Vapor Intrusion Concepts
Vapor Intrusion Concepts F Focus on Mitigation Miti ti Daniel B Carr P E P G Daniel B. Carr, P.E., P.G. Sanborn Head & Associates, Inc. Portland Maine, Westford Massachusetts
Environmental Business Council New England Site Remediation & Redevelopment Program Subslab Mitigation Systems for Vapor Intrusion
VI as a Pathway Pathway Requires: 1.
Source of VOC vapor
2 2.
Mechanism for sufficient Mechanism for sufficient transport from source to building space
3.
A receptor and an exposure point.
Primary Mechanisms
Phase Transfer
Advection‐ bulk flow Diffusion‐ mass transfer driven by a concentration gradient Partitioning‐ transfer from water to gas transfer from water to gas
Diffusion and Mass Flux 1.E+04 Model Simulation of VOC flux in response to groundwater cleanup p g p Mass Flux (ug/m m2‐day)
1.E+03
1 E+02 1.E+02 Mitigation Probably Necessary
C t J b De x
1.E+01 Some Probability That Mitigation is Necessary
1.E+00 Low Probability Mitigation Low Probability Mitigation
1.E‐01
Seasonal Moisture cycling effect
Advection: Structure as a Mixing Cell Qbld= exchange w ambient air 0.1s to 3/hr (AER) ~102 to 104 L/min
= Cindoor/Csoil ~ to Qsoil /Qbld.
Cindoor Air Mflux=Csubslab*Qsoil Qsoil ~ 0.1s to 10s L/min @40 L/min = 1.4 cfm or 2x10‐3 cfm/ft2
EBC Seminar, Burlington MA
Residential Buildings Indoor air exchange and pressure are not systematic Typically do not include engineered HVAC with outside makeup air. Air exchange and building pressure are nott predicable, di bl d depending di on thermal gradients, interior convection, wind effects, leakage, etc. etc We cannot easily quantify Qbld.
Mitigation by Substructure Depressurization
SSD Performance Metrics 10
1
Unit Ventilation Rate Unit Ventilation Rate
D 0.1
MADEP 8 to 10 Pa 0.01
Diffeerential ( Inchess H20)
Indoor Air to Substructure Differential Pressure Indoor Air to Substructure Differential Pressure
0.004”=1 Pa
350 structures mostly SFHs Uniform Design and d OC St Standard d d
UV VR (cfm/ /sf)
1.E+00
0.001 Unit Ventilation Rate (UVR)
1.E-01
1 E 02 1.E-02 @Qsoil
1.E-03
Post Mitigation Indoor Air Testing 1000.0
Indoor Airr Concentration ((μg/m3)
100 0 100.0
10 0 10.0
1.0
0.1 Pre-Ventilation Post-Ventilation Adjusted for Ambient Air
0.0
Property Address Sorted by Descending Concentration
SSD & Mass Flux Flux = rate of mass transfer per unit area
Flux= (Cairstream* Fan flow rate)/Building footprint= g/m2-day
In this case the area is the building footprint
Diffusion 10s to 1,000s g/m2-day
Mass Flux Rates Estimated From IA Statistics SFH and 1 ACH
Measured SSD Mass Flux Rate Apparent Ventilation Mass Flux Rate 2‐day) (g/m (g/m2‐day) (g/ y)
1.0E+06
1.3E+05
1.0E+05 1.0E+04
3.6E+04 2.3E+03 1.9E+03
1.0E+03 1 0E+02 1.0E+02 1.0E+01 1.0E+00 1.0E‐01 1.0E‐02 1.0E‐03
8.0E+03
7.7E+03
3.7E+03
6.4E+02
1.9E+03 440
1.1E+02
8.0E+01 1.2E+01 1.6E+01
RANGE OF FLUX WHERE SHUTDOWN MAY BE POSSIBLE RANGE OF FLUX WHERE SHUTDOWN IS PROBABLE
HVAC Basics • Fan: moves air, creates +/- pressure • Dampers: adjusts air flow through ducts • Coils: heat or cool air
Buildings with HVAC AHUs HVAC AHUs
Active Ventilation / Air Exchange Rate (AER) Q ft 3 1 60 min 1 3 AER hr V min ft 1 hr
Common default assumption for AER: 1/hr (ITRC, 2007); In practice AER, from 0.01s to 10s/hr;
Outdoor air design targets typically: 15 to 20 cfm per person, or 0.1 to 0.5 cfm/sq ft
Air Handling Unit Components • • • •
