Examples of Data Collection Strategies and Methods by Todd McAlary, Consultants, Inc. AEHS VI Workshop March 14, 2005
Outline External vs Internal Data Collection Typical Scenarios Strategies for Data Collection Methods and Alternatives Conclusions
Internal vs External Data Internal (sub-slab slab and indoor air samples) Access agreements, background challenges, scheduling External (main focus of revised Q5) Is the pathway incomplete? Data to support site-specific specific modeling Improve scoping of Q6 data collection
Define Strategy What is the best way to demonstrate whether or not vapor intrusion poses an unacceptable risk? Minimal risk of false negative AND false positive Resolution against background contributions Lowest overall cost may include proactive mitigation
Typical Sites or Scenarios 1) Dissolved groundwater plume under a community 2) Source directly under or beside commercial building 3) Lateral diffusion through vadose zone 4) Degradable compounds 5) Vacant land re-development
Data Collection Strategies 1) Dissolved Groundwater Plume Under a Community
Conceptual Model: Volatilization From Groundwater
Conceptual Model: Confined Aquifer
Conceptual Model: Fresh-Water Lens
Map the Soil Gas Plume
Fresh Water Lens Case Study? What is the influence of well design?
Data Collection Strategies 2) Source Directly Under or Beside Commercial Building
Ventilation Systems 20% of air is new air, blown in from rooftop HVACs Mechanical engineer monitors closely (energy efficiency) Operates year-round at this site
Ventilation Flow Measurement
Design of Footings
Elevator Shafts the elevator pit is usually the lowest point in the building Drain and/or Sump pump lines may not be directly connected to sewer lines, an air gap is required to prevent sewer gases from entering the elevator pit and hoistway (California Division of Occupational Safety and Health, elevfaq.html).
Data Collection Strategies 3) Lateral Diffusion Through Vadose Zone
Conceptual Model: Lateral Vapor Diffusion
Radial Diffusion Model C Co = a r r a erfc 4Deff t!
C/Co vs t "
Data Collection Strategies 4) Degradable Compounds
oxygen shadow # $! %%
O 2, CO 2, VOCs/SVOCs # $! %%
Degradable vs Less-Degradable An area of current and evolving research BTEX, aliphatics relatively degradable 2,2,4-trimethylpentane and cyclohexane less so MTBE, ETBE, PAHs, chlorinated compounds <<less so Look at relative diffusion coefficients and sorption too
Data Collection Strategies 5) Vacant Land Re-Development
Investigate and Remediate Soil gas Survey ~100 ft grid (maybe closer), may need vertical profiles TO-15 analysis, maybe SVOCs too - $$$ Excavation, SVE or other mass reduction (time=$$$) What residual mass is acceptable? Mass = C x V x AER x 30 years TCE: 1.7 grams Benzene: 24 grams Is it really practical to remediate?
Vapor Control System Cut-Away 99P04.PPT
Buildings on Stilts
Methods API - Collecting and Interpreting Soil Gas Samples from the Vadose Zone: A Practical Strategy for Assessing the Subsurface Vapor-to-Indoor-Air Migration Pathway at Petroleum Hydrocarbon Sites Final Draft, July 2004 Health Canada Soil Vapour Intrusion Guidance for Health Canada Screening Level Risk Assessment (SLRA) Final Draft, October 2004 EPRI Reference Handbook For Evaluating Subsurface Vapor Intrusion to Indoor Air March 2005 ITRC First Draft in Progress Others?
Annular Seals
Pneumatic Testing Ratio of flow/vacuum should be constant (Q/s) Calculate permeability Flow >100 ml/min at vacuum <100 in-h 2 O
Tracer Testing Add 10% to 50% helium to shroud Fill Tedlar bag via Lung Box and screen for helium reading
Field Screening O 2 /CO 2 /CH 4 /H 2 S PID or FID Helium detector Optional compound specific analysis (Draeger chips)
