REPORT OF THE PUMP TEST AND PRE-FEASIBILITY STUDY

Transcription

1 REPORT OF THE PUMP TEST AND PRE-FEASIBILITY STUDY FOR LANDFILL GAS RECOVERY AND UTILIZATION AT THE NUEVO LAREDO LANDFILL NUEVO LAREDO, MEXICO Prepared for: PA Consulting and United States Agency for International Development/Mexico Unit #3323 APO AA Nuevo Laredo, Mexico Prepared by: Roger Bacon Drive Reston, Virginia October 2006 File No

2 TABLE OF CONTENTS Section Page Executive Summary... ES Introduction Objectives and Approach Landfill Gas Utilization Background Project Limitations Project Background Information Landfill Background Waste Disposal Rates Waste Composition Landfill Gas Pump Test Program Pump Test Background Information Pump Test Activities and Results Interpretation of Pump Test Results Landfill Gas Recovery Projections Introduction Landfill Gas Mathematical Modeling Landfill Gas Modeling Results Landfill Gas Collection and Utilization System Introduction Collection and Control System Components Collection and Control System Construction Evaluation of Project Costs Landfill Gas Collection and Flaring System Costs Electrical Generation Project Costs Economic Evaluation Summary of Assumptions Project Expenditures Project Revenues Summary of Economic Evaluations i

3 8.0 Environmental Benefits Greenhouse Gas Emissions Reductions Environmental Benefits from Landfill Gas Utilization Conclusions and Recommendations TABLES 9.1 Conclusions and Recommendations ES-1 Summary of Economic Evaluation...ES Waste Disposal Rates - Nuevo Laredo Landfill, Mexico Waste Composition Data Pump Test Program - Static Conditions Summary of Well 1 Monitoring Results Summary of Well 2 Monitoring Results Summary of Well 3 Monitoring Results Summary of Monitoring Results for Probe 1A Summary of Monitoring Results for Probe 1B Summary of Monitoring Results for Probe 1C Summary of Monitoring Results for Probe 2A Summary Monitoring Results for of Probe 2B Summary of Monitoring Results for Probe 2C Summary of Monitoring Results for Probe 3A Summary of Monitoring Results for Probe 3B Summary of Monitoring Results for Probe 3C Summary of Blower Monitoring Results Comparison of Waste Composition (%) Calculation of the Lo Value Summary of LFG Modeling Results Under the Mid-Range Recovery Scenario - Nuevo Laredo Landfill Budgetary Costs for Initial LFG Collection and Control System Budgetary Costs for IC Engine Power Plant Summary of Economic Evaluation of Proposed Power Plant Project Summary of Projected GHG Emission Reductions FIGURES 2-1 Photograph of Nuevo Laredo Landfill Photograph of Active Disposal Area Nuevo Laredo Landfill Site Drawing Showing Projected Final Contours Venting Wells at Nuevo Laredo Landfill Typical Test LFG Extraction Well Typical Test Monitoring Probe Line Diagram - Pump Test Layout Pump Test Well Monitoring ii

4 3-5 Illustration of Pump Test Active Zones of Influence Conceptual Layout of Proposed LFG Collection System APPENDICES A B C D E Pump Test Well Logs Pump Test Results LFG Recovery Projections Construction Cost Estimates Economic Evaluation iii

5 EXECUTIVE SUMMARY This Pre-Feasibility Study Report addresses the potential implementation of a landfill gas (LFG) collection, control and utilization project at the Nuevo Laredo Landfill located in Nuevo Laredo, Mexico. SCS Engineers (SCS) has prepared this report for P.A. Consulting and the U.S. Agency for International Development (USAID). For this evaluation, it was assumed that the project would consist of the installation of a landfill gas collection system to extract LFG to fuel a power plant using internal combustion engine generators. The project also would involve flaring any unused LFG. Revenues for the project would be generated from the sale of credits for the reduction of greenhouse gas emissions and from energy sales (exporting power to the grid). The emission reductions are created by the combustion of methane, which makes up approximately 50 percent of LFG. Methane has a global warming potential about 21 times that of carbon dioxide (CO 2 ). As part of this investigation, a pump test was conducted at the Nuevo Laredo Landfill. This test has provided additional information regarding the available LFG volume and quality at the landfill, along with other physical information such as buried waste characteristics and leachate levels within the waste mass. The results of the test generally support the LFG recovery projections prepared via mathematical modeling. The following is a summary of the relevant project information: The Nuevo Laredo Landfill has been used historically as a disposal site for the City of Nuevo Laredo, Mexico. The landfill began receiving waste in 1994 and is anticipated to remain open until about 2010, with a total capacity of approximately 2.88 million U.S. tons (about 2.62 million tonnes) of municipal solid waste (MSW) and construction debris. The landfill is currently filling at a rate of approximately 175,000 tonnes per year, and presently has about 1.8 million tonnes of waste in place. The site comprises a total of about 17 hectares (ha) with waste depths ranging up to approximately 42 m. The landfill is owned by City of Nuevo Laredo. Site operations are managed by Servicios de Tecnoligia Ambiental, S.A. de C.V. (SETASA). The landfill has some existing passive gas vents, but does not have an existing active landfill gas collection and control system. There are good historical records of waste disposal, covering the period of 1995 through June Gas Recovery Projections: - Projected gas recovery in late 2007 after the completion of the gas collection and control system is estimated to be approximately 1,083 cubic meters per hour (638 ES-1

