ATTACHMENT A

GCCS Design Plan (2017)

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Landfill Gas Collection and Control System Design Report Rowan County Solid Waste Landfill

Woodleaf, North Carolina

Prepared for:

Rowan County Department of Environmental Management 2727 Old Concord Road, Suite D Salisbury, NC 28146

Issued June 3, 2016

Revised September 22, 2017 Revised November 27, 2017

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Landfill Gas Collection and Control System Design Report Rowan County Solid Waste Landfill i Issued June 3, 2016 - Revised November 27, 2017

Contents

1 Certification....................................................................................................................................... 1-1

2 Introduction ....................................................................................................................................... 2-1

2.1 Purpose .................................................................................................................................. 2-1

2.2 Site Background Information .................................................................................................. 2-1

3 Proposed Landfill Gas Collection and Control System .................................................................... 3-1

3.1 Landfill Gas Generation.......................................................................................................... 3-1

3.2 Landfill Gas Collection ............................................................................................................ 3-2

3.2.1 Vertical Collectors ..................................................................................................... 3-2

3.2.2 Well Placement and Radius of Influence .................................................................. 3-2

3.2.3 Wellhead Assemblies ................................................................................................ 3-3

3.3 Header and Lateral Collection Piping ..................................................................................... 3-3

3.3.1 Collection Piping Layout ............................................................................................ 3-3

3.3.2 Collection Pipe Sizing................................................................................................ 3-4

3.3.3 Condensate Management ......................................................................................... 3-5

3.4 Gas Blower/Flare Station ....................................................................................................... 3-5

3.4.1 Blowers ...................................................................................................................... 3-6

3.4.2 Flare .......................................................................................................................... 3-6

3.4.3 Blower/Flare Station Controls ................................................................................... 3-6

4 Future Site Development .................................................................................................................. 4-7

4.1 Landfill Development Plan...................................................................................................... 4-7

4.2 GCCS Expansion Capabilities ............................................................................................... 4-7

5 Compliance Review and Evaluation ................................................................................................. 5-1

5.1 Compliance with §60.759(a)(1) .............................................................................................. 5-1

5.1.1 Control of Surface Emissions .................................................................................... 5-1

5.1.2 Depths of Refuse ....................................................................................................... 5-2

5.1.3 Refuse Gas Generation Rates and Flow Characteristics ......................................... 5-2

5.1.4 Landfill Cover Properties ........................................................................................... 5-2

5.1.5 Gas System Expandability ........................................................................................ 5-2

5.1.6 Leachate and Condensate Management .................................................................. 5-3

5.1.7 Accessibility ............................................................................................................... 5-3

5.1.8 Compatibility with Waste Operations ........................................................................ 5-3

5.1.9 Integration with Closure End Use .............................................................................. 5-3

5.1.10 Air Intrusion Control ................................................................................................... 5-3

5.1.11 Corrosion Resistance ................................................................................................ 5-4

5.1.12 Fill Settlement ............................................................................................................ 5-4

5.1.13 Resistance to Decomposition Heat ........................................................................... 5-4

5.2 Compliance with §60.759(a)(2) .............................................................................................. 5-5

5.3 Compliance with §60.759(a)(3) .............................................................................................. 5-5

5.3.1 Asbestos and Nondegradable Materials ................................................................... 5-5

5.3.2 Nonproductive Areas ................................................................................................. 5-6

5.4 Compliance with §60.759(b)(1), (2) and (3) ........................................................................... 5-6

5.4.1 Landfill Gas Extraction Component Construction ..................................................... 5-6

5.4.2 Landfill Gas Extraction Component Installation ........................................................ 5-7

5.4.3 Connection of Landfill Gas Collection Device to Collection Header Pipes ............... 5-8

5.5 Compliance with §60.759(c)(1) and (2) .................................................................................. 5-9

5.5.1 Existing Landfill Gas Flow Rate Data ........................................................................ 5-9

5.5.2 Future Landfill Gas Flow Rate Estimates .................................................................. 5-9 ii | Issued June 3, 2016 – Revised November 27, 2017

5.6 Alternatives and Compliance with §60.759(b)(2) ................................................................... 5-9

5.6.1 Submit a Design Plan ................................................................................................ 5-9

5.6.2 Alternatives to the NSPS ......................................................................................... 5-10

Appendices

Appendix A: GCCS Design Plan Drawings Appendix B: Landfill Gas Generation Rate Modeling, Radius of Influence and Well Spacing

Calculations, Condensate Generation Estimates, Headloss Analysis, and Flare

PTE

Appendix C: Surface Emissions Monitoring Plan Appendix D: County Consistency Determination Letter

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1 Certification This New Source Performance Standards (NSPS) Landfill Gas Collection and Control System (GCCS) Design Report was prepared for the Rowan County Landfill as authorized by the Rowan County Department of Environmental Management.

