Soil Vapor Intrusion Training
g In
The New Economy*
Bill Wertz
Robert Ettinger
NYSDEC
Geosyntec
Consultants
*John Fitzgerald was supposed to do this, but
plans were impacted
p
by
y the New Economy
y
his p
NYSDEC
What is Soil Vapor Intrusion?
ntrusion?
Components of Soil Vapor Intrusion : 4 P’s
People
Pressure
Pathway
Pollutant
Pollutant
Paradigm Shift – What is a “Source
Source Area”
Area
At some sites,
it 5-10
5 10 ppbb VOCs
VOC
could be a problem.
Pathway
y
Soil Vapor Migration Pathway May Be Complex
Perched water table
Regional water table
graphic provided by Dominic DiGiulio, Ph.D.
Office of Research and Development
National Risk Management Research Laboratory, Ada, Oklahoma
Pressure
Pressure Gradients Change Through Time
p Pressure Gradients are the
d i i fforce
driving

Induced by:






convection (temp difference in winter)
mechanical equipment (clothes dryers, exhaust)
heating
eat g appliances
app a ces (combustion
(co b st o air)
a )
air handlers and return air ductwork (furnaces)
fireplace (combustion air)
weather - barometric pressure changes, wind, rain
14
H-005 Building Pressure Differential vs Temperature
0 0100
0.0100
80 00
80.00
Pressure Differentiall In H2O
P
70.00
60.00
Temperature F
0.0050
50 00
50.00
0.0000
40.00
30.00
-0.0050
0.0050
20.00
10.00
-0.0100
Avg Pressure
Differential
15
0.00
People
From Schuver USEPA
Vapor
p Intrusion Modeling
g
Models are used for vapor intrusion evaluation,
but there are a range of opinions about their use
Models underestimate risk
 Models overestimate risk
 Models
M d l h
have lilimited
it d applicability
li bilit Can they evaluate range of conditions?
 Sub
Sub--slab samples
p
 Crawl space construction
 NAPL sources
 Biodegradation
 Models are only as good as the inputs used
(GIGO)
Th
These
uncertainties
t i ti have
h
led
l d to
t frequent
f
t
suggestions to simply monitor indoor air

18
Modeling
g vs Monitoring
g



Indoor air sampling may be impractical due to
background effects
Models can aid in the determination of corrective
action strategies and/or remediation objectives
Risk evaluation for potential exposure scenarios
can be add
ca
addressed
essed with
t modeling
ode g
(key consideration for brownfields sites)
• Some combination of data collection and
modeling is usually appropriate
• Need to confirm quality of model inputs and
measured results before assessing whether
the model is providing representative results
19
Vapor Intrusion Models
There are more options than the Johnson and Ettinger Model
Empirical
USEPA Database
Analytical
Numerical
Johnson and Ettinger (1991)
VAPOURT (1989)
Little et al. (1991)
Sleep & Sykes (1989)
San Diego SAM
RUNSAT (1997)
VOLASOIL
VO
SO (1996)
( 996)
Abreu
b eu & Jo
Johnson
so (2005)
( 005)
Krylov and Ferguson (1998)
VIM (2007)
DLM - Johnson et al. (1999)
Brown University (2007)
BioVapor (2010)
Model selection is dependent
p
on what yyou know
about the site and the level of desired assessment
20
USEPA Empirical Attenuation Factors
21
USEPA Empirical Attenuation Factors
Empirical Attenuation Factors
Source
Median
95%ile
Crawl Space
p
0.5 – 0.7
NR
Sub-Slab Soil Gas
0.005
0.1
S il G
Soil
Gas
0 01
0.01
03
0.3
0.0001
0.001
Groundwater

Many regulators are focusing on 95%ile values

B careful
Be
f l if simply
i l using
i empirical
i i l factors
f
22
Baseline Vapor Intrusion Model
(Johnson and Ettinger,
Ettinger 1991)
Mixing in Breathing Zone
Convective Transport into Building
VOCs
OC
Diffusive Transport
Source




