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SfGNET 1400 STL Project No. 0010771 Page 3 TY.ShIl�,'Labs to the west by the Coast Ranges, to the east by the Sierra Nevada and to the south by transverse ranges. _ The valley was formed by the tilting of the Sierran Block, with the western side dropping to form the valley and the eastern side uplifted to form the Sierra Nevada Mountain Range. The valley is characterized by a thick sequence of sediments derived from erosion of the adjacent Sierra Nevada r Mountain Range to the east and the Coast Range to the west. These sedimentary rocks are mainly Cretaceous in age. The depths of sediments vary from a thin veneer at the edges of the valley to depths in excess of 50,000 feet near the western edge of the valley. In the vicinity of the project site, these sediments are approximately 15,000 feet deep. According to published geologic maps, the project site is underlain by the Basin Deposits. The Basin generally consists of unconsolidated silts and clays deposited during flood events. The Sacramento Valley has historically been a province of relatively low seismic activity. The nearest faults to the project site are the Foothills Fault system located near the base of the Sierra Nevada Mountain Range and the Coast Ranges Sierran Block Boundary Zone located along the base of the Coast Ranges. There are no known active fault traces in the project vicinity. FIELD AND LABORATORY INVESTIGATIONS Subsurface soil conditions we plored by illing four exploratory borings and two percolation test borings to depths ranging ftm 5 to 20 feet be w existing site grade (BSG) using a truck-mounted drill .. rig. In addition, one bulk bgrade s sample was obtained in the proposed pavement areas for laboratory R-value testing. The approximate boring and bulk sample locations are shown on Figure No. 1. During drilling operations, penetration tests were performed at regular intervals to evaluate the soil consistency, obtain information regarding the engineering properties of the subsoil, and to retain soil samples for laboratory testing. The soils encountered were continuously examined and visually classified in accordance with the Unified Soil Classification System. A more detailed description of the field investigation is presented in Appendix A. Laboratory tests were performed on selected soil samples to evaluate their physical characteristics and engineering properties. The laboratory-testing program was formulated with emphasis on the evaluation of gradation, Atterberg limits, shear strength, consolidation potential, and moisture-density relationships of the materials encountered. Details of the laboratory test program and the results of laboratory test are summarized in Appendix A. This information, along with the field observations, was used to prepare the final boring logs in Appendix A. v. NITRATE LOADING STUDY A nitrate loading study was performed to evaluate the concentration of leachate related to the on-site sewage disposal system and rainfall. The study was particularly focused on the potential for excessive nitrates that can lead to detrimental human health effects. In particular, the health risks associated with elevated nitrate concentrations are often referred to as " blue baby syndrome" or methemoglobinemia. 1417 No. Market Blvd., Suite 1 • Sacramento,CA 95834 • (916) 568-5858 . Fax: (916) 568-5813