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Kraus-Anderson Realty Company Project BL-11-01014 March 18, 2011 Page 15 A majority of the soil borings indicated the site predominantly consist of clayey soils.These soils are considered moderately-to highly-corrosive to metallic conduits.We recommend corrosion sensitive utilities be bedded in non-corrosive granular materials. D.B. Modular Block Retaining Wall Based upon the information provided to us,the proposed retaining wall to the north of the proposed building will be modular block construction.The wall will be approximately 4 feet in exposed height and constructed to retain a portion of the existing slope to the north of the property. Our scope of services for this project did not include a global stability analysis of the proposed modular block retaining wall. We recommend that the proposed wall be designed by a qualified retaining wall designer and that a global stability analysis be performed prior to construction. D.8.a. Wall Subgrade Based upon the results of this exploration,fill material will be encountered at the anticipated foundation bearing elevation of the proposed wall.The samples of fill obtained appeared relatively free of deleterious materials; however, information regarding the age, placement and compaction of the fill was not available at the time of this report. Due to access constraints, Boring ST-102 was placed about 20 feet south of the proposed wall location.Although the fill soils at the boring location (ST-102)appear well compacted,there is risk associated with using such fill for structural support. If the risks due to unknown,old fill conditions cannot be accepted by the owner,we do not recommend that existing fill soils be used for direct foundation support of the proposed wall.We recommend that existing fill soils be undercut and replaced prior to foundation construction. However, the risks could be reduced by further exploration of the existing fill conditions at or before the time of wall construction. Additional borings, test pits and compaction tests could be performed. D.8.b. Wall Foundations We recommend that foundations for the proposed wall bear in native soils and/or new engineered fill soils. Foundations bearing upon these materials should be designed to exert a maximum allowable soil bearing pressure of 1,500 PSF.This value includes a safety factor of at least 3.0 with regard to bearing capacity failure. D.8.c. Wall Backfill We recommend that backfill placed behind the modular block retaining wall consist of free-draining, clean sand with less than 5 percent by weight passing a size No. 200 sieve. On-site soils should not be considered for re-use as backfill behind the retaining wall unless the wall is designed for the higher B RAU N INTERTEC