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Project No. JB-569 20 June 2006 Revised 18 October 2006 Page 7 to our office for review. If the documentation is acceptable, we may allow the fill to remain in place. 6.1.3 Excavations and Utility Trenches As discussed earlier, stiff to very stiff silty clay and gravelly clay and medium dense to very dense clayey sand and silty sand was encountered at the time of drilling. We anticipate that the native soils may be excavated utilizing conventional equipment. Contractors, especially those digging utilities, should satisfy themselves as to the hardness of deposits and equipment required. If construction requires personnel to enter the excavation, the contractor must comply with the Occupational Health and Safety Administration regulations set forth in 29 CFR 1926. Utility trenches that parallel the sides of the buildings should be placed so that they do not extend below a line sloped down and away at a slope of 2H:1 V (horizontal to vertical) from the bottom outside edge of the perimeter foundations. All trenches should be backfilled with native materials compacted uniformly to the relative compaction specified in the following section. If local building codes require use of sand as the trench backfill, all utility trenches entering the building should be provided with an impervious seal of either cohesive soil or lean concrete where the trench passes under the building perimeter. The impervious plug should extend 4 feet into, and out of, the building perimeter. Jetting of trench backfill is not recommended as it may result in an unsatisfactory degree of compaction. 6.1.4 Fill Placement and Compaction After performing the required excavations and/or prior to foundation excavations, the exposed subgrade soil should be carefully inspected to verify removal of all unsuitable deposits. The exposed subgrade soil should then be scarified to a depth of 12 inches, moisture-conditioned, and compacted to a minimum of 90 percent relative compaction at a minimum of 3 percent over optimum moisture content according to the latest ASTM test methods and procedures. After compacting the subgrade soil, all required fill should be placed in loose lifts a maximum of 8 inches in thickness. On-site soil generated by site grading may be used as structural fill provided the soil is free of deleterious and organic materials and is approved for use as fill by our representative. Korbrnacher Engineering, Inc.