6 cubic feet per minute) under a mid-range estimate. This projection assumes that all portions of the landfill area with waste in place are available for installing LFG collection facilities. The recovery rate is expected to increase to a maximum of approximately 1,332 cubic meters per hour (784 cubic feet per minute) in 2011, following site closure and expansion of the wellfield into all areas of the landfill. Gas recovery is expected to decline thereafter, reaching about 611 cubic meters per hour in 2020 and 351 cubic meters per hour in Power Plant Sizing: - Assuming start-up of a power plant in 2008, it is estimated that there will be sufficient gas available to support a 1.70 MW power plant (consisting of two (2) 0.85 MW engines). Due to declining LFG recovery rates after 2011, it is anticipated that there will be insufficient LFG to support both 0.85 MW engines starting in As such, for the economic evaluation, SCS assumed a power plant size of 1.70 MW for and 0.85 MW for Projection of methane emissions reduction: - It is estimated that development of an LFG utilization project at the landfill would generate CO 2 equivalent (CO 2 e) emission reductions totaling approximately 831,210 tonnes for the period 2007 through 2021, through reduction of landfill methane emissions. It is estimated that development of an LFG-to-energy (LFGE) project at the landfill would result in an additional 133,057 tonnes of CO 2 e emission reductions for the period 2008 through 2021 by displacing electricity produced via other sources. The project economics were analyzed for the period under different scenarios, including initial equity investment percentage (25 or 100 percent), and emission reduction pricing ($6 or $10/tonne of CO 2 e for the period through 2012 only). A power sales price of $0.070/kWh was assumed for the LFGE project; this power sales rate is based on 80 percent of the average reported retail electricity sales price for industry in Mexico in The results of the analysis indicate that the project economic feasibility appears favorable enough to likely attract developers/investors under all project scenarios analyzed. A summary of economic indicators is presented in Table ES-1 below. 1 Source: U.S. Energy Information Administration, Electricity Prices for Industry. Table posted September 26, ES-2

7 TABLE ES-1: SUMMARY OF ECONOMIC EVALUATION Project Period Emission Reduction Price ($/tonne) Equity Investments (%) Net Present Value (x1,000 $) Internal Rate of Return (%) $1, % $2, % $1, % $2, % ES-3

8 SECTION 1.0 INTRODUCTION SCS Engineers (SCS) is pleased to present this Pre-Feasibility Study Report for the implementation of a LFG collection, control and utilization project at the Nuevo Laredo Landfill in Nuevo Laredo, Mexico. SCS has prepared this report for PA Consulting and USAID in accordance with SCS Contract Scope of Work. The Nuevo Laredo Landfill has been identified as a candidate for a LFG capture and utilization project for a number of reasons, including: Landfill size (volume), depth of fill, age, and future capacity. The continued filling and future capacity of the landfill would be expected to result in an increase in LFG supply in the future. Furthermore, the use of LFG as a fuel for a project at the landfill would result in a net reduction of carbon emissions directly from the combustion of methane, and perhaps also indirectly from the displacement of other carbon fuels. 1.1 OBJECTIVES AND APPROACH The objectives of this evaluation are as follows: Assess the technical and economic feasibility of the development of an LFG control and utilization project at the landfill. To quantify the potential greenhouse gas (GHG) emission reduction from implementing a project. To provide USAID and PA Consulting with a tool to assist potential project developers in making informed decisions regarding additional investigations or moving forward with a project at the landfill. The approach taken for this study is as follows: Reviewing site conditions and available background information, including waste quantities and composition, landfill type and configuration, and meteorological data. Visiting the site to observe site features and operations and meet with the landfill owner and operator. Installing three test extraction wells and monitoring probes for pump testing; conducting the pump test and evaluating the results (pump test performed by ETESIA). Estimating the LFG recovery potential from the landfill using computer modeling based on available information, pump test results, and engineering experience at similar landfills. 1-1

