vapor intrusion risk pathway regulatory updates & practical strategies

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Vapor Intrusion Risk Pathway Regulatory Updates & Practical Strategies. Kennedy-Jenks Webinar June 2010. Blayne Hartman Independent Consultant 760-925-7206 www.handpmg.com. What Is Vapor Intrusion?. Key Criteria Controlling Assessment: Risk level (1 in 10,000? 100,000? 1,000,000?) - PowerPoint PPT Presentation

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  • Vapor Intrusion Risk Pathway Regulatory Updates & Practical Strategies Blayne HartmanIndependent Consultant 760-925-7206www.handpmg.comKennedy-Jenks Webinar June 2010

    OH 9-07

  • What Is Vapor Intrusion?

    Key Criteria Controlling Assessment:Risk level (1 in 10,000? 100,000? 1,000,000?)Toxicity of CompoundsExposure Factors (time, rates, ventilation)

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  • Why Do You Care About VI?(Risk Often More Perceived Than Real)Health & Safety of OccupantsEPA, ITRC, & State Guidances ASTM New Phase 1 StandardAttorneys & Citizen GroupsFuture Liability

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  • When to Worry About VI?If VOC Contamination & Structures Exist: Laterally within 100 (EPA, DTSC)Vertically Within 100 (EPA, DTSC)NY: No Limits!!!Complaining OccupantsStructures With Odors, Wet BasementsSites With Contamination & Future UseAttorneys & CommunitiesEven Animals, Fruits, Vegetables

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  • EPA-OSWER Draft GuidanceTier 1: Primary ScreeningQ1: VOCs present?Q2: Near buildings?Q3: Immediate concern? Tier 2: Secondary ScreeningQ4: Generic screeningQ5: Semi-site specific screening (alphas from charts & tables) Tier 3: Site-Specific Pathway Assessment Q6: Indoor air (and/or subslab)

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  • Newest Changes (2010?) EPA OSWER VI GuidanceTier 1: Primary ScreeningQ1: VOCs present?Q2: Near buildings?Q3: Immediate concern? Tier 2: Source ScreeningGeneric screening using near-source samples Tier 3: Pathway (Building) AssessmentMultiple lines of evidence (sg & gw)Must go inside???

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  • EPA Guidance UpdatesFed EPA (OSWER & Superfund)Modeling no longer an exitMoving to sub-slab & indoor air7 to 30 day indoor air sampling periodAtt factor of 0.1 for SG & 0.001 for GWDecision matrix?EPA-OUST: Guidance for HCs by 2012Exclusion criteria by Fall 2010

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    Generic (delete)

    Generic Decision MatrixConcentration in Media 1

    Well above level of concernAround level of concernWell below level of concern

    Concentration in Media 2Well above level of concernMitigateMitigateImprove Understanding1

    Around level of concernMitigateImprove Understanding1 or MitigateImprove Understanding1

    Well below level of concernImprove Understanding1Improve Understanding1No Further Action2

    1 Further investigation to resolve discrepancies, reduce conservatism, or verify concern

    2 Requires multiple lines of evidence supporting little or no concern and/or verification sampling

    Pathway

    DRAFT Exterior Decision MatrixConcentration in Groundwater

    Well above level of concernAround level of concernWell below level of concern

    Concentration in Soil GasWell above level of concernInterior sampling or mitigationPossible vadose source; Interior sampling or mitigationPossible vadose source; Interior sampling or mitigation

    Around level of concernInterior sampling or mitigationInterior sampling or mitigationPossible vadose source; Interior sampling or mitigation

    Well below level of concernConsider geologic setting1, verification sampling in select locationsConsider geologic setting1, verification sampling in select locationsNFA unless nearby property has unacceptable risks (verification, monitoring)

    1 Review subsurface startigraphy, depth to water, to determine presence, integrity, effectiveness of geologic barriers to vapor migration.

