Science Advisory Board for Contaminated Sites Soil Vapour Forum July 8, 2008 Notes Key Issues (As Identified by Participants)

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1 Science Advisory Board for Contaminated Sites Soil Vapour Forum July 8, 2008 Notes Key Issues (As Identified by Participants) - role of biodegradation in guidance - detection limits - restrictions on instruments with regard to land use - shallow contamination close to buildings; characterization of sites with this condition - practical application for protection of human health - attenuation factor guidance - analytical method updates - VOC parameters - basic understanding, so that can understand what consultants are talking about - lateral migration and delineation - suitable materials for vapour collection - sampling flows and volumes - relation to soil concentration - shorter list of test compounds - differentiating sub-surface versus within building sources - sampling methodologies - shallow contamination, high groundwater tables - preferential pathways - ecological risk for vapour pathway - appropriate selection of COPCs for vapour - shallow contamination, background concentrations - confirmation sampling for in situ biodegradation - shallow contamination, assessing a vacant site - VHs, LEPH TRVs, utility of LEPH - mitigative measures in the building zone - shallow contamination and high water table - contaminants of potential concern (COPCs) what to analyze for - subslab attenuation factor - overall uncertainty analysis - characterization of bio-remediated soil - regional background - COPC selection and delineation - ranking priority on how to tackle all the COPCs - standardized COPC list - SUMMA canisters for C13? - shallow contamination 1

2 After identification of above issues, participants were asked to prioritize and vote on key issues of potential concern, which were: - COPC Selection -High Ground Water -Detection Limits -Attenuation Factor Guidance -Vapour Collection Materials -Regional Background Presentation 1: Recent Trends and Critical Issues for Assessment of Vapour Intrustion Pathway, by Dr. Ian Hers (Golder). Additional Notes: Slide 3 (CSM): - The vapour intrusion pathway is complex and challenging in terms of assessment and prediction. - Slide 5 (Historical Overview): - J&E Model historically significant uncertainty because of limited knowledge of the pathway Slide 6 (What we know): - Residential buildings often are depressurized, may be variable pressurization in commercial buildings, although buildings can breath both ways - Flux into building is often controlled by soil as opposed to building foundation, and therefore soil properties, depths and biodegradation are important Slide 7 (Comparison J&E AFs to Empirical Data): - Health Canada allows us to look at soil, soil vapour and groundwater - Site specific assessment and good quality data result in decreased variability - Empirical AF data indicates coarse grained soils have a higher alpha - Slide 8 (Redfield, Single Point vs Average Alpha): - graph shows temporal data over several years, and lower average alpha than point measurements - this is important for risk assessment (we are interested in long-term averages) Slide 9: - There are differences between chlorinated solvents and PHCs, which biodegrade - As source strength increases, chlorinated solvent AFs become stable (are not affected by concentration), which is interpreted to be because background is not affecting AF distribution - BTEX AF distribution shows a continuing decline with increasing concentration because background continues to have an affect on the AF distribution 2

3 Slide 10 (Comparison J&E AFs to Chlorinated and Petroleum Hydrocarbon Empirical Data): - The soil vapour AF charts were designed at zero depth to be consistent with the subslab alpha distribution. Although there is a scatter in the subslab AF data, the soil vapour AF curves at zero depth fall within the 50 th to 70 th percentile, which is considered reasonable Slide 11 (Chart alpha vs measured vapour concentration) - US EPA has moved away from the alpha approach - Due to controversy, the US EPA has avoided developing guidance using alpha Slide 14 (Photo of building; David Brenner, AWMA Pittsburgh, 2006) - There was vapour intrusion into a building like this (commercial), and elevated levels of TCE were found - The building has a false, raised floor, below which elevated readings were found. - Elevated TCE readings were also found in stairwells and below furniture - The building was de-pressurized (there was an HVAC system) - The building can also be de-pressurized in the summer; these systems are not designed to mitigate vapour intrusion - De-pressurization can occur in both the summer and winter Slide 15 (TCE Results): - Once the building was pressurized through HVAC modifications, the indoor TCE concentrations decreased. Slide 17 (Relationship Groundwater and Soil): - UST sites in Arizona - huge amount of scatter - difficult to predict concentrations in groundwater and/or air from soil Slide 18 (Meta-data Analysis Co-located soil-soil vapour): - measured concentrations are always less than predicted concentrations - this could be due to partitioning, degradation - for chlorinated solvents, data are so variable, therefore soil is not a good predictor of vapour concentrations Slide 21 (Endicott Case Study): - effect of low diffusivity soil layer and reduction in flux Slide 23 (Spring and Fall TCE in Soil Gas): - soil vapour concentrations over time - consistent pattern between Spring (wetter) and Fall (drier) and good relationship between sampling points - in the late Summer and early Fall, there is a decrease in soil moisture and a decrease in soil vapour concentrations 3

