List of Acronyms and Abbreviations

Transcription

1 Appendix G Area F Interior Wells Landfill Gas Flow Extraction Testing

2 Table of Contents 1.0 Introduction Data Quality Objectives Statement of the Problem Identify the Decision Identify Inputs to Decisions Define Study Boundaries Develop Decision Rules Specify Limits on Decision Errors Optimize the Design for Obtaining Data Test Configuration and Procedures Test Configuration Test Procedures Data Recording Instrumentation i

3 List of Figures 2-1a Extraction Test Flowchart, Area F Interior Wells, Phase 1 2-1b Extraction Test Flowchart, Area F Interior Wells, Phase 2A 2-1c Extraction Test Flowchart, Area F Interior Wells, Phase 2B 2-1d Extraction Test Flowchart, Area F Interior Wells, Phase 3 ii

4 List of Acronyms and Abbreviations DQO GAC KMnO 4 LFG scfm TTU data quality objective (s) granular activated carbon potassium permanganate landfill gas standard cubic feet per minute thermal treatment unit iii

5 1.0 Introduction This appendix describes the requirements and procedures for conducting an extraction test to estimate the available landfill gas (LFG) that will be produced from the five interior wells in Area F at the Operable Unit 2 Landfill. The extraction test that will be conducted under this work plan is designed to determine if Area F may provide sufficient LFG with adequate heat value to fuel treatment of the Area F perimeter LFG using a thermal treatment unit (TTU). The primary test efforts will be to collect physical and chemical data to characterize the LFG production from five extraction wells in the interior of Area F installed into the undisturbed soil berms between the original excavated waste trenches. After drilling, the header pipe from EW-31 through 34 will be immediately installed and temporarily connected to the existing header pipe (Appendix D, Sheet 1). The key data that are required to evaluate the effectiveness of using LFG as a fuel are sustainable LFG flow rate and methane concentration. During the field test, the LFG will be extracted and treated using the existing Area F LFG treatment equipment, consisting of granulated activated carbon (GAC) and potassium permanganate (KMnO 4 ). Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

6 2.0 Data Quality Objectives Each of the seven steps of the data quality objective (DQO) process is described below. 2.1 Statement of the Problem Define the problem so that the focus of the study will be unambiguous. Flow extraction testing will be conducted to evaluate whether the extracted LFG from the five extraction wells that will be drilled in the interior of Area F (into the undisturbed soil berms between the original excavated waste trenches) contains a high enough concentration of methane to support continuous auto-combustion in an enclosed flare, without use of a supplemental fuel supply. This information is needed prior to finalizing procurement of the proposed TTU. If the results indicate that the interior wells cannot supply sufficient fuel to maintain the required treatment temperature, a smaller thermal oxidizer would be used instead of the larger enclosed ground flare. The available methane flow from the interior wells will continue to be piped to the thermal oxidizer. This will remove volatile organic compounds from Area F and contribute heat value. A second focus of the study will be to evaluate the extent of the vacuum and LFG extraction influence of the five interior LFG extraction wells. 2.2 Identify the Decision Identify the principal study question. The principal study question is to determine if the five interior wells may provide additional LFG with adequate heat value for efficient operation of an enclosed flare. The secondary study question is to determine the extent of the influence area of the five interior wells. Define the alternative actions that could result from resolution of the principal study question. The alternative actions that could result from resolution of the principal study question are: If the interior wells are determined to contain significant high-methane LFG, then an enclosed flare will be specified for procurement and the interior extraction wells will be connected to a separate 6-inch high-density polyethylene header pipe. If the interior wells do not contain significant additional methane, then a smaller thermal oxidizer would be used and procurement of a supplemental fuel supplier will be required. The interior wells will be connected to the common 6-inch header pipe instead of a separate header pipe. Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

7 If the vacuum influence area from equilibrium operation of the five interior wells extends to portions of the Area F perimeter, long-term operation of some of the affected perimeter SVE extraction wells may be reduced or eliminated. 2.3 Identify Inputs to Decisions Identify the information that will be required to resolve the decision statement. The following information will be required to resolve the decision statement: Applied vacuum at the extraction well head induced pressure or vacuum at perimeter LFG monitoring probes and extraction wells LFG composition [methane, oxygen, carbon dioxide, balance gas (assumed to be nitrogen)] LFG flow rate LFG temperature Weather data (barometric pressure, ambient temperature, average wind speed, 24-hour precipitation) Determine the sources for each item of information identified A field portable LFG analyzer will be used to measure LFG composition, flow rate, temperature, and induced pressure (vacuum). A local weather service will be used to measure barometric pressure, ambient temperature, average wind speed, and precipitation. Confirm that appropriate analytical methods exist to provide the necessary data. All information collected from the test will be obtained using specialized field instruments, so that monitoring adjustments to the extracted LFG flow can be made in real time. Field data obtained using the specified instrumentation, correctly calibrated, will be sufficient for the accuracy level of this investigation. 2.4 Define Study Boundaries Define the spatial and temporal boundaries that are covered by the decision statement. The spatial study boundary is limited to the area within an approximate 1,000-foot radius of the interior LFG extraction well locations proposed for Area F. The temporal boundary for the field monitoring work is a period of approximately 21 calendar days after test inception. Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

