5.3. SR 06-21-2010 - Laserfiche WebLink

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a.~ Ms Rebecca Haug May 6, 2010 Page 2 of 3 design. Basegrades are acceptably configured with sufficient vertical separation from the gl•oundwater elevation based on historic monitoring data. The liner system and final 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 ni relation to the existing leachate management 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 Gradin /Dg rainage 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 over the perimeter access road and then offsite to the property to the south. Significant erosion is anticipated for the steep exterior berm slopes which are proposed at a 2:1 ratio. The perimeter access road needs to be redesigned to include au 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 fill limit of Cell 18. Page 3-9 Leachate and Gas Collection S, std ern, pa eg 310 ERL proposes leachate recirculation for Cell 18. This operation will greatly increase the amount of landfill gas tlTat will be generated from the landfill. The prunary 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 Celi 18 liner system. The supplemental LFG collection piping must extend up the sideslopes to enable corniection 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 maximum area allowed for inactive fill areas prior to placing temporary final cover need to be identified by the applicant. Page 3-10 Construction Quality Assurance Reports ERL must prepare detailed record 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 witlun 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. From the plans submitted, the current capacity of P2 is approximately 1 ac-ft or less. The design plans