1、Designation: E2993 16Standard Guide forEvaluating Potential Hazard as a Result of Methane in theVadose Zone1This standard is issued under the fixed designation E2993; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides a consistent basis for assessing sitemethane in the vadose zone, evaluating hazard and risk,determinin
3、g the appropriate response, and identifying theurgency of the response.1.2 PurposeThis guide covers techniques for evaluatingpotential hazards associated with methane present in thevadose zone beneath or near existing or proposed buildings orother structures (for example, potential fires or explosio
4、nswithin the buildings or structures), when such hazards aresuspected to be present based on due diligence or other siteevaluations (see 6.1.1).1.3 ObjectivesThis guide: (1) provides a practical andreasonable industry standard for evaluating, prioritizing, andaddressing potential methane hazards and
5、 (2) raises awarenessof the key variables needed to properly evaluate such hazards.1.4 This guide offers a set of instructions for performing oneor more specific operations. This guide cannot replace educa-tion or experience and should be used in conjunction withprofessional judgment. Not all aspect
6、s of this guide may beapplicable in all circumstances. This guide is not intended torepresent or replace the standard of care by which the adequacyof a given professional service should be judged, nor shouldthis guide be applied without consideration of a projects manyunique aspects. The word “Stand
7、ard” in the title means onlythat the guide has been approved through the ASTM Interna-tional consensus process.1.5 Not addressed by this guide are:1.5.1 Requirements or guidance or both with respect tomethane sampling or evaluation in federal, state, or localregulations. Users are cautioned that fed
8、eral, state, and localguidance may impose specific requirements that differ fromthose of this guide;1.5.2 Safety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applicabil-ity of r
9、egulatory limitations prior to use;1.5.3 Emergency response situations such as sudden rup-tures of gas lines or pipelines;1.5.4 Methane entry into an enclosure from other thanvadose zone soils (for example, methane evolved from wellwater brought into an enclosure; methane generated directlywithin th
10、e enclosure; methane from leaking natural gas lines orappliances within the enclosure, etc.);1.5.5 Methane entry into an enclosure situated atop orimmediately adjacent to a municipal solid waste (MSW)landfill;1.5.6 Potential hazards from other gases and vapors thatmay also be present in the subsurfa
11、ce such as hydrogen sulfide,carbon dioxide, and/or volatile organic compounds (VOCs);1.5.7 Anoxic conditions in enclosed spaces;1.5.8 The forensic determination of methane source; or1.5.9 Potential consequences of fires or explosions in en-closed spaces or other issues related to safety engineeringd
12、esign of structures or systems to address fires or explosions.1.6 UnitsThe values stated in SI units are to be regardedas the standard.1.6.1 ExceptionValues in inch/pound units are providedfor reference.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with
13、its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD1356 Ter
14、minology Relating to Sampling and Analysis ofAtmospheresD1946 Practice for Analysis of Reformed Gas by GasChromatography1This guide is under the jurisdiction ofASTM Committee E50 on EnvironmentalAssessment, Risk Management and Corrective Action and is the direct responsibil-ity of Subcommittee E50.0
15、2 on Real Estate Assessment and Management.Current edition approved March 15, 2016. Published May 2016. DOI: 10.1520/E2993162For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, r
16、efer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD2487 Practice for Class
17、ification of Soils for EngineeringPurposes (Unified Soil Classification System)D5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD6725 Practice for Direct Push Installation of PrepackedScreen Monitoring Wells in Unconsolidated AquifersD7663 Practice for Active Soil Gas Sampling
18、 in the VadoseZone for Vapor Intrusion EvaluationsE2600 Guide for Vapor Encroachment Screening on Prop-erty Involved in Real Estate TransactionsF1815 Test Methods for Saturated Hydraulic Conductivity,Water Retention, Porosity, and Bulk Density of AthleticField Rootzones2.2 Other Standards:California
19、 DTSC, Evaluation of Biogenic Methane for Con-structed Fills and Dairies Sites, March 28, 2012County of Los Angeles Building Code, Volume 1, Title 26,Section 110 Methane3ITRC Document VI-1 Vapor Intrusion Pathway: A PracticalGuideline4ITRC Document PVI-1 Petroleum Vapor Intrusion: Funda-mentals of S
20、creening, Investigation, and Management5EPA 530-R-10-003 Conceptual Model Scenarios for theVapor Intrusion Pathway29 CFR 1910.146 Permit-Required Confined Spaces63. Terminology3.1 Definitions:3.1.1 This section provides definitions and descriptions ofterms used in or related to this guide. An acrony