4 Slide 24 (Temporal Trends): - data from below a house in New York - sampled three locations below the building - there was a lot of spatial variability and some temporal variability - suggests that you need more than one point (sampling location) Slide 25: - Biodegradation happens for PHC compounds like BTEX and aliphatics (e.g., decane) - Biodegradation results in rapid attenuation of PHC vapours - We sometimes see this occurring over very thin layers (e.g., 1 to 2 feet) - The current BC guidance does not consider this can we develop guidance for this? Slide 26 (Aerobic Degradation): - Beside vs below buildings - See significant attenuation beside vs below the building Slide 28 (Sub-Slab O2 Transport Experiment): - diffusion was the most important factor - oxygen, wind and rainfall were also important Slide 30 (Casper, WY Site) - subslab vapour monitoring - looked at oxygen levels - saw high levels at the fringe of the slab - wind was pushing oxygen under the building, and decreasing the hydrocarbon concentrations - see elevated vapour concentrations where there is less oxygen below a building Slide 31 (Variability in Pressure Differentials): - pumping effect - diurnal (daily) fluctuations - sub-slab data are variable Slide 34 (Proposed Bioattenuation Adjustments for Health Canada Guidance): - currently 10x based on minimum depth and capping criteria - now looking at separation distance - for lower source strength, indoor vapour concentrations from vapour intrusion will tend to be less than background Slide 36 (Meta-Data Analysis Influence on Background): - equation for empirical alpha incorporates background - for a high source strength, background has no effect on alpha - if low source strength, significant influence of background on alpha need a high alpha to see levels above background 4

5 Presentation 2: BCELQAAC Technical Recommendations to BC MOE for Vapour Standards, by Mark Hugdahl (Chair, BCELQAAC). Additional Notes: Slide 6 (BCELQAAC Proposed Volatile Definition: Part 1 Henry s Law Constant) - Best single predictor of volatility under typical environmental conditions, where groundwater, rain water and soil moisture are present. If not, it may be under conservative Slide 7 (Part 2 Vapour Pressure Cutoff): - decreasing the Torr would be more conservative and would add more compounds to the list Slides 8 and 9 (Physical Constants for Example Substances): - Formaldehyde although formaldehyde has a high vapour pressure, because it is so water soluble, it is considered non-volatile Additional Notes: Representation from the Contaminated Sites Approved Professionals (CSAPs) would be helpful at the BCELQAAC meetings To develop the Schedule 11 Compounds a simple definition of Volatile Substances is needed Introduced criteria for determination of volatile compounds based on Henry s Law Constant and vapour pressure cut-offs for compounds Examples of compounds that would meet proposed criteria were provided. Relative to the current ACC list (March 2008), some compounds will be added, others will be removed. The more compounds you subtract from VPH, potentially additional individual compounds you need to analyze for. As an example, n-decane was brought up, and why subtract this? BTEX will be subtracted; hexane and decane are up to debate Biggest thing with the interim guidance is for the VPHv method Need confidence that we are protecting human health; the guidance should select contaminants of potential concern (COPCs) that account for >90-95% of the risk. Feedback is needed from the Science Advisory Board for Contaminated Sites (SABCS) and CSAPs on the definition of volatile compounds and ACC list given the relatively large number of compounds, standardized short-lists of compounds would be helpful (e.g., for gasoline-contaminated sites). 5

