic materials and soft clays consolidate. While lightweight structures such as metal storage buildings are more tolerant of differential movement, office /warehouse structures with light to moderately loaded lineal footings and columns are less forgiving to excessive total and differential settlement. In our opinion, supporting the buildings on typical spread footing foundations and supporting the slabs -on -grade would incur high risk — much higher than what would normally be acceptable. For this reason, deep soil corrections (soil corrections to at least remove the existing fill and organic tnaterials) or alternative deep foundation systems would be needed to provide suitable foundation support. Based on the borings, it appears that excavation depths needed to remove the existing fill and organic soils would range between about 11 to 23 feet. Given the depth of the excavations required and the presence of groundwater however, in our opinion, removing the unsuitable soils (an excavation/baclrfill approach), although possible, would be difficult. Additionally, settlement of unexcavated lacustrine soils (soft clays) would still occur under the weight of backlit] needed to achieve design grade that would necessitate at least a construction delay period. Even if spread footing construction is abandoned in favor of alternate support options such as drilled piers, piles or Geopiers , settlement of the ground in general should be expected to occur over time in areas where new fill is added to existing site grades. Settlement of the existing fill and organic soils under their own weight will also occur throughout much of the site as the materials continue to consolidate over time, For this reason, sidewalks, curbs, concrete and bituminous pavements, and other at grade structures will be subject to differential movements. Summary and Conclusions With the present information, it appears that performing an excavation to removo the unsuitable soils and accommodate spread footing foundations will be impractical. Given the soil conditions, in our opinion, deep foundations such as drilled piers, piles or GeopiersTm would be the most feasible foundation support option. 7 4iE'd 331b31NI Nflb1a Wd26•E0 20, 42 eldtl