CORRESPONDENCE_2005-2006 - Laserfiche WebLink

Home Browse Search

W. Michael Carroll -2 - 28 September 2005 San Joaquin County layer with non-woven geocomposite separator/filter; a 60-mil HDPE geomembrane; GCL and a prepared subgrade. The submitted design specification calls for a geocomposite drainage net and does not include a non-woven geocomposite separator/filter. The drainage net is required to have anon-woven geocomposite separator/filter component,please clarify this in the CQA document and drawings. 6. The proposed barrier liner design is not compliant with the WDRs or Title 27 for the side slope liner design. Construction Specification DA of the WDRs states: The Discharger may propose changes to the liner system design prior to construction, provided that approved components are not eliminated, the engineering properties of the components are not substantially reduced, and the proposed liner system results in the protection of water quality equal to or greater that the design prescribed by Title 27 and this Order. The proposed changes may be made following approval by the Executive Officer. Substantive changes to the design require reevaluation as an engineered alternative and approval by the Board. Staff cannot recommend that the Executive Officer approve the barrier liner design. ET Plan 1. The ET Plan states, "staff found that use of an ET cover would be acceptable for Module"P' (letter dated July 18, 2005) and requested that a test section of the proposed ET cover be constructed prior to the placement of the cap over Module "I"." Staff has stated in previous correspondence that the idea of utilizing anET cover is a viable option, but stated that a pilot study test pad would need to be installed and monitored over several seasons to verify that it can meet the performance goals of the prescriptive cover. 2. Two samples were collected and analyzed for particle size,plasticity, index,maximum dry density and optimal soil moisture. Hydraulic conductivity was determined from a composite of the two samples. The assessment and evaluation of the borrow pit area is an essential phase of the design and construction of an ET cover and two samples does not provide an adequate amount of testing. Refer to the guidance manual prepared by the Interstate Technology Regulatory Council(ITRC)entitled, Technical and Regulatory Guidance for Design, Installation, and Monitoring of Alternative Final Landfill Covers, December 2003. As stated in the ITRC guidance manual,proper design of an ET cover depends on a thorough understanding of three fundamental concepts: soil water storage, evapotranspiration and climatic factors, and critical design period. Additional soil sampling is warranted to demonstrates that the soil from the borrow pit is homogeneous and that the soil will be able to hold incoming precipitation until it is removed by evapotranspiration. Section 4 of the ITRC manual thoroughly details information that should be provided to support the design of an ET cover. 3. Soil specifications and corresponding soil sampling shall be provided in the CQA plan such that the soil placed within the ET cover is within specifications.