6 Questions: Q Will fractions between C6 and C13 be considered? A Not at this point. Q Is there also a screening step based on toxicity to determine whether the chemical should be on ACC list? A Yes there is a toxicity based screen. What is the basis for the toxicity screen? Presentation 3: Overview of Soil Vapour Assessment from a Laboratory Industry Perspective, by Brent Mussato (CARO Analytical Services). Additional Notes: - Interferences seen with soil vapours due to water vapour in soil gas - tends to shift things - managing moisture is a big issue for GC/MS instrumentation - Safe sampling volumes currently not well defined - chlorinated solvents have low safe sampling volumes - Most reference methods indicate < 10L of sampling volume - Sampling variability exceeds analytical variability - Lowest Practical Quantitation Limits are near the regulatory limits, which causes problems for the analytical chemistry - Encourages field QC Presentation 4: The ABCs of Thermal Desorption, by Chad Born (CANTEST). Additional Notes: - Cantest uses USEPA Method TO-17 via thermal desorption (TD) tubes - Moisture is generally not an issue, drying tubes can be used to remove moisture, but are not generally recommended because you may end up losing >10% of VOCs in the drying tube. - TD tubes are filled with carbonaceous material, and have a front and back tube that may be analyzed for QA/QC purposes - Tubes are cleaned after each run and gas is purged through. Selected tubes are tested again to ensure they are clean, this is part of the method and saves time vs Summa Canister method TO-15 - Detection limits for the current ACC Criteria Schedule 11 can all be achieved via TD tubes as long as sample volume is sufficient - Holding time for TD tubes is 30 days - Important to choose an accredited laboratory and one that can provide field sampling equipment Questions: 6

7 Q What do you with the tubes? A They are recycled; as the sample is extracted at the laboratory, the tube is cleaned. Q Don t you need to ensure that the tubes are clean? A No because of the heat used in the process, they are basically guaranteed to be clean. Q Will one tube give a full range? A Provides for analysis of wide range of compounds including volatiles and some semivolatiles. Presentation 5: Soil Vapour Sampling Using Summa Canisters, by Petro Oh (Maxxam Analytics). Additional Notes: - If have tight soils, may need to sample for longer period of time at lower flow rate - Stressed the importance of calculation of volume of well prior to sampling - Advised against sampling large volumes of air (e.g., 100 litres) because this would mean drawing soil gas from a large area - If sampling large volumes of air, may be drawing surface air into sample a helium tracer test could be used to check whether there is dilution by ambient air - Primary gaseous calibration standards must be commercially available relative to the current ACC list, not all are, which causes issues meeting the ACC - Field QC duplicate using a Y-splitter and single flow controller = a measure of precision - Field QC - field spike using gaseous calibration standard = to check accuracy of the laboratory - Some ACCs may be difficult to meet, unless analysis by GC/MS-SIM mode is conducted - C14-16 rarely found in soil gas - Give the laboratory sufficient time to get equipment together etc. - For legal cases, certify every SUMMA canister - SUMMA canister cleaning: The heating bands around the SUMMA canisters heat the canisters to 60 to 70 degrees Celcius over four hours. During heat air is pulled out of them. - Suggestion: collect samples with both SUMMA canisters and sorbent tubes if detection limit can not be met with the SUMMA then can test the tube. Q How can the vacuum gauge be cleaned? Questions: A It is put on a manifold, heated and tested. 7