9 Quantifying the potential for on-site electricity generation using LFG as a fuel, or for selling LFG to off-site industrial facilities. Estimating the required elements for the gas collection and utilization system (number and depth of wells, piping sizes and lengths, flare capacities, etc.) for the purpose of evaluating the capital and operational costs required for implementing gas collection and flaring at the landfill. Estimating the cost of implementing an energy recovery project, including capital and operational costs. Evaluating the project economics by quantifying capital and operational costs and sources of revenues, and calculating the net present value and internal rate of return. 1.2 LANDFILL GAS UTILIZATION BACKGROUND Landfills produce LFG as organic materials decompose under anaerobic (without oxygen) conditions. LFG is composed of approximately equal parts methane and carbon dioxide, with trace concentrations of volatile organic compounds (VOCs), hazardous air pollutants (HAPs), and other constituents. Both of the two primary constituents of LFG (methane and carbon dioxide) are considered to be greenhouse gases (GHG) which contribute to global warming, although the Intergovernmental Panel on Climate Change (IPCC) does not consider the carbon dioxide specifically present in raw LFG to be a GHG (it is considered to be biogenic, and therefore a natural part of the carbon cycle). Methane present in raw LFG is, however, considered to be a GHG. In fact, methane is a much more potent GHG than carbon dioxide, with a global warming potential of approximately 21 times that of CO 2. Therefore, the capture and combustion of methane (transforming it to carbon dioxide and water) in an LFG flare, an engine generator or other device, results in a substantial net reduction of GHG emissions. Additional benefits beyond GHG emission reductions include the potential for improvement in local air quality through the destruction of HAPs and VOCs through LFG combustion. LFG can leave a landfill by two natural pathways: by migration into the adjacent subsurface and by venting through the landfill cover system. In both cases, without capture and control the LFG (and methane) will ultimately reach the atmosphere. The volume and rate of methane emission from a landfill is a function of the total quantity of organic material buried in the landfill and its age and moisture content, compaction techniques, temperature, and waste type and particle size. While the methane emission rate will decrease after a landfill is closed (as the organic fraction is depleted), a landfill will typically continue to emit methane for many (20 or more) years after its closure. A common means for controlling LFG emissions is to install an LFG collection and control system. LFG control systems are typically equipped with a combustion (or other treatment) device designed to destroy methane, VOCs, and HAPs prior to their emission to the atmosphere. Good quality LFG (high methane content with low oxygen and nitrogen levels) can be utilized as a fuel to offset the use of conventional fossil fuels or other fuel types. The heating value typically 1-2

10 ranges from 400 to 600 Btus (British thermal units) per standard cubic foot (scf), which is approximately one half the heating value of natural gas. Existing and potential uses of LFG generally fall into one of the following categories: electrical generation, direct use for heating/boiler fuel (medium-btu), upgrade to high Btu gas, and other uses such as vehicle fuel. This study focuses on evaluation of a potential electrical generation project and a direct use project. 1.3 PROJECT LIMITATIONS During our evaluation, SCS relied upon information provided and various assumptions in completing the LFG recovery modeling and economic evaluation. Judgments and analysis are based upon this information and SCS experience with LFG collection and utilization systems. Specific limitations include: LFG production estimates are based on a desktop analysis and visual observation of the landfill and its operations. Because the landfill does not currently have an LFG recovery system, the economic analysis uses typical capital and operating cost data for similar systems rather than project specific information. The LFG recovery projections have been prepared in accordance with the care and skill generally exercised by reputable LFG professionals, under similar circumstances, in this or similar localities. No other warranty, express or implied, is made as to the professional opinions presented herein. Changes in the landfill property use and conditions (for example, variations in rainfall, water levels, landfill operations, final cover systems, or other factors) may affect future gas recovery at the landfill. SCS does not guarantee the quantity or quality of available LFG. This pre-feasibility study has made assumptions regarding the future availability and accessibility of areas of the landfill for installing a gas collection system, based on information available at the time this study was conducted. These assumptions were made in the absence of specific information regarding the dates that various portions of the landfill will become accessible for wellfield development, and the age of the waste in each area. Because the assumptions were used to estimate a schedule for collection system build-out and coverage of the LFG generating refuse mass, they have significant impacts on projected future LFG recovery and resulting estimates of project feasibility. Although a pump test helps reduce the uncertainties of predicting LFG recovery, it also has limitations. First, the pump test is conducted on only a limited area of the landfill and the results are assumed to apply to the entire site. Secondly, pump tests can only indicate the quantity of LFG during the period of the field test and don t provide any indication of future gas resources. This modeling work has been conducted exclusively for the use of PA Consulting and USAID for this Pre-Feasibility Study. No other party, known or unknown to SCS is intended as a beneficiary of this report or the information it contains. Third parties use 1-3

11 this report at their own risk. SCS assumes no responsibility for the accuracy of information obtained from, or provided by, third-party sources. 1-4

12 SECTION 2.0 PROJECT BACKGROUND INFORMATION 2.1 LANDFILL BACKGROUND The Nuevo Laredo Landfill is a municipal solid waste (MSW) landfill located in the City of Nuevo Laredo, State of Tamaulipas, in Northeastern Mexico. The landfill is owned by the City of Nuevo Laredo and is operated by Servicios de Tecnoligia Ambiental, S.A. de C.V. (SETASA). The landfill covers approximately 17 hectares, has approximately 1.8 million tonnes (Mg) of waste in place as of August 2006, and has an estimated total capacity of 2,616,000 Mg. The site reportedly began operations in 1994 and is expected to close in 2009 or 2010 (depending on future waste volumes). Waste depths range up to approximately 42 m in the eastern portion of the site. Waste is compacted using compactors and bulldozers (see Figures 2-1 and 2-2 below). Filling of the western area of the LF has not yet commenced. Figure 2-3 is a drawing showing the projected final landfill contours at closure. Figure 2-1. Photograph of Nuevo Laredo Landfill 2-1

