5.1. PCSR 06-08-2010 - Laserfiche WebLink

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Ms Rebecca Haug May 6, 2010 Page 2 of 3 design. Basegrades are acceptably configured with sufficient vertical separation froth the groundwater elevation based on historic motutoring data. The liner system and fmal cover system designs are acceptable and consistent with previous approvals. The design is missing engineering and construction details related to the leachate management system and other features. The detailed engineeruig design report and construction plans must provide hydraulic calculations for Cell 18 in relation to the existing leachate mauagetnent infrastructure to demonstrate sufficient capacity for the added liner area. It is recommended that the CUP and License contain conditions requiring the submittal and staff approval of the detailed engineering reports and construction plans prior to Cell 18 construction. Page 3-6 Grading/Draina~e Plan and Drainage Calculations The conceptual surface water drainage plan is generally acceptable; however modifications are necessary to meet standard landfill design guidelines. The application states that all of the stonnwater is controlled onsite, however, surface water drainage for approximately 4 acres of landfill slope is uncontrolled on the south side of Cell 18. Surface water is currently designed to sheet flow ovet• the perimeter access road and then offsite to the propet•ty to the south. Significant erosion is anticipated for the steep exterior berm slopes which ate proposed at a 2:1 ratio. The perimeter access road needs to be redesigned to include an interior ditch with sufficient hydraulic capacity and erosion control protection. Surface water should be routed to Pond P2 or other provisions made if sufficient capacity for P2 is not available. An additional surface water pond may need to be established at an offsite location considering that no buffer is provided adjacent to the south fall limit of Cell 18. Page 3-9 Leachate and Gas Collection S std em, pa e~- 3-10 ERL proposes leachate recirculation for Cell 18. This operation will gteatly increase the amount of landfill gas that will be generated from the landfill. The ptunary concerns relate to landfill gas collection and the prevention of fugitive gas emissions and odors. To provide additional LFG extraction capacity, the design must be modified to place horizontal LFG collection piping within the sand drainage layer at the east west ridge (high point} of the Cell 181iner system. The supplemental LFG collection piping must extend up the sideslopes to enable cotu~ection to the LFG extraction system and to enable cleanout maintenance. Temporary final cover is proposed as an element of the September 2008 "Leachate Recirculation Permit Application" proposal. The criteria for when an area would receive temporary final cover indicating the maximum length of time of inactive fill operations needs to be identified. Similarly, the tnaxitnum area allowed for inactive fill ateas prior to placing temporary final cover need to be identified by the applicant. Page 3-10 Construction Quality Assurance Reports ERL trust prepare detailed tecot•d drawings/documents of the leachate recirculation drainfield construction, which are certified by an engineer. The drawings will include survey measurements of the drainfield areas to document position within the cell, suitable base contours and piping elevations. All construction must be fully documented. This information is critical in potential problem resolution during later stages of landfill operation. Apuendix B Grading and Drainage Calculation The sedimentation basin design information for P2 indicates a total storage capacity of 8.7 ac-ft. Froth the plans submitted, the current capacity of P2 is appmxunately 1 ac-ft or less. The design plans