8 Presentation 6: Soil Vapour Forum Charcoal Tubes and Miscellaneous Sampling Methods, by Kari Mulroy (ALS Laboratory Group). Additional Notes: - Important to discuss project parameters with laboratory since different media are used to analyze for different compounds and detection limits - Important to analyze fronts and backs of tubes to assess possible breakthrough - Laboratories keep their workspaces clean so that volatiles do not interfere with sample results (example benzene) - Treat your blanks similar to how you treat your sample for best representation - To sample for chlorine, a treated filter is required Questions: Q Do you use different kinds of charcoal? A Depends on the method and compound; NIOSH methods are used as guidance to select sorbents. For chlorinated compounds, coconut shell carbon is used. Q Does charcoal allow analysis of heavier molecular weight compounds? A Naphthalene and other PAHs have poor recoveries with charcoal. Q What is the maximum volume that you can pull through a charcoal tube? A For benzene, the maximum volume is 50 litres at 200 litres/minute. Sampling for vinyl chloride would involve a smaller volume and requires analysis of two tubes, back to back, because it is a very light compound. All this information is in the NIOSH methods. Q What are the laboratories doing for background sampling of the laboratory environment? A Method validation. Laboraties are running blanks as well as daily QC blanks. Generally, a closed system is used for analysis, and there shouldn t be contamination of laboratory air. We also run media blanks and method blanks. Q What is the flow rate for XAD tubes? A 200 ml/minute for soil gas. 8

9 Breakout Sessions Session A: Specific Science, Regulatory Policy and Implementation Issues (facilitated by Brent Mussato) Questions 1. How to Identify COPCs: What constitutes a COPC for soil vapour? (i.e., how should COPCs be selected). What is the role of professional judgement in identification of COPCs? a. How do you determine what your analyte list should be? There are currently 101 chemicals on the ACC list, and possibly more to be added? b. If you analyze for and measure a volatile chemical in excess of the ACC, on what basis could you screen out (i.e., if you did not believe it to be a COPC)? c. What about volatiles that are detected but that are not on the ACC list? 2. What are Appropriate Analytical Methods and Sample Collection Devices? a. Canisters (TO-15) versus sorbent tubes. When should each be used? b. What type of sorbent should be used? Thermal tubes (T0-17) versus solvent extracted tubes (NIOSH or OSHA methods)? What should sampling durations be? c. When can Tedlar bags be used? d. What QC samples should be collected? (blanks, duplicates, trip blanks) e. How should duplicates samples be collected? (splitter) f. Standardization of methods between laboratories for CCME sub-fractions (apparently laboratories use different methods) g. Quantification of naphthalene using T0-15? h. Other QA/QC issues (shipping, storage) 3. Determination of Detection Limits: For some substances listed in the ACC (particularly semivolatiles), achievable laboratory detection limits for air or vapour samples may not be sufficiently low to meet the ACC or risk-based standards. a. Detection limits dependent on chemical (ACC), land use and whether dilution is allowed. b. Sorbent tube detection limits are dependent on volume. An increase in volume will lower the detection limit, however, this will also increase the potential for breakthrough. Some methods specify the volume that may be drawn through the sorbent (e.g., NIOSH 1501 generally specific 8 to 20 L depending on the chemical). 4. Approach for Hydrocarbon Fractions (VPH/LEPH): Under the Interim Guidance, VPH and LEPH are to be assessed following a long-standing surrogate approach. There are significant issues arising from often conservative assumptions for surrogates (when compared to site data) and detection limits, when limited or no dilution is allowed. Session Notes 1. How to Identify COPCs - Health Canada s guidance document is a good starting point. - BCELQAAC has had these discussions not sure it will come to a conclusion on COPCs - Health Canada has draft guidance on Environmental Site Characterization (3 volumes). It is going through final edits but a draft may be obtained by going to the Health Canada 9

