Analysis of Vapor Intrusion Mitigation and Monitoring Options for Improved Stewardship 26th Annual International Conference on Soil, Water, Energy and Air March 21-26, 2016, San Diego, California, Dr. Ian Hers Dr. Parisa Jourabchi Golder Associates Ltd.

Objectives  

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Provide an overview of mitigation options for existing and future buildings Evaluate mitigation effectiveness based on a review of empirical data and modeling study and builds on Hers March 2015 presentation at US EPA San Diego workshop “Residential Building Lifecycle Cost Evaluation for natural and controlled conditions”  Develop a better understanding of performance and sustainability of different soil vapor intrusion mitigation methods  Improved framework for monitoring that is efficient and considers exceedance ratio concept Note: Findings presented are partly based on an in-progress study for the Ontario Ministry of Environment and Climate Change *

2 * Quantitative values in lessons learned and monitoring slides are preliminary values considered by authors and should not be viewed as agency recommendations

Mitigation Options - Existing Buildings  

Subslab depressurization (SSD) Soil vapor extraction 

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Can be effective approach for deeper vadose zones and coarse-grained soils

Building HVAC modifications  

Install Heat Recovery Ventilator (if exhaust only ventilation) Modify HVAC to positively pressurize building and/or increase ventilation rate 

Energy cost associated with heating/cooling outdoor air  Brings more moisture inside the building envelope (mold)

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Air purifying unit 

Not a permanent solution

Mitigation Options – Future Buildings 

Venting layer options 

Aerated subfloor (e.g., Cupolex)  Conventional sand & gravel layer 

Barrier options 

Spray-applied  Sheet membranes 

Venting options 

Active (fan or blower)  Passive (stack effect, wind turbine) March 16, 2016

Heat absorbing materials

4

Venting options

Aerated Floor - Cupolex

Not shown are drainage nets

Empirical Data Evaluation of Mitigation System Effectiveness   

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Forty one studies with empirical vapor mitigation data for chemical VOCs, radon and methane reviewed 22 studies were for residential houses, 15 studies for institutional, commercial and/or industrial buildings For majority of studies, active subslab depressurization mitigation method employed (64% for residential, 73% for institutional, commercial or industrial) Other methods include passive venting (defined to include wind turbines), pressurization (infrequent) and soil vapor extraction (infrequent) Mitigation for new buildings at brownfields limited to institutional, commercial or industrial land use

Active SSD Performance for Existing Buildings - Chemical Study

Building ***

Chemical

Performance*

Lund et al. (2015) – New Mexico

Commercial N=6

PCE

91% - >99% 11X - >100X

Eernisse et al. (2009) Utah

Houses N = 50

TCE

84% 6.2X

Folkes & Kurtz (2002) Colorado

Houses

1,1-DCE

2-3 orders of magnitude 100X - 1000X.**

Hannu (2010) - Finland

Houses

Radon

70% - 90% 3.3X – 10X

Paridaens et al. (2005) Belgium

Houses N=1

Radon

90% 10X

Jiránek (2014) – Czech Republic

Houses N = 62

Radon

70% - 98% 3.3X – 50X

Golder (unpublished)

Houses N = 26

TCE

80 - 99% (Avg = 94%) 5X – 100X (Avg = 26X)

* Reduction in indoor air concentrations; ** Sufficient reduction was achieved in 75% of houses with initial system, in 25% additional measures required to achieve action levels, *** - all buildings sand and gravel venting layer

Passive Venting Performance for Existing Buildings – Chemical Study Holford and Freeman (1996) – Washington

Building ** House N=1

Chemical

Performance*

Radon

30% 1.4X

Weiffenbach and Marshall Houses (2003) – Wisconsin N=8

Radon

25% - 87% 1.3X - 8X

Hannu (2010) – Finland

Houses

Radon

50% 2X

Warkentin and Johnson (2015) - Manitoba

Houses N = 50

Radon

47% 2X (just Dranjer drain installed)

Active venting more effective than passive venting, active KEY venting case studies reviewed generally showed at least 5X POINTS: reduction in post-mitigation concentrations * Reduction in indoor air concentrations, ** all buildings sand and gravel venting layer

Passive Venting Performance for Existing Buildings – Pressure and Flow Study

Building

Performance

Abdelouhab et al. House Winter: ∆P* < -1 Pa for 90% (2010 – France N=1 Summer: passive venting limited With/without wind turbine Wind-turbine improved performance 2X Weiffenbach and Houses Marshall (2003) – N = 8 Wisconsin No wind turbines

Subslab vents under negative pressure, but sumps positively pressurized, indicating poor pressure extension

Lutes et al. (2015) Houses – Indiana N = 2 (duplexes) No wind turbines

∆P > zero much of time, and as high as 3 to 5 Pa (soil gas flow is potentially into building)

Passive venting alone variable effectiveness, poorer performance KEY POINTS: potentially in summer (because reverse stack effect in vents); wind turbines and aerated floor can improve performance

* Differential pressure between subslab and indoor air

Commercial Slab-at-grade Building – Wind Turbine Test – Aerated Subfloor

Wind generated by leaf blower

1746 m2 building

Hers and Hood (2012)  55 km/hr “wind”; vacuum (V) = 37 Pa; vent stack air flow rate (Q) = 72 cfm; equal to 33 L/min-kmhr-wind (could normalize to area but difficult to determine area of influence)  Scaled to 12 km/hr, 11 wind turbines equal to one 150W fan!