I certify that the GCCS as described in this plan meets the design requirements specified in 40 CFR 60.759, and any alternatives pursuant to 40 CFR 60.752(b)(2). I further certify that this report was prepared by me or under my direct supervision, and that I am a duly registered Professional Engineer under the laws of the State of North Carolina.

Michael D. Plummer, P.E.

Certifying Engineer

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2 Introduction

2.1 Purpose

This report was prepared by HDR Engineering Inc. (HDR) on behalf of the Rowan County Department of Environmental Management (Rowan County) to fulfill the requirements of the New Source Performance Standards (NSPS), 40 CFR Part 60, Subpart WWW, for a Landfill Gas Collection and Control System (GCCS) Design Plan for the Rowan County Landfill (Landfill). The Landfill is located in the Town of Woodleaf and is owned and operated by Rowan County. The recently published revisions to the NSPS regulations will lower the threshold for which landfills become regulated by the NSPS.

The revised threshold will be triggered when a landfill’s design capacity exceeds 2.5 million megagrams (Mg) and when its non-methane organic compounds (NMOC) emissions rate exceeds 34 megagrams (Mg) per year as opposed to 50Mg/yr. As such, the Landfill will be subject to NSPS regulations that will require the installation of a GCCS to manage landfill gas (LFG). The collected LFG will be directed to a flare that will reduce the NMOC emissions. This design plan was prepared in accordance with 40 CFR 60.752(b)(2) and fulfills the requirements of 40 CFR 60.752 and 60.759.

2.2 Site Background Information

The Landfill is located at 789 Campbell Road (SR 1947) in Woodleaf, North Carolina and is permitted under NCDENR Permit No. 80-03. The landfill property consists of approximately 375 acres. A closed land clearing and inert debris (LCID) landfill and a closed construction and demolition (C&D) landfill are located on the eastern portion of the property. In 1989, Rowan County constructed Phase I of the lined Subtitle D landfill.

The complete Subtitle D landfill area will consist of Phases I – IX with a total design capacity of approximately 15.071 million cubic yards. Currently, the landfill’s permitted capacity for Phases I, II, III, IIIA (vertical expansion) and IV totals 5,437,000 cubic yards.

Permitting a full build out of Phases I – IV would increase the landfill capacity to 7,160,000 cubic yards. Waste is currently being deposited in Phases I, II, III and IV. As of November 22, 2017, no landfill areas are capped.

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3 Proposed Landfill Gas Collection and Control System This section identifies the components of the proposed GCCS and describes how LFG will be managed. A phased GCCS was designed and constructed in order to provide NSPS compliance by April 2017 and continue compliance for the entire landfill lifespan.

The proposed GCCS design consists of sixty (60) vertical extraction wells. Twenty-seven

(27) of which will be installed within the Phase I and Phase II area by April 2017 and the remaining thirty-three (33) will be installed in Phases III and IV after final grades are reached. Due to the limited waste depth in the permitted Phase IV contours (I.e. 20 to 35 feet vertically) well heads will be connected to the leachate collection system in order to control and extract landfill gas. Future GCCS expansions beyond the 15year system life will be designed, permitted and installed as each future landfill lateral expansions into Phases V – IX) reaches completion. LFG collected from the landfill will be routed to a blower/flare station where the LFG will be combusted using a candlestick flare. The candlestick flare will be designed to provide a minimum 98 percent NMOC destruction efficiency required by §60.752(b)(2)(iii). If alternative utilization or control devices are used in the future, they will be designed to comply with the applicable NSPS requirements. The proposed GCCS design was designed so that future expansion of the system can be accommodated.

Permit level drawings depicting the proposed GCCS system (Phase I, II, III and IV) are included in Appendix A.

3.1 Landfill Gas Generation

Per NSPS requirements the GCCS is required to be sized to handle the maximum expected gas flow rate over the intended use period of the system. For design purposes the baseline years of 2017 through 2032 were used as the intended use period.

The United States Environmental Protection Agency (USEPA) LandGEM (Version 3.02) gas generation model was used to determine the total LFG generation rate over the 15 year collection system design life. The inputs to the model are consistent with AP-42 and EPA guidance. Waste tonnages used in the model were obtained from landfill records and assumed to remain constant from 2016. The waste design capacity was calculated using the full build out design capacity of 7.160 million cubic yards for Phases I through IV and the current average in-place density of 0.6575 tons per cubic yard (reported in the Rowan County Landfill Airspace Calculations Report dated July 24, 2017). The Phases I

– IV capacity is anticipated to last through the intended use period. The LandGEM model results are presented in Appendix B.

The maximum expected LFG generation rate during this design period is estimated to be 1,162 cfm.

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3.2 Landfill Gas Collection

LFG extraction will be achieved using a well field of vertical extraction wells. The well field is connected to the blowers which provide a negative vacuum across the landfill area via a system of lateral pipes and header pipes. While Rowan County intends to install vertical extraction wells to the extent practical, particularly in areas at or near final (or long-term interim) grades, initial gas collection may come through well head connections to the leachate collection system when installation of vertical wells is not feasible due to the site geometry, waste depth or filling sequence. In addition, although not shown in this design, horizontal collector wells may be employed as necessary to enhance collection.

