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August 28, 1991 BALBI g C14ANG ASSOCIATES File No. 1525-69 B. Field Investigation and Laboratory Testing Our subsurface investigation consisted of the drilling of four test borings at the approximate locations shown on the Boring Location Map, Plate 2. All borings were made with a CME- 55 truck-mounted drill rig equipped with 3.75-inch I.D. hollow-stem continuous-flight augers on August 8, 1991. All test borings were logged by our field engineer, who also obtained representative soil samples for laboratory testing. The soils encountered in test borings are shown on the Boring Logs, Plates A-2 through A-5, of Appendix A. A copy of the Unified Soil Classification System used to identify the site soils is presented on Plate A-1. Relatively undisturbed soil samples were obtained by driving a 2-inch I.D. Modified California Sampler containing thin brass liners into the bottom of borings. The procedures used in obtaining these samples are identical with the Standard Split Spoon Sampler (ASTM D1586-84). When the sampler was withdrawn from the borings, the brass liners containing the samples were removed, examined, and sealed to preserve their natural moisture content for laboratory testing. Laboratory tests were performed on selected samples obtained from the test borings to evaluate their strength and other physical properties. Tests performed included moisture content, dry unit weight, Atterberg limits, unconfined compressive strength, moisture-dry density relationship, and R-value. The moisture-density curve and R-value curve are presented on Plates A-6 and A-7 of Appendix A, respectively: A summary of all laboratory tests completed is presented on Table A-1 of Appendix A. C. Subsurface Soil Conditions Available geologic literatures indicate the soils underlying the project site is alluvium! 1Thi§ alluvial deposit is unconsolidated, and interstratified with,sand, silt,and clay. A generalized view of site soil conditions is presented below. Detailed descriptions of subsurface soils encountered at each test boring are presented on the Boring Logs in Appendix A. An idealized soil profile across the site would show a surficial stratum consists of dark brown to black silty clay. This surficial clayey soil is generally damp to moist, medium stiff, and high plasticity. Thickness of this layer varies with the location and ranges from 2 feet to 8 feet. Laboratory test reveals that the near surface clay has high volumetric.change potential. A horizon of brown and/or tannish brown silty clay to clayey silt underlies the surficial clayey soil and extends to the maximum explored depth of 41 feet below the existing ground s Page 3 of 17