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Are Industrial Buildings Different? Implication of a Quantitative Vapor Intrusion at DoD Industrial Buildings Nationwide
- 1. Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Are Industrial Buildings Different? Implication of A Quantitative Vapor Intrusion Analysis of DoD Industrial Buildings Nationwide Christopher Lutes, Loren Lund, Keri Hallberg, John Lowe, and Mike Novak (CH2M) Patricia Venable, Tanwir Chaudhry and Tara Meyers (NAVFAC EXWC), Ignacio Rivera - Duarte (SSC Pacific), Donna Caldwell (NAVFAC- ATLANTIC)
- 2. 2 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Outline • Database contents • Methods of data analysis • Comparison of DoD industrial buildings to EPA residential data set • Key individual factors controlling indoor air concentrations • Multiple regression analysis
- 3. 3 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Database of DoD Buildings with Chlorinated VOCs • 12 installations, 13 sites, and 49 commercial/industrial/institutional buildings • Average age of buildings in the database is 55 years • Majority of these sites have depths to water < 10 ft (<3 m) Typical Residence Project conducted under NESDI Project #476 (Navy Environmental Sustainability Development to Integration)
- 4. 4 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Database Structure • Sample zones = enclosed areas with indoor air samples • Primary release = historical release point i.e. UST, disposal pit
- 5. 5 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide DoD Data Analysis Methods • Example database fields: building footprint area, sample zone use, soil type, subgrade structures • Analysis showed nondetects had little effect on dataset • Screening approach paralleled EPA residential study • Results presented here screened to remove indoor sources based on a source strength screen • Data also filtered to remove atypical preferential pathways. • Subslab and indoor data paired by sample zones • Deep soil gas concentration calculated using Henry’s law = “groundwater vapor concentration” • Single and multivariate regression analyses conducted
- 6. 6 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Basis for Comparison – EPA Residential Database • Attenuation factor definition: AF’s: 1.0 0.1 0.01 0.001 0.0001
- 7. 7 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide PCE Concentration in Sub-slab vs. Indoor Air (DoD) Key Point A much higher subslab screening level is appropriate for industrial buildings than for residential buildings. *
- 8. 8 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide TCE in Sub-slab vs. Indoor Air (DOD) Key Point A much higher subslab screening level for TCE is appropriate for industrial buildings than for residential buildings. * * * *
- 9. 9 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Basis for Comparison – Groundwater to Indoor Air: EPA Residential Database EPA recommends a 95th percentile attenuation factor = 0.001 for groundwater vapor on the basis of this analysis.
- 10. 10 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide PCE Indoor Air vs. Groundwater Concentration (DoD) Key Point A 10X higher screening level could be applied to groundwater for industrial buildings.
- 11. 11 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide TCE Indoor Air vs. Groundwater Concentration (DoD) Key Point A 10X higher screening level could be applied to groundwater for industrial buildings.
- 12. 12 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Why Do Vapor Intrusion Plots Have Scatter: Many Variables Involved – Radon Experience “This paper identified about thirteen factors that can affect radon: …soil moisture content, soil permeability, wind, temperature, barometric pressure, rainfall, frozen ground, snow cover, earth tides, atmospheric tides, occupancy factors, season and time of day. ….. Four factors that influence radon concentrations indoors are properties of the building material and ground; building construction; meteorological conditions; and occupant activities. ” Lewis & Houle, A Living Radon Reference Manual (2009) 1
- 13. 13 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Key Difference in Commercial/Industrial Buildings: Sample Zone Size Effects
- 14. 14 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Key Difference in Commercial/Industrial Buildings: Rapid Drop-off In Subslab with Distance from Release
- 15. 15 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Key Difference in Commercial/Industrial Buildings: Rapid Drop-off In Indoor Air with Distance from Release r2 = 0.337 Distance to Primary Release (ft) PCE(µg/m3) 0.1 1 10 100 1000 1 10 100 1000 PCEConcentration(µg/m3) Distance to Primary Release (ft) Effect of Distance to Primary Release on PCE Indoor Concentration, Baseline, Source Strength and Preferential Pathway Screened Data; Log-Log Plot r2=0.3337
- 16. 16 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Key Difference in Commercial/Industrial Buildings: Role of Soil Type Residential – EPA Database – Fine Soil Slightly Lower Normalized Concentration DoD Buildings – Fine Soil – Higher Concentration: p value, 2 tailed = 8E-6 Coarse Fine Soil Type
- 17. 17 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Multiple Regression Analysis Results • Winter sampling the single strongest variable (stack effect) • Multivariate analyses explained the majority of the variance in indoor air concentration using a small number of variables: – Sampling season – Sample zone area, – Sub-slab soil gas concentration, – Groundwater concentration, and – Depth to groundwater – Distance to primary release. • i.e. TCE indoor (subset of winter data (n=19)) modeled with only four terms adjusted r2= 0.86; each p< 0.000001. • Models require confirmation; not enough data available to have separate training and test datasets.