21、m list is alsoincluded. The terms are an integral part of this guide and arecritical to an understanding of the guide and its use.3.1.2 advection, ntransport of molecules along with theflow of a greater medium as occurs because of differentialpressures.3.1.3 ambient air, nany unconfined portion of t
22、he atmo-sphere; open air.3.1.4 barometric lag, ntime difference between changes intotal atmospheric pressure (barometric pressure) and subse-quent changes in total gas pressure measured at a specific pointin the subsurface.3.1.4.1 DiscussionAtmospheric pressure variations in-clude routine diurnal hi
23、ghs and lows as well as changesassociated with exceptional meteorological conditions(weather fronts). The time lag means that differential pressurebetween the surface and the subsurface point may be out ofphase and may reverse (6 relative to zero) with resultingreversals in soil gas flow direction o
24、ver time between theshallow subsurface and the surface.3.1.5 barometric pumping, nvariation in the ambient at-mospheric pressure that causes motion of vapors in, or into,porous and fractured earth materials.3.1.6 biogas, nmixture of methane and carbon dioxideproduced by the microbial decomposition o
25、f organic wastes,also known as microbial gas.3.1.7 biogenic, advresulting from the activity of livingorganisms.3.1.8 contaminant, nsubstance not normally found in anenvironment at the observed concentration.3.1.9 continuous monitoring, nmeasurements of selectedparameters performed at a frequency suf
26、ficient to define criticaltrends, identify changes of interest, and allow for relationshipswith other attributes in a predictive capacity.3.1.10 dead volume, ntotal air-filled internal volume ofthe sampling system.3.1.11 differential pressure, nrelative difference in pres-sure between two measuremen
27、t points (P).3.1.11.1 DiscussionP measurements are typically thedifferences between pressure at some depth in the vadose zoneand pressure above ground at the same location (indoors oroutdoors), but also could refer to the difference in pressurebetween two subsurface locations. A P measurement repre-
28、sents a pressure gradient between the two locations.3.1.12 diffusion, ngas transport mechanism in which mol-ecules move along a concentration gradient from areas ofhigher concentration toward areas of lower concentration;relatively slow form of gas transport.3.1.13 effective porosity, namount of int
29、erconnected voidspace (within intergranular pores, fractures, openings, and thelike) available for fluid movement: generally less than totalporosity.3.1.14 flammable range, nconcentration range in air inwhich a flammable substance can produce a fire or explosionwhen an ignition source is present.3.1
30、.15 fracture, nbreak in the mechanical continuity of abody of rock or soil caused by stress exceeding the strength ofthe rock or soil and includes joints and faults.3.1.16 groundwater, npart of the subsurface water that isin the saturated zone.3.1.17 hazard, nsource of potential harm from current or
31、future methane exposures.3.1.18 microbial, advpertaining to or emanating from amicrobe.3.1.18.1 DiscussionThe preferred term fornonthermogenic, nonpetrogenic methane such as from anaero-bic activity in shallow soils or sanitary landfills is “microbial.”3.1.19 moisture content, namount of water lost
32、from a soilupon drying to a constant weight expressed as the weight perunit weight of dry soil or as the volume of water per unit bulkvolume of the soil.3.1.20 perched aquifer, nlens of saturated soil above themain water table that forms on top of an isolated geologic layerof low permeability.3Avail
33、able from dpw.lacounty.gov.4Available from the Interstate Technology soil gas is theair existing in void spaces in the soil between the groundwatertable and the ground surface.3.1.31 soil moisture, nwater contained in the pore spacesin the vadose zone.3.1.32 subslab vapor sampling, vcollection of va
34、por fromthe zone just beneath the lowest floor slab of a building orbelow paving or soil cap.3.1.33 thermogenic, adjmethane that is generated at depthunder elevated pressure and temperatures during and followingthe formation of petroleum (for example, in oil fields).3.1.34 tracer, nmaterial that can
35、 be easily identified anddetermined even at very low concentrations and may be addedto other substances to enable their movements to be followedor their presence to be detected.3.1.35 tracer gas, ngas used with a detection device todetermine the rate of air interchange within a space or zone orbetwe
36、en spaces or zones.3.1.36 vadose zone, nhydrogeological region extendingfrom the soil surface to the top of the principal water table.3.1.36.1 DiscussionPerched groundwater may existwithin this zone.3.1.37 vapor intrusion, nmigration of a volatile chemi-cal(s) from subsurface soil or water into an o
37、verlying or nearbybuilding or other enclosed space.3.1.38 volatile organic compound, VOC, nan organiccompound with a saturation vapor pressure greater than 10-2kPa at 25C (Terminology D1356-14).3.1.39 water table, ntop of the saturated zone in anunconfined aquifer.3.2 Acronyms and Abbreviations:3.2.