3.2.1 Vertical Collectors

In lined landfills, the vertical wells are typically drilled to 75 percent of the landfill depth but no closer than 15-feet above the liner. This standard practice is used to avoid accidental damage to the liner system. Vertical wells will be constructed of Schedule 80 PVC pipe installed in 36-inch diameter boreholes. Typically, the lower two-thirds of the well pipe is perforated. However, perforated pipe is typically not used closer than 10 feet from the landfill surface. Perforations are typically 3/4-inch diameter holes spaced 4-inches apart vertically and 90 degrees apart horizontally. However, alternative slot or perforation designs which provide comparable performance may be considered. The spacing between vertical gas extraction wells depends on the landfill characteristics (e.g., waste density, age, LFG generation rate, etc.) and the amount of applied vacuum.

3.2.2 Well Placement and Radius of Influence

The locations of gas extraction wells were selected to meet the NSPS requirements for sufficient density throughout all gas producing areas. When a well is placed under the influence of vacuum, the recoverable LFG in the immediate vicinity will begin to move towards the well. This area of gas movement is referred to as the well’s radius of influence (ROI).

Some factors that influence a well’s ROI include the depth of the well, the length of perforated pipe for gas collection, the refuse temperature, the in-situ LFG generation rate, the amount of vacuum applied to the well, and waste density. For design purposes, a theoretical ROI for a vertical gas extraction well was estimated. The estimation was calculated for a maximum expected LFG generation rate of 1,162 cfm and an average well depth of 58 feet with perforated pipe length of 42 feet. The estimated ROI was determined to be 121 feet. Actual ROI varies and cannot be measured until a well is installed. ROI calculations are included in Appendix B.

Specific locations for the vertical gas collection wells were initially selected based on a 200-foot grid pattern across the landfill area. Well locations were then adjusted to locations where the depth of waste was sufficient to accommodate 15 feet of clearance from the baseliner, 10 feet of solid pipe below the landfill surface grade, and a minimum 5 feet of perforated pipe length. Then well locations were adjusted to establish a vacuum across as much of the landfill as practical given the estimated ROI. Some overlap of the

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ROI is provided to provide for better collection efficiency. Finally, well locations were adjusted based on the topography and ability of a drill rig to access the area. For example, given that it is preferred to drill wells on a flat surface rather than a steep sideslope, well locations that fall on steep sideslopes based on the 200-foot grid pattern are relocated to nearby benches or plateau areas. In addition, the final location of gas extraction wells may be adjusted in the field based on the actual field conditions during installation.

The layout of the collection system is shown on Sheet 00C-02. Sixty (60) wells are positioned throughout the Phases I through IV. The vertical gas extraction well schedule is shown in the tables on Sheet 00C-03.

3.2.3 Wellhead Assemblies

Each LFG collection well will have a wellhead as shown on the design drawings. The wellhead will include a valve to regulate gas extraction rates and quick connect instrument ports compatible with a Landtec GEM-2000 landfill gas monitoring instrument (or similar monitoring device) to measure gas flow, temperature, pressure and major LFG constituents (methane, carbon dioxide, oxygen, nitrogen). Wellheads will be connected to the lateral pipes by means of flexible piping to accommodate for waste settlement.

3.3 Header and Lateral Collection Piping

3.3.1 Collection Piping Layout

The collection system pipes are installed to apply a vacuum across the well field and convey the gas collected to the blower/flare station. The collection piping for the landfill consists of header pipes and lateral pipes. Lateral pipes connect the vertical gas extraction wells to the header pipes. The header pipe system will incorporate a series of loops to allow for flexibility and redundancy. The collection system layout is illustrated in design drawing Sheets 00C-02 and 00C-04.

The header and lateral pipes will be constructed of fusion-welded HDPE pipe. Header and lateral pipes may be installed either below or above grade. In locations where above grade header and laterals are used, the piping will be appropriately anchored. The header pipe system was designed to drain condensate to low points via gravity.

Whenever possible, the header pipe has a minimum slope of 5 percent to facilitate condensate management after expected settlement. Condensate drip legs will be installed at each low point to capture condensate. The proposed drip legs are located near existing leachate cleanout risers and will drain via gravity to the nearest leachate collection system cleanout. The header system was designed so that it can be expanded as the Landfill is developed. As new phases are developed, interim headers will be installed between the phases to create new individual loops.

Additional features include isolation valves and header pipe access points. The header pipe isolation valves, located throughout the system, are used to isolate particular sections of header pipe for maintenance or vacuum control purposes. Header pipe access points, consisting of a blind flanged assembly that sweep into the header pipe will provide pipe pigging capacity and spare connection points for lateral tie-ins in case

3-4 |Issued June 03, 2016 - Revised November 27, 2017 existing laterals become compromised and/or additional wells are installed. Blind flanges will be installed at locations where tie-ins to future phases are planned. All GCCS construction materials will be constructed of corrosion resistant materials such as PVC, HDPE, and all metal parts potentially exposed to LFG will be stainless steel or coated to increase corrosion resistance. The seats, seals, and valve body material will be appropriate for use in a LFG environment.