Partitioning
Simplified screening model
Assumes 11-D, steady
steady--state transport
(i.e., source beneath building)
Background and biodegradation effects neglected
User inputs soil and building properties
23
Baseline Vapor Intrusion Model
US EPA VAPOR INTRUSION ASSESSMENT MODEL (VIA_MODEL.xls)


USEPA spreadsheets
available for typical model
application
li ti
 Input: generic soil and
building properties
 Output: alpha and risk
 Frequently used as black
box
USEPA spreadsheets to be
updated soon
Site Name:
Note: Cells with borders indicate parameters that may be changed by the user.
Parameter
Units
Symbol
Value
Source
Groundwater
(ug/L)
Cmedium
100
(m)
Ls
3.00
Default
Source Characteristics:
Source medium
Groundwater concentration
Depth below grade to water table
Average groundwater temperature
Calc: Source vapor concentration
o
( C)
Ts
15
(ug/m3)
Cs
44484
Chem
Tetrachloroethylene
15
Chemical:
Chemical Name
CAS No.
CAS
127184
(ug/m )
3 -1
URF
5.90E-06
5.90E-06
3
RfC
6.00E+02
6.00E+02
Toxicity Factors
Unit risk factor
Reference concentration
(ug/m )
Building Characteristics:
Building setting
Bldg_Setting
Residential
Residential
Found_Type
Basement w/ slab
Basement w/ slab
Lb
2.00
2.00
(m)
Lf
0.10
0.10
1.00E-03
Foundation type
Depth below grade to base of foundation
(m)
Foundation thickness
Fraction of foundation area with cracks
Enclosed space floor area
Enclosed space mixing height
Indoor air exchange rate
Qsoil/Qbuilding
(-)
eta
1.00E-03
(m2)
Ab
150
150
(m)
Hb
3.66
3.66
ach
(-)
Qsoil_Qb
0.020
0.020
Qb
274.50
274.50
Qsoil
5.49
5.49
SCS_A
Sand
Calc: Average vapor flow rate into building
(m3/hr)
0.50
0.50
(1/hr)
(m3/hr)
Calc: Building ventilation rate
Vadose zone characteristics:
Stratum A (Top of soil profile):
Stratum A SCS soil type
Stratum A thickness (from surface)
(m)
hSA
3.00
Stratum A total porosity
(-)
nSA
0.375
0.375
Stratum A water-filled porosity
(-)
nwSA
0.054
0.054
rhoSA
1 660
1.660
1 660
1.660
SCS_B
Not Present
Stratum A bulk density
3
(g/cm )
Stratum B (Soil layer below Stratum A):
Stratum B SCS soil type
Stratum B thickness
(m)
hSB
Stratum B total porosity
(-)
nSB
Stratum B water-filled porosity
(-)
nwSB
Stratum B bulk density
3
(g/cm )
rhoSB
Statum C (Soil layer below Stratum B):
Stratum C SCS soil type
Stratum C thickness
Stratum C total porosity
Stratum C water-filled porosity
Stratum C bulk density
SCS_C
(m)
hSC
(-)
nSC
(-)
Not Present
nwSC
3
(g/cm )
rhoSC
Stratum directly above the water table
Stratum A, B, or C
src_soil
Stratum A
(m)
hcz
0.170
0.170
Capillary zone total porosity
(-)
ncz
0.375
0.375
Capillary zone water filled porosity
(-)
nwcz
0.253
0.253
(-)
Target_CR
1.00E-06
1.00E-06
(-)
Target_HQ
Height of capillary fringe
Exposure Parameters:
Target risk for carcinogens
Target hazard quotient for non-carcinog
1
1
Scenario
Residential
Residential
(yrs)
ATc
70
70
(yrs)
ATnc
Exposure Scenario
Averaging time for carcinogens
Averaging time for non-carcinogens
Exposure duration
Exposure frequency
Exposure time
24
30
30
(yrs)
ED
30
30
(days/yr)
EF
350
350
(hrs/24 hrs)
ET
24
24
Flag
Comment
Baseline Vapor
p Intrusion Model
Typical sitesite-specific
considerations:
id ti
 Source concentration
 Soil porosity
 Soil moisture content
 Capillary fringe
parameters
t
 Building ventilation rate
Calculated Water Distribution in Soils
Default water content (cm3/cm3)
1000
Sand
Sandy Loam
Loamy Sand
Loam
Silty Clay
900
Height abo
ove water table (c
cm)

