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high rainfall events. This soil type is typically used for irrigated cropland, orchards, and sometimes irrigated pasture and urban development. Soil Properties. Subsurface soil properties onsite have been evaluated during three sepa- rate soil investigations. The first investigation of the onsite subsurface soils was performed by EMCON Associates in 1972. EMCON drilled a total of 17 borings ranging in depth from 38 feet to 178 feet. The locations of the EMCON boreholes are shown on the Exist- ing Conditions Plan, Drawing 1. Another subsurface investigation was performed by InsituTech in 1987 using Cone Penetration Testing (CPT) in the WMU E area. The exact locations of the CPTs were, unfortunately, not surveyed by InsituTech. The most recent subsurface investigation was performed by CH2M HILL in 1992; it con- sisted of four soil borings drilled in April and May, 1992. The Existing Conditions Plan, Drawing 1 shows the approximate location of these four borings, designated as BH-1 through BH-4. Pitcher Drilling Company of Palo Alto, California, was subcontracted to drill the soil borings. CH2M HILL personnel specified the locations, depths of borings, and sampling intervals and observed the drilling and sampling operations. All borehole logs available for the site are included as Appendix C. The CH2M HILL borings were 4-7/8-inch diameter and extended to depths ranging from 43 to 102 feet. The borings were advanced using mud rotary drilling methods with a truck-mounted Failing 750 drill rig. As each boring was completed, the hole was grouted to the surface using a "neat" cement grout. The borings were grouted from the bottom upward using a 2-inch drill pipe as a tremie. Relatively undisturbed samples were obtained using a 3-inch outside diameter Shelby tube sampler (ST samples) or Pitcher Barrel sampler (PB samples). The Pitcher Barrel sampler was used to obtain samples of very stiff clay where the Shelby tubes could not be pushed. This sampling was performed in general accordance with procedures for Thin-Walled Tube Sampling of Soils as described by the American Society of Testing and Materials (ASTM), Standard D1587. Disturbed soil samples were obtained from the borings using a 2-inch outside diameter split-spoon sampler, driven as described for the Standard Penetration Test (SPT), ASTM Standard D1586. Soil recovered during the drilling program was visually classified by a CH2M HILL engi- neer in general accordance with ASTM D2487 and D2488. The soil names on the boring logs reflect these ASTM standards. Pocket penetrometer tests were conducted on most cohesive samples. Samples were then prepared for storage by placing representative por- tions in plastic bags or by sealing the sampling tube with plastic cap and tape. Sample descriptions, blow counts recorded during the SPT, and other relevant information were recorded on the soil boring logs. Selected soil samples obtained by CH2M HILL from its subsurface investigation were tested in the laboratory by Harding Lawson Associates (HLA) of Concord, California. Index tests performed by HLA included determining the liquid limit, plastic limit, and na1oo49B64. si4o 9/29/94 40