3.3.2 Collection Pipe Sizing

The LFG flow characteristics through the refuse cannot be precisely predicted because of the non-homogeneous nature of refuse. For purposes of sizing the LFG transmission piping, estimates of the pipe frictional loss due to the LFG flow were calculated and were used to optimize the LFG pipe and blower sizes.

An analysis was performed on the proposed pipe network to model its ability to adequately handle the maximum LFG that may be generated from the Phases I through IV during the design period. This evaluation was performed using the KYGAS model.

KYGAS was developed by Dr. Don J. Wood and Dr. James E. Funk at the University of Kentucky. The program was based on the KYPIPE modeling program which models water distribution systems. KYGAS is used to calculate the head losses, system pressures, and velocities in piping systems controlled under vacuum. KYGAS operates under the assumptions that all flow in the piping network is steady, one-dimensional, isothermal flow. The program uses the Darcy-Weisbach equation for head losses related to incompressible flow and the Ideal Gas Law for pressure-temperature-density relationships.

The following parameters are required for operation of KYGAS.

Pipe inside diameter Pipe length Minor loss coefficient Roughness within the pipe LFG flow rate into the system at each well or node LFG operating temperature Specific gravity of the LFG Ratio of specific heats Absolute viscosity of LFG

The modeling started by first laying out the piping network including junctions, drip legs, blowers and flare by using engineering judgment. This information was imported from an AutoCAD drawing. After entering the system layout, an initial run of the conceptual layout was performed to determine if the design criteria was met. The design criteria for the header system were:

Maximum flow velocity: 40 feet per second (fps)

Maximum pressure drop: 0.36 psig per 1,000 feet

Minimum vacuum at the blower: 40 inch w.c.

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LFG flow: 1,162 cfm (consistent with the design period flow from 2017 through 2032 )

Using an iterative process, the LFG piping system was modified until all the design criteria were met.

The proposed GCCS configuration results in a calculated total system pressure drop of approximately 8-inch w.c.; the maximum flow velocity is 34.46 fps; and the maximum pressure drop is 0.17 psig/1000 ft. All values are within the design operational ranges.

The results of the KYGAS analysis are included in Appendix B.

The header loop sizing around the Phases I and II is 10” diameter SDR 17 HDPE pipe.

The lateral collection piping sizing is either 4” or 6”diameter SDR 11 HDPE pipe. The final design diameter of each segment of header pipe may vary in size, depending on the volume of LFG it will be expected to convey. The LFG collection system layout with header and lateral pipe size is illustrated in design drawing Sheet 00C-02.

3.3.3 Condensate Management

As LFG extracted from the warm waste mass cools in the collection network, condensate forms. If the gas condensate is not removed from the collection system, liquid buildup will occur and adversely affect gas flow rates or create a blockage. The condensate generation rate depends upon the LFG flow rate and the temperature differential between the LFG in the waste mass and temperature in the lateral and header piping.

The estimated daily condensate generation rate based on the maximum expected LFG generation rate of 1,162 cfm and an ambient temperature of 50 °F was approximately 551 gallons per day (gpd). Condensate generation was also estimated during summer months using an ambient temperature of 80 °F and the condensate generation was estimated to be 305 gpd. These values represent average anticipated daily condensate generation rates and are dependent upon seasonal weather. The condensate generation estimates are included in Appendix B.

The GCCS was designed to drain gas condensate by gravity to condensate drip legs located at low points throughout the header system. The drip legs will be connected to the existing leachate cleanout risers and will drain condensate back into the existing leachate collection system. In addition, a condensate sump will be installed at the header entering the blower/flare station and a condensate knockout pot at the blower/flare station to remove additional moisture from the LFG.

3.4 Gas Blower/Flare Station

The GCCS design utilizes a blower to exert vacuum across the well field and extract LFG from the Landfill. The collected LFG will be conveyed to the flare station for combustion.

The blower/flare station was sized to handle maximum expected gas flow rate during 2017 through 2032. The maximum expected gas flow rate for this period is 1,162 cfm.

The GCCS design will utilize a candlestick-type flare (also called an open or utility flare) as control equipment which combusts LFG outside the stack. The proposed location of a blower/flare station was selected based on safety considerations, access to 3-phased

3-6 |Issued June 03, 2016 - Revised November 27, 2017 electricity, and general accessibility by major equipment, proper drainage, future connection points, operational considerations, and other factors such as noise, odor, and visual impact to the surrounding area. The location of the blower/flare station is shown on the design drawings. This location also provides space for potential future landfill gas to energy (LFGTE) projects.