- 18. 18 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Conclusions • Commercial/industrial/Institutional buildings are different than single family residences in VI behavior • EPA’s Vapor Intrusion Screening Level (VISL) calculator likely overestimates concentrations in indoor air by a factor of 100x for subslab and 10x for groundwater. • Normalized indoor air concentrations decrease with increasing sample zone size (square footage). • Subslab (and indoor) concentrations fall off rapidly with distance to the point of primary release. • Soil type affects these large buildings differently than single family residences • These results were used to develop a quantitative decision framework (more information on this available)
- 19. Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide Thank You For more information, contact: Christopher.lutes@CH2M.com or Loren.Lund@CH2M.com
Editor's Notes
- The database structure is based on a hierarchy of geographical units starting at the installation, within installations are sites, associated with sites are buildings, and within buildings we define sample zones as enclosed areas where at least one indoor air sample is available. Then in the sample zones we define there key characteristics such as size, use etc….and have additional tables for groundwater information nearby, and the primary release point – the place where the historical release is believed to have occurred. That might be a pit, or vapor degreaser…..
- Conducted service wide data call, 2nd person QC of data entries ND results have limited influence on the overall shape or distribution of the data. Analysis suggested reporting limit values could be used with minimal effect on outcomes. A narrow category “strict preferential pathway” defined and populated as “true” only when there was a visually observable, atypical preferential pathway present. Examples included tunnels, utility trench leading directly to source areas and false walls with soil bottoms. Source strength screen chosen because this dataset provides the best balance between adequately excluding data controlled by indoor sources, while retaining as many data points as possible for analysis.
- EPA database is 41 sites, and filtered to just residences; dominated by northeastern and western sites (Colorado and California) It is conventional in the vapor intrusion field to speak of a normalized indoor concentration as shown here as an “attenuation factor”. Here those factors are portrayed as diagonal lines on a plot of subslab vs. indoor concentration drawn from the EPA residential database to which we will compare our commercial/industrial results. Note degree of scatter. Data shown is after source strength screen. EPA’s database report concludes that 0.03 is the 95th percentile subslab to indoor air attenuation factor but VISL calculator still uses 0.1
- Sample Zone Averages; shapes are individual bases Explain VISL = vapor intrusion screening level. EPA’s VISL calculator applied to commercial buildings would suggest you may reach a problematic indoor air concentration with a subslab concentration as low as 470 ug/m3 but our analysis shows not until 100,000 ug/m3 EPA’s database suggested 0.03 for residences, but they use 0.1 We recommend 0.001 AF for military nonresidential buildings.
- Similarly, EPA’s calculator would suggest that concentrations as low as 30 ug/m3 may be problematic in commercial buildings, while our database analysis suggests 2,000 ug/m3.
- Using the 0.001 attenuation factor EPA’s VISL calculator suggests concentrations as low as 47,000 ug/m3 in groundwater vapor (65 ug/l). We recommend a screening level 10x higher as shown by the dotted blue line be applied to DoD buildings.
- WEPA’s application of a 0.001 residential based attenuation factor to commercial buildings leads to groundwater vapor screening at 3,115 ug/m3 or 6.4 ug/l. We recommend a screening level 10x higher be applied to DoD and similar commercial/industrial buildings.
- We frequently turn to the decades of experience and research in the radon industry for a perspective on what to expect in chemical vapor intrusion studies. This review of the radon literature makes clear that radon VI is far from a simple process. So when we try to understand why commercial/industrial buildings behave differently from single family residences, we shouldn’t expect there to be a single answer!
- This graph shows the TCE Normalized Indoor Air Concentration (subslab to indoor air) vs. Sample Zone Area (both on log scales), it is after the source strength screen and screening out of atypical preferential pathways. While the data shows some scatter there was a statistically significant effect (p=0.009) although the r2 indicates that this single variable only explains about 8% of the total variation in indoor air concentrations. Note for comparison that the median US new single family house is around 2,100 sq ft (census bureau).
- EPA’s database of residences does not include many buildings where a release of contaminants occurred on the property. Rather it consists primarily of buildings at a considerable distance from the point of release. Our DoD database though does include many buildings at which the release occurred or immediately adjacent to it. We observe a very strong drop off in subslab concentration over the first 100 ft of distance from the point of release. This variable is one of the best single variables to explain vapor intrusion variability – explaining 37% in the variation of the subslab concentrations.
- PCE Indoor Air Concentration vs. Distance to Primary Release Log-Log Plot Baseline Screen + Source Strength Screen + Preferential Pathway=false
- In the residential cases, where the majority of VI is believed to be coming through groundwater fine soils have a weak protective effect (< 1 order of magnitude difference in the recommended 95% value). In the DoD buildings where the releases likely occurred close to the buildings the opposite effect is seen in both subslab and indoor air. The effect is quite significant.