10 Contaminated Sites website, and clicking on the link. The document includes information on background, past industrial uses and associated COPCs. The guidance is geared towards soil and soil vapour, but not how to model soil vapour intrusion. - Consultants want to see guidance on the selection of COPCs; the laboratories are looking for input from consultants - Science is changing so the ACC is list is constantly being updated. This is a headache for the laboratories they have to make custom packages for each project. - Role of professional judgement in a performance review, if the reviewer believes that more COPCs or other COPCs should have been analyzed for, they can reject the application for certificate of compliance - Sometimes it appears that there is no judgement in COPC selection it is just a list. - Looking for an 80% rule the 20% would be where the professional judgement comes in. - The Phase 1 ESA tells you what could be there. For example, if there was gasoline or diesel, and you know about the land use, you would test for PHCs and selected individual hydrocarbon compounds that may be associated with gasoline or diesel. The Stage 1/Phase 1 should be used to develop the list. - There is the issue of analyzing a large list of compounds and measuring a detectable concentration of something that you did not expect (e.g., chloroform is a common one) is it a COPC? It is very difficult and expensive to disqualify anomalies. You would need to look at surrounding land use could it have come from a neighbouring dry cleaner? If so, then it would be a COPC. - What about having a standard list of the most toxic compounds you would expect, and then if you get hits, refining that list? - Standard List the list should be based on: a) the proportion present in the product, b) the volatility of the substance and how much would move from source to exposure, and c) the potency of the substance - For example a short list for diesel could include contaminants that would add up to about 95% of the risk, and when you consider uncertainty with sampling, the laboratory, etc., then this should be an acceptable approach - Standard lists would be much easier for the laboratory - Some laboratories will do a full scan analysis, but only report the parameters that the consultant requests - These interim guidelines (standard lists) would be for non-risk assessment projects, for non-complex, not highly toxic sites. For a site needing risk assessment, you would analyze for all the compounds of potential concern - How can we see lists developed? (possibly SABCS, MoE and CSAP?) And who would implement them? - Although standardised lists could help, the analysis will still be relative complex if there are multiple contamination sources - Petroleum industry would support initiative for Standard List, but other industry sectors such as paint or dry cleaners are less well represented and organized. Would be easiest to develop Standard List first for PHC sites - There are sites/industries where you would not be able to do this and you would need to go to risk assessment 10

11 - Laboratory asked question if consultants would like laboratory reporting concentrations of chemicals not requested? General consensus is that consultants would prefer to see the compounds reported, as it gives them more information, and it would be important to know if there are high concentrations of substance not expected to be present. View of the CSAP is that the responsibility lies on the consultant and approved professional making recommendations for the certificate. - What is the obligation of the laboratory if they see elevated concentrations of a parameter not requested for analysis? General consensus is that the laboratory should tell the consultant. - What if a detected substance is not on Schedule 11? If you know an industry used chemicals not on the ACC list, you would have to include these as COPCs, and conduct a risk assessment (go beyond Schedule 11). 2. What are Appropriate Analytical Methods and Sample Collection Devices? - Lab methods (TO Compendium method and NIOSH) provide good summaries regarding method choices. - Canisters versus sorbent tubes? Both SUMMA canisters and tubes have pros and cons, the choice is project and site dependent - Once the analyte list is narrowed down, it may be possible to sample for all chemicals using one tube - There is no way to get around the need for different methods for exotic chemicals, but these are rare, so it is not a big issue - Consultants need to know what chemicals should be analyzed for, the sample volumes and what DLs can practically be achieved, so that they can choose an appropriate method. More work needs to be conducted to validate sample volumes for sorbent tubes - Occasionally you have matrix interferences there is nothing the lab can do and this results in an increase in the detection limits. Moisture can also be an issue. - The lab needs to demonstrate that they have validated the methods they are using, sampling methods should be verified by practitioners in field, although there is overlap in terms of sampling rates, sample container, etc. - Tedlar bags are semi-quantitative. They have a two-day holding time. They are not recommended for sample collection and analysis (by BCELQAAC); rather, they should be used for screening of fixed gases (e.g., oxygen and carbon dioxide) - While drying tubes can be used to remove moisture, there are potential problems in terms of removal of VOCs and alteration of sampling flow rate. Laboratories are generally not comfortable using drying tubes. If you choose to use drying tubes, the method should be validated. - Sample train materials. Material types used in wells studies show that some contribute to VOCs (for example, PVC), and some adsorb chemicals (which causes concern, especially when looking at trace levels). Health Canada guidance indicates which you should and should not use. - Can use field QC test to check but conducting equipment blank by pulling ultra-pure gas through the sampling train - Chloroform is often a detected as it is in water, and water is used to hydrate bentonite, so you sometimes get hits 11