3.4.1 Blowers

Blowers for the GCCS were sized and configured for incremental capacity to match the LFG generation and collection curves over the design life. The design allows for spare blower units and future blower upgrades. Over the design lifespan, the Landfill will generate between 776 cfm to 1,162 cfm of LFG. The initial phase of the gas collection system is designed to combust 1,500 cfm of landfill gas to control the maximum expected LFG generation. A dual blower system will be used to cover the maximum LFG generation rate. Each blower will be capable of applying a minimum of 40 inches of water column vacuum that can operate between flow rates of 0 to 1,000 cfm. A minimum of 40 inches water column vacuum will be applied to the header at the blower/flare station and the discharge pressure will be at least 10 inch water column. A condensate knock-out pot will be installed to remove additional condensate prior to proposed flare station. A fail-close actuator valve to shut off flow to the blowers will be installed.

3.4.2 Flare

A candlestick flare will be sized to combust the LFG and destroy NMOCs by a minimum 98 percent to comply with 40 CFR 60.18. The flare will have a maximum flow capacity of 1,500 cfm with a 5:1 turndown ratio capacity to allow for fluctuations in gas generation and collection over the design life of the equipment (2032). The flare will be skid mounted and fastened to a poured concrete pad along with the blowers.

3.4.3 Blower/Flare Station Controls

The controls at the blower/flare station will include the following:

• Programmable logic controller (PLC);

• LFG flow meter;

• Blower and flare controls interface for automatic motor starting following pilot ignition;

• Alarm indicators for high temperature, low temperature, flame failure, pilot failure, and blower failure; and,

• Chart recorder or digital data recorder for flare temperature and LFG flow rate.

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4 Future Site Development

4.1 Landfill Development Plan

The Landfill will continue to be filled with MSW in accordance with the solid waste permit.

Installation of GCCS components is anticipated to be coordinated with fill operations and the requirements of the NSPS regulations. Due to potential operational changes, the GCCS design presented in Appendix A may require minor modifications to maintain compliance with the provisions of the NSPS and to accommodate actual field conditions at the time of construction. Any major changes will be brought to the NCDEQ prior to initiation. Minor modifications will be reflected in the construction certification documents.

4.2 GCCS Expansion Capabilities

Typically, it is assumed that the GCCS components will have a maximum lifespan of 15 years. After that period it often becomes necessary to perform significant maintenance or to replace some of the components. Over time, as the Landfill expands and as site conditions dictate, various features of the GCCS may be relocated or replaced in order to accommodate future landfill operations.

It is intended that future GCCS designs will incorporate similar engineering judgment and methods as explained in this Design Report. The specific layout of future phases will be addressed as the expansions are developed and permitted. The GCCS design can accommodate the planned expansion of the Landfill Phases V through IX. Design considerations include appropriate header and condensate trap/sump sizing, additional blower and flare capacity, and tie-in locations for connection to the expansion areas. Header and condensate traps/sumps are sized based on the projected LFG recovery rates from the current landfill areas based on historical and projected future waste disposal rates.

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5 Compliance Review and Evaluation The purpose of this Section is to document and certify compliance of the proposed GCCS with the applicable sections of 40 CFR 60.759 - Specifications for Active Collection Systems, including:

• §60.759(a) - Compliance with §60.752(b)(2)(i).

• §60.759(b) - Construction equipment or procedures.

• §60.759(c) - Conveyance of LFG in compliance with §60.759(b)(2)(iii).

Additionally, portions of §60.755 - Compliance Provisions relevant to GCCS specifications are addressed, including:

• §60.755(a)(1) - Calculations for maximum expected gas generation flow rate.

• §60.755(a)(2) - Sufficient density of gas collectors.

• §60.755(a)(3) - Collection system flow rate sufficiency.

• §60.755(a)(5) - Identification of excess air infiltration.

5.1 Compliance with §60.759(a)(1)

§60.759(a)(1) states, “The collection devices within the interior and along the perimeter areas shall be certified to achieve comprehensive control of surface gas emissions by a professional engineer. The following issues shall be addressed in the design: depths of refuse, refuse gas generation rates and flow characteristics, cover properties, gas system expandability, leachate and condensate management, accessibility, compatibility with filling operations, integration with closure end use, air intrusion control, corrosion resistance, fill settlement, and resistance to the refuse decomposition heat.”

This GCCS was designed to be consistent with NSPS requirements to achieve comprehensive control of both lateral migration and surface emissions of LFG. Issues related to compliance with §60.759(a)(1) are discussed in the following sections.

Applicable information used in the design of the GCCS is included in Appendix A (GCCS Design Plans), Appendix B (Landfill Gas Generation Rate Modeling, Radius of Influence and Well Spacing Calculations, Condensate Generation Estimates and Head Loss Analysis) and Appendix C (Surface Emissions Monitoring Plan).

5.1.1 Control of Surface Emissions

The GCCS was designed to minimize both subsurface lateral migration and surface emissions of LFG. The proposed surface emissions monitoring route maps for Phases I, II, III and IV were prepared in accordance with §60.755(c)(1) and are included in Appendix C. Surface emissions monitoring will be conducted in accordance with §60.755(c) using the proposed route maps. The actual surface emissions monitoring routes may change depending on the site conditions.