2,000 1,800 1,600 1,400 1,200 1,000 800 600 400 200 0 0

10 20 Wind Speed (m/s)

30

Differential Pressure in Vent Pipe (Pa)

Flow Rate in Pipe (L/min)

Commercial Slab-at-grade Building – Wind Turbine Test – Gravel Venting Layer -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 0

10 20 Wind Speed (m/s)

30

Golder Associates 2015 Project (unpublished) (1,110 m2 building)  

Approximately 15 L/min-kmhr-wind Small flow likely due to stack effect (soil gas 1.5oC warmer than ambient air)

KEY POINTS: October 4, 2012

Wind turbine effect significant, recommend initially developing performance curves, subsequently simple 11 stack can be used for monitoring pressure measurement in

Passive Venting Performance for New Buildings – Pressure and Flow Study

Building

Performance

Reinis et al. Commercial, N = 28 Seasonal data: Vent air flow rate = 0.6-13.1 (2012) – Passive venting, barrier, scfm (mean 5.9 scfm), negative ∆P inferred, Oakland, CA wind turbines, gravel venting performance decreased with bed increasing ambient temperature Reinis et al. Commercial, N = 2 Seasonal data: vent air flow rate = 4.9-32 (2006) – Passive venting, barrier, scfm (mean 13 scfm), negative ∆P inferred, Oakland, CA wind turbines, gravel flow rate correlated to wind speed, but air flow bed measured even under calm conditions Golder (2015) Commercial, N = 2 Vent air flow rate = 1.2 cfm at v = 1.4 m/s, - unpublished Passive venting, barrier, pressure = - 0.026 in H20 in vent stack, temperature stack ~ 3oC > ambient wind turbines, gravel

KEY POINTS:

Both convection from stack effect and wind turbine important mechanisms for passive venting; positive airflows out of vent stacks were measured

* Subslab air change rate ~ 1 per day, all buildings sand and gravel venting layer, Negative ∆P means air flow out of vents

Active Venting Performance for New Buildings – Pressure and Flow Building Type

Reference 1. Folkes et al. (2006) 2. Al-Ahmady & Hintenlang (‘96) 3. Jourabchi et al. (2015) 4. Hers & Hood (2012) 5. Hers & Hood (2012) 6. Hers & Hood (2012)

Rec centre w\ basement Commercial building ** Commercial building ** Commercial building ** Commercial building ** Commercial building **

7. Folkes (2011)

Commercial building **

Measured Air Flow Rate

(m2)

Venting Layer Void Volume (m3)

(m3/min)

Venting Air Change Rate (hr-1)

1858

99.1

10.8

6.6

773

41.2

3.96

5.8

899

63

5.66

5.4

Aerated Floor Aerated Floor Aerated Floor

4 blowers (X HP) Single fan (0.1 HP) 1 blower (1.5 HP) 2 fans (0.2HP ea) 1 fan (0.2 HP) 1 fan (0.2 HP)

8880

1332

50

1.8

1750

262

16

2.9

2200

329

26

3.8

Aerated Floor

1 fan (0.03 HP)

400

75

4.6

3.7

Venting Material Gravel Gravel Gravel

Mitigation System

Building Footprint Area

More consistent negative pressures and higher air flows with active systems, KEY POINTS: with higher air flows in aerated floors than gravel systems, resulting in lower sub-slab vapor concentrations all else being equal, at lower energy cost.

•

Venting layer thickness is 0.15 m for 1 and 2, 0.2 m for 3 to 6 (assume Cupolex porosity of 0.75). ** slab-at-grade foundation

SSD Performance Endicott Site (courtesy Bill Wertz) Key is negative pressure extension below slab (6-9 Pa referenced in ASTM E2121-02 standard)

Sunquist et al. 2007 also indicate reduced efficiency in winter. “SSD System Performance Evaluation”, 3rd Conf. VI, AWMA, Rhode Is.