8 Determine the timeframe to which the decision applies. The decisions will be made within two weeks following the extraction test. Identify any practical constraints on data collection (e.g. meteorological, site access, etc) The most important practical consideration to consider during data collection procedures is the presence of LFG and the potential for fire or explosion. Detailed safety procedures are developed in Section 7.0 of the main Work Plan. Technical limitations for measuring low volume flow rates may occur if the extraction wells have low LFG productivity. Reduction in the diameter of the wellhead meter run may be necessary to achieve sufficient low flow measurement resolution. Air leakage through the final cover immediate to the extraction well casings could dilute the LFG within the landfill, initiate waste oxidation reactions, or increase the inaccuracy of the data. Substantial air leaks should be located and repaired as early in the test period as possible, if detected. Such leaks are not anticipated since the final cover geomembrane was recently installed and tested. The capacities of the existing blower or treatment units may impact the maximum attainable flow rate, if the extraction wells are significantly more productive than anticipated. 2.5 Develop Decision Rules Define the parameter of interest, specify the action level, and integrate previous DQO outputs into a single statement that describes a logical basis for choosing among alternative actions. The two parameters of primary interest are LFG volume flow rate and methane concentration. A target methane concentration will be established initially and periodically updated by the Project Engineer. A minimum flow rate of 45 standard cubic feet per minute (scfm) and methane concentration of 25 percent is required to maintain the stack temperature of the enclosed flare at 1400 F. A flowchart showing the initial decision tree is presented as Figures 2-1a through d. 2.6 Specify Limits on Decision Errors Identify sources of errors and biases that could affect the decision Decisions could be adversely affected by errors in field measurements. Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

9 Describe ways to minimize biases and errors Two types of decision errors are possible: Accepting field measurements when the measurements are higher than they truly are; and Accepting field measurements when the measurements are lower than they truly are. Errors associated with field instruments will be minimized by use of established methods and calibration according to manufacturers instructions. Either of these errors is readily correctable during the testing period and would not lead to endangerment of human health or the environment. 2.7 Optimize the Design for Obtaining Data Identify a resource-effective data collection design for generating data that are expected to satisfy the DQOs. The testing configuration and procedure are presented in Section 3.0. Formulate the mathematical expressions needed to solve the design problems for each design alternative. Determination of Steady-State Flow Conditions The methane concentrations in the LFG extraction flow from each interior well will be measured periodically during the extraction test. The standardized mass flow rate of methane will be plotted versus the following parameters: Elapsed test time, to determine gross heat value trends during the test Total pressure at the wellheads, to determine a limit of vacuum distribution (influence) Methane concentration, to determine the normal methane concentrations, as generated Total LFG flow, to determine a limit of LFG generation for the interior area The induced pressures (vacuums) will be measured periodically during the extraction test at the perimeter LFG extraction wells and probes. The absolute pressure at these subsurface locations will be plotted versus time, both before, during, and after operation of the five interior extraction wells, to determine where LFG extraction may influence the perimeter of Area F. Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

10 3.0 Test Configuration and Procedures 3.1 Test Configuration The test configuration will include: Five interior LFG extraction wells, monitoring wellheads, and conveyance piping Nearby perimeter LFG extraction wells and LFG monitoring probes (initially within 400 foot radius) Existing LFG blower and GAC / KMnO 4 treatment units. Portable field instrumentation for recording volume flow rate, induced vacuum, temperature, and LFG composition. Access to weather service for recording barometric pressure, ambient temperature, average wind speed, and 24-hour precipitation. Details of the interior LFG well field collection system construction are presented in Section 4.0 of the main Work Plan. 3.2 Test Procedures The following procedures will be implemented for the LFG flow extraction test as presented in the flowcharts included as Figures 2-1a through d: 1. Shut down the treatment system and disconnect header pipe from the Area F extraction system. Connect the Area F interior pipe header to the treatment system. 2. Conduct baseline monitoring to determine the concentration and pressure of the LFG in wells and probes prior to extraction activities. Prior to measurement, purge gas equivalent to approximately three times the collector pipe volume. 3. Set each well s flow rate to 10 scfm and operate treatment system continuously for 24 hours. Collect field data a minimum of three times during the day. Collect field data and evaluate methane concentrations as presented in Figure 2-1a: If methane concentration is < 45 percent, decrease flow rate by 30 percent and operate treatment system continuously for 24 hours. Continue with test following decision tree presented in Figure 2-1b. Collect field data a minimum of three times during the day. If methane concentration is > 55 percent, increase flow rate by 20 percent and operate treatment system continuously for 24 hours. Continue with test Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

