NOTE: This method does not include all of the specifications (e.g., equipment and supplies) and procedures (e.g., sampling and analytical) essential to its performance. Some material is incorporated by reference from other methods in this part. Therefore, to obtain reliable results, persons using this method should also have a thorough knowledge of at least the following additional test methods: Methods 2 and 3C.
This method applies to the measurement of landfill gas (LFG) production flow rate from municipal solid waste landfills and is used to calculate the flow rate of nonmethane organic compounds (NMOC) from landfills.
Adherence to the requirements of this method will enhance the quality of the data obtained from air pollutant sampling methods.
2.1 Extraction wells are installed either in a cluster of three or at five dispersed locations in the landfill. A blower is used to extract LFG from the landfill. LFG composition, landfill pressures, and orifice pressure differentials from the wells are measured and the landfill gas production flow rate is calculated.
5.1 Since this method is complex, only experienced personnel should perform the test. Landfill gas contains methane, therefore explosive mixtures may exist at or near the landfill. It is advisable to take appropriate safety precautions when testing landfills, such as refraining from smoking and installing explosion-proof equipment.
Capable of boring a 0.61 m (24 in.) diameter hole into the landfill to a minimum of 75 percent of the landfill depth. The depth of the well shall not extend to the bottom of the landfill or the liquid level.
No fines. Gravel diameter should be appreciably larger than perforations stated in Sections 6.10 and 8.2.
Clay, soil, and sandy loam have been found to be acceptable.
Minimum diameter of 3 in., constructed of polyvinyl chloride (PVC), high density polyethylene (HDPE), fiberglass, stainless steel, or other suitable nonporous material capable of transporting landfill gas.
Valve capable of adjusting gas flow, such as a gate, ball, or butterfly valve; sampling ports at the well head and outlet; and a flow measuring device, such as an in-line orifice meter or pitot tube. A schematic of the aboveground well head assembly is shown in Figure 2E-1.
Constructed of PVC or HDPE.
Constructed of PVC or HDPE.
Capable of boring a 0.15- to 0.23-m (6-to 9-in.) diameter hole to a depth equal to the top of the perforated section of the extraction well, for pressure Probe installation.
Constructed of PVC or stainless steel (316), 0.025-m (1-in.). Schedule 40 pipe. Perforate the bottom two-thirds. A minimum requirement for perforations is slots or holes with an open area equivalent to four 0.006-m (1/4-in.) diameter holes spaced 90E apart every 0.15 m (6 in.).
Explosion-proof blower, capable of extracting LFG at a flow rate of 8.5 m3/min (300 ft3/min), a water knockout, and flare or incinerator.
Same as Method 2, Sections 6.7 and 6.8.
Orifice plate, pressure tabs, and pressure measuring device to measure the LFG flow rate.
Same as Method 4, Section 6.1.5.
Water-filled U- tube manometer or equivalent, capable of measuring within 0.02 mm Hg (0.01 in. H2O), for measuring the pressure of the pressure Probes.
The landfill owner or operator may install a single cluster of three extraction wells in a test area or space five equal-volume wells over the landfill. The cluster wells are recommended but may be used only if the composition, age of the refuse, and the landfill depth of the test area can be determined.
Consult landfill site records for the age of the refuse, depth, and composition of various sections of the landfill. Select an area near the perimeter of the landfill with a depth equal to or greater than the average depth of the landfill and with the average age of the refuse between 2 and 10 years old. Avoid areas known to contain nondecomposable materials, such as concrete and asbestos. Locate the cluster wells as shown in Figure 2E-2.
184.108.40.206 The age of the refuse in a test area will not be uniform, so calculate a weighted average age of the refuse as shown in Section 12.2.
Divide the sections of the landfill that are at least 2 years old into five areas representing equal volumes. Locate an extraction well near the center of each area.
Use a well drilling rig to dig a 0.6 m (24 in.) diameter hole in the landfill to a minimum of 75 percent of the landfill depth, not to extend to the bottom of the landfill or the liquid level. Perforate the bottom two thirds of the extraction well pipe. A minimum requirement for perforations is holes or slots with an open area equivalent to 0.01-m (0.5-in.) diameter holes spaced 90E apart every 0.1 to 0.2 m (4 to 8 in.). Place the extraction well in the center of the hole and backfill with gravel to a level 0.30 m (1 ft) above the perforated section. Add a layer of backfill material 1.2 m (4 ft) thick. Add a layer of bentonite 0.9 m (3 ft) thick, and backfill the remainder of the hole with cover material or material equal in permeability to the existing cover material. The specifications for extraction well installation are shown in Figure 2E-3.