800
700
600
500
400
300
200
100
0
0
0.05
0.1
0.15
0.2
0.25
0.3
3
0.35
3
Water content (cm /cm )
Site-specific inputs may be different from
defaults, but proper justification is needed
25
0.4
0.45
0.5
Baseline Vapor Intrusion Model
Soil Gas Profile Modeling
Vapor
p Migration
g
Modeling
g
• Utilize
• Soil lithology,
• Concentration
measurements, and
• Modeling
• Demonstrate understanding
p
of subsub-surface transport
Soil Profile
0
10
Deptth (ft bgs)
20
30
40
50
60
70
80
1.E-03
1.E-02
1.E-01
Scaled Concentration
26
1.E+00
Biodegradation Model
(Johnson et al.,
(Johnson,
al 1999)
Mi i in
Mixing
i Breathing
B
thi
Zone
Z
Convective Transport into Building
Biodegradation Zone (Dominant Layer)
VOCs
Source



Diff i Transport
Diffusive
T
t
Partitioning
Similar to baseline model
Applicable for petroleum hydrocarbon sites
Limited availability
27
Biodegradation Model
Example
p Application
pp
Cluster 2
Benzene Detects
Benzene ND
DLM
1.E-05
1.E-04
PCE Detects
PCE NDs
JEM
0
10
Depth (ft)
D
20
30
40
50
t1/2 = 2.8 d
lambda = 0.25 day-1
DLM = 1-10 ft bgs
PCE Cgw = 0.79 ppb
Benzene Cgw = 52500 ppb
60
1.E-08
1.E-07
1.E-06
1.E-03
1.E-02
Dimensionless Concentration (C/Csource)
28
1.E-01
1.E+00
Lithology
BioVapor Model (API, 2010)
API Disclaimer: “The model is not expected to provide highly accurate predictions when a single set
of input parameter values is used to represent a single site.
site Rather,
Rather the model is expected to help the
user identify a reasonable range of potential outcomes that result from varying key input parameter
values to account for the uncertainty and variability associated with site conditions.”
29
Three-Dimensional Numerical Model
(Ab
(Abreu
and
d Johnson,
J h
2005)
200 )
D e p tth b g s (m )
0
-2
-4
-6
-8
0
10
20
30
40
50
60
70
80
90
100
x (m)
The “next
next generation”
generation for simulations
Provides many additional capabilities
30
Effect of Biodegradation on Attenuation Factors
1.E-02 Dissolved phase
NAPL
• Biodegradation is likely to
have a significant effect on
a for non-NAPL sources
• This effect is more
pronounced for deeper
sources
• For NAPL sources, effect
of biodegradation on a
may be minimal due to
oxygen depletion
A
Attenuation
n Factor
1E-03
1.E03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09
1.E-10
1E10
0.1
1
10
100
1000
Vapor Source Concentration (mg/L)
L = 1 m, λ = 0.79 (1/h)
L = 3 m, λ = 0.79 (1/h)
L = 10 m, λ = 0.79 (1/h)
L = 10 m, No Biodegradation
L = 2 mbgs, λ = 0.79 (1/h)
L = 5 m, λ = 0.79 (1/h)
L = 1 m, No Biodegradation
L: source-foundation distance
31
Modeling Assumptions:
Benzene source
Sand soil
Basement scenario
 = 0.79 h-1
Summary

Modeling provides an additional line of evidence for
evaluation
l ti off the
th vapor intrusion
i t i pathway
th

Exercise care in application of models


Confirm model is appropriate for site conditions

Verify model inputs
Vapor intrusion modeling can assist in:

Understanding the vapor intrusion pathway

Planning investigation and corrective action strategies

Simulate future conditions (i.e., redevelopment
scenarios)
32
VI Assessment Strategies
Action
Resources
Risk
Conceptual
Knowledge
Site Model
VI Evaluation Is An Iterative Process
Uncertainty
Uncertainty
Site Conceptual
Model
Uncertaint
Uncertainty
Site Conceptual Model
Data Collection
Data Collection
Site Conceptual Model
p
VI Decision
VI Decision
VI Decision
Sampling Round 1
Sampling Round 2
Sampling Round 3
There Will Always Be Uncertainty
As Perceived Risk
Allowable Uncertainty ↓
VI Evaluation
V
va uat o GOAL
GO
Determine the Nature and Extent of Contaminant “Source”
Determine The Extent of Potentially Impacted Structures
Take Necessaryy Actions to Address Exposures
p
(Short--Term)
(Short
Take Necessary Actions to Reduce Source of Contamination
(Long--Term)
(Long

Reducee Unceertaintty
R
Efficiently & Effectively
Identify & Address Impacted Structures
Typical VI Evaluation Process
Safety / Acute
Risk Screening
Immediate
Action?
Yes
No
No
Initial Screening
Confirmation
Sampling
?
N
No
Exceed
RBSLs?
Sufficient
Data?
Site-Specific
p
Assessment
Yes
No
Monitor
?
STOP
Risk
Exceedance?
Yes
Mitigation
Typical VI Investigation

Sites typically fall into 4 categories:
No Brainer
No problem
Mitigate
Not Sure
Collect data
Mitigate
or Monitor
An improved evaluation process should decrease
the uncertainty in the37 selected corrective action
Stack Effect (IA/SS Pressure Differential) Influenced
by
Temperature Differences
Furnace & Other Combustion Devices
Air Leakage
Wind Load
Advective Mass Flux Influenced by
Pressure Differential
Subslab Source Strength
Nature & Distribution of Flow Pathways
IA/SS Mixing
IA/SS Mixing
Source Concentration at Top of
Capillary Fringe Influenced by
Groundwater VOC Source Strength
Grain Size and Effective Porosity
(Height of Capillary Fringe)
Adsorbtion‐Desorbtion
Infiltration
Capillary Zone
From ITRC (Figure 2.1, 2007)
A
Attenuaation
Background Sources
Biodegradation
Non‐Chlorinated VOCs
Diffusive Mass Flux Influenced by
VOC Source Strength
Grain Size and Effective Porosity
Moisture Content
Adsorbtion‐Desorbtion
Identify the Nature and Extent of
C
Contaminant
i
S
Source

Look at Historical Data

C ll G
Collect
Groundwater
d
G
Grab
b SSamples
l and
d IInstallll
Groundwater Wells