Sensors: measure air temperature, humidity, pressure VFD: variable frequency drive, adjusts fan speed, air flow, pressure Dampers: adjusts air flow through ducts VAV: variable air volume unit adjusts air flow to specific zones VAV: variable air volume unit adjusts air flow to specific zones
Case Example: 330,000 sf Manufacturing Space
•Known air flow and concentration=known mass cycle thru bld. mass cycle thru bld. •Near neutral dp. •Diffusion through soil and concrete. •Mass Flux 104 to 105 g/m2‐day
Mitigation thru Adjustments to HVAC AHU: Indoor PCE reduced consistent with increased AER Indoor PCE reduced consistent with increased AER HVAC Zone
AER Before HVAC Mods [hr-1]
AER After HVAC Mods [hr-1]
1
0.01
13
2
1.0
6.8
3
0.31
2.5
4
0.01
3.1
5
1.2
2.3
Expected Reduction Factor = 1 – (AERbefore / AERafter)
80
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01
% % PCE Red duction
Ma ass Flux g/m2-day
100
Before After
60 40
E Expected t d Actual
20 0 1
2
3
4
HVAC Zone
5
SSD Pilot Testing • Targeting subslab >105 μg/m3 and 105 ug/m2‐day • 80 cfm to depressurize 3,100 m2 >0.02 in H20 or 5 Pa • UVR of 10‐5 to 10‐7 cfm/sf • 2 lbs/hr mass removal ~7x106 μg/m2‐day if sustained.
Effective Sustainable Mitigation • Concept of mass flux useful in site characterization, mitigation engineering and post‐mitigation monitoring. – Advection vs diffusion control
• dp and UVR as performance metrics w limited post mitigation indoor air testing. • SSD flux monitoring. • B Buildings with HVAC AHU – ildi ith HVAC AHU knowledge of operating conditions and air flow k l d f ti diti d i fl patterns.
Questions? Sanborn Head Services: •Work Planning •VI VI Site Characterization Screening •Peer Review Soil Gas and VI Sampling Mitigation Engineering •Mitigation •Post Mitigation Monitoring
Daniel B. Carr, P.E. P.G. V ce es de t Vice President Sanborn, Head & Associates, Inc. 95 High Street, Portland Maine, 04101 207‐347‐4714 direct [email protected]
Environmental Business Council New England Site Remediation & Redevelopment Program Subslab Mitigation Systems for Vapor Intrusion
VI as a Pathway Pathway Requires: 1.
Source of VOC vapor
2 2.
Mechanism for sufficient Mechanism for sufficient transport from source to building space
3.
A receptor and an exposure point.
Primary Mechanisms
Phase Transfer
Advection‐ bulk flow Diffusion‐ mass transfer driven by a concentration gradient Partitioning‐ transfer from water to gas transfer from water to gas
Diffusion and Mass Flux 1.E+04 Model Simulation of VOC flux in response to groundwater cleanup p g p Mass Flux (ug/m m2‐day)
1.E+03
1 E+02 1.E+02 Mitigation Probably Necessary
C t J b De x
1.E+01 Some Probability That Mitigation is Necessary
1.E+00 Low Probability Mitigation Low Probability Mitigation
1.E‐01
Seasonal Moisture cycling effect
Advection: Structure as a Mixing Cell Qbld= exchange w ambient air 0.1s to 3/hr (AER) ~102 to 104 L/min
= Cindoor/Csoil ~ to Qsoil /Qbld.
Cindoor Air Mflux=Csubslab*Qsoil Qsoil ~ 0.1s to 10s L/min @40 L/min = 1.4 cfm or 2x10‐3 cfm/ft2
EBC Seminar, Burlington MA
Residential Buildings Indoor air exchange and pressure are not systematic Typically do not include engineered HVAC with outside makeup air. Air exchange and building pressure are nott predicable, di bl d depending di on thermal gradients, interior convection, wind effects, leakage, etc. etc We cannot easily quantify Qbld.