Shallow pressure Probes are used in the check for infiltration of air into the landfill, and deep pressure Probes are use to determine the radius of influence. Locate pressure Probes along three radial arms approximately 120E apart at distances of 3, 15, 30, and 45 m (10, 50, 100, and 150 ft) from the extraction well. The tester has the option of locating additional pressure Probes at distances every 15 m (50 feet) beyond 45 m (150 ft). Example placements of Probes are shown in Figure 2E-4. The 15-, 30-, and 45-m, (50-, 100-, and 150-ft) Probes from each well, and any additional Probes located along the three radial arms (deep Probes), shall extend to a depth equal to the top of the perforated section of the extraction wells. All other Probes (shallow Probes) shall extend to a depth equal to half the depth of the deep Probes.
8.3.1 Use an auger to dig a hole, 0.15- to 0.23-m (6- to 9-in.) in diameter, for each pressure Probe. Perforate the bottom two thirds of the pressure Probe. A minimum requirement for perforations is holes or slots with an open area equivalent to four 0.006-m (0.25-in.) diameter holes spaced 90E apart every 0.15 m (6 in.). Place the pressure Probe in the center of the hole and backfill with gravel to a level 0.30 m (1 ft) above the perforated section. Add a layer of backfill material at least 1.2 m (4 ft) thick. Add a layer of bentonite at least 0.3 m (1 ft) thick, and backfill the remainder of the hole with cover material or material equal in permeability to the existing cover material. The specifications for pressure Probe installation are shown in Figure 2E-5.
Place the flow measurement device, such as an orifice meter, as shown in Figure 2E-1. Attach the wells to the blower and flare assembly. The individual wells may be ducted to a common header so that a single blower, flare assembly, and flow meter may be used. Use the procedures in Section 10.1 to calibrate the flow meter.
A leak-check of the above ground system is required for accurate flow rate measurements and for safety. Sample LFG at the well head sample port and at the outlet sample port. Use Method 3C to determine nitrogen (N2) concentrations. Determine the difference between the well head and outlet N2 concentrations using the formula in Section 12.3. The system passes the leak-check if the difference is less than 10,000 ppmv.
Close the control valves on the well heads during static testing. Measure the gauge pressure (Pg) at each deep pressure Probe and the barometric pressure (Pbar) every 8 hours (hr) for 3 days. Convert the gauge pressure of each deep pressure Probe to absolute pressure using the equation in Section 12.4. Record as Pi (initial absolute pressure).
8.6.1 For each Probe, average all of the 8-hr deep pressure Probe readings (Pi) and record as Pia (average absolute pressure). Pia is used in Section 8.7.5 to determine the maximum radius of influence.
8.6.2 Measure the static flow rate of each well once during static testing.
The purpose of short-term testing is to determine the maximum vacuum that can be applied to the wells without infiltration of ambient air into the landfill. The short-term testing is performed on one well at a time. Burn all LFG with a flare or incinerator.
8.7.1 Use the blower to extract LFG from a single well at a rate at least twice the static flow rate of the respective well measured in Section 8.6.2. If using a single blower and flare assembly and a common header system, close the control valve on the wells not being measured. Allow 24 hr for the system to stabilize at this flow rate.
8.7.2 Test for infiltration of air into the landfill by measuring the gauge pressures of the shallow pressure Probes and using Method 3C to determine the LFG N2 concentration. If the LFG N2 concentration is less than 5 percent and all of the shallow Probes have a positive gauge pressure, increase the blower vacuum by 3.7 mm Hg (2 in. H2O), wait 24 hr, and repeat the tests for infiltration. Continue the above steps of increasing blower vacuum by 3.7 mm Hg (2 in. H2O), waiting 24 hr, and testing for infiltration until the concentration of N2 exceeds 5 percent or any of the shallow Probes have a negative gauge pressure. When this occurs,reduce the blower vacuum to the maximum setting at which the N2 concentration was less than 5 percent and the gauge pressures of the shallow Probes are positive.
8.7.3 At this blower vacuum, measure atmospheric pressure (Pbar) every 8 hr for 24 hr, and record the LFG flow rate (Qs) and the Probe gauge pressures (Pf) for all of the Probes. Convert the gauge pressures of the deep Probes to absolute pressures for each 8-hr reading at Qs as shown in Section 12.4.