38、1 ACHair changes per hour3.2.2 CSMconceptual site model3.2.3 FIDflame ionization detector3.2.4 HVACheating, ventilation, and air conditioning3.2.5 In. H2Oinches of water, a measure of pressureexerted by a column of water 1 in. (2.54 cm) in height; 1 in.H2O equals approximately 250 Pa3.2.6 LELlower e
39、xplosive limit (same as lower flammablelimit)3.2.7 PaPascal, a measure of pressure3.2.8 ppmvpart per million on a volume basis3.2.9 psipounds per square inch3.2.10 QA/QCquality assurance/quality control3.2.11 UELupper explosive limit (same as upper flam-mable limit)3.2.12 USEPAU.S. Environmental Pro
40、tection Agency3.2.13 VOCvolatile organic compound3.2.14 v/vby volume, as in percent by volume (% v/v)4. Summary of Guide4.1 This guide describes site screening, testing, dataanalysis, evaluation, and selection of mitigation alternatives.4.2 Three-Tiered ApproachThis guide provides an ap-proach for a
41、ssessing and interpreting site methane, evaluatinghazard and risk, determining the appropriate response, andidentifying the urgency of the response. A three-tiered ap-proach is given that uses a decision matrix based on methaneconcentrations in the vadose zone and other factors such asindoor air con
42、centrations, differential pressure measurements,and estimates of the volume of methane within soil gas near aE2993 163building to determine the potential hazard. The first tierconsists of a site evaluation that can typically be done usingexisting, available information. This information is compiled,
43、reviewed, and used to develop a conceptual site model (CSM).The CSM should describe and summarize the source of anymethane that is present, vadose zone conditions (for example,depth to groundwater and soil type), size of impacted area,design and use of any existing buildings, exposure scenario,and o
44、ther relevant lines of evidence for a given site.Adecisionmatrix is applied to get an initial prediction of hazard. For sitesin which potentially significant data gaps are identified duringthe Tier 1 review, the second tier consists of a refined siteevaluation. Additional field work is performed to
45、address thedata gaps. The results are compared with the CSM and theCSM revised, as necessary. The decision matrix is againapplied to the new, expanded data set to get an updatedprediction of hazard. If it is determined that more data areneeded, the third tier consists of a special case evaluation. F
46、orall three tiers, the path forward at any point should respectapplicable regulatory guidance and consider risk managementprinciples, technical feasibility, and community concerns.4.2.1 The evaluation process is typically implemented in atiered approach involving increasingly sophisticated levels of
47、data collection, analysis, and evaluation. Users may choose toproceed directly to the most sophisticated tier, to pre-emptivemitigation, or to routine monitoring based on site-specificcircumstances.4.2.2 For some sites, a limited number of samples may notbe sufficient to address potential hazard bec
48、ause there are (1)significant potential methane source(s) in the vicinity of the site(for example, a large mass of buried organic matter such asplants, wood, etc.) (2) high-permeability preferential pathwayspresent that may result in higher than typical rates of vaportransport (for example, gravel t
49、rench for utility lines), (3)relatively high permeability soils (for example, sand or gravel)with insufficient moisture to support methanotrophic bacteria,or (4) changes in groundwater elevation over short timeperiods, which can create pressure gradients in the vadosezone. For such sites, presumptive mitigation or Tier 3 evalua-tion (for example, continuous or regular monitoring) should beconsidered.4.3 Site CategorizationThis guide is designed to promoterapid site characterization so that low-risk sites can be identi-fied and