    Interior

    Interior Decision MatrixIndoor Air Concentration

    Well above level of concernAround level of concernWell below level of concern

    Subslab ConcentrationWell above level of concernMitigateMitigateAction to prevent future exposures

    Around level of concernMitigate or MonitorMitigate or MonitorAction to prevent future exposures

    Well below level of concernImprove understanding (e.g., background sources, subslab spatial variability)Improve understanding (e.g., background sources, subslab spatial variability)No further action

    Model

    Model Decision MatrixModeled Media Concentration

    Well above level of concernAround level of concernWell below level of concern

    Measured Media ConcentrationWell above level of concernMitigateMitigateMitigate

    Around level of concernCalibrate Model, Improve Understanding1, or MitigateImprove Understanding1 or MitigateCalibrate Model, Improve Understanding1, or Mitigate

    Well below level of concernConfirmatory Samples, Calibrate ModelCalibrate ModelNo Further Action2

    1 Further investigation to resolve discrepancies, reduce conservatism, or verify concern

    2 Requires multiple lines of evidence supporting little or no concern and/or verification sampling

    Model (2)

    Model Decision MatrixModeled Attenuation Factors

    Well above level of concernAround level of concernWell below level of concern

    Measured Attenuation FactorsWell above level of concernMitigateMitigateMitigate

    Around level of concernCalibrate Model, Improve Understanding1, or MitigateImprove Understanding1 or MitigateCalibrate Model, Improve Understanding1, or Mitigate

    Well below level of concernConfirmatory Samples, Calibrate ModelCalibrate ModelNo Further Action2

    1 Further investigation to resolve discrepancies, reduce conservatism, or verify concern

    2 Requires multiple lines of evidence supporting little or no concern and/or verification sampling

    Model (3)

    Model Decision MatrixModeled Attenuation Factors

    Well above level of concernAround level of concernWell below level of concern

    Generic Attenuation FactorsWell above level of concernMitigateMitigateMitigate

    Around level of concernCalibrate Model, Improve Understanding1, or MitigateImprove Understanding1 or MitigateCalibrate Model, Improve Understanding1, or Mitigate

    Well below level of concernConfirmatory Samples, Calibrate ModelCalibrate ModelNo Further Action2

    1 Further investigation to resolve discrepancies, reduce conservatism, or verify concern

    2 Requires multiple lines of evidence supporting little or no concern and/or verification sampling

  • Allowable Benzene in GW 1e-6 riskNew OSWER Guidance:0.31 ug/m3/0.001 = 0.31 ug/L/0.2 = 1.5 ug/L

    Robin Davis Exclusion Value: 1000 ug/L

    ~700 times lower than database suggests!!

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  • Allowable Soil Gas Levels(Benzene 1e-6 Risk, residential)

    StateAlpha1/Alpha Risk Based Level (ug/m3)EPA Now0.002500155EPA 2012?0.1103.1CA0.00250042NJ (Subslab)0.0520060MO118,000TN0.00137802,414CT0.110192

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  • State Guidance UpdatesStates With Recent Guidances/Policy OR, OH, MT, WAStates Rethinking Guidances/Policy IL, NJ, MA, MO, TN, ME, CA

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  • CA AgenciesCA-DTSC (& LA-RWQCB)Soil Gas, VI, & Mitigation AdvisoryCHHSLs (thanks to OEHHA)EPA Region 9 Follows the EPA Draft VI GuidanceAdopted Region 3 Screening Levels SF-RWQCB ESLs include aliphatics!Central Valley Boards Want Residential Criteria Applied Regardless of Site Use

    OH 9-07

  • Uh-Oh I wanted to provide a heads up that R2 (SF) is poised to modify its Environmental Screening Levels (ESLs) with respect to the vapor intrusion pathway ... the consequence of this change would be much lower groundwater ESLs for this pathway (20 to 30x lower for most VOCs and over 200x lower for biodegradable VOCs such as BTEX) ... details below ... cheers E-mail received on 9/15/09:

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  • ITRC VI GUIDANCE

    Practical How-to GuideStepwise ApproachInvestigatory Tools (Toolkit)Thorough Discussion of MitigationScenarios DocumentThree Training Dates in 2010

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  • The Net Widens: ASTM VI Standard

    Focus on Property TransactionsPrescriptive Screening DistancesNo RBSLs (RBC)No Assessment RecommendationsLegal StandardsMitigation Released March 3, 2008

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  • ASTM VI Standard Vapor Intrusion Condition (VIC) is defined as the presence or likely presence of any volatile chemical of concern in existing or planned structures on a property resulting from an existing release or a past release from contaminated soil or groundwater on the property or within close proximity to the property, at a concentration that presents or may present a human health risk.

