CORRESPONDENCE_1990-1991 - Laserfiche WebLink

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. � 0 HARNEY LANE LANDFILL -2- 12 July 1991 CLOSURE PLAN REVIEW in a large increase in construction costs. The unacceptable process used large rototiller type equipment. Details of the Harney Lane mixing process must be given. The CQA testing protocol states that additional material will be needed from an area just south and west of the source area. The Closure Plan does not discuss this additional material in the operation work or cost estimates sections. Section 17774 (e) of Title 14 states that "Analysis of the earthen materials should be performed prior to their placement onto the final cover. . ." Therefore, the blended soil mixture for the clay cover must be determined and tested to see if it meets the performance goals of Chapter 15 prior to use of the soil mixture as a clay cover. The County should recognize that lab permeabilities are typically ten to one hundred times lower than field permeabilities. If this observation holds for the proposed soil mixture, it will fail to meet the Chapter 15 permeability requirements. 2. DESIGN CRITERIA - The County has not conducted sufficient soil tests to identify the density and moisture conditions necessary during construction to achieve the required permeability. There is no discussion in the Closure Plan of key construction factors relevant to building a low permeability soil liner. These factors include destruction of soil clods, maximum allowable clod size, interlift bonding, water content of soil during compaction, degree of saturation, and the type and weight of roller. Part I B. 1. of Closure Operations states that moisture conditioning will occur after the soil has been removed from the borrow area and placed in the lifts for compaction. Water should be added to soils at least 24 hours before determining if the soil is at proper moisture content for compaction. This will allow the soils to fully absorb applied water so that moisture content is uniform throughout. Since the lifts are proposed at 9 inches thick, adding moisture just prior to compaction will not result in uniform saturation. Moisture conditioning is best accomplished on a mixing table or in the borrow area. 3. CONSTRUCTION QUALITY ASSURANCE (CQA) PLAN - The purpose of the CQA plan should be to identify defects in the cap construction and provide a process to remedy these defects. The CQA plan does not contain any corrective actions to be taken where the soil mixture fails to meet the required construction specifications. The CQA Testing Protocol does not include any testing of the borrow material and relies on the 1987 Kleinfelder report which simply states that it is possible to achieve 10-6 cm/sec permeability by the proper blending of soils. As stated above, we suspect the permeability requirements will be difficult to achieve. As a result, CQA testing must be extensive to insure that permeability requirements are met. Borrow material should be tested in order to set up specifications and a procedure for determining a proper mix. Tests to insure a proper mix must be specified. A qualified soils person must be on site to direct the borrow material excavation and mixing to make certain that a proper mixture is achieved.