13 Figure 2-2. Photograph of Active Disposal Area at Nuevo Laredo Landfill The landfill was lined with a low permeability clay layer. Intermediate soil cover is applied periodically to inactive disposal areas. The landfill was designed with a leachate collection system that transports leachate by gravity to a leachate sump. Leachate is then pumped to the leachate evaporation pond located on the southeast corner of the site. Leachate generation is limited due to the relatively dry climate. Average annual precipitation is approximately 524 mm (20.6 inches) per year. No active LFG collection system exists at the site. Currently, several venting wells are installed which passively vent LFG to the atmosphere. Figure 2-4 shows two of the venting wells installed at the site. 2-2

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15 Figure 2-4. Venting Wells at Nuevo Laredo Landfill 2.2 WASTE DISPOSAL RATES Historical records of waste disposal rates at Nuevo Laredo Landfill covering 1995 through June 2006 were provided by PA Consulting. These records, which are based on scale weights of incoming refuse trucks, show that 1,739,600 Mg of waste was disposed during this period. Waste disposal in 1994 was estimated assuming that operations began in June of that year. Future disposal rates were estimated assuming future annual increases in disposal equivalent to the average increase over the past 5 years (2.2%). Table 2-1 summarizes the estimates of disposal from 1994 through

16 TABLE 2-1. WASTE DISPOSAL RATES NUEVO LAREDO LANDFILL, MEXICO Waste Disposed Cumulative Waste Year (Mg/year) Disposed (Mg) ,000 50, , , , , , , , , , , , , , , ,160 1,169, ,430 1,342, ,080 1,518, ,190 1,701, ,440 1,877, ,300 2,056, ,240 2,239, ,270 2,427, ,840 2,616, WASTE COMPOSITION Waste composition is an important consideration in evaluating a LFG recovery project, in particular the organic content, moisture content, and degradability of the various waste fractions. For example, landfills with a high amount of food wastes, which are highly degradable, will tend to produce LFG sooner but over a shorter length of time. The effect of waste composition on LFG production is discussed further in Section 4. Recent waste composition data was provided by SETASA. This data was evaluated in combination with waste composition data from 2002 (collected as part of the U.S. EPA s LMOP Mexico Model study) to reflect the characteristics of waste in place. Table 2-2 presents a summary of the waste composition data for the landfill. Waste materials observed during the pump test well drilling operations were recorded but did not provide a representative sampling for estimating the percentages of each waste type. 2-5

17 TABLE 2-2. WASTE COMPOSITION DATA COMPONENT FRACTION OF WASTE STREAM (%) Food Waste 17.7 Garden Waste (leaves and small branches) 24.3 Wood Waste (including large branches) 1.3 Paper and Cardboard 13.9 Plastics 11.3 Leather, Textiles, other slowly decaying organic materials 11.3 Other Organics 4.2 Metals 2.5 Glass 4.2 Other Inerts, including Construction Debris 9.3 TOTAL

18 SECTION 3.0 LANDFILL GAS PUMP TEST PROGRAM 3.1 PUMP TEST BACKGROUND INFORMATION A pump test program was conducted at the Nuevo Laredo Landfill. The objectives of the pump test were: To measure vacuum (pressure) and flow relationships while actively extracting LFG from the landfill. To measure sustainable methane levels of the extracted LFG during the pump test. To measure vacuum (pressure) in probes to estimate the lateral vacuum influence of the active pump test. To measure oxygen levels of the extracted biogas during the pump test to check for air infiltration through the landfill cover soil during pump test. Utilize the results of the pump test to refine the projections of landfill gas recovery. The pump test generally consisted of the following physical elements and equipment: A total of three vertical extraction wells constructed with HDPE piping (referred to as Wells 1, 2, and 3). All three wells were installed at a depth of about 15 m. The extraction wells were spaced generally in triangular fashion about 65 m apart. Figure 3-1 presents a typical detail of construction for the extraction wells. Well construction logs are provided in Appendix A. A total of nine gas and pressure monitoring probes. Three probes were installed for each extraction well. The probes were installed to a depth of approximately 2 meters, and were spaced in line at distances of about 5, 15 and 25 meters from each extraction well. Figure 3-2 presents a typical detail of construction for the monitoring probes. An electrically-powered mechanical blower, to exert a vacuum on the extraction wells and withdrawal LFG from the wells. The blower was powered on-site by a portable diesel powered electrical generator and run continuously during the pump test. Interconnection of the three extraction wells and the blower with 4-inch diameter flexible piping. Flow control valves were installed at each extraction well as well as at the blower inlet to allow adjustment of vacuum and flow both system-wide and at individual wells. Figure 3-3 is a schematic diagram showing the typical layout for the pump test system. Gas testing, and flow and pressure monitoring equipment. Gas quality (methane, oxygen) and static pressure measurements were taking using a Landtec GEM 500 Infrared Gas Analyzer (GEM 500). Gas flow measurements were taken using an Accu-Flow meter and the GEM