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  • Liability ConcernsPhase I Environmental ConsultantProspective/Current/Past Property OwnerProperty LenderProperty Insurer

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  • Regulatory Approach for HC SitesCurrent Regulatory Approaches:USEPA: Guidance not recommended for UST sitesASTM: Screening distance reduced from 100 to 30Some agencies include a 10X biodegradation factor ITRC: Use vertical profile to demonstrate

    Data suggests these approaches are overly conservative for most petroleum release sites

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  • Methods to Assess VIIndoor Air Sampling Groundwater SamplingSoil Phase SamplingPredictive ModelingMeasure Flux DirectlySoil Gas SamplingSupplemental Tools/Data

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  • Ingredients for Effective VI AssessmentsInvestigatory ApproachDetermine Correct Screening LevelsSample & Analyze ProperlyKnow & Use Supplemental ToolsDemonstrating Bioattenuation

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  • Some Key VI Assessment Issues

    Experience of the Collector/ConsultantHave they done this before?Do they understand RBSLs? Quality/experience of field staff? Sr or Jr?

    Get Enough Data Near/Around/Under

    Legal PerspectiveHow conservative to be or not be?

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  • Most Common VI BloopersUnit Confusion:Assuming ug/L equivalent to ppbvAssuming ug/m3 equivalent to ppbvVacuum units: in Hg to inches H20

    Screening Levels:Comparing to CHHSLsNot calculating correct levels

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  • Approach GeneralizationsIndoor AirAlways find something Multiple sampling rounds: extra time & $Groundwater DataTypically over-predicts riskSoil Phase DataTypically not allowed; over-predicts riskSoil Gas DataTransfer rate unknownSub-slab intrusive

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  • Indoor Air MeasurementPros:Actual Indoor ConcentrationCons:Where From?Inside sources (smoke, cleaners)Outside sources (exhaust, cleaners)People activities NO CONTROL!Time-intensive protocolsSnapshot, limited data points Expensive!!

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  • Ambient Air Benzene at 23 CA Sites

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  • ARAMCO Art and Crafts GoopAleenes Patio & Garden AdhesiveConsumer Products Containing PCEProductGumout Brake CleanerPCE ConcentrationHagerty Silversmith Spray PolishChampion Spot it GonePlumbers Goop AdhesiveLiquid Wrench Lubricant w/ TeflonNot Specified70%50 - 90%67.5%30.5%20 - 25%65 - 80%KEY POINT:Wide variety of consumer products still contain high concentrations of PCE.Indoor Air

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  • Indoor concentration of 1,2-DCA increasing over time. New indoor source = molded plastic (e.g., toys, Christmas decorations).New Indoor Source of 1,2-DCAKEY POINT:CONCENTRATIONDETECTION FREQUENCY1,2-DCA Detection Frequency (%) 1,2-DCA Concentration (ug/m3)USEPA INDOOR AIR LIMIT
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  • Passive Soil Gas SamplersAdsorbent inside tube open on one endAdsorbent inside badgeAdsorbent inside vapor permeable, waterproof membrane

  • Approach GeneralizationsIndoor AirAlways find something Multiple sampling rounds: extra time & $Groundwater DataTypically over-predicts riskSoil Phase DataTypically not allowed; over-predicts riskSoil Gas DataTransfer rate unknownSub-slab intrusive

    OH 9-07

  • ModelingJohnson-Ettinger Most CommonGW, soil, soil gas spreadsheetsScreen & advanced versionsEPA-OSWER: no longer an exit BiovaporIncludes bioattenuationAgency acceptance?