What Is The Necessary Data Density ?
Identify Structures With Potential VI Impacts
Model - Sample Soil Gas? - Sample Structures
[Less
ess Certain
Ce ta ---------- More
o e Certain]
Certain
Ce ta ]
Look at Historical Data
Soil Source vs Groundwater Source
(B h?)
(Both?)
Chlorinated vs NonNon-chlorinated
Compounds
DNAPL or LNAPL Present
Geologic Setting
Population Setting
Quality of The Information?
Some Broad Generalizations
Soil Source Site (No Groundwater Impacts)
Focus on Vadose Zone Transport:
Diff i
Diffusion
Advective Flow (Near Buildings)
Preferential Pathways
Modeling - Soil Gas - Structure Samples
Some Broad Generalizations
Non-Chlorinated Groundwater Source
(Including LNAPL & Smear Zone)
Establish
E
t bli h N
Nature
t
and
dE
Extent
t t off G
Groundwater
d t
Contamination (at the Water Table)
Is it necessary to Find the edge of the plume?
Focus on Vadose
F
V d
Zone
Z
Transport:
T
Biodegradation – Vadose Zone Stratigraphic Profiling
Methane ppmv
Benzene
Benzene ug/m3
CO2 %
O2 %
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
No Substantial Biodegradation
Monitoring
1S - 1D
MP­1 (2008)
( g Points
)
Concentration
BGS
Methane
2.5
7.5
165000
204000
Benzene
57300
405000
Co2
O2
19.4
0.3
20
1.1
25
2
20
2
15
1
10
1
5
0
500000
400000
300000
200000
100000
0
30000
00
20000
00
10000
00
Depth BGS
0
10.0
Methane ppmv
Benzene ug/m3
CO2 %
O2 %
0.0
1.0
2.0
3.0
4.0
5.0
60
6.0
7.0
8.0
9.0
Substantial Biodegradation
Monitoring
Points 10S - 10D
MP-10 (2008)
BGS
Methane
Benzene
Co2
O2
2680
1630
3.8
19.6
98100
338000
20
0.2
2.5
7.5
25
20
15
10
5
0
40
00000
30
00000
20
00000
10
00000
0
200000
100000
0
10.0
Methane ppmv
Benzene ug/m3
CO2 %
O2 %
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
MP­2
BGS
Methane
2.5
7.5
Monitoring
Points
Benzene
Co2 2S - 2DO2
5
1.6
31800
91000
20.7
15.8
0.20
0
?
25
5
20
0
15
5
10
0
5
0
100000
0
0
0
100000
0
10.0
Structure Sampling
O2 Fosters Biodegradation
Results of Greenpoint Structure Sampling for Benzene
Benzene
Ambient
First Floor
B
Basement
t
14
Subslab
12
ug/m3
10
8
6
4
2
0
Sample ID
R l off S
Results
Structure S
Sampling
li ffor m,p -Xylene
X l
m,p-Xylene
Ambient
70
First Floor
60
Subslab
Basement
ug/m3
50
40
30
20
10
0
Sample ID
At Petroleum Sites Environmental Data
(Groundwater and Soil Gas Profiles) May Often
Be Sufficient For Making Good VI Decisions
Some
So e Broad
oad Ge
Generalizations
e a at o s
Chlorinated Groundwater Source
Establish Nature and Extent of
Groundwater Contamination ((at the
Water Table)
Is it necessary to Find the edge of the
plume?
Soil Gas vs. Subslab Data
Identify the Nature and Extent of
Contaminant Source
Groundwater Data Collected
September 2007-December 2007
From 125 Water Table Grabs &
43 Wells
Natural Neighbor Interpolation
Identify Structures With Potential VI
Impacts
Previously Sampled
113
Identify Structures With Potential VI
Impacts
Natural Neighbor
g
Interpolation
“Test” Conceptual Model
Area of Subslab Impacts
Mirrors
Area of Groundwater Impacts
But
Not All Structures Above The Plume Are
Impacted
I
d
One Possible
O
P ibl Approach
A
h
“Blanket” Mitigate Structures Above Hot Spots
Increase Sampling Density in “Uncertain”
Uncertain Areas
The Patchy Fog Conceptual Model
When Designing A Structure Sampling Plan
You Need To Recognize That There May Be
A Considerable Range in Subslab
Concentrations Between and Beneath
Structures In A Given Area!
Legend
OA = Outdoor Air
BA= Basement
SSA = Subslab A
SSB = Subslab B
SSC = Subslab C
November 2006April 2007
Structure Sampling
Results
TCE Structure Sampling Results
Indoor Air Sampling and Addressing
Background Sources


Indoor air sampling may seem to be a direct
assessment approach,
h b
but iis typically
i ll conducted
d
d
during higher tier of investigation
Several challenges to indoor air sampling
 Occupant
disruption
 Temporal and spatial variability
 Background
g
effects
 Discovery of data

May be more practical to collect indoor
air samples in occupational setting
61
Indoor Air Background

Definition


Concentrations of chemicals found in indoor
air that are not due to subsurface impacts
f
from
a release.
l
Background Sources




Ambient Air
Building Materials
Household Activities
Consumer Products
62
Indoor Air Sources
Paints
Glues/Adhesives
Gasoline Powered
Equipment
i
Dry Cleaning
Expect detections of VOCs in any indoor air sample
63
Tobacco Smoke
Cleaners/
Solvents
Chemicals in Household Products

NIH Household Products Database
 http://householdproducts.nlm.nih.gov/index.htm
64
Ratio of Indoor to Outdoor Concentrations
From USEPA BASE study Minimum, maximum, 5, 25, 50, 75, 95th percentiles
From: Girman, J. Air Toxics Exposure in Indoor Environments, EPA Workshop on Air Toxics
Exposure Assessment, 2002. http://www.epa.gov/osp/regions/airtox.htm
65
Background and
Target Indoor Air Concentrations
USEPA, 2008
66
Resolving Background Contributions