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5.1.2 Depths of Refuse

Depths of refuse were calculated based upon existing topography, permit plans and record documentation of landfill base liner grades. Surveyed baseliner grades were not available for Phase I. The baseliner grades for Phase I were estimated by adding 10-feet of elevation onto historical groundwater elevations ensuring a conservative vertical separation distance between the base grades and the ground water level. The surveyed record baseliner grades for Phases II, III and IV were utilized to calculate the depths of refuse within these three phases. The depths of refuse for the proposed vertical LFG extraction wells were estimated based on the differences between the final grades and the record/created baseliner grades. The estimated depths of refuse vary between 52 feet to 123 feet for Phases I and II and 38 to 127 feet for Phases III and IV.

5.1.3 Refuse Gas Generation Rates and Flow Characteristics

A maximum LFG generation rate of 1,162 cfm during the design period (2017 through 2032) was estimated as detailed in Section 3.1.

5.1.4 Landfill Cover Properties

Areas currently at interim grade are covered with daily cover and 12-inches of cover soil.

These conditions are factored into the design of the LFG collectors and wells in order to minimize the potential for pulling ambient air into the landfill. The final cover system was designed in accordance with the NCDEQ solid waste permit closure details and the applicable rules at the time of closure. According to the application for permit to construct Phase IV, the proposed components of the final cap system for Phases I through IV from the top surface to the bottom will consist of:

6 inches of vegetative cover 18 inches of compacted soil cover Geonet drainage media 40 mil LLDPE geomembrane Geosynthetic clay liner 12 inches intermediate cover layer

5.1.5 Gas System Expandability

The GCCS was designed to account for future expansion by providing sufficient capacity for 1,162 cfm during the proposed design period, which is the expected typical design life of these components. The LFG blowers, flare and the LFG collection headers are sized to adequately collect and control LFG by creating optimum vacuum condition within the collection system and controlling fugitive LFG emissions to the required levels. Inclusion of tees and wyes with bling flanges along the LFG transmission piping provide planned access for future expansion. Please note Appendix A, Drawing 00D-04 for typical expansion (i.e. blind flange) locations. If actual LFG flow rates do exceed the capacity of the system, additional GCCS components can be designed and installed in accordance with the NSPS requirements.

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5.1.6 Leachate and Condensate Management

Leachate management is accomplished through the use of an engineered leachate collection and management system (LCS). The LCS is designed according to Subtitle D standards (40 CFR§257 and §258). Leachate is collected through perforated pipes overlaying the bottom liner system to sump areas and from there leachate is pumped through forcemain to the existing 1.35 million gallon lined leachate storage basin at the site. LFG headers will be sloped to gain the maximum slope practicable (the goal is 5-percent slope) to promote condensate to flow by gravity to engineered low points.

Condensate collected in these low points is drained back into the lined landfill area where it is collected by the LCS. Condensate drip legs are shown on Drawing 00D-02 in Appendix A.

5.1.7 Accessibility

The majority of the GCCS piping will be installed below grade and accessibility to these components will be achieved through wellheads, valves and access points located throughout the system. Accessibility to the blower/flare station equipment is readily available as this equipment is installed at grade and outside the limits of waste.

5.1.8 Compatibility with Waste Operations

Initially, the GCCS will be installed in areas that are near final grade within Phases I and II. The gas collection system was designed for integration into the permitted final-grade configuration of the Landfill. As filling operations proceed and portions of the site reach final (or near-final) grades, the GCCS will be expanded to incorporate these areas.

Some vertical wells may be installed in areas that will receive additional waste and these wells are extended as filling progresses. Wells can be raised 20 to 30 feet in active areas and still maintain adequate LFG collection rates. This method of installation allows GCCS components to be constructed in accordance with §60.752(b)(2)(ii)(A)(2)(i) and (ii) while minimizing interference of the GCCS with ongoing filling operations.

5.1.9 Integration with Closure End Use

According to the Closure and Post-closure End Use Plan (CPC Plan) the Landfill will be developed as a grassed area and maintained as pasture land or possibly as a recreational/wildlife area following closure. Any modifications to the CPC Plan will be reviewed by the County to evaluate their compatibility with the GCCS. Well heads and other GCCS appurtenances can be modified as needed to not interfere with the proposed CPC Plan. The design, construction or modification of any component of the GCCS will be performed or restored in accordance with the applicable rules and the approved permit to install.

5.1.10 Air Intrusion Control

Air intrusion will be controlled by the landfill's cover system, by utilizing at least 10-feet of solid pipe near the ground surface for vertical LFG extraction wells, and by installing hydrated bentonite plugs around the vertical well casings where they penetrate the

5-4 |Issued June 03, 2016 - Revised November 27, 2017 landfill cover. To accommodate the penetration of the future final cap geomembrane, the geomembrane will be fitted to the pipe penetrations utilizing a “pipe boot”. Furthermore, air intrusion will be controlled through periodic monitoring and adjustment of the GCCS vacuum in accordance with NSPS requirements and appropriate maintenance of the landfill cover system.

