ARCHIVED REPORTS_JULY 2014 FINAL RCSI

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2-12 Forward Composting Facility SWT Engineering Report of Composting Site Information - July 2014 z:\projects\allied waste\forward\resource recovery facility\5 yr permit rvw 2013-14\rcsi 2014\text\sec 2.doc 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 engineer 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 portions in plastic bags or by sealing the sampling tube with plastic cap and tape. Sample description s, 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 moisture content of the selected samples. Engineering property tests performed included Unconsolidated Undrained (UU) triaxial compression and consolidation tests. Detailed results of the tests performed are included in the Stability and Settlement Analysis of that report. The soil encountered during the CH2M HILL field investigation generally consists of interbedded layers of sand, silt, and lean clay. The cohesive materials are generally of very stiff to hard consistency. The cohesionless materials can be characterized as dense to very dense. The soil deposits at the site were found to be heterogeneous and laterally and vertically discontinuous. Based on the four soil borings performed for this geotechnical exploration, the subsurface soils at the site can be divided into six general layers of interest. It should be noted that the generalized subsurface profile described below has been greatly simplified for the purpose of this report. Beginning at the existing ground surface (approximately elevation 39 feet MSL), these six layers are as follows: ♦ A 10- to 15-foot layer of light brown material ranging from lean clay to silt and silty clay. This layer is dry and very stiff to hard in consistency, with moisture contents typically at or below the plastic limit. A UU triaxial compression test performed on a sample at a depth of 15 feet in CH2M HILL Boring BH-4, which indicated an undrained shear strength of 5,145 pounds per square foot (psf). SPT blow- counts in this layer are typically greater than 50. ♦ A 16- to 20-foot layer of material ranging from silty sand to clayey sand. This layer is dry to moist and typically dense to very dense. Within this layer, a 5-foot zone of very stiff lean clay (UU shear strength of 2,262 psf) was encountered in Boring BH-2 at an approximate depth of 19 feet. This layer was not encountered in other borings and is believed to be discontinuous. ♦ A 5- to 10-foot layer of very stiff yellowish-brown lean clay. This material is moist, with moisture contents between the plastic and liquid limits. A consolidation test indicates that this material is consolidated to approximately three times the effective overburden stress overconsolidation ratio (OCR) of 3. The OCR is the ratio of the maximum effective stress the soil has been subjected to in the past (preconsolidation pressure) to the existing effective stress in the soil. A UU triaxial compression test at an approximate depth of 34 feet in CH2M HILL Boring BH-1 indicated a shear strength of 2,286 psf.