Comparison to Literature Values

T
Tracer
compounds
d

Mitigation System Evaluation
67
Example Background Indoor Air
Concentrations
Consider background range as well68as typical values
Background Concentration of 1,21,2-DCA
DETECTION FREQUENCY
1.0
1,2-DCA C
Concentratiion
(ug/m3)
100%
1,2-DC
CA Detection
Freq
quency (%))
CONCENTRATION
90%
80%
70%
60%
50%
40%
30%
20%
10%
2004
2005
2006
2007
2008
90%ile 1
1,2-DCA
2 DCA Conc.
Conc
0.8
0.7
0.6
0.5
0.4
USEPA INDOOR AIR LIMIT
0.3
0.2
0.1
0.0
0%
Median 1,2-DCA Conc.
0.9
<0.08
2004
<0.08
2005
1,2 DCA Background Source:
Detailed study identified molded plastic ornaments
manufactured in China as source for 1,2 DCA.
Note: 1) 1,2-DCA = 1,2-dichloroethane
From McHugh et al., 2009. Also see Doucette et al., GWMR, 2010
<0.08
2006
2007
2008
Attenuation Factors for Single Building
Biased by Background Sources
Note number of
compounds with
attenuation
factor > 1
Variability in
attenuation
factors due to
background
effects or
analytical
limitations
From USEPA, 2006. Assessment of Vapor Intrusion in Homes Near the Raymark
Superfund Site Using Basement and SubSub-Slab Air Samples.
70
Attenuation Factors for Single Building
Potentially biased by
background sources
From USEPA, 2006. Assessment of Vapor Intrusion in Homes Near the Raymark
Superfund Site Using Basement and SubSub-Slab Air Samples.
71
Biased by
Background
Sources
Evaluation of Engineering Controls: Colorado Redfield Study
From: Folkes, D.: Vapor Intrusion Assessment and Mitigation - Practical
Issues and Lessons Learned, EPA Office of Solid Waste RCRA Corrective
72
Action EI Forum, August 15-17, 2000
Summary


Chemicals from occupant activities and/or building
construction
t ti will
ill result
lt iin d
detection
t ti d
during
i iindoor
d
air
i sampling
li
Background sources make evaluation of vapor intrusion
pathway more difficult






Source determination
Risk management
Pathway modeling
Assessment of engineering controls
Background sources must be considered when collecting
indoor air samples
Communication of background issues with building
occupants is key
73
Data Interpretation
More to Come Tomorrow
NYSDEC
Vapor Intrusion Mitigation

Active Remediation

Institutional Controls

Engineering
g ee g Controls
Co t o s
o
“Radon System” (Sub-slab Depressurization)
o
Passive Vapor Barrier
o
HVAC System Modifications
o
I d
Indoor
Air
Ai Filtration
Fil i
o
Intrinsically Safe Building Design
75
Mitigation System Considerations

Effectiveness


O&M Requirements



SSystem O&M
O M
Performance monitoring
C
Cost


Mi i i systems are not typically
Mitigation
i ll 100% effective
ff i
Installation costs may be much less than monitoring
costs
Impact on Occupants


A th ti
Aesthetics
Costs
76
Sub--Slab Depressurization
Sub
77
Sub--Slab Depressurization
Sub
Can be designed for large buildings
78
Active Systems for New Buildings
79
Sub--Slab Depressurization
Sub
Initial Performance Verification
 Sub
Sub--slab vacuum confirmation
 Confirm vacuum on vent pipe
and/or crosscross-slab vacuum
 Indoor air sampling
Long--Term Performance
Long
Monitoring
 Monitor vacuum on vent
pipe and/or crosscross-slab
vacuum
80
DCE Conc
D
centration (ug/m3)
Sub--Slab Depressurization
Sub
100
10
Action Level
1
0.1
0.01
-300
-100
100
300
Days After System Installation
Redfields Site - Source:
So rce: Folkes
Folkes, 2002
Common to achieve 90 – 99+% reduction
81
500
Sub--Slab Depressurization
Sub
Disadvantages
Advantages