8.7.4 For each Probe, average the 8-hr deep pressure Probe absolute pressure readings and record as Pfa (the final average absolute pressure).
8.7.5 For each Probe, compare the initial average pressure (Pia) from Section 8.6.1 to the final average pressure (Pfa). Determine the furthermost point from the well head along each radial arm where Pfa < Pia. This distance is the maximum radius of influence (Rm), which is the distance from the well affected by the vacuum. Average these values to determine the average maximum radius of influence (Rma).
8.7.6 Calculate the depth (Dst) affected by the extraction well during the short term test as shown in Section 12.6. If the computed value of Dst exceeds the depth of the landfill, set Dst equal to the landfill depth.
8.7.7 Calculate the void volume (V) for the extraction well as shown in Section 12.7.
8.7.8 Repeat the procedures in Section 8.7 for each well.
8.8 Calculate the total void volume of the test wells (Vv) by summing the void volumes (V) of each well.
The purpose of long-term testing is to extract two void volumes of LFG from the extraction wells. Use the blower to extract LFG from the wells. If a single blower and flare assembly and common header system are used, open all control valves and set the blower vacuum equal to the highest stabilized blower vacuum demonstrated by any individual well in Section 8.7. Every 8 hr, sample the LFG from the well head sample port, measure the gauge pressures of the shallow pressure Probes, the blower vacuum, the LFG flow rate, and use the criteria for infiltration in Section 8.7.2 and Method 3C to test for infiltration. If infiltration is detected, do not reduce the blower vacuum, instead reduce the LFG flow rate from the well by adjusting the control valve on the well head. Adjust each affected well individually. Continue until the equivalent of two total void volumes (Vv) have been extracted, or until Vt = 2 Vv.
8.9.1 Calculate Vt, the total volume of LFG extracted from the wells, as shown in Section 12.8.
8.9.2 Record the final stabilized flow rate as Qf and the gauge pressure for each deep Probe. If, during the long term testing, the flow rate does not stabilize, calculate Qf by averaging the last 10 recorded flow rates.
8.9.3 For each deep Probe, convert each gauge pressure to absolute pressure as in Section 12.4. Average these values and record as Psa. For each Probe, compare Pia to Psa. Determine the furthermost point from the well head along each radial arm where Psa < Pia. This distance is the stabilized radius of influence. Average these values to determine the average stabilized radius of influence (Rsa).
8.10 Determine the NMOC mass emission rate using the procedures in Section 12.9 through 12.15.
|Quality Control measure
|LFG flow rate meter calibration
|Ensures accurate measurement of LFG flow rate and sample volume
Locate a standard pitot tube in line with an orifice meter. Use the procedures in Section 8, 12.5, 12.6, and 12.7 of Method 2 to determine the average dry gas volumetric flow rate for at least five flow rates that bracket the expected LFG flow rates, except in Section 8.1, use a standard pitot tube rather than a Type S Pitot Tube. Method 3C may be used to determine the dry molecular weight. It may be necessary to calibrate more than one orifice meter in order to bracket the LFG flow rates. Construct a calibration curve by plotting the pressure drops across the orifice meter for each flow rate versus the average dry gas volumetric flow rate in m3/min of the gas.
A = Age of landfill, yr.
Aavg = Average age of the refuse tested, yr.
Ai = Age of refuse in the ith fraction, yr.
Ar = Acceptance rate, Mg/yr.
CNMOC = NMOC concentration, ppmv as hexane (CNMOC = Ct/6).
Co = Concentration of N2 at the outlet, ppmv.
Ct = NMOC concentration, ppmv (carbon equivalent) from Method 25C.
Cw = Concentration of N2 at the wellhead, ppmv.
D = Depth affected by the test wells, m.
Dst = Depth affected by the test wells in the short-term test, m.
e = Base number for natural logarithms (2.718).
f = Fraction of decomposable refuse in the landfill.
fi = Fraction of the refuse in the ith section.
k = Landfill gas generation constant, yr-1.
Lo = Methane generation potential, m3/Mg.
Lo' = Revised methane generation potential to account for the amount of nondecomposable material in the landfill, m3/Mg.
Mi = Mass of refuse in the ith section, Mg.
Mr = Mass of decomposable refuse affected by the test well, Mg.