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  • What is BioVapor? Free, easy-to-use vapor intrusion model that accounts for oxygen-limited aerobic vapor intrusion.KEY POINT:1-D Analytical ModelOxygen Mass BalanceVersion of Johnson & Ettinger vapor intrusion model modified to include aerobic biodegradation (DeVaull, 2007).Uses iterative calculation method to account for limited availability of oxygen in vadose zone.Simple interface intended to facilitate use by wide range of environmental professionals.User-FriendlySIMPLE MATHConceptual Model

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  • 3Advection, diffusion, and dilution through building foundation2Diffusion & 1st order biodegradation in aerobic zone1Diffusion only in anaerobic zoneAlgebra Solution for: Oxygen demand = Oxygen SupplyBioVapor API 1-D Steady State VI Model

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  • Which Soil Gas Method?Active?Passive? (limited use)Flux Chambers? (limited use)

    Active method most often employed for VI

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  • Probe ConsiderationsTubing TypeRigid wall tubing ok (nylon, teflon, SS)Flexible tubing not (tygon, hardware store)Small diameter best (1/8 or )Probe Tip Beware metal tips (may have cutting oils)Equilibration TimeEffects by air knife, rotary, air percussion, sonicEquipment BlanksNeed to collect blank through collection system

    OH 9-07

  • Soil Gas Sampling Issues

    Sample Size Greater the volume, greater the uncertaintySmaller volumes faster & easier to collectContainersCanisters: More blank potential. Higher cost Tedlars: Good for ~2 days. Easier to collect Flow RateReally not imp. But most agencies < 200 ml/minTracer/Leak CompoundCrucial for sub-slab & larger sample volumes Gases (He, SF6, Propane) & Liquids (IPA)

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  • Beware of the Hardware

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  • Poor Hardware

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  • Container IssuesLarge vs. mini-canistersFilling a tedlar bag with syringe

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  • Common Soil Gas Analyses

    VOCsSoil & Water Methods: 8021, 8260Air Methods: TO-14, TO-15, TO-17Hydrocarbons8015 m, TO-3Oxygen, Carbon DioxideASTM 1945-96SVOCs (sorbent methods)Air Methods: TO-4, TO-10, TO-13

    OH 9-07

  • On-site TO-15 Scan/SIMSimultaneous Scan/SIM mode enables < 10 ug/m3 for All VOCs & ~ 1 ug/m3 for subset of compounds.Only 2cc of Sample. Eliminates HardwareReal-time Analysis in Structures: Control!Two Mobile Air Labs Now OperationalCan Go Into Automated Mode

    OH 9-07

  • Dont Forget 8021Can get to 1 ug/m3 for TCE, CCl4, PCECan get to ~25 ug/m3 for Benz & Napthalene5 minute run time for benzene, TCE & PCECost ~ 1/5 of TO-15

    OH 9-07

  • Supplemental Tools/Data

    Site Specific Alpha Using RadonFactor of 10 to 100. $100/sampleIndoor Air Ventilation RateFactor of 2 to 10.

  • Soil Gas Sampling for HCs

    Might Need to Sample 5 bgs exceed allowable levelsHow to know? On-site analysis bestIf not, collect samples anywayAlways Collect Oxygen DataMight Need Soil Phase Data

    OH 9-07

  • Sub-Slab vs. Near-Slab Samples

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  • Dirty Groundwater (>100 ug/l) at Site

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  • Dirty Soil (>1 ppm) at Site

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  • Subslab Data (ug/m3 benzene)Service station8.34.34.6NDND11107.26.96.510125.33.15.912.4.92013/7.7108.3128.38.48.3NDNDNDND9.29.816/245.46.7GW0100 ft