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22 SCS contracted with a local driller Perforsonda -Mexico, C.A. (Perfosonda) to perform the drilling and a local general contractor Tecnicas, Equipos y Servicios (T.E.S.) for construction of the three extraction wells, the installation of the nine monitoring probes, and the installation of the blower, motor, and generator, and the interconnecting piping. SCS provided construction oversight. SCS personnel was on-site during drilling and well installation activities and observed the following: The types of municipal solid waste materials encountered during drilling were recorded and are listed in the well logs provided in Attachment A. Waste materials and soil cuttings were observed to be relatively dry. No leachate was encountered during well drilling and installation. ETESIA performed monitoring of the wells and probes and recorded the data (see Figure 3-4 below). Figure 3-4. Pump Test Well Monitoring 3-5

23 3.2 PUMP TEST ACTIVITIES AND RESULTS Test Program: Passive Conditions During the afternoon of August 14, prior to activating the blower, ETESIA performed gas quality and pressure monitoring to document system conditions under static (i.e., passive) conditions for comparison with data to be taken under active conditions. Table 3-1 presents a summary of the average static conditions at each monitoring point. Additional pump test monitoring results are provided in Appendix B. In general, gas quality measured at the wells under static conditions was observed to be very good (i.e., high methane levels, with no oxygen). Monitoring probes 1B, 1C, 2B, and 2C were found to have low methane content (below 30 percent), suggesting a lack of LFG in these probes. TABLE 3-1: PUMP TEST PROGRAM - STATIC CONDITIONS (1) Location Methane (%) Oxygen (%) Static Pressure (inches w.c.) Well Probe 1A Probe 1B Probe 1C Well N/A(2) Probe 2A Probe 2B Probe 2C Well Probe 3A Probe 3B Probe 3C (1) Data measured and recorded by ETESIA. (2) Recorded static pressure at Well 1 was inches, which was assumed to be an instrument error and not reflective of static conditions. Static pressure readings were taken at the wells to assess the amount of gas buildup within the landfill. Wells 1 and 3 were found to have positive static pressure, indicating LFG generation. The Well 2 reading was recorded as inches; this was assumed to be an erroneous reading since no vacuum had yet been applied to the well, and the reading was discarded. 3-6

24 Test Program: Active Conditions On August 14, the blower was turned on and active extraction conditions were established. During active gas pumping, wells, probes, and the blower were monitored two to five times daily for the following parameters: Wells: methane, carbon dioxide, oxygen, balance gas, static pressure; Probes: methane, carbon dioxide, oxygen, balance gases, and static pressure; and Blower: methane, carbon dioxide, oxygen, balance gas, static pressure, and flow. Appendix B provides a complete data set showing all monitoring data for the three wells, 9 probes, and blower. Extraction Well Data-- Tables 3-2 through 3-4 summarize the monitoring results for Wells 1 through 3, respectively, and show the average of the measured values for each day. Monitoring conducted throughout the pump test indicated that all three wells consistently had good gas quality (i.e., high methane content and low oxygen and balance gas content). TABLE 3-2. SUMMARY OF WELL 1 MONITORING RESULTS DATE Methane (%) Oxygen (%) Carbon Dioxide (%) Balance (%) Pressure (in. w.c.) 14-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug

25 TABLE 3-3. SUMMARY OF WELL 2 MONITORING RESULTS DATE Methane (%) Oxygen (%) Carbon Dioxide (%) Balance (%) Pressure (in. w.c.) 14-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug TABLE 3-4. SUMMARY OF WELL 3 MONITORING RESULTS DATE Methane (%) Oxygen (%) Carbon Dioxide (%) Balance (%) Pressure (in. w.c.) 14-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug

26 The results of the extraction well monitoring indicate that gas quality was generally excellent (i.e., high methane content with low oxygen and balance gas content) throughout the pump test. Initially the applied vacuum was approximately 5 inches w.c. at each well; this vacuum was increased on August 16 to approximately 15 inches w.c. for the balance of the pump test. Gas quality remained generally excellent for the duration of the test at the higher vacuum. Monitoring Probe Data-- As mentioned previously, a total of nine monitoring probes (three per well) were installed. The objective of these probes is to measure gas quality and static pressures at varying distances from each extraction well in order to estimate the radius/volume of influence of each well. The most direct indication that a monitoring probe is within the influence of an extraction well is the establishment of a vacuum at the probe. Another indication is a decline in methane content accompanied by an increase in the concentrations of oxygen and balance gases. Tables 3-5 through 3-13 present a summary of the monitoring data for each of the probes. The complete set of probe monitoring data is provided in Appendix B. TABLE 3-5. SUMMARY OF MONITORING RESULTS FOR PROBE 1A (5m from Well 1) DATE Methane (%) Oxygen (%) Static Pressure (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES

27 TABLE 3-6. SUMMARY OF MONITORING RESULTS FOR PROBE 1B (15m from Well 1) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES TABLE 3-7. SUMMARY OF MONITORING RESULTS FOR PROBE 1C (25m from Well 1) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES

28 TABLE 3-8. SUMMARY OF MONITORING RESULTS FOR PROBE 2A (5m from Well 2) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES TABLE 3-9. SUMMARY OF MONITORING RESULTS FOR PROBE 2B (15m from Well 2) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES

29 TABLE SUMMARY OF MONITORING RESULTS FOR PROBE 2C (25m from Well 2) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES TABLE SUMMARY OF MONITORING RESULTS FOR PROBE 3A (5m from Well 3) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES

30 TABLE SUMMARY OF MONITORING RESULTS FOR PROBE 3B (15m from Well 3) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES TABLE SUMMARY OF MONITORING RESULTS FOR PROBE 3C (25m from Well 3) DATE Methane (%) Oxygen (%) Probe Vacuum (in. w.c.) 15-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES

31 Under active conditions, monitoring data indicates that vacuum was established at all 9 probes by the second full day of active system operation, and was generally maintained consistently throughout the pump test. This is a clear indication that the probes were within the radius of influence (ROI) of the respective extraction wells. Furthermore, for the probes at all three extraction wells the measured vacuum at the probes was generally consistent at probes 5, 15 and 25 meters from the well, with no significant decline in measured vacuum further from the extraction well. This suggests that the ROI of each extraction well at the applied vacuums likely extended beyond the farthest probes (1C, 2C and 3C), which are located about 25 meters from the respective extraction wells. Blower Data-- Monitoring was conducted at the inlet to the gas blower, including both gas quality and velocity (which was utilized to calculate gas flows). A summary of the monitoring results for the blower is provided below in Table The complete set of blower monitoring data is provided in Appendix B. TABLE SUMMARY OF BLOWER MONITORING RESULTS DATE Methane (%) Oxygen (%) LFG Flow (scfm) LFG Methane (scfm) 16-Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug AVERAGES The blower data show a good quantity of LFG (generally 150 to 170 scfm) with a high methane content (generally 55 percent or greater) throughout the pump test. Overall, gas quality and flow only slightly decline throughout the test. This suggests that the measured rate and quality of gas collection within the area of the pump test may reflect the steady-state methane flow for these three extraction wells (where methane capture rates are approximately equal to gas generation rates within the ROI of the wells). 3-14

32 3.3 INTERPRETATION OF PUMP TEST RESULTS SCS utilized the results of the pump test during the projection of LFG recovery rates at the landfill (see Section 4.0). The general procedure by which the pump test data are utilized for this purpose is as follows: Estimate the maximum steady-state flow rate achievable in the pump test area. Because gas quality and flows were generally consistent throughout the test, SCS feels that the average recovery rate observed during the pump test represents steady-state conditions. The average LFG recovery rate observed during the pump test was scfm or 263 cubic meters per hour (m 3 /hour) at 57.1 percent methane, which is equivalent to scfm or 300 m 3 /hour at 50 percent methane. Estimate the radius of influence (ROI) of the extraction wells. The monitoring data indicates that the ROI of each of the three extraction wells extends at least to the outermost probes (Probes 1C, 2C, and 3-C) located 25 meters from each well, and likely beyond. This may be a function of the dry conditions at the landfill, which could contribute to a relatively high permeability of the waste under vacuum. General industry guidelines suggest that the ROI of an extraction well is a function of the well depth, and that extraction wells typically have a ROI between 1.25 and 3 times its depth, depending on well construction, refuse permeability, and other factors. SCS expects that refuse permeability is relatively high at this landfill due to the monitoring data (discussed above), because it is located in a fairly dry climate, and because it contains a moderate amount of wet, organic wastes. The high refuse permeability suggests that the ROI is likely near the high end of the typical range, i.e., approximately 3 times the well depth. 2 Given these considerations and the results of the pump test, SCS estimates the average ROI of Wells 1 through 3 under the conditions established during the pump test to be approximately 45 meters (equal to 3 times the well depth of 15 meters). Figure 3-5 presents a diagram of a typical pump test cross-section showing theoretical zones of influence under active conditions. Estimate the volume of refuse within the ROI of the extraction wells. Using an estimated ROI of 45 meters for each well, the volume of refuse within the influence of the three wells during the pump test was calculated using the existing waste contours and landfill bottom contours; this volume is estimated to be approximately 488,880 cubic meters. Estimate the unit recovery rate for the pump test in cubic feet of LFG per year per pound of waste. Based on drawings provided by SETASA showing existing waste volumes, the refuse density is estimated to be approximately 768 kg per m 3 (approximately 1,295 lbs/yd 3 ). This density can be applied to the volume of waste estimated to be within the influence of the pump test (488,880 m 3 ), which results in 375,460 Mg. The flow rate of 300 m 3 /hour converts to 2,628,000 cubic meters per year, which results in a unit recovery rate of approximately 7 cubic meters per Mg per year. 2 Note that a higher ROI tends to give a more conservative estimate of LFG recovery per Mg of waste. 3-15