Golder Modified J&E Model – Case Study to Evaluate Venting Performance Modified Johnson and Ettinger Model Features

Conceptual Site Model

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Sub-building garage

slab on grade

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Benchmarked to the US EPA Superfund J & E Model

March 16, 2016

15

Soil gas diffusion through multiple (up to 5) soil layers Diffusion through bulk concrete Diffusion through geomembrane 𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒 = 𝐷𝐷𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 + 𝐷𝐷𝑎𝑎𝑎𝑎𝑎𝑎 𝑅𝑅𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑡𝑡

Sub-building ventilated layer:  Parking garage  Crawl-space  Aerated floor or gravel layer

𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑜𝑜𝑜𝑜 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎

Baseline Model Inputs - Small Commercial Building J&E Parameters Parameter

Venting Layer Baseline

Unit

Value

Building width

(m)

20

Air change rate1

Building length

(m)

15

Foundation thickness

(-)

0.11

(mm)

1

(-)

2.3E-04

Air change rate

(hr-1)

1

Building height

(m)

3.0

Thickness of barrier

Distance building to vapor source

(m)

0.3

Permeation Coefficient2 (m2/s) 2E-12

Air-filled porosity

(-)

0.39

Total porosity (gravel)

(-)

0.40

Crack width Foundation crack ratio

Parameter

Unit

Value

(hr-1)

1

Thickness

(m)

0.3

Air-filled porosity

(-)

0.39

Total porosity (gravel)

(-)

0.40

Barrier Layer Baseline Parameter

Defect (“crack”) Ratio3

Soil gas advection rate L/min (Qsoil)

9.8

1

Unit

Value

(mm)

1.5

(-)

7.5E-08

Conservative estimate based on empirical data; 2 Based on published values for 60 mil Liquid Boot, 60 mil GeoSeal, 80 mil HDPE (McWatters & Rowe, 2010); 3 Based on landfill studies

Modeling Study Results – Passive Venting, Geombrane Barrier 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06

Poorer performance

2

507

461

Better performance

11 AF RF

No mitigation: 6.1E-04

4.9/0

0.8/0

0/0

0/0.5

Qsoil (∆P) and Vent Layer Air Change Varied

AF = attenuation factor RF = No mitigation AF / mitigation AF

Qsoil (L/min) / Vent ACH

Passive venting performance variable, depends mostly on

KEY POINT: whether Qsoil = 0, therefore venting efficiency and barrier quality control is important, barrier diffusion properties not as important

Modeling Study Results – Active Venting, No Barrier 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07

KEY POINT:

507

930

5159

AF

Vent Layer Air Change Varied (Qsoil = 0)

RF

0.1

1.0

10

Vent Layer ACH

Approximate three orders of magnitude reduction in attenuation factor for conservative venting rate (1 hr-1)

Modeling Study Results – Active Venting, No Barrier 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08

93

930

9300

AF

Crack Ratio Varied (Vent ACH = 1 hr-1)

RF

2.3E-3

2.3E-4

2.3E-5

Crack Ratio KEY Crack ratio is sensitive parameter therefore important to POINT: seal foundation

Mitigation System Design and Performance 

Factors influencing design and performance  Type of system (active vs passive) – potentially achieve greater reduction in VI for active than passive system  Exceedance Ratio - Measured or predicted indoor air concentration / acceptable concentration  Existing or future building – greater reductions possible for engineered systems for future buildings  Chronic vs acute (developmental toxicant) concern  Season for passive venting (but performance generally indicated to be favorable)  Preferential pathways (if not controlled)

Mitigation System Monitoring 

Physical Measurements (both active and passive systems) 

Vacuum in vent pipe and monitoring port – sensitive transducers available  Stack flow rate using anemometer  Pressure field extension (PFE)  Pressure differential switch and modem call-out or telemetry 

Chemical measurements 

Design program to address potential background sources of chemicals  Avoid use of glue for sampling ports and piping  Avoid sampling after painting & installation of new building furnishings

Lessons Learned and Optimization Passive Venting

 

Pressure gradients/flow variable  Convection important, wind turbines help  Modeling suggests barrier provides some reduction in VI but ∆P key  Optimization  Aerated floor or very high K gravel  Sufficient risers (1 per 200-400 m2)  Riser Dia > lateral Dia (depending on # of laterals connected to riser)  Include wind turbines to improve efficiency

Active Venting

 

Pressure gradients can be controlled, minimal ∆P required  Barrier may not be warranted but sealing building envelope is important (conduct smoke tests)  Optimization  Aerated floor (added benefit dilution)  Riser design depend on venting layer & foundation (grade beams)  Small fan often sufficient  Air entry pipes to minimize shortcircuiting and losses

Both active and passive vent acceptable; active systems can be KEY reliably engineered to achieve reductions – Use civil engineering POINTS: design tools for this purpose.

Monitoring Framework Study

Building

Exceedance Ratio

Existing Building

Active Venting - Low SSD High

A

Future Building

Active Venting – Low Barrier Optional High

>B C