12 3. Federal versus Provincial Approach for Hydrocarbons - The surrogate approach (provincial) for hydrocarbon will no longer be applicable after VPH ACC developed - Using provincial vs federal standards and guidelines and methodologies adds to costs, i.e., analyzing for federal F1, F2 versus provincial VPH, LEPH. Laboratories do these analyses differently, and how they look at the peaks is very different between laboratories. Laboratories need guidance so they can resolve this issue. - What about a combined test e.g., using the same tube for the federal and provincial approach - Many costs arise from the aliphatic and aromatic separation (identifying the peaks and adding them is very time consuming). - However, aliphatic and aromatic separation is needed for risk assessment, as the TRVs are for the aliphatic and aromatic sub-fractions. Wrap-up Questions/Comments: - Proposed VPH 6-13 represents are significant new development, which may limit necessity for assessment of surrogate or fractions at many sites. - There will continue to be need for analysis of (CCME) aromatic and aliphatic subfractions for Federal sites and projects that require higher level risk assessment - The CCME methods for analysis of soil vapour hydrocarbon fractions are not well defined and laboratories conduct these analyses using different procedures a standardized method is needed - There may be an opportunity for Federal and Provincial agencies to work on this together and for BCELQAAC to come up with a standard method? At least for BC? - There is a need for Standard Lists for different COPCs given the number of potential substances that could be analyzed. Session B: Soil Vapour Assessment and Data Interpretation (facilitated by John Wiens) Questions 5. Delineation of Soil Vapour: What are the requirements for delineation of soil vapour within a DSI? How is this information useful for remediation planning purposes? a. What are requirements in terms of vertical and lateral location and spacing of probes? Minimum depth requirements. b. If there is a shallow contamination source (less than 1 m), can a soil vapour sample be obtained? (with appropriate pre-cautions yes, however, may not be possible to follow numerical standards approach) c. What are requirements with respect to temporal sampling (rainfall, barometric pressure, seasonal water table fluctuation). 6. Soil Vapour Sampling: What are the methods and quality control procedures that should be employed for soil vapour characterization? a. Probe design? 12

13 b. What should tracer test requirements be? Are these needed? What is your experience with this testing? c. What about sampling existing wells? d. Vacuum and flow check, purging requirements, flow rate requirements? e. Use of vacuum chamber? f. Equipment blanks? 7. Confirmation of Remediation: What are the practical implications for confirmation of remediation when contaminated soil is excavated? How should soil vapour pathway be assessed? a. Typically for remediation of petroleum contaminated sites, confirmatory soil samples are obtained at limits of excavation b. Collection of soil vapour samples adds to time and cost to project c. If soil excavated to bedrock, difficult (if not practically impossible) to collect soil vapour samples. d. For petroleum contamination, development of soil standards for soil vapour pathway may be reasonable approach. 8. Background Issues: How are background issues to be addressed when conducting soil vapour or indoor air assessments (e.g., chloroform, PCE, benzene). a. At some sites there is elevated concentrations of chemicals such as methylene chloride and chloroform in shallow soil vapour that exceed ACCs. This is particularly an issue when no dilution is allowed. b. Important to understand APECs c. Chloroform may be related to leaking municipal water supply lines or laboratory contamination. Methylene chloride may be related to laboratory contamination. Session Notes 1. Confirmation of Remediation - After excavation and backfilling, what is a sufficient soil vapour assessment? Does soil vapour assessment make sense? If so, how many soil gas probes should be installed? Where should probes be installed? At what depth should probes be installed? If the site is remediated and no contamination is left, what would an appropriate investigation design in terms of probe location and depth? Some of this guidance is provided in Health Canada environmental site characterization guidance. - Question about use of volatilization to outdoor air model (VF model), could use, but not applicable to BC regulatory framework - May help to have multiple line of evidence soil, groundwater and 2. Soil Sampling During Remediation - Guidance needed on how to collect and interpret samples during remedial excavation so that vapour pathway is addressed. 3. Stockpile Sampling and Re-Use of Soil Several work shop participants were dealing with large treated stockpiles which were going to be re-used on a site. How would one ensure that remediation successfully addresses vapour pathway. There are no guidelines available that defines post remediation assessment requirements for vapour pathway. How would one design 13