Pbar = Atmospheric pressure, mm Hg.
Pf = Final absolute pressure of the deep pressure Probes during short-term testing, mm Hg.
Pfa = Average final absolute pressure of the deep pressure Probes during short-term testing, mm Hg.
Pgf = Final gauge pressure of the deep pressure Probes, mm Hg.
Pgi = Initial gauge pressure of the deep pressure Probes, mm Hg.
Pi = Initial absolute pressure of the deep pressure Probes during static testing, mm Hg.
Pia = Average initial absolute pressure of the deep pressure Probes during static testing, mm Hg.
Ps = Final absolute pressure of the deep pressure Probes during long-term testing, mm Hg.
Psa = Average final absolute pressure of the deep pressure Probes during long-term testing, mm Hg.
Qf = Final stabilized flow rate, m3/min.
Qi = LFG flow rate measured at orifice meter during the ith interval, m3/min.
Qs = Maximum LFG flow rate at each well determined by short-term test, m3/min.
Qt = NMOC mass emission rate, m3/min.
Rm = Maximum radius of influence, m.
Rma = Average maximum radius of influence, m.
Rs = Stabilized radius of influence for an individual well, m.
Rsa = Average stabilized radius of influence, m.
ti = Age of section i, yr.
tt = Total time of long-term testing, yr.
tvi = Time of the ith interval (usually 8), hr.
V = Void volume of test well, m3.
Vr = Volume of refuse affected by the test well, m3.
Vt = Total volume of refuse affected by the long-term testing, m3.
Vv = Total void volume affected by test wells, m3.
WD = Well depth, m.
D = Refuse density, Mg/m3 (Assume 0.64 Mg/m3 if data are unavailable).
12.2 Use the following equation to calculate a weighted average age of landfill refuse.
12.3 Use the following equation to determine the difference in N2 concentrations (ppmv) at the well head and outlet location.
12.4 Use the following equation to convert the gauge pressure (Pg) of each initial deep pressure Probe to absolute pressure (Pi).
12.5 Use the following equation to convert the gauge pressures of the deep Probes to absolute pressures for each 8-hr reading at Qs.
12.6 Use the following equation to calculate the depth (Dst) affected by the extraction well during the short-term test.
12.7 Use the following equation to calculate the void volume for the extraction well (V).
12.8 Use the following equation to calculate Vt, the total volume of LFG extracted from the wells.
12.9 Use the following equation to calculate the depth affected by the test well. If using cluster wells, use the average depth of the wells for WD. If the value of D is greater than the depth of the landfill, set D equal to the landfill depth.
12.10 Use the following equation to calculate the volume of refuse affected by the test well.
12.11 Use the following equation to calculate the mass affected by the test well.
12.12 Modify Lo to account for the nondecomposable refuse in the landfill.
12.13 In the following equation, solve for k (landfill gas generation constant) by iteration. A suggested procedure is to select a value for k, calculate the left side of the equation, and if not equal to zero, select another value for k. Continue this process until the left hand side of the equation equals zero, ±0.001.
12.14 Use the following equation to determine landfill NMOC mass emission rate if the yearly acceptance rate of refuse has been consistent (±10 percent) over the life of the landfill.
12.15 Use the following equation to determine landfill NMOC mass emission rate if the acceptance rate has not been consistent over the life of the landfill.
1. Same as Method 2, Appendix A, 40 CFR Part 60.
2. Emcon Associates, Methane Generation and Recovery from Landfills. Ann Arbor Science, 1982.
3. The Johns Hopkins University, Brown Station Road Landfill Gas Resource Assessment, Volume 1: Field Testing and Gas Recovery Projections. Laurel, Maryland: October 1982.
4. Mandeville and Associates, Procedure Manual for Landfill Gases Emission Testing.
5. Letter and attachments from Briggum, S., Waste Management of North America, to Thorneloe, S., EPA. Response to July 28, 1988 request for additional information. August 18, 1988.
6. Letter and attachments from Briggum, S., Waste Management of North America, to Wyatt, S., EPA. Response to December 7, 1988 request for additional information. January 16, 1989.
Figure 2E-1. Schematic of Aboveground Well Head Assembly.
Figure 2E-2. Cluster Well Placement.
Figure 2E-3. Gas Extraction Well.
Figure 2E-4. Cluster Well Configuration.
Figure 2E-5. Pressure Probe.