5.1.11 Corrosion Resistance

Corrosion resistance of the GCCS is achieved through the use of corrosion resistant materials or materials that have a corrosion resistant coating, in accordance with 40 CFR §60.759(b)(1). The primary component used in the construction of the GCCS is HDPE and PVC piping and associate appurtenances. All HDPE and PVC piping will have a minimum rating of SDR 17 and Schedule 80, respectively. Components will be inspected during routine GCCS monitoring for abrasion, chipping, or other potential deterioration of the components. If damage to the materials is observed that may be detrimental to the performance of the GCCS, the components will be replaced or repaired.

5.1.12 Fill Settlement

Settlement will occur due to decomposition of the refuse. To accommodate refuse settlement, the GCCS components were designed with several features to account for this settlement that includes:

LFG transmission piping will be sloped at sufficient grades (a goal of 5 percent slope within waste limits and a minimum of 0.5-percent slope outside the waste limits) so that reasonable amounts of differential and total settlement may occur without causing pipe breakage, or disrupting the overall flow gradient of the LFG transmission piping.

Fusion welded HDPE piping will be used for the construction of the header and lateral piping and transmission system. HDPE piping is flexible and absorbs differential settlement without breaking or cracking.

Periodic header access riser will be installed that will allow landfill personnel to identify the location of the below grade header to aid in troubleshooting and repairs as settlement occurs.

LFG extraction well heads will connect to the LFG transmission piping via a flexible pipe or hose connection. This allows the LFG piping to accommodate changes in the orientation of the LFG transmission piping or LFG extraction well.

Well casings will be placed in 36-inch diameter boreholes, which will provide additional separation between the waste and the well casings and reduce the potential for differential stresses being placed on the casings.

5.1.13 Resistance to Decomposition Heat

Resistance of the GCCS to the heat generated as a result of refuse decomposition will be achieved through the use of materials tested and proven to withstand temperatures

5-5 Issued June 3, 2016 - Revised November 27, 2017 well above those typically found in landfills. The maximum operating temperature for HDPE is in excess of 150°F under low vacuum application conditions such as LFG extraction. The softening temperature, the temperature at which the PVC and HDPE materials begins to exhibit plasticity, is in excess of 250°F which is far in excess of normal LFG system operating conditions of 90°F to 120°F. The GCCS will be inspected during routine LFG system monitoring for heat damage. If heat damage of the GCCS components is observed and is believed to be detrimental to the operation of the GCCS, the cause of the elevated landfill temperature will be investigated, and the GCCS will be adjusted or modified to mitigate the effects of the elevated temperatures.

5.2 Compliance with §60.759(a)(2)

§60.759(a)(2) states, “The sufficient density of gas collection devices determined in paragraph (a)(1) of this section shall address landfill gas migration issues and augmentation of the collection system through the use of active or passive systems at the landfill perimeter or exterior.”

As described in Section 3.2.2, the LFG extraction wells were designed to provide comprehensive coverage with appropriate zones of influence. Well spacing was estimated by calculating the well ROI using an equation from the 1991 NSPS Background Information Document. This GCCS design was developed using a conservative ROI to ensure sufficient density of wells and some overlap was provided for radius of influence of individual wells, allowing better collection efficiency.

To determine the performance of the GCCS with respect to migration control, quarterly monitoring for off-site migration of combustible gases will be performed at landfill gas probe locations around the perimeter of the facility. The Landfill will conduct surface monitoring in accordance with NSPS/Federal EG requirements. If the GCCS does not meet the requirements, the GCCS will be adjusted or modified to meet the requirements.

Adjustments or modifications may include the installation of additional collection elements, cap repairs or other actions defined by field conditions at the time of monitoring. Since installation of the LFG collection system, the current results indicate that the GCCS is effective in controlling gas migration beyond the landfill footprint.

5.3 Compliance with §60.759(a)(3)

§60.759(a)(3) states, “The placement of gas collection devices determined in paragraph (a)(1) of this section shall control all gas producing areas, except as provided by paragraphs (a)(3)(i) and (a)(3)(ii) of this section.”

Collection devices will be installed in all landfill areas based on the site conditions and where waste is at or near its final grade. Vertical well spacing was based on a conservative estimated ROI value of 121 feet to ensure adequate control of LFG in gas producing areas.

5.3.1 Asbestos and Nondegradable Materials

§40 CFR 60.759(a)(3)(i) states, “Any segregated area of asbestos or nondegradable material may be excluded from collection if documented as provided under

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§60.758(d). The documentation shall provide the nature, date of deposition, location and amount of asbestos or nondegradable material deposited in the area, and shall be provided to the Administrator upon request.”

There is no known area where asbestos and other non-degradable items have been deposited.