Effective for most
building types
>90% concentration
reductions possible
Performance monitoring
can be nonnon-chemical
(vacuum measurements,
electrical consumption
records)






82
LLong-term
Longt
O&M
May not work in wet
soil conditions (shallow
water table)
Suction pit and riser
pipe need to be located
inside building
Aesthetics / Noise
M require
May
eq i e sealing
e ling
floors & walls
May require air permit
Passive Vapor Barrier
83
Passive Vapor Barrier
Concrete Floor Slab
Sand
Geomembrane
Gravel
PVC Pipe w. holes
Sub--slab base
Sub
84
Roof Top Turbines
This system sucks, and
that’s exactlyy what
w we
w
wanted it to do
86
Passive Vapor Barrier
Advantages



Disadvantages
Applicable to new or
existing buildings

Minimal O&M due to
no moving parts

Convertible to active
if required to meet
objectives
87
Possible diffusion
through barrier
Stakeholder
confidence
HVAC System
y
Modification
Increased fresh air intake &
positive pressurization
Confirmed P of 0.01 to 0.08 in-H2O
88
Evaluation of Engineering Controls: Building Pressurization
Trichloroethene
1000
Calculated from Soil Pre-Mitigation Indoor
Gas
Air
Outdoor Air
maximum
75th
median
25th
minimum
100
TCE Conc
centration (
g/m3)
Post-Mitigation
Indoor Air
10
1
0.1
0.01
TCE
0.001
89
Evaluation of Engineering Controls: Building Pressurization
Benzene
Benzen
ne Concentra
ation (g/m3)
10
Calculated from
Soil Gas
Pre-Mitigation
Indoor Air
Outdoor Air
Post-Mitigation
Indoor Air
maximum
75th
median
25th
minimum
1
0.1
0.01
0.001
Benzene
90
HVAC Modification
Disadvantages
Advantages




Effective, especially
for large
commercial or
industrial buildings


Applies to new or
existing buildings

Rapid to implement
May already be
happening…
91
Generally more costly
than other approaches in
hot or cold climates
Control - Settings may be
modified by occupant
Not commonly an option
for single family
residences
Indoor Air Filtration
Typical Residential Unit
• Size of a shop vac
•
22 lbs. carbon
•
Effective up
p to 1500 sq.
q ft.
•
3-speed 400 cfm fan, runs
whisper
p q
quiet
•
Electricity = 60 watt light bulb
92
Indoor Air Filtration
Advantages



Disadvantages
Applicable to new or
existing buildings

Quick & easy to
install in residences

Improves air quality
in general (including
background)

93
Not effective in “high
VOC background”
scenarios (e.g., smoker)
Spent carbon waste
stream
Rely on building occupant
to operate

Aesthetics

Costly O&M
Intrinsicallyy Safe Building
d g Design
g
94
Intrinsicallyy Safe Building
d g Design
g
95
Mitigation Technologies
Technology
Pros
Cons
Applications
P i Barrier
Passive
B i
Often simple
Oft
i l addition
dditi
to construction
activities
Limited
Li
it d data
d t on long-term
l
t
effectiveness
N Construction
New
C t ti
Passive Venting
Low O&M cost
Upgradeable to SSD
Limited effectiveness
Lower
concentration areas
Sub-Slab
Depressurization
p
Proven technology
Wide acceptance
p
Higher capital cost
Air p
permittingg needs
variable
Similar to Rn
systems.
y
Proven
effectiveness.
HVAC Operation
Modification
Potentially low capital
cost
High O&M cost
Occupant comfort
Difficult to control
Indoor Air
Treatment
Quick Installation
Potentially higher capital
cost
Diffi l to controll
Difficult
96
Buildings with
continuous HVAC
operation
Interim Measure
Summary

Not all sites are the same – Select p
preferred method
considering geology, source location & type, &
magnitude of required reduction

Active and passive controls may be used to address VI
concerns

Cost of installation can be significantly less than O&M
costs
97
Expect Surprises