33 Extrapolate the unit recovery rate achieved during the pump test to the total amount of refuse in the landfill that is available for LFG recovery. This is done by multiplying the pump test unit recovery rate (7 m3/mg-year) by the total estimated amount of waste in place as of August 2006 from Table 2-3 (1.8 million Mg). Based on this, SCS estimates that the average gas capture at the entire landfill in 2006 (if a comprehensive gas collection system were in place) would be approximately 1,438 m 3 /hour, or about 847 scfm. This estimate for the potential recovery rate was used for refining the LFG recovery projections in Section

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35 SECTION 4.0 LANDFILL GAS RECOVERY PROJECTIONS 4.1 INTRODUCTION For projecting LFG recovery rates from the Nuevo Laredo Landfill, SCS utilized the results of the pump test (see Section 3) to refine the mathematical modeling parameters. Specifically, the projected rate of 847 cfm (1,438 m 3 /hour) for the entire landfill was used to evaluate the model and make adjustments as needed. The specific modeling approach is discussed below. 4.2 LANDFILL GAS MATHEMATICAL MODELING Landfill gas is generated by the anaerobic decomposition of solid waste within a landfill. It is typically composed of between 40 to 60 percent methane, with the remainder primarily being carbon dioxide. The rate at which LFG is generated is largely a function of the type of waste buried and the moisture content and age of the waste. It is widely accepted throughout the industry that the LFG generation rate generally can be described by a first-order decay equation. To estimate the potential LFG recovery rate for the landfill, SCS utilized the Mexico LFG Model which it developed for the U.S. EPA s Landfill Methane Outreach Program (LMOP), with modifications to project LFG recovery directly and to account for site-specific conditions. The Mexico LFG Model and SCS modifications are described in detail below. In 2003 SCS developed a first-order decay model for estimating the LFG generation and recovery at landfills in Mexico (Mexico LFG Model). The model, essentially a modified version of the EPA s LandGEM, was developed using waste composition data from 31 cities in four regions of Mexico, and actual LFG collection/recovery data from two landfills in Mexico. The Mexico LFG Model employs different values for the ultimate methane recovery potential [Lo] and the decay rate constant [k], depending upon the amount of precipitation a landfill receives. For the Nuevo Laredo Pre-Feasibility Study, SCS modified the Mexico LFG Model to estimate recovery directly. This approach involves an evaluation or estimate of the current and future coverage of the LFG collection system, generally defined as that fraction of the landfill under active collection. Many factors can affect system coverage, including: well spacing and depth, depth of well perforations, presence of a flexible membrane liner (FML) or low-permeability cover system, landfill type and depth, condition of LFG collection system, and other design and operational issues. SCS used the model to estimate the projected LFG recovery rates for the landfill through 2035 using the following criteria and assumptions: Refuse Disposal Rates - The historical and projected future filling rates used in the model are provided in Table 2-1. Site closure is projected to occur in late 2010 when the landfill reaches its estimated 2,616,000 Mg capacity. 4-1

36 Methane Content of LFG Because the methane content of LFG fluctuates over time, it is standard industry practice to normalize the methane content to 50 percent for the purposes of LFG modeling. Methane Rate Constant [k] - The decay rate constant is a function of refuse moisture content, nutrient availability, ph, and temperature. For the Nuevo Laredo evaluation, SCS refined the Mexico LFG Model to more directly reflect site-specific conditions by employing three different k values based on the degradability of the waste components (see discussion of model inputs below). Methane Recovery Potential [Lo] - The methane recovery potential is the total amount of methane that a unit mass of refuse will produce given enough time. The Lo is a function of the organic content of the waste. For the Nuevo Laredo Landfill, SCS started with a default Lo value of 71.4 cubic meters per tonne (2,290 ft 3 /ton) for recovery, based on the Mexico LFG Model value of 84 cubic meters per tonne (2,690 ft 3 /ton) for Lo when modeling LFG generation at landfills experiencing 500 to 1,000 mm per year precipitation, and the AP-42 recommended value of 85 percent for the maximum achievable collection efficiency. This default value was then adjusted based on the ratios of the organic content of average Mexico waste and waste at the landfill (see discussion of model inputs below). LFG System Coverage. Varies. The model estimates both the potential recoverable LFG from a landfill assuming a 100 percent comprehensive LFG collection system, and the projected rate of LFG recovery using the estimated LFG system coverage. System coverage is a measure of the fraction of the refuse mass which is under active collection. The LFG system coverage factor is based on engineering judgment, and considers many factors including: whether the landfill is closed or active, the type of well construction and gas system construction, the level of operation that is provided, the likelihood that system components such pipes and wells may be damaged by landfill operations and/or settlement, how quickly damaged pipes and wells (and other equipment, such as blowers, etc.) are likely to be repaired, leachate levels in wells, and other factors. This value falls within the range of 0 percent (for no gas collection system) to 100 percent (for a comprehensive collection system over a closed landfill with excellent construction and operation). Modifications to the LFG system coverage can be made to account for expected collection system expansions or if other changes to the LFG system or landfill are anticipated (e.g., landfill closure or partial capping, increasing flows due to the presence of additional fill material). Active landfills generally tend to have lower system coverage than closed landfills due to the interferences caused by active filling operations or by scavengers ( pepenadores ). Another potential issue that can limit system coverage is concern over security of equipment (wells, piping, etc.), particularly at landfills that allow public access. Although Nuevo Laredo is an active site, no scavengers exist. Security is not expected to be a significant problem at Nuevo Laredo because the site is privately operated, and 4-2