14 vapour sampling program for stockpiles. Soil standards for vapour pathway for some situations would be helpful. 4. Seasonality of Sampling Seasonal sampling often will be needed to adequately characterize sites. Wrap-up Questions/Comments: - Q - Is there a need and means to correct results of soil vapour measurements for background ambient conditions? A Background is relevant for indoor air, but less relevant for soil vapour, although it may be possible to collect data on regional background soil vapour concentrations. - The issues surrounding soil remediation programs and how to ensure vapour standards are met are significant practical issues that require resolution. - Evaluation of soil vapour intrusion pathway is now part of the Stage 1 and 2 process. Further clarity is needed on level of investigation required and the methods followed for roster submissions. What will be trigger during PSI to identify sites that will require vapour intrusion investigation? (i.e., as provided in ASTM E2600 standard). Guidance from MoE or CSAP is needed to avoid different interpretations by professionals during the roster review process. - The SABCS has received funding for research on soil vapour migration and attenuation factors, but this research could potentially be expanded to also evaluate methods in conjunction with laboratories and BCELQAAC. What are the key questions that need to be answered? Session C: Soil Vapour Intrusion Prediction and Management (facilitated by Will Gaherty) Questions 9. Lateral Soil Vapour Attenuation: How should lateral soil vapour migration be dealt with? What if contamination is laterally removed from an existing or proposed building or only under a portion of a large building? a. When applying a numerical standards approach, it is assumed that a building may be present anywhere on the site, therefore, lateral screening criteria would not apply. However, for off-site building, an evaluation based on lateral distance may be relevant (if distance from edge of contamination to property line is > 30 m, then OK, if less, further evaluation required? Notification?) b. Under risk assessment approach, application of lateral attenuation modeling to evaluate existing building may be appropriate. Health Canada has developed 30 m cut-off (some jurisdictions have different cut-off depending on whether chlorinated solvent or petroleum hydrocarbon). 10. Soil & Groundwater Standards: When soil and groundwater concentrations are non-detect (or very low), can a numerical standards approach be followed without having to collect soil vapour data? Should soil and/or groundwater standards for the soil vapour pathway be developed? 14

15 a. There are significant differences between petroleum hydrocarbon and chlorinated solvent chemicals in terms of distribution and migration, biodegradation potential and background concentrations. b. Petroleum hydrocarbons are LNAPLs, which tend to be form smear zones at water tables, and which are easier to characterize than chlorinated solvents, which are DNAPLs c. Petroleum hydrocarbon vapours are readily degraded in presence of oxygen, chlorinated solvent compounds (except vinyl chloride) are much more persistent in the vadose zone. d. Background concentrations of petroleum hydrocarbons in buildings for most chemicals tend to be higher than for chlorinated solvents. e. When petroleum hydrocarbon concentrations are below a certain threshold, the potential for vapour intrusion resulting in indoor vapour concentrations above background levels is negligible. f. There are disadvantages with soil and groundwater standards for the soil vapour pathway, but given some of the challenges with use of soil vapour for this pathway and limited flexibility particularly for confirmation of remediation, vapour pathway standards (or pathway exclusion factors) for soil and groundwater for petroleum hydrocarbons should be considered. 11. Attenuation Factors: What are appropriate (external) attenuation factors for soil vapour > 1 m depth? For subslab vapour samples? a. Current ministry policy is not to allow any dilution when samples are taken within 1.5 m of building (recommend reducing minimum distance to 1 m). b. External soil vapour attenuation factors on average less than about 10-3 but significant variability c. Subslab soil vapour attenuation factors 90th ~ 2x10-2 for representative data. 12. Shallow Contamination: With shallow contamination (less than 1.0 m), current options are limited to risk assessment or mitigation? Is there a different approach that could be adopted for shallow contamination? a. One option could possibly be to obtain subslab vapour samples and apply an reasonably conservative attenuation factor as part of numerical standards approach. b. However, with shallow contamination that is near to building there is potential for direct contact between building and contamination, migration through utility lines into building. Therefore caution should be exercised and thus risk assessment approach (and typically indoor air testing may be appropriate). 13. Significant Change in Site Conditions/Land use: For urban settings where development will involve substantial excavation or where excavation is planned to remediate site, what is appropriate pre-remedial site investigation? a. If you need to test soil vapour after excavation, how much soil vapour testing would be required before excavation? 14. Modeling: What are acceptable models for site specific modeling? Biodegradation, source depletion, lateral migration? What measurement data is warranted to support modeling and to what extent can and should models be calibrated using site data? 15. Vapour Intrusion Mitigation: What are reasonable approaches and designs for vapour mitigation systems? Given that the cost of soil vapour site investigation for some sites will rival or exceed the cost of mitigation what is role of pre-emptive mitigation? a. What are minimum design requirements? 15