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34)" *+)5..)/ Interior Concentration Action Level* Active Soil Gas Screening / Crawl Space Air Screening Concentrations Che mica l Method Typical RL (ppbv) ( µg/m 3 ) ppbv ( µg/m 3 ) ppbv Acrolein TO-15 0.5 2.00E-02 8.73E-03 2.00E-01 8.73E-02 Acrylonitrile TO-15 0.5 3.60E-02 1.70E-02 3.60E-01 1.70E-01 Benzylchloride TO-15 0.2 5.00E-02 9.70E-03 5.00E-01 9.70E-02 Butadiene; 1,3- TO-15 0.2 8.70E-03 3.90E-03 8.70E-02 3.90E-02 Chlorodibromomethane TO-15 0.2 1.00E-01 1.20E-02 1.00E+00 1.20E-01 Crotonaldehyde (2-butenal) TO-15 0.2 4.50E-03 1.60E-03 4.50E-02 1.60E-02 Dibromoethane (ethylene dibromide); 1,2- TO-15 0.2 1.10E-02 1.40E-03 1.10E-01 1.40E-02 Hexachloro-1,3-butadiene TO-15 0.2 1.10E-01 1.00E-02 1.10E+00 1.00E-01 Hexachlorobenzene TO-15 0.2 5.30E-03 4.50E-04 5.30E-02 4.50E-03 Tetrachloroethane; 1,1,2,2- TO-15 0.2 4.20E-02 6.10E-03 4.20E-01 6.10E-02 Trichloroethylene TO-15 0.2 2.20E-02 4.10E-03 2.20E-01 4.10E-02
0*+ / *"# *67 8%9 *7 1% 8 1:7 8+"#;/. / <=
"> Interior Concentration Action Level* CAS No. Che mica l Method RL (ug/puf) (µg/m 3 ) ppbv Volume needed (L) 83329 Acenaphthene TO-13A 10 2.10E+02 3.30E+01 48 75058 Acetonitrile TO-13A 10 6.00E+01 3.58E+01 167 100527 Benzaldehyde TO-13A 10 3.50E+02 8.07E+01 29 205992 Benzo(b)fluoranthene TO-13A 10 1.70E-02 1.63E-03 586918 111444 Bis(2-chloroethyl)ether TO-13A 10 1.08E-02 1.87E-03 926712 95578 Chlorophenol; 2- TO-13A 10 1.75E+01 3.31E+00 571 218019 Chrysene TO-13A 10 1.70E+00 1.81E-01 5869 86737 Fluorene TO-13A 10 1.40E+02 2.10E+01 71 319846 HCH; alpha- (alpha-bhc) 10 1.98E-03 1.66E-04 5054795 58899 HCH; gamma- (Lindane) 10 9.60E-03 8.18E-04 1041849 77474 Hexachlorocyclopentadiene TO-13A 10 2.00E-01 1.80E-02 50000 67721 Hexachloroethane TO-13A 10 8.90E-01 9.26E-02 11233 126987 Methacrylonitrile TO-13A 10 7.00E-01 8.56E-02 14286 91576 Methylnaphthalene; 2- TO-13A 10 7.00E+01 1.21E+01 143 98953 Nitrobenzene TO-13A 10 2.00E+00 4.00E-01 5000 79469 Nitropropane; 2- TO-13A 10 1.32E-03 3.64E-04 7554110
Pyrene 1000000 100000 10000 1000 100 10 1 0.1 0.01 " SAMPLE VOLUME TO ACHIEVE OSWER GUIDANCE TABLE 2C SUB-SLAB TARGET CONCENTRATION Acetonitrile Benzaldehyde Benzo(b)fluoranthene Bis(2-chloroethyl)ether Chlorophenol; 2- Chrysene Fluorene HCH; alpha- (alpha-bhc) HCH; gamma- (Lindane) Hexachlorocyclopentadiene Hexachloroethane Methacrylonitrile Methylnaphthalene; 2- Nitrobenzene Nitropropane; 2- Nitrotoluene;o- Propylbenzene; n- Acenaphthene Sample Volume (L)
Temporal Variability
BP >200Pa in this example Compare this to 4Pa stack effect!
Implications for Data Variability How much of this is due to: short-term term barometric pressure fluctuations? undetected leaks? background? ventilation?
Alternative Sampling Options Option 1: More Integrated Data Time-Integrated: to smooth temporal variability Volume-Integrated: to smooth spatial variability Option 2: More Discrete Data Real-time continuous monitoring Vertical Profiling Monitor BP and delta P to establish correlation
Time-Integrated Samples 7-day flow controllers for Summa canisters Slower flow-rates and longer time for ATD tubes Larger sorbent tubes (VOST tubes) and larger volume samples
0* # -35 Canister V acuum - inches Hg -30-25 -20-15 -10-5 0 1 2 3 4 5 6 7 Sampling Time (days)
Volume Integrated Samples 600 Representative Purge Volume? 500 Concentration (ppbv) 400 300 200 100 1,1,1-TCA TCE 1,1-DCE c-1,2-dce 0 0 1 2 3 4 5 6 Sampled Volume (L) (DiGiulio, 2004)
35 30 25 20 15 10 5 0 Continuous Real-Time Monitoring HUNTINGTON BEACH SITE - SOIL GAS &'(! %%) 8:00:00 PM 8:50:00 PM 9:41:00 PM 10:32:00 PM 11:23:00 PM 12:13:00 AM 1:04:00 AM 1:55:00 AM 2:45:00 AM 3:36:00 AM 4:27:00 AM 5:18:00 AM 6:08:00 AM 6:59:00 AM 7:50:00 AM 8:41:00 AM 9:31:00 AM 10:22:00 AM 11:13:00 AM 12:03:00 PM 12:54:00 PM 1:45:00 PM 2:36:00 PM 3:26:00 PM 4:17:00 PM 5:08:00 PM 5:59:00 PM 6:23:00 PM Time CH4 CO2 O2 6:18:00 PM 7:09:00 PM Value (%)
Barometric Monitoring Atmospheric Pressure vs Weather Station Data 0.350 0.300 0.250 Inches of H2O 0.200 0.150 0.100 Atmospheric Pressure Weather Station Data 0.050 0.000-0.050-0.100 0 5 10 15 20 25 30 35 40 45 50 Elapsed Time (min)
P and Barometric Monitoring
Summary & Conclusions Revised Q5 allows more options for exterior assessment Not all sites are the same select Strategy using Conceptual Model as a guide Soil gas data is often more reliable than indoor air data easier to resolve vs background and reporting limits Rigorous protocols are required for high quality data At a minimum, exterior data can help scope interior data