11 following decision tree presented in Figure 2-1c. Collect field data a minimum of three times during the day. If methane concentration is between 45 percent and 55 percent, operate treatment system continuously for 24 hours. Continue with test following decision tree presented in Figure 2-1d. Collect field data a minimum of three times during the day. 4. Monitor passive soil gas pressures in nearby perimeter LFG extraction wells and monitoring probes, twice daily. Correct to absolute pressure values, using local barometric data during the time of monitoring. 5. After completion of test, disconnect the Area F interior pipe header from the treatment system and reconnect the header pipe from the Area F extraction system. During the Area F LFG flow extraction test, probes along the perimeter of Area F will be monitored to check that the methane concentrations remain below the 5 percent standard. If perimeter probes show methane concentrations at or near 5 percent, then the Area F extraction test will be suspended and the treatment system vacuum reapplied to the Area F perimeter header pipe and operated until methane concentrations are below 5 percent Data Recording The following data will be recorded in the sample collection log (Form 6-2 in the main Work Plan): Name of person(s) taking readings Date and time of each reading Pressure (applied or induced vacuum, as applicable) Methane Oxygen Carbon Dioxide Balance Gas (assumed to be nitrogen) LFG flow rate LFG temperature Weather data: Barometric pressure, ambient temperature, average wind speed, previous 24-hour precipitation Observations/comments Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

12 Measurement will be taken a minimum of three times a day (approximately 0800, 1200, and 1600) unless otherwise specified in Figures 2-1a through d. A Field Activity Daily Log will also be prepared (Form 6-3 in the main Work Plan) Instrumentation A GEM-500 (CES-Landec) gas analyzer will be used for all field measurements, including total pressure, differential pressure, and LFG composition (methane, carbon dioxide, oxygen, and balance gas). Section of the main Work Plan presents calibration details. Revision Landfill Gas Flow Extraction Test Appendix G Work Plan, LFG System Expansion OU2 Landfills Former Fort Ord, California

13 Figures

14 Phase 1 (Determine initial state) Initial flow setting 0.05 scfm / LF of trench (~30 scfm). Test for 24 hours Is CH4 < 40% for 3 consecutive Readings? Begin Phase 2A (p. 2) (Decrease Flow to Find Steady State) Is CH4 > 50% for 3 consecutive readings? Begin Phase 2B (p. 3) (Increase Flow to Find Steady State) Is 40% < CH 4 < 50%? Begin Phase 3 (p. 4) (Confirm Equilibrium) Note: Measurement frequency shall typically be 3 times daily, at approximately 0800, 1200, & 1600 unless otherwise noted. Measured parameters: SP, T, Q, [CH4], [CO2], [O2], [N2]

15 Begin Phase 2A (Decrease Flow to Find Steady State) Adjust Flow Rate by -30% Repeat for 24 hours To total 72 hours, max. Is CH4 < 45%? Is flow rate < 5 scfm? Re-evaluate target parameters Repeat Phase 1 with new targets Is CH 4 > 55%? Begin Phase 2B (p. 3) (Increase Flow to Find Steady State) Begin Phase 3 (p. 4) (Confirm Equilibrium) Note: Measurement frequency shall typically be 3 times daily, at approximately 0800, 1200, & 1600 unless otherwise noted. Measured parameters: SP, T, Q, [CH4], [CO2], [O2], [N2]

16 Begin Phase 2B (Increase Flow to Find Steady State) Adjust Flow Rate by +20% Repeat for 24 hours To total 72 hours, max. Is CH4 >55 %? Is CH 4 > 60%? Re-evaluate target parameters Repeat Phase 1 w/ new targets Is CH 4 < 45%? Begin Phase 2A (p. 2) (Decrease Flow to Find Steady State) Begin Phase 3 (p. 4) (Confirm Equilibrium) Note: Measurement frequency shall typically be 3 times daily, at approximately 0800, 1200, & 1600 unless otherwise noted. Measured parameters: SP, T, Q, [CH4], [CO2], [O2], [N2]

17 Begin Phase 3 (Confirm Steady State Equilibrium) Test for 24 hours To total 72 hours, max. Is CH4 > 52%? Increase Flow Rate by +5% Is CH 4 < 47%? Decrease Flow Rate by -5% Hold flow rate for 24 hours End Test Note: Measurement frequency shall typically be 3 times daily, at approximately 0800, 1200, & 1600 unless otherwise noted. Measured parameters: SP, T, Q, [CH4], [CO2], [O2], [N2]