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  • The Culprit

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  • BBQ Sample Results

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    Sheet1

    370 Electric Sub-Slab & Gas BBQ Results

    AnalyteBBQGaragePatioGarage #2Closet

    methane40%90%100%nd (0.1%)nd (0.1%)

    ug/m3ug/m3ug/m3ug/m3ug/m3

    n-hexane1700200010000nd (15)nd (15)

    cy-hexane750550012000nd (20)21

    n-heptane4607103100nd (50)nd (50)

    benzene27034019006.57.9

    toluene1501101204462

    xylenes4010517711333

    tri-methyl benzene38525110nd (10)

    tri-methyl pentanend (200)300nd (200)nd (20)nd (20)

    Sheet2

    Sheet3

  • Previews of the VI FutureVI Likely to be a Concern at Your Sites Variable Regulatory Guidance Makes Assessment Tricky & SlowNew EPA & DTSC Guidance to be StricterESLs to Go Lower?Hydrocarbons to be Less of a Concern

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  • Want to Know More?ITRC 2-day VI Training 2010July 12: BostonOctober 4: AtlantaAWMA 2-day Chicago 9/29/2010Tanks Conf, PVI Workshop, Boston 9/2010AEHS MA: PVI Workshop Oct 2010

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  • Existing Documents & TrainingSoil Gas Sampling SOPsSoil Gas Sampling, Sub-slab Sampling, Vapor Monitoring Wells/Implants, Flux Chambers (www.handpmg.com)

    Other ITRC VI Guidance (www.itrcweb.org)API Soil Gas Document (api.org)ASTM E2600-08: Good Summary Table in App X

    OH 9-07

  • VI Documents

    Overview of SV Methods (www.handpmg.com)LustLine Part 1 - Active Soil Gas Method, 2002LustLine Part 2 - Flux Chamber Method, 2003LustLine Part 3 - FAQs October, 2004LustLine Part 4 Soil Gas Updates, Sept 2006LustLine VI For Petroleum Hydrocarbons, May 2010 Robin Davis Articles on Bioattenuation:Lustline #61 May 2009 LustLine #52 May 2006 (www.neiwpcc.org)

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  • Blayne HartmanHartman Environmental GeoscienceH&P Mobile Geochemistry 858-925-7206www.handpmg.com

    OH 9-07

    This presentation is a condensed version of the vapor intrusion training that Dr. Hartman has been presenting to Federal & State regulatory agencies, DOD facilities, consulting groups, and stakeholders around the country. As of September 2008, this training has been given to over 30 State Regulatory agencies, including ASTSWMO and the State Coalition of Dry Cleaners. Training has also been given to many PRPs such as the major oil companies, Armed Services, & EPRI.

    Lecture notes are at the bottom of each slide so that if played out as a hard-copy, the presentation can be a useful reference document.

    Vapor intrusion refers to the upward migration of contaminants in the vapor phase from groundwater, soil, or soil gas contamination sources.

    Key criteria to the risk determination are the risk level, the toxicity of the contaminant, and the exposure factors. These parameters are often much more important than model parameters such as soil porosity and pressure gradients.In some cases, there is a real threat to occupants.

    But in the majority of cases, the risk to occupants is exaggerated, hence the perception is greater than the real risk. Nevertheless, you need to worry about it because the EPA has identified it as a risk pathway, numerous states have their own guidance or policies, and citizen groups and of course, attorneys are making it an issue.

    The EPA & many State guidances use the distance criteria listed above to screen sites needing to assess the pathway. At sites with existing contamination but no current buildings, the pathway will need to be assessed when development is proposed. Attorneys and community activist groups can expand these criteria beyond the EPA limits. In some recent cases, concern about the safety of burrowing animals, and fruits & vegetables has been the reason to assess the vapor intrusion pathway.The current EPA draft VI guidance consists of 3 tiers, consisting of 6 questions. Tier 1 is essentially a screening survey asking basic questions such as whether volatile compound contamination exists and whether buildings exist.

    Tier 2 consists of 2 questions/steps: Q4 & Q5. Question 4 is so restrictive (i.e., very low fail levels) that just about every site fails, similar to a vortex or hopper. Question 5 allows more sampling options, is not as conservative, and may be the best tier/question to work within.