Mitigation by Substructure Depressurization
SSD Performance Metrics 10
1
Unit Ventilation Rate Unit Ventilation Rate
D 0.1
MADEP 8 to 10 Pa 0.01
Diffeerential ( Inchess H20)
Indoor Air to Substructure Differential Pressure Indoor Air to Substructure Differential Pressure
0.004”=1 Pa
350 structures mostly SFHs Uniform Design and d OC St Standard d d
UV VR (cfm/ /sf)
1.E+00
0.001 Unit Ventilation Rate (UVR)
1.E-01
1 E 02 1.E-02 @Qsoil
1.E-03
Post Mitigation Indoor Air Testing 1000.0
Indoor Airr Concentration ((μg/m3)
100 0 100.0
10 0 10.0
1.0
0.1 Pre-Ventilation Post-Ventilation Adjusted for Ambient Air
0.0
Property Address Sorted by Descending Concentration
SSD & Mass Flux Flux = rate of mass transfer per unit area
Flux= (Cairstream* Fan flow rate)/Building footprint= g/m2-day
In this case the area is the building footprint
Diffusion 10s to 1,000s g/m2-day
Mass Flux Rates Estimated From IA Statistics SFH and 1 ACH
Measured SSD Mass Flux Rate Apparent Ventilation Mass Flux Rate 2‐day) (g/m (g/m2‐day) (g/ y)
1.0E+06
1.3E+05
1.0E+05 1.0E+04
3.6E+04 2.3E+03 1.9E+03
1.0E+03 1 0E+02 1.0E+02 1.0E+01 1.0E+00 1.0E‐01 1.0E‐02 1.0E‐03
8.0E+03
7.7E+03
3.7E+03
6.4E+02
1.9E+03 440
1.1E+02
8.0E+01 1.2E+01 1.6E+01
RANGE OF FLUX WHERE SHUTDOWN MAY BE POSSIBLE RANGE OF FLUX WHERE SHUTDOWN IS PROBABLE
HVAC Basics • Fan: moves air, creates +/- pressure • Dampers: adjusts air flow through ducts • Coils: heat or cool air
Buildings with HVAC AHUs HVAC AHUs
Active Ventilation / Air Exchange Rate (AER) Q ft 3 1 60 min 1 3 AER hr V min ft 1 hr
Common default assumption for AER: 1/hr (ITRC, 2007); In practice AER, from 0.01s to 10s/hr;
Outdoor air design targets typically: 15 to 20 cfm per person, or 0.1 to 0.5 cfm/sq ft
Air Handling Unit Components • • • •
Sensors: measure air temperature, humidity, pressure VFD: variable frequency drive, adjusts fan speed, air flow, pressure Dampers: adjusts air flow through ducts VAV: variable air volume unit adjusts air flow to specific zones VAV: variable air volume unit adjusts air flow to specific zones
Case Example: 330,000 sf Manufacturing Space
•Known air flow and concentration=known mass cycle thru bld. mass cycle thru bld. •Near neutral dp. •Diffusion through soil and concrete. •Mass Flux 104 to 105 g/m2‐day
Mitigation thru Adjustments to HVAC AHU: Indoor PCE reduced consistent with increased AER Indoor PCE reduced consistent with increased AER HVAC Zone
AER Before HVAC Mods [hr-1]
AER After HVAC Mods [hr-1]
1
0.01
13
2
1.0
6.8
3
0.31
2.5
4
0.01
3.1
5
1.2
2.3
Expected Reduction Factor = 1 – (AERbefore / AERafter)
80
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01
% % PCE Red duction
Ma ass Flux g/m2-day
100
Before After
60 40
E Expected t d Actual
20 0 1
2
3
4
HVAC Zone
5
SSD Pilot Testing • Targeting subslab >105 μg/m3 and 105 ug/m2‐day • 80 cfm to depressurize 3,100 m2 >0.02 in H20 or 5 Pa • UVR of 10‐5 to 10‐7 cfm/sf • 2 lbs/hr mass removal ~7x106 μg/m2‐day if sustained.
Effective Sustainable Mitigation • Concept of mass flux useful in site characterization, mitigation engineering and post‐mitigation monitoring. – Advection vs diffusion control
• dp and UVR as performance metrics w limited post mitigation indoor air testing. • SSD flux monitoring. • B Buildings with HVAC AHU – ildi ith HVAC AHU knowledge of operating conditions and air flow k l d f ti diti d i fl patterns.
Questions? Sanborn Head Services: •Work Planning •VI VI Site Characterization Screening •Peer Review Soil Gas and VI Sampling Mitigation Engineering •Mitigation •Post Mitigation Monitoring
Daniel B. Carr, P.E. P.G. V ce es de t Vice President Sanborn, Head & Associates, Inc. 95 High Street, Portland Maine, 04101 207‐347‐4714 direct [email protected]
