Agenda - 03-24-2011 - 1 - Laserfiche WebLink

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37 ONE COMPANY M e m o ~~ Many Solutions`" To: Gayle Wilson (Orange County) From: Doug DeCesare (HDR) Froiect Orange County MSW Landfill cc: Ed Shuffler (HDR) Date: October 28, 2010 ,lob No: 35207-142839-018 Revised February 3, 2011 RE: MSW Landfill Expansion Capacity Under Work Order No. 2 .HDR has prepared different options regarding the proposed final grades of the landfill. It is intended to prepare a permit modification that revises the current permitted side slopes of 4:1 to 3:1. The steeper side slopes provide better drainage, enhances positive drainage after settlement, and provides additional capacity. If the revised permitted capacity of the landfill increases by 10% or more, North Carolina General Statutes considers the permit modification to be a substantial amendment. A substantial amendment requires public involvement during the review and approval process with NCDENR. The public involvement process would generally follow 15NCAC 13B .1603(c) of the Solid Waste Management Rules. Upon approval of a substantial amendment, NCDENR would prepare a draft, permit and a fact sheet for the applicant and anyone who may request a copy. When the draft permit is ready, NCDENR would give public notice that a draft permit has been prepared at which time a 45-day public comment period is opened and/or a public hearing is scheduled. The public notice may be in the form of publication in a daily or weekly local newspaper of general circulation or by posting the notice in the post office and public places of the municipalities nearest the site. All comments received would be considered by NCDENR in making the final decision. At the time of final permit decision, NCDENR would provide a response to all comments received. Currently the bottom third of the landfill has been constructed at slopes steeper than 4:1 to account for future settlement. HDR has projected the remaining final grades at a 3:1 beginning at existing side slopes that closely represent 3:1 slopes. By projecting 3:1 slopes and remaining below the 10% threshold, the landfill would have a remaining capacity of about 452,000 CY as of 3/19/10 (date of latest survey). At 51,120 tons/year and a waste density of 1,320 Ib/cy, the remaining site life would be 70 months and reach capacity in January 2016. Additional capacity could be realized beyond the 452,000 CY if the 10% threshold were exceeded. In the event the County elects to maximize the landfill, HDR projected the final grades at a 3:1 slope from the existing slopes to a higher elevation that results in a remaining capacity of about 530,000 CY. In this case the remaining site life would be 82 months and reach capacity in January 2017. Maximizing the landfill capacity based on these grades is achievable and can be easily constructed. If the County was interested in reworking all the slopes and begin the 3:1 slopes at the toe of the landfill (at the base liner anchor trench), the maximum capacity of the landfill would be greater than 530,000 CY. In addition to projecting the 3:1 slopes from the existing slopes, HDR projected grades from the toe of the landfill which creates an additional wedge of airspace between the existing slopes and the projected slopes. With the additional wedge, the maximum remaining capacity of the landfill is about 617,000 CY. This yields a remaining site life of about 96 months which reaches capacity in March 2018. Per our meeting October 27, 2010, it was concluded to proceed with the permit modification such that the 10% threshold will not be exceeded. Unless otherwise directed by the County, HDR proceeded with the preparation of a permit modification to steepen the side slopes and remain under the 10% capacity increase threshold. HDR Engineering, InC. 13733 National Drive I Phone (919) 7851118 I Page 1 of 1 C:lpwworldnglfpa1d023525112011-02-04 DTD-Wilson Capacity Memo.DOC Suite 207 Fax (919) 7651187 Raleigh, NC 27612 vnvw.hddnc.com