    Tier 3, question 6, allows for only two investigatory methods, indoor air or sub-slab soil gas, and has very restrictive (i.e., very low fail levels) criteria. Once at this level, it is extremely hard to get out and requires expensive and repeated sampling.*The changes currently being considered by the EPA would make the vapor intrusion pathway even more stringent. Few sites would screen out and indoor sampling (sub-slab or indoor air) is required in most cases.

    Here is a summary of existing Federal & State guidances as of January 2010.This is one idea being contemplated by EPA for site screening using only exterior data. As you can see, there is only one box that does not require any further action in this matrix. This is still very much in the draft stages and is being discussed by EPA with experts and stakeholders.

    Slide courtesy of Henry Schuver of EPA

    For the vapor intrusion risk pathway, acceptable concentration levels are 1000 to 10,000 times lower than acceptable levels for soil and water. So essentially, this increases the number of sites that have to be evaluated.

    A summary of the alpha factor and corresponding acceptable soil gas levels for various States and the EPA draft guidance shows large variation and illustrates the main point: the levels are variable from State to State.

    Notice the difference in allowable values for the different EPA VI guidance questions.

    Here is a summary of existing Federal & State guidances as of January 2010.Here is a summary of the vapor intrusion policy/guidances for some California regulatory agencies. DTSC has soil gas collection & analytical guidance document, a vapor intrusion guidance document, and recently issued a mitigation document. The San Francisco Water Board has issued their own ESLs. The Central Valley & some Bay Area agencies are requiring residential criteria at all sites, whether current use is commercial or residential, to avoid hassles of deed restrictions and future monitoring of property use.The SF-RWQCB is considering lowering screening levels which will suck in more sites.

    ITRC has recently finished its vapor intrusion guidance document. It consists of 2 documents: A practical guideline and a separate scenarios document. A 2-day classroom training course will be held at 3 locations in the US in 2010.ASTM convened a technical workgroup in 2005 to write a standard for vapor intrusion as it applies to property transactions. The standard was released on March 3, 2008.

    The Standard defines a new term/arconym: the Vapor Intrusion Condition.

    Slide courtesy of Anthony Buonicore, Chairman ASTM VI Task Group

    The Standard identifies the following search distances. Note the long distances.

    Slide courtesy of Anthony Buonicore, Chairman ASTM VI Task Group

    Liability concerns is a big part of vapor intrusion. Those at risk include consultants, property owners (past, current & future), lenders, and insurance companies.

    Slide courtesy of Anthony Buonicore, Chairman ASTM VI Task Group

    Presently, most vapor intrusion guidances ignore bioattenuation. For those that discuss or consider it, there is a range of approaches to account for it. Some States simply decrease the distance of concern. Some give a 10 times allowance (typically by increasing screening levels) for bioattenuation.There is general recognition that these regulatory approaches tend to be overly conservativeIn this part of the seminar, we will discuss the primary techniques/tools used to assess the vapor intrusion pathway, including the pros & cons of each.The keys to effective vapor intrusion assessments are picking the proper approach, determining the correct screening levels, sample & analyze correctly and efficiently, know when and how to use supplemental assessment tools, and to know how to demonstrate bioattenuation if petroleum hydrocarbons are the COC.The most important ingredient for cost effective and efficient VI investigations is the experience of the person/firm doing the collection. Is the collection being done by a firm that has prior experience? Is it a routine part of their services or an occasional part? Do they put experienced people in the field who can think or junior staff who arent well versed? This applies to the consultant and their subcontractors.

    Soil gas, like soil, is not homogenous in most cases. So you need enough data to give decent coverage near, around, or under the receptor. Simpler collection systems with small volumes are advantageous as there is less to go wrong and enable higher production per day (20+ samples per day). Less expensive analytical methods (8021, 8260) enable more analyses for reasonable cost. Real-time data can be extremely helpful to track soil gas contamination laterally and vertically.

    Legal considerations often dictate what additional work needs to be done at what standards.