16 b. What models may be used for design purposes? c. What are appropriate liner materials? d. What are monitoring requirements? Session Notes Shallow Soil Sampling - Some sites have shallow water tables (i.e., less than one metre) - Discussion of adding temporary fill, temporary slabs, slab surrogates, buildings, flux chambers, mass balance models, SLRA2 as possible resolutions, but recognition that most of these are more properly part of a risk assessment. MOE indicated that they were hoping that the consulting community had some ideas on how to resolve this. - What is the best method to sample for contamination from surface spills? - The interim guidance indicates 1.5 metres as a minimum depth, but many practitioners are using 1 metre. Clarification is needed on this issue. - Q - Any experience with diffusive/passive samplers? A - They are used for investigative purposes, not for risk assessment. - Q - What about sampling near buildings? A - Mostly default to risk assessment. - Q - As part of a DSI, at what point should we be sampling for soil vapour? A Same approach as for soil and groundwater. - Q - What constitutes delineation for soil vapour? A Need to consider preferential pathways, buildings, etc. Seasonality should also be considered in terms of need for repeat sampling. - Q Is tracer testing being commonly done? A At some sites, not all. - With shallow probes, tracer testing is important, and more important for a smaller number of samples (early stage investigations) - There is soil sampling guidance that addresses how to deal with hot spots, etc. Similar guidance would be helpful for soil vapour investigations that provides information on number of probes, depths, etc. Do what degree can methods for soil vapour be prescribed? For shallow soils need better science and ability for screening out of sites perhaps based on other factors so don t always have to go to risk assessment or preemptive mitigation. - Is there any reason in looking at soil vapour if you know it will be excavated? Why can t you just measure vapours later? This is an issue at PHC sites. It is easier to define PHC versus solvent problems. - Schedule 6 of the CSR will be dealing with soil vapour, and will provide information on delineation, at what stage soil vapour sampling should be used, and what is considered adequate. 2. Shallow Contamination - When dealing with shallow contamination, you are in risk assessment, not standards assessment - Would be difficult to decrease minimum depth too much to less than 1 m, need some buffer in terms of obtaining valid samples - How would you collect shallow samples? Should conduct leak tracer test, could also place small liner at ground surface to avoid break-through. 16

17 - One must be very careful in collecting shallow soil vapour sample beside building if goal is to predict concentration below building. If there is shallow contamination source beside building, should collect sample directly above contamination, or alternately collect subslab sample - For future building may need to collect samples from directly above contamination - Can t use alpha for shallow groundwater - Site-specific alpha = risk assessment scenario. Need vertical profiles to allow you to develop site specific attenuation factor, nested wells, match sample volume to sample container - Knowing exactly where your sample is coming from vertically is a significant challenge 4. Soil Standards - Could develop screening standards with a margin of safety but may no help much because with safety margins, you would be looking at very low concentrations, for PHC compounds, such standards may warrant further evaluation, would need to look at pro s and con s, several individuals indicated an opportunity for developing exclusion factors when vapour intrusion may not be a concern, ie., no NAPL, no preferential pathways, etc. - Also problem with guidance is that it tends to become a de facto standard 5. Mitigation - Room to suggest to MOE to look at presumptive remedies to allow different investigation for vapour mitigation - What are necessary preconditions? - Must address lateral, and will generally be an engineered design - Analogies and approaches can be adopted from radon and methane management, but both have important differences (radon is non-degrading, methane is actually being produced and migration can be driven by production pressure gradients) - Mitigation may be safer, as it is not subject to sample collection error, analytical uncertainty, site heterogeneity Wrap Up 17