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Mr. Gabriel Karam, P.E. <br />Page 4 of 5 <br />Board staff runoff coefficients for the prescriptive <br />standard cap should range from 0.6 to 0.9. <br />3. No design calculations were provided for the drainage <br />basins. Is the purpose of the retention basins to <br />retain the runoff from the landfill , sedimentation, or <br />both? Basin volume and spillway design are required. <br />Note that holding facilities shall be designed so that <br />they will overtopped during the 100 -year, 24-hour <br />frequency precipitation event [14 CCR 17778(h)]. <br />4. The Air Solid Waste Assessment Test (SWAT) indicates a <br />potential off-site gas migration (methane levels of 50 <br />percent and 30 percent by volume at probes P-1 and P-6, <br />respectively). The landfill gas monitoring system <br />should be installed as soon as possible to determine if <br />landfill gas is migrating off site. Please ensure that <br />the proposed perimeter monitoring system is in <br />compliance with 14 CCR 17783.5. The probe <br />specifications on sheet 5 do not indicate what material <br />will be used to fill the annular space between the <br />bentonite seals and screened intervals. Due to <br />irregularities in the native material and difficulties <br />in achieving adequate compaction, native borehole <br />material is not an adequate fill material and bentonite <br />or a bentonite/cement grout should be used. <br />5. Please see the RWQCB's comments regarding the final <br />closure plan and particularly the Construction Quality <br />Assurance Plan. <br />6. Page 8 of the text in the closure plan states that <br />slopes will be graded to a maximum slope of 3:1 <br />(horizontal:vertical). The landfill does not appear to <br />be in an unstable area and does not appear to require a <br />slope stability analysis under 14 CCR 17777. <br />7. The Emergency Response Plan is incomplete. No sequence <br />or implementation timetables are specified (e.g., how <br />soon after drainage problems are discovered will action <br />to remedy the problem be taken?). Only events listed <br />in 14 CCR 17766 are listed. What about hazardous <br />materials spills on Interstate 580 adjacent to the <br />landfill or other potential emergencies? The emergency <br />response plan should also identify appropriate agencies <br />to notify (e.g., the Sheriff's department in the event <br />of vandalism) and the appropriate emergency numbers of <br />all potential responding agencies and relevant county <br />departments (e.g., fire department, police, hospitals, <br />Board, LEA, RWQCB, Department of Public Works, etc.). <br />