    All of these issues affect the investigation progress.Each investigatory approach has pros and cons that must be considered before choosing the one to use at a site.Measuring indoor air might seem to be the most direct and simplest approach, but it has its share of problems. The biggest problem is background sources of contaminants. Many commonly used household products contain some of the target compounds of concern. For example, benzene from gasoline, PCE from dry cleaned clothes, TCA from degreasing cleaners. In addition, the protocols are laborious, intrusive, offer little control, and are expensive. For these reasons, the EPA and many States shy away from this method. However, this method may still be the method of choice if the contaminant of concern is not one commonly found in household products (e.g., 1,1 DCE). Ambient air benzene levels at 23 sites around California are greater than 10 times the 1 in 1 million cancer risk level.

    Contaninants in indoor air may be from household products, not vapor intrusion.

    Slide courtesy of Dr. Tom McHugh, GSI, Houston, TXA recently discovered source for 1,2 DCA: molded plastics from China!

    Slide courtesy of Dr. Tom McHugh, GSI, Houston, TX

    Examples of passive collectors.Each investigatory approach has pros and cons that must be considered before choosing the one to use at a site.The use of models to calculate an indoor air concentration, and in turn a health risk, is commonplace. Existing models use groundwater, soil, or soil gas data and are relatively easy to use. In general, if default parameters are used, they tend to over calculate the risk for most situations.

    The Johnson-Ettinger model/spreadsheet is the most commonly used model. Several versions currently exist with different default values for various parameters, so one must be careful to know what version they are using. There are many parameters that can be changed, some more easily that the others.

    EPA OSWERs current position is to use the models as a screening tool, but not for closing the pathway. API has developed a new spreadsheet based upon the J-E model which includes bioattenuation. The spreadsheet is now available from the API website.Conceptual model of the API Biovapor model/spreadsheetThere are three types of soil gas methods. Active refers to actively withdrawing vapor out of the ground. It gives quantitative values. Passive refers to burying an adsorbent in the ground and letting the vapors passively contact and adsorb onto the collector. It does not give quantitative data and hence can not be used for risk applications, except for screening. Surface flux chambers were discussed previously.

    The active method is the one most applicable to risk assessments.Some of the issues that need to be considered when installing probes include:

    Tubing Type: Small diameter tubing offers advantages over large PVC pipe. Flexible tubing tends to leak.

    Probe tip: Metal tips may have blanks due to the cutting process.

    Equilibration time: How long to wait, especially if air knives are used to clear holes or larger drill rigs are used?.

    Equipment blanks: need to collect blank through the collection system. Trip blanks not enough.Lower detection levels requires more careful protocols. Important sampling considerations include sample volume, container type, flow rate, and leak testing to ensure valid samples are collected. Smaller volumes require less complicated sampling systems and minimize the chances for leakage from the surface and desorption off soil. Recent studies have shown no difference in soil gas values regardless of whether small (0.5 L) or large (100 L) volumes are collected.Sample containers must be inert, clean, and handled properly (no cooling or heat). Canisters have longer holding times, but have the potential for blanks (carry-over from previous samples), cost more, and can be trickier to fill. Tedlar bags are good for ~2 days, are less expensive, and suitable for concentrations of 1 ppbv or higher.

    Sample flow rate is of concern to many agencies, but recent data are showing it not to be a factor.

    Tracer/leak compounds are generally required to ensure sample integrity because small leaks can create significant effects at such low concentrations. The larger the volume extracted and the more complicated the sampling system, the greater the potential for leaks.

    The tackle box on the left shows the required hardware to collect soil gas samples in Summas.

    The syringe to the right is the only collection device required for on-site analysis of soil gas.

    Canister sampling is hardware intensive. Only use labs that have good, well-kept hardware.

    Issues currently being debated.This slide gives a summary of the most common analytical methods used for soil gas samples. More discussion on these methods follows.New equipment allows on-site TO-15 analyses. New GC/MS equipment enables simultaneous Scan/SIM mode meaning you can measure for all VOCs (>60 compounds) at DLs < 10 ug/m3 while simultaneously measuring for a subset of compounds at lower detection levels (