37 access to areas with wellfield equipment can be controlled. Discounts to system coverage to account for the expected level of skill and effort employed to operate and maintain the system to maximize recovery are described below. For this evaluation, SCS has employed three system coverage scenarios in order to develop a range of estimates of predicted recovery with the proposed collection system. All three scenarios assume that a comprehensive LFG collection system will be installed, and that leachate management activities, including pumping out leachate accumulated in extraction wells, will be employed to limit the impact on LFG collection rates if leachate is encountered. System coverage in August 2006, during the operation of the pump test wells, is estimated to be approximately 21 percent under all three scenarios, based on the results of the pump test. Estimates of collection system coverage in future years assume system start-up on July 1, 2007 and vary under each of the three scenarios. The three scenarios result in low, mid-range, and high projections and are as follows: 1. The low recovery scenario assumes that a moderate level of skill and effort is employed in the operation and maintenance of the collection system. System coverage is assumed to be 60 percent from 2007 through Starting in 2011 after site closure, system coverage is assumed to increase to 65 percent. SCS considers the low recovery estimates to be conservative and should be employed only if a large margin of safety is needed. 2. The mid-range recovery scenario assumes that a moderately high level of skill and effort is employed in the operation and maintenance of the collection system. System coverage is assumed to be 75 percent from 2007 through Starting in 2011 after site closure, system coverage is assumed to increase to 80 percent. SCS considers the mid-range recovery scenario to be its best estimates of likely recovery and recommends its use in the economic evaluation. 3. The high recovery scenario assumes that highest possible level of skill and effort is employed in the operation and maintenance of the collection system. System coverage is assumed to be 85 percent from 2007 through Starting in 2011 after site closure, system coverage is assumed to increase to 90 percent. SCS considers the high recovery estimates to be ambitious and attainable only if the maintenance of an optimal LFG recovery system is considered to be a top priority. Note that, in addition to the potential variability in system coverage and the level of operation and maintenance, mathematical modeling of LFG is inherently uncertain. SCS considered (and tried to account for) this modeling uncertainty in selecting the values for the high and low recovery scenarios when estimating the LFG recovery potential. Model Inputs-- For estimating the model parameters decay rate (k) and methane recovery capacity (Lo) for the landfill, SCS took into consideration the typical composition of waste buried in Nuevo Laredo Landfill. SCS compared site waste composition data from the landfill with waste composition data from the Mexico LFG Model study. These data are presented in Table

38 TABLE 4-1: COMPARISON OF WASTE COMPOSITION (%) COMPONENTS NUEVO LAREDO LANDFILL 1 AVERAGE MEXICO 2 DEGRADABILITY CATEGORY DECAY RATE (k) Food Fast 0.15 Green Waste Fast 0.15 Other Organic Fast 0.15 Green Waste Medium Paper Medium Wood Slow Rubber, Leather, Textiles Slow Plastics, Metals, Glass Inert 0.0 Other Inorganic Inert 0.0 Notes to Table 4-1: 1. Nuevo Laredo waste composition was estimated based on the data provided by SETASA and data from 2002 obtained by SCS for the LMOP Mexico LFG model study (equal weight to each). 2. Average Mexico waste composition is based on data collected from 31 cities in Mexico in 2003 during the development of the Mexico LFG Model; values were weighted based on the cities relative waste generation rates. 3. Assumes 50 percent of green waste in the U.S. waste stream is highly degradable (grass, etc.) and 50 percent of green waste is moderately degradable (branches, wood, etc.). Data provided on green (garden) waste disposed at Nuevo Laredo provided a breakdown of types of garden waste. Although data from the recent waste characterization study at the Nuevo Laredo Landfill showed a low amount of food wastes (8.4%) as compared to the average amount disposed at landfills in Mexico (36%), data from a previous study completed in 2002 found 27 percent food waste, for an estimated long-term average of 17.7 percent. Because food waste is readily degraded, it produces LFG sooner, but over a shorter length of time. Therefore, a graph of LFG generation from wastes that are high in food waste, green waste, and other similar readily-degraded wastes will show a steeper slope in the LFG generation rate (reaching peak flows more rapidly), but a lower sustainable long term yield than the generation rate from waste with slower-degrading components. In the model, this effect is reflected in the parameter k. Wastes disposed at Nuevo Laredo contain a large amount of green wastes (24.3%), mostly consisting of leaves, prunings, and small branches. As a result, the waste stream contains approximately the same percentage of organic materials as Mexico wastes. Because it has less food wastes, the Nuevo Laredo waste stream contains a lower level of moisture. Waste streams with a higher organic content will tend to have a higher potential for methane generation per tonne of waste. Conversely, however, wastes with a higher moisture content (which is inert) will tend to have a lower potential for methane generation per tonne of waste. In the model, these effects are reflected in the parameter Lo. 4-4