5.3.2 Nonproductive Areas

§40 CFR 60.759(a)(3)(ii) states, “Any nonproductive area of the landfill may be excluded from control, provided that the total of all excluded areas can be shown to contribute less than 1 percent of the total amount of Non-Methane Organic Compound (NMOC) emissions from the landfill. The amount, location, and age of the material shall be documented and provided to the Administrator upon request. A separate NMOC emissions estimate shall be made for each section proposed for exclusion, and the sum of all such sections shall be compared to the NMOC emissions estimate for the entire landfill.”

At the time of the design of the GCCS, no areas within Phases I through IV were determined to be non-productive. Therefore, no areas of the landfill were excluded from the coverage of the GCCS.

5.4 Compliance with §60.759(b)(1), (2) and (3)

5.4.1 Landfill Gas Extraction Component Construction

§40 CFR 60.759(b)(1)states, “The landfill gas extraction components shall be constructed of polyvinyl chloride (PVC), high density polyethylene (HDPE) pipe, fiberglass, stainless steel, or other nonporous corrosion resistant material of suitable dimensions to: convey projected amounts of gases; withstand installation, static, and settlement forces; and withstand planned overburden or traffic loads. The collection system shall extend as necessary to comply with emission and migration standards.

Collection devices such as wells and horizontal collectors shall be perforated to allow gas entry without head loss sufficient to impair performance across the intended extent of control. Perforations shall be situated with regard to the need to prevent excessive air infiltration.”

5.4.1.1 Materials

The GCCS components will be constructed of PVC, HDPE, stainless steel, and other nonporous corrosion resistant materials.

5.4.1.2 Component Sizing

The GCCS components were sized for the maximum LFG generation rate expected from the site (1,162 cfm) during the design period as described in Section 3.3 of this design report. If future GCCS components are required, they will be sized in accordance with NSPS requirements.

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5.4.1.3 Component Loading

The GCCS components were designed to withstand the estimated installation, static, settlement, overburden, and traffic loads. The designed GCCS components within the landfill are consistent with those at other landfills that have operated for extended periods of time.

5.4.1.4 System Expansion

The GCCS will be expanded as necessary to conform to emission standards set forth in the NSPS. Future expansion of the GCCS will be performed in accordance with scheduling requirements set forth in the NSPS or an approved alternative schedule.

Additionally, if surface emissions and migration monitoring indicate a need for additional GCCS components, the system shall be expanded as necessary to comply with NSPS requirements. Expansions of the GCCS will be certified by a professional engineer and the measures of performance of the LFG system verified as set forth in the NSPS.

5.4.1.5 Component Perforation

The collection pipes for extraction wells will be perforated to allow LFG entry without inducing head losses sufficient to impair performance across the intended extent of control.

5.4.1.6 Air Infiltration

The LFG extraction wells were designed to prevent excessive air infiltration through the use of solid pipe near the ground surface and with the installation of hydrated bentonite plugs around the vertical well casing where they penetrate the landfill cover. The effective depth of perforations will typically be at least 10 feet below existing grade, which will be sufficient to control excessive air infiltration.

5.4.2 Landfill Gas Extraction Component Installation

§40 CFR 60.759(b)(2) states, “Vertical wells shall be placed so as not to endanger underlying liners and shall address the occurrence of water within the landfill. Holes and trenches constructed for piped wells and horizontal collectors shall be of sufficient cross-section so as to allow for their proper construction and completion including, for example, centering of pipes and placement of gravel backfill. Collection devices shall be designed so as not to allow indirect short circuiting of air into the cover or refuse into the collection system or gas into the air. Any gravel used around pipe perforations should be of a dimension so as not to penetrate or block perforations.”

5.4.2.1 Component Placement

Where possible, survey data for the base liner will be used for vertical well design depths. Vertical extraction wells will be installed with the bottom of the borehole at least 15 feet above the liner system.

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Leachate within the landfill will be managed by the leachate and condensate management system as described in Section 3.3. If free liquids are encountered during well drilling, the drilling contractor will drill through the perched zone of liquids allowing drainage into the underlying waste mass and the leachate collection system. If perched liquids are observed within the extraction well affecting efficient LFG extraction, leachate levels will be reduced by pumping the well. Liquids removed from the well casings will be discharged to the leachate collection system.

5.4.2.2 Holes and Trenches

Vertical wells will be installed within 36-inch diameter boreholes that are sufficient for installation of well casings and backfill materials. All holes and trenches for piped wells and horizontal collectors will be of sufficient cross-sectional area so as to allow for their proper construction and completion including the centering of pipes and placement of gravel backfill.

5.4.2.3 Component Short Circuiting

LFG collection elements were designed to prevent air infiltration through the cover, refuse contamination of the collection elements, and direct venting of LFG to the atmosphere. Air intrusion control will be verified through monitoring of operational standards for the LFG collection elements and maintaining of the landfill cover in accordance with NSPS requirements. Contamination of the collection elements by the refuse will be prevented by placing gravel backfill in the extraction well bore holes to provide a filter pack between the refuse and the LFG collection elements.